Λ-Cold Dark Matter cosmological simulations of the Universe predict that major (mass ratio > 1/4) and minor mergers (mass ratio < 1/4) both play a significant role in shaping the galaxies that populate our Universe today. Due to the long timescales of galaxy mergers, we must infer their occurrence and properties in observations through merger features, such as the tidal debris around a galaxy. Tidal features form from stars that have been pulled into specific orbits during mergers, creating low-surface-brightness structures around galaxies (e.g., streams, tails, and shells). The properties of the tidal feature can provide insights into the merger that created it. With the upcoming Legacy Survey of Space and Time (LSST) on the Rubin Observatory, we will have an unprecedented sample of these low-surface-brightness features, enabling us to use tidal features to test how mergers transform galaxies. To make a like-for-like comparison with LSST, we have produced a sample of idealized mock observations from four cosmological simulations: EAGLE, IllustrisTNG, Magneticum Pathfinder, and NewHorizon. Using different simulations, we probe the influence of subgrid physics models and simulation resolution on the occurrence and characteristics of tidal features. We have studied the properties of galaxies with and without tidal features in an observationally motivated manner and examined how the occurrence of tidal features around galaxies varies as a function of galaxy colour, stellar mass, group/cluster halo mass and distance from the group/cluster center in the velocity-radius phase space, therefore probing whether the occurrence of tidal features around galaxies reflects the trends regarding the occurrence of mergers as a function of galaxy stellar mass and environment. A natural continuation is to leverage the opportunity to directly connect mergers in simulated galaxies to the tidal features characterized in previous work. This will provide a valuable test, quantifying the extent to which the role of mergers in transforming galaxies varies across different simulations with varying subgrid physics prescriptions and resolutions. Furthermore, we aim to quantify the lifetimes of the visible tidal features and potentially probe the morphological properties of the progenitor galaxies through the photometric properties of tidal features, providing a framework to interpret tidal features in the LSST survey.

We perform a data-driven test of the FLRW metric and the flatness of the Universe, independently of any Dark Energy model, and in light of the latest DESI DR2 results. We use Pantheon+ and DES Dovekie SNIa data to reconstruct the distance modulus, dimensionless comoving distance and Hubble parameter, using an iterative smoothing algorithm. Then, combining the various reconstructions with the recent BAO measurements from DESI DR2, we perform the Ok diagnostic, a litmus test of the FLRW metric and the flatness of the Universe. We obtain robust results that do not depend on Dark Energy models and test some of the underlying hypotheses of the concordance model. We find that when the reconstructed Ok diagnostic is consistent with the FLRW metric, then the median value of Ωk,0 over all reconstructions that provide an improved fit relative to the flat ΛCDM model is: Ωk,0med = 0.035+0.046−0.079 ± 0.037 for the Pantheon+ & DESI DR2 data combination, Ωk,0med = 0.092+0.055−0.132 ± 0.064 for the same data but with the Pantheon+ SNIa cut at redshift z = 1.13, which is the maximum redshift of the DES Dovekie data, and Ωk,0med = −0.101+0.088−0.024 ± 0.044 for DES Dovekie & DESI DR2. The first uncertainties correspond to the spread in Ωk,0 over all reconstructions, followed by the median 1σ error.

Recently, JWST enables detailed investigations of high-redshift galaxies with its unprecedented imaging sensitivity and spatial resolution. These observations provide a great opportunity to test whether the properties of early galaxies are consistent with predictions from cosmological simulations. Lee, J. H., et al. (2024) analyzed the morphological distributions of ~19,000 high-redshift galaxies within six JWST fields (~0.1 deg^2 in total) and reported that galaxies at z>4 predominantly exhibit disk-like morphologies, in good agreement with the HR5 simulation results (Park, C. et al. 2022). As an extension of this previous work, we perform a comprehensive comparison of high-redshift galaxy properties, including their morphology, star formation activity, and environmental properties, using wider JWST fields and the HR5 simulation. Our analysis sample incorporates the COSMOS-Web field and multiple DAWN archive fields (GOODS-N, GOODS-S, PRIMER-UDS-N, PRIMER-UDS-S, including ~200,000 galaxies within ~0.62 deg^2. In particular, the abundance of quiescent galaxies at z=3-6 is an intriguing issue in recent JWST studies, as the observed number densities are significantly higher than the results from previous simulations. This discrepancy implies that star formation activity in high-redshift galaxies may be quenched much earlier than expected, posing a challenge to the current galaxy formation and evolution scenarios. We conduct a comparative analysis of the number densities of high-redshift quiescent galaxies, using consistent criteria for quiescence definition based on the star formation main sequence in each redshift bin. Our results showed that while HR5 successfully reproduces the observed galaxy morphologies, it substantially underestimates the number density of quiescent galaxies. This comparison highlights the successes and limitations of current cosmological simulations in reproducing the observed properties of high-redshift galaxies.

The study of galaxy formation and evolution has progressed significantly in recent decades, with numerical simulations producing galaxies matching observed properties. However, the inner workings of the feedback processes that regulate the growth of galaxies are not fully understood. To address this, a new generation of high-resolution simulations has been developed, using subgrid models to describe unresolved phenomena at the resolution scale. While these simulations can produce galaxies comparable to observations, there is a degeneracy between subgrid models which can only be lifted by observables beyond galactic properties, such as the CGM. In this talk, I will introduce ARCHITECTS, a series of zoom-in cosmological simulations of the same galaxy run with different subgrid models. I will discuss how these models influence the CGM and outline the current challenges faced by both simulations and observations in this field.

X-rays in the early Universe play a critical role in the formation of metal-free Population III (Pop III) stars. They not only heat the intergalactic medium but also ionize it, thereby enhancing gas-phase molecular hydrogen formation, which is the primary coolant of metal-free gas. In this talk, I will present results from our numerical simulations and discuss how X-ray radiation backgrounds affect (1) the initial mass function of Pop III stars and (2) the conditions required for their formation. Under X-ray irradiation, Pop III stars tend to be less massive and show reduced multiplicity. In addition, a moderate X-ray background enhances Pop III star formation, increasing the number of Pop III–forming halos per comoving Mpc/h³. Finally, I will discuss the implications of X-rays for the formation of the first galaxies.

Observations of the large-scale structure and the spatial distribution of galaxies in the Universe indicate that galaxies are mainly located in the densest regions, such as galaxy clusters. These systems are crucial for investigating the role of environment in galaxy evolution at different epochs. In the early Universe, the progenitors of galaxy clusters are protoclusters. Therefore, the search for and identification of protoclusters is a way to investigate the formation and assembly of clusters. Using lightcone data from the Horizon Run 5 (HR5) simulation, we search for spherical regions that are protocluster candidates and will collapse into clusters by z=0. The HR5 simulation covers a wide volume on Gpc scales, with spatial resolution down to 1 kpc, allowing us to investigate the properties of protoclusters across different scales. The protocluster identification method has been tested using snapshot data and is now applied to lightcone data from HR5, with future applications to observations such as Rubin LSST.

Galaxies in the local universe can be viewed as complex ecosystems where energy flows and matter cycles are regulated through internal processes and environmental effects. Investigating the ISM, star formation, and quenching mechanisms is essential for a comprehensive understanding of the regulation and evolution of galaxy ecosystems. In this talk, I will highlight our statistical results derived from extensive multi-wavelength surveys of local galaxies. Our analysis reveals that central disk galaxies with star formation rates significantly below the star-forming main sequence unexpectedly possess HI gas reservoirs comparable to those of star-forming galaxies, but exhibit significantly lower molecular gas content and star formation efficiency. We further demonstrate that quenching in these central disk galaxies is closely linked to bulge growth, bar-induced activities, and feedback from low-luminosity AGN. These results lead to a coherent picture of how internal “mass quenching” operates. Additionally, we find that the residual HI gas content provides a robust diagnostic for distinguishing between internal-driven and environmentally-driven quenching channels in satellite galaxies. Finally, I will present our latest insights into the star formation law, derived from studies of dust properties of the local galaxy population.

Inflation provides a compelling framework for the early Universe, involving physics at extremely high energy scales that often require extensions beyond the standard model of particle physics. Such models can leave distinct imprints on cosmological observables, making the early Universe a powerful laboratory for probing fundamental physics. In this talk, I will briefly review observational constraints on inflationary models, with particular emphasis on the Cosmic Microwave Background. I will then focus on my recent work exploring the redshifted 21 cm signal from neutral hydrogen at high redshifts. The primary goal of this work is to demonstrate how upcoming 21 cm observations can provide complementary and powerful constraints on inflationary physics beyond the CMB.

I will describe the current status of the CMB polarisation field, including the impact and the aftermath of the CMB-S4 cancellation. I will overview the science goals as defined for on-going and future efforts, major challenges to reaching them, and new technologies devised for overcoming those. I will conclude with an outlook for the future.

