29 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
A Statistical Method for Estimating Luminosity Functions using Truncated Data
The observational limitations of astronomical surveys lead to significant
statistical inference challenges. One such challenge is the estimation of
luminosity functions given redshift and absolute magnitude measurements
from an irregularly truncated sample of objects. This is a bivariate density
estimation problem; we develop here a statistically rigorous method which (1)
does not assume a strict parametric form for the bivariate density; (2) does
not assume independence between redshift and absolute magnitude (and hence
allows evolution of the luminosity function with redshift); (3) does not
require dividing the data into arbitrary bins; and (4) naturally incorporates a
varying selection function. We accomplish this by decomposing the bivariate
density into nonparametric and parametric portions. There is a simple way of
estimating the integrated mean squared error of the estimator; smoothing
parameters are selected to minimize this quantity. Results are presented from
the analysis of a sample of quasars.Comment: 30 pages, 9 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
Tests of Statistical Methods for Estimating Galaxy Luminosity Function and Applications to the Hubble Deep Field
We studied the statistical methods for the estimation of the luminosity
function (LF) of galaxies. We focused on four nonparametric estimators:
estimator, maximum-likelihood estimator of Efstathiou et al.
(1988), Cho{\l}oniewski's estimator, and improved Lynden-Bell's estimator. The
performance of the estimator has been recently questioned,
especially for the faint-end estimation of the LF. We improved these estimators
for the studies of the distant Universe, and examined their performances for
various classes of functional forms by Monte Carlo simulations. We also applied
these estimation methods to the mock 2dF redshift survey catalog prepared by
Cole et al. (1998). We found that estimator yields a completely
unbiased result if there is no inhomogeneity, but is not robust against
clusters or voids. This is consistent with the well-known results, and we did
not confirm the bias trend of estimator claimed by Willmer
(1997) in the case of homogeneous sample. We also found that the other three
maximum-likelihood type estimators are quite robust and give consistent results
with each other. In practice we recommend Cho{\l}oniewski's estimator for two
reasons: 1. it simultaneously provides the shape and normalization of the LF;
2. it is the fastest among these four estimators, because of the algorithmic
simplicity. Then, we analyzed the photometric redshift data of the Hubble Deep
Field prepared by Fern\'{a}ndez-Soto et al. (1999) using the above four
methods. We also derived luminosity density at - and
-band. Our -band estimation is roughly consistent with that of Sawicki,
Lin, & Yee (1997), but a few times lower at . The evolution of
is found to be less prominent.Comment: To appear in ApJS July 2000 issue. 36 page
The luminosity function of field galaxies
Schmidt's method for construction of luminosity function of galaxies is
generalized by taking into account the dependence of density of galaxies from
the distance in the near Universe. The logarithmical luminosity function (LLF)
of field galaxies depending on morphological type is constructed. We show that
the LLF for all galaxies, and also separately for elliptical and lenticular
galaxies can be presented by Schechter function in narrow area of absolute
magnitudes. The LLF of spiral galaxies was presented by Schechter function for
enough wide area of absolute magnitudes: . Spiral galaxies differ slightly by
parameter . At transition from early spirals to the late spirals parameter in
Schechter function is reduced. The reduction of mean luminosity of galaxies is
observed at transition from elliptical galaxies to lenticular galaxies, to
early spiral galaxies, and further, to late spiral galaxies, in a bright end, .
The completeness and the average density of samples of galaxies of different
morphological types are estimated. In the range the mean number density of all
galaxies is equal 0.127 Mpc-3.Comment: 14 page, 8 figures, to appear in Astrophysic
Comparing galaxy populations in compact and loose groups of galaxies
We perform a comparison of the properties of galaxies in compact groups,
loose groups and in the field to deepen our understanding of the physical
mechanisms acting upon galaxy evolution in different environments. We select
samples of galaxies in compact groups identified by McConnachie et al., loose
groups identified by Zandivarez and Martinez, and field galaxies from the Sloan
Digital Sky Survey. We compare properties of the galaxy populations in these
different environments: absolute magnitude, colour, size, surface brightness,
stellar mass and concentration. We also study the fraction of red and early
type galaxies, the luminosity function, the colour-luminosity and
luminosity-size relations. The population of galaxies in compact groups differ
from that of loose groups and the field. The fraction of read and early type
galaxies is higher in compact groups. On average, galaxies in compact groups
are systematically smaller, more concentrated and have higher surface
brightness than galaxies in the field and in loose groups. For fixed absolute
magnitude, or fixed surface brightness, galaxies in compact groups are smaller.
