2,738 research outputs found
The Stellar Populations of Low-redshift Clusters
We present some preliminary results from an on-going study of the evolution
of stellar populations in rich clusters of galaxies. This sample contains core
line-strength measurements from 183 galaxies with b_J <= 19.5 from four
clusters with ~0.04. Using predictions from stellar population models to
compare with our measured line strengths we can derive relative
luminosity-weighted mean ages and metallicities for the stellar populations in
each of our clusters. We also investigate the Mgb'-sigma and Hbeta_G'-sigma
scaling relations. We find that, consistent with previous results, Mgb' is
correlated with sigma, the likely explanation being that larger galaxies are
better at retaining their heavier elements due to their larger potentials.
Hbeta', on the other hand, we find to be anti-correlated with sigma. This
result implies that the stellar populations in larger galaxies are older than
in smaller galaxies.Comment: 3 pages, 2 figures, to appear in the Proceedings of IAU Colloquium
195: "Outskirts of Galaxy Clusters: intense life in the suburbs", Torino
Italy, March 12-16 200
Cluster Galaxy Evolution from a New Sample of Galaxy Clusters at 0.3 < z < 0.9
(Abridged) We analyze photometry and spectroscopy of a sample of 63 clusters
at 0.3<z<0.9 drawn from the Las Campanas Distant Cluster Survey to empirically
constrain models of cluster galaxy evolution. Specifically, by combining data
on our clusters with those from the literature we parametrize the redshift
dependence of 1) M*_I in the observed frame; 2) the V-I color of the E/S0 red
sequence in the observed frames; and 3) the I-K' color of the E/S0 red sequence
in the observed frame. Using the peak surface brightness of the cluster
detection, S, as a proxy for cluster mass, we find no correlation between S and
M* or the location of the red envelope in V-I. We suggest that these
observations can be explained with a model in which luminous early type
galaxies (or more precisely, the progenitors of current day luminous early type
galaxies) form the bulk of their stellar populations at high redshift (>~ 5)
and in which many of these galaxies, if not all, accrete mass either in the
form of evolved stellar populations or gas that causes only a short term
episode of star formation at lower redshifts (1.5 < z < 2). Our data are too
crude to reach conclusions regarding the evolutionary state of any particular
cluster or to investigate whether the morphological evolution of galaxies
matches the simple scenario we discuss, but the statistical nature of this
study suggests that the observed evolutionary trends are universal in massive
clusters.Comment: 35 pages, accepted for publication in Ap
The WINGS Survey: a progress report
A two-band (B and V) wide-field imaging survey of a complete, all-sky X-ray
selected sample of 78 clusters in the redshift range z=0.04-0.07 is presented.
The aim of this survey is to provide the astronomical community with a complete
set of homogeneous, CCD-based surface photometry and morphological data of
nearby cluster galaxies located within 1.5 Mpc from the cluster center. The
data collection has been completed in seven observing runs at the INT and
ESO-2.2m telescopes. For each cluster, photometric data of about 2500 galaxies
(down to V~23) and detailed morphological information of about 600 galaxies
(down to V~21) are obtained by using specially designed automatic tools.
As a natural follow up of the photometric survey, we also illustrate a long
term spectroscopic program we are carrying out with the WHT-WYFFOS and AAT-2dF
multifiber spectrographs. Star formation rates and histories, as well as
metallicity estimates will be derived for about 350 galaxies per cluster from
the line indices and equivalent widths measurements, allowing us to explore the
link between the spectral properties and the morphological evolution in high-
to low-density environments, and across a wide range in cluster X-ray
luminosities and optical properties.Comment: 12 pages, 10 eps figures, Proceedings of the SAIt Conference 200
OmegaWINGS: OmegaCAM@VST observations of WINGS galaxy clusters
The Wide-field Nearby Galaxy-cluster Survey (WINGS) is a wide-field
multi-wavelength survey of X-ray selected clusters at z =0.04-0.07. The
original 34'x34' WINGS field-of- view has now been extended to cover a 1 sq.deg
field with both photometry and spectroscopy. In this paper we present the
Johnson B and V-band OmegaCAM/VST observations of 46 WINGS clusters, together
with the data reduction, data quality and Sextractor photometric catalogs.
