275 research outputs found
Dynamical Characterization of Galaxies at z~4-6 via Tilted Ring Fitting to ALMA [CII] Observations
Until recently, determining the rotational properties of galaxies in the
early universe (z>4, Universe age <1.5Gyr) was impractical, with the exception
of a few strongly lensed systems. Combining the high resolution and sensitivity
of ALMA at (sub-) millimeter wavelengths with the typically high strength of
the [CII] 158um emission line from galaxies and long-developed dynamical
modeling tools raises the possibility of characterizing the gas dynamics in
both extreme starburst galaxies and normal star forming disk galaxies at z~4-7.
Using a procedure centered around GIPSY's ROTCUR task, we have fit tilted ring
models to some of the best available ALMA [CII] data of a small set of
galaxies: the MS galaxies HZ9 & HZ10, the Damped Lyman-alpha Absorber (DLA)
host galaxy ALMA J0817+1351, the submm galaxies AzTEC/C159 and COSMOS
J1000+0234, and the quasar host galaxy ULAS J1319+0950. This procedure directly
derives rotation curves and dynamical masses as functions of radius for each
object. In one case, we present evidence for a dark matter halo of O(10^11)
solar masses. We present an analysis of the possible velocity dispersions of
AzTEC/C159 and ULAS J1319+0950 based on matching simulated observations to the
integrated [CII] line profiles. Finally, we test the effects of observation
resolution and sensitivity on our results. While the conclusions remain limited
at the resolution and signal-to-noise ratios of these observations, the results
demonstrate the viability of the modeling tools at high redshift, and the
exciting potential for detailed dynamical analysis of the earliest galaxies, as
ALMA achieves full observational capabilities.Comment: 20 pages, 6 figures, Accepted for publication in Ap
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Reproducing the kinematics of damped Lyman α systems
We examine the kinematic structure of Damped Lyman-alpha Systems (DLAs) in a
series of cosmological hydrodynamic simulations using the AREPO code. We are
able to match the distribution of velocity widths of associated low ionisation
metal absorbers substantially better than earlier work. Our simulations produce
a population of DLAs dominated by halos with virial velocities around 70 km/s,
consistent with a picture of relatively small, faint objects. In addition, we
reproduce the observed correlation between velocity width and metallicity and
the equivalent width distribution of SiII. Some discrepancies of moderate
statistical significance remain; too many of our spectra show absorption
concentrated at the edge of the profile and there are slight differences in the
exact shape of the velocity width distribution. We show that the improvement
over previous work is mostly due to our strong feedback from star formation and
our detailed modelling of the metal ionisation state
Massive, Absorption-selected Galaxies at Intermediate Redshifts
The nature of absorption-selected galaxies and their connection to the
general galaxy population have been open issues for more than three decades,
with little information available on their gas properties. Here we show, using
detections of carbon monoxide (CO) emission with the Atacama Large
Millimeter/submillimeter Array (ALMA), that five of seven high-metallicity,
absorption-selected galaxies at intermediate redshifts, ,
have large molecular gas masses, and high molecular gas fractions (. Their modest star
formation rates (SFRs), yr, then
imply long gas depletion timescales, Gyr. The
high-metallicity absorption-selected galaxies at appear
distinct from populations of star-forming galaxies at both ,
during the peak of star formation activity in the Universe, and lower
redshifts, . Their relatively low SFRs, despite the large
molecular gas reservoirs, may indicate a transition in the nature of star
formation at intermediate redshifts, .Comment: 8 pages, 3 figures; accepted for publication in Astrophysical Journal
Letters. Minor changes to match the version in press in ApJ
Rates, risk factors & methods of self harm among minority ethnic groups in the UK: a systematic review
<p>Abstract</p> <p>Background</p> <p>Studies suggest that the rates of self harm vary by ethnic group, but the evidence for variation in risk factors has not been synthesised to inform preventive initiatives.</p> <p>Methods</p> <p>We undertook a systematic literature review of research about self harm that compared at least two ethnic groups in the United Kingdom.</p> <p>Results</p> <p>25 publications from 1765 titles and abstracts met our inclusion criteria. There was higher rate of self harm among South Asian women, compared with South Asian men and White women. In a pooled estimate from two studies, compared to their white counterparts, Asian women were more likely to self harm (Relative Risk 1.4, 95%CI: 1.1 to 1.8, p = 0.005), and Asian men were less likely to self harm (RR 0.5, 95% CI: 0.4 to 0.7, p < 0.001). Some studies concluded that South Asian adults self-harm impulsively in response to life events rather than in association with a psychiatric illness. Studies of adolescents showed similar methods of self harm and interpersonal disputes with parents and friends across ethnic groups. There were few studies of people of Caribbean, African and other minority ethnic groups, few studies took a population based and prospective design and few investigated self harm among prisoners, asylum seekers and refugees.</p> <p>Conclusion</p> <p>This review finds some ethnic differences in the nature and presentation of self harm. This argues for ethnic specific preventive actions. However, the literature does not comprehensively cover the UK's diverse ethnic groups.</p
ALMA observations of a metal-rich damped Ly{\alpha} absorber at z = 2.5832: evidence for strong galactic winds in a galaxy group
We report on the results of a search for CO(3-2) emission from the galaxy
counterpart of a high-metallicity Damped Ly-alpha Absorber (DLA) at z=2.5832
towards the quasar Q0918+1636. We do not detect CO emission from the previously
identified DLA galaxy counterpart. The limit we infer on M_gas / M_star is in
the low end of the range found for DLA galaxies, but is still consistent with
what is found for other star-forming galaxies at similar redshifts. Instead we
detect CO(3-2) emission from another intensely star-forming galaxy at an impact
parameter of 117 kpc from the line-of-sight to the quasar and 131 km s^-1
redshifted relative to the velocity centroid of the DLA in the quasar spectrum.
