4,591 research outputs found
The Ontology Lookup Service: more data and better tools for controlled vocabulary queries
The Ontology Lookup Service (OLS) (http://www.ebi.ac.uk/ols) provides interactive and programmatic interfaces to query, browse and navigate an ever increasing number of biomedical ontologies and controlled vocabularies. The volume of data available for querying has more than quadrupled since it went into production and OLS functionality has been integrated into several high-usage databases and data entry tools. Improvements have been made to both OLS query interfaces, based on user feedback and requirements, to improve usability and service interoperability and provide novel ways to perform queries
The Next Generation Virgo Cluster Survey (NGVS). XVIII. Measurement and Calibration of Surface Brightness Fluctuation Distances for Bright Galaxies in Virgo (and Beyond)
We describe a program to measure surface brightness fluctuation (SBF)
distances to galaxies observed in the Next Generation Virgo Cluster Survey
(NGVS), a photometric imaging survey covering of the Virgo cluster
in the bandpasses with the Canada-France Hawaii Telescope. We
describe the selection of the sample galaxies, the procedures for measuring the
apparent -band SBF magnitude , and the calibration of the absolute
as a function of observed stellar population properties. The
multi-band NGVS data set provides multiple options for calibrating the SBF
distances, and we explore various calibrations involving individual color
indices as well as combinations of two different colors. Within the color range
of the present sample, the two-color calibrations do not significantly improve
the scatter with respect to wide-baseline, single-color calibrations involving
. We adopt the calibration as reference for the present
galaxy sample, with an observed scatter of 0.11 mag. For a few cases that lack
good photometry, we use an alternative relation based on a combination
of and colors, with only a slightly larger observed scatter of
0.12 mag. The agreement of our measurements with the best existing distance
estimates provides confidence that our measurements are accurate. We present a
preliminary catalog of distances for 89 galaxies brighter than
mag within the survey footprint, including members of the background M and W
Clouds at roughly twice the distance of the main body of the Virgo cluster. The
extension of the present work to fainter and bluer galaxies is in progress.Comment: ApJ accepte
Correlations of Globular Cluster Properties: Their Interpretations and Uses
Correlations among the independently measured physical properties of globular
clusters (GCs) can provide powerful tests for theoretical models and new
insights into their dynamics, formation, and evolution. We review briefly some
of the previous work, and present preliminary results from a comparative study
of GC correlations in the Local Group galaxies. The results so far indicate
that these diverse GC systems follow the same fundamental correlations,
suggesting a commonality of formative and evolutionary processes which produce
them.Comment: An invited review, to appear in "New Horizons in Globular Cluster
Astronomy", eds. G. Piotto, G. Meylan, S.G. Djorgovski, and M. Riello, ASPCS,
in press (2003). Latex file, 8 pages, 5 eps figures, style files include
The Next Generation Virgo Cluster Survey. VII. The intrinsic shapes of low-luminosity galaxies in the core of the Virgo cluster, and a comparison with the Local Group
(Abridged) We investigate the intrinsic shapes of low-luminosity galaxies in
the central 300 kpc of the Virgo cluster using deep imaging obtained as part of
the NGVS. We build a sample of nearly 300 red-sequence cluster members in the
yet unexplored magnitude range. The observed distribution of
apparent axis ratios is then fit by families of triaxial models with
normally-distributed intrinsic ellipticities and triaxialities. We develop a
Bayesian framework to explore the posterior distribution of the model
parameters, which allows us to work directly on discrete data, and to account
for individual, surface brightness-dependent axis ratio uncertainties. For this
population we infer a mean intrinsic ellipticity E=0.43, and a mean triaxiality
T=0.16. This implies that faint Virgo galaxies are best described as a family
of thick, nearly oblate spheroids with mean intrinsic axis ratios 1:0.94:0.57.
We additionally attempt a study of the intrinsic shapes of Local Group
satellites of similar luminosities. For the LG population we infer a slightly
larger mean intrinsic ellipticity E=0.51, and the paucity of objects with round
apparent shapes translates into more triaxial mean shapes, 1:0.76:0.49. We
finally compare the intrinsic shapes of NGVS low-mass galaxies with samples of
more massive quiescent systems, and with field, star-forming galaxies of
similar luminosities. We find that the intrinsic flattening in this
low-luminosity regime is almost independent of the environment in which the
galaxy resides--but there is a hint that objects may be slightly rounder in
denser environments. The comparable flattening distributions of low-luminosity
galaxies that have experienced very different degrees of environmental effects
suggests that internal processes are the main drivers of galaxy structure at
low masses--with external mechanisms playing a secondary role.Comment: Accepted to ApJ. 18 pages, 12 figure
The ACS Virgo Cluster Survey II. Data Reduction Procedures
The ACS Virgo Cluster Survey is a large program to carry out multi-color
imaging of 100 early-type members of the Virgo Cluster using the Advanced
Camera for Surveys (ACS) on the Hubble Space Telescope. Deep F475W and F850LP
images (~ SDSS g and z) are being used to study the central regions of the
program galaxies, their globular cluster systems, and the three-dimensional
structure of Virgo itself. In this paper, we describe in detail the data
reduction procedures used for the survey, including image registration,
drizzling strategies, the computation of weight images, object detection, the
identification of globular cluster candidates, and the measurement of their
photometric and structural parameters.Comment: 33 pages, 8 figures. Accepted for publication in ApJS. Also available
at http://www.physics.rutgers.edu/~pcote/acs/publications.htm
The Environment of M85 optical transient 2006-1: constraints on the progenitor age and mass
M85 optical transient 2006-1 (M85 OT 2006-1) is the most luminous member of
the small family of V838 Mon-like objects, whose nature is still a mystery.
