arXiv subjects

M. Brodwin

Publications and source records attributed to M. Brodwin.

At least 127 records · Page 7Linked to original sources

arXiv2007

The Local Galaxy 8 micron Luminosity Function

A SST survey in the NOAO Deep-Wide Field in Boötes provides a complete, 8-micron-selected sample of galaxies to a limiting (Vega) magnitude of 13.5. In the 6.88 deg$^2$ field sampled, 79% of the 4867 galaxies have spectroscopic redshifts, allowing an accurate determination of the local (z<0.3) galaxy luminosity function. Stellar and dust emission can be separated on the basis of observed galaxy colors. Dust emission (mostly PAH) accounts for 80% of the 8 micron luminosity, stellar photospheres account for 19%, and AGN emission accounts for roughly 1 %. A sub-sample of the 8 micron-selected galaxies have blue, early-type colors, but even most of these have significant PAH emission. The luminosity functions for the total 8 micron luminosity and for the dust emission alone are both well fit by Schechter functions. For the 8 micron luminosity function, the characteristic luminosity is νL_ν^*(8.0 \micron) = 1.8 \times 10^{10}$ \Lsun while for the dust emission alone it is 1.6 x 10^{10}$ \Lsun\null. The average 8 \micron luminosity density at z<0.3 is 3.1 x 10^7 \Lsun Mpc^{-3}, and the average luminosity density from dust alone is 2.5 x 10^7 \Lsun Mpc^{-3}. This luminos ity arises predominantly from galaxies with 8 \micron luminosities ($νL_ν$) between $2\times 10^9$ and $2 x 10^{10}$ \Lsun, i.e., normal galaxies, not LIRGs or ULIRGs.

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arXiv2006

A SCUBA/Spitzer Investigation of the Far Infra-Red Extragalactic Background

We have measured the contribution of submillimeter and mid-infrared sources to the extragalactic background radiation at 70 and 160um. Specifically, we have stacked flux in 70 and 160um Spitzer Space Telescope (Spitzer) observations of the Canada-UK Deep Sub-millimeter Survey 14h field at the positions of 850um sources detected by SCUBA and also 8 and 24um sources detected by Spitzer. We find that per source, the SCUBA galaxies are the strongest and the 8um sources the weakest contributors to the background flux at both 70 and 160um. Our estimate of the contribution of the SCUBA sources is higher than previous estimates. However, expressed as a total contribution, the full 8um source catalogue accounts for twice the total 24um source contribution and ~10 times the total SCUBA source contribution. The 8um sources account for the majority of the background radiation at 160um with a flux of 0.87+/-0.16 MJy/sr and at least a third at 70um with a flux of 0.103+/-0.019 MJy/sr. These measurements are consistent with current lower limits on the background at 70 and 160um. Finally, we have investigated the 70 and 160um emission from the 8 and 24um sources as a function of redshift. We find that the average 70um flux per 24um source and the average 160um flux per 8 and 24um source is constant over all redshifts, up to z~4. In contrast, the low-redshift half (z<1) of the of 8um sample contributes approximately four times the total 70um flux of the high-redshift half. These trends can be explained by a single non-evolving SED.

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arXiv2006

A rich bounty of AGN in the 9 square degree Bootes survey: high-z obscured AGN and large-scale structure

We use observations from the 9 square degree multiwavelength survey in Bootes to identify hundreds of obscured active galactic nuclei (AGN) with high redshifts (z > 0.7), luminosities (L_bol > 10^45 ergs/s), and moderate obscuring columns (N_H > 10^22 cm^-2), and to measure the clustering properties of X-ray AGN at z > 1. In the Bootes region, shallow (5 ks) Chandra X-ray observations have detected ~4,000 X-ray sources, and the same region has been mapped with deep optical imaging and by Spitzer IRAC, which detects ~300,000 point sources, of which ~30,000 have detections in all four IRAC bands, for which we can select AGN on the basis of their mid-IR colors. With the MMT/Hectospec we have obtained modest resolution optical spectra for about half the X-ray sources (out to z > 3) and ~20,000 galaxies (out to z = 0.7). With this multiwavelength data we select >400 AGN per square degree (compared to 12 per square degree from SDSS). Among a sample of IRAC-selected AGN we identify 641 candidate obscured objects based on their R band and IRAC luminosities. We use X-ray stacking techniques to verify that they are obscured AGN and measure their absorbing column densities. We also measure the three-dimensional two-point correlation function for X-ray selected AGN.

