1,156 research outputs found
The XMM-Newton Project
The abundance of high-redshift galaxy clusters depends sensitively on the
matter density \OmM and, to a lesser extent, on the cosmological constant
. Measurements of this abundance therefore constrain these fundamental
cosmological parameters, and in a manner independent and complementary to other
methods, such as observations of the cosmic microwave background and distance
measurements. Cluster abundance is best measured by the X-ray temperature
function, as opposed to luminosity, because temperature and mass are tightly
correlated, as demonstrated by numerical simulations. Taking advantage of the
sensitivity of XMM-Newton, our Guaranteed Time program aims at measuring the
temperature of the highest redshift (z>0.4) SHARC clusters, with the ultimate
goal of constraining both \OmM and .Comment: To appear in the Proceedings of the XXI Moriond Conference: Galaxy
Clusters and the High Redshift Universe Observed in X-rays, edited by D.
Neumann, F. Durret, & J. Tran Thanh Va
Sequential and Spontaneous Star Formation Around the Mid-Infrared Halo HII Region KR 140
We use 2MASS and MSX infrared observations, along with new molecular line
(CO) observations, to examine the distribution of young stellar objects (YSOs)
in the molecular cloud surrounding the halo HII region KR 140 in order to
determine if the ongoing star-formation activity in this region is dominated by
sequential star formation within the photodissociation region (PDR) surrounding
the HII region. We find that KR 140 has an extensive population of YSOs that
have spontaneously formed due to processes not related to the expansion of the
HII region. Much of the YSO population in the molecular cloud is concentrated
along a dense filamentary molecular structure, traced by C18O, that has not
been erased by the formation of the exciting O star. Some of the previously
observed submillimetre clumps surrounding the HII region are shown to be sites
of recent intermediate and low-mass star formation while other massive starless
clumps clearly associated with the PDR may be the next sites of sequential star
formation.Comment: Accepted for publication in MNRAS, 8 pages, 10 figure
Submillimeter mapping and analysis of cold dust condensations in the Orion M42 star forming complex
We present here the continuum submillimeter maps of the molecular cloud
around the M42 Nebula in the Orion region. These have been obtained in four
wavelength bands (200, 260, 360 and 580 microns) with the ProNaOS two meter
balloon-borne telescope. The area covered is 7 parsecs wide (50 arcmin at a
distance of 470 pc) with a spatial resolution of about 0.4 parsec. Thanks to
the high sensitivity to faint surface brightness gradients, we have found
several cold condensations with temperatures ranging from 12 to 17 K, within 3
parsecs of the dense ridge. The statistical analysis of the temperature and
spectral index spatial distribution shows an evidence of an inverse correlation
between these two parameters. Being invisible in the IRAS 100 micron survey,
some cold clouds are likely to be the seeds for future star formation activity
going on in the complex. We estimate their masses and we show that two of them
have masses higher than their Jeans masses, and may be gravitationally
unstable.Comment: 4 figures, The Astrophysical Journal, Main Journal, in pres
Role of the (Mn)superoxide dismutase of Enterococcus faecalis in the in vitro interaction with microglia
Enterococcus faecalis is a significant human pathogen worldwide and is responsible for severenosocomial and community-acquired infections. Although enterococcal meningitis is rare,mortality is considerable, reaching 21 %. Nevertheless, the pathogenetic mechanisms of thisinfection remain poorly understood, even though the ability of E. faecalis to avoid or survivephagocytic attack in vivo may be very important during the infection process. We previouslyshowed that the manganese-cofactored superoxide dismutase (MnSOD) SodA of E. faecalis wasimplicated in oxidative stress responses and, interestingly, in the survival within mouse peritonealmacrophages using an in vivo\u2013in vitro infection model. In the present study, we investigated therole of MnSOD in the interaction of E. faecalis with microglia, the brain-resident macrophages. Byusing an in vitro infection model, murine microglial cells were challenged in parallel with the wildtypestrain JH2-2 and its isogenic