arXiv subjects

D. T. Frayer

Publications and source records attributed to D. T. Frayer.

At least 55 records · Page 3Linked to original sources

arXiv2007

Absolute Calibration and Characterization of the Multiband Imaging Photometer for Spitzer. III. An Asteroid-based Calibration of MIPS at 160 microns

We describe the absolute calibration of the Multiband Imaging Photometer for Spitzer (MIPS) 160 micron channel. After the on-orbit discovery of a near-IR ghost image that dominates the signal for sources hotter than about 2000 K, we adopted a strategy utilizing asteroids to transfer the absolute calibrations of the MIPS 24 and 70 micron channels to the 160 micron channel. Near-simultaneous observations at all three wavelengths are taken, and photometry at the two shorter wavelengths is fit using the Standard Thermal Model. The 160 micron flux density is predicted from those fits and compared with the observed 160 micron signal to derive the conversion from instrumental units to surface brightness. The calibration factor we derive is 41.7 MJy/sr/MIPS160 (MIPS160 being the instrumental units). The scatter in the individual measurements of the calibration factor, as well as an assesment of the external uncertainties inherent in the calibration, lead us to adopt an uncertainty of 5.0 MJy/sr/MIPS160 (12%) for the absolute uncertainty on the 160 micron flux density of a particular source as determined from a single measurement. For sources brighter than about 2 Jy, non-linearity in the response of the 160 micron detectors produces an under-estimate of the flux density: for objects as bright as 4 Jy, measured flux densities are likely to be ~20% too low. This calibration has been checked against that of ISO (using ULIRGS) and IRAS (using IRAS-derived diameters), and is consistent with those at the 5% level.

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arXiv2007

Absolute Calibration and Characterization of the Multiband Imaging Photometer for Spitzer. I. The Stellar Calibrator Sample and the 24 micron Calibration

We present the stellar calibrator sample and the conversion from instrumental to physical units for the 24 micron channel of the Multiband Imaging Photometer for Spitzer (MIPS). The primary calibrators are A stars, and the calibration factor based on those stars is 4.54*10^{-2} MJy sr^{-1} (DN/s)^{-1}, with a nominal uncertainty of 2%. We discuss the data-reduction procedures required to attain this accuracy; without these procdures, the calibration factor obtained using the automated pipeline at the Spitzer Science Center is 1.6% +/- 0.6% lower. We extend this work to predict 24 micron flux densities for a sample of 238 stars which covers a larger range of flux densities and spectral types. We present a total of 348 measurements of 141 stars at 24 micron. This sample covers a factor of ~460 in 24 micron flux density, from 8.6 mJy up to 4.0 Jy. We show that the calibration is linear over that range with respect to target flux and background level. The calibration is based on observations made using 3-second exposures; a preliminary analysis shows that the calibration factor may be 1% and 2% lower for 10- and 30-second exposures, respectively. We also demonstrate that the calibration is very stable: over the course of the mission, repeated measurements of our routine calibrator, HD 159330, show a root-mean-square scatter of only 0.4%. Finally, we show that the point spread function (PSF) is well measured and allows us to calibrate extended sources accurately; Infrared Astronomy Satellite (IRAS) and MIPS measurements of a sample of nearby galaxies are identical within the uncertainties.

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arXiv2007

Measuring PAH Emission in Ultradeep Spitzer IRS Spectroscopy of High Redshift IR Luminous Galaxies

The study of the dominant population of high redshift IR-luminous galaxies (10^11 - 10^12 Lsun at 1<z<3), requires observation of sources at the ~0.1 mJy level in the mid-IR. We present the deepest spectra taken to date with the Infrared Spectrograph (IRS) on the Spitzer Space Telescope. We targeted two faint (f24~0.15 mJy) sources in the Southern GOODS field at z=1.09 and z=2.69. Spectra of the lower redshift target were taken in the observed-frame 8--21 micron range, while the spectrum of the higher redshift target covered 21--37 microns. We also present the spectra of two secondary sources within the slit. We detect strong PAH emission in all four targets, and compare the spectra to those of local galaxies observed by the IRS. The z=1.09 source appears to be a typical, star-formation dominated IR-luminous galaxy, while the z=2.69 source is a composite source with strong star formation and a prominent AGN. The IRAC colors of this source show no evidence of rest-frame near-infrared stellar photospheric emission. We demonstrate that an AGN which contributes only a small (~10%) fraction of the bolometric luminosity can produce enough hot dust emission to overwhelm the near-IR photospheric emission from stars. Such sources would be excluded from photometric surveys which rely on the near-IR bump to identify starbursts, leading to an underestimate of the star formation rate density.

