Scott Burles

University of Utah, Salt Lake City, Utah, United States

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Publications (175)621.28 Total impact

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    Rebecca A. Bernstein · Scott M. Burles · J. Xavier Prochaska ·
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    ABSTRACT: This manuscript describes the design, usage, and data-reduction pipeline developed for the Magellan Inamori Kyocera Echelle (MIKE) spectrometer used with the Magellan telescope at the Las Campanas Observatory. We summarize the basic characteristics of the instrument and discuss observational procedures recommended for calibrating the standard data products. We detail the design and implementation of an IDL based data-reduction pipeline for MIKE data (since generalized to other echelle spectrometers, e.g. Keck/HIRES, VLT/UVES). This includes novel techniques for flat-fielding, wavelength calibration, and the extraction of echelle spectroscopy. Sufficient detail is provided in this manuscript to enable inexperienced observers to understand the strengths and weaknesses of the instrument and software package and an assessment of the related systematics.
    Publications of the Astronomical Society of the Pacific 06/2015; 127(955). DOI:10.1086/683015 · 3.50 Impact Factor
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    ABSTRACT: We present an absorption-line survey of optically thick gas clouds -- Lyman Limit Systems (LLSs) -- observed at high dispersion with spectrometers on the Keck and Magellan telescopes. We measure column densities of neutral hydrogen NHI and associated metal-line transitions for 157 LLSs at z=1.76-4.39 restricted to 10^17.3 < NHI < 10^20.3. An empirical analysis of ionic ratios indicates an increasing ionization state of the gas with decreasing NHI and that the majority of LLSs are highly ionized, confirming previous expectations. The Si^+/H^0 ratio spans nearly four orders-of-magnitude, implying a large dispersion in the gas metallicity. Fewer than 5% of these LLSs have no positive detection of a metal transition; by z~3, nearly all gas that is dense enough to exhibit a very high Lyman limit opacity has previously been polluted by heavy elements. We add new measurements to the small subset of LLS (~5-10) that may have super-solar abundances. High Si^+/Fe^+ ratios suggest an alpha-enhanced medium whereas the Si^+/C^+ ratios do not exhibit the super-solar enhancement inferred previously for the Lya forest.
    The Astrophysical Journal Supplement Series 06/2015; 221(1). DOI:10.1088/0067-0049/221/1/2 · 11.22 Impact Factor
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    ABSTRACT: The PRIsm MUti-object Survey (PRIMUS) is a spectroscopic galaxy redshift survey to z~1 completed with a low-dispersion prism and slitmasks allowing for simultaneous observations of ~2,500 objects over 0.18 square degrees. The final PRIMUS catalog includes ~130,000 robust redshifts over 9.1 sq. deg. In this paper, we summarize the PRIMUS observational strategy and present the data reduction details used to measure redshifts, redshift precision, and survey completeness. The survey motivation, observational techniques, fields, target selection, slitmask design, and observations are presented in Coil et al 2010. Comparisons to existing higher-resolution spectroscopic measurements show a typical precision of sigma_z/(1+z)=0.005. PRIMUS, both in area and number of redshifts, is the largest faint galaxy redshift survey completed to date and is allowing for precise measurements of the relationship between AGNs and their hosts, the effects of environment on galaxy evolution, and the build up of galactic systems over the latter half of cosmic history.
