Huan Lin

Fermi National Accelerator Laboratory (Fermilab), Winfield, IL, United States

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Publications (105)379.18 Total impact

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    ABSTRACT: We describe ten strong lensing galaxy clusters of redshift 0.26-0.56 that were found in the Sloan Digital Sky Survey. We present measurements of richness, mass and velocity dispersion for the clusters. We find that in order to use the mass-richness relation from Johnston et al. (2007), which was established at mean redshift of 0.25, it is necessary to scale measured richness values up by 1.47. We also present measurements of Einstein radius, mass and velocity dispersion for the lensing systems. The Einstein radii are all relatively small, between 5.4-13 arcseconds. Finally we consider if there is evidence that our clusters are more concentrated than standard cosmology would predict. We find that six of our clusters do not show evidence of overconcentration, while four of our clusters do. We note a correlation between overconcentration and mass, as the four clusters showing evidence of overconcentration are all lower-mass clusters.
    The Astrophysical Journal 11/2012; · 6.73 Impact Factor
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    ABSTRACT: This white paper describes the LSST Dark Energy Science Collaboration (DESC), whose goal is the study of dark energy and related topics in fundamental physics with data from the Large Synoptic Survey Telescope (LSST). It provides an overview of dark energy science and describes the current and anticipated state of the field. It makes the case for the DESC by laying out a robust analytical framework for dark energy science that has been defined by its members and the comprehensive three-year work plan they have developed for implementing that framework. The analysis working groups cover five key probes of dark energy: weak lensing, large scale structure, galaxy clusters, Type Ia supernovae, and strong lensing. The computing working groups span cosmological simulations, galaxy catalogs, photon simulations and a systematic software and computational framework for LSST dark energy data analysis. The technical working groups make the connection between dark energy science and the LSST system. The working groups have close linkages, especially through the use of the photon simulations to study the impact of instrument design and survey strategy on analysis methodology and cosmological parameter estimation. The white paper describes several high priority tasks identified by each of the 16 working groups. Over the next three years these tasks will help prepare for LSST analysis, make synergistic connections with ongoing cosmological surveys and provide the dark energy community with state of the art analysis tools. Members of the community are invited to join the LSST DESC, according to the membership policies described in the white paper. Applications to sign up for associate membership may be made by submitting the Web form at http://www.slac.stanford.edu/exp/lsst/desc/signup.html with a short statement of the work they wish to pursue that is relevant to the LSST DESC.
    11/2012;
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    ABSTRACT: We present the first results of the SOAR (Southern Astrophysical Research) Gravitational Arc Survey (SOGRAS). The survey imaged 47 clusters in two redshift intervals centered at $z=0.27$ and $z=0.55$, targeting the richest clusters in each interval. Images were obtained in the $g'$, $r'$ and $i'$ bands using the SOAR Optical Imager (SOI), with a median seeing of 0.83, 0.76 and 0.71 arcsec, respectively, in these filters. Most of the survey clusters are located within the Sloan Digital Sky Survey (SDSS) Stripe 82 region and all of them are in the SDSS footprint. Photometric calibration was therefore performed using SDSS stars located in our SOI fields. We reached for galaxies in all fields the detection limits of $g \sim 23.5$, $r \sim 23$ and $i \sim 22.5$ for a signal-to-noise ratio (S/N) = 3. As a by-product of the image processing, we generated a source catalogue with 19760 entries, the vast majority of which are galaxies, where we list their positions, magnitudes and shape parameters. We compared our galaxy shape measurements to those of local galaxies and concluded that they were not strongly affected by seeing. From the catalogue data, we are able to identify a red sequence of galaxies in most clusters in the lower $z$ range. We found 16 gravitational arc candidates around 8 clusters in our sample. They tend to be bluer than the central galaxies in the lensing cluster. A preliminary analysis indicates that $\sim 10%$ of the clusters have arcs around them, with a possible indication of a larger efficiency associated to the high-$z$ systems when compared to the low-$z$ ones. Deeper follow-up images with Gemini strengthen the case for the strong lensing nature of the candidates found in this survey.
    Monthly Notices of the Royal Astronomical Society 10/2012; 432(1). · 5.52 Impact Factor