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arXiv2006

Mid-Infrared Selection of Brown Dwarfs and High-Redshift Quasars

We discuss color selection of rare objects in a wide-field, multiband survey spanning from the optical to the mid-infrared. Simple color criteria simultaneously identify and distinguish two of the most sought after astrophysical sources: the coolest brown dwarfs and the most distant quasars. We present spectroscopically-confirmed examples of each class identified in the IRAC Shallow Survey of the Bootes field of the NOAO Deep Wide-Field Survey. ISS J142950.9+333012 is a T4.5 brown dwarf at a distance of approximately 42 pc, and ISS J142738.5+331242 is a radio-loud quasar at redshift z=6.12. Our selection criteria identify a total of four candidates over 8 square degrees of the Bootes field. The other two candidates are both confirmed 5.5<z<6 quasars, previously reported by Cool et al. (2006). We discuss the implications of these discoveries and conclude that there are excellent prospects for extending such searches to cooler brown dwarfs and higher redshift quasars.

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arXiv2006

The Canada-France Deep Fields III: Photometric Redshift Distribution to I(AB) ~ 24

We compute accurate redshift distributions to I(AB) = 24 and R(AB) = 24.5 using photometric redshifts estimated from six-band UBVRIZ photometry in the Canada-France Deep Fields-Photometric Redshift Survey (CFDF-PRS). Our photometric redshift algorithm is calibrated using hundreds of CFRS spectroscopic redshifts in the same fields. The dispersion in redshift is σ/(1+z) \la 0.04 to the CFRS depth of I(AB) = 22.5, rising to σ/(1+z) \la 0.06 at our nominal magnitude and redshift limits of I(AB) = 24 and z \le 1.3, respectively. We describe a new method to compute N(z) that incorporates the full redshift likelihood functions in a Bayesian iterative analysis and we demonstrate in extensive Monte Carlo simulations that it is superior to distributions calculated using simple maximum likelihood redshifts. The field-to-field differences in the redshift distributions, while not unexpected theoretically, are substantial even on 30' scales. We provide I(AB) and R(AB) redshift distributions, median redshifts, and parametrized fits of our results in various magnitude ranges, accounting for both random and systematic errors in the analysis.

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arXiv2006

Photometric Redshifts in the IRAC Shallow Survey

Accurate photometric redshifts are calculated for nearly 200,000 galaxies to a 4.5 micron flux limit of ~13 uJy in the 8.5 deg^2 Spitzer/IRAC Shallow survey. Using a hybrid photometric redshift algorithm incorporating both neural-net and template-fitting techniques, calibrated with over 15,000 spectroscopic redshifts, a redshift accuracy of σ= 0.06(1+z) is achieved for 95% of galaxies at 0 1) galaxy clusters. We present one such spectroscopically confirmed cluster at =1.24, ISCS J1434.5+3427. Finally, we present a measurement of the 4.5 micron-selected galaxy redshift distribution.

