The 2dF Galaxy Redshift Survey: the environmental dependence of galaxy star formation rates near clusters

Abstract

We have measured the equivalent width of the Hα emission line for 11 006 galaxies brighter than Mb=−19 (ΩΛ= 0.7, Ωm= 0.3, H0= 70 km s−1 Mpc−1) at 0.05 < z < 0.1 in the 2dF Galaxy Redshift Survey (2dFGRS), in the fields of 17 known galaxy clusters. The limited redshift range ensures that our results are insensitive to aperture bias, and to residuals from night sky emission lines. We use these measurements to trace μ*, the star formation rate normalized to L*, as a function of distance from the cluster centre, and local projected galaxy density. We find that the distribution of μ* steadily skews toward larger values with increasing distance from the cluster centre, converging to the field distribution at distances greater than ∼3 times the virial radius. A correlation between star formation rate and local projected density is also found, which is independent of cluster velocity dispersion and disappears at projected densities below ∼1 galaxy Mpc−2 (brighter than Mb=−19). This characteristic scale corresponds approximately to the mean density at the cluster virial radius. The same correlation holds for galaxies more than two virial radii from the cluster centre. We conclude that environmental influences on galaxy properties are not restricted to cluster cores, but are effective in all groups where the density exceeds this critical value. The present‐day abundance of such systems, and the strong evolution of this abundance, makes it likely that hierarchical growth of structure plays a significant role in decreasing the global average star formation rate. Finally, the low star formation rates well beyond the virialized cluster rule out severe physical processes, such as ram pressure stripping of disc gas, as being completely responsible for the variations in galaxy properties with environment.

The SAMI Galaxy Survey: spatially resolving the environmental quenching of star formation in GAMA galaxies

“…The inferred quenching timescales were therefore long, roughly a few Gyrs, which is comparable to the cluster crossing time. This conclusion is in agreement with Lewis et al (2002) and Gómez et al (2003) who note the existence of galaxies with low specific star formation rates at large distances from the centres of clusters and conclude that rapid environmental quenching alone cannot explain the population of galaxies seen in the local Universe.…”

Evidence of pre-processing and a dependence on dynamical state for low-mass satellite galaxies

“…Previous studies (Lewis et al 2002;Gray et al 2004;Rines et al 2005;Verdugo et al 2008) have similarly found that star formation of galaxies within infall regions remains suppressed compared to the field out to radii of ∼ 2 − 3 R 200 . This suppression is often attributed to backsplash galaxies which have already made a passage through the halo centre, the pre-processing of galaxies in small groups prior to infall, or some combination of the two.…”

Warm gas in and around simulated galaxy clusters as probed by absorption lines

“…The flow of gas into and out of galaxies within clusters, and into the cluster itself, is strongly affected by the cluster environment. Our understanding of the competing processes involved is still forming, from galaxy level processes such as galactic outflows and inflows to cluster specific processes such as rampressure stripping, galaxy mergers, galaxy harassment, and starvation (e.g., Cayatte et al, 1990;Vollmer et al, 2001; Lewis et al, 2002;Roediger & Hensler, 2005;Chung et al, 2007;Tonnesen, Bryan & van Gorkom, 2007;Yoon et al, 2012). In addition, our understanding of gas flows onto clusters from IGM filaments is incomplete.…”