Molecular hydrogen in IllustrisTNG galaxies: carefully comparing signatures of environment with local CO and SFR data

Abstract

We examine how the post-processed content of molecular hydrogen (H2) in galaxies from the TNG100 cosmological, hydrodynamic simulation changes with environment at z = 0, assessing central/satellite status and host halo mass. We make close comparisons with the carbon monoxide (CO) emission survey xCOLD GASS where possible, having mock-observed TNG100 galaxies to match the survey’s specifications. For a representative sample of host haloes across 1011 ≲ M200c/M⊙ < 1014.6, TNG100 predicts that satellites with m* ≥ 109 M⊙ should have a median deficit in their H2fractions of ∼0.6 dex relative to centrals of the same stellar mass. Once observational and group-finding uncertainties are accounted for, the signature of this deficit decreases to ∼0.2 dex. Remarkably, we calculate a deficit in xCOLD GASS satellites’ H2content relative to centrals of 0.2–0.3 dex, in line with our prediction. We further show that TNG100 and SDSS data exhibit continuous declines in the average star formation rates of galaxies at fixed stellar mass in denser environments, in quantitative agreement with each other. By tracking satellites from their moment of infall in TNG100, we directly show that atomic hydrogen (H i) is depleted at fractionally higher rates than H2on average. Supporting this picture, we find that the H2/H i mass ratios of satellites are elevated relative to centrals in xCOLD GASS. We provide additional predictions for the effect of environment on H2 — both absolute and relative to H i — that can be tested with spectral stacking in future CO surveys.

WALLABY Pilot Survey: the diversity of ram pressure stripping of the galactic HI gas in the Hydra Cluster

“…We can thus expect that there is a diversity of the way that galaxies experience ram pressure stripping, as infalling galaxies have different distributions of mass and gas, and travel along different orbits and with different disk inclinations against the ICM wind. Hydrodynamical simulations of cluster systems confirm these complexities (Tonnesen 2019;Lotz et al 2019;Bekki 2014;Jáchym et al 2009;Roediger & Brüggen 2007Vollmer et al 2001;Abadi et al 1999) and further elaborate on the influence of other factors such as the multi-phase nature of gas (Stevens et al 2020;Lee et al 2020;Tonnesen & Bryan 2010, magnetic fields (Ramos-Martínez et al 2018;Tonnesen & Stone 2014), and sub-structures in clusters (Ruggiero et al 2019;Tonnesen & Bryan 2008). Probing the observational dependence of ram pressure stripping on galaxy properties requires statistically mapping the Hi in cluster galaxies with high resolution.…”

“…Hydrodynamic (Oman et al 2021;Ayromlou et al 2020;Stevens et al 2020;Lotz et al 2019;Bahé et al 2019;Jung et al 2018;Bahé & McCarthy 2015;Bahé et al 2013) and semi-analytical (Xie et al 2020;De Lucia et al 2019;Stevens & Brown 2017;Luo et al 2016) models have made progress in recent years narrowing the differences between predicted and observed distribution of Hi density within galaxies and scaling relations of Hi mass in galaxies. However, because galaxies are complex systems, many different mechanisms produce a similar trend (Stevens & Brown 2017).…”

Simulating Groups and the IntraGroup Medium: The Surprisingly Complex and Rich Middle Ground between Clusters and Galaxies

“…Both observations (e.g., Moretti et al (2020)) and idealized hydrodynamic simulations (e.g., Tonnesen & Bryan (2009)) clearly indicate that ram pressure has a different effect on the dense molecular phase from which stars are formed than the more tenuous, warmer components traced by H I and H II. Although post-processing can be used to estimate the molecular content of group satellites (albeit with strong assumptions; Stevens et al (2021)), it cannot capture the different dynamical evolution of the two phases. Simulations with direct modeling of molecular gas-as is now often done in high-resolution zooms of individual galaxies (e.g., Hopkins et al (2018); Applebaum et al (2021))-would therefore reveal a fundamentally new aspect of the interaction between the IGrM and satellite galaxies.…”

WALLABY pre-pilot survey: Two dark clouds in the vicinity of NGC 1395

“…The grey shaded region mark when each TNG-DGC became a satellite. To account for the reduced information available in TNG 'mini snapshots', we follow appendix B of Stevens et al (2021) to calculate the neutral and HI mass at each snapshot for these panels.…”