We briefly describe the relevance of combining the datasets from operating and future CMB and LSS probes, for addressing the open issues in Cosmology as outlined in the talk by Radek Stompor. We review the recent results along these lines, in terms of cross-correlation and combination, and the future challenges towards the next decade.

Supernova (SN) cosmology is based on the key assumption that the luminosity standardization process of Type Ia SNe remains invariant with progenitor age. However, direct and extensive age measurements of SN host galaxies reveal a significant (5.5 σ) correlation between standardized SN magnitude and progenitor age, which is expected to introduce a serious systematic bias with redshift in SN cosmology. This systematic bias is largely uncorrected by the commonly used mass-step correction, as progenitor age and host galaxy mass evolve very differently with redshift. After correcting for this age bias as a function of redshift, the SN dataset aligns more closely with the wowaCDM model recently suggested by the DESI BAO project from a combined analysis using only BAO and CMB data. This result is further supported by an evolution-free test that uses only SNe from young, coeval host galaxies across the full redshift range. When the three cosmological probes (SNe, BAO, and CMB) are combined, we find a significantly stronger (> 9 σ) tension with the LCDM model than that reported in the DESI papers, suggesting a time-varying dark energy equation of state in a currently non-accelerating universe.

Simulation is a powerful tool that plays a pivotal role at the intersection of computational astrophysics, galaxy formation, and cosmology. Because the physical processes involved span a vast range of spatial and temporal scales, subgrid models serve as essential bridges for phenomena that lie below the resolution limits of current simulations. These models critically shape the predictive power of simulations and our understanding of the Universe. In this talk, I will present strategies for calibrating subgrid models to reproduce a realistic Universe and examine how different model choices influence the properties of simulated galaxies. I will also discuss how simulations can be used both to interpret observations and to propose new mechanisms for the formation and evolution of galaxies. Finally, I will explore how pushing simulations to their limits can offer meaningful constraints on cosmology.

The standard model of cosmology, ΛCDM, has been a fundamental framework for understanding the universe from a theoretical perspective and for explaining a wide range of astrophysical and cosmological observations. Nonetheless, the increasing amount of observational data have given rise to the era of precision cosmology, revealing discrepancies in parameter values across different observables and experiments, challenging the ΛCDM’s capacity to comprehensively elucidate the universe’s structure and evolution. To address these pressing gaps, I focus on studying the observational signatures of different dark energy frameworks, with an emphasis on interacting dark sector models. I test the capabilities of interacting dark energy as an alternative framework to tackle significant issues such as the Hubble constant (H0) tension and the S8 parameter tension in cosmology. In this talk, I will discuss the development of the background and perturbation evolution equations for an interaction model of dark matter and quintessence dark energy. Further, I will talk about the data analysis and evaluation of the model using observations from various sources like CMB from Planck2018, BAO from several galaxy surveys, SN-Ia from Pantheon Plus, Masers galaxy samples, cosmic chronometers (CC), growth rate (fσ8) data, and H0 measurements from SH0ES study and strong lensing time delay (SLTD). Due to the uncertainty involved in the dark energy physics and in the observational measurements, our results demonstrates that the data constrains H0 towards Planck CMB+ΛCDM results when SH0ES H0 is excluded and it shifts the H0 towards results with <1σ consistency when H0 from SH0ES is included. Additionally, by freely evolving the interaction parameter, the analysis predicted that while the interaction remains small, it is not disfavoured by the data at late times. These results found to be more robust in tightening constraints on H0, S8, and dark matter density parameter (ΩDM) together at 68% confidence, and justify the reduced uncertainty and hence the parameter space. Next, I will discuss the coupled quintessence model within the framework of curved spatial geometry (Coupled+ΩK model) and examine the inconsistencies in spatial curvature and their implications for the H0 and S8 tensions. The obtained results provide evidence for an open universe in the Coupled+ΩK model. I will delve deeper into how these findings within the Coupled+ΩK picture suggest that relaxing the flatness assumption in coupled dark sector models leads to more precise constraints on H0 and S8. In the end, I will shed light on the ongoing research with DESI data.

We use high-resolution zoom-in cosmological simulations to study the evolution of circumgalactic medium (CGM) at high redshifts. Filamentary and diffuse accretion in conjunction with stellar and galactic outflows have been analyzed for central galaxies in the similar mass DM halos, log M/Mo ~ 10.75, at the final z=6, 4, and 2. Two feedback mechanisms, steady and variable winds, have been implemented in high and low-density environments. We focused on the evolution of baryonic filamentary and diffuse accretion processes within few virial radii. Specifically, we have addressed the developing turbulence and ablation of penetrating streamers, and their interactions with the galactic outflows, thus determinig the kinematic and thermodynamic properties of the CGM between the central galaxy and the backsplah radii. In addition, we have post-processed our galaxy sample with a radiative transfer scheme to obtain their observational properties, for the future observations with the JWST.

The observed large-scale structure, as traced by galaxy redshift surveys, appears distorted due to the fact that our observations are based on light. While the dominant contribution comes from the Doppler effect caused by galaxy peculiar velocities, subdominant relativistic effects can also leave observable imprints. In this talk, we explore the detectability of such effects in upcoming/ongoing galaxy surveys, and show that gravitational redshift effect can be detected with high statistical significance.

Recent JWST observations have revealed superbubbles (SBs)—cavity-shell structures distributed across the galactic disk—formed by successive supernova explosions. The potential fluctuations generated by SBs can dynamically heat galactic systems. Using the orbit-averaged Fokker-Planck equation, we investigate the role of SB-driven stochastic heating in the context of cusp-core transformation. This formalism describes the cumulative impact of weak, local encounters induced by stochastic noise sources. By modeling the expansion and collapse of SBs, along with their inhomogeneous spatial distribution, we derive diffusion coefficients linked to the power spectrum of SB-induced fluctuations. Furthermore, we find simple analytic scaling relations that provide an intuitive understanding of how diffusion efficiency depends on noise source and system parameters.

The Vera C. Rubin Observatory’s Legacy Survey of Space and Time (LSST) is poised to revolutionise our understanding of the Universe.The first set of images from Rubin highlight its performance and promise. With its unprecedented depth, area, and cadence, LSST will deliver a ten-year imaging survey of roughly 20 billion galaxies and about 10 million supernovae, offering transformative potential for cosmology. In this talk, I will discuss the role LSST will play to address the S8 tension. I will present some forecasts based on tomographic cross-correlation measurements and discuss how the redshift bin mismatch of galaxies can alter our inferences on the S8 tension. The second part of the talk will be on prospects for probing primordial physics with joint LSST and CMB Stage-4 analyses, focusing on how LSST can aid in delensing the CMB to improve constraints on the tensor-to-scalar ratio. Together, these efforts highlight the critical role LSST will play in the next generation of cosmological discoveries.

The Om diagnostics, derived from the Hubble parameter and distance measurements directly obtained from observational data, serve as a null test for the flat ΛCDM model. To perform a statistically robust analysis of the Om diagnostics, we generate DESI-like mock data based on various dark energy models, consisting of joint catalogs of both the Hubble parameter and the transverse comoving distance. We then apply Gaussian Process Regression (GPR) to analyze the Om diagnostics, with a detailed examination of the GPR methodology. Our results demonstrate that the expansion history and Om diagnostics can be accurately reconstructed regardless of the fiducial dark energy model. We also highlight the significant impact of the input mean function, an often overlooked factor in many GPR analyses.

We carry out a comprehensive hierarchical multi-scale morphological analysis to search for anomalous behaviour in the large-scale matter distribution using the convergence map provided by the Atacama Cosmology Telescope Data Release 6. We use a suite of morphological statistics consisting of Minkowski functionals, contour Minkowski tensor, and Betti numbers for the analysis, and compute their deviations from the ensemble expectations and median values obtained from isotropic ΛCDM simulations provided by ACT. To assess the statistical significance of these deviations, we devise a general methodology based on the persistence of the deviations across threshold ranges and spatial resolutions, while taking into account correlations among the statistics. From the analysis of the full dataset and hemispherical regions, we find consistency with isotropic ΛCDM simulations provided by ACT. Since deviations in smaller sky regions tend to get washed out when averaged over larger regions, we further analyze smaller sky patches. This localized analysis reveals some patches that exhibit statistically significant deviations which we refer to as ‘anomalous’. We find that near the CMB cold spot, both the positive and negative density fluctuations are anomalous, at 99% CL and 95% CL respectively. This region also encompasses an anomalous southern spot previously identified in Planck CMB temperature data. We also carry out a comparison of anomalous patches identified here for ACT data with a previous analysis of the convergence map from Planck. We do not find common patches between the two datasets, which suggests that the anomalous behavior of the Planck data arises from noise in the map. Further investigation of the atypical patches using large-scale structure surveys is warranted to determine their physical origin.

