36,387 research outputs found
WSRT observations and surface photometry of two unusual spiral galaxies
We discuss the results of a mass decomposition of two spiral galaxies, NGC
6824 and UGC 11919. In a previous analysis of the Hyperleda catalog, the
galaxies were identified as having a peculiar dynamical . The aim of this
study is to confirm or disprove the preliminary findings, indicating a
non-standard stellar initial mass function (IMF) for the galaxies. The surface
photometry in B, V, and R bands was carried out with the Apache Point 0.5-m
telescope and the \ion{H}{I} data cubes were obtained with the Westerbork
Synthesis Radio Telescope (WSRT). Photometric profiles were decomposed into
bulge and exponential disk components. Using the obtained \ion{H}{I} data
cubes, rotation curves of both galaxies were constructed. Employing the
photometric profiles, the mass distribution of the galaxies was decomposed into
mass components: bulge, stellar disk, gas, and pseudo-isothermal dark halo. We
conclude that NGC 6824 possesses a stellar disk with mass-to-light ratio
, in agreement with its color . On the
contrary, UGC 11919 appears to have a very lightweight disk. Its dynamically
estimated mass corresponds to a low stellar disk mass-to-light ratio
. Under standard assumptions, this ratio does
not agree with the relatively red color of the disk, while a bottom light
stellar initial mass function is needed to explain the observations.Comment: 14 pages, 14 figures, accepted for publication in Astronomy and
Astrophysic
Pathway to the Square Kilometre Array - The German White Paper -
The Square Kilometre Array (SKA) is the most ambitious radio telescope ever
planned. With a collecting area of about a square kilometre, the SKA will be
far superior in sensitivity and observing speed to all current radio
facilities. The scientific capability promised by the SKA and its technological
challenges provide an ideal base for interdisciplinary research, technology
transfer, and collaboration between universities, research centres and
industry. The SKA in the radio regime and the European Extreme Large Telescope
(E-ELT) in the optical band are on the roadmap of the European Strategy Forum
for Research Infrastructures (ESFRI) and have been recognised as the essential
facilities for European research in astronomy.
This "White Paper" outlines the German science and R&D interests in the SKA
project and will provide the basis for future funding applications to secure
German involvement in the Square Kilometre Array.Comment: Editors: H. R. Kl\"ockner, M. Kramer, H. Falcke, D.J. Schwarz, A.
Eckart, G. Kauffmann, A. Zensus; 150 pages (low resolution- and colour-scale
images), published in July 2012, language English (including a foreword and
an executive summary in German), the original file is available via the MPIfR
homepag
The XMM-LSS survey. Survey design and first results
We have designed a medium deep large area X-ray survey with XMM - the XMM
Large Scale Structure survey, XMM-LSS - with the scope of extending the
cosmological tests attempted using ROSAT cluster samples to two redshift bins
between 0<z<1 while maintaining the precision of earlier studies. Two main
goals have constrained the survey design: the evolutionary study of the
cluster-cluster correlation function and of the cluster number density. The
results are promising and, so far, in accordance with our predictions as to the
survey sensitivity and cluster number density. The feasibility of the programme
is demonstrated and further X-ray coverage is awaited in order to proceed with
a truly significant statistical analysis. (Abridged)Comment: Published in Journal of Cosmology and Astroparticle Physic
Dissecting the Gravitational Lens B1608+656. II. Precision Measurements of the Hubble Constant, Spatial Curvature, and the Dark Energy Equation of State
Strong gravitational lens systems with measured time delays between the
multiple images provide a method for measuring the "time-delay distance" to the
lens, and thus the Hubble constant. We present a Bayesian analysis of the
strong gravitational lens system B1608+656, incorporating (i) new, deep Hubble
Space Telescope (HST) observations, (ii) a new velocity dispersion measurement
of 260+/-15 km/s for the primary lens galaxy, and (iii) an updated study of the
lens' environment. When modeling the stellar dynamics of the primary lens
galaxy, the lensing effect, and the environment of the lens, we explicitly