The physical mechanisms that transform galaxies into earlier types could be
more effective within compact groups given the high densities and low velocity
dispersion that characterise that particular environment, this could explain
the large fraction of red and early type galaxies we found in compact groups.
Galaxies inhabiting compact groups have undergone a major transformation
compared to galaxies that inhabit loose groups.Comment: 12 pages, 14 figures, accepted for publication in Astronomy &
Astrophysics (A&A
The dynamical state of galaxy groups and their luminosity content
We analyse the dependence of the luminosity function of galaxies in groups
(LF) on group dynamical state. We use the Gaussianity of the velocity
distribution of galaxy members as a measurement of the dynamical equilibrium of
groups identified in the SDSS Data Release 7 by Zandivarez & Martinez. We apply
the Anderson-Darling goodness-of-fit test to distinguish between groups
according to whether they have Gaussian or Non-Gaussian velocity distributions,
i.e., whether they are relaxed or not. For these two subsamples, we compute the
band LF as a function of group virial mass and group total
luminosity. For massive groups, ${\mathcal M}>5 \times 10^{13} \ M_{\odot} \
h^{-1}\sim0.3\sim0.25M^{group}_{^{0.1}r}-5\log(h)<-23.5$) Gaussian and Non-Gaussian
groups. Our results indicate that, for massive/luminous groups, the dynamical
state of the system is directly related with the luminosity of its galaxy
members.Comment: 5 pages, 5 figures, accepted in MNRAS letter
Luminosity function of galaxies in groups in the SDSS DR7: the dependence on mass, environment and galaxy type
We perform an analysis of the luminosities of galaxies in groups in the SDSS
DR7. We analyse the luminosity function (LF) as a function of group mass for
different photometric bands, galaxy populations, galaxy positions within the
groups, and the group surrounding large scale density. We find that M*
brightens and alpha becomes steeper as a function of mass in all SDSS
photometric bands, in agreement with previous results. From the analysis of
different galaxy populations, we observe that different methods to split galaxy
populations, based on the concentration index or the colour-magnitude diagram,
produce quite different behaviours in the luminosity trends, mainly for alpha.
These discrepancies and the trends with mass mentioned above are explained when
analysing the LF of galaxies classified simultaneously according to their
concentrations and colours. We find that only the red spheroids have a LF that
strongly depends on group mass. Late type galaxies, whether blue or red, have
luminosity functions that do not depend on group mass. The intrinsic change in
the LF of spheroids and the varying number contributions of the different types
explain all the observed trends with group mass. On the other hand, dividing
the galaxy members in the inner and outer regions of the groups do not
introduce a significant difference in the Schechter parameter trends, except
for the characteristic absolute magnitude in the high group virial mass range
(M>1x10^13 M_sun/h) which is an indication of luminosity segregation in massive
groups. Finally, we also analyse the possible influence of the large scale
surrounding environment on the LF. We find that galaxies inhabiting groups at
low density regions experience more pronounced variations on the Schechter
parameters as a function of groups mass, while galaxies in groups at high
density regions show an almost constant behaviour.Comment: 14 pages, 9 figures, 1 table, final version published in MNRA
The Dust Opacity of Star-Forming Galaxies
Presence of dust in galaxies removes half or more of the stellar energy from
the UV-optical budget of the Universe and has profound impact on our
understanding of how galaxies evolve. Measures of opacity in local galaxies are
reviewed together with widely used theoretical and empirical methods for
quantifying its effects. Existing evidence shows that the dust content of
nearby galaxies depends not only on their morphology, but also on their
luminosity and activity level. A digression is devoted to starbursts in view of
their potential relevance for measures of opacity in distant galaxies. Scarcity
of coherent multiwavelength datasets hampers our ability to derive reliable
obscuration estimates in intermediate and high redshift galaxies. This, in
turn, limits the reliability of inferred physical quantities, such as star
formation rates, stellar population ages, galaxy luminosity functions, and
others.Comment: Invited Review for PASP, to appear in December 2001. 84 pages,
including 6 tables and 11 embedded figures; uses AAS Latex macr