STELLAR POPULATIONS AND EVOLUTION OF EARLY-TYPE CLUSTER GALAXIES: CONSTRAINTS FROM OPTICAL IMAGING AND SPECTROSCOPY OFz= 0.5–0.9 GALAXY CLUSTERS

Abstract

We present an analysis of stellar populations and evolutionary history of galaxies in three similarly rich galaxy clusters MS0451.6-0305 (z = 0.54), RXJ0152.7-1357 (z = 0.83), and RXJ1226.9+3332 (z = 0.89). Our analysis is based on high signal-to-noise ground-based optical spectroscopy and Hubble Space Telescope imaging for a total of 17-34 members in each cluster. Using the dynamical masses together with the effective radii and the velocity dispersions we find no indication of evolution of sizes or velocity dispersions with redshift at a given galaxy mass. We establish the Fundamental Plane (FP) and scaling relations between absorption line indices and velocity dispersions. We confirm that the FP is steeper at z ≈ 0.86 compared to the low redshift FP, indicating that under the assumption of passive evolution the formation redshift, z form , depends on the galaxy velocity dispersion (or alternatively mass). At a velocity dispersion of σ = 125 km s −1 (Mass = 10 10.55 M ⊙ ) we find z form = 1.24 ± 0.05, while at σ = 225 km s −1 (Mass = 10 11.36 M ⊙ ) the formation redshift is z form = 1.95 +0.3 −0.2 , for a Salpeter initial mass function. The three clusters follow similar scaling relations between absorption line indices and velocity dispersions as those found for low redshift galaxies. The zero point offsets for the Balmer lines depend on cluster redshifts. However, the offsets indicate a slower evolution, and therefore higher formation redshift, than the zero point differences found from the FP, if interpreting the data using a passive evolution model. Specifically, the strength of the higher order Balmer lines Hδ and Hγ implies z form > 2.8. The scaling relations for the metal indices in general show small and in some cases insignificant zero point offsets, favoring high formation redshifts for a passive evolution model. Based on the absorption line indices and recent stellar population models from Thomas et al. we find that MS0451.6-0305 has a mean metallicity [M/H] approximately 0.2 dex below that of the other clusters and our low redshift sample. We confirm our previous result that RXJ0152.7-1357 has a mean abundance ratio [α/Fe] approximately 0.3 dex higher than that of the other clusters. The differences in [M/H] and [α/Fe] between the high-redshift clusters and the low redshift sample are inconsistent with a passive evolution scenario for early-type cluster galaxies over the redshift interval studied. Low-level star formation may be able to bring the metallicity of MS0451.6-0305 in agreement with the low redshift sample, while we speculate whether galaxy mergers can lead to sufficiently large changes in the abundance ratios for the RXJ0152.7-1357 galaxies to allow them to reach the low redshift sample values in the time available.

The KMOS Cluster Survey (KCS). I. The Fundamental Plane and the Formation Ages of Cluster Galaxies at Redshift 1.4 < Z < 1.6*

“…Our results for the size evolution partly disagree with a recent work by Jørgensen et al (2014), where almost no size variation with redshift is found from their sample of clusters at z 1 < (from e.g., Jørgensen & Chiboucas 2013); their cluster at z 1.27 > shows trends similar to ours, suggesting that larger effects of size-evolution can be seen at z 1 > . We note that the difference with the cluster sample at z 1 < could also be related to the different selections used in our sample and the sample of Jørgensen et al (2014).…”

“…We test that our M L log are consistent with the the M L log we derive by fitting a linear relation between the logarithms of the age, metallicity, and M/L of Maraston (2005) SSPs with an age 1 Gyr and metallicity Z Z log  between −0.3 and 0.3 (total metallicity relative to solar), as done in Jørgensen et al (2005), Jørgensen & Chiboucas (2013), and Jørgensen et al (2014). In the following, we adopt the M L log obtained via interpolation of the SSPs because the relation between M/L and age log becomes strongly nonlinear at young ages, which could potentially make our linear relation more uncertain.…”

“…The FP is tilted with respect to the virial prediction; the tilt is related to the change of the mass-to-light (M/L) ratio with galaxy luminosity, which is due to a contribution of variations of the galaxy stellar populations, dark matter fractions, and nonhomology (e.g., Bender et al 1992;Renzini & Ciotti 1993;Jørgensen et al 1996;Cappellari et al 2006Cappellari et al , 2013bRenzini 2006;Scott et al 2015;Cappellari 2016). While there is still debate on whether the coefficients of the FP remain constant up to z 1 (see Holden et al 2010;Saglia et al 2010a;Jørgensen & Chiboucas 2013), there is a clear consensus about the variation of its zero-point with redshift. The zero-point can vary as a result of evolving M/L (Faber et al 1987) caused by the change in galaxy luminosity that is due to the younger stellar population at high-z (e.g., van Dokkum & Franx 1996;Bender et al 1998;Kelson et al 2000;Gebhardt et al 2003;Wuyts et al 2004;Holden et al 2005;di Serego Alighieri et al 2005;Jørgensen et al 2006;Holden et al 2010;Toft et al 2012;Bezanson et al 2013;Jørgensen et al 2014); some contribution is also expected from the galaxy structural evolution with redshift (e.g., Saglia et al 2010aSaglia et al , 2016.…”

The evolution of the ages and metallicities of massive galaxies since z = 0.7

“…Based on deep, medium-resolution IMACS spectroscopy of a sample of ∼ 70 massive galaxies at z = 0.7, we characterize for the first time at these redshifts the stellar metallicity and age scaling relations for the population as a whole and for quiescent and star-forming galaxies separately We find that z = 0.7 quiescent galaxies have stellar metallicities and stellar ages consistent with local quiescent galaxies under passive evolution hypothesis, in qualitative agreement with results on cluster quiescent galaxies by Sánchez-Blázquez et al (2009) and Jørgensen & Chiboucas (2013). However, we also show that the scatter in age of z = 0.7 quiescent galaxies is too low to reproduce the scatter of the local relation.…”

“…Most of these works target red-sequence galaxies in clusters (e.g. Sánchez-Blázquez et al 2009;Jørgensen & Chiboucas 2013) and find their properties to be consistent with passive evolution at high masses. So far only few works have presented the ages and metal abundances of massive quiescent galaxies in the field at z 0.7 (Schiavon et al 2006;Gallazzi et al 2014;Choi et al 2014).…”