L. J. Storrie-Lombardi

Carnegie Institution for Science, Washington, West Virginia, United States

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Publications (153)385.32 Total impact

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    ABSTRACT: We present luminosity functions derived from a spectroscopic survey of AGN selected from Spitzer Space Telescope imaging surveys. Selection in the mid-infrared is significantly less affected by dust obscuration. We can thus compare the luminosity functions of the obscured and unobscured AGN in a more reliable fashion than by using optical or X-ray data alone. We find that the AGN luminosity function can be well described by a broken power-law model in which the break luminosity decreases with redshift. At high redshifts ($z>1.6$), we find significantly more AGN at a given bolometric luminosity than found by either optical quasar surveys or hard X-ray surveys. The fraction of obscured AGN decreases rapidly with increasing AGN luminosity, but, at least at high redshifts, appears to remain at $\approx 50$\% even at bolometric luminosities $\sim 10^{14}L_{\odot}$. The data support a picture in which the obscured and unobscured populations evolve differently, with some evidence that high luminosity obscured quasars peak in space density at a higher redshift than their unobscured counterparts. The amount of accretion energy in the Universe estimated from this work suggests that AGN contribute about 12\% to the total radiation intensity of the Universe, and a high radiative accretion efficiency $\approx 0.18^{+0.12}_{-0.07}$ is required to match current estimates of the local mass density in black holes.
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    ABSTRACT: We present the results of a program of optical and near-infrared spectroscopic follow-up of candidate active galactic nuclei (AGNs) selected in the mid-infrared. This survey selects both normal and obscured AGNs closely matched in luminosity across a wide range, from Seyfert galaxies with bolometric luminosities L bol ~ 1010 L ⊙ to highly luminous quasars (L bol ~ 1014 L ⊙), all with redshifts ranging from 0 to 4.3. Samples of candidate AGNs were selected with mid-infrared color cuts at several different 24 μm flux density limits to ensure a range of luminosities at a given redshift. The survey consists of 786 candidate AGNs and quasars, of which 672 have spectroscopic redshifts and classifications. Of these, 137 (20%) are type 1 AGNs with blue continua, 294 (44%) are type 2 objects with extinctions AV >~ 5 toward their AGNs, 96 (14%) are AGNs with lower extinctions (AV ~ 1), and 145 (22%) have redshifts, but no clear signs of AGN activity in their spectra. Of the survey objects 50% have L bol > 1012 L ⊙, in the quasar regime. We present composite spectra for type 2 quasars and objects with no signs of AGN activity in their spectra. We also discuss the mid-infrared—emission-line luminosity correlation and present the results of cross correlations with serendipitous X-ray and radio sources. The results show that: (1) obscured objects dominate the overall AGN population, (2) mid-infrared selected AGN candidates exist which lack AGN signatures in their optical spectra but have AGN-like X-ray or radio counterparts, and (3) X-ray and optical classifications of obscured and unobscured AGNs often differ.
    The Astrophysical Journal Supplement Series 10/2013; 208(2):24-. DOI:10.1088/0067-0049/208/2/24 · 14.14 Impact Factor
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    ABSTRACT: A wide range of optical facilities and instruments were used for spectroscopic follow-up of our AGN candidates. Most of the bright samples were followed up with 3-5m telescopes and longslit spectroscopy (Hale with COSMIC, SOAR with Goodman, and Shane with Kast), whereas the fainter samples were followed up with multifiber and/or 6-8m class telescopes (Blanco with Hydra, MMT with Hectospec, and Gemini-South with GMOS (program GS-2008B-C4)). We also obtained spectra of some of the bright candidates with a successful poor weather (scheduling band 4) program at Gemini-South (program GS-2008B-Q86). Some objects had spectra available in archives from the SDSS, 2dF, (Colless et al. 2001, Cat. VII/250) or 6dF (Jones et al. 2009, Cat. VII/259) surveys and some have redshifts and classifications in the literature, all found using the NASA Extragalactic Database (NED). Table 2 gives details of the spectroscopic observations or literature references as appropriate. For some high-redshift candidates with ambiguous or low signal-to-noise optical spectra, we were able to obtain near-infrared spectra with the IRTF using SpeX (2007 June), Gemini with NIRI (program GN2009B-C-8), and Triplespec (2008 July and 2011 July) on Palomar. (5 data files).
