The growth and enrichment of intragroup gas

Abstract

The observable properties of galaxy groups, and especially the thermal and chemical properties of the intragroup medium (IGrM), provide important constraints on the different feedback processes associated with massive galaxy formation and evolution. In this, the first in a series of studies aimed at identifying and exploring these constraints, we present a detailed analysis of the global properties of simulated galaxy groups with X-ray temperatures in the range 0.5 − 2 keV over the redshift range 0 ≤ z ≤ 3. The groups are drawn from a cosmological simulation that includes a well-constrained prescription for galactic outflows powered by stars and supernovae, but no AGN feedback. Our aims are (a) to establish a baseline against which we will compare future models; (b) to identify model successes that are genuinely due to stellar/supernovae-powered outflows; and (c) to pinpoint features that not only signal the need for AGN feedback but also constrain the nature of this feedback.We find that even without AGN feedback, our simulation successfully reproduces the observed present-day group global IGrM properties such as the hot gas mass fraction, the various X-ray luminosity-temperature-entropy scaling relations, as well as the mass-weighted and emission-weighted IGrM iron and silicon abundance versus group X-ray temperature trends, for all but the most massive groups. We also show that these trends evolve self-similarly for z < 1, in agreement with the observations. Contrary to expectations, we do not see any evidence of the IGrM undergoing catastrophic cooling. And yet, the z = 0 group stellar mass is a factor of ∼ 2 too high. Probing further, we find that the latter is due to the build-up of cold gas in the massive galaxies before they are incorporated inside groups. This, in turn, indicates that other feedback mechanisms must activate in real galaxies as soon as their stellar mass grows to M * ≈ a few ×10 10 M . We show that these must be powerful enough to expel a significant fraction of the halo gas component from the galactic halos. Gentle "maintenance-mode" AGN feedback, as has been suggested to occur in galaxy clusters, will not do; it cannot bring the stellar and the baryonic fractions into agreement with the observations at the same time. Just as importantly, we find that stellar/supernovae-powered winds are vital for explaining the metal abundances in the IGrM, and these results ought to be relatively insensitive to the addition of AGN feedback.

The Baryonic Collapse Efficiency of Galaxy Groups in the RESOLVE and ECO Surveys

“…Examining simulations of lower mass galaxies (M halo ∼ 10 11 M ⊙ ), Wang et al (2017) also find that baryons are expelled beyond twice the virial radius. Such feedback may also cause groups groups to begin forming with a depleted baryon fraction (Liang et al 2016). Thus the expectation that we should be able to account for all the baryons in groups and clusters to the virial radius may be false, and the shortfall, while interesting, may not necessarily be problematic.…”

The robustness of cosmological hydrodynamic simulation predictions to changes in numerics and cooling physics

“…The agreement between the two ezw simulations is also good, though the slope is slightly steeper in the PESPH simulation. Also, compared to the nw runs, the stellar feedback in the ezw runs only contributes a little extra hot gas to massive groups, as also found in Ford et al (2014) and Liang et al (2016), owing both to the small mass loading factors in massive galaxies and the short wind recycling time-scales. The differences between the ezw simulations seems to maximise around M h ∼ 10 13 M⊙, which is the key regime for galaxy transformation.…”

Radial metal abundance profiles in the intra-cluster medium of cool-core galaxy clusters, groups, and ellipticals

“…The origin of such a difference of ICM enrichment between cooler and hotter objects is still unclear, and has been already debated in the literature (e.g. Rasmussen & Ponman 2009;Liang et al 2016;Yates et al 2017). For example, in contrast to clusters, galaxy groups may not be closed boxes (e.g.…”