This event took place in the Virgo cluster of galaxies and peaked at an
absolute magnitude of I~-13. Here we present Hubble Space Telescope images of
M85 OT 2006-1 and its environment, taken before and after the eruption, along
with a spectrum of the host galaxy at the transient location. We find that the
progenitor of M85 OT 2006-1 was not associated with any star forming region.
The g and z-band absolute magnitudes of the progenitor were fainter than about
-4 and -6 mag, respectively. Therefore, we can set a lower limit of ~50 Myr on
the age of the youngest stars at the location of the progenitor that
corresponds to a mass of <7 solar mass. Previously published line indices
suggest that M85 has a mean stellar age of 1.6+/-0.3 Gyr. If this mean age is
representative of the progenitor of M85 OT 2006-1, then we can further
constrain its mass to be less than 2 solar mass. We compare the energetics and
mass limit derived for the M85 OT 2006-1 progenitor with those expected from a
simple model of violent stellar mergers. Combined with further modeling, these
new clues may ultimately reveal the true nature of these puzzling events.Comment: 4 pages, accepted to Ap
Trends in the Globular Cluster Luminosity Function of Early-Type Galaxies
We present results from a study of the globular cluster luminosity function
(GCLF) in a sample of 89 early-type galaxies observed as part of the ACS Virgo
Cluster Survey. Using a Gaussian parametrization of the GCLF, we find a highly
significant correlation between the GCLF dispersion, sigma, and the galaxy
luminosity, M_B, in the sense that the GC systems in fainter galaxies have
narrower luminosity functions. The GCLF dispersions in the Milky Way and M31
are fully consistent with this trend, implying that the correlation between
sigma and galaxy luminosity is more fundamental than older suggestions that
GCLF shape is a function of galaxy Hubble type. We show that the sigma - M_B
relation results from a bonafide narrowing of the distribution of (logarithmic)
cluster masses in fainter galaxies. We further show that this behavior is
mirrored by a steepening of the GC mass function for relatively high masses, M
>~ 3 x 10^5 M_sun, a mass regime in which the shape of the GCLF is not strongly
affected by dynamical evolution over a Hubble time. We argue that this trend
arises from variations in initial conditions and requires explanation by
theories of cluster formation. Finally, we confirm that in bright galaxies, the
GCLF "turns over" at the canonical mass scale of M_TO ~ 2 x 10^5 M_sun.
However, we find that M_TO scatters to lower values (~1-2 x 10^5 M_sun) in
galaxies fainter than M_B >~ -18.5, an important consideration if the GCLF is
to be used as a distance indicator for dwarf ellipticals.Comment: 4 pages, 3 figures. Accepted for publication in ApJ Letters. Also
available at http://www.cadc.hia.nrc.gc.ca/community/ACSVCS/publications.htm
The ACS Virgo Cluster Survey XV. The Formation Efficiencies of Globular Clusters in Early-Type Galaxies: The Effects of Mass and Environment
The fraction of stellar mass contained in globular clusters (GCs), also
measured by number as the specific frequency, is a fundamental quantity that
reflects both a galaxy's early star formation and its entire merging history.
We present specific frequencies, luminosities, and mass fractions for the
globular cluster systems of 100 early-type galaxies in the ACS Virgo Cluster
Survey, the largest homogeneous catalog of its kind. We find that 1) GC mass
fractions can be high in both giants and dwarfs, but are universally low in
galaxies with intermediate luminosities. 2) The behavior of specific frequency
across galaxy mass is dominated by the blue GCs. 3) The GC fractions of
low-mass galaxies exhibit a dependence on environment. Nearly all dwarf
galaxies with high GC fractions are within 1 Mpc of the cD galaxy M87,
presenting the first strong evidence that GC formation in dwarfs is biased
toward dense environments. 4) GC formation in central dwarfs is biased because
their stars form earliest and most intensely. Comparisons to the Millennium
Simulation show that central dwarfs have older stellar populations and form
more stars at higher star formation rates (SFRs) and SFR surface densities. The
SFR surface density in simulated dwarfs peaks before the total SFR, naturally
producing GC populations that are older and more metal-poor than the field
stars. 5) Dwarfs within ~40 kpc of the giant ellipticals M87 and M49 are red
and have few or no GCs, suggesting that they have been tidally stripped and
have contributed their GCs to the halos of their giant neighbors. The central
dwarfs with high GC mass fractions are thus likely to be the survivors most
similar to the protogalaxies that assembled the rich M87 globular cluster
system.(Abridged)Comment: 27 pages, 21 figures, 7 tables. Accepted for publication in the
Astrophysical Journa
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