Morphologies and stellar populations of galaxies in the core of Abell 2218
Sánchez, S. F.; Cardiel, N.; Verheijen, M. A. W.;Pedraz, S.; Covone, G.. Morphologies and stellar populations of galaxies in the core of Abell 2218. Monthly Notices of the Royal Astronomical Soc. 2007, Vol. Volume 376, Issue 1, pp. 125-150., p. -2007.
We present a study of the stellar populations and morphologies of
galaxies in the core of the galaxy cluster Abell 2218. Integral field
spectroscopy (IFS) observations were performed using PMAS in the PPAK
mode covering a field of view of ~74 × 64 arcsec<SUP>2</SUP>
centred on the core of the cluster, in order to obtain spectroscopy of
an unbiased flux-limited sample of cluster galaxies. 43 objects were
detected in the IFS data, 31 of them with enough signal-to-noise ratio
to derive the redshift, all of them brighter than I < 21.5 mag. 28
are at the redshift of the cluster (17 with previously unknown
redshift). Individual spectra of the cluster members were extracted and
compared with single stellar population models to derive the
luminosity-weighted ages and metallicities. In addition, deep Hubble
Space Telescope (HST)/ACS F475W-, F555W-, F625W- and F850LP-band images
centred on the cluster core were obtained from the HST archive
(z<SUB>lim</SUB> ~ 28 mag). A detailed morphological analysis of all the
galaxies within the field of view of these images down to
z<SUB>lim</SUB> < 22.5 mag was performed classifying them as
late-type, intermediate and early-type, on the basis of their
Sérsic indices. The literature was scanned to look for
spectroscopically confirmed cluster members located within the field of
view of the ACS image. The final sample of 59 galaxies comprises our
reported sample of 28 galaxies in the core, and 31 additional galaxies
in the outer regions. In addition, multiband broad-band photometry was
extracted from the literature for all objects.
The morphologically segregated colour-magnitude diagram shows that the
early-type galaxies cover the range of brighter and redder colours (the
so-called `red sequence'). A large fraction of spiral galaxies (~50 per
cent) is found, most of them fainter than the limit of previous studies.
They cover a wide range in colours, from blue colours typical of
Butcher-Oemler galaxies to red colours similar to those of early-type
galaxies. This result indicates that early-type galaxies are more
massive and have older stellar populations, while late-type galaxies are
less massive and have a wider range of stellar populations. The
distribution of luminosity-weighted ages as a function of metallicities
and luminosity-weighted masses, and the distribution of Sérsic
indices as a function of the luminosity-weighted masses confirm these
results. They in fact agree with a proposed two-step scenario for the
evolution of galaxies in clusters, where the star formation is quenched
first in the infalling spirals, after which a morphological
transformation follows that requires larger time-scales. This scenario
naturally explains the population faint late-type galaxies with old
stellar populations observed in this cluster. In addition, an extremely
blue merging galaxy system is found at the core, with the nominal
redshift of the cluster.
We present a study of the stellar populations and morphologies of
galaxies in the core of the galaxy cluster Abell 2218. Integral field
spectroscopy (IFS) observations were performed using PMAS in the PPAK
mode covering a field of view of ~74 × 64 arcsec<SUP>2</SUP>
centred on the core of the cluster, in order to obtain spectroscopy of
an unbiased flux-limited sample of cluster galaxies. 43 objects were
detected in the IFS data, 31 of them with enough signal-to-noise ratio
to derive the redshift, all of them brighter than I < 21.5 mag. 28
are at the redshift of the cluster (17 with previously unknown
redshift). Individual spectra of the cluster members were extracted and
compared with single stellar population models to derive the
luminosity-weighted ages and metallicities. In addition, deep Hubble
Space Telescope (HST)/ACS F475W-, F555W-, F625W- and F850LP-band images
centred on the cluster core were obtained from the HST archive
(z<SUB>lim</SUB> ~ 28 mag). A detailed morphological analysis of all the
galaxies within the field of view of these images down to
z<SUB>lim</SUB> < 22.5 mag was performed classifying them as
late-type, intermediate and early-type, on the basis of their
Sérsic indices. The literature was scanned to look for
spectroscopically confirmed cluster members located within the field of
view of the ACS image. The final sample of 59 galaxies comprises our
reported sample of 28 galaxies in the core, and 31 additional galaxies
in the outer regions. In addition, multiband broad-band photometry was
extracted from the literature for all objects.
The morphologically segregated colour-magnitude diagram shows that the
early-type galaxies cover the range of brighter and redder colours (the
so-called `red sequence'). A large fraction of spiral galaxies (~50 per
cent) is found, most of them fainter than the limit of previous studies.
They cover a wide range in colours, from blue colours typical of
Butcher-Oemler galaxies to red colours similar to those of early-type
galaxies. This result indicates that early-type galaxies are more
massive and have older stellar populations, while late-type galaxies are
less massive and have a wider range of stellar populations. The
distribution of luminosity-weighted ages as a function of metallicities
and luminosity-weighted masses, and the distribution of Sérsic
indices as a function of the luminosity-weighted masses confirm these
results. They in fact agree with a proposed two-step scenario for the
evolution of galaxies in clusters, where the star formation is quenched
first in the infalling spirals, after which a morphological
transformation follows that requires larger time-scales. This scenario
naturally explains the population faint late-type galaxies with old
stellar populations observed in this cluster. In addition, an extremely
blue merging galaxy system is found at the core, with the nominal
redshift of the cluster.