3,366 research outputs found
Stellar mass versus stellar velocity dispersion: which is better for linking galaxies to their dark matter halos?
It was recently suggested that, compared to its stellar mass (M*), the
central stellar velocity dispersion (sigma*) of a galaxy might be a better
indicator for its host dark matter halo mass. Here we test this hypothesis by
estimating the dark matter halo mass for central alaxies in groups as function
of M* and sigma*. For this we have estimated the redshift-space
cross-correlation function (CCF) between the central galaxies at given M* and
sigma* and a reference galaxy sample, from which we determine both the
projected CCF, w_p(r_p), and the velocity dispersion profile (VDP) of
satellites around the centrals. A halo mass is then obtained from the average
velocity dispersion within the virial radius. At fixed M*, we find very weak or
no correlation between halo mass and sigma*. In contrast, strong mass
dependence is clearly seen even when sigma* is limited to a narrow range. Our
results thus firmly demonstrate that the stellar mass of central galaxies is
still a good (if not the best) indicator for dark matter halo mass, better than
the stellar velocity dispersion. The dependence of galaxy clustering on sigma*
fixed M*, as recently discovered by Wake et al. (2012), may be attributed to
satellite galaxies, for which the tidal stripping occurring within halos has
stronger effect on stellar mass than on central stellar velocity dispersion.Comment: 4 pages, 4 figures, accepted for publication in ApJ Letters, minor
revisions in the tex
Detection of the large scale alignment of massive galaxies at z~0.6
We report on the detection of the alignment between galaxies and large-scale
structure at z~0.6 based on the CMASS galaxy sample from the Baryon Oscillation
Spectroscopy Survey data release 9. We use two statistics to quantify the
alignment signal: 1) the alignment two-point correlation function which probes
the dependence of galaxy clustering at a given separation in redshift space on
the projected angle (theta_p) between the orientation of galaxies and the line
connecting to other galaxies, and 2) the cos(2theta)-statistic which estimates
the average of cos(2theta_p) for all correlated pairs at given separation. We
find significant alignment signal out to about 70 Mpc/h in both statistics.
Applications of the same statistics to dark matter halos of mass above 10^12
M_sun/h in a large cosmological simulation show similar scale-dependent
alignment signals to the observation, but with higher amplitudes at all scales
probed. We show that this discrepancy may be partially explained by a
misalignment angle between central galaxies and their host halos, though
detailed modeling is needed in order to better understand the link between the
orientations of galaxies and host halos. In addition, we find systematic trends
of the alignment statistics with the stellar mass of the CMASS galaxies, in the
sense that more massive galaxies are more strongly aligned with the large-scale
structure.Comment: 6 pages, 3 figures, accepted for publication in ApJ Letter
The dependence of the pairwise velocity dispersion on galaxy properties
(abridged) We present measurements of the pairwise velocity dispersion (PVD)
for different classes of galaxies in the Sloan Digital Sky Survey. For a sample
of about 200,000 galaxies, we study the dependence of the PVD on galaxy
properties such as luminosity, stellar mass (M_*), colour (g-r), 4000A break
strength (D4000), concentration index (C), and stellar surface mass density
(\mu_*). The luminosity dependence of the PVD is in good agreement with the
results of Jing & B\"orner (2004) for the 2dFGRS catalog. The value of
\sigma_{12} measured at k=1 h/Mpc decreases as a function of increasing galaxy
luminosity for galaxies fainter than L*, before increasing again for the most
luminous galaxies in our sample. Each of the galaxy subsamples selected
according to luminosity or stellar mass is divided into two further subsamples
according to colour, D4000, C and \mu_*. We find that galaxies with redder
colours and higher D4000, C, and \mu_* values have larger PVDs on all scales
and at all luminosities/stellar masses. The dependence of the PVD on parameters
related to recent star formation(colour, D4000) is stronger than on parameters
related to galaxy structure (C, \mu_*), especially on small scales and for
faint galaxies. The reddest galaxies and galaxies with high surface mass
densities and intermediate concentrations have the highest pairwise peculiar
velocities, i.e. these move in the strongest gravitational fields. We conclude
that the faint red population located in rich clusters is responsible for the
high PVD values that are measured for low-luminosity galaxies on small scales.Comment: 14 pages, 13 figures; reference updated and text slightly changed to
match the published version; data of measurements of power spectrum and PVD
available at http://www.mpa-garching.mpg.de/~leech/papers/clustering
Quantum tunneling time of a Bose-Einstein condensate traversing through a laser-induced potential barrier
We theoretically study the effect of atomic nonlinearity on the tunneling
