45 research outputs found
The Radio Continuum of the Metal-Deficient Blue Compact Dwarf Galaxy SBS0335-052
We present new Very Large Array observations at five frequencies, from 1.4 to
22GHz, of the extremely low-metallicity blue compact dwarf SBS0335-052. The
radio spectrum shows considerable absorption at 1.49GHz, and a composite
thermal+non-thermal slope. After fitting the data with a variety of models, we
find the best-fitting geometry to be one with free-free absorption
homogeneously intermixed with the emission of both thermal and non-thermal
components. The best-fitting model gives an an emission measure EM ~ 8x10^7pc
cm^{-6} and a diameter of the radio-emitting region D ~17pc. The inferred
density is n_e ~ 2000 cm^{-3}. The thermal emission comes from an ensemble of
\~9000 O7 stars, with a massive star-formation rate (>=5Msun) of 0.13-0.15
yr^{-1}, and a supernova rate of 0.006 yr^{-1}. We find evidence for ionized
gas emission from stellar winds, since the observed Bralpha line flux
significantly exceeds that inferred from the thermal radio emission. The
non-thermal fraction at 5GHz is ~0.7, corresponding to a non-thermal luminosity
of ~2x10^{20} W Hz^{-1}. We attribute the non-thermal radio emission to an
ensemble of compact SN remnants expanding in a dense interstellar medium, and
derive an equipartition magnetic field of ~0.6-1 mG, and a pressure of
\~3x10^{-8}-1x10^{-7} dyne cm^{-2}. If the radio properties of SBS0335-052 are
representative of star formation in extremely low-metallicity environments,
derivations of the star formation rate from the radio continuum in high
redshift primordial galaxies need to be reconsidered. Moreover, photometric
redshifts inferred from ``standard'' spectral energy distributions could be
incorrect.Comment: 25 pages, including 3 figures, accepted for publication in Ap
VISIR/VLT mid-infrared imaging of Seyfert nuclei: Nuclear dust emission and the Seyfert-2 dichotomy
Half of the Seyfert-2 galaxies escaped detection of broad lines in their
polarised spectra observed so far. Some authors have suspected that these
non-HBLRs contain real Sy2 nuclei without intrinsic broad line region hidden
behind a dust torus. If this were true, then their nuclear structure would
fundamentally differ from that of Sy2s with polarised broad lines: in
particular, they would not be explained by orientation-based AGN unification.
Further arguments for two physically different Sy2 populations have been
derived from the warm and cool IRAS F25/F60 ratios. These ratios, however,
refer to the entire host galaxies and are unsuitable to conclusively establish
the absence of a nuclear dust torus. Instead, a study of the Seyfert-2
dichotomy should be performed on the basis of nuclear properties only. Here we
present the first comparison between [OIII] 5007A and mid-infrared imaging at
matching spatial resolution. Exploring the Seyfert-2 dichotomy we find that the
distributions of nuclear mid-infrared/[OIII] luminosity ratios are
indistinguishable for Sy1s and Sy2s with and without detected polarised broad
lines and irrespective of having warm or cool IRAS F25/F60 ratios. We find no
evidence for the existence of a population of real Sy2s with a deficit of
nuclear dust emission. Our results suggest 1) that all Seyfert nuclei possess
the same physical structure including the putative dust torus and 2) that the
cool IRAS colours are caused by a low contrast of AGN to host galaxy. Then the
Seyfert-2 dichotomy is explained in part by unification of non-HBLRs with
narrow-line Sy1s and to a larger rate by observational biases caused by a low
AGN/host contrast and/or an unfavourable scattering geometry.Comment: 11 pages, 6 figures, accepted by A&
Mrk 609: resolving the circum-nuclear structure with near-infrared integral field spectroscopy
We present first results of near infrared J and H+K ESO-SINFONI integral
field spectroscopy of the composite starburst/Seyfert 1.8 galaxy Mrk 609. The
data were taken during the science verification period of SINFONI. We aim to
investigate the morphology and excitation conditions within the central 2 kpc.
