We present cosmological-scale three-dimensional neutral hydrogen (H
This content will become publicly available on June 26, 2025
The presence of dense, neutral hydrogen clouds in the hot, diffuse intragroup and intracluster (IC) medium is an important clue to the physical processes controlling the survival of cold gas and sheds light on cosmological baryon flows in massive halos. Advances in numerical modeling and observational surveys mean that theory and observational comparisons are now possible. In this paper, we use the high-resolution TNG50 cosmological simulation to study the H
- Award ID(s):
- 2108470
- PAR ID:
- 10545115
- Publisher / Repository:
- IOP
- Date Published:
- Journal Name:
- The Astrophysical Journal
- Volume:
- 969
- Issue:
- 1
- ISSN:
- 0004-637X
- Page Range / eLocation ID:
- 28
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
Abstract i ) tomographic maps atz = 2–3 over a total of 837 deg2in two blank fields that are developed with Lyα forest absorptions of 14,736 background Sloan Digital Sky Survey (SDSS) quasars atz = 2.08–3.67. Using the tomographic maps, we investigate the large-scale (≳10h −1cMpc) average Hi radial profiles and two-direction profiles of the line-of-sight (LOS) and transverse directions around galaxies and active galactic nuclei (AGNs) atz = 2–3 identified by the Hobby–Eberly Telescope Dark Energy eXperiment survey and SDSS, respectively. The peak of the Hi radial profile around galaxies is lower than the one around AGNs, suggesting that the dark matter halos of galaxies are less massive on average than those of AGNs. The LOS profile of AGNs is narrower than the transverse profile, indicating the Kaiser effect. There exist weak absorption outskirts at ≳30h −1cMpc beyond Hi structures of galaxies and AGNs found in the LOS profiles that can be explained by the Hi gas at ≳30h −1cMpc falling toward the source position. Our findings indicate that the Hi radial profile of AGNs has transitions from proximity zones (≲a fewh −1cMpc) to the Hi structures (∼1–30h −1cMpc) and the weak absorption outskirts (≳30h −1cMpc). Although there is no significant dependence of AGN types (type 1 vs. type 2) on the Hi profiles, the peaks of the radial profiles anticorrelate with AGN luminosities, suggesting that AGNs’ ionization effects are stronger than the gas mass differences. -
Abstract The properties of warm-hot gas around ∼
L *galaxies can be studied with absorption lines from highly ionized metals. We predict Neviii column densities from cosmological zoom-in simulations of halos with masses in ∼1012and ∼1013M ☉from the Feedback in Realistic Environments (FIRE) project. Neviii traces the volume-filling, virial-temperature gas in ∼1012M ☉halos. In ∼1013M ☉halos the Neviii gas is clumpier, and biased toward the cooler part of the warm-hot phase. We compare the simulations to observations from the COS Absorption Survey of Baryon Harbors (or CASBaH) and COS Ultraviolet Baryon Survey (or CUBS). 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 atM ⋆≳ 1010.5M ☉. Median Neviii 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 Neviii 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) ∼0.1, indicating that observations are consistent with plausible circumgalactic medium temperatures, metallicities, and gas masses. Variants of the FIRE simulations with a modified supernova feedback model and/or active galactic nuclei feedback included (as well as some other cosmological simulations from the literature) more systematically underpredict Neviii columns. The circumgalactic Neviii observations therefore provide valuable constraints on simulations that otherwise predict realistic galaxy properties. -
Abstract Measuring the properties of the cold neutral medium (CNM) in low-metallicity galaxies provides insights into heating and cooling mechanisms in early Universe-like environments. We report detections of two localized atomic neutral hydrogen (H
