335 research outputs found
The Frequency of Tidal Features Associated with Nearby Luminous Elliptical Galaxies from a Statistically Complete Sample
We present a deep broadband optical imaging study of a complete sample of
luminous elliptical galaxies (M_B<-20) at distances 15 Mpc - 50 Mpc, selected
from the Tully catalog of nearby galaxies. The images are flat to ~0.35% across
the 20' field and reach a V band depth of 27.7 mag arcsec^-2. We derive an
objective tidal interaction parameter for all galaxies and find that 73% of
them show tidal disturbance signatures in their stellar bodies. This is the
first time that such an analysis is done on a statistically complete sample and
it confirms that tidal features in ellipticals are common even in the local
Universe. From the dynamical time of the sample galaxies at the innermost
radius where tidal features are detected we estimate the mass assembly rate of
nearby ellipticals to be dM/M 0.2 per Gyr with large uncertainty. We explore
the relation between gravitational interaction signatures and the galaxy
environment and find that galaxies in clusters are less disturbed than group
and field galaxies. We also study how these interactions affect the broadband
colors of ellipticals and find a moderate correlation, suggesting that the
mergers are not accompanied by significant star-formation. Lastly, we find no
correlation between AGN activity, as measured by 6cm radio emission, and large
scale tidal distortions. This implies that gravitational interactions are not
the only, and perhaps not the most important, trigger of nuclear activity. In
summary, we find that elliptical galaxies in groups and low density
environments continue to grow at the present day through mostly "dry" mergers
involving little star formation.Comment: Accepted for publication in AJ. Appendix and full dataset available
online at: http://www.astro.yale.edu/obe
The Relation between Dynamical Mass-to-light Ratio and Color for Massive Quiescent Galaxies out to z ~ 2 and Comparison with Stellar Population Synthesis Models
Article / Letter to editorSterrewach
An Absence of Radio-Loud Active Galactic Nuclei in Geometrically Flat Quiescent Galaxies: Implications for Maintenance-Mode Feedback Models
Maintenance-mode feedback from low-accretion rate AGN, manifesting itself
observationally through radio-loudness, is invoked in all cosmological galaxy
formation models as a mechanism that prevents excessive star-formation in
massive galaxies (M 310 M). We
demonstrate that at a fixed mass the incidence of radio-loud AGN (L
10 WHz) identified in the FIRST and NVSS radio surveys among a
large sample of quiescent (non-star forming) galaxies selected from the SDSS is
much higher in geometrically round galaxies than in geometrically flat,
disk-like galaxies. As found previously, the RL AGN fraction increases steeply
with stellar velocity dispersion and stellar mass, but even at a
fixed velocity dispersion of 200-250 kms this fraction increases from
0.3% for flat galaxies (projected axis ratio of q 0.4) to 5% for round
galaxies (q 0.8). We rule out that this strong trend is due to projection
effects in the measured velocity dispersion. The large fraction of radio-loud
AGN in massive, round galaxies is consistent with the hypothesis that such AGN
deposit energy into their hot gaseous halos, preventing cooling and
star-formation. However, the absence of such AGN in disk-like quiescent
galaxies -- most of which are not satellites in massive clusters, raises
important questions: is maintenance-mode feedback a generally valid explanation
for quiescence; and, if so, how does that feedback avoid manifesting at least
occasionally as a radio-loud galaxy?Comment: 7 pages, 5 figures, accepted for publication in ApJ Letter
Addressing obstacles to the inclusion of palliative care in humanitarian health projects: a qualitative study of humanitarian health professionals’ and policy makers’ perceptions
© 2020, The Author(s). Background: Humanitarian non-governmental organizations provide assistance to communities affected by war, disaster and epidemic. A primary focus of healthcare provision by these organizations is saving lives; however, curative care will not be sufficient, appropriate, or available for some patients. In these instances, palliative care approaches to ease suffering and promote dignity are needed. Though several recent initiatives have increased the probability of palliative care being included in humanitarian healthcare response, palliative care remains minimally integrated in humanitarian health projects. Methods: We conducted a qualitative study using interpretive description methodology to investigate humanitarian policy-makers’ and health care professionals’ experiences and perceptions of palliative care during humanitarian crises. In this article, we report on the analysis of in-depth interviews with 24 participants related to their perceptions of obstacles to providing palliative care in humanitarian crises, and opportunities for overcoming these obstacles. Among the participants, 23 had experience as humanitarian health professionals, and 12 had experience with policy development and organizational decision-making. Results: Participants discussed various obstacles to the provision of palliative care in humanitarian crises. More prominent obstacles were linked to the life-saving ethos of humanitarian organizations, priority setting of scarce resources, institutional and donor funding, availability of guidance and expertise in palliative care, access to medication, and cultural specificity around death and dying. Less prominent obstacles related to continuity of care after project closure, equity, security concerns, and terminology. Conclusion: Opportunities exist for overcoming the obstacles to providing palliative care in humanitarian crises. Doing so is necessary to ensure that humanitarian healthcare can fulfill its objectives not only of saving lives, but also of alleviating suffering and promoting dignity of individuals who are ill or injured during a humanitarian crises, including persons who are dying or likely to die
