1,675 research outputs found
A two-dimensional Kolmogorov-Smirnov test for crowded field source detection: ROSAT sources in NGC 6397
We present a two-dimensional version of the classical one-dimensional
Kolmogorov-Smirnov (K-S) test, extending an earlier idea due to Peacock (1983)
and an implementation proposed by Fasano & Franceschini (1987). The
two-dimensional K-S test is used to optimise the goodness of fit in an
iterative source-detection scheme for astronomical images. The method is
applied to a ROSAT/HRI x-ray image of the post core-collapse globular cluster
NGC 6397 to determine the most probable source distribution in the cluster
core. Comparisons to other widely-used source detection methods, and to a
Chandra image of the same field, show that our iteration scheme is superior in
measuring statistics-limited sources in severely crowded fields.Comment: 12 pages, 6 figures, 6 tables. Accepted by MNRA
Dual Supermassive Black Hole Candidates in the AGN and Galaxy Evolution Survey
Dual supermassive black holes (SMBHs) with kiloparsec scale separations in
merger-remnant galaxies are informative tracers of galaxy evolution, but the
avenue for identifying them in large numbers for such studies is not yet clear.
One promising approach is to target spectroscopic signatures of systems where
both SMBHs are fueled as dual active galactic nuclei (AGNs), or where one SMBH
is fueled as an offset AGN. Dual AGNs may produce double-peaked narrow AGN
emission lines, while offset AGNs may produce single-peaked narrow AGN emission
lines with line-of-sight velocity offsets relative to the host galaxy. We
search for such dual and offset systems among 173 Type 2 AGNs at z<0.37 in the
AGN and Galaxy Evolution Survey (AGES), and we find two double-peaked AGNs and
five offset AGN candidates. When we compare these results to a similar search
of the DEEP2 Galaxy Redshift Survey and match the two samples in color,
absolute magnitude, and minimum velocity offset, we find that the fraction of
AGNs that are dual SMBH candidates increases from z=0.25 to z=0.7 by a factor
of ~6 (from 2/70 to 16/91, or 2.9% to 18%). This may be associated with the
rise in the galaxy merger fraction over the same cosmic time. As further
evidence for a link with galaxy mergers, the AGES offset and dual AGN
candidates are tentatively ~3 times more likely than the overall AGN population
to reside in a host galaxy that has a companion galaxy (from 16/173 to 2/7, or
9% to 29%). Follow-up observations of the seven offset and dual AGN candidates
in AGES will definitively distinguish velocity offsets produced by dual SMBHs
from those produced by narrow-line region kinematics, and will help sharpen our
observational approach to detecting dual SMBHs.Comment: 10 pages, 8 figures, accepted for publication in Ap
Requirements for maintenance and live weight gain of moose and wapiti calves during winter
Energy requirements of moose (Alces alces) and wapiti (Cervus elaphus) calves were compared from December to February to determine whether metabolic requirements were lower in a boreal-adapted than in a parkland-adapted wild cervid. Eight calves of each species were divided equally into groups given high or low quality diets. Regression of metabolizable energy intake on liveweight gain provided estimates for maintenance and gain, Metabolizable energy requirements for liveweight maintenance were 560 kj/kg0.75.d and for gain were 27 kj/g. Neither value was significantly different between moose and wapiti nor between genders within species. This similariry in winter metabolism and consistency with the interspecies mean suggests that winter metabolic dormancy is not necessarily an important part of a seasonal energetic strategy. The main difference was that moose calves maintained appetite and continued to grow throughout the winter
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
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