The shape and spin of galaxies are often aligned with specific orientations rather than being random because of the influence of the surrounding large-scale structure in the universe. This phenomenon, known as the intrinsic alignment (IA) of galaxies, is closely related to galaxy formation and the matter distribution in the universe. Previous studies have shown that the amplitude of the IA depends on galaxy properties such as color and luminosity. Understanding its redshift evolution is important, especially as recent observations span a wide range of redshifts, which requires a model for redshift-dependent bias to weak lensing. In this talk, I will present the redshift evolution of the IA of galaxies and subhalos with the large-scale structure using cosmological hydrodynamical simulation, Horizon Run 5. I will also compare our findings with those from previous studies.

The Universe went through an early period known as the Dark Ages, during which the primeval density fluctuations left over from the Big Bang grew to form the first luminous objects. The 21-cm line of neutral hydrogen is the most promising probe of these epochs, driving extensive observational efforts. We combine hydrodynamical simulations with a large-scale grid to precisely calculate the impact of nonlinear structure formation on the mean 21-cm intensity during the Dark Ages and early Cosmic Dawn. Our results reveal a potential opportunity to probe the properties of dark matter in a new regime, corresponding to a warm dark matter masses around 7 keV and fuzzy dark matter masses around 2×10^-20 eV. This effect can, in principle, be detected unambiguously with future lunar experiments.

Feedback from massive stars is the main regulator of star formation in giant molecular clouds (GMCs) where all star formation is observed to occur. Through their powerful radiation fields, these stars act to disperse the clouds that made them in multiple ways. Two of the most powerful mechanisms are bubbles blown by the the shocked gas created by winds from these stars and the over-pressurized, ionized gas created by the stars' hard ionizing spectra. In this talk I will review how these two mechanisms impact one another and physical principles for how to quantify their relative importance. I will show that, for parameters relevant to Milky-Way like GMCs and dense, low-metallicity environments as may be present in the high-redshift universe, both mechanisms are of nearly equal importance. To better understand this scenario, I develop a semi-analytic "Co-Evolution Model" for the evolution of both feedback mechanisms together and test the model against 3D Radiation Magneto-Hydrodynamic simulations. I will review possible improvements to the model and how it could potentially be used for inference based on observations of star-formation in the nearby and distant universe.

The structure and kinematics of the gas around and in galaxies are crucial for understanding the multiphase flows within the galactic ecosystem and, thus, galaxy evolution and star formation. Recent advancements in instruments and techniques offer a new perspective on circumgalactic gas flows through emission lines such as Hydrogen Lyman-α and resonance lines of metals (e.g., Mg II, C IV, O VI, and N V). In particular, the Mg II λλ2796, 2803 doublet has emerged as a promising tracer of cold gas at T ~ 10^4 K. To decode the message carried by the Mg II doublet emission, we developed a 3D Monte-Carlo radiative transfer code ‘RT-scat’. In this talk, I will present simulated results from ‘RT-scat’, demonstrating how Mg II lines form in various environments, including inflowing/outflowing, smooth/clumpy, and dusty gas. In particular, I will also highlight how the MgII doublet line ratio can serve as a potential indicator of LyC escape. Furthermore, I will introduce our new radiative transfer modeling of Mg II emission halos around star-forming galaxies at z ~ 1 from the MAGG and MUDF survey. Our results indicate the presence of slowly moving or outflowing cold gas and reveal strong anisotropy in its distribution. If time allows, I will also discuss other metal resonance lines as tracers of multiphase gas.

Active Galactic Nuclei (AGNs) exhibit complex central structures that can be explored through their variability across multiple wavelengths. In this talk, I will present our current understanding of AGN central structures, focusing on the variability characteristics of nearby AGNs from ultraviolet to mid-infrared wavelengths and their implications for revealing the physical properties of accretion disks and dusty tori. Finally, I will provide a brief introduction to the SPHEREx mission, an all-sky spectroscopic survey in the near-infrared, and discuss its potential contributions to advancing our knowledge of AGN physics.

Bars are commonly observed in the local Universe. As non-axisymmetric features, bars drive gas inflow toward the central regions of galaxies. Numerical simulations suggest that shocks and shear occur along the bar dust lanes as the gas flows inward. These shocks and shear can influence star formation (SF) and alter the gas properties. In this talk, I will present a method for identifying bar-driven shocks and shear using observational datasets from the PHANGS-MUSE and PHANGS-ALMA surveys, which provide unprecedented detail in studying bar kinematics. I will demonstrate how we reached the conclusion that SF is suppressed in regions where bar-driven shear and shocks are strong. Additionally, I will discuss the implications of our findings for future studies examining the impact of bars on SF. Finally, I will share a serendipitous discovery of HII regions that are expanding or moving relative to their surroundings.

The standard model of cosmology, ΛCDM, has been a fundamental framework for understanding the universe from a theoretical perspective and for explaining a wide range of astrophysical and cosmological observations. Nonetheless, the increasing amount of observational data have given rise to the era of precision cosmology, revealing discrepancies in parameter values across different observables and experiments, challenging the ΛCDM’s capacity to comprehensively elucidate the universe’s structure and evolution. To address these pressing gaps, I focus on studying the observational signatures of various dark energy frameworks, with a primary emphasis on investigating interacting dark sector models and exploring alternatives to the standard cosmological model. I test their capabilities in an attempt - to tackle significant issues such as the cosmological coincidence problem, the Hubble constant (H0) tension and the S8 parameter tension related to matter structure growth, combining theoretical and observational approaches. In this talk, I will discuss about the observational data analysis of an interaction model of dark matter and quintessence dark energy [1]. I evaluated this model using cosmological observations from various sources like the latest observational data like CMB from Planck2018, BAO from several galaxy surveys, SN-Ia, Masers galaxy samples, cosmic chronometers (CC), growth rate (fσ8) data, and H0 measurements from SH0ES study and strong lensing time delay (SLTD). Due to the uncertainty involved in the dark energy physics and in the observational measurements, we found that the data constrains H0 towards Planck CMB+ΛCDM results [3] when SH0ES H0 is excluded and it shifts the H0 towards [4] results with <1σ consistency when H0 from SH0ES is included. Additionally, by freely evolving the interaction parameter, we found that while the interaction remains small, it is not disfavoured by the data at late times. These results found to be more robust in tightening constraints on H0, S8, and dark matter density parameter (ΩDM) together at 68% confidence, and justify the reduced uncertainty and hence the parameter space. Next, I will discuss the coupled quintessence model within the framework of curved spatial geometry (Coupled+ΩK model) and examine the inconsistencies in spatial curvature and their implications for the H0 and S8 tensions[2]. The obtained results provide evidence for an open universe in the Coupled+ΩK model. Moreover, the results also indicate a lower value of dark energy equation of state (ωde) parameter compared to the flat interacting scenario, attributable to the curvature effect. I will delve deeper into how these findings within the Coupled+ΩK picture suggest that relaxing the flatness assumption in coupled dark sector models leads to more precise constraints on H0 and S8, as well as significantly better agreement between theory and observations. In the end, I will shed light on the ongoing research with DESI data.

The concordance model of cosmology, known as LambdaCDM, has provided a range of specific predictions that have been consistent with many observations in the past, but is now facing serious challenges. Expansion history data indicate inconsistency with the theory (deviations from Lambda) or from each other (H0 tension). Large-scale structure surveys such as SDSS, BOSS and DESI have shown that the distribution of galaxies in three-dimensions can be used to measure the expansion history, through standard rulers such as the Alcock-Paczynski test and baryon acoustic oscillations. The distribution of matter and growth rate of structure can also be measured by such a data set, providing complementary cosmological tests. This future data will confront these challenges, and provide evidence to potentially resolve the tensions. In this talk, we will present our plans and forecasts for a future dedicated large-scale spectroscopic survey, and the use of the data to probe the expansion history, and test models of dark energy. We will motivate our proposed survey and instrument design by considering carefully choices of target galaxy, redshift range, and area coverage.

Cosmological QUOKKAS is an ambitious project to create a Hubble Diagram over the redshift range 0 < z < 5 in a way completely independent of the Distance Ladder. The method, known as a 'causality distance' uses the speed-of-light to calibrate a standard ruler in the flaring regions of blazars. The apparant size is measured with Very Long Baseline Interferometry (VLBI) and a distance can be determined. Currently, weekly observations are ongoing with the Korean VLBI Network (KVN), the Mopra telescope in Australia and the Hartebeesthoek telescope in South Africa. Early results from archival data show hints of a deviation from the expected cosmology at high-z, but further work to calibrate systematic errors will be needed to confirm or deny such a finding.