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    ABSTRACT: We present the results of a program of optical and near-infrared spectroscopic follow-up of candidate Active Galactic Nuclei (AGN) selected in the mid-infrared. This survey selects both normal and obscured AGN closely matched in luminosity across a wide range, from Seyfert galaxies with bolometric luminosities L_bol~10^10L_sun, to highly luminous quasars (L_bol~10^14L_sun), and with redshifts from 0-4.3. Samples of candidate AGN were selected through mid-infrared color cuts at several different 24 micron flux density limits to ensure a range of luminosities at a given redshift. The survey consists of 786 candidate AGN and quasars, of which 672 have spectroscopic redshifts and classifications. Of these, 137 (20%) are type-1 AGN with blue continua, 294 (44%) are type-2 objects with extinctions A_V>~5 towards their AGN, 96 (14%) are AGN with lower extinctions (A_V~1) and 145 (22%) have redshifts, but no clear signs of AGN activity in their spectra. 50% of the survey objects have L_bol >10^12L_sun, in the quasar regime. We present composite spectra for type-2 quasars and for objects with no signs of AGN activity in their spectra. We also discuss the mid-infrared - emission-line luminosity correlation and present the results of cross-correlations with serendipitous X-ray and radio sources. The results show that: (1) obscured objects dominate the overall AGN population, (2) there exist mid-infrared selected AGN candidates which lack AGN signatures in their optical spectra, but have AGN-like X-ray or radio counterparts, and (3) X-ray and optical classifications of obscured and unobscured AGN often differ.
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    ABSTRACT: This document summarizes the results of a community-based discussion of the potential science impact of the Mayall+BigBOSS highly multiplexed multi-object spectroscopic capability. The KPNO Mayall 4m telescope equipped with the DOE- and internationally-funded BigBOSS spectrograph offers one of the most cost-efficient ways of accomplishing many of the pressing scientific goals identified for this decade by the "New Worlds, New Horizons" report. The BigBOSS Key Project will place unprecedented constraints on cosmological parameters related to the expansion history of the universe. With the addition of an open (publicly funded) community access component, the scientific impact of BigBOSS can be extended to many important astrophysical questions related to the origin and evolution of galaxies, stars, and the IGM. Massive spectroscopy is the critical missing ingredient in numerous ongoing and planned ground- and space-based surveys, and BigBOSS is unique in its ability to provide this to the US community. BigBOSS data from community-led projects will play a vital role in the education and training of students and in maintaining US leadership in these fields of astrophysics. We urge the NSF-AST division to support community science with the BigBOSS multi-object spectrograph through the period of the BigBOSS survey in order to ensure public access to the extraordinary spectroscopic capability.
  • Lisa J. Storrie-Lombardi, Suzanne R. Dodd
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    ABSTRACT: The Spitzer Space Telescope is executing the third observing cycle in the `warm' extended phase of the mission. For the warm mission, the observatory was effectively reinvented as a new, scientifically productive mission operating at a substantially lower cost. In this paper we describe the ongoing implementation of improvements in science capabilities during the extended mission phase even as the project budget continues to shrink. Improvements in pointing stability, data compression and data analysis techniques allow for new science opportunities more than 8 years after launch. Engineering analyses have shown that the mission can operate with high reliability and minimal technical risk through at least January 2017.