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arXiv2007

The Spitzer Legacy Survey of the HST-ACS 2 sq. deg. COSMOS Field: survey strategy and first analysis

The Spitzer-COSMOS survey (S-COSMOS) is a Legacy program (Cycles 2+3) designed to carry out a uniform deep survey of the full 2 sq deg COSMOS field in all seven Spitzer bands (3.6, 4.5, 5.6, 8.0, 24.0, 70.0, 160.0 u). This paper describes the survey parameters, mapping strategy, data reduction procedures, achieved sensitivities to date, and the complete data set for future reference. We show that the observed infrared backgrounds in the S-COSMOS field are within 10% of the predicted background levels. The fluctuations in the background at 24u have been measured and do not show any significant contribution from cirrus, as expected. In addition, we report on the number of asteroid detections in the low galactic latitude COSMOS field. We use the Cycle 2 S-COSMOS data to determine preliminary number counts, and compare our results with those from previous Spitzer Legacy surveys (e.g. SWIRE, GOODS). The results from this "first analysis" confirm that the S-COSMOS survey will have sufficient sensitivity with IRAC to detect ~ L* disks and spheroids out to z ~ 3, and with MIPS to detect ultraluminous starbursts and AGN out to z ~3 at 24u and out to z ~1.5-2 at 70u and 160u.

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arXiv2006

Spitzer 70-micron Source Counts in GOODS-North

We present ultra-deep Spitzer 70-micron observations of GOODS-North. For the first time, the turn-over in the 70-micron Euclidean-normalized differential source counts is observed. We derive source counts down to a flux density of 1.2mJy. From the measured source counts and fluctuation analysis, we estimate a power-law approximation of the faint 70-micron source counts of dN/dS proportional to S^{-1.6}, consistent with that observed for the faint 24-micron sources. An extrapolation of the 70-micron source counts to zero flux density implies a total extragalactic background light (EBL) of 7.4+/-1.9 nW m^{-2} sr^{-1}. The source counts above 1.2mJy account for about 60% of the estimated EBL. From fluctuation analysis, we derive a photometric confusion level of sigma_c = 0.30+/-0.15 mJy (q=5) for the Spitzer 70-micron band.

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arXiv2006

Spitzer Massive Lensing Cluster Survey

We are currently undertaking a Spitzer GTO program to image ~30 massive lensing clusters at moderate redshift with both IRAC and MIPS. By taking advantage of the gravitatinoal lensing power of these clusters, we will study the population of faint galaxies that are below the nominal Spitzer detection limits. Here, we present a few examples of our science programs.

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arXiv2006

Spitzer Observations of the Brightest Galaxies in X-ray-Luminous Clusters

We have studied the infrared properties of the brightest cluster galaxies (BCGs) located in the cores of X-ray-luminous clusters at 0.15 < z < 0.35. The majority of the BCGs are not particularly infrared-luminous compared with other massive early-type galaxies, suggesting that the cluster environment has little influence on the infrared luminosities of the BCGs. The exceptions, however, are the BCGs in the three X-ray-brightest clusters in the sample, A1835, Z3146, and A2390. These BCGs have a prominent far-infrared peak in their spectral energy distributions (SEDs), and two of them (those in A1835 and Z3146) can be classified as luminous infrared galaxies (LIRGs: L_{IR} > 10^{11} L_{sun}). Although radio AGNs are found to be prevalent among the BCGs, the infrared luminosities of these three BCGs, judged from the infrared SED signatures, are likely to be powered by star formation. Considering the overall trend that clusters with shorter radiative gas cooling times harbor more infrared-luminous BCGs, the enhanced star formation may be caused by the cooling cluster gas accreting onto the BCGs.

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arXiv2006

The Spitzer Space Telescope Extra-Galactic First Look Survey: 24 micron data reduction, catalog, and source identification

We present the reduction of the 24 micron data obtained during the first cosmological survey performed by the Spitzer Space Telescope (First Look Survey, FLS). The survey consists of a shallow observation of 2.5x2 sq deg centered at 17h18m +59d30m (main survey) and a deeper observation of 1x0.5 sq deg centered at 17h17m +59d45m(verification survey). Issues with the reduction of the 24 micron MIPS data are discussed and solutions to attenuate instrumental effects are proposed and applied to the data. Approximately 17000 sources are extracted with a SNR greater than five. The photometry of the point sources is evaluated through PSF fitting using an empirical PSF derived from the data. Aperture corrections and the absolute calibration have been checked using stars in the field. Astrometric and photometric errors depend on the SNR of the source varying between 0.35-1 arcsec and 5-15%, respectively, for sources detected at 20-5 sigma. The flux of the 123 extended sources have been estimated through aperture photometry. The extended sources cover less than 0.3% of the total area of the survey. Based on simulations, the main and verification surveys are 50% complete at 0.3 and 0.15 mJy, respectively. Counterparts have been searched for in optical and radio catalogs. More than 80% of the 24 micron sources have a reliable optical counterpart down to R=25.5. 16% of the sources have a 20 cm counterpart down to 0.1 mJy and ~ 80% of the radio-infrared associations have a reliable optical counterpart. A residual map is obtained by subtracting point sources detected at the 3-sigma level and interpolating the regions occupied by extended sources. Several galactic clouds with low and intermediate velocities are identified by comparison with neutral Hydrogen data from this field.