i ) absorption features in NGC 6822, a low-metallicity (0.2Z ⊙) dwarf galaxy in the Local Group. These are the first unambiguous CNM detections in a low-metallicity dwarf galaxy outside the Magellanic Clouds. The Local GroupL -band Survey (LGLBS) enabled these detections, due to its high spatial (15 pc for Hi emission) and spectral (0.4 km s−1) resolution. We introduce LGLBS and describe a custom pipeline for searching for Hi absorption at high angular resolution and extracting associated Hi emission. A detailed Gaussian decomposition and radiative transfer analysis of the NGC 6822 detections reveals five CNM components, with key properties: a mean spin temperature of 32 ± 6 K, a mean CNM column density of 3.1 × 1020cm−2, and CNM mass fractions of 0.33 and 0.12 for the two sightlines. Stacking nondetections does not reveal low-level signals below our median optical depth sensitivity of 0.05. One detection intercepts a star-forming region, with the Hi absorption profile encompassing the CO (2−1) emission, indicating coincident molecular gas and a depression in high-resolution Hi emission. We also analyze a nearby sightline with deep, narrow Hi self-absorption dips, where the background warm neutral medium is attenuated by intervening CNM. The association of CNM, CO, and Hα emissions suggests a close link between the colder, denser Hi phase and star formation in NGC 6822. -
Abstract We present the discovery of neutral gas detected in both damped Ly
α absorption (DLA) and Hi 21 cm emission outside of the stellar body of a galaxy, the first such detection in the literature. A joint analysis between the Cosmic Ultraviolet Baryon Survey and the MeerKAT Absorption Line Survey reveals an Hi bridge connecting two interacting dwarf galaxies (log (M star/M ⊙) = 8.5 ± 0.2) that host az = 0.026 DLA with log[N (Hi )/cm−2] = 20.60 ± 0.05 toward the QSO J2339−5523 (z QSO= 1.35). At impact parameters ofd = 6 and 33 kpc, the dwarf galaxies have no companions more luminous than ≈0.05L *within at least Δv = ±300 km s−1andd ≈ 350 kpc. The Hi 21 cm emission is spatially coincident with the DLA at the 2σ –3σ level per spectral channel over several adjacent beams. However, Hi 21 cm absorption is not detected against the radio-bright QSO; if the background UV and radio sources are spatially aligned, the gas is either warm or clumpy (with a spin temperature to covering factor ratioT s /f c > 1880 K). Observations with VLT-MUSE demonstrate that theα -element abundance of the ionized interstellar medium (ISM) is consistent with the DLA (≈10% solar), suggesting that the neutral gas envelope is perturbed ISM gas. This study showcases the impact of dwarf–dwarf interactions on the physical and chemical state of neutral gas outside of star-forming regions. In the SKA era, joint UV and Hi 21 cm analyses will be critical for connecting the cosmic neutral gas content to galaxy environments. -
Abstract We present an in-depth analysis of gas morphologies for a sample of 25 Milky Way–like galaxies from the IllustrisTNG TNG50 simulation. We constrain the morphology of cold, warm, hot gas, and gas particles as a whole using a local shell iterative method and explore its observational implications by computing the hard-to-soft X-ray ratio, which ranges between 10−3and 10−2in the inner ∼50 kpc of the distribution and 10−5–10−4at the outer portion of the hot gas distribution. We group galaxies into three main categories: simple, stretched, and twisted. These categories are based on the radial reorientation of the principal axes of the reduced inertia tensor. We find that a vast majority (77%) of the galaxies in our sample exhibit twisting patterns in their radial profiles. Additionally, we present detailed comparisons between (i) the gaseous distributions belonging to individual temperature regimes, (ii) the cold gas distributions and stellar distributions, and (iii) the gaseous distributions and dark matter (DM) halos. We find a strong correlation between the morphological properties of the cold gas and stellar distributions. Furthermore, we find a correlation between gaseous distributions with a DM halo that increases with gas temperature, implying that we may use the warm–hot gaseous morphology as a tracer to probe the DM morphology. Finally, we show gaseous distributions exhibit significantly more prolate morphologies than the stellar distributions and DM halos, which we hypothesize is due to stellar and active galactic nucleus feedback.