Early Dark Energy (EDE) models which were proposed to help resolve the Hubble tension have received a lot of attention recently. Interestingly, these models are also capable of providing an explanation for the observed signal of Cosmic Birefringence in the Cosmic Microwave Background (CMB) data. In this talk, I will briefly review the ultralight axion-like EDE models with n=3 and present our work testing the model against cosmological observations. While previous articles in the literature argue that the n=3 EDE model is not consistent with observations of cosmic birefringence, we show that it is a consequence of the assumptions made about the dependence of the CMB power spectrum on the model parameters. We relax these assumptions and do an exploration of the full parameter space and find that the model can fit the observations quite well. EDE remains a promising candidate to explain the Hubble tension and cosmic birefringence, hitting two birds with one stone.

The Dark Energy Spectroscopic Instrument (DESI) collaboration is conducting a five-year redshift survey of 40 million extra-galactic sources over 14,000 square degrees of the northern sky up to the redshift of 4 with the Mayall 4-meter telescope at Kitt Peak National Laboratory. One of its primary goals is to measure the cosmic expansion history precisely and accurately through the measurements of baryon acoustic oscillations (BAO). In this talk, I will present the analysis of the DESI First Year Baryon Acoustic Oscillations using the distributions of galaxies and quasars over the redshift range of 0.1-2, the estimates of the relevant systematics, and their intriguing cosmological implications, including the time-evolving dark energy. If time permits, I will also present the study of the imaging systematics mitigation for the DESI survey as well as the BAO using the combined tracers.

Internal kinematics of galaxies, traced through the stellar rotation curve or two dimensional velocity map, carry important information on galactic structure and dark matter. With upcoming surveys, the velocity map may play a key role in the development of kinematic lensing as an astrophysical probe. We improve techniques for extracting velocity information from integral field spectroscopy at low signal-to-noise ( S/N), without a template, and demonstrate substantial advantages over the standard Penalized PiXel-Fitting method (pPXF) approach. We note that Robust rotation curves can be derived down to S/N≈2 using our method.

UV photons produced by young massive stars are the major source of heating and ionization in the interstellar medium (ISM). H II regions created by ionizing photons photoevaporate and expel the surrounding molecular gas that would otherwise fuel further star formation, regulating the star formation efficiency and lifetime of giant molecular clouds. UV radiation (both Lyman continuum and far-UV) escaping into the large-scale ISM produces the interstellar radiation field (ISRF). The LyC ISRF maintains the ionization of diffuse ionized gas while the FUV ISRF controls the thermal pressure in the diffuse neutral gas, providing pressure support needed to balance the ISM weight on galactic scales. In this talk, I will overview key physical processes driven by UV radiation and introduce radiation MHD simulations of the multiphase, star-forming ISM incorporating these effects. I will highlight key findings from our models, focusing on the role of UV radiation in controlling star formation on cloud and galactic scales.

The tensor Minkowski functionals or Minkowski tensors (MTs) are generalizations of the usual Minkowski Functionals, which are scalar quantities. The MTs are a set of statistics defined as integrals over the boundary of an excursion set, with integrands related to symmetric tensor products of position vectors and normals to the boundary. They provide directional or anisotropy information that is not present in the scalar Minkowski functionals. Since 2017, the MTs have been used in cosmology. Efficient and accurate algorithms have been developed for calculation of rank-two MTs for analyses of cosmic microwave background radiation anisotropy on the surface of the celestial sphere, and matter and galaxy density fluctuations in 3D space or in 2D slice. Extensive studies have been made to examine the impacts of the nonlinear gravitational evolution, galaxy bias, and redshift space distortion on the MTs of large-scale structures in the universe. The recent developments in the application of the MTs in the large-scale structure cosmology are reviewed.

In light of advancements in precise cosmology and the emergence of cosmic tensions, we are faced with the question of whether the standard model of cosmology needs to be extended and whether doing so can alleviate the tensions? In this talk, we investigate whether there is a relation between these tensions and beyond cold dark matter (CDM) scenarios and try to address the intriguing tensions of the standard model of cosmology with recent cosmological data. To model non-cold dark matter, we assume 1) Decaying dark matter, characterized by instability and the possibility of decay into two daughter particles. 2) Varying forms of viscous dark matter, 3) Dark matter models featuring a non-zero equation of state so that the behavior of this dark matter changes according to the scale of k. Through a systematic examination of these models, we endeavor to shed light on the intricate interplay between cosmological tensions and extensions beyond the standard cold dark matter paradigm.

The spatially-resolved kinematics of bulge and disk components derived from 3D spectroscopy explain a diverse range of stellar kinematics in galaxies across different types. Kinematic scaling relations highlight a consistent correlation between galaxy stellar mass and kinematics in both bulge and disk components, irrespective of galaxy types. This suggests that the kinematics of these components are less influenced by galaxy populations and are primarily determined by mass. Our findings also indicate that the relative contributions of bulge and disk components play a significant role in explaining the complex kinematic behavior observed in galaxies of varying types. Additionally, 3D spectroscopy enables the investigation of AGN feedback on gas and stellar velocity dispersions (σgas and σstar). We observe that σstar (derived from absorption lines) tends to be higher than σgas (measured using emission lines), implying that stars are generally dynamically hotter than ionized gas. The ratio of σgas to σ∗ (Δσ = log σgas/σ∗) strongly correlates with the contribution of AGN, suggesting that AGN activity inflates gas velocity dispersions—potentially through AGN-driven outflows. This impact of AGN on gas kinematics is further confirmed by fitting emission lines with both broad and narrow components. Galaxies with a broad component exhibit inflated gas velocity dispersions compared to predictions by the stellar mass. Notably, a tight correlation exists between the velocity dispersion of the broad component (σbroad) and the contribution of AGN. In conclusion, our study emphasizes the sensitivity of gas kinematics to power sources, particularly highlighting the significant contribution of AGN to inflated gas velocity dispersions.

In a novel approach employing implicit likelihood inference (ILI), also known as likelihood-free inference, we calibrate the parameters of cosmological hydrodynamic simulations against observations, which have previously been unfeasible due to the high computational cost of these simulations. For computational efficiency, we train neural networks as emulators on ~1000 cosmological simulations from the CAMELS project to estimate simulated observables, taking as input the cosmological and astrophysical parameters, and use these emulators as surrogates to the cosmological simulations. Using the cosmic star formation rate density (SFRD) and, separately, stellar mass functions (SMFs) at different redshifts, we perform ILI on selected cosmological and astrophysical parameters (Omega_m, sigma_8, stellar wind feedback, and kinetic black hole feedback) and obtain full 6-dimensional posterior distributions. In the performance test, the ILI from the emulated SFRD (SMFs) can recover the target observables with a relative error of 0.17% (0.4%). We find that degeneracies exist between the parameters inferred from the emulated SFRD, confirmed with new full cosmological simulations. We also find that the SMFs can break the degeneracy in the SFRD, which indicates that the SMFs provide complementary constraints for the parameters. Further, we find that the parameter combination inferred from an observationally-inferred SFRD reproduces the target observed SFRD very well, whereas, in the case of the SMFs, the inferred and observed SMFs show significant discrepancies that indicate potential limitations of the current galaxy formation modeling and calibration framework, and/or systematic differences and inconsistencies between observations of the stellar mass function.

Classic galaxy formation models predict a linear relationship between galaxy size and the radius of dark matter halo. However, the status of this predicted relationship is uncertain as empirical models and simulations in the past decade find both supporting and opposing results on this supposed linear relation. In this work, we re-examine the galaxy size-halo radius relation using weak gravitational lensing which is a direct method of probing dark matter distribution around luminous galaxies. Our sample consists of ~38,000 galaxies more massive than logM*=8 and within redshift z<0.3 drawn from the overlap of GAMA survey DR4 and Subaru-HSC survey PDR2. We confirm that the galaxy size - halo radius relation is linear for galaxies more massive than logM*~9. Below this mass limit, i.e., for low mass/dwarf galaxies, we find an indication of a non-linear galaxy size-halo radius relation. The possible existence of such a trend in dwarf galaxy sector calls for either modification in models employing a constant fraction of halo angular momentum transferred to explain sizes of dwarfs or else points towards our lack of knowledge about dark matter halos of low-mass galaxies.

We build a model to predict from first principles the properties of major mergers. We predict these from the coalescence of peaks and saddle points in the vicinity of a given larger peak, as one increases the smoothing scale in the initial linear density field as a proxy for cosmic time. Our model allows us to recover that the typical spin brought by mergers: it is of the order of a few tens of per cent.

