arXiv subjects

F. R. Marleau

Publications and source records attributed to F. R. Marleau.

43 records · Page 3Linked to original sources

arXiv2005

Spitzer 70 and 160-micron Observations of the Extragalactic First Look Survey

We present Spitzer 70um and 160um observations of the Spitzer extragalactic First Look Survey (xFLS). The data reduction techniques and the methods for producing co-added mosaics and source catalogs are discussed. Currently, 26% of the 70um sample and 49% of the 160um-selected sources have redshifts. The majority of sources with redshifts are star-forming galaxies at z<0.5, while about 5% have infrared colors consistent with AGN. The observed infrared colors agree with the spectral energy distribution (SEDs) of local galaxies previously determined from IRAS and ISO data. The average 160um/70um color temperature for the dust is Td~= 30+/-5 K, and the average 70um/24um spectral index is alpha~= 2.4+/-0.4. The observed infrared to radio correlation varies with redshift as expected out to z~1 based on the SEDs of local galaxies. The xFLS number counts at 70um and 160um are consistent within uncertainties with the models of galaxy evolution, but there are indications that the current models may require slight modifications. Deeper 70um observations are needed to constrain the models, and redshifts for the faint sources are required to measure the evolution of the infrared luminosity function.

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arXiv2005

The Infrared Array Camera component of the Spitzer Space Telescope Extragalactic First Look Survey

We present Infrared Array Camera (IRAC) data and source catalogs from the Spitzer Space Telescope Extragalactic First Look Survey. The data were taken in four broad bands centered at nominal wavelengths of 3.6, 4.5, 5.8 and 8.0 microns. A set of mosaics and catalogs have been produced which are ~80% complete and ~99% reliable to their chosen flux density limits. The main field survey covers 3.8 deg^2, and has flux density limits of 20muJy, 25muJy, 100muJy and 100muJy at wavelengths of 3.6, 4.5, 5.8 and 8.0 microns,respectively. The deeper ``verification'' survey covers 0.25 deg^2 with limits of 10muJy, 10muJy, 30muJy and 30muJy, respectively. We also include deep data in the ELAIS-N1 field which covers 0.041deg^2 with limits of 4muJy, 3muJy, 10muJy and 10muJy, respectively, but with only two wavelength coverage at a given sky position. The final bandmerged catalogs contain 103193 objects in the main field, 12224 in the verification field and 5239 in ELAIS-N1. Flux densities of high signal-to-noise objects are accurate to about 10%, and the residual systematic error in the absolute flux density scale is ~2-3%. We have successfully extracted sources at source densities as high as 100000 deg^-2 in our deepest 3.6 and 4.5 micron data. The mosaics and source catalogs will be made available through the Spitzer Science Center archive and the Infrared Science Archive.

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arXiv2004

Excitation of Molecular Material Near the Young Stellar Object LkHalpha-234 in NGC 7129

With the Spitzer-IRS we have obtained the first mid-IR spectroscopy of NGC 7129, in the unusually strong outflow and in a ridge of H_2 emission near the Herbig Be star LkHalpha-234. The UV radiation field strength is estimated from PAH band intensities in the H_2 ridge, and from the rotational H_2 emission lines we have deduced aperture average excitation temperatures and column densities in the two regions, finding the H_2 ridge values to be consistent with pumping by UV fluorescence, but also comparable to regions that form H_2 in non-dissociative C-shocks. The H_2 emission in the outflow is consistent with formation by collisional excitation in J-shocks, with shock velocities of 10 - 30 km/sec. A photodissociating component may be present in the outflow, by similarity of S(0) line intensities in both regions. There is no indication of warm dust in the outflow. We also present the first 16um imaging of a Galactic nebula using the unique imaging capabilities of the IRS, and combine with ground-based 2.12um (H_2 1-0 S(1)) imaging. Candidate pre-main sequence objects are clearly evident in these data. We also find extended emission not previously observed around the young B star BD+65 1638, ~22'' across, showing that the region is not free of material as otherwise inferred by recent high angular resolution mapping at submillimeter wavelengths. The presence of this material complicates interpretation of the surrounding CO cavity and origin(s) of the photodissociated region, and further spectroscopic observations are needed to characterize its nature.

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arXiv2004

The Far- and Mid-Infrared/Radio Correlations in the Spitzer Extragalactic First Look Survey

Using the SPITZER SPACE TELESCOPE and the VLA, we present the first DIRECT evidence that the well-known far-infrared/radio correlation is valid to cosmologically significant redshift. We also confirm, with improved statistics compared with previous surveys, a similar result for the Mid-IR/radio correlation. We explore the dependence of monochromatic q_{24} and q_{70} on z. The results were obtained by matching Spitzer sources at 24 and 70 microns with VLA 1.4 GHz micro-Jy radio sources obtained for the SPITZER FLS. Spectroscopic redshifts have been obtained for over 500 matched IR/radio sources using observations at WIYN, Keck and archival SDSS data extending out to z > 2. We find that q_{24} shows significantly more dispersion than q_{70}. By comparing the observed fluxes at 70, 24 and 4.5 microns with a library of SED templates, we find that the larger dispersion in q_{24} is predictable in terms of systematic variations in SED shape throughout the population. Although the models are not able to encompass the full range of observed behavior (both the presence of either extremely flat or extremely steep IR SEDs), the fitting parameters were used to `k-correct' the higher-z galaxies which resulted in a reduced scatter in q. For comparison, we also corrected these data using the SED for M82. The results for 24 and 70 microns provide strong consistent evidence for the universality of the mid-IR/radio and far-IR/radio correlations out to redshifts of at least z = 1.

