31 research outputs found
HCO+ in the Starburst Galaxy M82
We report observations and an analysis of the distribution of HCO+(1-0) and HCO+(4-3) emission in the central 1 kpc star forming region of M82. Comparisons are made with other star formation indicators such as the mm continuum, the distribution of radio SNR's and the molecules CO and OH. In a broad sense, the HCO+ is distributed in a way similar to the CO, although there are noticeable differences in detail, including an inward displacement of spiral arm emission relative to CO. A comparison of the position-velocity plots for CO, HCO+(1-0), HCO+(4-3), and ionized gas, with orbits expected in the presence of the nuclear bar suggest an inward transfer of gas associated with star formation toward the nucleus. The HCO+(4-3)/(1-0) line ratios are comparatively uniform in the observed region, and according to an LVG analysis, reflect mean gas densities in the range 10^4 cm^{-3} - 10^5 cm^{-3} for kinetic temperatures in the range 20K - 60K. The comparative uniformity of these conditions and the low filling factor suggest that each sampled point comprises alarge number of clouds occupying a broad range of density, and possibly temperature. We briefly examine fractal type models in the context of the HCO+ data as an alternative way to analyze molecular line emission in M82
Mid-IR Spectroscopy of High-z SMGs: First Results
We present mid-infrared spectra of 5 submmillimeter galaxies at redshifts z = 0.65 â 2.38 taken with the Infrared Spectrograph aboard the Spitzer Space Telescope. Four of these sources have strong PAH features and the strength of these features are consistent with these galaxies being dominated by star formation. The other source displays a Mrk 231-type broad emission feature at restframe ~8 ÎŒm that does not conform to the typical 7.7/8.6 ÎŒm PAH complex in starburst galaxies, suggesting a more substantial AGN contribution
No Evidence for Evolution in the Far-Infrared-Radio Correlation out to z ~ 2 in the eCDFS
We investigate the 70 um Far-Infrared Radio Correlation (FRC) of star-forming
galaxies in the Extended Chandra Deep Field South (ECDFS) out to z > 2. We use
70 um data from the Far-Infrared Deep Extragalactic Legacy Survey (FIDEL),
which comprises the most sensitive (~0.8 mJy rms) and extensive far-infrared
deep field observations using MIPS on the Spitzer Space Telescope, and 1.4 GHz
radio data (~8 uJy/beam rms) from the VLA. In order to quantify the evolution
of the FRC we use both survival analysis and stacking techniques which we find
give similar results. We also calculate the FRC using total infrared luminosity
and rest-frame radio luminosity, qTIR, and find that qTIR is constant (within
0.22) over the redshift range 0 - 2. We see no evidence for evolution in the
FRC at 70 um which is surprising given the many factors that are expected to
change this ratio at high redshifts.Comment: 18 pages, 13 figures. Accepted for publication in Ap
Understanding Infrared Galaxy Populations: the SWIRE Legacy Survey
We discuss spectral energy distributions, photometric redshifts, redshift
distributions, luminosity functions, source-counts and the far infrared to
optical luminosity ratio for sources in the SWIRE Legacy Survey. The spectral
energy distributions of selected SWIRE sources are modelled in terms of a
simple set of galaxy and quasar templates in the optical and near infrared, and
with a set of dust emission templates (cirrus, M82 starburst, Arp 220
starburst, and AGN dust torus) in the mid infrared. The optical data, together
with the IRAC 3.6 and 4.5 mu data, have been used to determine photometric
redshifts. For galaxies with known spectroscopic redshifts there is a notable
improvement in the photometric redshift when the IRAC data are used, with a
reduction in the rms scatter from 10% in (1+z) to 5%. While further
spectroscopic data are needed to confirm this result, the prospect of
determining good photometric redshifts for the 2 million extragalactic objects
in SWIRE is excellent. The distribution of the different infrared sed types in
the L{ir}/L{opt} versus L{ir} plane, where L{ir} and L{opt} are the infrared
and optical bolometric luminosities, is discussed. Source-counts at 24, 70 and
160 mu are discussed, and luminosity functions at 3.6 and 24 mu are presented.Comment: 8 pages, 14 figures, to appear in proceedings of 'Spitzer IR
Diagnostics Conference, Nov 14-16, 2005
MAMBO 1.2mm observations of luminous starbursts at z~2 in the SWIRE fields
We report on--off pointed MAMBO observations at 1.2 mm of 61 Spitzer-selected
star-forming galaxies from the SWIRE survey. The sources are selected on the
basis of bright 24um fluxes (f_24um>0.4mJy) and of stellar dominated
near-infrared spectral energy distributions in order to favor z~2 starburst
galaxies. The average 1.2mm flux for the whole sample is 1.5+/-0.2 mJy. Our
analysis focuses on 29 sources in the Lockman Hole field where the average
1.2mm flux (1.9+/-0.3 mJy) is higher than in other fields (1.1+/-0.2 mJy). The
analysis of the sources multi-wavelength spectral energy distributions
indicates that they are starburst galaxies with far-infrared luminosities