    Proceedings of SPIE - The International Society for Optical Engineering 09/2012; DOI:10.1117/12.925249 · 0.20 Impact Factor
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    ABSTRACT: A number of popular software tools in the public domain are used by astronomers, professional and amateur alike, but some of the tools that have similar purposes cannot be easily interchanged, owing to the lack of a common standard. For the case of image distortion, SCAMP and SExtractor, available from Astromatic.net, perform astrometric calibration and source-object extraction on image data, and image-data geometric distortion is computed in celestial coordinates with polynomial coefficients stored in the FITS header with the PV i_j keywords. Another widely-used astrometric-calibration service, Astrometry.net, solves for distortion in pixel coordinates using the SIP convention that was introduced by the Spitzer Science Center. Up until now, due to the complexity of these distortion representations, it was very difficult to use the output of one of these packages as input to the other. New Python software, along with faster-computing C-language translations, have been developed at the Infrared Processing and Analysis Center (IPAC) to convert FITS-image headers from PV to SIP and vice versa. It is now possible to straightforwardly use Astrometry.net for astrometric calibration and then SExtractor for source-object extraction. The new software also enables astrometric calibration by SCAMP followed by image visualization with tools that support SIP distortion, but not PV . The software has been incorporated into the image-processing pipelines of the Palomar Transient Factory (PTF), which generate FITS images with headers containing both distortion representations. The software permits the conversion of archived images, such as from the Spitzer Heritage Archive and NASA/IPAC Infrared Science Archive, from SIP to PV or vice versa. This new capability renders unnecessary any new representation, such as the proposed TPV distortion convention.
    Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series; 09/2012
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    ABSTRACT: We present current and future planned modifications to the operations of the Spitzer Space Telescope to facilitate science during the ongoing warm Spitzer mission. The 3.6 and 4.5 micron cameras of the IRAC instrument have been operating flawlessly and almost identically as they did in the cryogenic mission since the start of warm science operations in August 2009. The operations of the instrument and spacecraft continue to evolve as attempts are made to optimize observations for the expanding field of exoplanet transit studies. A significant improvement in the pointing stability was made in September 2010 by modifying the cycling temperatures of a spacecraft battery heater. Experiments aimed at improving the pointing drift and improving initial pointing accuracy are currently being planned or executed. To permit useful operations beyond 2013, methods of improving onboard data compression are being explored to mitigate the decreased bandwidth of data downlinks with Spitzer's increasing distance from Earth. This work is based on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. Support for this work was provided by NASA through an award issued by JPL/Caltech.
    American Astronomical Society Meeting Abstracts #218; 05/2011
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    Lisa J. Storrie-Lombardi, Suzanne R. Dodd
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    ABSTRACT: The Spitzer Space Telescope transitioned from the cryogen mission to the IRAC warm mission during 2009. This transition involved changing several areas of operations in order to cut the mission annual operating costs to 1/3 of the cryogen mission amount. In spite of this substantial cut back, Spitzer continues to have one of the highest science return per dollar ratio of any of NASA's extended missions. This paper will describe the major operational changes made for the warm mission and how they affect the science return. The paper will give several measures showing that warm Spitzer continues as one of the most scientifically productive mission in NASA's portfolio. This work was performed at the California Institute of Technology under contract to the National Aeronautics and Space Administration.
    Proceedings of SPIE - The International Society for Optical Engineering 07/2010; DOI:10.1117/12.857827 · 0.20 Impact Factor
  • Lisa J. Storrie-Lombardi, A. Petric, M. Lacy, D. Dowell, A. Martinez Sansigre, K. Dasyra
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    ABSTRACT: We present a study of the radio properties of a sample of 400 MIR-selected AGN. We compare narrow and broad-line AGN in terms of the fraction of radio-loud sources, location on the radio-to-FIR correlation and luminosity distribution with redshift. Type-2 AGN tend to have higher FIR-to radio ratios and their detection rates at longer IR wavelengths suggest that they form more stars than type-1 AGN. Support for this work was provided by NASA.
