arXiv subjects

Imran Sultan

Publications and source records attributed to Imran Sultan.

8 recordsLinked to original sources

arXiv2026

Cold vs. Hot Gas Accretion and Angular Momentum in FIRE Simulations: From Halo to Galaxy Scales

We present a systematic study of gas accretion and angular momentum in the circumgalactic medium (CGM) using high-resolution FIRE cosmological simulations. Our analysis includes halos spanning the critical $\sim 10^{12}\ \mathrm{M}_{\odot}$ scale where several transitions have been identified, including inner CGM virialization, the transition from bursty to steady star formation, and the emergence of thin disks. We find that the temperature of inflowing gas is correlated with the virialization of the inner CGM. CGM inflows are almost entirely cold ($T < 10^5$ K) in pre-virialized halos, while hot inflows ($T > 10^5$ K) dominate in virialized halos. When hot inflows dominate, cooling generally occurs simultaneously with circularization at galaxy radii. The dominance of hot inflows onto massive galaxies persists even at high redshift, where cold streams may coexist. Consistent with previous studies, cold inflows have higher specific angular momentum than dark matter and hot gas. However, in bursty, low-mass galaxies, cold inflows do not circularize prior to star formation, while in steady, massive galaxies, hot inflows circularize, cool, and form stars with disk-like kinematics. We additionally find that in bursty galaxies, accreted gas typically forms stars after residing in the galaxy for less than $\sim 5$ galaxy free-fall times, while in steady galaxies, gas can persist for up to $\sim 25$ free-fall times before forming stars. This highlights a key difference between star formation in bursty galaxies fed by cold accretion and steady equilibrium disks fed by hot accretion.

astro-ph.GA↗

arXiv2025

Hot accretion onto spiral galaxies: the origin of extended and warped HI discs

Gas accretion, hot ($\sim 10^6$ K) atmospheres, and a tilt between the rotation axes of the disc and the atmosphere are all common predictions of standard galaxy evolution theory for massive star-forming galaxies at low redshift. Using idealised hydrodynamic simulations, we demonstrate that the central regions of hot galaxy atmospheres continuously condense into cool ($\sim 10^4$ K) discs, while being replenished by an inflow from larger scales. The size and orientation of the condensed disc are determined by the angular momentum of the atmosphere, so the condensed disc is expected to often be tilted and more extended than the stellar disc. Continuous accretion from hot atmospheres can thus explain the ubiquity of extended and warped HI discs around local spirals, and also potentially provide the necessary fuel for star formation. This hot accretion scenario predicts the absence of significant HI from galaxy halos, consistent with recent 21 cm constraints on nearby spirals (the so-called `HI desert'). Moreover, our analysis indicates that observations of HI warps can be used to constrain the angular momentum, accretion rate, and gas metallicity of hot galaxy atmospheres, important parameters for disc galaxy evolution that are hard to determine by other means.

astro-ph.GA↗

arXiv2024

Cooling Flows as a Reference Solution for the Hot Circumgalactic Medium

The circumgalactic medium (CGM) in $\gtrsim 10^{12}$ $\mathrm{M}_{\odot}$ halos is dominated by a hot phase ($T \gtrsim 10^{6}$ K). While many models exist for the hot gas structure, there is as yet no consensus. We compare cooling flow models, in which the hot CGM flows inward due to radiative cooling, to the CGM of $\sim 10^{12}-10^{13}$ $\mathrm{M}_{\odot}$ halos in galaxy formation simulations from the FIRE project at $z\sim0$. The simulations include realistic cosmological evolution and feedback from stars but neglect AGN feedback. At both mass scales, CGM inflows are typically dominated by the hot phase rather than by the `precipitation' of cold gas. Despite being highly idealized, we find that cooling flows describe $\sim 10^{13}$ $\mathrm{M}_{\odot}$ halos very well, with median agreement in the density and temperature profiles of $\sim 20\%$ and $\sim 10\%$, respectively. This indicates that stellar feedback has little impact on CGM scales in those halos. For $\sim 10^{12}$ $\mathrm{M}_{\odot}$ halos, the thermodynamic profiles are also accurately reproduced in the outer CGM. For some of these lower-mass halos, cooling flows significantly overpredict the hot gas density in the inner CGM. This could be due to multidimensional angular momentum effects not well captured by our 1D cooling flow models and/or to the larger cold gas fractions in these regions. Turbulence, which contributes $\sim 10-40\%$ of the total pressure, must be included to accurately reproduce the temperature profiles. Overall, cooling flows predict entropy profiles in better agreement with the FIRE simulations than other idealized models in the literature.

astro-ph.GA↗

arXiv2024

Ne VIII in the warm-hot circumgalactic medium of FIRE simulations and in observations

