117 research outputs found
Using member galaxy luminosities as halo mass proxies of galaxy groups
Reliable halo mass estimation for a given galaxy system plays an important
role both in cosmology and galaxy formation studies. Here we set out to find
the way that can improve the halo mass estimation for those galaxy systems with
limited brightest member galaxies been observed. Using four mock galaxy samples
constructed from semi-analytical formation models, the subhalo abundance
matching method and the conditional luminosity functions, respectively, we find
that the luminosity gap between the brightest and the subsequent brightest
member galaxies in a halo (group) can be used to significantly reduce the
scatter in the halo mass estimation based on the luminosity of the brightest
galaxy alone. Tests show that these corrections can significantly reduce the
scatter in the halo mass estimations by to in massive
halos depending on which member galaxies are considered. Comparing to the
traditional ranking method, we find that this method works better for groups
with less than five members, or in observations with very bright magnitude cut.Comment: ApJ accepte
The Fundamental Plane of Open Clusters
We utilize the data from the Apache Point Observatory Galactic Evolution
Experiment-2 (APOGEE-2) in the fourteenth data release of the Sloan Digital Sky
Survey (SDSS) to calculate the line-of-sight velocity dispersion
of a sample of old open clusters (age larger than 100\,Myr) selected from the
Milky Way open cluster catalog of Kharchenko et al. (2013). Together with their
band luminosity , and the half-light radius of the most
probable members, we find that these three parameters show significant pairwise
correlations among each other. Moreover, a fundamental plane-{\it like}
relation among these parameters is found for the oldest open clusters (age
older than 1\,Gyr), with \,mag in the band absolute
magnitude. The existence of this relation, which deviates significantly from
the virial theorem prediction, implies that the dynamical structures of the old
open clusters are quite similar, when survived from complex dynamical evolution
to age older than 1 Gyr.Comment: accepted publication for ApJ lette
An Apparent Redshift Dependence of Quasar Continuum: Implication for Cosmic Dust Extinction?
We investigate the luminosity and redshift dependence of the quasar continuum
by means of composite spectrum using a large non-BAL radio-quiet quasar sample
drawn from the Sloan Digital Sky Survey. Quasar continuum slopes in the UV-Opt
band are measured at two different wavelength ranges, i.e.,
() and () derived
from power law fitting. Generally, the UV spectra slope becomes harder (higher
) towards higher bolometric luminosity. On the other hand, when
quasars are further grouped into luminosity bins, we find both
and show significant anti-correlation with redshift (i.e.,
quasar continuum becomes redder towards higher redshift). We suggest that the
cosmic dust extinction is very likely the cause of this observed
relation. We build a simple cosmic dust extinction model to quantify the
observed reddening tendency and find an effective dust density at . The other possibilities that could produce
such a reddening effect have also been discussed.Comment: 6 pages, 5 figures; published in ApJ
Linking the Metallicity Enrichment History to the Star Formation History: An SFH-regulated Chemical Evolution Model and Its Implications for the Gas Cycling Process
The metallicity enrichment history (MEH) of a galaxy is determined by its
star formation history (SFH) and the gas cycling process. In this paper, we
construct a chemical evolution model that is regulated by the SFH of the
system. In this SFH-regulated model, the evolution of all other variables,
including the MEH, can be determined by the SFH. We test this model on six
locally isolated dwarf galaxies covering three dwarf types that were observed
by the Local Cosmology from Isolated Dwarfs (LCID) project. The SFHs and MEHs
of these LCID galaxies have been measured from the deep color-magnitude
diagrams that are down to the main sequence turn-offs stars. With simple
assumptions of the star formation law and the mass-dependent outflows, our
SFH-regulated model successfully reproduces the MEHs of all six LCID galaxies
from their SFHs, with only one free parameter, the wind efficiency , for all six galaxies. This model provides a physically motivated link
that directly connects the SFH and MEH of a galaxy, which will be useful to
accommodate into the state-of-the-art stellar population synthesis models to
help relieve the nuisance of the heavy degeneracy between the ages and
metallicities of the stellar populations.Comment: 18 pages, 5 figures, accepted for publication in Ap
The statistical nature of the brightest group galaxies
We examine the statistical properties of the brightest group galaxies (BGGs)
using a complete spectroscopic sample of groups/clusters of galaxies selected
from the Data Release 7 of the Sloan Digital Sky Survey. We test whether BGGs
and other bright members of groups are consistent with an ordered population
among the total population of group galaxies. We find that the luminosity
distributions of BGGs do not follow the predictions from the order statistics
(OS). The average luminosities of BGGs are systematically brighter than OS
predictions. On the other hand, by properly taking into account the brightening
effect of the BGGs, the luminosity distributions of the second brightest
galaxies are in excellent agreement with the expectations of OS. The
brightening of BGGs relative to the OS expectation is consistent with a
scenario that the BGGs on average have over-grown about 20 percent masses
relative to the other member galaxies. The growth () is not
stochastic but correlated with the magnitude gap () between the
brightest and the second brightest galaxy. The growth () is larger
for the groups having more prominent BGGs (larger ) and averagely
contributes about 30 percent of the final of the groups of galaxies.Comment: ApJ accepted, replaced with the accepted versio
The Fundamental Plane of Spiral Galaxies: Theoretical Expectations
Current theory of disk galaxy formation is used to study fundamental-plane
(FP) type of relations for disk galaxies. We examine how the changes in model
parameters affect these relations and explore the possibility of using such
relations to constrain theoretical models. The distribution of galaxy disks in
the space of their fundamental properties are predicted to be concentrated in a
plane, with the Tully-Fisher (TF) relation (a relation between luminosity
and maximum rotation velocity ) being an almost edge-on view. Using
rotation velocities at larger radii generally leads to larger TF scatter. In
searching for a third parameter, we find that both the disk scale-length
(or surface brightness) and the rotation-curve shape are correlated with the TF
scatter. The FP relation in the (\Log L, \Log V_m, \Log R_d)-space obtained
from the theory is , with and , consistent with the preliminary result we obtain
from observational data. Among the model parameters we probe, variation in any
of them can generate significant scatter in the TF relation, but the effects of
the spin parameter and halo concentration can be reduced significantly by
introducing while the scatter caused by varying (the ratio between
disk mass and halo mass) is most effectively reduced by introducing the
parameters which describes the rotation-curve shape. The TF and FP relations
combined should therefore provide useful constraints on models of galaxy
formation.Comment: 25 pages, 11 figures, 4 tables; submitted to MNRA
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