75 research outputs found
Disentangling Morphology, Star Formation, Stellar Mass, and Environment in Galaxy Evolution
We present a study of the spectroscopic and photometric properties of
galaxies in six nearby clusters. We perform a partial correlation analysis on
our dataset to investigate whether the correlation between star formation rates
in galaxies and their environment is merely another aspect of correlations of
morphology, stellar mass, or mean stellar age with environment, or whether star
formation rates vary independently of these other correlations. We find a
residual correlation of ongoing star formation with environment, indicating
that even galaxies with similar morphologies, stellar masses, and mean stellar
ages have lower star formation rates in denser environments. Thus, the current
star formation gradient in clusters is not just another aspect of the
morphology-density, stellar mass-density, or mean stellar age-density
relations. Furthermore, the star formation gradient cannot be solely the result
of initial conditions, but must partly be due to subsequent evolution through a
mechanism (or mechanisms) sensitive to environment. Our results constitute a
true ``smoking gun'' pointing to the effect of environment on the later
evolution of galaxies.Comment: 31 pages, including 5 figures; accepted for publication in Ap
The U-band Galaxy Luminosity Function of Nearby Clusters
Despite the great potential of the U-band galaxy luminosity function (GLF) to
constrain the history of star formation in clusters, to clarify the question of
variations of the GLF across filter bands, to provide a baseline for
comparisons to high-redshift studies of the cluster GLF, and to estimate the
contribution of bound systems of galaxies to the extragalactic near-UV
background, determinations have so far been hampered by the generally low
efficiency of detectors in the U-band and by the difficulty of constructing
both deep and wide surveys. In this paper, we present U-band GLFs of three
nearby, rich clusters to a limit of M_U=-17.5 (M*_U+2). Our analysis is based
on a combination of separate spectroscopic and R-band and U-band photometric
surveys. For this purpose, we have developed a new maximum-likelihood algorithm
for calculating the luminosity function that is particularly useful for
reconstructing the galaxy distribution function in multi-dimensional spaces
(e.g., the number of galaxies as a simultaneous function of luminosity in
different filter bands, surface brightness, star formation rate, morphology,
etc.), because it requires no prior assumptions as to the shape of the
distribution function.
The composite luminosity function can be described by a Schechter function
with characteristic magnitude M*_U=-19.82+/-0.27 and faint end slope
alpha_U=-1.09+/-0.18. The total U-band GLF is slightly steeper than the R-band
GLF, indicating that cluster galaxies are bluer at fainter magnitudes.
Quiescent galaxies dominate the cumulative U-band flux for M_U<-14. The
contribution of galaxies in nearby clusters to the U-band extragalactic
background is <1% Gyr^-1 for clusters of masses ~3*10^14 to 2*10^15 M_solar.Comment: 44 pages, 11 figures, accepted for publication in Ap
VPMS J1342+2840 - an unusual quasar from the variability and proper motion survey
We report the discovery of the highly peculiar, radio-loud quasar VPMS
J1342+2840 (z ~ 1.3) from the variability and proper motion survey. We present
spectroscopic, imaging and photometric observations. The unusual spectrum shows
a strong depression of the continuum over a wide wavelength range in the blue
part without the typical structures of broad absorption line (BAL) troughs. The
image of the quasar is unresolved and there is no evidence for a foreground
object on the line of sight. The broad-band spectral energy distribution is not
consistent with obvious dust reddening with the standard SMC extinction curve.
The downturn of the continuum flux of VPMS J1342+2840 at short wavelengths can
be caused by dust reddening only if the reddening curve is steeper then the SMC
curve in the ultraviolet and is very flat at longer wavelengths. Alternatively,
the dominant spectral features can be explained by low-ionization BALs forming
unusually wide, overlapping absorption troughs.Comment: 4 pages, 3 figures, accepted for publication in A&A Letter
Clustering and descendants of MUSYC galaxies at z<1.5
We measure the evolution of galaxy clustering out to a redshift of z~1.5
using data from two MUSYC fields, the Extended Hubble Deep Field South (EHDF-S)
and the Extended Chandra Deep Field South (ECDF-S). We use photometric redshift
information to calculate the projected-angular correlation function,
omega(sigma), from which we infer the projected correlation function Xi(sigma).
