Gas loss in simulated galaxies as they fall into clusters

Abstract

We use high-resolution cosmological hydrodynamic galaxy formation simulations to gain insights into how galaxies lose their cold gas at low redshift as they migrate from the field to the highdensity regions of clusters of galaxies. We find that beyond three cluster virial radii, the fraction of gas-rich galaxies is constant, representing the field. Within three cluster-centric radii, the fraction of gas-rich galaxies declines steadily with decreasing radius, reaching <10% near the cluster center. Our results suggest galaxies start to feel the effect of the cluster environment on their gas content well beyond the cluster virial radius. We show that almost all gas-rich galaxies at the cluster virial radius are falling in for the first time at nearly radial orbits. Furthermore, we find that almost no galaxy moving outward at the cluster virial radius is gas-rich (with a gas-to-baryon ratio greater than 1%). These results suggest that galaxies that fall into clusters lose their cold gas within a single radial round-trip.cosmology | observations | large-scale structure of universe | intergalactic medium I t has long been known that the local environment affects galaxy properties. Earlier work (1)(2)(3)(4) showed that the fraction of early-type galaxies increases dramatically toward the central regions of clusters of galaxies, whereas the less-dense regions of the field are dominated by spiral galaxies. Similarly, the "color-density relation" (5-8) indicates that red, old galaxies are found preferentially in overdense environments, and galaxies with bluer, younger stellar populations are more common in the field. This color bimodality is linked to a transition in star formation rates between the low-density field and the high-density regions inside clusters (4, 9). However, we still do not have a complete picture of the process through which blue, late-type, star-forming galaxies in the field transform into red, early-type galaxies when entering a cluster. We know that cold gas in galaxies is spatially extended and often distributed far beyond the optical disks (10). Cosmologically, some of the cold gas that feeds galaxy formation may come from the intergalactic medium (11,12). Observations suggest that neutral hydrogen feeds galaxies and turns into molecular hydrogen at a high column density of ∼10 22 cm −2 (13), within which star formation is observed to occur. Together, these facts suggest that the amount of neutral hydrogen supply may ultimately set the rate of star formation. The environmental dependence of galaxy properties may thus be related to the availability of cold gas in or around galaxies. This expectation is supported by observations of galaxies in different environments, showing the well-known depletion of both cold gas and star formation toward the high-density central regions of clusters; this is likely caused by ram pressure stripping of the cold gas by the hot intracluster medium (plus additional gravitational interactions) in the dense environments (refs. 14-24 and references therein). Recent deta...

The stripping of a galaxy group diving into the massive cluster A2142

“…Therefore, we conclude that our observations are consistent with the expectations of ram-pressure stripping. Our results demonstrate that during infall, the hot gas content of such groups is efficiently stripped already at these large distances from the cluster core, in agreement with the recent simulations of Cen et al (2014).…”

Quenching of the star formation activity in cluster galaxies

“…18, where the fraction of late-type galaxies with a quenching factor QF > 0.8 and an HI-deficiency HI − de f > 0.4 are plotted versus the distance from the core of the Virgo cluster. Figure 18 clearly shows that both fractions drop by a factor of 5 from the core of the cluster (R/R vir < 0.5), where the hot X-ray gas is detected by ROSAT (Bohringer et al 1994), to the cluster periphery (R/R vir > ∼ 4), in agreement with models and simulations (Tonnesen et al 2007;Bahe et al 2013;Cen et al 2014). Recent observations of nearby clusters with 4−8 m class telescopes equipped with wide-field panoramic detectors and narrow-band filters revealed several star forming galaxies with long tails of ionised gas that are typically produced by a ram-pressure-stripping event up to the cluster virial radius Sun et al 2007;Yagi et al 2010;Fossati et al 2012).…”

Changing Ionization Conditions in SDSS Galaxies With Active Galactic Nuclei as a Function of Environment From Pairs to Clusters

“…Recent hydrodynamic simulations demonstrate that the fraction of gas-rich galaxies steadily declines from the field to the cluster center (Cen et al 2014). A possible auxiliary effect comes from AGN heating through radio jets that keeps the intracluster medium from condensing onto galaxies.…”