We build a model to predict from first principles the properties of major mergers. We predict these from the coalescence of peaks and saddle points in the vicinity of a given larger peak, as one increases the smoothing scale in the initial linear density field as a proxy for cosmic time. Our model allows us to recover that the typical spin brought by mergers: it is of the order of a few tens of per cent.

The z = 2 - 3 regime is a pivotal epoch in the history of galaxy clusters, where baryons in the largest dark matter halos gradually transition from a mode of efficient accretion to one where the now-hot intrahalo medium (IHM) effectively prevents cold gas from reaching the center. On the other hand, halos in this late-stage protocluster regime still host large amounts of star formation and AGN activity. The heating up of these halos can be traced in at least two ways: through its effect on cold/warm gas, as traced by Lyman alpha emission, and by directly detecting the IHM, in particular through the Sunyaev-Zel'dovich (SZ) effect. However, SZ observations at high redshift are not free of biases related to the galaxy content of the halos. In this regard, ALMA has proved to be a powerful machine for high redshift ICM studies. Its large collecting area and excellent spatial filtering capability, makes it so far the only facility able to constrain the distribution of hot gas at z ~ 2 and beyond.

The 21-cm hyperfine line of neutral hydrogen is set to revolutionize studies of the first billion years, spanning the cosmic dawn of the first stars and eventual reionization of our Universe. I will discuss the potential of this probe in learning about the unknown astrophysics of the first galaxies as well as physical cosmology. Current upper limits on the cosmic 21-cm power spectrum already provide new insights into the heating of the intergalactic medium, and the X-ray sources in the first galaxies. I will discuss the upcoming steps, including the main challenges, that will eventually lead to the Nobel prize-worthy 3D map of half of our observable Universe with the Square Kilometer Array (SKA) telescope.

Traditionally, galaxies in clusters are known to be bulge-dominated, optically red and evolving passively, while their counterparts further away are dominated by blue disky galaxies, vigorously forming stars. The wide-field surveys carried out in the past two decades however, have shown that the outskirts of galaxy clusters, the regions where large-scale filaments intersect the boundary of the cluster, are breeding grounds for galaxies in transition phase. This is due to the fact that the evolution of galaxies is accelerated on the outskirts of clusters. It is in these suburbs of clusters, that the infalling galaxies are likely to lose their gas due to gravitational interactions with each other, and even change in morphology and colour, much before they encounter the hostile environment of the galaxy cluster. With this in mind, we started a campaign to observe the outskirts of nearby clusters of galaxies with the Ultraviolet Imaging Telescope (UVIT) aboard the multiwave Indian satellite mission AstroSat. We have combined our newly acquired FUV data with the arsenal of multiband data available in the archives to understand the nature and evolution of galaxies in clusters, as well as study properties of other sources observed by the UVIT. In this talk I will present results from our analysis indicating that several FUV-bright galaxies could have recently fallen into the Coma cluster and are currently experiencing ram-pressure stripping. I will also present the properties, plausible origin, and evolution of some of the distorted FUV galaxies discovered in the Coma and other nearby clusters. The presence of these galaxies not only emphasize the impact of environment on the evolution of galaxies, but also provides an insight into how mass assembles into galaxy clusters to give us the distribution of matter observed today.

The next generation of galaxy surveys will provide more precise measurements of galaxy clustering than have previously been possible. The 21 cm radio signals that are emitted from neutral atomic hydrogen (H I) gas will be detected by large-area radio surveys such as the Widefield Australian Square Kilometre Array (SKA) Pathfinder L-band Legacy All-sky Blind Survey and SKA, and deliver galaxy positions and velocities that can be used to measure galaxy clustering statistics. However, to harness this information to improve our cosmological understanding and learn about the physics of dark matter and dark energy, we need to accurately model the manner in which galaxies detected in H I trace the underlying matter distribution of the universe. For this purpose, we develop a new H I-based halo occupation distribution (HOD) model, which makes predictions for the number of galaxies present in dark matter halos conditional on their H I mass. The parameterized HOD model is fit and validated using the DARK SAGE semi-analytic model, where we show that the HOD parameters can be modeled by simple linear and quadratic functions of the H I mass. This work enables-for the first time-a simple prescription for placing galaxies of different H I masses within dark matter halos in a way that is able to reproduce the H I mass-dependent galaxy clustering and H I mass function simultaneously and without requiring knowledge of the optical properties of the galaxies. We also present a new halo density profile model for galaxies, which makes predictions for the positions of galaxies in the host halo, different to the widely adopted Navarro-Frenk-White (NFW) profile, since galaxies tend to be found more in the outskirts of halos (nearer the virial radius) than an NFW profile. The parameterised density profile model is fit and tested using the DarkSage semi-analytic model of galaxy formation. We find that our density profile model can accurately reproduce the halo occupation distribution and galaxy two-point correlation function of the DarkSage simulation. We also derive the analytic expressions for the circular velocity and gravitational potential energy for this density profile. We use the SDSS DR10 galaxy group catalogue to validate this halo density profile model. Compared to the NFW profile, we find that our model more accurately predicts the positions of galaxies in their host halo and the galaxy two-point correlation function.

The next generation of galaxy surveys will provide more precise measurements of galaxy clustering than have previously been possible. The 21 cm radio signals that are emitted from neutral atomic hydrogen (H I) gas will be detected by large-area radio surveys such as the Widefield Australian Square Kilometre Array (SKA) Pathfinder L-band Legacy All-sky Blind Survey and SKA, and deliver galaxy positions and velocities that can be used to measure galaxy clustering statistics. However, to harness this information to improve our cosmological understanding and learn about the physics of dark matter and dark energy, we need to accurately model the manner in which galaxies detected in H I trace the underlying matter distribution of the universe. For this purpose, we develop a new H I-based halo occupation distribution (HOD) model, which makes predictions for the number of galaxies present in dark matter halos conditional on their H I mass. The parameterized HOD model is fit and validated using the DARK SAGE semi-analytic model, where we show that the HOD parameters can be modeled by simple linear and quadratic functions of the H I mass. This work enables-for the first time-a simple prescription for placing galaxies of different H I masses within dark matter halos in a way that is able to reproduce the H I mass-dependent galaxy clustering and H I mass function simultaneously and without requiring knowledge of the optical properties of the galaxies. We also present a new halo density profile model for galaxies, which makes predictions for the positions of galaxies in the host halo, different to the widely adopted Navarro-Frenk-White (NFW) profile, since galaxies tend to be found more in the outskirts of halos (nearer the virial radius) than an NFW profile. The parameterised density profile model is fit and tested using the DarkSage semi-analytic model of galaxy formation. We find that our density profile model can accurately reproduce the halo occupation distribution and galaxy two-point correlation function of the DarkSage simulation. We also derive the analytic expressions for the circular velocity and gravitational potential energy for this density profile. We use the SDSS DR10 galaxy group catalogue to validate this halo density profile model. Compared to the NFW profile, we find that our model more accurately predicts the positions of galaxies in their host halo and the galaxy two-point correlation function.

We have explored the dynamical and mass evolution of halos driven by large-scale filaments using a dark matter-only cosmological simulation with the help of a phase-space analysis. Since a non-negligible number of galaxies is expected to fall into the cluster environment through large-scale filaments, tracking how halos move around large-scale filaments can provide a more comprehensive view on the evolution of cluster galaxies. Halos exhibit orbital motions around filaments, which emerge as specific trajectories in a phase space composed of halos' perpendicular distance and velocity component with respect to filaments. These phase-space trajectories can be represented by three cases according to their current states. We parameterize the trajectories with halos' initial position and velocity, maximum velocity, formation time, and time since first crossing, which are found to be correlated with each other. These correlations are explained well in the context of the large-scale structure formation. The mass evolution and dynamical properties of halos seem to be affected by the density of filaments, which can be shown from the fact that halos around denser filaments are more likely to lose their mass and be bound within large-scale filaments. Finally we reproduce the mass segregation trend around filaments found in observations. It is resulted because halos that formed earlier arrived filaments earlier, and grew efficiently there being more massive. We also found that dynamical friction helps to retain this segregation trend.

Lyman alpha emitters (LAEs) and Lyman-break galaxies (LBGs) are widely used for observing large-scale structures at high redshifts. However, how well they trace those structures has not been thoroughly investigated. In this study, we test LAEs and LBGs as tracers of large-scale structures at high redshifts using the data of Horizon Run 5 cosmological hydrodynamical simulation. We first construct samples of LAEs, LBGs, all galaxies, and dark matter particles. We then compare spatial distributions of our samples around the filamentary structures defined by dark matter particles. We also examine the thickness of the filamentary structures of each sample. Finally, we examine how the filamentary structures of galaxy samples (i.e., LAEs, LBGs, and all galaxies) are different compared to those of dark matter particles. From these results, I would like to discuss the feasibility of LAEs and LBGs as tracers of large-scale structures at high redshifts.