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arXiv2006

Mid-Infrared Identifications of SCUBA Galaxies in the CUDSS 14-Hour Field with the Spitzer Space Telescope

We identify 17 possible 8.0 micron-selected counterparts to the submillimeter galaxies in the CUDSS 14-hour field, derived from deep imaging carried out with the IRAC and MIPS instruments aboard the Spitzer Space Telescope. Ten of the 17 counterparts are not the same as those previously identified at shorter wavelengths. We argue that 8.0 micron selection offers a better means for identifying counterparts to submillimeter galaxies than near-infrared or optical selection. Based on the panchromatic SEDs, most counterparts appear to be powered by ongoing star formation. Power-law fits to the SEDs suggest that five objects in the 8.0 micron-selected counterpart sample harbor dominant AGNs; a sixth object is identified as a possible AGN. The 3.6 to 8.0 micron colors of the infrared-selected counterparts are significantly redder than the general IRAC galaxy population in the CUDSS 14-hour field.

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arXiv2006

X-ray and infrared properties of galaxies and AGNs in the 9 square degree Bootes field

We examine the X-ray and infrared properties of galaxies and AGNs in the 9 square degree Bootes field, using data from the Chandra XBootes and Spitzer IRAC Shallow Surveys, as well as optical spectroscopy from the AGES survey. A sample of ~30,000 objects are detected in all four IRAC bands, of which ~2,000 are associated with X-ray sources. We also study X-ray fainter sources using stacking techniques, and find that X-ray fluxes are highest for objects with IRAC colors that are known to be characteristic of AGNs. Because these are shallow, wide-field surveys, they probe the bright end of the AGNluminosity function out to spectroscopic redshifts as high as z=3-4. We can use this multiwavelength dataset to explore the properties and redshift evolution of a large sample of luminous active galaxies.

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arXiv2005

An investigation of the submillimeter background radiation using SCUBA and Spitzer

We investigate the redshift dependence of the contribution to the extragalactic far-infrared/sub-millimeter background from galaxies detected by the Spitzer Space Telescope at 8um and 24um. Using seven-band optical to mid-infrared photometry, we estimate photometric redshifts for the Spitzer sources which appear to be mostly L* galaxies at a median redshift of z=1.0. These sources, extracted from deep 8um and 24um mosaics of the CUDSS 14-hour field with 5sigma limits of 5.8uJy and 70uJy respectively, exhibit significant 850um and 450um emission as observed by SCUBA. At 850um, after removing >=4sigma sources and those securely identified in our previous cross-matching paper, we measure stacked flux at the significance level of 4.4sigma and 2.9sigma from the full 8um and 24um galaxy catalogue respectively. At 450um, flux is detected from all 8um galaxies at the level of 3.5sigma, while there is no significant emission from the 24um galaxies. We find that the 850um flux is emitted almost exclusively at z>~1.3 from the Spitzer sources with 0.44mJy (4.7sigma) per 8um source and 0.51mJy (2.8sigma) per 24um source. This corresponds to a contribution of (16+/-3)% toward the 850um extra-galactic background from the 8um sources and (5.0+/-1.8)% from the 24um sources. At 450um, only the 8um sources within the redshift interval 1<z<2 exhibit significant emission with an average flux per source of 3.35mJy (3.0sigma). This is a contribution of (37+/-12)% to the 450um background.

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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

Near-Infrared Spectroscopy of 0.4<z<1.0 CFRS Galaxies: Oxygen Abundances, SFRs and Dust

Using new J-band VLT-ISAAC and Keck-NIRSPEC spectroscopy, we have measured Halpha and [NII] line fluxes for 0.47 0.1 for most (but not all) of the CFRS galaxies indicate that they lie on the high-metallicity branch of the R23 calibration; d) about one third of the 0.47<z<0.92 CFRS galaxies in our sample have lower metallicities than local galaxies with similar luminosities and star formation rates; e) comparison with a chemical evolution model indicates that these low metallicity galaxies are unlikely to be the progenitors of metal-poor dwarf galaxies at z~0.