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    ABSTRACT: The detection of CO(1→0) emission in the massive (i.e., MH ~ –26.13 mag), z ~ 0.3 host-galaxy system of the broad absorption line quasi-stellar object (QSO) PG1700+518 is reported. The host system has a CO luminosity of L'_CO ~ 1.4 × 10^(10) K km s^(–1) pc^2, and thus a star-forming molecular gas mass of M(H_2) ~ 6 × 10^(10) M_☉ (adopting an α = 4 M_☉[K km s^(–1) pc^2]^(–1)), making it one of the most molecular gas-rich Palomar-Green QSO hosts observed to date. New Hubble Space Telescope WFPC2 direct and NICMOS coronagraphic images show the highest resolution view yet of the host and companion. The new NICMOS image reveals the underlying, apparently tidally disrupted structure seen previously from high-resolution ground-based optical imaging. Light from the host galaxy is overwhelmed by the central point source in the WFPC2 images. The companion galaxy is well resolved in both data sets, and the WFPC2 provides for the first time a clear picture of the optically visible ring structure. The CO redshift is within the range of redshifts derived from optical QSO emission lines, thus the observed CO is associated with the QSO host. However, it cannot be ruled out that the companion has at least ~10^(10) M_☉ of molecular gas. Finally, if the far-infrared luminosity, which is 1/5 of the bolometric luminosity, is the luminosity of the starburst population, the star formation rate is estimated to be ~210 M_☉ yr^(–1). There is thus sufficient molecular gas in the QSO host galaxy to fuel both star formation and QSO activity for another ~10^8 yr. We speculate that we may be witnessing the fueling event in progress that resulted from a collision between the QSO host and the companion galaxy, and that there is an accompanying expulsion of material along our line of sight in the form of broad absorption line gas.
    The Astronomical Journal 07/2009; DOI:10.1088/0004-6256/138/1/262; · 4.05 Impact Factor
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    ABSTRACT: Type 2 or ``obscured'' AGN have long been identified at low AGN luminosities (e.g. Seyfert 2s) or through their radio luminosities (e.g. radio galaxies). But radio-quiet quasars (RQQs) are many times more common than radio-loud quasars, and it's therefore unsurprising that recent searches have revealed that radio-quiet quasar 2s also form a significant population. Finding the numbers, properties, and redshift distribution of quasar 2s will be very important to resolving questions about the formation and co-evolution of black holes and galaxies. We have selected a sample of Type 2 and Type 1 quasars matched in their mid-infrared luminosity from the Spitzer First Look Survey by selecting on their mid-infrared dust emission properties (as measured by Spitzer IRAC photometry). This emission provides a distinctive signature of AGN activity but should not be affected by orientation or torus opening angle. We have obtained mid-infrared IRS spectroscopy of these samples to study star formation activity in the host galaxies and the dust environments of the AGN, using measurements of the PAH features, the shape of the mid-infrared SED, and the equivalent width of the silicate features at 10 microns. We find that the quasar 2s have more diverse mid-IR spectral properties, and that obscuration of the AGN is linked to star formation activity in the host.
  • Gordon K. Squires, L. J. Storrie-Lombardi, M. W. Werner, B. T. Soifer
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    ABSTRACT: Spitzer enters a new phase of its mission in spring 2009: the Spitzer "warm" mission. The combination of Spitzer's unprecedented sensitivity, Earth-trailing orbit and efficiency in mapping large regions provides new opportunities for scientific research. With over 6,500 hours of observing time available yearly, investigations requiring large amount of observing time are for the first time enabled by warm Spitzer. This brief introductory talk will introduce the ten large "Exploration Science" programs for the warm Spitzer mission, and also describe opportunities for the general observer community. An update on warm Spitzer status will also be provided. Information on the Exploration Science programs is available at: http://ssc.spitzer.caltech.edu/geninfo/es/
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    Lin Yan, Patrick J. McCarthy, Lisa J. Storrie-Lombardi, and Ray J. Weymann
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    ABSTRACT: We present deep galaxy counts and half-light radii from F160W (λc=1.6 μm) images obtained with the Near-Infrared Camera and Multiobject Spectrograph on the Hubble Space Telescope. Nearly 9 arcmin2 have been imaged with camera 3, with 3 σ depths ranging from H=24.3 to 25.5 in a 06 diameter aperture. The slope of the counts fainter than H=20 is 0.31, and the integrated surface density to H≤24.75 is 4×105 galaxies deg-2. The half-light radii of the galaxies decline steeply with apparent magnitude. At H=24, we are limited by both the delivered FWHM and the detection threshold of the images.
