TY - JOUR
T1 - ACCESS - IV. The quenching of star formation in a cluster population of dusty S0s
AU - Haines, Christopher
AU - Merluzzi, P
AU - Busarello, G
AU - Dopita, MA
AU - Smith, Graham
AU - La Barbera, F
AU - Gargiulo, A
AU - Raychaudhury, Somak
AU - Smith, RJ
PY - 2011/11/11
Y1 - 2011/11/11
N2 - We present an analysis of the mid-infrared (MIR) colours of 165
70-μm-detected galaxies in the Shapley supercluster core (SSC) at z=
0.048 using panoramic Spitzer/MIPS 24- and 70-μm imaging. While the
bulk of galaxies show f70/f24 colours typical of
local star-forming galaxies, we identify a significant subpopulation of
23 70-μm-excess galaxies, whose MIR colours
(f70/f24 > 25) are much redder and cannot be
reproduced by any of the standard model IR spectral energy distributions
(SEDs). These galaxies are found to be strongly concentrated towards the
cores of the five clusters that make up the SSC, and also appear rare
among local field galaxies, confirming them as a cluster-specific
phenomenon. Their optical spectra and lack of significant ultraviolet
emission imply little or no ongoing star formation, while fits to their
panchromatic SEDs require the far-IR emission to come mostly from a
diffuse dust component heated by the general interstellar radiation
field rather than ongoing star formation. Most of these 70-μm-excess
galaxies are identified as ˜L* S0s with smooth profiles.
We find that almost every cluster galaxy in the process of star
formation quenching is already either an S0 or Sa, while we find no
passive galaxies of class Sb or later. Hence the formation of passive
early-type galaxies in cluster cores must involve the prior
morphological transformation of late-type spirals into Sa/S0s, perhaps
via pre-processing or the impact of cluster tidal fields, before a
subsequent quenching of star formation once the lenticular encounters
the dense environment of the cluster core. In the cases of many cluster
S0s, this phase of star formation quenching is characterized by an
excess of 70-μm emission, indicating that the cold dust content is
declining at a slower rate than star formation. We suggest that the
excess 70-μm emission during quenching is due to either (i) a
reduction of the star formation efficiency as proposed within the
morphological quenching scenario or (ii) a 2-3 times increase in the
dust-to-gas ratio or metallicity of the remaining interstellar medium,
as predicted by chemical evolutionary models of galaxies undergoing
ram-pressure stripping or starvation.
AB - We present an analysis of the mid-infrared (MIR) colours of 165
70-μm-detected galaxies in the Shapley supercluster core (SSC) at z=
0.048 using panoramic Spitzer/MIPS 24- and 70-μm imaging. While the
bulk of galaxies show f70/f24 colours typical of
local star-forming galaxies, we identify a significant subpopulation of
23 70-μm-excess galaxies, whose MIR colours
(f70/f24 > 25) are much redder and cannot be
reproduced by any of the standard model IR spectral energy distributions
(SEDs). These galaxies are found to be strongly concentrated towards the
cores of the five clusters that make up the SSC, and also appear rare
among local field galaxies, confirming them as a cluster-specific
phenomenon. Their optical spectra and lack of significant ultraviolet
emission imply little or no ongoing star formation, while fits to their
panchromatic SEDs require the far-IR emission to come mostly from a
diffuse dust component heated by the general interstellar radiation
field rather than ongoing star formation. Most of these 70-μm-excess
galaxies are identified as ˜L* S0s with smooth profiles.
We find that almost every cluster galaxy in the process of star
formation quenching is already either an S0 or Sa, while we find no
passive galaxies of class Sb or later. Hence the formation of passive
early-type galaxies in cluster cores must involve the prior
morphological transformation of late-type spirals into Sa/S0s, perhaps
via pre-processing or the impact of cluster tidal fields, before a
subsequent quenching of star formation once the lenticular encounters
the dense environment of the cluster core. In the cases of many cluster
S0s, this phase of star formation quenching is characterized by an
excess of 70-μm emission, indicating that the cold dust content is
declining at a slower rate than star formation. We suggest that the
excess 70-μm emission during quenching is due to either (i) a
reduction of the star formation efficiency as proposed within the
morphological quenching scenario or (ii) a 2-3 times increase in the
dust-to-gas ratio or metallicity of the remaining interstellar medium,
as predicted by chemical evolutionary models of galaxies undergoing
ram-pressure stripping or starvation.
U2 - 10.1111/j.1365-2966.2011.19445.x
DO - 10.1111/j.1365-2966.2011.19445.x
M3 - Article
SN - 1365-2966
VL - 417
SP - 2831
EP - 2845
JO - Royal Astronomical Society. Monthly Notices
JF - Royal Astronomical Society. Monthly Notices
IS - 4
ER -