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arXiv2004

Spitzer 24micron Observations of Optical/Near-IR Selected Extremely Red Galaxies: Evidence for Assembly of Massive Galaxies at z~1-2 ?

We carried out the direct measurement of the fraction of dusty sources in a sample of extremely red galaxies with (R - Ks) > 5.3mag and Ks < 20.2mag, using 24um data from the Spitzer Space Telescope. Combining deep 24um, Ks- and R-band data over an area of 64sq.arcmin in ELAIS N1, we find that 50%+-6% of our ERO sample have measurable 24um flux above the 3sigma flux limit of 40uJy. This flux limit corresponds to a SFR of 12Msun/yr at z~1. The 24um-detected EROs have 24-to-2.2 and 24-to-0.7um flux ratios consistent with infrared luminous, dusty sources at z>1, and an order of magnitude too red to be explained by an infrared quiescent spiral or a pure old stellar population at any redshift. Keck optical spectroscopy of a sample of similarly selected EROs in the FLS field suggests that most of the EROs in ELAIS N1 are probably at z~1. The mean 24um flux (167uJy) of the 24um-detected ERO sample roughly corresponds to the total infrared luminosity of (3-10)x10^(11)Lsun at z=1-1.5, which is similar to that of local LIRGs and ULIGs. The corresponding SFR is ~(50-170)Msun/yr. If the time scale of this starbursting phase is on the order of 10^8yr as inferred for the local LIRGs and ULIGs, the lower limit on the masses of these 24um-detected EROs is (5-20)x10^9Msun. It is plausible that some of the starburst EROs are in the midst of violent transformation to become massive early type galaxies at the epoch of z ~ 1-2.

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arXiv2004

Characterization of Extragalactic 24micron Sources in the Spitzer First Look Survey

In this Letter, we present the initial characterization of extragalactic 24um sources in the Spitzer First Look Survey (FLS) by examining their counterparts at 8um and R-band. The color-color diagram of 24-to-8 vs. 24-to-0.7um is populated with 18,734 sources brighter than the 3sigma flux limit of 110uJy, over an area of 3.7sq.degrees. The 24-to-0.7um colors of these sources span almost 4 orders of magnitudes, while the 24-to-8um colors distribute at least over 2 orders of magnitudes. In addition to identifying ~30% of the total sample with infrared quiescent, mostly low redshift galaxies, we also found that: (1) 23% of the 24um sources (~1200/sq.degrees) have very red 24-to-8 and 24-to-0.7 colors and are probably infrared luminous starbursts with L(IR)>3x10^(11)Lsun at z>1. In particular, 13% of the sample (660/sq.degrees) are 24um detected only, with no detectable emission in either 8um or R-band. These sources are the candidates for being ULIRGs at z>2. (2) 2% of the sample (85/sq.degrees) have colors similar to dust reddened AGNs, like Mrk231 at z~0.6-3. (3) We anticipate that some of these sources with extremely red colors may be new types of sources, since they can not be modelled with any familiar type of spectral energy distribution. We find that 17% of the 24um sources have no detectable optical counterparts brighter than R limit of 25.5mag. Optical spectroscopy of these optical extremely faint 24um sources would be very difficult, and mid-infrared spectroscopy from the Spitzer would be critical for understanding their physical nature (Abridged).

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arXiv2004

Obscured and unobscured active galactic nuclei in the Spitzer Space Telescope First Look Survey

Selection of active galactic nuclei (AGN) in the infrared allows the discovery of AGN whose optical emission is extinguished by dust. In this paper, we use the Spitzer Space Telescope First Look Survey (FLS) to assess what fraction of AGN with mid-infrared luminosities comparable to quasars are missed in optical quasar surveys due to dust obscuration. We begin by using the Sloan Digital Sky Survey (SDSS) database to identify 54 quasars within the 4 deg^2 extragalactic FLS. These quasars occupy a distinct region in mid-infrared color space by virtue of their strong, red, continua. This has allowed us to define a mid-infrared color criterion for selecting AGN candidates. About 2000 FLS objects have colors consistent with them being AGN, but most are much fainter in the mid-infrared than the SDSS quasars, which typically have 8 micron flux densities, S(8.0), ~1 mJy. We have investigated the properties of the 43 objects with S(8.0) >= 1 mJy satisfying our AGN color selection. This sample should contain both unobscured quasars, and AGN which are absent from the SDSS survey due to extinction in the optical. After removing 16 known quasars, three probable normal quasars, and eight spurious or confused objects from the initial sample of 43, we are left with 16 objects which are likely to be obscured quasars or luminous Seyfert-2 galaxies. This suggests the numbers of obscured and unobscured AGN are similar in samples selected in the mid-infrared at S(8.0)~1 mJy.

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