Astrophysics

Fast radio bursts (FRBs) are dispersed and scattered by plasma density fluctuations along the line-of-sight, making them sensitive probes of diffuse ionized gas across interstellar, circumgalactic, and intergalactic media. In this talk I will discuss how FRB propagation effects are unveiling cosmic plasmas at extremely small (sub-au) spatial scales in both interstellar and circumgalactic media, and how they may be used in tandem with quasars to constrain the turbulent dynamics of ionized gas in these environments.

The intergalactic medium gas is usually believed to simply trace the cosmic web structures traced by dark matter, but AGN feedback (especially jets) will probably modify this simple picture especially the IGM and CGM baryon budgets. I will talk primarily about the combining spectroscopic galaxy surveys with FRBs to probe the IGM and CGM balance, which is being implemented in the FLIMFLAM survey. I will highlight the role of Subaru PFS, the world's most powerful multiobject spectrograph, in efficiently mapping the cosmic web out to high redshift, and new applications of the field level inference technique towards this problem.

The cosmic web in the distant universe is generally mapped by observing the positions of galaxies. Recently a new perspective has been gained by mapping the diffuse gas in the intergalactic medium (IGM). The Lyman-Alpha Tomography IMACS Survey (LATIS) has now produced 3D maps of the IGM at redshift z~2.5, covering a volume of about 10^7 Mpc^3. I will present the LATIS maps and discuss how they inform our understanding of the interplay between early galaxies and their large-scale environments.

Remarkable parallels exist between observations of diffuse baryons and their connections to galaxies in the high redshift universe compared to z~0 ... in spite of apparently vast differences between the properties of the galaxies themselves and the nature and intensity of the feedback processes operating within them. I will attempt to draw connections between "contemporaneous" observations of galaxy-scale feedback in the adolescent universe with observable signatures "today", and attempt to distinguish between evolutionary sequences and possible coincidences that need further investigation.

Recent observations of the CGM reveal that it is extended, multiphase, and ubiquitous, detected around star forming and quiescent galaxies. However, many questions remain open - how much gas is out there, what are its thermal properties, spatial distribution, and morphology? These are linked to the properties of gas accretion onto galaxies, star formation, and feedback processes, and are crucial to our holistic understanding of galactic ecosystems. I will present the multiphase CGM modeling framework I developed with collaborators and showcase examples of its application to a wide range of absorption measurements, constraining the CGM mass, thermodynamics, energetics, and cool gas cloud sizes. I will also demonstrate how predictions from these models can be used to test them with upcoming and future multi-wavelength observations.

The cosmic far-infrared background (CIB) encodes dust emission from all galaxies and carries valuable information on structure formation, star formation, and chemical enrichment across cosmic time. However, its redshift-dependent spectrum remains poorly constrained due to line-of-sight projection effects. We address this in [arXiv:2504.05384][1] by cross-correlating 11 far-infrared intensity maps spanning a 50-fold frequency range from Planck, Herschel, and IRAS, with spectroscopic galaxies and quasars from SDSS I-IV tomographically. We mitigate foregrounds using [CSFD][2], a CIB-free Milky Way dust map, and also remove the tomographic SZ background from hot gas in the cosmic web detected in [arXiv:2006.14650][3]. These cross-correlation amplitudes on two-halo scales trace bias-weighted CIB redshift distributions and collectively yield a 60σ detection of the evolving CIB spectrum, sampled across hundreds of rest-frame frequencies over 0 < z < 4. We break the bias-intensity degeneracy by adding monopole information from FIRAS. The recovered CIB spectrum reveals a dust temperature distribution that is broad, spanning the full range of host environments, and moderately evolving. Using low-frequency CIB amplitudes, we constrain cosmic dust density, Ω_dust, which peaks at z = 1-1.5 and declines threefold to the present. Our wide spectral and sky coverages enable a determination of the total infrared luminosity density with negligible cosmic variance across 90% of cosmic time. This yields a more precise yet consistent constraint on the cosmic star formation history compared to the Madau & Dickinson (2014) compilation. Additionally, we find that star formation occurs in a mode that is, on average, 80% dust-obscured at z = 0 and 60% at z = 4. Our results, based on intensity mapping, are complete, requiring no extrapolation to faint galaxies or low-surface-brightness components. We release our tomographic CIB spectrum and redshift distributions in [this link][4] as a public resource for future studies of the CIB, both as a cosmological matter tracer and CMB foreground. [1]: https://arxiv.org/abs/2504.05384 [2]: https://arxiv.org/abs/2306.03926 [3]: https://arxiv.org/abs/2006.14650 [4]: https://zenodo.org/records/15149425

