310 research outputs found
Signatures of Interstellar-Intracluster Medium Interactions: Spiral Galaxy Rotation Curves in Abell 2029
We investigate the rich cluster Abell 2029 (z~0.08) using optical imaging and
long-slit spectral observations of 52 disk galaxies distributed throughout the
cluster field. No strong emission-line galaxies are present within ~400 kpc of
the cluster center, a region largely dominated by the similarly-shaped X-ray
and low surface brightness optical envelopes centered on the giant cD galaxy.
However, two-thirds of the galaxies observed outside the cluster core exhibit
line emission. H-alpha rotation curves of 14 cluster members are used in
conjunction with a deep I band image to study the environmental dependence of
the Tully-Fisher relation. The Tully-Fisher zero-point of Abell 2029 matches
that of clusters at lower redshifts, although we do observe a relatively larger
scatter about the Tully-Fisher relation. We do not observe any systematic
variation in the data with projected distance to the cluster center: we see no
environmental dependence of Tully-Fisher residuals, R-I color, H-alpha
equivalent width, and the shape and extent of the rotation curves.Comment: 22 pages, 6 figures, 3 tables; to appear in the August 2000
Astronomical Journa
Signatures of Galaxy-Cluster Interactions: Tully-Fisher Observations at z~0.1
We have obtained new optical imaging and spectroscopic observations of 78
galaxies in the fields of the rich clusters Abell 1413 (z = 0.14), Abell 2218
(z = 0.18) and Abell 2670 (z = 0.08). We have detected line emission from 25
cluster galaxies plus an additional six galaxies in the foreground and
background, a much lower success rate than what was found (65%) for a sample of
52 lower-richness Abell clusters in the range 0.02 < z < 0.08. We have combined
these data with our previous observations of Abell 2029 and Abell 2295 (both at
z = 0.08), which yields a sample of 156 galaxies. We evaluate several
parameters as a function of cluster environment: Tully-Fisher residuals,
H-alpha equivalent width, and rotation curve asymmetry, shape and extent.
Although H-alpha is more easily detectable in galaxies that are located further
from the cluster cores, we fail to detect a correlation between H-alpha extent
and galaxy location in those where it is detected, again in contrast with what
is found in the clusters of lesser richness. We fail to detect any
statistically significant trends for the other parameters in this study. The
zero-point in the z~0.1 Tully-Fisher relation is marginally fainter (by 1.5
sigma) than that found in nearby clusters, but the scatter is essentially
unchanged.Comment: 27 pages including 5 figures; accepted for publication in the
Astronomical Journa
Correcting direction-dependent gains in the deconvolution of radio interferometric images
Astronomical imaging using aperture synthesis telescopes requires
deconvolution of the point spread function as well as calibration of
instrumental and atmospheric effects. In general, such effects are
time-variable and vary across the field of view as well, resulting in
direction-dependent (DD), time-varying gains. Most existing imaging and
calibration algorithms assume that the corruptions are direction independent,
preventing even moderate dynamic range full-beam, full-Stokes imaging. We
present a general framework for imaging algorithms which incorporate DD errors.
We describe as well an iterative deconvolution algorithm that corrects known DD
errors due to the antenna power patterns and pointing errors for high dynamic
range full-beam polarimetric imaging. Using simulations we demonstrate that
errors due to realistic primary beams as well as antenna pointing errors will
limit the dynamic range of upcoming higher sensitivity instruments and that our
new algorithm can be used to correct for such errors. We have applied this
algorithm to VLA 1.4 GHz observations of a field that contains two ``4C''
sources and have obtained Stokes-I and -V images with systematic errors that
are one order of magnitude lower than those obtained with conventional imaging
tools. Our simulations show that on data with no other calibration errors, the
algorithm corrects pointing errors as well as errors due to known asymmetries
in the antenna pattern.Comment: submitted to A&A; some clarifications added in the text; accepted for
publication in A&
X-ray observations of the galaxy cluster Abell 2029 to the virial radius
We present Suzaku observations of the galaxy cluster Abell 2029, which
exploit Suzaku's low particle background to probe the ICM to radii beyond those
possible with previous observations (reaching out to the virial radius), and
with better azimuthal coverage. We find significant anisotropies in the
temperature and entropy profiles, with a region of lower temperature and
entropy occurring to the south east, possibly the result of accretion activity
in this direction. Away from this cold feature, the thermodynamic properties
are consistent with an entropy profile which rises, but less steeply than the
predictions of purely gravitational hierarchical structure formation. Excess
emission in the northern direction can be explained due to the overlap of the
emission from the outskirts of Abell 2029 and nearby Abell 2033 (which is at
slightly higher redshift). These observations suggest that the assumptions of