    The Astrophysical Journal 03/2013; 767(2). DOI:10.1088/0004-637X/767/2/118 · 5.99 Impact Factor
  • S. Kent · D. Schlegel · S. Burles · E. Malanushenko ·

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    ABSTRACT: We present the design and performance of the multi-object fiber spectrographs for the Sloan Digital Sky Survey (SDSS) and their upgrade for the Baryon Oscillation Spectroscopic Survey (BOSS). Originally commissioned in Fall 1999 on the 2.5-m aperture Sloan Telescope at Apache Point Observatory, the spectrographs produced more than 1.5 million spectra for the SDSS and SDSS-II surveys, enabling a wide variety of Galactic and extra-galactic science including the first observation of baryon acoustic oscillations in 2005. The spectrographs were upgraded in 2009 and are currently in use for BOSS, the flagship survey of the third-generation SDSS-III project. BOSS will measure redshifts of 1.35 million massive galaxies to redshift 0.7 and Lyman-alpha absorption of 160,000 high redshift quasars over 10,000 square degrees of sky, making percent level measurements of the absolute cosmic distance scale of the Universe and placing tight constraints on the equation of state of dark energy. The twin multi-object fiber spectrographs utilize a simple optical layout with reflective collimators, gratings, all-refractive cameras, and state-of-the-art CCD detectors to produce hundreds of spectra simultaneously in two channels over a bandpass covering the near ultraviolet to the near infrared, with a resolving power R = \lambda/FWHM ~ 2000. Building on proven heritage, the spectrographs were upgraded for BOSS with volume-phase holographic gratings and modern CCD detectors, improving the peak throughput by nearly a factor of two, extending the bandpass to cover 360 < \lambda < 1000 nm, and increasing the number of fibers from 640 to 1000 per exposure. In this paper we describe the original SDSS spectrograph design and the upgrades implemented for BOSS, and document the predicted and measured performances.
    The Astronomical Journal 08/2012; 146(2). DOI:10.1088/0004-6256/146/2/32 · 4.02 Impact Factor
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    ABSTRACT: (abridged) We describe the automated spectral classification, redshift determination, and parameter measurement pipeline in use for the Baryon Oscillation Spectroscopic Survey (BOSS) of the Sloan Digital Sky Survey III (SDSS-III) as of Data Release 9, encompassing 831,000 moderate-resolution optical spectra. We give a review of the algorithms employed, and describe the changes to the pipeline that have been implemented for BOSS relative to previous SDSS-I/II versions, including new sets of stellar, galaxy, and quasar redshift templates. For the color-selected CMASS sample of massive galaxies at redshift 0.4 <~ z <~ 0.8 targeted by BOSS for the purposes of large-scale cosmological measurements, the pipeline achieves an automated classification success rate of 98.7% and confirms 95.4% of unique CMASS targets as galaxies (with the balance being mostly M stars). Based on visual inspections of a subset of BOSS galaxies, we find that ~0.2% of confidently reported CMASS sample classifications and redshifts are incorrect, and ~0.4% of all CMASS spectra are objects unclassified by the current algorithm which are potentially recoverable. The BOSS pipeline confirms that ~51.5% of the quasar targets have quasar spectra, with the balance mainly consisting of stars. Statistical (as opposed to systematic) redshift errors propagated from photon noise are typically a few tens of km/s for both galaxies and quasars, with a significant tail to a few hundreds of km/s for quasars. We test the accuracy of these statistical redshift error estimates using repeat observations, finding them underestimated by a factor of 1.19 to 1.34 for galaxies, and by a factor of 2 for quasars. We assess the impact of sky-subtraction quality, S/N, and other factors on galaxy redshift success. Finally, we document known issues, and describe directions of ongoing development.
    The Astronomical Journal 07/2012; 144(5). DOI:10.1088/0004-6256/144/5/144 · 4.02 Impact Factor
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    ABSTRACT: We present evidence that the incidence of active galactic nuclei (AGNs) and the distribution of their accretion rates do not depend on the stellar masses of their host galaxies, contrary to previous studies. We use hard (2-10 keV) X-ray data from three extragalactic fields (XMM-LSS, COSMOS, and ELAIS-S1) with redshifts from the Prism Multi-object Survey to identify 242 AGNs with L 2-10 keV = 1042-44 erg s–1 within a parent sample of ~25,000 galaxies at 0.2 < z < 1.0 over ~3.4 deg2 and to i ~ 23. We find that although the fraction of galaxies hosting an AGN at fixed X-ray luminosity rises strongly with stellar mass, the distribution of X-ray luminosities is independent of mass. Furthermore, we show that the probability that a galaxy will host an AGN can be defined by a universal Eddington ratio distribution that is independent of the host galaxy stellar mass and has a power-law shape with slope –0.65. These results demonstrate that AGNs are prevalent at all stellar masses in the range and that the same physical processes regulate AGN activity in all galaxies in this stellar mass range. While a higher AGN fraction may be observed in massive galaxies, this is a selection effect related to the underlying Eddington ratio distribution. We also find that the AGN fraction drops rapidly between z ~ 1 and the present day and is moderately enhanced (factor ~2) in galaxies with blue or green optical colors. Consequently, while AGN activity and star formation appear to be globally correlated, we do not find evidence that the presence of an AGN is related to the quenching of star formation or the color transformation of galaxies.