The properties of warm-hot gas around $\sim L_{*}$ galaxies can be studied with absorption lines from highly ionized metals. We predict Ne VIII column densities from cosmological zoom-in simulations of halos with masses in $\sim 10^{12}$ and $\sim 10^{13}\,\mathrm{M}_{\odot}$ from the FIRE project. Ne VIII traces the volume-filling, virial-temperature gas in $\sim 10^{12}\,\mathrm{M}_{\odot}$ halos. In $\sim 10^{13}\,\mathrm{M}_{\odot}$ halos the Ne VIII gas is clumpier, and biased towards the cooler part of the warm-hot phase. We compare the simulations to observations by the CASBaH and CUBS surveys. We show that when inferring halo masses from stellar masses to compare simulated and observed halos, it is important to account for the scatter in the stellar-mass-halo-mass relation, especially at $\,\mathrm{M}_{\star} \gtrsim 10^{10.5} \,\mathrm{M}_{\odot}$. Median Ne VIII columns in the fiducial FIRE-2 model are about as high as observed upper limits allow, while the simulations analyzed do not reproduce the highest observed columns. This suggests that the median Ne VIII profiles predicted by the simulations are consistent with observations, but that the simulations may underpredict the scatter. We find similar agreement with analytical models that assume a product of the halo gas fraction and metallicity (relative to solar) $\sim 0.1$-$0.3$, indicating that observations are consistent with plausible CGM temperatures, metallicities, and gas masses. Variants of the FIRE simulations with a modified supernova feedback model and/or AGN feedback included (as well as some other cosmological simulations from the literature) more systematically underpredict Ne VIII columns. The circumgalactic Ne VIII observations therefore provide valuable constraints on simulations that otherwise predict realistic galaxy properties.

astro-ph.GA↗

arXiv2023

Effects of multi-channel AGN feedback in FIRE cosmological simulations of massive galaxies

Feedback from supermassive black holes is believed to be a critical driver of the observed color bimodality of galaxies above the Milky Way mass scale. AGN feedback has been modeled in many galaxy formation simulations, but most implementations have involved simplified prescriptions or a coarse-grained interstellar medium (ISM). We present the first set of FIRE-3 cosmological zoom-in simulations with AGN feedback evolved to $z\sim0$, examining the impact of AGN feedback on a set of galaxies with halos in the mass range $10^{12}-10^{13} M_{\odot}$. These simulations combine detailed stellar and ISM physics with multi-channel AGN feedback including radiative feedback, mechanical outflows, and in some simulations, cosmic rays (CRs). We find that massive (>L*) galaxies in these simulations can match local scaling relations including the stellar mass-halo mass relation and the $M_{\rm BH}$-$\sigma$ relation; in the stronger model with CRs, they also match the size-mass relation and the Faber-Jackson relation. Many of the massive galaxies in the simulations with AGN feedback have quenched star formation and elliptical morphologies, in qualitative agreement with observations. In contrast, simulations at the massive end without AGN feedback produce galaxies that are too massive and form stars too rapidly, are order-of-magnitude too compact, and have velocity dispersions well above Faber-Jackson. Despite these successes, the AGN models analyzed do not produce uniformly realistic galaxies when the feedback parameters are held constant: while the stronger model produces the most realistic massive galaxies, it tends to over-quench the lower-mass galaxies. This indicates that further refinements of the AGN modeling are needed.

astro-ph.GA↗

arXiv2021

Farpoint: A High-Resolution Cosmology Simulation at the Gigaparsec Scale

In this paper we introduce the Farpoint simulation, the latest member of the Hardware/Hybrid Accelerated Cosmology Code (HACC) gravity-only simulation family. The domain covers a volume of (1000$h^{-1}$Mpc)$^3$ and evolves close to two trillion particles, corresponding to a mass resolution of $m_p\sim 4.6\cdot 10^7 h^{-1}$M$_\odot$. These specifications enable comprehensive investigations of the galaxy-halo connection, capturing halos down to small masses. Further, the large volume resolves scales typical of modern surveys with good statistical coverage of high mass halos. The simulation was carried out on the GPU-accelerated system Summit, one of the fastest supercomputers currently available. We provide specifics about the Farpoint run and present an initial set of results. The high mass resolution facilitates precise measurements of important global statistics, such as the halo concentration-mass relation and the correlation function down to small scales. Selected subsets of the simulation data products are publicly available via the HACC Simulation Data Portal.

astro-ph.CO↗

arXiv2020

The Last Journey. II. SMACC -- Subhalo Mass-loss Analysis using Core Catalogs

This paper introduces SMACC -- Subhalo Mass-loss Analysis using Core Catalogs. SMACC adds a mass model to substructure merger trees based on halo "core tracking." Our approach avoids the need for running expensive subhalo finding algorithms and instead uses subhalo mass-loss modeling to assign masses to halo cores. We present details of the SMACC methodology and demonstrate its excellent performance in describing halo substructure and its evolution. Validation of the approach is carried out using cosmological simulations at significantly different resolutions. We apply SMACC to the 1.24 trillion-particle Last Journey simulation and construct core catalogs with the additional mass information. These catalogs can be readily used as input to semi-analytic models or subhalo abundance matching approaches to determine approximate galaxy distributions, as well as for in-depth studies of small-scale structure evolution.

astro-ph.CO↗

arXiv2020

The Last Journey. I. An Extreme-Scale Simulation on the Mira Supercomputer

The Last Journey is a large-volume, gravity-only, cosmological N-body simulation evolving more than 1.24 trillion particles in a periodic box with a side-length of 5.025Gpc. It was implemented using the HACC simulation and analysis framework on the BG/Q system, Mira. The cosmological parameters are chosen to be consistent with the results from the Planck satellite. A range of analysis tools have been run in situ to enable a diverse set of science projects, and at the same time, to keep the resulting data amount manageable. Analysis outputs have been generated starting at redshift z~10 to allow for construction of synthetic galaxy catalogs using a semi-analytic modeling approach in post-processing. As part of our in situ analysis pipeline we employ a new method for tracking halo sub-structures, introducing the concept of subhalo cores. The production of multi-wavelength synthetic sky maps is facilitated by generating particle lightcones in situ, also beginning at z~10. We provide an overview of the simulation set-up and the generated data products; a first set of analysis results is presented. A subset of the data is publicly available.

astro-ph.CO↗