Redshift Evolution of the Galaxy Velocity Dispersion Function
We present a study of the evolution of the galaxy Velocity Dispersion
Function (VDF) from z=0 to z=1.5 using photometric data from the UKIDSS Ultra
Deep Survey (UDS) and Newfirm Medium Band Survey (NMBS) COSMOS surveys. The VDF
has been measured locally using direct kinematic measurements from the Sloan
Digital Sky Survey, but direct studies of the VDF at high redshift are
difficult as they require velocity dispersion measurements of many thousands of
galaxies. Taylor et al. (2010) demonstrated that dynamical and stellar mass are
linearly related when the structure of the galaxy is accounted for. We show
that the stellar mass, size and S\'ersic index can reliably predict the
velocity dispersions of SDSS galaxies. We apply this relation to galaxies at
high redshift and determine the evolution of the inferred VDF. We find that the
VDF at z~0.5 is very similar to the VDF at z=0. At higher redshifts, we find
that the number density of galaxies with dispersions <~200 km/s is lower, but
the number of high dispersion galaxies is constant or even higher. At fixed
cumulative number density, the velocity dispersions of galaxies with
logN[Mpc^{-3}]<-3.5 increase with time by a factor of ~1.4 from z~1.5-0,
whereas the dispersions of galaxies with lower number density are approximately
constant or decrease with time. The VDF appears to show less evolution than the
stellar mass function, particularly at the lowest number densities. We note
that these results are still somewhat uncertain and we suggest several avenues
for further calibrating the inferred velocity dispersions.Comment: 6 pages, 4 figures, Accepted for publication in ApJ Letter
Stellar Kinematics of z ~ 2 Galaxies and the Inside-out Growth of Quiescent Galaxies
Using stellar kinematics measurements, we investigate the growth of massive, quiescent galaxies from z ~{} 2 to today. We present X-Shooter spectra from the UV to NIR and dynamical mass measurements of five quiescent massive ({gt}10 M ) galaxies at z ~{} 2. This triples the sample of z {gt} 1.5 galaxies with well-constrained ({}{} {lt} 100 km s) velocity dispersion measurements. From spectral population synthesis modeling we find that these galaxies have stellar ages that range from 0.5 to 2 Gyr, with no signs of ongoing star formation. We measure velocity dispersions (290-450 km s) from stellar absorption lines and find that they are 1.6-2.1 times higher than those of galaxies in the Sloan Digital Sky Survey at the same mass. Sizes are measured using GALFIT from Hubble Space Telescope Wide Field Camera 3 H and UDS K-band images. The dynamical masses correspond well to the spectral energy distribution based stellar masses, with dynamical masses that are ~{}15% higher. We find that M /M may decrease slightly with time, which could reflect the increase of the dark matter fraction within an increasing effective radius. We combine different stellar kinematic studies from the literature and examine the structural evolution from z ~{} 2 to z ~{} 0: we confirm that at fixed dynamical mass, the effective radius increases by a factor of ~{}2.8, and the velocity dispersion decreases by a factor of ~{}1.7. The mass density within one effective radius decreases by a factor of ~{}20, while within a fixed physical radius (1 kpc) it decreases only mildly (factor of ~{}2). When we allow for an evolving mass limit by selecting a population of galaxies at fixed number density, a stronger size growth with time is found (factor of ~{}4), velocity dispersion decreases by a factor of ~{}1.4, and interestingly, the mass density within 1 kpc is consistent with no evolution. This finding suggests that massive quiescent galaxies at z ~{} 2 grow inside out, consistent with the expectations from minor mergers
Stellar Kinematics of z ~ 2 Galaxies and the Inside-out Growth of Quiescent Galaxies
Using stellar kinematics measurements, we investigate the growth of massive, quiescent galaxies from z ~{} 2 to today. We present X-Shooter spectra from the UV to NIR and dynamical mass measurements of five quiescent massive ({gt}10 M ) galaxies at z ~{} 2. This triples the sample of z {gt} 1.5 galaxies with well-constrained ({}{} {lt} 100 km s) velocity dispersion measurements. From spectral population synthesis modeling we find that these galaxies have stellar ages that range from 0.5 to 2 Gyr, with no signs of ongoing star formation. We measure velocity dispersions (290-450 km s) from stellar absorption lines and find that they are 1.6-2.1 times higher than those of galaxies in the Sloan Digital Sky Survey at the same mass. Sizes are measured using GALFIT from Hubble Space Telescope Wide Field Camera 3 H and UDS K-band images. The dynamical masses correspond well to the spectral energy distribution based stellar masses, with dynamical masses that are ~{}15% higher. We find that M /M may decrease slightly with time, which could reflect the increase of the dark matter fraction within an increasing effective radius. We combine different stellar kinematic studies from the literature and examine the structural evolution from z ~{} 2 to z ~{} 0: we confirm that at fixed dynamical mass, the effective radius increases by a factor of ~{}2.8, and the velocity dispersion decreases by a factor of ~{}1.7. The mass density within one effective radius decreases by a factor of ~{}20, while within a fixed physical radius (1 kpc) it decreases only mildly (factor of ~{}2). When we allow for an evolving mass limit by selecting a population of galaxies at fixed number density, a stronger size growth with time is found (factor of ~{}4), velocity dispersion decreases by a factor of ~{}1.4, and interestingly, the mass density within 1 kpc is consistent with no evolution. This finding suggests that massive quiescent galaxies at z ~{} 2 grow inside out, consistent with the expectations from minor mergers
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