Feedback processes, particularly from active galactic nuclei (AGN), play a crucial role in redistributing baryons within halos. These mechanisms can displace gas to halo outskirts or eject it entirely, leading to baryon fractions below the cosmic mean. While simulations such as TNG, SIMBA, and EAGLE predict these effects across a wide halo mass range, observational constraints remain largely limited to high-mass groups and clusters. In this talk, I will present a systematic analysis of the observed baryon content of halos in the local universe across a mass range of $10^{10} - 10^{15} M_{\odot}$​, using a compilation of empirical measurements from the literature. We quantify the contributions of hot gas, stars, and cold gas to the total baryon budget, constructing baryonic mass-to-halo mass scaling relations. We also use the latest eROSITA and ASKAP data to provide the current constraints on the average hot gas and cold gas content in halos through stacking analysis. The baryonic scaling relations are constructed from group- and cluster-scale halos down to $10^{12} M_{\odot}$​ for all three components, while additional individual galaxy measurements allow us to extend HI and stellar mass scaling relations to $10^{10} M_{\odot}$​. By combining these relations with the halo mass function, we then determine the baryon density distribution as a function of halo mass and calculate the cosmic mass densities of stars, HI, and hot gas within halos in the local universe. Our results provide key observational constraints on the distribution of baryons in the local universe, offering insights into potential mechanisms, such as feedback, that regulate baryon retention and redistribution.

Weak gravitational lensing is the only way to probe the total matter distribution on the scales of galaxies and the surrounding cosmic web. Understanding the dark matter distribution and its link to galaxies is critical not only galaxy formation and evolution, but also to correctly extract the cosmological parameters from weak lensing surveys. I will highlight recent results from the Ultraviolet Near Infrared Optical Northern Survey (UNIONS), a major weak lensing survey of 6000 square degrees of the northern sky, that probe the dark matter distribution around luminous red galaxies, allowing us to see the feedback-affected matter profiles, around galaxy mergers and in filaments of the cosmic web. If time permits, I will discuss prospect for future weak lensing surveys such as Euclid.

I will present an overview of the work of the "GM Galaxies" project, which explores the relationship between history of a galaxy and its observable traits. I will give three examples of our work, looking at how dwarf galaxies change their properties based on their mass assembly, the Milky Way stellar halo responds to variations in its merging history, and the circumgalactic medium of massive galaxies mediates the transition from star-forming to quiescent.

Line Intensity Mapping (LIM) experiments are innovative techniques for studying structures at high redshift. They allow us to uncover previously inaccessible astrophysical data by making 3D tomographic maps with 2D spatial line intensity fluctuations. As efforts like COMAP progress in detecting carbon monoxide (CO) and other spectral lines, generating precise mock maps becomes crucial for data analysis, prediction of future observations, and development of new statistical methods for LIM analysis. These mock maps are generated by interpolating line luminosities across the specified dark matter halo distribution, using response functions that are defined by the relationship between the line luminosities and both observable and derived properties of simulated galaxies. In my presentation, I will elucidate the statistical relationship between the calculated line luminosity and inherent/derived observables for simulated FIRE (Feedback In Realistic Environment) galaxies, focusing on CO(1-0) to CO(8-7) lines at four different redshift regimes: z=0, 1, 2, and 3. I will examine the correlations between CO emission and galactic properties at different redshifts and explore the potential causal relationships they may suggest as well as how they can define essential response functions for creating mock maps.

The CGM is sensitive to various baryonic flows (e.g. stellar winds, supernovae, etc.) occurring on different timescales. Chemical abundance patterns in circumgalactic clouds provide a unique timing clock for constraining the dominant source of feedback regulating galaxy growth. In this talk, I will discuss how we leverage multiwavelength quasar spectra from surveys like the Cosmic Ultraviolet Baryon Survey (CUBS) to constrain the gas ionization state and elemental abundances of cool/warm-hot CGM absorbers. We find relatively cool (~1-5e4 K), diffuse (~0.001-0.01 cm^-3) photoionized gas clumps exhibiting a variety of chemical enrichment patterns. Several absorbers show an enhancement in non-alpha elements (e.g. carbon, nitrogen) reflecting metal production by secondary nucleosynthetic pathways. We also find chemically mature, metal-poor absorbers, showing evidence of mixing between pre-enriched gas and pristine inflows. These results demonstrate the value of using elemental abundances to understand which feedback processes are most critical in shaping the cosmic baryon cycle.