12,274 research outputs found
The nature of obscuration in AGN: II. insights from clustering properties
Based on large optical and mid-infrared (IR) surveys, we investigate the
relation between nuclear activity in local Seyfert 2 galaxies and galaxy
interactions using a statistical neighbour counting technique. At the same
level of host galaxy star formation (SF), we find that active galactic nuclei
(AGNs) with stronger [OIII] emission lines do not show an excess of near
neighbours, while AGNs with stronger mid-IR emission do have more near
neighbours within a projected distance of 100 kpc. The excess neighbour count
increases with decreasing projected radius. These results suggest a phase of
torus formation during galaxy interactions.Comment: 5 pages, 2 figures, accepted to MNRA
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
A probabilistic method for gradient estimates of some geometric flows
In general, gradient estimates are very important and necessary for deriving
convergence results in different geometric flows, and most of them are obtained
by analytic methods. In this paper, we will apply a stochastic approach to
systematically give gradient estimates for some important geometric quantities
under the Ricci flow, the mean curvature flow, the forced mean curvature flow
and the Yamabe flow respectively. Our conclusion gives another example that
probabilistic tools can be used to simplify proofs for some problems in
geometric analysis.Comment: 22 pages. Minor revision to v1. Accepted for publication in
Stochastic Processes and their Application
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
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