255 research outputs found
Hubble Space Telescope Planetary Camera Images of NGC 1316
We present HST Planetary Camera V and I~band images of the central region of
the peculiar giant elliptical galaxy NGC 1316. The inner profile is well fit by
a nonisothermal core model with a core radius of 0.41" +/- 0.02" (34 pc). At an
assumed distance of 16.9 Mpc, the deprojected luminosity density reaches \sim
2.0 \times 10^3 L_{\sun} pc.
Outside the inner two or three arcseconds, a constant mass-to-light ratio of
is found to fit the observed line width measurements. The
line width measurements of the center indicate the existence of either a
central dark object of mass 2 \times 10^9 M_{\sun}, an increase in the
stellar mass-to-light ratio by at least a factor of two for the inner few
arcseconds, or perhaps increasing radial orbit anisotropy towards the center.
The mass-to-light ratio run in the center of NGC 1316 resembles that of many
other giant ellipticals, some of which are known from other evidence to harbor
central massive dark objects (MDO's).
We also examine twenty globular clusters associated with NGC 1316 and report
their brightnesses, colors, and limits on tidal radii. The brightest cluster
has a luminosity of 9.9 \times 10^6 L_{\sun} (), and the
faintest detectable cluster has a luminosity of 2.4 \times 10^5 L_{\sun}
(). The globular clusters are just barely resolved, but their core
radii are too small to be measured. The tidal radii in this region appear to be
35 pc. Although this galaxy seems to have undergone a substantial merger
in the recent past, young globular clusters are not detected.Comment: 21 pages, latex, postscript figures available at
ftp://delphi.umd.edu/pub/outgoing/eshaya/fornax
VII Zw 403: H I structure in a blue compact dwarf galaxy
‘In these times, during the rise in the popularity of institutional repositories, the Society does not forbid authors from depositing their work in such repositories. However, the AAS regards the deposit of scholarly work in such repositories to be a decision of the individual scholar, as long as the individual's actions respect the diligence of the journals and their reviewers.’ Original article can be found at : http://iopscience.iop.org/ Copyright American Astronomical SocietyWe present optical (UBVJ), ultraviolet (FUV, NUV), and high-resolution atomic hydrogen (H I) observations of the nearby blue compact dwarf (BCD), VII Zw 403. We find that VII Zw 403 has a relatively high H I mass-to-light ratio for a BCD. The rotation velocity is nominally 10-15 km s(-1), but rises to similar to 20 km s(-1) after correction for the similar to 8-10 km s(-1) random motions present in the gas. The velocity field is complex, including a variation in the position angle of the major axis going from the northeast to the southwest parts of the galaxy. Our high-resolution Hi maps reveal structure in the central gas, including a large, low-density Hi depression or hole between the southern and northern halves of the galaxy, coincident with an unresolved X-ray source. Although interactions have been proposed as the triggering mechanism for the vigorous star formation occurring in BCDs, VII Zw 403 does not seem to have been tidally triggered by an external interaction, as we have found no nearby possible perturbers. It also does not appear to fall in the set of galaxies that exhibit a strong central mass density concentration, as its optical scale length is large in comparison to similar systems. However, there are some features that are compatible with an accretion event: optical/Hi axis misalignment, a change in position angle of the kinematic axis, and a complex velocity field.Peer reviewe
MS 2053.7-0449: Confirmation of a bimodal mass distribution from strong gravitational lensing
We present the first strong lensing study of the mass distribution in the
cluster MS 2053-04 based on HST archive data. This massive, X-ray luminous
cluster has a redshift z=0.583, and it is composed of two structures that are
gravitationally bound to each other. The cluster has one multiply imaged system
constituted by a double gravitational arc.
We have performed a parametric strong lensing mass reconstruction using NFW
density profiles to model the cluster potential. We also included perturbations
from 23 galaxies, modeled like elliptical singular isothermal sphere, that are
approximately within 1'x1' around the cluster center. These galaxies were
constrained in both the geometric and dynamical parameters with observational
data. Our analysis predicts a third image which is slightly demagnified. We
found a candidate for this counter-image near the expected position and with
the same F702W-F814W colors as the gravitational arcs in the cluster. The
results from the strong lensing model shows the complex structure in this
cluster, the asymmetry and the elongation in the mass distribution, and are
consistent with previous spectrophotometric results that indicate that the
cluster has a bimodal mass distribution. Finally, the derived mass profile was
used to estimate the mass within the arcs and for comparison with X-ray
estimates.Comment: To be published in ApJ (accepted
Disks around Hot Stars in the Trifid Nebula
We report on mid-IR observations of the central region in the Trifid nebula,
carried out with ISOCAM in several broad-band infrared filters and in the low
resolution spectroscopic mode provided by the circular variable filter.