include the total mass distribution profile logarithmic slope gamma' and the
external convergence kappa_ext; we marginalize over these parameters, assigning
well-motivated priors for them, and so turn the major systematic errors into
statistical ones. The HST images provide one such prior, constraining the lens
mass density profile logarithmic slope to be gamma'=2.08+/-0.03; a combination
of numerical simulations and photometric observations of the B1608+656 field
provides an estimate of the prior for kappa_ext: 0.10 +0.08/-0.05. This latter
distribution dominates the final uncertainty on H_0. Compared with previous
work on this system, the new data provide an increase in precision of more than
a factor of two. In combination with the WMAP 5-year data set, we find that the
B1608+656 data set constrains the curvature parameter to be -0.031 < Omega_k <
0.009 (95% CL), a level of precision comparable to that afforded by the current
Type Ia SNe sample. Asserting a flat spatial geometry, we find that, in
combination with WMAP, H_0 = 69.7 +4.9/-5.0 km/s/Mpc and w=-0.94 +0.17/-0.19
(68% CL), suggesting that the observations of B1608+656 constrain w as tightly
as do the current Baryon Acoustic Oscillation data. (abridged)Comment: 24 pages, 8 figures, revisions based on referee's comments, accepted
for publication in Ap
A GBT Survey of the HALOGAS Galaxies and Their Environments I: Revealing the full extent of HI around NGC891, NGC925, NGC4414 & NGC4565
We present initial results from a deep neutral hydrogen (HI) survey of the
HALOGAS galaxy sample, which includes the spiral galaxies NGC891, NGC925,
NGC4414, and NGC4565, performed with the Robert C. Byrd Green Bank Telescope
(GBT). The resulting observations cover at least four deg around these
galaxies with an average 5 detection limit of 1.210
cm over a velocity range of 20 km s and angular scale of 9.1.
In addition to detecting the same total flux as the GBT data, the spatial
distribution of the GBT and original Westerbork Synthesis Radio Telescope
(WSRT) data match well at equal spatial resolutions. The HI mass fraction below
HI column densities of 10 cm is, on average, 2\%. We discuss the
possible origins of low column density HI of nearby spiral galaxies. The
absence of a considerable amount of newly detected HI by the GBT indicates
these galaxies do not have significant extended diffuse HI structures, and
suggests future surveys planned with the SKA and its precursors must go
\textit{at least} as deep as 10 cm in column density to
significantly increase the probability of detecting HI associated with the
cosmic web and/or cold mode accretion.Comment: Accepted for publication in The Astrophysical Journal; 28 pages, 15
figure
Non-parametric modeling of the intra-cluster gas using APEX-SZ bolometer imaging data
We demonstrate the usability of mm-wavelength imaging data obtained from the
APEX-SZ bolometer array to derive the radial temperature profile of the hot
intra-cluster gas out to radius r_500 and beyond. The goal is to study the
physical properties of the intra-cluster gas by using a non-parametric
de-projection method that is, aside from the assumption of spherical symmetry,
free from modeling bias. We use publicly available X-ray imaging data from the
XMM-Newton observatory and our Sunyaev-Zel'dovich Effect (SZE) imaging data
from the APEX-SZ experiment at 150 GHz to de-project the density and
temperature profiles for the relaxed cluster Abell 2204. We derive the gas
density, temperature and entropy profiles assuming spherical symmetry, and
obtain the total mass profile under the assumption of hydrostatic equilibrium.
For comparison with X-ray spectroscopic temperature models, a re-analysis of
the recent Chandra observation is done with the latest calibration updates.
Using the non-parametric modeling we demonstrate a decrease of gas temperature
in the cluster outskirts, and also measure the gas entropy profile. These
results are obtained for the first time independently of X-ray spectroscopy,
using SZE and X-ray imaging data. The contribution of the SZE systematic
uncertainties in measuring T_e at large radii is shown to be small compared to
the Chandra systematic spectroscopic errors. The upper limit on M_200 derived
from the non-parametric method is consistent with the NFW model prediction from
weak lensing analysis.Comment: Replaced with the published version; A&A 519, A29 (2010
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