~10^12-10^13.3 Lsun, and stellar masses of ~0.2-6 x10^11 M_sun. Compared to
sub-millimeter selected galaxies (SMGs), the SWIRE-MAMBO sources are among
those with the largest 24um/millimeter flux ratios. The origin of such large
ratios is investigated by comparing the average mid-infrared spectra and the
stacked far-infrared spectral energy distributions of the SWIRE-MAMBO sources
and of SMGs. The mid-infrared spectra exhibit strong PAH features, and a warm
dust continuum. The warm dust continuum contributes to ~34% of the mid-infrared
emission, and is likely associated with an AGN component. This constribution is
consistent with what is found in SMGs. The large 24um/1.2mm flux ratios are
thus not due to AGN emission, but rather to enhanced PAH emission compared to
SMGs. The analysis of the stacked far-infrared fluxes yields warmer dust
temperatures than typically observed in SMGs. Our selection favors warm
ultra-luminous infrared sources at high-z, a class of objects that is rarely
found in SMG samples. Our sample is the largest Spitzer-selected sample
detected at millimeter wavelengths currently available.Comment: Accepted for publication in ApJ (51 pages; 16 figures). The quality
of some figures has been degraded for arXiv purposes. Full resolution version
available at this
http://www.iasf-milano.inaf.it/~polletta/mambo_swire/lonsdale08_ApJ_accepted.pd
Absolute Calibration and Characterization of the Multiband Imaging Photometer for Spitzer. II. 70 micron Imaging
The absolute calibration and characterization of the Multiband Imaging
Photometer for Spitzer (MIPS) 70 micron coarse- and fine-scale imaging modes
are presented based on over 2.5 years of observations. Accurate photometry
(especially for faint sources) requires two simple processing steps beyond the
standard data reduction to remove long-term detector transients. Point spread
function (PSF) fitting photometry is found to give more accurate flux densities
than aperture photometry. Based on the PSF fitting photometry, the calibration
factor shows no strong trend with flux density, background, spectral type,
exposure time, or time since anneals. The coarse-scale calibration sample
includes observations of stars with flux densities from 22 mJy to 17 Jy, on
backgrounds from 4 to 26 MJy sr^-1, and with spectral types from B to M. The
coarse-scale calibration is 702 +/- 35 MJy sr^-1 MIPS70^-1 (5% uncertainty) and
is based on measurements of 66 stars. The instrumental units of the MIPS 70
micron coarse- and fine-scale imaging modes are called MIPS70 and MIPS70F,
respectively. The photometric repeatability is calculated to be 4.5% from two
stars measured during every MIPS campaign and includes variations on all time
scales probed. The preliminary fine-scale calibration factor is 2894 +/- 294
MJy sr^-1 MIPS70F^-1 (10% uncertainty) based on 10 stars. The uncertainty in
the coarse- and fine-scale calibration factors are dominated by the 4.5%
photometric repeatability and the small sample size, respectively. The 5-sigma,
500 s sensitivity of the coarse-scale observations is 6-8 mJy. This work shows
that the MIPS 70 micron array produces accurate, well calibrated photometry and
validates the MIPS 70 micron operating strategy, especially the use of frequent
stimulator flashes to track the changing responsivities of the Ge:Ga detectors.Comment: 19 pages, PASP, in pres
Complete Multiwavelength Characterization of Faint Chandra X-ray Sources Seen in the Spitzer Wide-Area IR Extragalactic (SWIRE) Survey
We exploit deep combined observations with Spitzer and Chandra of the SWIRE
survey in the ELAIS-N1 region, to investigate the nature of the faint X-ray and
IR sources in common, to identify AGN/starburst diagnostics, and to study the
sources of the X-ray and IR cosmic backgrounds. In the 17'x17' area of the
Chandra ACIS-I image there are 3400 SWIRE near-IR sources with 4 sigma
detections in at least 2 IRAC bands and 988 sources detected at 24micron with
MIPS brighter than 0.1 mJy. Of these, 102 IRAC and 59 MIPS sources have Chandra
counterparts, out of a total of 122 X-ray sources present in the area with
S(0.5-8 kev)>10^(-15) erg/cm^2/s. We have constructed SEDs for each source
using data from the 4 IRAC wavebands, Chandra fluxes, and optical follow-up
data in the wavebands U, g', r', i', Z, and H. We fit a number of spectral
templates to the SEDs at optical and infrared wavelengths to determine
photometric redshifts and spectral categories, and also make use of diagnostics
based on the X-ray luminosities, hardness ratios, X-ray to infrared spectral
slopes and optical morphologies. Although we have spectroscopic redshifts for
only a minority of the Chandra sources, the available SEDs constrain the
redshifts for most of the sample sources, which turn out to be typically at
0.5<z<2. We find that 39% of the Chandra sources are dominated by type-1 AGN
emission, 23% display optical/IR spectra typical of type-2 AGNs, while the
remaining 38% fraction show starburst-like or even normal galaxy spectra. Since
we prove that all these galaxies are dominated by AGN emission in X-rays this
brings the fraction of type-1 AGNs to be 80% of the type-2: even assuming that
all the Chandra sources undetected by Spitzer are type-2 AGNs, the type-1