sodA deletion mutant. While both strains were phagocytosedby microglia efficiently and to a similar extent, the DsodA mutant was found to be significantlymore susceptible to microglial killing than JH2-2, as assessed by the antimicrobial protectionassay. In addition, a significantly higher percentage of acidic DsodA-containing phagosomes wasfound and these also underwent enhanced maturation as determined by the expression ofendolysosomal markers. In conclusion, these results show that the MnSOD of E. faecaliscontributes to survival of the bacterium in microglial cells by influencing their antimicrobial activity,and this could even be important for intracellular killing in neutrophils and thus for E. faecalispathogenesis
A Sample of Intermediate-Mass Star-Forming Regions: Making Stars at Mass Column Densities <1 g/cm^2
In an effort to understand the factors that govern the transition from low-
to high-mass star formation, we identify for the first time a sample of
intermediate-mass star-forming regions (IM SFRs) where stars up to - but not
exceeding - 8 solar masses are being produced. We use IRAS colors and Spitzer
Space Telescope mid-IR images, in conjunction with millimeter continuum and CO
maps, to compile a sample of 50 IM SFRs in the inner Galaxy. These are likely
to be precursors to Herbig AeBe stars and their associated clusters of low-mass
stars. IM SFRs constitute embedded clusters at an early evolutionary stage akin
to compact HII regions, but they lack the massive ionizing central star(s). The
photodissociation regions that demarcate IM SFRs have typical diameters of ~1
pc and luminosities of ~10^4 solar luminosities, making them an order of
magnitude less luminous than (ultra)compact HII regions. IM SFRs coincide with
molecular clumps of mass ~10^3 solar masses which, in turn, lie within larger
molecular clouds spanning the lower end of the giant molecular cloud mass
range, 10^4-10^5 solar masses. The IR luminosity and associated molecular mass
of IM SFRs are correlated, consistent with the known luminosity-mass
relationship of compact HII regions. Peak mass column densities within IM SFRs
are ~0.1-0.5 g/cm^2, a factor of several lower than ultra-compact HII regions,
supporting the proposition that there is a threshold for massive star formation
at ~1 g/cm^2.Comment: 61 pages, 6 tables, 20 figures. Accepted for publication in the
Astronomical Journa
Submillimeter dust emission of the M17 complex measured with PRONAOS
We map a 50' x 30' area in and around the M17 molecular complex with the
French submillimeter balloon-borne telescope PRONAOS, in order to better
understand the thermal emission of cosmic dust and the structure of the
interstellar medium. The PRONAOS-SPM instrument has an angular resolution of
about 3', corresponding to a size of 2 pc at the distance of this complex, and
a high sensitivity up to 0.8 MJy/sr. The observations are made in four wide
submillimeter bands corresponding to effective wavelengths of 200, 260, 360 and
580 um. Using an improved map-making method for PRONAOS data, we map the M17
complex and faint condensations near the dense warm core. We derive maps of
both the dust temperature and the spectral index, which vary over a wide range,
from about 10 K to 100 K for the temperature and from about 1 to 2.5 for the
spectral index. We show that these parameters are anticorrelated, the cold
areas (10-20 K) having a spectral index around 2, whereas the warm areas have a
spectral index between 1 and 1.5. We discuss possible causes of this effect,
and we propose an explanation involving intrinsic variations of the grain
properties. Indeed, to match the observed spectra with two dust components
having a spectral index equal to 2 leads to very large and unlikely amounts of
cold dust. We also give estimates of the column densities and masses of the
studied clumps. Three cold clumps (14-17 K) could be gravitationally unstable.Comment: 16 pages, 4 figures, accepted June 2002 in Astronomy & Astrophysic
TURBULENCE IN MOLECULAR CLOUDS
We generate random Gaussian turbulent velocity fields with a Kolmogorov
spectrum and use these to obtain synthetic line-of-sight velocity profiles. The
profiles are found to be similar to line profiles observed in molecular clouds.
We suggest methods for analysing measured line profiles to test whether they
might arise from Gaussian Kolmogorov turbulence.Comment: accepted in ApJ, compressed postscript, figures not included.
