1,093 research outputs found
Physical conditions in the ISM towards HD185418
We have developed a complete model of the hydrogen molecule as part of the
spectral simulation code Cloudy. Our goal is to apply this to spectra of
high-redshift star-forming regions where H2 absorption is seen, but where few
other details are known, to understand its implication for star formation. The
microphysics of H2 is intricate, and it is important to validate these
numerical simulations in better-understood environments. This paper studies a
well-defined line-of-sight through the Galactic interstellar medium (ISM) as a
test of the microphysics and methods we use. We present a self-consistent
calculation of the observed absorption-line spectrum to derive the physical
conditions in the ISM towards HD185418, a line-of-sight with many observables.
We deduce density, temperature, local radiation field, cosmic ray ionization
rate, chemical composition and compare these conclusions with conditions
deduced from analytical calculations. We find a higher density, similar
abundances, and require a cosmic ray flux enhanced over the Galactic background
value, consistent with enhancements predicted by MHD simulations.Comment: 31 pages, accepted for publication in Ap
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
The Anatomy of Star Formation in NGC 300
The Spitzer Space Telescope was used to study the mid-infrared to
far-infrared properties of NGC 300, and to compare dust emission to Halpha to
elucidate the heating of the ISM and the star formation cycle at scales < 100
pc. The new data allow us to discern clear differences in the spatial
distribution of 8 micron dust emission with respect to 24 micron dust and to
HII regions traced by the Halpha light. The 8 micron emission highlights the
rims of HII regions, and the 24 micron emission is more strongly peaked in star
forming regions than at 8 microns. We confirm the existence and approximate
amplitude of interstellar dust emission at 4.5 microns, detected statistically
in Infrared Space Observatory (ISO) data, and conclude it arises in star
forming regions. When averaging over regions larger than ~ 1 kpc, the ratio of
Halpha to Aromatic Feature emission in NGC 300 is consistent with the values
observed in disks of spiral galaxies. The mid-to-far-infrared spectral energy
distribution of dust emission is generally consistent with pre-Spitzer models.Comment: to appear in the ApJS Spitzer special issue (September 2004
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
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
Warm molecular hydrogen in the Spitzer SINGS galaxy sample
(simplified) Results on the properties of warm H2 in 57 normal galaxies are
derived from H2 rotational transitions, obtained as part of SINGS. This study
extends previous extragalactic surveys of H2, the most abundant constituent of
the molecular ISM, to more common systems (L_FIR = e7 to 6e10 L_sun) of all
morphological and nuclear types. The S(1) transition is securely detected in
the nuclear regions of 86% of SINGS galaxies with stellar masses above 10^9.5
M_sun. The derived column densities of warm H2 (T > ~100 K), even though
averaged over kiloparsec-scale areas, are commensurate with those of resolved
PDRs; the median of the sample is 3e20 cm-2. They amount to between 1% and >30%
of the total H2. The power emitted in the sum of the S(0) to S(2) transitions
is on average 30% of the [SiII] line power, and ~4e-4 of the total infrared
power (TIR) within the same area for star-forming galaxies, which is consistent
with excitation in PDRs. The fact that H2 emission scales tightly with PAH
emission, even though the average radiation field intensity varies by a factor
ten, can also be understood if both tracers originate predominantly in PDRs,
either dense or diffuse. A large fraction of the 25 LINER/Sy targets, however,
strongly depart from the rest of the sample, in having warmer H2 in the excited
states, and an excess of H2 emission with respect to PAHs, TIR and [SiII]. We
propose a threshold in H2 to PAH power ratios, allowing the identification of
low-luminosity AGNs by an excess H2 excitation. A dominant contribution from
shock heating is favored in these objects. Finally, we detect, in nearly half
the star-forming targets, non-equilibrium ortho to para ratios, consistent with
FUV pumping combined with incomplete ortho-para thermalization by collisions,
or possibly non-equilibrium PDR fronts advancing into cold gas.Comment: ApJS, in pres
The HII Region KR 140: Spontaneous Formation of a High Mass Star
We have used a multiwavelength data set from the Canadian Galactic Plane
Survey (CGPS) to study the Galactic HII region KR 140, both on the scale of the
nebula itself and in the context of the star forming activity in the nearby
W3/W4/W5 complex of molecular clouds and HII regions. From both radio and
infrared data we have found a covering factor of about 0.5 for KR 140 and we
interpret the nebula as a bowl-shaped region viewed close to face on.
Extinction measurements place the region on the near side of its parent
molecular cloud. The nebula is kept ionized by one O8.5 V(e) star, VES 735,
which is less than a few million years old. CO data show that VES 735 has
disrupted much of the original molecular cloud for which the estimated mass and
density are about 5000 and 100 cm, respectively. KR 140 is
isolated from the nearest star forming activity, in W3. Our data suggest that
KR 140 is an example of spontaneous (i.e., non-triggered) formation of,
unusually, a high mass star.Comment: 46 pages; includes 15 figures; accepted by the Ap
Planck's Dusty GEMS: Gravitationally lensed high-redshift galaxies discovered with the Planck survey
We present an analysis of 11 bright far-IR/submm sources discovered through a
combination of the Planck survey and follow-up Herschel-SPIRE imaging. Each
source has a redshift z=2.2-3.6 obtained through a blind redshift search with
EMIR at the IRAM 30-m telescope. Interferometry obtained at IRAM and the SMA,
and optical/near-infrared imaging obtained at the CFHT and the VLT reveal
morphologies consistent with strongly gravitationally lensed sources.
Additional photometry was obtained with JCMT/SCUBA-2 and IRAM/GISMO at 850 um
and 2 mm, respectively. All objects are bright, isolated point sources in the
18 arcsec beam of SPIRE at 250 um, with spectral energy distributions peaking
either near the 350 um or the 500 um bands of SPIRE, and with apparent
far-infrared luminosities of up to 3x10^14 L_sun. Their morphologies and sizes,
CO line widths and luminosities, dust temperatures, and far-infrared
luminosities provide additional empirical evidence that these are strongly
gravitationally lensed high-redshift galaxies. We discuss their dust masses and
temperatures, and use additional WISE 22-um photometry and template fitting to
rule out a significant contribution of AGN heating to the total infrared
luminosity. Six sources are detected in FIRST at 1.4 GHz. Four have flux
densities brighter than expected from the local far-infrared-radio correlation,
but in the range previously found for high-z submm galaxies, one has a deficit
of FIR emission, and 6 are consistent with the local correlation. The global
dust-to-gas ratios and star-formation efficiencies of our sources are
predominantly in the range expected from massive, metal-rich, intense,
high-redshift starbursts. An extensive multi-wavelength follow-up programme is
being carried out to further characterize these sources and the intense
star-formation within them.Comment: A&A accepte
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