We demonstrate that this technique delivers accurate measurements of clustering
even when large redshift measurement errors affect the data. To this aim we use
two mock MUSYC fields extracted from a LambdaCDM simulation populated with
GALFORM semi-analytic galaxies which allow us to assess the degree of accuracy
of our estimates of Xi(sigma) and to identify and correct for systematic
effects in our measurements. We study the evolution of clustering for volume
limited subsamples of galaxies selected using their photometric redshifts and
rest-frame r-band absolute magnitudes. We find that the real-space correlation
length r_0 of bright galaxies, M_r<-21 (rest-frame) can be accurately recovered
out to z~1.5, particularly for ECDF-S given its near-infrared photometric
coverage. There is mild evidence for a luminosity dependent clustering in both
fields at the low redshift samples (up to =0.57), where the correlation
length is higher for brighter galaxies by up to 1Mpc/h between median
rest-frame r-band absolute magnitudes of -18 to -21.5. As a result of the
photometric redshift measurement, each galaxy is assigned a best-fit template;
we restrict to E and E+20%Sbc types to construct subsamples of early type
galaxies (ETGs). Our ETG samples show a strong increase in r_0 as the redshift
increases, making it unlikely (95% level) that ETGs at median redshift
z_med=1.15 are the direct progenitors of ETGs at z_med=0.37 with equivalent
passively evolved luminosities. (ABRIDGED)Comment: 16 pages, 12 figures, 2 tables, accepted for publication in MNRA
Properties of satellite galaxies in the SDSS photometric survey: luminosities, colours and projected number density profiles
We analyze photometric data in SDSS-DR7 to infer statistical properties of
faint satellites associated to isolated bright galaxies (M_r<-20.5) in the
redshift range 0.03<z<0.1. The mean projected radial profile shows an excess of
companions in the photometric sample around the primaries, with approximately a
power law shape that extends up to ~700kpc. Given this overdensity signal, a
suitable background subtraction method is used to study the statistical
properties of the population of bound satellites, down to magnitude M_r=-14.5,
in the projected radial distance range 100 < r_p/kpc < 3 R_{vir}. We have also
considered a color cut consistent with the observed colors of spectroscopic
satellites in nearby galaxies so that distant redshifted galaxies do not
dominate the statistics. We have tested the implementation of this procedure
using a mock catalog. We find that the method is effective in reproducing the
true projected radial satellite number density profile and luminosity
distributions, providing confidence in the results derived from SDSS data. The
spatial extent of satellites is larger for bright, red primaries. Also, we find
a larger spatial distribution of blue satellites. For the different samples
analyzed, we derive the average number of satellites and their luminosity
distributions down to M_r=-14.5. The mean number of satellites depends very
strongly on host luminosity. Bright primaries (M_r<-21.5) host on average ~6
satellites with M_r<-14.5, while primaries with -21.5<M_r<-20.5 have less than
1 satellite per host. We provide Schechter function fits to the luminosity
distributions of satellite galaxies with faint-end slopes -1.3+/-0.2. This
shows that satellites of bright primaries lack an excess population of faint
objects, in agreement with the results in the Milky Way and nearby galaxies.Comment: 14 pages, 13 figures. Accepted for publication in Astronomical
Journa
Star Formation in the Milky Way and Nearby Galaxies
We review progress over the past decade in observations of large-scale star
formation, with a focus on the interface between extragalactic and Galactic
studies. Methods of measuring gas contents and star formation rates are
discussed, and updated prescriptions for calculating star formation rates are
provided. We review relations between star formation and gas on scales ranging
from entire galaxies to individual molecular clouds.Comment: 55 pages, 15 figures, in press for Annual Reviews of Astronomy and
Astrophysics; Updated with corrected equation 5, improved references, and
other minor change
Brane World Cosmologies and Statistical Properties of Gravitational Lenses
Brane world cosmologies seem to provide an alternative explanation for the
present accelerated stage of the Universe with no need to invoke either a
cosmological constant or an exotic \emph{quintessence} component. In this paper