Additional Nobeyama 45 m CO(1-0) data are presented, which we used to estimate
the molecular gas mass. The source was selected from a sample of adaptive
optics suitable, SDSS/ROSAT based, X-ray bright AGN with redshifts of 0.03 < z
< 1. This sample allows for a detailed study of the NIR properties of the
nuclear and host environments with high spectral and spatial resolution. Our
NIR data reveal a complex emission-line morphology, possibly associated with a
nuclear bar seen in the reconstructed continuum images. The detections of
[SiVI] and a broad Pa alpha component are clear indicators for the presence of
an accreting super-massive black hole at the center of Mrk 609. In agreement
with previous observations we find that the circum-nuclear emission is not
significantly extincted. The analysis of the high angular resolution
rotational-vibrational molecular hydrogen and forbidden [FeII] emission reveals
a LINER character of the nucleus. The large H_2 gas mass deduced from the
CO(1-0) observation provides the fuel needed to feed the starburst and Seyfert
activity in Mrk 609. High angular resolution imaging spectroscopy provides an
ideal tool to resolve the nuclear and starburst contribution in active
galaxies. We show that Mrk 609 exhibits LINER features, that appear to be
hidden in larger aperture visible/NIR spectra.Comment: published by A&A, 19 pages, 16 figures, version with high resolution
figures is available via http://www.ph1.uni-koeln.de/~zuther/mrk609.pd
The spiral galaxy M33 mapped in the FIR by ISOPHOT: A spatially resolved study of the warm and cold dust
The Sc galaxy M33 has been mapped with ISOPHOT in the far-infrared, at 60,
100, and 170mue. The spatial resolution of these FIR maps allows the separation
of spiral arms and interarm regions and the isolation of a large number of
star-forming regions. The spectral energy distribution in the FIR indicates a
superposition of two components, a warm one originating from dust at ~45K, and
a cold one, at ~16K. The warm component is concentrated towards the spiral arms
and the star-forming regions, and is likely heated by the UV radiation from OB
stars. The cold component is more smoothly distributed over the disk, and
heated by the diffuse interstellar radiation. For the about 60 star-forming
regions detected the H-alpha/FIR flux ratio increases significantly with the
distance from the galaxy center, probably due to decreasing extinction. An
anti-correlation of F_Ha/F_60 with F_170 suggests the intrinsic extinction to
be related to the cold dust surface brightness according to
A_V/S_170~0.03mag/MJy*sr. For the total galaxy the star formation rate (SFR)
derived from the FIR is in agreement with that derived from the de-extincted
H-alpha emission. For individual star-forming regions, a consistency between
SFRs derived from the optical and from the FIR requires only a fraction of the
UV radiation to be absorbed locally. The individual star-forming regions also
show a local radio-FIR correlation. This local correlation is, however, due to
quite different components than to those that lead to the well-known global
radio-FIR correlation for entire galaxies.Comment: 10 pages, 9 figures; the full resolution images of Fig.1 can be
obtained by anonymous ftp from ftp.mpia.de /pub/iso-arc
The [OIII] emission line luminosity function of optically selected type-2 AGN from zCOSMOS
We present a catalog of 213 type-2 AGN selected from the zCOSMOS survey. The
selected sample covers a wide redshift range (0.15<z<0.92) and is deeper than
any other previous study, encompassing the luminosity range 10^{5.5} < Lsun<
L[OIII] < 10^{9.1} Lsun. We explore the intrinsic properties of these AGN and
the relation to their X-ray emission (derived from the XMM-COSMOS
observations). We study their evolution by computing the [OIII]5007A line
luminosity function (LF) and we constrain the fraction of obscured AGN as a
function of luminosity and redshift. The sample was selected on the basis of
the optical emission line ratios, after applying a cut to the signal-to-noise
ratio (S/N) of the relevant lines. We used the standard diagnostic diagrams
[OIII]/Hbeta versus [NII]/Halpha and ([OIII]/Hbeta versus [SII]/Halpha) to
isolate AGN in the redshift range 0.15<z<0.45 and the diagnostic diagram
[OIII]/Hbeta versus [OII]/Hbeta to extend the selection to higher redshift
(0.5<z<0.92). Combining our sample with one drawn from SDSS, we found that the
best description of the evolution of type-2 AGN is a luminosity-dependent
density evolution model. Moreover, using the type-1 AGN LF we were able to
constrain the fraction of type-2 AGN to the total (type-1 + type-2) AGN