    The Astrophysical Journal 01/2009; 503(1):L19. DOI:10.1086/311521 · 6.28 Impact Factor
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    ABSTRACT: We present the first results of a survey of random fields with the slitless G141 (λc = 1.5 μm, Δλ = 0.8 μm) grism on the near-IR camera and multiobject spectrometer (NICMOS) on board the Hubble Space Telescope (HST). Approximately 64 arcmin2 have been observed at intermediate and high Galactic latitudes. The 3 σ limiting line and continuum fluxes in each field vary from 7.5 × 10-17 to 1 × 10-17 ergs cm-2 s-1, and from H = 20 to 22, respectively. Our median and area-weighted 3 σ limiting line fluxes within a 4 pixel aperture are nearly identical at 4.1 × 10-17 ergs cm-2 s-1 and are 60% deeper than the deepest narrowband imaging surveys from the ground. We have identified 33 emission-line objects and derive their observed wavelengths, fluxes, and equivalent widths. We argue that the most likely line identification is Hα and that the redshift range probed is from 0.75 to 1.9. The 2 σ rest-frame equivalent width limits range from 9 to 130 Å, with an average of 40 Å. The survey probes an effective comoving volume of 105 h-350 Mpc3 for q0 = 0.5. Our derived comoving number density of emission-line galaxies in the range 0.7 < z < 1.9 is 3.3 × 10-4 h350 Mpc-3, very similar to that of the bright Lyman break objects at z ~ 3. The objects with detected emission lines have a median F160W magnitude of 20.4 (Vega scale) and a median Hα luminosity of 2.7 × 1042 ergs s-1. The implied star formation rates range from 1 to 324 M☉ yr-1, with an average [N II] λλ6583, 6548 corrected rate of 21 M☉ yr-1 for H0 = 50 km s-1 Mpc and q0 = 0.5 (34 M☉ yr-1 for q0 = 0.1).
    The Astrophysical Journal 01/2009; 520(2):548. DOI:10.1086/307491 · 6.28 Impact Factor
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    ABSTRACT: We report results of a high-resolution imaging search for the galaxy associated with the damped Lyα (DLA) absorber at z = 1.892 toward the zem = 2.543 quasar LBQS 1210+1731, using the Hubble Space Telescope (HST) NICMOS. The images were obtained in the broad filter F160W and the narrow filter F190N with camera 2 on NICMOS and were aimed at detecting the absorber in the rest-frame optical continuum and in Hα line emission from the DLA absorber. After suitable point-spread function (PSF) subtractions, a feature is seen in both the broadband and narrowband images, at a projected separation of 025 from the quasar. This feature may be associated with the DLA absorber, although we cannot completely rule out that it could be a PSF artifact. If associated with the DLA, the object would be ≈2-3 h kpc in size with a flux of 9.8 ± 2.4 μJy in the F160W filter, implying a luminosity at λcentral = 5500 Å in the rest frame of 1.5 × 1010 h L☉ at z = 1.89, for q0 = 0.5. However, a comparison of the fluxes in the broad and narrow filters indicates that most of the flux in the narrowband filter is continuum emission, rather than redshifted Hα line emission. This suggests that if this object is the absorber, then either it has a low star formation rate (SFR), with a 3 σ upper limit of 4.0 h M☉ yr-1, or dust obscuration is important. It is possible that the Hα emission may be extinguished by dust, but this seems unlikely, given the typically low dust-to-gas ratios observed in DLAs. Alternatively, the object, if real, may be associated with the host galaxy of the quasar rather than with the damped Lyα absorber. H-band images obtained with the NICMOS camera 2 coronagraph show a much fainter structure ≈4-5 h kpc in size and containing four knots of continuum emission, located 07 away from the quasar. This structure is not seen in images of comparison stars after similar PSF subtractions and is also likely to be associated with the absorbing galaxy or its companions, although we do not know its redshift. We have probed regions far closer to the quasar sight line than in most previous studies of high-redshift intervening DLAs. The two objects we report mark the closest detected high-redshift DLA candidates yet to any quasar sight line. If the features in our images are associated with the DLA, they suggest faint, compact, somewhat clumpy objects rather than large, well-formed protogalactic disks or spheroids. If the features are PSF artifacts, then the constraints on sizes and star formation rates of the DLA are even more severe. The size, luminosity, and SFR estimates mentioned above should therefore be conservatively considered as upper limits.