Analysis of the emission indicates the presence of a hot dust component (500 to
1000 K) and a warm dust component at lower temperatures (150-200 K) around
several members of the cluster exciting the HII region, and other stars
undetected at optical wavelengths. Complementary VLA observations suggest that
the mid-IR emission could arise from a dust cocoon or a circumstellar disk,
evaporated under the ionization of the central source and the exciting star of
the nebula. In several sources the silicate band is seen in
emission. One young stellar source shows indications of crystalline silicates
in the circumstellar dust.Comment: 4 pages with 1 figur
The Ray Bundle method for calculating weak magnification by gravitational lenses
We present here an alternative method for calculating magnifications in
gravitational lensing calculations -- the Ray Bundle method. We provide a
detailed comparison between the distribution of magnifications obtained
compared with analytic results and conventional ray-shooting methods. The Ray
Bundle method provides high accuracy in the weak lensing limit, and is
computationally much faster than (non-hierarchical) ray shooting methods to a
comparable accuracy.
The Ray Bundle method is a powerful and efficient technique with which to
study gravitational lensing within realistic cosmological models, particularly
in the weak lensing limit.Comment: 9 pages Latex, 8 figures, submitted to MNRA
Arc Statistics in Clusters: Galaxy Contribution
The frequency with which background galaxies appear as long arcs as a result
of gravitational lensing by foreground clusters of galaxies has recently been
found to be a very sensitive probe of cosmological models by Bartelmann et al.
(1998). They have found that such arcs would be expected far less frequently
than observed (by an order of magnitude) in the currently favored model for the
universe, with a large cosmological constant . Here we
analyze whether including the effect of cluster galaxies on the likelihood of
clusters to generate long-arc images of background galaxies can change the
statistics. Taking into account a variety of constraints on the properties of
cluster galaxies, we find that there are not enough sufficiently massive
galaxies in a cluster for them to significantly enhance the cross section of
clusters to generate long arcs. We find that cluster galaxies typically enhance
the cross section by only .Comment: 19 pages, 1 figure, uses aasms4.sty, submitted to Ap
Searching (the) FIRST radio arcs near ACO clusters
Gravitational lensing (GL) of distant radio sources by galaxy clusters should
produce radio arc(let)s. We extracted radio sources from the FIRST survey near
Abell cluster cores and found their radio position angles to be uniformly
distributed with respect to the cluster centres. This result holds even when we
restrict the sample to the richest or most centrally condensed clusters, and to
sources with high S/N and large axial ratio. Our failure to detect GL with
statistical methods may be due to poor cluster centre positions. We did not
find convincing candidates for arcs either. Our result agrees with theoretical
estimates predicting that surveys much deeper than FIRST are required to detect
the effect. This is in apparent conflict with the detection of such an effect
claimed by Bagchi & Kapahi (1995).Comment: 6 pages; 8 figures and 1 style file are included; to appear in Proc.
"Observational Cosmology with the New Radio Surveys", eds. M. Bremer, N.
Jackson & I. Perez-Fournon, Kluwer Acad. Pres
An S-shaped arc in the galaxy cluster RXJ0054.0-2823
The center of the galaxy cluster RX J0054.0-2823 at z = 0.292 is a
dynamically active region which includes an interacting system of three
galaxies surrounded by a large halo of intra-cluster light. We report here the
discovery of an S-shaped feature of total length 11 arcsec in the central
region of this cluster and discuss its physical nature. We test the
gravitational lensing assumption by doing a mass modelling of the central part
of the galaxy cluster. We very naturally reproduce position and form of this
S-shape feature as a gravitationally lensed background object at redshift
between 0.5 and 1.0. We conclude that the lensing nature is the very probable
explanation for this S-shaped arc; the ultimate proof will be the spectroscopic
confirmation by measuring the high redshift of this elongated feature with
surface brightness V~24mag/arcsec2.Comment: 6 pages, accepted for publication in A&
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