spherical symmetry and hydrostatic equilibrium break down in the outskirts of
galaxy clusters, which poses challenges for modelling cluster masses at large
radii and presents opportunities for studying the formation and accretion
history of clusters.Comment: 15 pages, 14 figures. Accepted for publication in the Monthly Notices
of the Royal Astronomical Societ
Evaluación objetiva de destrezas laparoscópicas básicas a partir de métricas obtenidas con el simulador virtual SINERGIA
Las tĂ©cnicas laparoscĂłpicas se han convertido en patrĂłn oro en muchos procedimientos quirĂşrgicos, pero implican un proceso de adquisiciĂłn de destrezas más complejo que en el caso de la cirugĂa abierta. En esta fase formativa, los simuladores virtuales tienen un papel muy importante puesto que permiten evaluar de forma objetiva la ejecuciĂłn de una tarea quirĂşrgica mediante la extracciĂłn automática de mĂ©tricas. Este trabajo de investigaciĂłn presenta un análisis de las mĂ©tricas calculadas por el simulador virtual SINERGIA con el fin de poder llevar a cabo una evaluaciĂłn objetiva de las destrezas laparoscĂłpicas básicas
Diffuse light and galaxy interactions in the core of nearby clusters
The kinematics of the diffuse light in the densest regions of the nearby
clusters can be unmasked using the planetary nebulae (PNs) as probes of the
stellar motions. The position-velocity diagrams around the brightest cluster
galaxies (BCGs) identify the relative contributions from the outer halos and
the intracluster light (ICL), defined as the light radiated by the stars
floating in the cluster potential. The kinematics of the ICL can then be used
to asses the dynamical status of the nearby cluster cores and to infer their
formation histories. The cores of the Virgo and Coma are observed to be far
from equilibrium, with mergers currently on-going, while the ICL properties in
the Fornax and Hydra clusters show the presence of sub-components being
accreted in their cores, but superposed to an otherwise relaxed population of
stars. Finally the comparison of the observed ICL properties with those
predicted from Lambda-CDM simulations indicates a qualitative agreement and
provides insights on the ICL formation. Both observations and simulations
indicate that BCG halos and ICL are physically distinct components, with the
``hotter" ICL dominating at large radial distances from the BCGs halos as the
latter become progressively fainter.Comment: 14 pages, 5 figures. Invited review to appear in the proceedings of
"Galaxies and their masks" eds. Block, D.L., Freeman, K.C. and Puerari, I.,
2010, Springer (New York
Large scale diffuse light in the Coma cluster: a multi-scale approach
We have obtained wide field images of the Coma cluster in the B, V, R and I
bands with the CFH12K camera at CFHT. In order to search for large scale
diffuse emission, we have applied to these images an iterative multi scale
wavelet analysis and reconstruction technique which allowed to model all the
sources (stars and galaxies) and subtract them from the original images. We
found various concentrations of diffuse emission present in the central zone
around the central galaxies NGC4874 and NGC4889. We characterize the positions,
sizes and colors of these concentrations. Some sources do not seem to have
strong star formation, while another one probably exhibits spiral-like color.
One possible origin for the star forming diffuse emission sources is that in
the region of the two main galaxies NGC4874 and NGC4889 spiral galaxies have
recently been disrupted and star formation is still active in the dispersed
material. We also use the characteristics of the sources of diffuse emission to
trace the cluster dynamics. A scenario in which the group around NGC 4874 is
moving north is consistent with our data.Comment: 11 pages, accepted in A&A, jpg figure
A survey for redshifted molecular and atomic absorption lines I
We are currently undertaking a large survey for redshifted atomic and
molecular absorption ... only one clear and one tentative detection were
obtained: HI absorption at z = 0.097 in PKS 1555-140 and OH absorption at z
=0.126 in PKS 2300-189, respectively... In order to determine why no clear
molecular absorption was detected in any of the 13 sources searched, we
investigate the properties of the five redshifted systems currently known to
exhibit OH absorption. In four of these, molecules were first detected via
millimetre-wave transitions and the flat radio spectra indicate compact
background continuum sources, which may suggest a high degree of coverage of
the background source by the molecular clouds in the absorber. Furthermore, for
these systems we find a relationship between the molecular line strength and
red optical--near infrared (V-K) colours, thus supporting the notion that the
reddening of these sources is due to dust, which provides an environment
conducive to the formation of molecules. Upon comparison with the V-K colours
of our sample, this relationship suggests that, presuming the reddening occurs
at the host galaxy redshift at least in some of the targets, many of our
observations still fall short of the sensitivityrequired to detect OH
absorption, although a confirmation of the ``detection'' of OH in 2300-189
could contravene this.Comment: 13 pages, loads of figures, accepted by MNRA
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