Recent integral field spectroscopic observations of galaxies have shown that the radial dependence of galaxy rotation is very diverse. To better understand the physical origin of this diversity, we analyze the cosmological hydrodynamic simulation data of IllustrisTNG. We use the galaxies with 9.4 < log(Mstar/M☉) < 11.5 to make a sample comparable to that of observations. We construct the mock line-of-sight velocity IFU data and conduct 2D fitting to determine the rotational velocity and the slope of the rotation curve in the outer region. The outer slopes of the simulated galaxies show diverse patterns, which are consistent with observational results. We examine the relation between the outer slope and the galaxy properties, and successfully reproduce the observed dependence of the outer slope on morphology and stellar mass. The outer slope increases as galaxies are more disky, and decreases as galaxies are more massive in terms of stellar mass except for the high mass of early-type galaxies. We quantitatively verify that the dark matter fraction is the dominant factor affecting the slope of the outer region of the rotation curves. We plan to investigate the environmental effect and galaxy formation history to find out the origin of the diverse rotation curves of galaxies.

Iterative Smoothing Method is a non-parametric regression approach for reconstruction of expansion history of the Universe and properties of dark energy. We can apply this method in various aspects of cosmology and astrophysics with no cosmological model assumption. We have worked on constraining SN Ia light-curve hyperparameters, searching for features in the data which can be a hint for systematics or new physics, parameter estimation and model selection. Our most recent application of the method is comparing our novel frequentist approach for model selection with conventional Bayesian evidence model selection. We show that when none of the candidate models (proposed to fit a data) is the true model, our novel frequentist approach can rule out all candidates while conventional Bayesian approach selects the least incorrect model. For more practical application of the method, our ongoing task is developing method of iterative smoothing for reconstructing the expansion history using combination of data with different natures. The method using combination of Type Ia supernova and BAO data is in preparation. We expect that the new method can be applied for cosmological studies using the real data from present and forthcoming surveys including DESI, Rubin, Roman, etc.

Using simulated Supernovae (SN), Baryon Acoustic Oscillations (BAO) and Redshift-Space Distortions (RSD) measurements from the next generation of (Stage-IV) cosmological surveys — and in particular the 14K deg2 data from DESI — we jointly reconstruct the growth and expansion histories using forward modeling and Gaussian Processes. Our approach only relies on few reasonable assumptions, namely: A (flat) Friedmann-Lemaître-Robertson-Walker metric, an Einstein De Sitter Universe at high-redshift. We forecast the future surveys’ potential to accurately reconstruct the Dark Energy (DE) evolution and thus to detect any possible deviation from a cosmological constant. We generate mock data for various alternative Dark Energy (DE) models, and illustrate how our method captures the correct DE behaviour in all cases — being capable of distinguishing them from \Lambda at more than 95% C.L. We extend our methodology to include possible deviations from General Relativity (GR) at low-z, by also reconstructing the phenomenological function Geff(z) governing the growth of (dust-like) matter density perturbations.

Brief information of his research area: I work mostly on the statistical models/techniques and try to apply them in Cosmological data-sets. One of my completed work is "Reconstruction of late-time cosmology using Principal Component Analysis". Combination of different statistical methods is one of my major fields of interest. In the above mentioned work we combine PCA with Correlation Coefficient Calculation to make the reconstruction unbiased. Our ongoing work is in combination of PCA and MCMC along with the combination of PCA with Gaussian Process.

The appropriate mathematical representation of cosmological observables is in the language of random fields. Traditional extraction of physical information has mostly relied on the two-point function. Increasing availability of good quality data makes alternative methods that exploit the geometrical and topological properties of random fields very attractive for cosmological data analysis. A brief overview of such morphological tools and physics questions that can be probed by them will be presented. A couple of new morphological ideas will also be presented.

This will be a small talk giving details about the progress made on the project. I will also be discussing the data available for the galaxies in HR5 and future analysis.

I am going to present my previous and current research projects, which all span around peculiar velocities and the Comicflows galaxy distance catalogs, from observations to more theoretical work.

We employ a set of high resolution N-body simulations to study the merger rate of dark matter halos. We define a specific merger rate by normalizing the average number of mergers per halo with the logarithmic mass growth change of the hosts at the time of accretion. Based on the simulation results, we find that this specific merger rate, $\mathrm{d}N_{\mathrm{merge}}(\xi|M,z)/\mathrm{d}\xi/\mathrm{d}\log M(z)$, has a universal form, which is only a function of the mass ratio of merging halo pairs, $\xi$, and does not depend on the host halo mass, $M$, or redshift, $z$, over a wide range of masses ($10^{12}\lesssim M \lesssim10^{14}\,M_\odot/h$) and merger ratios ($\xi\ge 1e-2$). We further test with simulations of different $\Omega_m$ and $\sigma_8$, and get the same specific merger rate. The universality of the specific merger rate shows that halos in the universe are built up self-similarly, with a universal composition in the mass contributions and an absolute merger rate that grows in proportion to the halo mass growth. As a result, the absolute merger rate relates with redshift and cosmology only through the halo mass variable, whose evolution can be readily obtained from the universal mass accretion history (MAH) model of \cite{2009ApJ...707..354Z}. Lastly, we show that this universal specific merger rate immediately predicts an universal un-evolved subhalo mass function that is independent on the redshift, MAH or the final halo mass, and vice versa.

Aspera is a new UV Small-Satellite mission to detect and map the warm-hot phase halo gas (10^5-10^6 K) around the nearby galaxy, led by the University of Arizona (PI: Carlos Vargas). The warm-hot phase gas occupies a considerable fraction of the galaxy baryonic mass budget. However, its amount and distribution are poorly unknown observationally. Aspera is specifically designed to observe those gas via UV spectroscopic observation of O VI line emission at 103.2 nm, a proxy of hot phase gas. High sensitivity of Aspera down to 5E-19 ergs/s/cm^2/arcsec^2 as well as a large field of view of 30 arcsec x 1 degrees allow detecting the faint O VI line emission efficiently. Aspera has been selected as one of the inaugural NASA Astrophysics Pioneers missions in early 2021. It has passed its conceptual design review and is now in the preliminary design phase, with a launch date of mid-2025. In this talk, I will present the science, instrument design and the status of the Aspera mission.

The discrepancy between the Hubble parameter inferred from local measurements and that from the cosmic microwave background (CMB) has motivated careful scrutiny of the assumptions that enter both analyses. Here we point out that the location of the recombination peak in the CMB B-mode power spectrum is determined by the light horizon at the surface of last scatter and thus provides an alternative early-Universe standard ruler. It can thus be used as a cross-check for the standard ruler inferred from the acoustic peaks in the CMB temperature power spectrum and to test various explanations for the Hubble tension. The measurement can potentially be carried out with a precision of ≲2% with stage-IV B-mode experiments. The measurement can also be used to measure the propagation speed of gravitational waves in the early Universe.

I will be discussing my latest progress on the project. I will be describing the motivation, method, and a few results on the topic.

We introduce a novel method for reconstructing the projected matter distributions of galaxy clusters with weak-lensing (WL) data based on convolutional neural network (CNN). Training datasets are generated with ray-tracing through cosmological simulations. We control the noise level of the galaxy shear catalog such that it mimics the typical properties of the existing ground-based WL observations of galaxy clusters. We find that the mass reconstruction by our multi-layered CNN with the architecture of alternating convolution and trans-convolution filters significantly outperforms the traditional reconstruction methods. The CNN method provides better pixel-to-pixel correlations with the truth, restores more accurate positions of the mass peaks, and more efficiently suppresses artifacts near the field edges. In addition, the CNN mass reconstruction lifts the mass-sheet degeneracy when applied to sufficiently large fields. This implies that this CNN algorithm can be used to measure cluster masses in a model independent way for future wide-field WL surveys.

Matter distribution around clusters is highly anisotropic from their being the nodes of the cosmic web. First, I investigate the influence of mass assembly history on both the shape and local connectivity of about 415 clusters of galaxies from IllustrisTNG simulation at z=0. The mass of clusters mainly influences the geometry of the matter distribution: massive halos are more elliptical, and more connected to the cosmic web than low-mass ones. Beyond the mass-driven effect, ellipticity and connectivity appear to trace different dynamical states, and it seems to result of different accretion histories. Secondly, I will present the statistical exploration of radial and azimuthal gas distribution around the same simulated galaxy cluster sample. Whereas hot plasma is virialised inside clusters, the warm diffuse gas phases is infalling from cosmic filaments to cluster peripheries. Azimuthal symmetries of gas and DM are directly related to the physical and dynamical properties of galaxy clusters.

please refer to the paper link, https://arxiv.org/abs/2109.12121.