    The Astrophysical Journal 01/2012; 746(1):90. DOI:10.1088/0004-637X/746/1/90 · 5.99 Impact Factor

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    ABSTRACT: We present the PRIsm MUlti-object Survey (PRIMUS), a spectroscopic faint galaxy redshift survey to z ~ 1. PRIMUS uses a low-dispersion prism and slitmasks to observe ~2500 objects at once in a 0.18 deg2 field of view, using the Inamori Magellan Areal Camera and Spectrograph camera on the Magellan I Baade 6.5 m telescope at Las Campanas Observatory. PRIMUS covers a total of 9.1 deg2 of sky to a depth of i AB ~ 23.5 in seven different deep, multi-wavelength fields that have coverage from the Galaxy Evolution Explorer, Spitzer, and either XMM or Chandra, as well as multiple-band optical and near-IR coverage. PRIMUS includes ~130,000 robust redshifts of unique objects with a redshift precision of σ z /(1 + z) ~ 0.005. The redshift distribution peaks at z ~ 0.6 and extends to z = 1.2 for galaxies and z = 5 for broad-line active galactic nuclei. The motivation, observational techniques, fields, target selection, slitmask design, and observations are presented here, with a brief summary of the redshift precision; a forthcoming paper presents the data reduction, redshift fitting, redshift confidence, and survey completeness. PRIMUS is the largest faint galaxy survey undertaken to date. The high targeting fraction (~80%) and large survey size will allow for precise measures of galaxy properties and large-scale structure to z ~ 1.
    The Astrophysical Journal 10/2011; 741(1):8. DOI:10.1088/0004-637X/741/1/8 · 5.99 Impact Factor

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    ABSTRACT: Tidal interactions between galaxies can trigger star formation, which contributes to the global star formation rate (SFR) density of the universe and could be a factor in the transformation of blue, star-forming galaxies to red, quiescent galaxies over cosmic time. We investigate tidally triggered star formation in isolated close galaxy pairs drawn from the Prism Multi-Object Survey (PRIMUS), a low-dispersion prism redshift survey that has measured ~120,000 robust galaxy redshifts over 9.1 deg2 out to z ~ 1. We select a sample of galaxies in isolated galaxy pairs at redshifts 0.25 ≤ z ≤ 0.75, with no other objects within a projected separation of 300 h –1 kpc and Δz/(1 + z) = 0.01, and compare them to a control sample of isolated galaxies to test for systematic differences in their rest-frame FUV – r and NUV – r colors as a proxy for relative specific star formation rates (SSFRs). We find that galaxies in rp ≤ 50 h –1 kpc pairs have bluer dust-corrected UV – r colors on average than the control galaxies by –0.134 ± 0.045 mag in FUV – r and –0.075 ± 0.038 mag in NUV – r, corresponding to an ~15%-20% increase in SSFR. This indicates an enhancement in SSFR due to tidal interactions. We also find that this relative enhancement is greater for a subset of rp ≤ 30 h –1 kpc pair galaxies, for which the average color offsets are –0.193 ± 0.065 mag in FUV – r and –0.159 ± 0.048 mag in NUV – r, corresponding to an ~25%-30% increase in SSFR. We test for evolution in the enhancement of tidally triggered star formation with redshift across our sample redshift range and find marginal evidence for a decrease in SSFR enhancement from 0.25 ≤ z ≤ 0.5 to 0.5 ≤ z ≤ 0.75. This indicates that a change in enhanced star formation triggered by tidal interactions in low-density environments is not a contributor to the decline in the global SFR density across this redshift range.
