1,769 research outputs found
On the origin of the 40-120 micron emission of galaxy disks: A comparison with H-alpha fluxes
A comparison of 40 to 120 micron Infrared Astronomy Satellite (IRAS) fluxes with published H alpha and UBV photometry shows that the far infrared emission of galaxy disks consists of at least two components: a warm one associated with OB stars in HII-regions and young star-forming complexes, and a cooler one from dust in the diffuse, neutral interstellar medium, heated by the more general interstellar radiation field of the old disk population (a cirrus-like component). Most spiral galaxies are dominated by emission from the cooler component in this model. A significant fraction of the power for the cool component must originate with non-ionizing stars. For a normal spiral disk there is a substantial uncertainty in a star formation rate derived using either the H alpha or the far infrared luminosity
Small scale variations of abundances of transiently heated grains in molecular clouds
IRAS images of a variety of fragments in nearby molecular clouds show that the energy distribution of their IR emission varies widely from cloud to cloud and from place to place within a given cloud. These variations at small scale are all the more unexpected since the colors of the IR emission of cold material differ very little at large scale: the colors of the cirrus emission above the 3kpc molecular ring are the same as those of the cirrus emission in the solar neighborhood. To quantitatively study these variations, 12, 60, and 100 microns brightnesses were obtained of small areas centered at different positions within the set of clouds and complexes. The range of observed 12/100 micron colors is given for each cloud. Variations by an order of magnitude are found in most clouds. Variations by a factor of 2 to 3 are observed within a cloud on scales as small as 0.5pc, the resolution of this study. It is concluded that large variations of the abundances of small particles with respect to those of the large grains responsible for the 100 micron emission are required to explain the observed color variations and that these abundances have to vary by large factors; an order of magnitude from cloud to cloud
Modeling the evolution of infrared luminous galaxies: the influence of the Luminosity-Temperature distribution
The evolution of the luminous infrared galaxy population is explored using a
pure luminosity evolution model which incorporates the locally observed
luminosity-temperature distribution for IRAS galaxies. Pure luminosity
evolution models in a fixed CDM cosmology are fitted to submillimeter
(submm) and infrared counts, and backgrounds. It is found that the differences
between the locally determined bivariate model and the single variable
luminosity function (LF) do not manifest themselves in the observed counts, but
rather are primarily apparent in the dust temperatures of sources in flux
limited surveys. Statistically significant differences in the redshift
distributions are also observed. The bivariate model is used to predict the
counts, redshifts and temperature distributions of galaxies detectable by {\it
Spitzer}. The best fitting model is compared to the high-redshift submm galaxy
population, revealing a median redshift for the total submm population of
, in good agreement with recent spectroscopic studies of
submillimeter galaxies. The temperature distribution for the submm galaxies is
modeled to predict the radio/submm indices of the submm galaxies, revealing
that submm galaxies exhibit a broader spread in spectral energy distributions
than seen in the local IRAS galaxies.Comment: Accepted for publication in ApJ. Quality of several figures reduced
due to size restriction
The bandmerged Planck Early Release Compact Source Catalogue: Probing sub-structure in the molecular gas at high Galactic latitude
The Planck Early Release Compact Source Catalogue (ERCSC) includes nine lists
of highly reliable sources, individually extracted at each of the nine Planck
frequency channels. To facilitate the study of the Planck sources, especially
their spectral behaviour across the radio/infrared frequencies, we provide a
"bandmerged" catalogue of the ERCSC sources. This catalogue consists of 15191
entries, with 79 sources detected in all nine frequency channels of Planck and
6818 sources detected in only one channel. We describe the bandmerging
algorithm, including the various steps used to disentangle sources in confused
regions. The multi-frequency matching allows us to develop spectral energy
distributions of sources between 30 and 857 GHz, in particular across the 100
GHz band, where the energetically important CO J=1->0 line enters the Planck
bandpass. We find ~3-5sigma evidence for contribution to the 100 GHz intensity
from foreground CO along the line of sight to 147 sources with |b|>30 deg. The
median excess contribution is 4.5+/-0.9 percent of their measured 100 GHz flux
density which cannot be explained by calibration or beam uncertainties. This
translates to 0.5+/-0.1 K km s^{-1} of CO which must be clumped on the scale of
the Planck 100 GHz beam, i.e., ~10 arcmin. If this is due to a population of
low mass (~15 Msun) molecular gas clumps, the total mass in these clumps may be
more than 2000 Msun. Further, high-spatial-resolution, ground-based
observations of the high-latitude sky will help shed light on the origin of
this diffuse, clumpy CO emission.Comment: 15 pages, 15 figures, MNRAS in pres
NGC1377: An Extragalactic Proto-Starburst
NGC1377 is the archetype of a class of galaxies called nascent starbursts, selected by their very high infrared to radio continuum flux ratios and their high dust temperatures. This nearby galaxy is an ideal test case to refine the understanding of the mechanisms of the infrared-radio correlation of star-forming galaxies; to characterize the physical conditions of an embedded starburst at its very onset; and to gain a better knowledge of the activity of a class of ultraluminous galaxies sharing the main infrared-radio properties of NGC1377. We present new data on NGC1377 obtained as part of the Spitzer Infrared Nearby Galaxies Survey (SINGS) Legacy program and discuss briefly our interpretation of the combined optical, infrared and radio properties
Hubble Space Telescope images of submillimeter sources: large, irregular galaxies at high redshift
We present new Hubble Space Telescope STIS, high-resolution optical imaging
of a sample of 13 submillimeter (submm) luminous galaxies, for which the
optical emission has been pinpointed either through radio-1.4 GHz or millimeter
interferometry. We find a predominance of irregular and complex morphologies in
the sample, suggesting that mergers are likely common for submm galaxies. The
component separation in these objects are on average a factor two larger than
local galaxies with similarly high bolometric luminosities. The sizes and star
formation rates of the submm galaxies are consistent with the maximal star
formation rate densities of 20 Msun kpc^{-2} in local starburst galaxies
(Lehnert & Heckman 1996). We derive quantitative morphological information for
the optical galaxies hosting the submm emission; total and isophotal
magnitudes, Petrosian radius, effective radius, concentration, aspect ratio,
surface brightness, and asymmetry. We compare these morphological indices with
those of other galaxies lying within the same STIS images. Most strikingly, we
find ~70% of the submm galaxies to be extraordinarily large and elongated
relative to the field population, regardless of optical magnitude. Comparison
of the submm galaxy morphologies with those of optically selected galaxies at
z~2-3 reveal the submm galaxies to be a morphologically distinct population,
with generally larger sizes, higher concentrations and more prevalent
major-merger configurations.Comment: 16 pages, 6 figures, scheduled for ApJ, v599, Dec10, 2003. Minor
edits. For version with higher resolution figures, see
http://www.submm.caltech.edu/~schapman/ms_v3.ps.g
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