We investigate the formation of jellyfish galaxies using radiation-hydrodynamic simulations of gas-rich dwarf galaxies with a multi-phase interstellar medium (ISM). We find that the ram-pressure-stripped (RPS) ISM is the dominant source of molecular clumps in the near wake within 10 kpc from the galactic plane}, while in-situ formation is the major channel for dense gas in the distant tail of the gas-rich galaxy. Only 20% of the molecular clumps in a near wake originates from the intracluster medium (ICM); however, the fraction reaches 50% in the clumps located at 80kpc from the galactic center since the cooling time of the RPS gas tends to be short due to the ISM-ICM mixing (< 10 Myr). The tail region exhibits a star formation rate of 0.001-0.01Msun/yr, and most of the tail stars are born in the stripped wake within 10\,kpc from the galactic plane. These stars induce bright H-alpha blobs in the tail, while H-alpha tails fainter than 10^38 erg/s/kpc^2 are formed via processes other than star formation. We also find that the stripped tails have intermediate X-ray to H-alpha surface brightness ratios (1< Xray/Halpha< 10), compared to the ISM (<1) or ICM (>>10). Our results suggest that jellyfish features emerge when the ISM from gas-rich galaxies is stripped by strong ram pressure, mixes with the ICM, and enhances the cooling in the tail.

Supernovae classes have been defined phenomenologically, based on spectral features and time series data, since the specific details of the physics of the different explosions remain unrevealed. However, the number of these classes is increasing as objects with new features are observed, and the next generation of large-surveys will only bring more variety to our attention. We apply the machine learning technique of multi-label classification to the spectra of supernovae. By measuring the probabilities of specific features or ‘tags’ in the supernova spectra, we can compress the information from a specific object down to that suitable for a human or database scan, without the need to directly assign to a reductive ‘class’. We use logistic regression to assign tag probabilities, and then a feed-forward neural network to filter the objects into the standard set of classes, based solely on the tag probabilities. We present STag, a software package that can compute these tag probabilities and make spectral classifications.

The small but measurable effect of weak gravitational lensing on the cosmic microwave background radiation provides information about the large-scale distribution of matter in the universe. We use the all sky distribution of matter, as represented by the convergence map that is inferred from CMB lensing measurement by Planck survey, to test the fundamental assumption of Statistical Isotropy (SI) of the universe. For the analysis we use the α statistic that is devised from the contour Minkowski tensor, a tensorial generalization of the scalar Minkowski functional, the contour length. In essence, the α statistic captures the ellipticity of iso-field contours at any chosen threshold value of a smooth random field and provides a measure of anisotropy. The SI of the observed convergence map is tested against the suite of realistic simulations of the convergence map provided by the Planck collaboration. We first carry out a global analysis using the full sky data after applying the galactic and point sources mask. We find that the observed data is consistent with SI. Further we carry out a local search for departure from SI in small patches of the sky using α. This analysis reveals several sky patches which exhibit deviations from simulations with statistical significance higher than 95% confidence level (CL). Our analysis indicates that the source of the anomalous behaviour of most of the outlier patches is inaccurate estimation of noise. We identify two outlier patches which exhibit anomalous behaviour originating from departure from SI at higher than 95% CL. Most of the anomalous patches are found to be located roughly along the ecliptic plane or in proximity to the ecliptic poles.

Accurate component separation of full-sky maps in the microwave frequencies relies on a thorough understanding of the statistical properties of the Galactic foreground emissions. Using scalar Minkowski functionals and their tensorial generalization known as Minkowski tensors, we analyze the statistical properties of one of the major foreground components, namely, the Galactic synchrotron given by the full sky 408 MHz Haslam map. We find that the overall level of the non-Gaussian deviations does decrease as more high emission regions are masked and as we go down to smaller scales, in agreement with results obtained in earlier works. However, they remain significantly high, of order 3-σ, at the smallest angular scales relevant for the Haslam map. We carry out a detailed examination of the non-Gaussian nature using the generalized skewness and kurtosis cumulants that arise in the perturbative expansion of Minkowski functionals for weakly non-Gaussian fields. We find that the leading sources of non-Gaussianity are the kurtosis terms which are considerably larger than the skewness terms at all angular scales. Further, for the cooler regions of the Haslam map, we find that the non-Gaussian deviations of the Minkowski functionals can be well explained by the perturbative expansion up to second order (up to kurtosis terms), with the first-order terms being sub-dominant. Lastly, we test the statistical isotropy of the Haslam map and find that it becomes increasingly more isotropic at smaller scales.

The consensus appears to be that cosmic voids or underdensities cannot explain Hubble tension. I will review some of the recent literature.

We investigate the impact of ram pressure stripping due to the intracluster medium (ICM) on star-forming disk galaxies with a multi-phase interstellar medium (ISM) maintained by strong stellar feedback. We carry out radiation-hydrodynamics simulations of an isolated disk galaxy embedded in a 10^11Msun dark matter halo with various ICM winds mimicking the cluster outskirts (moderate) and the central environment (strong). We find that both star formation quenching and triggering occur in ram pressure-stripped galaxies, depending on the strength of the winds. HI and H_2 in the outer galactic disk are significantly stripped in the presence of the moderate winds, whereas turbulent pressure provides support against ram pressure in the central region where star formation is active. Moderate ICM winds facilitate gas collapsing, increasing the total star formation rates by ~40% when the wind is oriented face-on or ~80% when it is edge-on. In contrast, strong winds rapidly blow away neutral and molecular hydrogen gas from the galaxy, suppressing the star formation by a factor of two within ~200 Myr. Dense gas clumps with N_H >10 Msun/pc^2 are easily identified in extraplanar regions, but no significant young stellar populations are found in such clumps. In our attempts to enhance radiative cooling by adopting a colder ICM of T=10^6 K, only a few additional stars are formed in the tail region, even if the amount of newly cooled gas increases by an order of magnitude.

String theorists have made some recent bold conjectures, arguably the most controversial of which precludes de Sitter vacua. Naturally, this is at odds with the current cosmological model, Lambda-CDM. In this talk, I will review observational evidence supporting the conjecture, i. e. a breakdown in Lambda-CDM, while demonstrating that the Quintessence models advocated by string theorists only exacerbate the tension in the Hubble CONSTANT. I will discuss the potential loopholes and set it as a non-trivial exercise to the audience to disprove string theory (even in a limited sense).

Low density regions are less affected by the nonlinear structure formation and baryonic physics, so they are ideal places to probe the dark energy. In this talk I will introduce our new method to define the low-density-positions (LDPs) with galaxies. With the CFHTLenS shear catalogue, we study the stacked lensing signals around LDPs in observation, which are found to achieve very high S/N. These lensing signals are then used to make simple constraints on the dark energy model. Furthermore, in my most recent work we find that LDP is a very good large scale structure tracer. So we extend it to measure the ISW effect, which is indeed a very weak signal. With the DESI photometric galaxy catalogue and Planck temperature map, now we have successfully measured the ISW signals, which will provide independent cross-checks for existing tensions.

I shall introduce a new technique of magnetic field studies that employs the advances of the theory of MHD turbulence and magnetic reconnection. This is the gradient technique that is subdivided into velocity gradients, synchrotron intensity gradients and synchrotron polarization gradients. These techniques provide unique opportunities to explore the 3D structure of magnetic field and also predict the foreground polarization. I shall discuss observational results obtained with the techniques. ********************************************************************** A Special KDESci Group Seminar ********************************************************************** Date & Place: 1:30pm Nov. 28 (Thursday), 2019. Room #8309 Speaker: Karim Benabed (IAP) Title: The Planck Legacy Results

The morphology of a surface can be well studied by the four Minkowski functionals (MFs). MFs contain information from all higher order correlation functions and, therefore, can complement the traditional N-point correlation statistics. The importance of MFs in analysing large-scale structure datasets is increasing rapidly with recent advances in observation and simulation. The Shapefinders are the ratios of these MFs and assess the three physical dimensions of a cluster/void. Similar to the large-scale structure of the universe, the reionization landscape is also very rich in geometrical properties which can be feasibly probed by MFs and Shapefinders. We explored the topology and morphology of simulated HI fields using 3D MFs and Shapefinders during the Epoch of Reionization (EoR). Using the advanced code SURFGEN2, we studied the shapes of the HI isodensity surfaces, together with the percolation process, at different stages of reionization. In this talk, I will briefly explain our novel approach and the results revealing some interesting geometrical features of the HI field during EoR. We are ambitious that our results, based on the simulations, can be compared with that of future observations using the upcoming low-frequency radio interferometers, such as the Square Kilometre Array (SKA).