    The Astrophysical Journal 01/2011; 728(2):119. DOI:10.1088/0004-637X/728/2/119 · 5.99 Impact Factor
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    ABSTRACT: We quantify the fraction of galaxies at moderate redshifts (0.1 < z < 0.5) that appear red-and-dead in the optical, but in fact contain obscured star formation detectable in the infrared (IR), with the PRIsm MUlti-object Survey (PRIMUS). PRIMUS has measured ~120,000 robust redshifts with a precision of σ z /(1 + z) ~ 0.5% over 9.1 deg2 of the sky to the depth of i ~ 23 (AB), up to redshift z ~ 1. We specifically targeted 6.7 deg2 fields with existing deep IR imaging from the Spitzer Space Telescope from the SWIRE and S-COSMOS surveys. We select in these fields an i-band flux-limited sample (i < 20 mag in the SWIRE fields and i < 21 mag in the S-COSMOS field) of 3310 red-sequence galaxies at 0.1 < z < 0.5 for which we can reliably classify obscured star-forming (SF) and quiescent galaxies using IR color. Our sample constitutes the largest galaxy sample at intermediate redshift to study obscured star formation on the red sequence, and we present the first quantitative analysis of the fraction of obscured SF galaxies as a function of luminosity. We find that on average, at L ~ L*, about 15% of red-sequence galaxies have IR colors consistent with SF galaxies. The percentage of obscured SF galaxies increases by ~8% per mag with decreasing luminosity from the highest luminosities to L ~ 0.2 L*. Our results suggest that a significant fraction of red-sequence galaxies have ongoing star formation and that galaxy evolution studies based on optical color therefore need to account for this complication.
    The Astrophysical Journal 12/2010; 726(2):110. DOI:10.1088/0004-637X/726/2/110 · 5.99 Impact Factor
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    ABSTRACT: We use stellar masses, photometry, lensing, and velocity dispersions to investigate empirical correlations for the final sample of 73 early-type lens galaxies (ETGs) from the SLACS survey. The traditional correlations (Fundamental Plane [FP] and its projections) are consistent with those found for non-lens galaxies, supporting the thesis that SLACS lens galaxies are representative of massive ETGs. The addition of strong lensing estimates of the total mass allows us to gain further insights into their internal structure: i) the mean slope of the total mass density profile is <gamma'> = 2.078+/-0.027 with an intrinsic scatter of 0.16+/-0.02; ii) gamma' correlates with effective radius and central mass density, in the sense that denser galaxies have steeper profiles; iii) the dark matter fraction within reff/2 is a monotonically increasing function of galaxy mass and size; iv) the dimensional mass M_dim is proportional to the total mass, and both increase more rapidly than stellar mass M*; v) the Mass Plane (MP), obtained by replacing surface brightness with surface mass density in the FP, is found to be tighter and closer to the virial relation than the FP and the M*P, indicating that the scatter of those relations is dominated by stellar population effects; vi) we construct the Fundamental Hyper-Plane by adding stellar masses to the MP and find the M* coefficient to be consistent with zero and no residual intrinsic scatter. Our results demonstrate that the dynamical structure of ETGs is not scale invariant and that it is fully specified by the total mass, r_eff, and sigma. Although the basic trends can be explained qualitatively in terms of varying star formation efficiency as a function of halo mass and as the result of dry and wet mergers, reproducing quantitatively the observed correlations and their tightness may be a significant challenge for galaxy formation models. Comment: 16 pages, 9 figures; submitted to ApJ after responding to the referee comments
    The Astrophysical Journal 07/2010; 724(1). DOI:10.1088/0004-637X/724/1/511 · 5.99 Impact Factor
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    ABSTRACT: The Prism Multi-Object Survey (PRIMUS) is a galaxy redshift survey covering ˜10 square degrees to a flux limit of i ˜ 23 mag. We acquire roughly 200,000 spectra of galaxies out to z ˜ 1 in fields with existing multiwavelength data in the UV, X-ray, and infrared. By mutiplexing in the wavelength direction, we sacrifice spectral resolution for throughput, allowing us to observe ˜3000 objects per mask for 121 masks over just 39 dark nights at Magellan. Our goal is to combine our redshifts with the existing data to study various aspects of galaxy evolution with redshift, such as star formation rates, stellar mass, luminosity functions, and clustering properties. One of the initial science projects will be to use UV data from the Galaxy Evolution Explorer (GALEX) to derive specific star formation rates for close galaxy pairs (projected separation