In the velocity profile of the low- and high-ionisation absorption lines of the
DLA there is an absorption component consistent with the redshift of this
CO-emitting galaxy. It is plausible that this component is physically
associated with a strong outflow in the plane of the sky from the CO-emitting
galaxy. If true, this would be further evidence, in addition to what is already
known from studies of Lyman-break galaxies, that galactic outflows can be
traced beyond 100 kpc from star-forming galaxies. The case of this z=2.583
structure is an illustration of this in a group environment.Comment: 7 pages, 5 figures, accepted for publication in MNRA
The Evolution of O i over 3.2 < z < 6.5: Reionization of the Circumgalactic Medium
We present a survey for metal absorption systems traced by neutral oxygen over 3.2 0.05 Å, of which there are 49 nonproximate systems in our sample. We find that the number density does not monotonically increase with decreasing redshift, as would naively be expected from the buildup of metal-enriched circumgalactic gas with time. The number density over 4.9 < z < 5.7 is a factor of 1.7–4.1 lower (68% confidence) than that over 5.7 < z < 6.5, with a lower value at z < 5.7 favored with 99% confidence. This decrease suggests that the fraction of metals in a low-ionization phase is larger at z ~ 6 than at lower redshifts. Absorption from highly ionized metals traced by C iv is also weaker in higher-redshift O i systems, supporting this picture. The evolution of O i absorbers implies that metal-enriched circumgalactic gas at z ~ 6 is undergoing an ionization transition driven by a strengthening ultraviolet background. This in turn suggests that the reionization of the diffuse intergalactic medium may still be ongoing at or only recently ended by this epoch
Reverberation Mapping of the Kepler-Field AGN KA1858+4850
KA1858+4850 is a narrow-line Seyfert 1 galaxy at redshift 0.078 and is among
the brightest active galaxies monitored by the Kepler mission. We have carried
out a reverberation mapping campaign designed to measure the broad-line region
size and estimate the mass of the black hole in this galaxy. We obtained 74
epochs of spectroscopic data using the Kast Spectrograph at the Lick 3-m
telescope from February to November of 2012, and obtained complementary V-band
images from five other ground-based telescopes. We measured the H-beta light
curve lag with respect to the V-band continuum light curve using both
cross-correlation techniques (CCF) and continuum light curve variability
modeling with the JAVELIN method, and found rest-frame lags of lag_CCF = 13.53
(+2.03, -2.32) days and lag_JAVELIN = 13.15 (+1.08, -1.00) days. The H-beta
root-mean-square line profile has a width of sigma_line = 770 +/- 49 km/s.
Combining these two results and assuming a virial scale factor of f = 5.13, we
obtained a virial estimate of M_BH = 8.06 (+1.59, -1.72) x 10^6 M_sun for the
mass of the central black hole and an Eddington ratio of L/L_Edd ~ 0.2. We also
obtained consistent but slightly shorter emission-line lags with respect to the
Kepler light curve. Thanks to the Kepler mission, the light curve of
KA1858+4850 has among the highest cadences and signal-to-noise ratios ever
measured for an active galactic nucleus; thus, our black hole mass measurement
will serve as a reference point for relations between black hole mass and
continuum variability characteristics in active galactic nuclei
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