Complete preprint available at http://ucowww.ucsc.edu/~dubinski/home.html or
by request to [email protected]
A multiwavelength study of Galactic HII region Sh2-294
We present the observational results of Galactic HII region S294, using
optical photometry, narrow-band imaging and radio continuum mapping at 1280
MHz, together with archival data from 2MASS, MSX and IRAS surveys. The stellar
surface density profile indicates that the radius of the cluster associated
with the S294 region is ~ 2.3 arcmin. We found an anomalous reddening law for
the dust inside the cluster region and the ratio of total-to-selective
extinction is found to be 3.8+-0.1. We estimate the minimum reddening E (B-V) =
1.35 mag and distance of 4.8+-0.2 kpc to the region from optical CC and CM
diagrams. We identified the ionizing source of the HII region, and spectral
type estimates are consistent with a star of spectral type ~ B0 V. The 2MASS
JHKs images reveal a partially embedded cluster associated with the ionizing
source along with a small cluster towards the eastern border of S294. The
ionization front seen along the direction of small cluster in radio continuum
and Halpha images, might be due to the interaction of ionizing sources with the
nearby molecular cloud. We found an arc shaped diffuse molecular hydrogen
emission at 2.12 micron and a half ring of MSX dust emission which surrounds
the ionized gas in the direction of the ionization front. Self consistent
radiative transfer model of mid- to far-infrared continuum emission detected
near small cluster is in good agreement with the observed spectral energy
distribution of a B1.5 ZAMS star. The morphological correlation between the
ionised and molecular gas, along with probable time scale involved between the
ionising star, evolution of HII region and small cluster, indicates that the
star-formation activity observed at the border is probably triggered by the
expansion of HII region.Comment: 50 pages, 21 figures: Accepted by The Astrophysical Journal; Also
available at http://www.tifr.res.in/~ojha/S294.pd
The complete submillimetre spectrum of NGC 891
Submillimetre maps of NGC 891 have been obtained with the PRONAOS
balloon-borne telescope and with the ISOPHOT instrument on board the ISO
satellite. In this article, we also gather data from IRAS and SCUBA to present
the complete submillimetre spectrum of this nearby edge-on spiral galaxy. We
derive submillimetre emission profiles along the major axis. The modified
blackbody fits, assuming a single dust component, lead to temperatures of 19-24
K toward the centre and 18-20 K toward the edges, with possible variations of
the dust spectral index from 1.4 to 2. The two-component fits lead to a warm
component temperature of 29 K all along the galaxy with a cold component at 16
K. The interstellar medium masses derived by these two methods are quite
different: 4.6 x 10^9 Mo in the case of the one-component model and 12 x 10^9
Mo in the case of the two-component one. This two-component fit indicates that
the cold dust to warm dust ratio is 20 to 40, the highest values being in the
wings of this galaxy. Comparing to dust mass estimates, both estimations of the
ISM mass are consistent with a gas to dust mass ratio of 240, which is close to
the Milky Way value. Our results illustrate the importance of accurate
submillimetre spectra to derive masses of the interstellar medium in galaxies.Comment: 5 pages, 2 figures, accepted May 2003 in the MNRA
Emission Features and Source Counts of Galaxies in Mid-Infrared
In this work we incorporate the newest ISO results on the mid-infrared
spectral-energy-distributions (MIR SEDs) of galaxies into models for the number
counts and redshift distributions of MIR surveys. A three-component model, with
empirically determined MIR SED templates of (1) a cirrus/PDR component (2) a
starburst component and (3) an AGN component, is developed for infrared
(3--120\micron) SEDs of galaxies. The model includes a complete IRAS 25\micron
selected sample of 1406 local galaxies (; Shupe et al. 1998a).
Results based on these 1406 spectra show that the MIR emission features cause
significant effects on the redshift dependence of the K-corrections for fluxes
in the WIRE 25\micron band and ISOCAM 15\micron band. This in turn will affect
deep counts and redshift distributions in these two bands, as shown by the
predictions of two evolution models (a luminosity evolution model with
and a density evolution model with ).
The dips-and-bumps on curves of MIR number counts, caused by the emission
features, should be useful indicators of evolution mode. The strong emission
features at --8\micron will help the detections of relatively high
redshift () galaxies in MIR surveys. On the other hand, determinations
of the evolutionary rate based on the slope of source counts, and studies on
the large scale structures using the redshift distribution of MIR sources, will
have to treat the effects of the MIR emission features carefully. We have also
estimated a 15\micron local luminosity function from the predicted 15\micron
fluxes of the 1406 galaxies using the bivariate (15\micron vs. 25\micron
luminosities) method. This luminosity function will improve our understanding
of the ISOCAM 15\micron surveys.Comment: 24 pages, 14 EPS figures. Accepted by Ap
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