population. We found that the type-2 fraction decreases with luminosity, in
agreement with the most recent results, and shows signs of a slight increase
with redshift. However, the trend with luminosity is visible only after
combining the SDSS+zCOSMOS samples. From the COSMOS data points alone, the
type-2 fraction seems to be quite constant with luminosity.Comment: 20 pages, 11 figures, accepted for publication in Astronomy and
Astrophysic
The stellar and sub-stellar IMF of simple and composite populations
The current knowledge on the stellar IMF is documented. It appears to become
top-heavy when the star-formation rate density surpasses about 0.1Msun/(yr
pc^3) on a pc scale and it may become increasingly bottom-heavy with increasing
metallicity and in increasingly massive early-type galaxies. It declines quite
steeply below about 0.07Msun with brown dwarfs (BDs) and very low mass stars
having their own IMF. The most massive star of mass mmax formed in an embedded
cluster with stellar mass Mecl correlates strongly with Mecl being a result of
gravitation-driven but resource-limited growth and fragmentation induced
starvation. There is no convincing evidence whatsoever that massive stars do
form in isolation. Various methods of discretising a stellar population are
introduced: optimal sampling leads to a mass distribution that perfectly
represents the exact form of the desired IMF and the mmax-to-Mecl relation,
while random sampling results in statistical variations of the shape of the
IMF. The observed mmax-to-Mecl correlation and the small spread of IMF
power-law indices together suggest that optimally sampling the IMF may be the
more realistic description of star formation than random sampling from a
universal IMF with a constant upper mass limit. Composite populations on galaxy
scales, which are formed from many pc scale star formation events, need to be
described by the integrated galactic IMF. This IGIMF varies systematically from
top-light to top-heavy in dependence of galaxy type and star formation rate,
with dramatic implications for theories of galaxy formation and evolution.Comment: 167 pages, 37 figures, 3 tables, published in Stellar Systems and
Galactic Structure, Vol.5, Springer. This revised version is consistent with
the published version and includes additional references and minor additions
to the text as well as a recomputed Table 1. ISBN 978-90-481-8817-
Stomach cancer and occupational exposure to asbestos: a meta-analysis of occupational cohort studies
BACKGROUND: A recent Monographs Working Group of the International Agency for Research on Cancer concluded that there is limited evidence for a causal association between exposure to asbestos and stomach cancer. METHODS: We performed a meta-analysis to quantitatively evaluate this association. Random effects models were used to summarise the relative risks across studies. Sources of heterogeneity were explored through subgroup analyses and meta-regression. RESULTS: We identified 40 mortality cohort studies from 37 separate papers, and cancer incidence data were extracted for 15 separate cohorts from 14 papers. The overall meta-SMR for stomach cancer for total cohort was 1.15 (95% confidence interval 1.03–1.27), with heterogeneous results across studies. Statistically significant excesses were observed in North America and Australia but not in Europe, and for generic asbestos workers and insulators. Meta-SMRs were larger for cohorts reporting a SMR for lung cancer above 2 and cohort sizes below 1000. CONCLUSIONS: Our results support the conclusion by IARC that exposure to asbestos is associated with a moderate increased risk of stomach cancer
Re-evaluation of histological diagnoses of malignant mesothelioma by immunohistochemistry
<p>Abstract</p> <p>Background</p> <p>In order to provide reliable tissue material for malignant mesothelioma (MM) studies, we re-evaluated biopsies and autopsy material from 61 patients with a diagnosis of MM from the period of 1980-2002.</p> <p>Methods</p> <p>Basic positive (Calretinin, EMA, Podoplanin, Mesothelin) and negative (CEA, Ber-Ep4) immunohistochemical (IHC) marker reactions were determined. If needed, more markers were used. Histological diagnoses were made by three pathologists. Survival data were calculated.</p> <p>Results</p> <p>49 cases (80%) were considered being MM by a high degree of likelihood, five more cases possible MM. Of the remaining seven cases, three were diagnosed as adenocarcinoma, three as pleomorphic lung carcinoma, in one peritoneal case a clear entity diagnosis could not be given. One of the possible MM cases and two of the lung carcinoma cases had this already as primary diagnoses, but were registered as MM.