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arXiv2005

XMM-Newton Surveys of the Canada-France Redshift Survey Fields - III: The Environments of X-ray Selected AGN at 0.4<z<0.6

The environmental properties of a sample of 31 hard X-ray selected AGN are investigated, from scales of 500 kpc down to 30 kpc, and are compared to a control sample of inactive galaxies. The AGN all lie in the redshift range 0.4 =0 clusters. It is suggested that minor mergers with low mass companions is a likely candidate for the mechanism by which these modest luminosity AGN are fuelled.

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arXiv2005

Discovery of a Large ~200 kpc Gaseous Nebula at z=2.7 with the Spitzer Space Telescope

We report the discovery of a very large, spatially extended Ly alpha -emitting nebula at z=2.656 associated with a luminous mid-infrared source. The bright mid-infrared source (F(24um)=0.86 mJy) was first detected in observations made using the Spitzer Space Telescope. Existing broad-band imaging data from the NOAO Deep Wide-Field Survey revealed the mid-infrared source to be associated with a diffuse, spatially extended, optical counterpart in the Bw band. Spectroscopy and further imaging of this target reveals that the optical source is an almost purely line-emitting nebula with little, if any, detectable diffuse continuum emission. The Lya nebula has a luminosity of L[Lya] ~ 1.7e44 erg/s and an extent of at least 20 arcsec (160 kpc). Its central ~8 arcsec shows an ordered, monotonic velocity profile; interpreted as rotation, this region encloses a mass M = 6e12 Msun. Several sources lie within the nebula. The central region of the nebula shows narrow (~365 km/s) emission lines of CIV and HeII. The mid-infrared source is a compact object lying within the nebula, but offset from the center by a projected distance of ~2.5 arcsec (20 kpc), and likely to be an enshrouded AGN. A young star-forming galaxy lies near the northern end of the nebula. We suggest that the nebula is a site of recent multiple galaxy and AGN formation, with the spatial distribution of galaxies within the nebula perhaps tracking the formation history of the system.

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arXiv2004

The IRAC Shallow Survey

The IRAC shallow survey covers 8.5 square degrees in the NOAO Deep Wide-Field Survey in Bootes with 3 or more 30 second exposures per position. An overview of the survey design, reduction, calibration, star-galaxy separation, and initial results is provided. The survey includes approximately 370,000, 280,000, 38,000, and 34,000 sources brighter than the 5 sigma limits of 6.4, 8.8, 51, and 50 microJy at 3.6, 4.5, 5.8, and 8 microns respectively, including some with unusual spectral energy distributions.

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arXiv2004

Number Counts At 3 < lambda < 10 um From the Spitzer Space Telescope

Infrared source counts at wavelengths 3 < lambda < 10 um cover more than 10 magnitudes in source brightness, four orders of magnitude in surface density, and reach an integrated surface density of 10^5 sources/deg^2. At m<14 mag, most of the sources are Galactic stars, in agreement with models. After removal of Galactic stars, galaxy counts are consistent with what few measurements exist at nearby wavelengths. At 3.6 and 4.5 um, the galaxy counts follow the expectations of a Euclidean world model down to ~16 mag and drop below the Euclidean curve for fainter magnitudes. Counts at these wavelengths begin to show decreasing completeness around magnitude 19.5. At 5.8 and 8 um, the counts relative to a Euclidean world model show a large excess at bright magnitudes. This is probably because local galaxies emit strongly in the aromatic dust (``PAH'') features. The counts at 3.6 um resolve <50% of the Cosmic Infrared Background at that wavelength.