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    ABSTRACT: We introduce a data-reduction package written in Interactive Data Language (IDL) for the Magellan Echellete Spectrograph (MAGE). MAGE is a medium-resolution (R 4100), cross-dispersed, optical spectrograph, with coverage from . The MAGE Spectral Extractor (MASE) incorporates the entire image reduction and calibration process, including bias subtraction, flat fielding, wavelength calibration, sky subtraction, object extraction, and flux calibration of point sources. We include examples of the user interface and reduced spectra. We show that the wavelength calibration is sufficient to achieve 5 km s-1 rms accuracy and relative flux calibrations better than 10%. A lightweight version of the full reduction pipeline has been included for real-time source extraction and signal-to-noise estimation at the telescope. National Science Foundation (AST- 0215989) Massachusetts Institute of Technology. School of Science Carnegie Observatories
    Publications of the Astronomical Society of the Pacific 12/2009; 121(886). DOI:10.1086/648597 · 3.50 Impact Factor
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    ABSTRACT: We present an absorption line analysis of the Lyman limit system (LLS) at z=3.55 in our Magellan/MIKE spectrum of PKS2000-330. Our analysis of the Lyman limit and full HI Lyman series constrains the total HI column density of the LLS (N_HI = 10^[18.0 +/- 0.25] cm^{-2} for b_HI >= 20 km/s) and also the N_HI values of the velocity subsystems comprising the absorber. We measure ionic column densities for metal-line transitions associated with the subsystems and use these values to constrain the ionization state (>90% ionized) and relative abundances of the gas. We find an order of magnitude dispersion in the metallicities of the subsystems, marking the first detailed analysis of metallicity variations in an optically thick absorber. The results indicate that metals are not well mixed within the gas surrounding high $z$ galaxies. Assuming a single-phase photoionization model, we also derive an N_H-weighted metallicity, <[Si/H]> = -1.66 +/- 0.25, which matches the mean metallicity in the neutral ISM in high z damped Lya systems (DLAs). Because the line density of LLSs is ~10 times higher than the DLAs, we propose that the former dominate the metal mass-density at z~3 and that these metals reside in the galaxy/IGM interface. Considerations of a multi-phase model do not qualitatively change these conclusions. Finally, we comment on an anomalously large O^0/Si^+ ratio in the LLS that suggests an ionizing radiation field dominated by soft UV sources (e.g. a starburst galaxy). Additional abundance analysis is performed on the super-LLS systems at z=3.19. Comment: 20 pages, 7 figures (most in color). Accepted to ApJ
    The Astrophysical Journal 12/2009; 708(2). DOI:10.1088/0004-637X/708/2/1221 · 5.99 Impact Factor
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    ABSTRACT: Based on 58 SLACS strong-lens early-type galaxies with direct total-mass and stellar-velocity dispersion measurements, we find that inside one effective radius massive elliptical galaxies with M_eff >= 3x10^10 M_sun are well-approximated by a power-law ellipsoid with an average logaritmic density slope of <gamma'_LD> = -dlog(rho_tot)/dlog(r)=2.085^{+0.025}_{-0.018} (random error on mean) for isotropic orbits with beta_r=0, +-0.1 (syst.) and sigma_gamma' <= 0.20^{+0.04}_{-0.02} intrinsic scatter (all errors indicate the 68 percent CL). We find no correlation of gamma'_LD with galaxy mass (M_eff), rescaled radius (i.e. R_einst/R_eff) or redshift, despite intrinsic differences in density-slope between galaxies. Based on scaling relations, the average logarithmic density slope can be derived in an alternative manner, fully independent from dynamics, yielding <gamma'_SR>=1.959 +- 0.077. Agreement between the two values is reached for =0.45 +- 0.25, consistent with mild radial anisotropy. This agreement supports the robustness of our results, despite the increase in mass-to-light ratio with total galaxy mass: M_eff ~ L_{V,eff}^(1.363+-0.056). We conclude that massive early-type galaxies are structurally close-to homologous with close-to isothermal total density profiles (<=10 percent intrinsic scatter) and have at most some mild radial anisotropy. Our results provide new observational limits on galaxy formation and evolution scenarios, covering four Gyr look-back time. Comment: Accepted for publication by ApJL; 4 pages, 2 figures
    The Astrophysical Journal 06/2009; 703(1). DOI:10.1088/0004-637X/703/1/L51 · 5.99 Impact Factor
  • T. Treu · A. Bolton · L. Koopmans · R. Gavazzi · L. Moustakas · S. Burles ·

  • J. X. Prochaska · A. M. Wolfe · J. C. Howk · E. Gawiser · S. M. Burles · J. Cooke ·
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    ABSTRACT: For nearly all observations, the HIRES spectra were acquired using either a 0.8" or 1.1" wide decker (FWHM about 6 and 8km/s, respectively) and the ESI observations were carried out with the 0.5" or 0.75" slit (FWHM about 33 and 44km/s, respectively). All of the HIRES spectra were acquired with the original Tektronix 2048*2048CCD. In general we strove to achieve a final signal-to-noise ratio (S/N) of >15pixel-1^ (2km/s/pix for HIRES, 11km/s/pix for ESI). ESI has a fixed format that covers the spectral region {lambda}=4000 to 10000{AA}. (2 data files).