    The Astrophysical Journal 12/2008; 536(1):36. DOI:10.1086/308904 · 6.28 Impact Factor
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    ABSTRACT: We present Multiband Imaging Photometer for Spitzer (MIPS) observations of M81 at 24, 70, and 160 μm. The grand design nature of M81 is clearly seen, showing two well-resolved spiral arms containing numerous bright star-forming regions. The MIPS images reveal a significant amount of cold dust associated with the spiral arms. We investigate the variation of the ultraviolet (UV), Hα, and infrared (IR) luminosities and star formation rate (SFR) indicators across the face of M81 using the MIPS images and archival UV and Hα images. For regions in M81, we find that UV and Hα SFRs (uncorrected for dust attenuation) are always lower than the IR SFR. The cause of this behavior is dust attenuation and/or using SFR calibrations appropriate for entire galaxies, not regions in galaxies. The characteristics of the dust attenuation for the regions indicate the dust grains and/or geometry are different from those in starburst galaxies. The behavior of the infrared-radio correlation in M81 is seen to vary from the global average, with variations correlated with the morphology of M81.
    The Astrophysical Journal Supplement Series 12/2008; 154(1):215. DOI:10.1086/422714 · 14.14 Impact Factor
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    ABSTRACT: We have carried out a high-resolution imaging search for the galaxy associated with the damped Lyα absorber (DLA) at z = 1.859 toward the zem = 2.48 quasar QSO 1244+3443, using the Hubble Space Telescope (HST) and the near-infrared camera and multiobject spectrometer (NICMOS). Images were obtained in the broad filter F160W and the narrow filter F187N with camera 2 on NICMOS with the goal of detecting the rest-frame optical continuum and the Hα line emission from the DLA. After point-spread function (PSF) subtraction, two weak features are seen at projected separations of 016-024 from the quasar. Parts of these features may be associated with the DLA, although we cannot completely rule out that they could be artifacts of the PSF. If associated with the DLA, the objects would be ≈1-2 h kpc in size with integrated flux densities of 2.5 and 3.3 μJy in the F160W filter, implying luminosities at λcentral = 5600 Å in the DLA rest frame of 4.4-5.9 × 109 h L☉ at z = 1.86, for q0 = 0.5. However, no significant Hα line emission is seen from these objects, suggesting low star formation rates (SFRs). Our 3 σ upper limit on the SFR in the DLA is 1.3 h-270 M☉ yr-1 for q0 = 0.5 (2.4 h-270 M☉ yr-1 for q0 = 0.1). This together with our earlier result for LBQS 1210 + 1731 mark a significant improvement over previous constraints on the star formation rates of DLAs. Dust within the DLA could extinguish Hα emission, but this would require the dust content in the DLA to be much higher than that inferred from previous DLA observations. A combination of low star formation rate and some dust extinction is likely to be responsible for the lack of Hα emission. Alternatively, the objects, if real, may be associated with the host galaxy of the quasar rather than with the DLA. In any case, our observations suggest that the DLA is not a large bright protodisk, but a compact object or a low surface brightness galaxy. If the two features are PSF artifacts or associated with the quasar host, then the constraints on the size and luminosity of the DLA are even more severe.
