1,703 research outputs found
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
Identification of Faint Chandra X-ray Sources in the Core-Collapsed Globular Cluster NGC 6752
We have searched for optical identifications for 39 Chandra X-ray sources
that lie within the 1.9 arcmin half-mass radius of the nearby (d = 4.0 kpc),
core-collapsed globular cluster, NGC 6752, using deep Hubble Space Telescope
ACS/WFC imaging in B435, R625, and H alpha. Photometry of these images allows
us to classify candidate counterparts based primarily on color-magnitude and
color-color diagram location. The color-color diagram is particularly useful
for quantifying the H alpha line equivalent width. In addition to recovering 11
previously detected optical counterparts, we propose 20 new optical IDs. In
total, there are 16 likely or less certain cataclysmic variables (CVs), nine
likely or less certain chromospherically active binaries, three galaxies, and
three active galactic nuclei (AGNs). The latter three sources, which had been
identified as likely CVs by previous investigations, now appear to be
extragalactic objects based on their proper motions. As we previously found for
NGC 6397, the CV candidates in NGC 6752 fall into a bright group that is
centrally concentrated relative to the turnoff-mass stars and a faint group
that has a spatial distribution that is more similar to that of the
turnoff-mass stars. This is consistent with an evolutionary scenario in which
CVs are produced by dynamical interactions near the cluster center and diffuse
to larger radius orbits as they age.Comment: 26 pages, 18 figure
Discovery of an anomalous Sub Giant Branch in the Color Magnitude Diagram of omega Centauri
Using deep high-resolution multi-band images taken with the Very Large
Telescope and the Hubble Space Telescope, we discovered a new anomalous
sequence in the Color Magnitude Diagram of omega Cen. This feature appears as a
narrow, well-defined Sub Giant Branch (SGB-a), which merges into the Main
Sequence of the dominant cluster population at a magnitude significantly
fainter than the cluster Turn-Off (TO). The simplest hypothesis assumes that
the new feature is the extension of the anomalous Red Giant Branch (RGB-a)
metal-rich population discovered by Lee et al. (1999) and Pancino et al.
(2000). However, under this assumption the interpretation of the SGB-a does not
easily fit into the context of a self-enrichment scenario within omega Cen. In
fact, its TO magnitude, shape and extension are not compatible with a young,
metal-rich population, as required by the self-enrichment process. The TO level
of the SGB-a suggests indeed an age as old as the main cluster population,
further supporting the extra-cluster origin of the most metal rich stars, as
suggested by Ferraro, Bellazzini & Pancino (2002). Only accurate measurements
of radial velocities and metal abundances for a representative sample of stars
will firmly establish whether or not the SGB-a is actually related to the RGB-a
and will finally shed light on the origin of the metal rich population of omega
Cen.Comment: ApJL, in pres
Screening methods for age-related hearing loss in older patients with cancer: A review of the literature
© 2018 by the authors. As people grow older, they may experience loss in hearing sensitivity. Age-related hearing loss may negatively affect the patient's quality of life as it may lead to social isolation. In older patients with cancer, hearing loss can seriously interfere with the patient's ability to deal properly with all aspects of their disease, and may have a cumulative effect on their already decreased quality of life. Therefore, the proper screening of those conditions is essential in order to optimise the patient's comfort during and after treatment. This review article aims at providing a concise image of the nature of age-related hearing loss, and provides an overview of the screening methods that could be used in older patients with cancer
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