760 research outputs found
Chandra View of the Dynamically Young Cluster of Galaxies A1367 I. Small-Scale Structures
The 40 ks \emph{Chandra} ACIS-S observation of A1367 provides new insights
into small-scale structures and point sources in this dynamically young
cluster. Here we concentrate on small-scale extended structures. A ridge-like
structure around the center (``the ridge'') is significant in the \chandra\
image. The ridge, with a projected length of 8 arcmin (or 300
h kpc), is elongated from northwest (NW) to southeast (SE), as is
the X-ray surface brightness distribution on much larger scales ( 2
h Mpc). The ridge is cooler than its western and southern
surroundings while the differences from its eastern and northern surroundings
are small. We also searched for small-scale structures with sizes
arcmin. Nine extended features, with sizes from 0.5 to 1.5, were
detected at significance levels above 4 . Five of the nine features are
located in the ridge and form local crests. The nine extended features can be
divided into two types. Those associated with galaxies (NGC 3860B, NGC 3860 and
UGC 6697) are significantly cooler than their surroundings (0.3 - 0.9 keV vs. 3
- 4.5 keV). The masses of their host galaxies are sufficient to bind the
extended gas. These extended features are probably related to thermal halos or
galactic superwinds of their host galaxies. The existence of these relatively
cold halos imply that galaxy coronae can survive in cluster environment (e.g.,
Vikhlinin et al. 2001). Features of the second type are not apparently
associated with galaxies. Their temperatures may not be significantly different
from those of their surroundings. This class of extended features may be
related to the ridge. We consider several possibilities for the ridge and the
second type of extended features. The merging scenario is preferred.Comment: To appear in ApJ, Vol 576, 2002, Sep., a high-resolution version is
in http://cfa160.harvard.edu/~sunm/a1367_a.ps.g
UV properties of early-type galaxies in the Virgo cluster
We study the UV properties of a volume limited sample of early-type galaxies
in the Virgo cluster combining new GALEX far- (1530 A) and near-ultraviolet
(2310 A) data with spectro-photometric data available at other wavelengths. The
sample includes 264 ellipticals, lenticulars and dwarfs spanning a large range
in luminosity (M(B)<-15). While the NUV to optical or near-IR color magnitude
relations (CMR) are similar to those observed at optical wavelengths, with a
monotonic reddening of the color index with increasing luminosity, the (FUV-V)
and (FUV-H) CMRs show a discontinuity between massive and dwarf objects. An
even more pronounced dichotomy is observed in the (FUV-NUV) CMR. For
ellipticals the (FUV-NUV) color becomes bluer with increasing luminosity and
with increasing reddening of the optical or near-IR color indices. For the
dwarfs the opposite trend is observed. These observational evidences are
consistent with the idea that the UV emission is dominated by hot, evolved
stars in giant systems, while in dwarf ellipticals residual star formation
activity is more common.Comment: 5 pages, 2 figures, 1 table. Accepted for publication in
Astrophysical Journal Letter
The Arecibo Galaxy Environment Survey V : The Virgo Cluster (I)
We present 21 cm observations of a 10 2 degree region in the Virgo
cluster, obtained as part of the Arecibo Galaxy Environment Survey. 289 sources
are detected over the full redshift range (-2,000 + 20,000
km/s) with 95 belonging to the cluster ( 3,000 km/s). We combine
our observations with data from the optically selected Virgo Cluster Catalogue
(VCC) and the Sloan Digital Sky Survey (SDSS). Most of our detections can be
clearly associated with a unique optical counterpart, and 30% of the cluster
detections are new objects fainter than the VCC optical completeness limit. 7
detections may have no optical counterpart and we discuss the possible origins
of these objects. 7 detections appear associated with early-type galaxies. We
perform HI stacking on the HI-undetected galaxies listed in the VCC in this
region and show that they must have significantly less gas than those actually
detected in HI. Galaxies undetected in HI in the cluster appear to be really
devoid of gas, in contrast to a sample of field galaxies from ALFALFA.Comment: 23 pages, 22 figures, 4 table
Ending Neglect of older people in the response to Humanitarian Emergencies
Older people make up a significant and growing number of those affected by humanitarian crises, yet they are often not sought out or prioritised within the humanitarian response. Humanitarian agencies, donors, and international bodies neglect older people's health and nutrition. The gaps in knowledge and research about the needs of older people in emergencies are considerable. Older people are not monitored in emergencies and they are not prioritised despite evidence of disproportionate mortality and morbidity in this group. We call for policy changes by humanitarian agencies and donors to ensure that the needs of this vulnerable group are met
1.65 micrometers (H-band) surface photometry of galaxies. III: observations of 558 galaxies with the TIRGO 1.5m telescope
We present near-infrared H-band (1.65 micron) surface photometry of 558
galaxies in the Coma Supercluster and in the Virgo cluster. This data set,
obtained with the Arcetri NICMOS3 camera ARNICA mounted on the Gornergrat
Infrared Telescope, is aimed at complementing, with observations of mostly
early-type objects, our NIR survey of spiral galaxies in these regions,
presented in previous papers of this series. Magnitudes at the optical radius,
total magnitudes, isophotal radii and light concentration indices are derived.