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arXiv2005

Star Formation Rates and Extinction Properties of IR-Luminous Galaxies in the Spitzer First Look Survey

We investigate the instantaneous star formation rates (SFR) and extinction properties for a large (N=274), near-infrared (2.2 micron) + mid-infrared (24 micron) selected sample of normal to ultra-luminous infrared galaxies (ULIRGs) [10^9 ~0.8 in the Spitzer Extragalactic First Look Survey. We combine Spitzer MIPS 24-micron observations with high-resolution, optical Keck Deimos spectroscopy to derive optical emission-line and infrared star formation rates (SFR_{opt} & SFR_{IR}, respectively). Direct comparison of these SFR diagnostics reveals that our sample exhibits a wide range of extinction (1.0 1, which make up a large fraction of our sample, have SFR~100 M_{sun}/yr and ~2.5 mag. This translates to a 97% mean attenuation of the [OII] forbidden line doublet, with the most extreme sources having as much as 99.7% of their [OII] line flux extinguished by dust. Based on a SFR_{IR}/SFR_{opt} diagnostic, we derive an IR-luminosity-dependent Av^{IR} function [Av^{IR}=0.75*log(L_{IR}/L_{sun})-6.35 mag] that we use to extinction correct our emission line luminosities. Application of this correction results in a correlation between SFR_{IR} and SFR_{opt} that has a dispersion of 0.2 dex. Investigation of the Av dependence on redshift reveals that for a fixed L_{IR}, there is no significant Av evolution. The mean attenuation of our sample is intermediate between that of local optical/UV- and radio-selected samples and has a marginally stronger L_{IR} dependence.

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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

MIPS J142824.0+352619: A Hyperluminous Starburst Galaxy at z=1.325

Using the SHARC-II camera at the Caltech Submillimeter Observatory to obtain 350 micron images of sources detected with the MIPS instrument on Spitzer, we have discovered a remarkable object at z=1.325+/-0.002 with an apparent Far-Infrared luminosity of 3.2(+/-0.7) x 10^13 Lsun. Unlike other z>1 sources of comparable luminosity selected from mid-IR surveys, MIPS J142824.0+352619 lacks any trace of AGN activity, and is likely a luminous analog of galaxies selected locally by IRAS, or at high redshift in the submillimeter. This source appears to be lensed by a foreground elliptical galaxy at z=1.034, although the amplification is likely modest (~10). We argue that the contribution to the observed optical/Near-IR emission from the foreground galaxy is small, and hence are able to present the rest-frame UV through radio Spectral Energy Distribution of this galaxy. Due to its unusually high luminosity, MIPS J142824.0+352619 presents a unique chance to study a high redshift dusty starburst galaxy in great detail.

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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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arXiv2005

Molecular Gas and Nuclear Activity in Radio Galaxies Detected by IRAS

This paper reports the latest results from a millimeter-wave (CO) spectroscopic survey of IRAS-detected radio galaxies with L_1.4GHz ~ 10^23-28 W/Hz in the redshift range z ~ 0.02-0.15. The IRAS flux-limited sample contains 33 radio galaxies with different radio morphologies and a broad range of infrared luminosities L_IR = 10^9-12 L_sun), allowing for an investigation of (a) whether low-z radio-selected AGN reside in molecular gas-rich host galaxes, and (b) whether the CO properties are correlated with the properties of the host galaxy or the AGN. All of the radio galaxies in Mazzarella et al. (1993) and Mirabel et al. (1989) have been reobserved. Three new CO detections have been made, raising the total number of CO detections to nine and setting the survey detection rate at ~ 25%. Many of the CO lines have double-peaked profiles, and the CO line widths are broad (average Delta v_FWHM ~ 500+/-130 km/s), exceeding the average CO widths of both ultraluminous infrared galaxies (300+/-90 km/s) and Palomar-Green QSOs (260+/-160 km/s), and thus being indicative of massive host galaxies. The CO luminosities translate into molecular gas masses of ~ 0.4-7x10^9 M_sun, however, the 3-sigma CO upper limits for nondetections do not rule out a molecular gas mass as high as that of the Milky Way (~ 3x10^9 M_sun). Optical images of eight out of nine molecular gas-rich radio galaxies show evidence of close companions and/or tidal features. Finally, there is no obvious correlation between radio power and molecular gas mass. However, it is notable that only one F-R II galaxy out of 12 is detected in this CO survey; the remaining detections are of galaxies hosting F-R I and compact radio jets.

