2,330 research outputs found
Counts-in-Cylinders in the Sloan Digital Sky Survey with Comparisons to N-body Simulations
Environmental statistics provide a necessary means of comparing the
properties of galaxies in different environments and a vital test of models of
galaxy formation within the prevailing, hierarchical cosmological model. We
explore counts-in-cylinders, a common statistic defined as the number of
companions of a particular galaxy found within a given projected radius and
redshift interval. Galaxy distributions with the same two-point correlation
functions do not necessarily have the same companion count distributions. We
use this statistic to examine the environments of galaxies in the Sloan Digital
Sky Survey, Data Release 4. We also make preliminary comparisons to four models
for the spatial distributions of galaxies, based on N-body simulations, and
data from SDSS DR4 to study the utility of the counts-in-cylinders statistic.
There is a very large scatter between the number of companions a galaxy has and
the mass of its parent dark matter halo and the halo occupation, limiting the
utility of this statistic for certain kinds of environmental studies. We also
show that prevalent, empirical models of galaxy clustering that match observed
two- and three-point clustering statistics well fail to reproduce some aspects
of the observed distribution of counts-in-cylinders on 1, 3 and 6-Mpc/h scales.
All models that we explore underpredict the fraction of galaxies with few or no
companions in 3 and 6-Mpc/h cylinders. Roughly 7% of galaxies in the real
universe are significantly more isolated within a 6 Mpc/h cylinder than the
galaxies in any of the models we use. Simple, phenomenological models that map
galaxies to dark matter halos fail to reproduce high-order clustering
statistics in low-density environments.Comment: 17 pages, 10 figures. Accepted, Ap
The size distribution of galaxies in the Sloan Digital Sky Survey
abridged: We use a complete sample of about 140,000 galaxies from the Sloan
Digital Sky Survey (SDSS) to study the size distribution of galaxies and its
dependence on their luminosity, stellar mass, and morphological type. The large
SDSS database provides statistics of unprecedented accuracy. For each type of
galaxy, the size distribution at given luminosity (or stellar mass) is well
described by a log-normal function, characterized by its median and
dispersion . For late-type galaxies, there is a characteristic
luminosity at (assuming ) corresponding to a stellar
mass M_0\sim 10^{10.6}\Msun. Galaxies more massive than have
and , while less massive
galaxies have and . For
early-type galaxies, the - relation is significantly steeper,
, but the - relation is similar
to that of late-type galaxies. Faint red galaxies have sizes quite independent
of their luminosities.Comment: 42 pages, 18 figures, 2 tables; replaced with the version accepted by
MNRA
PRIMUS: The Effect of Physical Scale on the Luminosity-Dependence of Galaxy Clustering via Cross-Correlations
We report small-scale clustering measurements from the PRIMUS spectroscopic
redshift survey as a function of color and luminosity. We measure the
real-space cross-correlations between 62,106 primary galaxies with PRIMUS
redshifts and a tracer population of 545,000 photometric galaxies over
redshifts from z=0.2 to z=1. We separately fit a power-law model in redshift
and luminosity to each of three independent color-selected samples of galaxies.
We report clustering amplitudes at fiducial values of z=0.5 and L=1.5 L*. The
clustering of the red galaxies is ~3 times as strong as that of the blue
galaxies and ~1.5 as strong as that of the green galaxies. We also find that
the luminosity dependence of the clustering is strongly dependent on physical
scale, with greater luminosity dependence being found between r=0.0625 Mpc/h
and r=0.25 Mpc/h, compared to the r=0.5 Mpc/h to r=2 Mpc/h range. Moreover,
over a range of two orders of magnitude in luminosity, a single power-law fit
to the luminosity dependence is not sufficient to explain the increase in
clustering at both the bright and faint ends at the smaller scales. We argue
that luminosity-dependent clustering at small scales is a necessary component
of galaxy-halo occupation models for blue, star-forming galaxies as well as for
red, quenched galaxies.Comment: 13 pages, 6 figures, 5 tables; published in ApJ (revised to match
published version
What triggers galaxy transformations? The environments of post-starburst galaxies
(abridged) There are good observational reasons to believe that the
progenitors of red galaxies have undergone starbursts, followed by a
post-starburst phase. We investigate the environments of post-starburst
galaxies by measuring \textsl{(1)} number densities in
radius comoving spheres, \textsl{(2)} transverse distances to nearest
Virgo-like galaxy clusters, and \textsl{(3)} transverse distances to nearest
luminous-galaxy neighbors. We compare the post-starburst galaxies to currently
star-forming galaxies identified solely by A-star excess or \Halpha emission.
We find that post-starburst galaxies are in the same kinds of environments as
star-forming galaxies; this is our ``null hypothesis''. More importantly, we
find that at each value of the A-star excess, the star-forming and
post-starburst galaxies lie in very similar distributions of environment. The
only deviations from our null hypothesis are barely significant: a slight
deficit of post-starburst galaxies (relative to the star-forming population) in
very low-density regions, a small excess inside the virial radii of clusters,
and a slight excess with nearby neighbors. None of these effects is strong
enough to make the post-starburst galaxies a high-density phenomenon, or to
argue that the starburst events are primarily triggered by external tidal
impulses (e.g., from close passages of massive galaxies). The small excess
inside cluster virial radii suggests that some post-starbursts are triggered by
interactions with the intracluster medium, but this represents a very small
fraction of all post-starburst galaxies.Comment: ApJ in pres
A Contrast/Comparison of Needs Assessment and Curricular Evaluation for Management Careers in Hostelries/Travel, Private Sport Clubs, and Agencies
The purposes of this study were to: (a) assess the needs for sport management positions; and (b) obtain the evaluation of sport management programs/curricula by management personnel from different business perspectives, i.e., hostelries/travel, private sport clubs, and agencies. According to curriculum theorists, there has been an increase in the demand for sport management positions, but there is a real lack of and need for empirical evidence upon which to establish the theoretical basis and content for programs/curricula to meet this demand. Thus, the significance of this research is that it provides a basis for planning utilizing the empirical evidence of the needs assessment and program evaluation by/for professional sport managers in hostelries/travel, private sport clubs, and agencies
Very large scale correlations in the galaxy distribution
We characterize galaxy correlations in the Sloan Digital Sky Survey by
measuring several moments of galaxy counts in spheres. We firstly find that the
average counts grows as a power-law function of the distance with an exponent
D= 2.1+- 0.05 for r in [0.5,20] Mpc/h and D = 2.8+-0.05 for r in [30,150]
Mpc/h. In order to estimate the systematic errors in these measurements we
consider the counts variance finding that it shows systematic finite size
effects which depend on the samples sizes. We clarify, by making specific
tests, that these are due to galaxy long-range correlations extending up to the
largest scales of the sample. The analysis of mock galaxy catalogs, generated
from cosmological N-body simulations of the standard LCDM model, shows that for
r<20 Mpc/h the counts exponent is D~2.0, weakly dependent on galaxy luminosity,
while D=3 at larger scales. In addition, contrary to the case of the observed
galaxy samples, no systematic finite size effects in the counts variance are
found at large scales, a result that agrees with the absence of large scale,
r~100 Mpc/h, correlations in the mock catalogs. We thus conclude that the
observed galaxy distribution is characterized by correlations, fluctuations and
hence structures, which are larger, both in amplitude and in spatial extension,
than those predicted by the standard model LCDM of galaxy formation.Comment: 6 pages, 7 figures to be published in Europhysics Letter
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
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