We confirm the existence of a positive correlation between the near-infrared
concentration index and the galaxy H-band luminosity. (Tables 1 and 2 are only
available in electronic form upon request to [email protected])Comment: 12 pages, 6 figures. Accepted for publication in A&A
1.65 micron H-band Surface Photometry of Galaxies. X: Structural and Dynamical Properties of Elliptical Galaxies
We analyse the structural and dynamical properties of a sample of 324 nearby
elliptical and dwarf elliptical galaxies observed during an extensive NIR
survey in H-band (1.65 micron). The Fundamental Plane (FP) is determined and a
significant tilt is assessed. The origins of such a tilt are investigated by
means of a spherically symmetric, isotropic pressure supported dynamical model
relying on the observed surface brightness profiles. The systematic variation
of the shape coefficient converting the measured central velocity dispersion into the virial rms velocity is found to be the main
cause of the tilt, due to aperture effects. Moreover the ratio between the
dynamical mass and the total H-band luminosity turns out to be
roughly constant along the luminosity sequence of ellipticals: H-band
luminosity is therefore a reliable and cheap estimator of the dynamical mass of
the Es.Comment: 28 pages, 6 figures, accepted for publication on Ap
Star-forming galaxies in low-redshift clusters: Data and integrated galaxy properties
This paper is a continuation of an ongoing study of the evolutionary
processes affecting cluster galaxies. Both CCD R band and H alpha narrow-band
imaging was used to determine photometric parameters (m_(r), r_(24), H alpha
flux and equivalent width) and derive star formation rates for 227 CGCG
galaxies in 8 low-redshift clusters. The galaxy sample is a subset of CGCG
galaxies in an objective prism survey of cluster galaxies for H alpha emission.
It is found that detection of emission-line galaxies in the OPS is 85%, 70%,
and 50% complete at the mean surface brightness values of 1.25 x 10^(-19), 5.19
x 10^(-20), and 1.76 x 10^(-20) W m^(-2) arcsec^(-2), respectively, measured
within the R band isophote of 24 mag arcsec^(-2) for the galaxy. The CCD data,
together with matched data from a recent H alpha galaxy survey of UGC galaxies
within 3000 km s^(-1), will be used for a comparative study of R band and H
alpha surface photometry between cluster and field spirals.Comment: Accepted for publication in A&A. 11 pages, including 6 figure
Halpha3: Halpha imaging survey of HI selected galaxies from ALFALFA
We present Halpha3 (acronym for Halpha-alpha-alpha), an Halpha narrow-band
imaging survey of ~400 galaxies selected from the HI Arecibo Legacy Fast ALFA
Survey (ALFALFA) in the Local Supercluster, including the Virgo cluster. By
using hydrogen recombination lines as a tracer of recent star formation, we aim
to investigate the relationships between atomic neutral gas and newly formed
stars in different environments (cluster and field), morphological types
(spirals and dwarfs), and over a wide range of stellar masses (~10^7.5-10^11.5
Msun). We image in Halpha+[NII] all the galaxies that contain more than 10^7
Msun of neutral atomic hydrogen in the sky region 11^h < R.A. <16^h 4^o < Dec.
<16^o; 350< cz <2000 km/s using the San Pedro Martir 2m telescope. This survey
provides a complete census of the star formation in HI rich galaxies of the
local universe. We present the properties of the galaxy sample, together with
Halpha fluxes and equivalent widths. We find an excellent agreement between the
fluxes determined from our images in apertures of 3 arcsec diameter and the
fluxes derived from the SDSS spectral database. From the Halpha fluxes
corrected for galactic and internal extinction and for [NII] contamination we
derive the global star formation rates (SFRs).Comment: 22 pages, 8 figures. A&A accepted. Atlas available upon reques
Comment on Path Integral Derivation of Schr\"odinger Equation in Spaces with Curvature and Torsion
We present a derivation of the Schr\"odinger equation for a path integral of
a point particle in a space with curvature and torsion which is considerably
shorter and more elegant than what is commonly found in the literature.Comment: LaTeX file in sr
Star-forming galaxies in low-redshift clusters: Comparison of integrated properties of cluster and field galaxies
We investigate the effect of the cluster environment on the star formation
properties of galaxies in 8 nearby Abell clusters. Star formation properties
are determined for individual galaxies using the equivalent width of H alpha
plus [NII] line emission from narrow-band imaging. Equivalent width
distributions are derived for each galaxy type in each of 3 environments -
cluster, supercluster (outside the cluster virial radius) and field. The
effects of morphological disturbance on star formation are also investigated.
We identify a population of early-type disk galaxies in the cluster population
with enhanced star formation compared to their field counterparts. The enhanced
cluster galaxies frequently show evidence of disturbance, and the disturbed
galaxies show marginal evidence for a higher velocity dispersion, possibly
indicative of an infalling population.Comment: 9 pages, 10 figures, accepted for publication in Astronomy and
Astrophysic
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