    The Astrophysical Journal 12/2008; 551(1):37. DOI:10.1086/320079 · 6.28 Impact Factor
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    ABSTRACT: We present the Spitzer Multiband Imaging Photometer 24 μm source counts in the Extragalactic First Look Survey (FLS) main, verification, and European Large Area ISO Survey N1 fields. Spitzer's increased sensitivity and efficiency in large areal coverage over previous infrared telescopes, coupled with the enhanced sensitivity of the 24 μm band to sources at intermediate redshift, dramatically improve the quality and statistics of number counts in the mid-infrared. The FLS observations cover areas of 4.4, 0.26, and 0.015 deg2, respectively, and reach 3 σ depths of 0.11, 0.08, and 0.03 mJy. The extragalactic counts derived for each survey agree remarkably well. The counts can be fitted by a super-Euclidean power law of index α = -2.9 from 0.2 to 0.9 mJy, with a flattening of the counts at fluxes fainter than 0.2 mJy. Comparison with infrared galaxy evolution models reveals a peak's displacement in the 24 μm counts. This is probably due to the detection of a new population of galaxies with redshift between 1 and 2, previously unseen in the 15 μm deep counts.
    The Astrophysical Journal Supplement Series 12/2008; 154(1):66. DOI:10.1086/422584 · 14.14 Impact Factor
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    ABSTRACT: We present an analysis of the mid-infrared (MIR) and optical properties of type 1 (broad-line) quasars detected by the Spitzer Space Telescope. The MIR color-redshift relation is characterized to z~3, with predictions to z=7. We demonstrate how combining MIR and optical colors can yield even more efficient selection of active galactic nuclei (AGNs) than MIR or optical colors alone. Composite spectral energy distributions (SEDs) are constructed for 259 quasars with both Sloan Digital Sky Survey and Spitzer photometry, supplemented by near-IR, GALEX, VLA, and ROSAT data, where available. We discuss how the spectral diversity of quasars influences the determination of bolometric luminosities and accretion rates; assuming the mean SED can lead to errors as large as 50% for individual quasars when inferring a bolometric luminosity from an optical luminosity. Finally, we show that careful consideration of the shape of the mean quasar SED and its redshift dependence leads to a lower estimate of the fraction of reddened/obscured AGNs missed by optical surveys as compared to estimates derived from a single mean MIR to optical flux ratio.
    The Astrophysical Journal Supplement Series 12/2008; DOI:10.1086/506525 · 14.14 Impact Factor

Publication Stats

3k Citations
385.32 Total Impact Points

Institutions

  • 1998–2009
    • Carnegie Institution for Science
      Washington, West Virginia, United States
  • 2000–2008
    • California Institute of Technology
      • Spitzer Science Center
      Pasadena, CA, United States
  • 2007
    • University of California, San Diego
      • Center for Astrophysics and Space Sciences (CASS)
      San Diego, CA, United States
  • 2006
    • University of California, Riverside
      • Department of Physics and Astronomy
      Riverside, California, United States
  • 1999
    • The University of Arizona
      • Department of Astronomy
      Tucson, Arizona, United States
    • Clemson University
      Clemson, South Carolina, United States
  • 1996
    • University of Cambridge
      • Institute of Astronomy
      Cambridge, England, United Kingdom
  • 1994
    • Cancer Research UK Cambridge Institute
      Cambridge, England, United Kingdom
  • 1992
    • University of Pittsburgh
      • Physics and Astronomy
      Pittsburgh, Pennsylvania, United States