we investigate statistical properties of gravitational lenses for some
particular scenarios based on this large scale modification of gravity. We show
that a large class of such models are compatible with the current lensing data
for values of the matter density parameter
(). If one fixes to be , as suggested by
most of the dynamical estimates of the quantity of matter in the Universe, the
predicted number of lensed quasars requires a slightly open universe with a
crossover distance between the 4 and 5-dimensional gravities of the order of
.Comment: 6 pages, 3 figures, revte
The Stellar Populations of Stripped Spiral Galaxies in the Virgo Cluster
(Abridged) We present an analysis of the stellar populations of the
gas-stripped outer disks of ten Virgo Cluster spiral galaxies, utilizing
SparsePak integral field spectroscopy on the WIYN 3.5m telescope and GALEX UV
photometry. The galaxies in our sample show evidence for being gas-stripped
spiral galaxies, with star formation within a truncation radius, and a passive
population beyond the truncation radius. We find that all of the galaxies with
spatially truncated star formation have outer disk stellar populations
consistent with star formation ending within the last 500 Myr. The synthesis of
optical spectroscopy and GALEX observations demonstrate that star formation was
relatively constant until the quenching time, after which the galaxies
passively evolved. Large starbursts at the time of quenching are excluded for
all galaxies. For approximately half of our galaxies, timescales derived from
our observations are consistent with galaxies being stripped in or near the
cluster core, where simple ram-pressure estimates can explain the stripping.
However, the other half of our sample galaxies were clearly stripped outside
the cluster core. Such galaxies provide evidence that the intra-cluster medium
is not static and smooth. For three of our sample galaxies, our stripping
timescales agree with those from the gas stripping simulations, suggesting that
star formation is quenched near the time of peak pressure. While the stripping
of star-forming gas in the outer disk creates a passive population in our
galaxies, there is still normal star formation in the center of our sample
galaxies. It may be that Virgo is not massive enough to completely strip these
spiral galaxies and, in a more dynamically active cluster or a cluster with a
higher density ICM, such a process would lead to passive spirals and/or S0s.Comment: 17 pages, 19 figures, accepted for publication in AJ. Replaced
submission corrects Table names and matches figure style of Journal articl
WINGS: a WIde-field Nearby Galaxy-cluster Survey. I - Optical imaging
This is the first paper of a series that will present data and scientific
results from the WINGS project, a wide-field, multiwavelength imaging and
spectroscopic survey of galaxies in 77 nearby clusters. The sample was
extracted from the ROSAT catalogs with constraints on the redshift
(0.0420). The global goal of
the WINGS project is the systematic study of the local cosmic variance of the
cluster population and of the properties of cluster galaxies as a function of
cluster properties and local environment. This data collection will allow to
define a local 'Zero-Point' reference against which to gauge the cosmic
evolution when compared to more distant clusters. The core of the project
consists of wide-field optical imaging of the selected clusters in the B and V
bands. We have also completed a multi-fiber, medium resolution spectroscopic
survey for 51 of the clusters in the master sample. In addition, a NIR (JK)
survey of ~50 clusters and an H_alpha + UV survey of some 10 clusters are
presently ongoing, while a very-wide-field optical survey has also been
programmed. In this paper we briefly outline the global objectives and the main
characteristics of the WINGS project. Moreover, the observing strategy and the
data reduction of the optical imaging survey (WINGS-OPT) are presented. We have
achieved a photometric accuracy of ~0.025mag, reaching completeness to V~23.5.
Field size and resolution (FWHM) span the absolute intervals (1.6-2.7)Mpc and
(0.7-1.7)kpc, respectively, depending on the redshift and on the seeing. This
allows the planned studies to get a valuable description of the local
properties of clusters and galaxies in clusters.Comment: 24 pages, 15 figures, Accepted by Astronomy and Astrophysic
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