Issue |
A&A
Volume 518, July-August 2010
Herschel: the first science highlights
|
|
---|---|---|
Article Number | L18 | |
Number of page(s) | 5 | |
Section | Letters | |
DOI | https://doi.org/10.1051/0004-6361/201014691 | |
Published online | 16 July 2010 |
Letter to the Editor
LoCuSS: Probing galaxy transformation physics with Herschel *,**
1
School of Physics and Astronomy, University of
Birmingham, Edgbaston B15 2TT, UK e-mail: gps@star.sr.bham.ac.uk
2
Steward Observatory, University of Arizona, 933 North Cherry
Avenue, Tucson, AZ85721, USA
3
Department of Physics and Astronomy, The Johns Hopkins
University, 3400 N. Charles Street, Baltimore, MD 21218, USA
4
Rensselaer Polytechnic Institute (RPI) 110 Eighth Street, Troy,
NY 12180, USA
5
Department of Physics and Astronomy, University of Victoria, 3800
Finnerty Road, Victoria, BC, Canada
6
Argelander-Institut für Astronomie, Universität Bonn, Auf
dem Hügel 71, 53121 Bonn, Germany
7
Max-Planck-Institut für extraterrestrische Physik,
Giessenbachstraße, 85748 Garching, Germany
8
Center for Space Science Technology, University of Maryland Baltimore County, 1000 Hilltop Circle, Baltimore, MD 21250, USA
9
Academia Sinica Institute of Astronomy and Astrophysics,
PO Box 23-141, 10617 Taipei, Taiwan
10
Institute of Computational Cosmology, University of Durham, South
Road, Durham, DH1 3LE, UK
11
Institute for Physics & Mathematics of the Universe,
University of Tokyo, 5-1-5 Kashiwa-no-Ha, Kashiwa City
277-8582, Japan
Received:
31
March
2010
Accepted:
19
May
2010
We present an early broad-brush analysis of
Herschel/PACS observations of star-forming galaxies in 8
galaxy clusters drawn from our survey of 30 clusters at
z 0.2. We define a complete sample of 192 spectroscopically confirmed cluster members down to LTIR > 3 × 1010
and LK > 0.25
.
The
average K-band and bolometric infrared luminosities of these
galaxies both fade by a factor of ~2 from clustercentric
radii of ~2 r200 to ~0.5 r200, indicating that
as galaxies enter the clusters ongoing star-formation stops first
in the most massive galaxies, and that the specific
star-formation rate (SSFR) is conserved. On smaller scales the
average SSFR jumps by ~25%, suggesting that in cluster
cores processes including ram pressure stripping may trigger a
final episode of star-formation that presumably exhausts the
remaining gas. This picture is consistent with our comparison of
the Herschel-detected cluster members with the cluster
mass distributions, as measured in our previous weak-lensing
study of these clusters. For example, the spatial distribution
of the Herschel sources is positively correlated with the
structures in the weak-lensing mass maps at ~5σ
significance, with the strongest signal seen at intermediate
group-like densities. The strong dependence of the total cluster
IR luminosity on cluster mass – LTIR
Mvirial2 – is also consistent with accretion of galaxies and
groups of galaxies (i.e. the substructure mass function) driving
the cluster IR luminosity. The most surprising result is that
roughly half of the Herschel-detected cluster members have
redder S100/S24 flux ratios than expected, based on the
Rieke et al. models. On average cluster members are redder than
non-members, and the fraction of red galaxies increases towards
the cluster centers, both of which indicate that these colors are
not attributable to systematic photometric errors. Our future
goals include to intepret physically these red galaxies, and to
exploit this unique large sample of clusters with unprecedented
multi-wavelength observations to measure the cluster-cluster
scatter in S0 progenitor populations, and to intepret that
scatter in the context of the hierarchical assembly of
clusters.
Key words: galaxies: clusters: general / galaxies: star formation / Galaxy: evolution / infrared: galaxies
© ESO, 2010
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