In the standard cosmological model, LCDM model, dark matter and dark energy are the most abundant two components of the universe. However, we almost know nothing about the nature of these dark sectors. A natural question can be raised, do these two components have some interaction beyond gravity? After many years of effort, we can finally answer this question, making full use of all the current observations, which has never been done before. We conclude that the LCDM model is still favored by our analysis. We also disclose the possibility to look for smoking guns of dark matter dark energy interaction. In this talk, I will introduce how we model such interaction, how we do simulations and how we use weak lensing to test it. I will also introduce how to use the newly developed ME-Gadget code to perform non-standard cosmological model N-body simulations, such as modified gravity.

Nonlinearities in the gravitational evolution, galaxy bias, and redshift-space distortion drive the observed galaxy density fields away from the initial near-Gaussian states. Exploiting such a non-Gaussian galaxy density field requires measuring higher-order correlation functions, or, its Fourier counterpart, polyspectra. Here, we present an efficient parallel algorithm for estimating higher-order polyspectra. Based upon the Scoccimarro estimator, the estimator avoids direct sampling of polygons by using the Fast-Fourier Transform (FFT), and the parallelization overcomes the large memory requirement of the original estimator. In particular, we design the memory layout to minimize the inter-CPU communications, which excels in the code performance.

Although multiple cosmological observations indicate the existence of dark matter and dark energy, cosmological tests of interactions between them have not yet been established. We point out that, in the presence of a coupling between dark matter and dark energy, a peculiar velocity of total matter field is determined not only by a logarithmic time-derivative of its density perturbation but also by density perturbations for both dark matter and baryonic matter, leading to a large modification of the physical interpretation of observed data obtained by measurements of redshift-space distortions. We reformulate a galaxy two-point correlation function in the redshift space based on the modified continuity and Euler equations. We conclude from the resultant formula that redshift space distortions provide us information on the coupling between dark matter and the scalar field by combining weak lensing measurements. We will also discuss future prospects of constraining specific models using future surveys

We propose a set of new topological variables that can be used to characterize the large scale structure of the universe. The MGS (Mul-Guisin) algorithm was first introduced in the LHC experiment as a jet finder software. The algorithm creates particle clusters by grouping tracks that are close to each other with a certain distance measure. It is quite similar to the MST (Minimal Spanning Tree) that is popularly used in Astronomy, but the way of clustering particles is different and thus yields different shapes of the clusters. In this presentation we describe how the algorithm works in detail and introduce some topological variables that make differences in the SDSS observation data and the HR4 simulation data. We expect that the MGS variables can give a new angle to study the large scale structure of the universe along with the two-point correlation function and the MST.

Intensity mapping using the 21cm line promises to map out large volumes of the universe directly in three-dimensions at redshifts difficult to access using conventional surveys from the ground. HIRAX is a 1024-dish array to be deployed in the Karoo desert in South Africa next to the SKA site. HIRAX will map the 21cm emission over a large fraction of the southern sky from z=0.8 to 2.5. This survey will characterize the baryon acoustic oscillations in this redshift range, thus contributing new constraints regarding the nature of the dark energy. I will summarize this experiment and its advantages as well as outlining some of the challenges to be overcome. I will also discuss some of the other science that will be enabled by HIRAX such as understanding fast radio bursts and searching for new pulsars.

I will present results from the KMOS Redshift One Spectroscopic Survey (KROSS). Using the K-band Multi-object Spectrograph (KMOS) at the Very Large Telescope (VLT), KROSS has gathered integral-field data for ~800 star-forming galaxies at a redshift z~1, when the universe was roughly half its current age and forming the bulk of its stars. KROSS aims to study the spatially-resolved dynamics, star formation properties and metallicities of those middle-aged galaxies. First, I will quantify the dynamical state of the galaxies, thus constraining their likely mass growth mechanisms (e.g. mergers versus secular evolution), painting a picture of galaxies that are both gas-rich and highly turbulent. Second, I will describe the properties of the galaxies departing from the star formation main sequence, revealing that star formation in highly star-forming galaxies is also more concentrated and arises from lower metallicity gas. Third, I will present the observed and baryonic Tully-Fisher (luminosity - rotation velocity) relation, thus constraining the mass-to-light ratios and luminous+dark masses of the galaxies. Last, by degrading and analogously analysing integral-field data of hundreds of local galaxies from the Sydney-AAO Multi-object Integral-field Spectrograph (SAMI) survey, I will derive a comparison Tully-Fisher relation at z=0, thus constraining the luminous+dark mass growth of disk galaxies over the last 7 billions years. This unique comparison also highlights that the systematic effects associated with sample selection and analysis methods are as large as the effects expected from cosmological evolution, and thus that most other results can safely be ignored.

Thermal inflation is an additional inflationary mechanism before the big bang nucleosynthesis, which solves the moduli problem and naturally provides a plausible dark matter candidate. Thermal inflation leaves a slight enhancement followed by huge suppression of a factor of ~50 in the curvature and matter power spectrum, which can be expressed in terms of a single characteristic scale k_b. Here we describe the observability of the small-scale features of thermal inflation from various observations, such as CMB distortion, satellite galaxy abundance in the Milky-Way-sized galaxies, and 21-cm power spectrum before the epoch of reionization.

I will describe how to follow the gravitational evolution of the cosmic large scale structure using counts-in-cells statistics. Based on the theory of large deviations, I will argue that spherical collapse dynamics can be used to predict the statistics of average densities in spherical cells. I will then compare analytical predictions for counts-in-cells statistics against state of the art dark matter simulations showing that they can access a mildly nonlinear regime beyond perturbative calculations. Finally, I will discuss its potential to constrain cosmology using future galaxy surveys by describing biased tracers and angular clustering.

COBE/DIRBE satellite revealed that the central region of our Milky Way hosts a boxy shaped bulge rather than a spheroidal one. A number of evidences have established that the Millky Way also hosts a stellar bar in the disk mid-plane and the boxy-bulge is thought to have formed as a result of buckling instability of the bar. N-body modelling of the kinematic data from recently completed surveys such as BRAVA, VVV etc., indicates that our Milky Way is a pure disk galaxy without a classical bulge. However, stellar population and metallicity gradients in the bulge do not rule out the possible existence of a classical bulge. After giving a brief overview of the current status of the Milky Way's bulge, I will discuss some new results that might shed some new light on this ongoing debate.

Tensor Minkowski Functionals (TMF) are tensor generalizations of the usual scalar Minkowski Functionals. They carry shape and alignment information for a given set of structures, which their scalar counterparts are unable to capture. In this seminar we introduce TMFs for application to cosmological datasets, particularly the CMB.

Density inhomogeneity in the intergalactic medium (IGM) on sub-Mpc scales can boost the recombination rate of ionized gas substantially, affecting the growth of H II regions during the Epoch of Reionization (EoR). Previous attempts to express this in terms of a clumping factor, C, typically failed to resolve the full range of mass scales which are important in establishing this effect, down to the Jeans scale in the pre-ionization IGM, along with the hydrodynamical back-reaction of reionization on it. Towards that end, we introduce GADGET-RT, a GADGET code with a new algorithm to transfer H-ionizing radiation, and perform a set of radiation-hydrodynamics simulations from cosmological initial conditions. We extend the mass resolution of previous work to the scale of minihalos, simulating sub-Mpc volumes. Pre-reionization structure is evolved until a redshift z_i at which the ionizing radiation from external sources arrives to sweep an R-type ionization front supersonically across the volume in a few Myr, until it is trapped on the surfaces of minihalos and converted to D-type. Small-scale density structures during this time lead to a high (C > 10) clumping factor for ionized gas. This high clumping factor hugely boosts the recombination rate until the structures are mostly disrupted by the hydrodynamic feedback after ~ 10 - 100 Myr. For incoming radiation with intensity J_21, a number of extra recombinations result per H atom, on top of what is expected from gas at the mean density, is given by 0.32 [J_21]^0.12 [(1 + z_i)/11]^-1.7. In models in which most of the volume is ionized toward the end of reionization, this can add up to~ 0.7 per H atom to the ionizing photon budget to achieve reionization. Even more recombinations will result when full account is also taken of the matter density inhomogeneity on scales larger than that of our sub-Mpc simulation volumes.

We constrain the energy scale of noncommutativity of spacetime using CMB data from PLANCK. We find that PLANCK data puts the lower bound on the noncommutativity energy scale to about 20 TeV, which is about a factor of 2 larger than a previous constraint that was obtained using data from WMAP. We further show that inclusion of data of $E$ mode of CMB polarization will not significantly change the constraint. Title: Data Science and Cosmology (Amir Aghamousa) Abstract: I will explain basic statistical concepts in statistics and gradually some statistical techniques for data inference. It will be started by an introduction to R and accompanied with several demonstrations. Then I will continue the data analysis in Cosmology by discussing some practical projects in Cosmology using introduced statistical tools.