fraction would exceed 1/3 of the total population (abridged).Comment: Accepted for publication in AJ, March 2005 issu
Multiply-imaged submm galaxy in a z~2.5 group
We present observations of a remarkable submillimetre-selected galaxy,
SMMJ16359+6612. This distant galaxy lies behind the core of a massive cluster
of galaxies, A2218, and is gravitationally lensed by the foreground cluster
into three discrete images which were identified in deep submillimetre maps of
the cluster core at both 450 and 850micron. Subsequent follow-up using deep
optical and NIR images identify a faint counterpart to each of the 3 images,
with similar red optical--NIR colours and HST morphologies. By exploiting a
detailed mass model for the cluster lens we estimate that the combined images
of this galaxy are magnified by a factor of ~45, implying that this galaxy
would have un-lensed magnitudes K_s=22.9 and I=26.1, and an un-lensed 850micron
flux density of only 0.8mJy. Moreover, the highly constrained lens model
predicted the redshift of SMMJ16359+6612 to be z=2.6+/-0.4. We confirm this
estimate using deep optical and NIR Keck spectroscopy, measuring a redshift of
z=2.516. SMMJ16359+6612 is the faintest submm-selected galaxy so far identified
with a precise redshift. Thanks to the large gravitational magnification of
this source, we identify 3 sub-components in this submm galaxy, which are also
seen in the NIRSPEC data, arguing for either a strong dust (lane) absorption or
a merger. Interestingly, there are 2 other highly-amplified galaxies at almost
identical redshifts in this field (although neither is a strong submm emitter).
The 3 galaxies lie within a ~100kpc region on the background sky, suggesting
this submm galaxy is located in a dense high-redshift group.Comment: 7 pages, 1 JPEG figure, MNRAS in pres
Spitzer Warm Mission Archive Science Opportunities
The rich data archive from the Spitzer cryogenic mission will be comprised of approximately 25 TB of data. A five-year warm mission would add an additional 15â20 TB. All of these data will be processed and archived to form homogeneous, reliable database to support research for decades after the end of the Spitzer mission. The SSC proposes a robust archival research program during the warm mission phase. A sampling of possible archival programs are described
SWIRE: The SIRTF WideâArea Infrared Extragalactic Survey
The SIRTF Wide-Area Infrared Extragalactic Survey (SWIRE), the largest SIRTF Legacy program, is a wide-area imaging survey to trace the evolution of dusty, star-forming galaxies, evolved stellar populations, and active galactic nuclei (AGNs) as a function of environment, from redshifts to the current z ⌠3 epoch. SWIRE will survey seven high-latitude fields, totaling 60â65 deg2 in all seven SIRTF bands: Infrared Array Camera (IRAC) 3.6, 4.5, 5.6, and 8 mm and Multiband Imaging Photometer for SIRTF (MIPS) 24, 70, and 160 mm. Extensive modeling suggests that the Legacy Extragalactic Catalog may contain in excess of 2 million IR-selected galaxies, dominated by (1) âŒ150,000 luminous infrared galaxies (LIRGs; LFIR 1 1011 L,) detected by MIPS (and significantly more detected by IRAC), âŒ7000 of these with ; (2) 1 million IRAC- z 1 2 detected early-type galaxies (⌠with and âŒ10,000 with ); and (3) âŒ20,000 classical AGNs 5 2 # 10 z 1 1 z 1 2 detected with MIPS, plus significantly more dust-obscured quasi-stellar objects/AGNs among the LIRGs. SWIRE will provide an unprecedented view of the evolution of galaxies, structure, and AGNs.
The key scientific goals of SWIRE are (1) to determine the evolution of actively star forming and passively evolving galaxies in order to understand the history of galaxy formation in the context of cosmic structure formation; (2) to determine the evolution of the spatial distribution and clustering of evolved galaxies, starbursts, and AGNs in the key redshift range over which much of cosmic evolution has occurred; and (3) to 0.5 ! z ! 3 determine the evolutionary relationship between ânormal galaxiesâ and AGNs and the contribution of AGN accretion energy versus stellar nucleosynthesis to the cosmic backgrounds. The large area of SWIRE is important to establish statistically significant population samples over enough volume cells that we can resolve the star formation history as a function of epoch and environment, i.e., in the context of structure formation. The large volume is also optimized for finding rare objects.
The SWIRE fields are likely to become the next generation of large âcosmic windowsâ into the extragalactic sky. They have been uniquely selected to minimize Galactic cirrus emission over large scales. The Galaxy Evolution Explorer will observe them as part of its deep 100 deg2 survey, as will Herschel. SWIRE includes âŒ9 deg2 of the unique large-area XMM Large Scale Structure hard X-ray imaging survey and is partly covered by the UKIDSS deep J and K survey. An extensive optical/near-IR imaging program is underway from the ground. The SWIRE data are nonproprietary; catalogs and images will be released twice yearly, beginning about 11 months after SIRTF launch. Details of the data products and release schedule are presented