With a median seeing of 1arcs in both bands, our 25-minutes exposures in each
band typically reach the 50% completeness level at V=23.1 mag. The quality of
the astrometric and photometric accuracy has been verified by comparison with
the 2MASS as well as with SDSS astrometry, and SDSS and previous WINGS imaging.
Star/galaxy separation and sky-subtraction procedure have been tested comparing
with previous WINGS data.
The Sextractor photometric catalogues are publicly available at the CDS, and
will be included in the next release of the WINGS database on the VO together
with the OmegaCAM reduced images. These data form the basis for a large ongoing
spectroscopic campaign with AAOmega/AAT and is being employed for a variety of
studies. [abridged]Comment: submitted to A&
Evidence for the Evolution of Young Early-Type Galaxies in the GOODS/CDF-S Field
We have developed an efficient photometric technique for identifying young
early-type galaxy candidates using a combination of photometric redshifts,
spectral-type classification, and optical/near-infrared colors. Applying our
technique to the GOODS HST/ACS and VLT/ISAAC data we have selected a complete
and homogeneous sample of young elliptical candidates among early-type field
galaxies. The distribution of structural parameters for these candidates shows
that their selection, which is based on early spectral types, is fully
consistent with early morphological types. We investigate the evolution of
their luminosities and colors as a function of redshift and galaxy mass and
find evidence for an increasing starburst mass fraction in these young
early-type galaxy candidates at higher redshifts, which we interpret in terms
of massive field galaxies experiencing more massive/intense starbursts at
higher redshifts. Moreover, we find indications for a systematically larger
young elliptical fraction among sub-L*/2 early-type galaxies compared to their
brighter counterparts. The total fraction among the field early-type galaxies
increases with redshift, irrespective of galaxy luminosity. Our results are
most consistent with galaxy formation scenarios in which stars in massive
early-type field galaxies are assembled earlier than in their low-mass
counterparts.Comment: 11 pages, 10 figures, accepted for publication in A
Hot melt adhesive attachment pad
A hot melt adhesive attachment pad for releasably securing distinct elements together is described which is particularly useful in the construction industry or a spatial vacuum environment. The attachment pad consists primarily of a cloth selectively impregnated with a charge of hot melt adhesive, a thermo-foil heater, and a thermo-cooler. These components are securely mounted in a mounting assembly. In operation, the operator activates the heating cycle transforming the hot melt adhesive to a substantially liquid state, positions the pad against the attachment surface, and activates the cooling cycle solidifying the adhesive and forming a strong, releasable bond
Observations of Stripped Edge-on Virgo Cluster Galaxies
We present observations of highly inclined, HI deficient, Virgo cluster
spiral galaxies. Our high-resolution VLA HI observations of edge-on galaxies
allow us to distinguish extraplanar gas from disk gas. All of our galaxies have
truncated H-alpha disks, with little or no disk gas beyond a truncation radius.
