Differential Galaxy Evolution in Cluster and Field Galaxies at z ≈ 0.3

Balogh, M.L.; Morris, S.L.; Yee, H.K.C.; Carlberg, R.G.; Ellingson, E.

Abstract

We measure spectral indexes for 1823 galaxies in the Canadian Network for Observational Cosmology 1 (CNOC1) sample of 15 X-ray luminous clusters at 0.18 \ z\ 0.55 to investigate the mechanisms responsible for di†erential evolution between galaxy cluster and Ðeld environments. The radial trends of D4000, and W II) are all consistent with an age sequence, in the sense that the last episode of 0 (Hd), W0 (O star formation occurred more recently in galaxies farthest from the cluster center. Throughout the cluster environment, galaxies show evidence for older stellar populations than Ðeld galaxies ; they have weaker W II) and lines and stronger D4000 indexes. From our primary sample of 1413 galaxies, 0 (O W0 (Hd) statistically corrected for incompleteness and selection e†ects, we identify a sample of K]A galaxies, which have strong Hd absorption lines but no [O [W II] emission II)\ 5 0 (Hd)[ 5 AŽ ] [W0 (O AŽ], perhaps indicative of recently terminated star formation. The observed fraction of 4.4% ^ 0.7% in the cluster sample is an overestimate due to a systematic e†ect that results from the large uncertainties on individual spectral index measurements. Corrected for this bias, we estimate that K]A galaxies make up only 2.1%^ 0.7% of the cluster sample and 0.1% ^ 0.7% of the Ðeld. From the subsample of galaxies more luminous than which is statistically representative of a complete sample to Mr \ [18.8] 5 log h, this limit, the corrected fraction of K]A galaxies is 1.5%^ 0.8% in the cluster and 1.2%^ 0.8% in the Ðeld. Compared with the zB 0.1 fraction of 0.30%, the fraction of K]A galaxies in the CNOC1 Ðeld sample is greater by perhaps a factor of 4, but with only 1 p signiÐcance ; no further evolution of this fraction is detectable over our redshift range. We compare our data with the results of PEGASE and GISSEL96 spectrophotometric models and conclude, from the relative fractions of red and blue galaxies with no [O II] j3727 emission and strong Hd absorption, that up to 1.9% ^ 0.8% of the cluster population may have had its star formation recently truncated without a starburst. However, this is still not signiÐcantly greater than the fraction of such galaxies in the Ðeld, 3.1%^ 1.0%. Furthermore, we do not detect an excess of cluster galaxies that have unambiguously undergone starbursts within the last 1 Gyr. In fact, at 6.3%^ 2.1%, the A]em galaxies that Poggianti et al. have recently suggested are dusty starbursts are twice as common in the Ðeld as in the cluster environment. Our results imply that these cluster environments are not responsible for inducing starbursts ; thus, the increase in cluster blue galaxy fraction with redshift may not be a strictly cluster-speciÐc phenomenon. We suggest that the truncation of star formation in clusters may largely be a gradual process, perhaps due to the exhaustion of gas in the galactic disks over fairly long timescales ; in this case di†erential evolution may result because Ðeld galaxies can refuel their disks with gas from extended halos, thus regenerating star formation, while cluster galaxies may not have such halos and so continue to evolve passively.

Citation

Balogh, M., Morris, S., Yee, H., Carlberg, R., & Ellingson, E. (1999). Differential Galaxy Evolution in Cluster and Field Galaxies at z ≈ 0.3. Astrophysical Journal, 527(1), 54-79. https://doi.org/10.1086/308056

• Journal Article Type: Article
• Acceptance Date: Jul 28, 1999
• Publication Date: 1999-12
• Deposit Date: Feb 16, 2012
• Journal: Astrophysical Journal
• Print ISSN: 0004-637X
• Electronic ISSN: 1538-4357
• Publisher: American Astronomical Society
• Peer Reviewed: Peer Reviewed
• Volume: 527
• Issue: 1
• Pages: 54-79
• DOI: https://doi.org/10.1086/308056
• Public URL: https://durham-repository.worktribe.com/output/1482083