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The Star Formation Epoch of the Most Massive Early-Type Galaxies

van Dokkum, Pieter G. and van der Marel, Roeland P. (2007) The Star Formation Epoch of the Most Massive Early-Type Galaxies. Astrophysical Journal, 655 (1). pp. 30-50. ISSN 0004-637X.

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We present new spatially resolved Keck spectroscopy of early-type galaxies in three galaxy clusters at z ≈ 0.5. We focus on the fundamental plane (FP) relation and combine the kinematics with structural parameters determined from HST images. The galaxies obey clear FP relations, which are offset from the FP of the nearby Coma Cluster due to passive evolution of the stellar populations. The z ≈ 0.5 data are combined with published data for 11 additional clusters at 0.18 ≤ z ≤ 1.28, to determine the evolution of the mean M/L_B ratio of cluster galaxies with masses M ≳ 10^(11) M_☉, as implied by the FP. We find d log(M/L_B)/dz = -0.555 ± 0.042, stronger evolution than was previously inferred from smaller samples. The observed evolution depends on the luminosity-weighted mean age of the stars in the galaxies, the IMF, selection effects due to progenitor bias, and other parameters. Assuming a normal IMF but allowing for various other sources of uncertainty, we find z_* = 2.01^(+0.22)_(-0.17) for the luminosity-weighted mean star formation epoch. The main uncertainty is the slope of the IMF in the range 1-2 M_☉: we find z_* = 4.0 for a top-heavy IMF with slope x = 0. The M/L_B ratios of the cluster galaxies are compared to those of field early-type galaxies at 0.32 ≤ z ≤ 1.14. Assuming that progenitor bias and the IMF do not depend on environment, we find that the present-day age of stars in massive field galaxies is 4.1% ± 2.0% (≈0.4 Gyr) less than that of stars in massive cluster galaxies. This relatively small age difference is surprising in the context of expectations from "standard" hierarchical galaxy formation models and provides a constraint on the physical processes that are responsible for halting star formation in the progenitors of today's most massive galaxies.

Item Type:Article
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URLURL TypeDescription
van Dokkum, Pieter G.0000-0002-8282-9888
van der Marel, Roeland P.0000-0001-7827-7825
Additional Information:© 2007 American Astronomical Society. Received 2006 July 19; accepted 2006 September 19. We thank Arjen van derWel and Brad Holden for their sleuthing and the referee, Inger Jørgensen, for her comments and generous sharing of unpublished data. Support from NASA grants HF 01126.01-99A, HST AR-09541.01-A, and LTSA NNG04GE12G and from National Science Foundation grant NSF CAREER AST 04-49678 is gratefully acknowledged. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain.
Funding AgencyGrant Number
NASAHF 01126.01-99A
NASAHST AR-09541.01-A
NSFAST 04-49678
Subject Keywords:cosmology: observations; galaxies: evolution; galaxies: formation
Issue or Number:1
Record Number:CaltechAUTHORS:20100421-095257302
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Official Citation:Pieter G. van Dokkum and Roeland P. van der Marel 2007 ApJ 655 30 doi: 10.1086/509633
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:18035
Deposited By: Jason Perez
Deposited On:21 Apr 2010 18:35
Last Modified:06 Nov 2019 22:27

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