time in the case of an atomic Bose-Einstein condensate (BEC) traversing the
laser-induced potential barrier. The atomic nonlinearity is controlled to
appear only in the region of the barrier by employing the Feshbach resonance
technique to tune interatomic interaction in the tunneling process. Numerical
simulation shows that the atomic nonlinear effect dramatically changes the
tunneling behavior of the BEC matter wave packet, and results in the violation
of Hartman effect and the occurrence of negative tunneling time.Comment: 4 pages, 5 figure
The Alignment between Satellites and Central Galaxies: Theory vs. Observations
Recent studies have shown that the distribution of satellite galaxies is
preferentially aligned with the major axis of their central galaxy. The
strength of this alignment has been found to depend strongly on the colours of
the satellite and central galaxies, and only weakly on the mass of the halo in
which the galaxies reside. In this paper we study whether these alignment
signals, and their dependence on galaxy and halo properties, can be reproduced
in a hierarchical structure formation model of a CDM concordance
cosmology. To that extent we use a large -body simulation which we populate
with galaxies following a semi-analytical model for galaxy formation. We find
that if the orientation of the central galaxy is perfectly aligned with that of
its dark matter halo, then the predicted central-satellite alignment signal is
much stronger than observed. If, however, the minor axis of a central galaxy is
perfectly aligned with the angular momentum vector of its dark matter halo, we
can accurately reproduce the observed alignment strength as function of halo
mass and galaxy color. Although this suggests that the orientation of central
galaxies is governed by the angular momentum of their dark matter haloes, we
emphasize that any other scenario in which the minor axes of central galaxy and
halo are misaligned by (on average) will match the data
equally well. Finally, we show that dependence of the alignment strength on the
color of the central galaxy is most likely an artefact due to interlopers in
the group catalogue. The dependence on the color of the satellite galaxies, on
the other hand, is real and owes to the fact that red satellites are associated
with subhaloes that were more massive at their time of accretion.Comment: 13 Pages, 10 Figures, one figure replaced. added in discussion about
comparison with others results, Updated version to match accepted version to
MNRA
Constraining the HI-Halo Mass Relation From Galaxy Clustering
We study the dependence of galaxy clustering on atomic gas mass using a
sample of 16,000 galaxies with redshift in the range of
and HI mass of , drawn from the 70% complete sample
of the Arecibo Legacy Fast ALFA survey. We construct subsamples of galaxies
with above different thresholds, and make volume-limited
clustering measurements in terms of three statistics: the projected two-point
correlation function, the projected cross-correlation function with respect to
a reference sample selected from the Sloan Digital Sky Survey, and the
redshift-space monopole moment. In contrast to previous studies, which found
no/weak HI-mass dependence, we find both the clustering amplitude on scales
above a few Mpc and the bias factors to increase significantly with increasing
HI mass for subsamples with HI mass thresholds above . For HI
mass thresholds below , while the measurements have large
uncertainties caused by the limited survey volume and sample size, the inferred
galaxy bias factors are systematically lower than the minimum halo bias factor
from mass-selected halo samples. The simple halo model, in which galaxy content
is only determined by halo mass, has difficulties in interpreting the
clustering measurements of the HI-selected samples. We extend the simple model
by including the halo formation time as an additional parameter. A model that
puts HI-rich galaxies into halos that formed late can reproduce the clustering
measurements reasonably well. We present the implications of our best-fitting
model on the correlation of HI mass with halo mass and formation time, as well
as the halo occupation distributions and HI mass functions for central and
satellite galaxies. These results are compared with the predictions from
semi-analytic galaxy formation models and hydrodynamic galaxy formation
simulations.Comment: Accepted for publication in ApJ. The 2PCF measurements are available
at http://sdss4.shao.ac.cn/guoh
Transverse localization and slow propagation of light
The effect of finite control beam on the transverse spatial profile of the
slow light propagation in an electromagnetically induced transparency medium is
studied. We arrive at a general criterion in terms of eigenequation, and
demonstrate the existence of a set of localized, stationary transverse modes
for the negative detuning of the probe signal field. Each of these
diffraction-free transverse modes has its own characteristic group velocity,
smaller than the conventional theoretical result without considering the
transverse spatial effect
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