While all the gas disks are truncated, the observations show evidence for a
continuum of stripping states: symmetric, undisturbed truncated gas disks
indicate galaxies that were stripped long ago, while more asymmetric disks
suggest ongoing or more recent stripping. We compare these timescale estimates
with results obtained from two-dimensional stellar spectroscopy of the outer
disks of galaxies in our sample. One of the galaxies in our sample, NGC 4522 is
a clear example of active ram-pressure stripping, with 40% of its detected HI
being extraplanar. As expected, the outer disk stellar populations of this
galaxy show clear signs of recent (and, in fact, ongoing) stripping. Somewhat
less expected, however, is the fact that the spectrum of the outer disk of this
galaxy, with very strong Balmer absorption and no observable emission, would be
classified as ``k+a'' if observed at higher redshift. Our observations of NGC
4522 and other galaxies at a range of cluster radii allow us to better
understand the role that clusters play in the structure and evolution of disk
galaxies.Comment: 4 pages, 2 figures, to appear in the proceedings of the Island
Universes conference held in Terschelling, Netherlands, July 2005, ed. R. de
Jong, version with high resolution figures can be downloaded from
ftp://ftp.astro.yale.edu/pub/hugh/papers/iu_crowl_h.ps.g
The hybrid solution for the Fundamental Plane
By exploiting the database of early-type galaxies (ETGs) members of the WINGS
survey of nearby clusters, we address here the long debated question of the
origin and shape of the Fundamental Plane (FP). Our data suggest that different
physical mechanisms concur in shaping and tilting the FP with respect to the
virial plane (VP) expectation. In particular, an hybrid solution in which the
structure of galaxies and their stellar population are the main contributors to
the FP tilt seems to be favoured. We find that the bulk of the tilt should be
attributed to structural non-homology, while stellar population effects play an
important but less crucial role. Our data indicate that the differential FP
tilt between the V and K-band is due to a sort of entanglement between
structural and stellar population effects, for which the inward steepening of
color profiles (V-K) tends to increase at increasing the stellar mass of ETGs.
The same analysis applied to the ATLAS3D and SDSS data in common with WINGS
(WSDSS throughout the paper) confirms our results, the only remarkable
difference being the less important role of the stellar mass-to-light-ratio in
determining the FP tilt. The ATLAS3D data also suggest that the tilt depends as
well on the dark matter (DM) fraction and on the rotational contribution to the
kinetic energy (Vrot/sigma). We show that the global properties of the FP can
be understood in terms of the underlying correlation among mass, structure and
stellar population of ETGs, for which, at increasing the stellar mass, ETGs
become (on average) older and more centrally concentrated. Finally, we show
that a Malmquist-like selection effect may mimic a differential evolution of
the mass-to-light ratio for galaxies of different masses. This should be taken
into account in the studies investigating the amount of the so called
downsizing phenomenon.Comment: 22 pages, 17 figure
The Large Area Radio Galaxy Evolution Spectroscopic Survey (LARGESS): survey design, data catalogue and GAMA/WiggleZ spectroscopy
© 2016 The Authors. We present the Large Area Radio Galaxy Evolution Spectroscopic Survey (LARGESS), a spectroscopic catalogue of radio sources designed to include the full range of radio AGN populations out to redshift z ~ 0.8. The catalogue covers ~800 deg 2 of sky, and provides optical identifications for 19 179 radio sources from the 1.4 GHz Faint Images of the Radio Sky at Twenty-cm (FIRST) survey down to an optical magnitude limit of i mod < 20.5 in Sloan Digital Sky Survey (SDSS) images. Both galaxies and point-like objects are included, and no colour cuts are applied. In collaboration with the WiggleZ and Galaxy And Mass Assembly (GAMA) spectroscopic survey teams, we have obtained new spectra for over 5000 objects in the LARGESS sample. Combining these new spectra with data from earlier surveys provides spectroscopic data for 12 329 radio sources in the survey area, of which 10 856 have reliable redshifts. 85 per cent of the LARGESS spectroscopic sample are radio AGN (median redshift z = 0.44), and 15 per cent are nearby star-forming galaxies (median z = 0.08). Low-excitation radio galaxies (LERGs) comprise the majority (83 per cent) of LARGESS radio AGN at z < 0.8, with 12 per cent being high-excitation radio galaxies (HERGs) and 5 per cent radioloud QSOs. Unlike the more homogeneous LERG and QSO sub-populations, HERGs are a heterogeneous class of objects with relatively blue optical colours and a wide dispersion in mid-infrared colours. This is consistent with a picture in which most HERGs are hosted by galaxies with recent or ongoing star formation as well as a classical accretion disc
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