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arXiv2005

MIPS 70-micron Observations of the Spitzer Extragalactic First Look Survey

Early results from the 70-micron observations of the Spitzer Extragalactic First Look Survey are presented. As a whole, about 90% of the population show infrared colors that are consistent with the spectral energy distributions of the local IRAS population of luminous infrared starbursts, while approximately 10% of the sample show warm infrared colors consistent with AGN activity. The mean redshift for the population is z=0.2, and the mean total infrared luminosity is about L(ir)= 2x10^{11} L(sun).

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arXiv2005

Reduction Algorithms for the Multiband Imaging Photometer for Spitzer: 6 Months of Flight Data

The first six months of flight data from the Multiband Imaging Photometer for Spitzer (MIPS) were used to test MIPS reduction algorithms based on extensive preflight laboratory data and modeling. The underlying approach for the preflight algorithms has been found to be sound, but some modifications have improved the performance. The main changes are scan mirror dependent flat fields at 24 micron, hand processing to remove the time dependent stim flash latents and fast/slow response variations at 70 micron, and the use of asteroids and other sources instead of stars for flux calibration at 160 micron due to a blue ``leak.'' The photometric accuracy of flux measurpements is currently 5%, 10%, and 20% at 24, 70, and 160 micron, respectively. These numbers are expected to improve as more flight data are analyzed and data reduction algorithms refined.

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arXiv2005

Reduction Algorithms for the Multiband Imaging Photometer for Spitzer

We describe the data reduction algorithms for the Multiband Imaging Photometer for Spitzer (MIPS) instrument. These algorithms were based on extensive preflight testing and modeling of the Si:As (24 micron) and Ge:Ga (70 and 160 micron) arrays in MIPS and have been refined based on initial flight data. The behaviors we describe are typical of state-of-the-art infrared focal planes operated in the low backgrounds of space. The Ge arrays are bulk photoconductors and therefore show a variety of artifacts that must be removed to calibrate the data. The Si array, while better behaved than the Ge arrays, does show a handful of artifacts that also must be removed to calibrate the data. The data reduction to remove these effects is divided into three parts. The first part converts the non-destructively read data ramps into slopes while removing artifacts with time constants of the order of the exposure time. The second part calibrates the slope measurements while removing artifacts with time constants longer than the exposure time. The third part uses the redundancy inherit in the MIPS observing modes to improve the artifact removal iteratively. For each of these steps, we illustrate the relevant laboratory experiments or theoretical arguments along with the mathematical approaches taken to calibrate the data. Finally, we describe how these preflight algorithms have performed on actual flight data.

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arXiv2004

The First Measurements of Galaxy Clustering from IRAC Data of the Spitzer First Look Survey

We present the first results of the angular auto-correlation function of the galaxies detected by the Infrared Array Camera (IRAC) instrument in the First Look Survey (FLS) of the Spitzer Space Telescope. We detect significant signals of galaxy clustering within the survey area. The angular auto-correlation function of the galaxies detected in each of the four IRAC instrument channels is consistent with a power-law form $w(θ)=Aθ^{1-γ}$ out to $θ= 0.2\arcdeg$, with the slope ranging from $γ= 1.5$ to 1.8. We estimate the correlation amplitudes $A$ to be $2.95 \times 10^{-3}$, $2.03 \times 10^{-3}$, $4.53 \times 10^{-3}$, and $2.34 \times 10^{-3}$ at $θ=1\arcdeg$ for galaxies detected in the IRAC 3.6$μ$m, 4.5$μ$m, 5.8$μ$m, and 8.0$μ$m instrument channels, respectively. We compare our measurements at 3.6$μ$m with the previous K-band measurements, and discuss the implications of these results.

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arXiv2004

Far Infrared Source Counts at 70 and 160 microns in Spitzer Deep Surveys

We derive galaxy source counts at 70 and 160 microns using the Multiband Imaging Photometer for Spitzer (MIPS) to map the Chandra Deep Field South (CDFS) and other fields. At 70 microns, our observations extend upwards about 2 orders of magnitude in flux density from a threshold of 15 mJy, and at 160 microns they extend about an order of magnitude upward from 50 mJy. The counts are consistent with previous observations on the bright end. Significant evolution is detected at the faint end of the counts in both bands, by factors of 2-3 over no-evolution models. This evolution agrees well with models that indicate most ofthe faint galaxies lie at redshifts between 0.7 and 0.9. The new Spitzer data already resolve about 23% of the Cosmic Far Infrared Background at 70 microns and about 7% at 160 microns.

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