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    Arlin P. S. Crotts · Scott Burles · and David Tytler ·
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    ABSTRACT: We observe with Keck/HIRES the z ≈ 2.5 QSO triplet 1623+27 in order to explore on the scale of 1 Mpc the spatial clustering of C IV absorbers between adjacent sight lines. We find this signal to be significantly weaker than the clustering in velocity on corresponding scales along single sight lines, assuming that the relative velocity of absorbers is dominated by the Hubble flow. This indicates that small-scale clustering (200 km s-1 < Δv < 600 km s-1) of the C IV absorbers cannot be interpreted in terms of the positions of the absorbers in space but must be considered as internal motions within individual absorbers or within clusters of absorbers whose internal velocities dominate over Hubble expansion across the cluster scale. If the single sight line signal is due to spatial clustering, it is caused by absorber clusters smaller than would be implied by their velocities if a Hubble flow is assumed. The spatial clustering of C IV absorbers at z ≈ 2 is consistent with data on Lyα forest clustering measured in the same way at the same redshifts. However, present-day galaxy clustering, evolved back to z ≈ 2, is consistent with C IV spatial clustering but perhaps not with that of the Lyα forest. Even so, one cannot as yet distinguish the two absorber populations on the basis of spatial clustering on these small scales.
    The Astrophysical Journal 01/2009; 489(1):L7. DOI:10.1086/310948 · 5.99 Impact Factor

Publication Stats

16k Citations
621.28 Total Impact Points


  • 2012
    • University of Utah
      • Department of Physics and Astronomy
      Salt Lake City, Utah, United States
  • 2002-2012
    • Massachusetts Institute of Technology
      • • Department of Physics
      • • Kavli Institute for Astrophysics and Space Research
      Cambridge, Massachusetts, United States
    • CUNY Graduate Center
      New York City, New York, United States
  • 1998-2009
    • University of Chicago
      • Department of Astronomy and Astrophysics
      Chicago, Illinois, United States
  • 1996-2009
    • University of California, San Diego
      • Center for Astrophysics and Space Sciences (CASS)
      San Diego, CA, United States
  • 2008
    • University of California, Santa Barbara
      • Department of Physics
      Santa Barbara, California, United States
  • 2007-2008
    • Fermi National Accelerator Laboratory (Fermilab)
      Batavia, Illinois, United States
    • Space Telescope Science Institute
      Baltimore, Maryland, United States
    • University of Pittsburgh
      • Physics and Astronomy
      Pittsburgh, Pennsylvania, United States
  • 2002-2008
    • California Institute of Technology
      • Department of Astronomy
      Pasadena, California, United States
  • 2005
    • Harvard-Smithsonian Center for Astrophysics
      • Smithsonian Astrophysical Observatory
      Cambridge, Massachusetts, United States
    • Tokyo Institute of Technology
      • Department of Physics
      Edo, Tōkyō, Japan
    • Princeton University
      • Department of Astrophysical Sciences
      Princeton, New Jersey, United States
  • 2003
    • Pennsylvania State University
      • Department of Astronomy and Astrophysics
      University Park, Maryland, United States
  • 2001
    • Carnegie Mellon University
      • Department of Physics
      Pittsburgh, Pennsylvania, United States