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arXiv2004

XMM-Newton Surveys of the Canada-France Redshift Survey Fields - II: The X-ray Catalogues, the Properties of the Host Galaxies, and the Redshift Distribution

We present the X-ray source catalogues for the XMM surveys of the 3-h and 14-h Canada-France Redshift Survey fields (0.5-10 keV flux range ~2E-15 - 1E-13 erg cm^-2 s^-1). We use a subset of the XMM sources, which have Chandra positions, to determine the best method of obtaining optical identifications of sources with only XMM positions. We find optical identifications for 79% of the XMM sources for which there are deep optical images. The sources without optical identifications are likely to be optically fainter and have higher redshifts than the sources with identifications. We have estimated `photometric redshifts' for the identified sources, calibrating our method using ~200 galaxies in the fields with spectroscopic redshifts. We find that the redshift distribution has a strong peak at z~0.7. The host galaxies of AGN identified in this work cover a wide range of optical properties with every galaxy type being represented, and no obvious preference for one type over another. Redder types tend to be more luminous than blue types, particularly at lower redshifts. The host galaxies also span a wide range of optical luminosity, in contrast to the narrow range found for the starburst galaxies detected in micro Jy radio surveys. We find a strong correlation between optical and X-ray luminosity similar to the Magorrian relation, although selection effects cannot be ruled out.

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arXiv2003

The Canada-France deep fields survey-II: Lyman-break galaxies and galaxy clustering at z~3

(abridged) We present a large sample of z~3 U- band dropout galaxies extracted from the Canada-France deep fields survey (CFDF). Our catalogue covers an effective area of ~1700 arcmin^2 divided between three large, contiguous fields separated widely on the sky. To IAB=24.5, the survey contains 1294 Lyman-break candidates, in agreement with previous measurements by other authors. Based on comparisons with spectroscopic observations and simulations, we estimate that our sample of Lyman-break galaxies is contaminated by stars and interlopers at no more than ~30%. We find that ω(θ) is well fitted by a power-law of fixed slope, γ=1.8, even at small (θ<10'') angular separations. In two of our three fields, we are able to fit simultaneously for both the slope and amplitude and find a slope γ~ 1.81. Our data marginally indicates in one field (at a 3 σlevel) that the Lyman-break correlation length r_0 depends on sample limiting magnitude: brighter Lyman-break galaxies are more clustered than fainter ones. For the entire CFDF sample, assuming a fixed slope γ= 1.8 we find r_0 = (5.9\pm0.5)h^{-1} Mpc. Using these clustering measurements and prediction for the dark matter density field, we derive a linear bias of b = 3.5 +/- 0.3. Finally we show that the dependence of the correlation length with the surface density of Lyman-break galaxies is in good agreement with a simple picture where more luminous galaxies are hosted by more massive dark matter halos with a simple one-to-one correspondence.

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arXiv2002

The Canada-UK Deep Submillimeter Survey V: The Submillimeter Properties of Lyman-Break Galaxies

We have used 850$μ$m maps obtained as part of the Canada-UK Deep Submillimeter Survey (CUDSS) to investigate the sub-mm properties of Lyman-break galaxies (LBGs). We used three samples of Lyman-break galaxies: two from the Canada-France Deep Fields (CFDF) survey covering CUDSS-14 and CUDSS-3, and one from Steidel and collaborators also covering CUDSS-14. We measure a mean flux from both CFDF LBG samples at a level of $\sim2σ$ of 0.414 $\pm$ 0.263 mJy for CUDSS-03 and 0.382 $\pm$ 0.206 mJy for CUDSS-14, but the Steidel et al. sample is consistent with zero flux. From this we place upper limits on the Lyman-break contribution to the $850μm$ background of $\sim$20%. We have also measured the cross-clustering between the LBGs and SCUBA sources. From this measurement we infer a large clustering amplitude of $r_o$ = 11.5 $\pm$ 3.0 $\pm$ 3.0 $h^{-1}$Mpc for the Steidel et al. sample (where the first error is statistical and the second systematic), $r_o$ = 4.5 $\pm$ 7.0 $\pm$ 5.0 $h^{-1}$Mpc for CFDF-14 and $r_o$ = 7.5 $\pm$ 7.0 $\pm$ 5.0 $h^{-1}$Mpc for CFDF-3. The Steidel et al sample, for which we have most only significant detection of clustering is also the largest of the three samples and has spectroscopically confirmed redshifts.

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