</p> <p>With a sensitivity of 100%, Calretinin and CEA were the most reliable single markers. The amount of MM cells with positive immunoreactivity (IR) for Podoplanin and Mesothelin showed most reliable inverse relation to the degree of atypia.</p> <p>In the confirmed MM cases, there had been applied either no IHC or between one and 18 markers.</p> <p>The cases not confirmed by us had either lacked IHC (n = 1), non-specific markers were used (n = 4), IR was different (n = 1), or specific markers had not shown positive IR in the right part of the tumour cells (n = 3).</p> <p>46 of the 49 confirmed and three of the not confirmed cases had been diagnosed by us as most likely MM before IHC was carried out.</p> <p>Conclusions</p> <p>In order to use archival tissue material with an earlier MM diagnosis for studies, histopathological re-evaluation is important. In possible sarcomatous MM cases without any positive IR for positive MM markers, radiology and clinical picture are essential parts of diagnostics. IHC based on a panel of two positive and two negative MM markers has to be adapted to the differential diagnostic needs in each single case. New diagnostic tools and techniques are desirable for cases where IHC and other established methods cannot provide a clear entity diagnosis, and in order to improve MM treatment.</p
Spectral energy distribution and radio halo of NGC253 at low radio frequencies
A. D. Kapinska, 'Spectral Energy Distribution and Radio Halo of NGC 253 at Low Radio Frequencies', The Astrophysical Journal, Vol. 838(68), 15 pp, March 2017. The version of record is available online at doi: https://doi.org/10.3847/1538-4357/aa5f5d. © 2017. The American Astronomical Society. All rights reserved.We present new radio continuum observations of NGC253 from the Murchison Widefield Array at frequencies between 76 and 227 MHz. We model the broadband radio spectral energy distribution for the total flux density of NGC253 between 76 MHz and 11 GHz. The spectrum is best described as a sum of central starburst and extended emission. The central component, corresponding to the inner 500pc of the starburst region of the galaxy, is best modelled as an internally free-free absorbed synchrotron plasma, with a turnover frequency around 230 MHz. The extended emission component of the NGC253 spectrum is best described as a synchrotron emission flattening at low radio frequencies. We find that 34% of the extended emission (outside the central starburst region) at 1 GHz becomes partially absorbed at low radio frequencies. Most of this flattening occurs in the western region of the SE halo, and may be indicative of synchrotron self-absorption of shock re-accelerated electrons or an intrinsic low-energy cut off of the electron distribution. Furthermore, we detect the large-scale synchrotron radio halo of NGC253 in our radio images. At 154 - 231 MHz the halo displays the well known X-shaped/horn-like structure, and extends out to ~8kpc in z-direction (from major axis).Peer reviewedFinal Published versio
Ultraluminous Infrared Galaxies
Ever since their discovery in the 1970's, UltraLuminous InfraRed Galaxies
(ULIRGs; classically Lir>10^12Lsun) have fascinated astronomers with their
immense luminosities, and frustrated them due to their singularly opaque
nature, almost in equal measure. Over the last decade, however, comprehensive
observations from the X-ray through to the radio have produced a consensus
picture of local ULIRGs, showing that they are mergers between gas rich
galaxies, where the interaction triggers some combination of dust-enshrouded
starburst and AGN activity, with the starburst usually dominating. Very recent
results have thrown ULIRGs even further to the fore. Originally they were
thought of as little more than a local oddity, but the latest IR surveys have
shown that ULIRGs are vastly more numerous at high redshift, and tantalizing
suggestions of physical differences between high and low redshift ULIRGs hint
at differences in their formation modes and local environment. In this review
we look at recent progress on understanding the physics and evolution of local
ULIRGs, the contribution of high redshift ULIRGs to the cosmic infrared
background and the global history of star formation, and the role of ULIRGs as
diagnostics of the formation of massive galaxies and large-scale structures.Comment: Review article, published in "Astrophysics Update 2 - topical and
timely reviews on astronomy and astrophysics". Ed. John W. Mason.
Springer/Praxis books. ISBN: 3-540-30312-X. 53 pages, 5 figures. Higher
quality figures available on reques