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    ABSTRACT: We describe the preliminary design of the Dark Energy Spectrometer (DESpec), a fiber-fed spectroscopic instrument concept for the Blanco 4-meter telescope at Cerro Tololo Inter-American Observatory (CTIO). DESpec would take advantage of the infrastructure recently deployed for the Dark Energy Camera (DECam). DESpec would be mounted in the new DECam prime focus cage, would be interchangeable with DECam, would share the DECam optical corrector, and would feature a focal plane with ~4000 robotically positioned optical fibers feeding multiple high-throughput spectrometers. The instrument would have a field of view of 3.8 square degrees, a wavelength range of approximately 500&lt<1000 nm, and a spectral resolution of R~3000. DESpec would provide a powerful spectroscopic follow-up system for sources in the Southern hemisphere discovered by the Dark Energy Survey and LSST.λ
    Proc SPIE 09/2012;
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    ABSTRACT: The Dark Energy Survey (DES) is a 5000 deg2 grizY survey reaching characteristic photometric depths of 24th magnitude (10 sigma) and enabling accurate photometry and morphology of objects ten times fainter than in SDSS. Preparations for DES have included building a dedicated 3 deg2 CCD camera (DECam), upgrading the existing CTIO Blanco 4m telescope and developing a new high performance computing (HPC) enabled data management system (DESDM). The DESDM system will be used for processing, calibrating and serving the DES data. The total data volumes are high (~2PB), and so considerable effort has gone into designing an automated processing and quality control system. Special purpose image detrending and photometric calibration codes have been developed to meet the data quality requirements, while survey astrometric calibration, coaddition and cataloging rely on new extensions of the AstrOmatic codes which now include tools for PSF modeling, PSF homogenization, PSF corrected model fitting cataloging and joint model fitting across multiple input images. The DESDM system has been deployed on dedicated development clusters and HPC systems in the US and Germany. An extensive program of testing with small rapid turn-around and larger campaign simulated datasets has been carried out. The system has also been tested on large real datasets, including Blanco Cosmology Survey data from the Mosaic2 camera. In Fall 2012 the DESDM system will be used for DECam commissioning, and, thereafter, the system will go into full science operations.
    Proc SPIE 07/2012;
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    ABSTRACT: We use N-body-spectro-photometric simulations to investigate the impact of incompleteness and incorrect redshifts in spectroscopic surveys to photometric redshift training and calibration and the resulting effects on cosmological parameter estimation from weak lensing shear-shear correlations. The photometry of the simulations is modeled after the upcoming Dark Energy Survey and the spectroscopy is based on a low/intermediate resolution spectrograph with wavelength coverage of 5500{\AA} < {\lambda} < 9500{\AA}. The principal systematic errors that such a spectroscopic follow-up encounters are incompleteness (inability to obtain spectroscopic redshifts for certain galaxies) and wrong redshifts. Encouragingly, we find that a neural network-based approach can effectively describe the spectroscopic incompleteness in terms of the galaxies' colors, so that the spectroscopic selection can be applied to the photometric sample. Hence, we find that spectroscopic incompleteness yields no appreciable biases to cosmology, although the statistical constraints degrade somewhat because the photometric survey has to be culled to match the spectroscopic selection. Unfortunately, wrong redshifts have a more severe impact: the cosmological biases are intolerable if more than a percent of the spectroscopic redshifts are incorrect. Moreover, we find that incorrect redshifts can also substantially degrade the accuracy of training set based photo-z estimators. The main problem is the difficulty of obtaining redshifts, either spectroscopically or photometrically, for objects at z > 1.3. We discuss several approaches for reducing the cosmological biases, in particular finding that photo-z error estimators can reduce biases appreciably.
    07/2012;
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    ABSTRACT: The shapes of distant galaxies are sheared by intervening galaxy clusters. We examine this effect in Stripe 82, a 275 deg2 region observed multiple times in the Sloan Digital Sky Survey (SDSS) and co-added to achieve greater depth. We obtain a mass-richness calibration that is similar to other SDSS analyses, demonstrating that the co-addition process did not adversely affect the lensing signal. We also propose a new parameterization of the effect of tomography on the cluster lensing signal which does not require binning in redshift, and we show that using this parameterization we can detect tomography for stacked clusters at varying redshifts. Finally, due to the sensitivity of the tomographic detection to accurately marginalize over the effect of the cluster mass, we show that tomography at low redshift (where dependence on exact cosmological models is weak) can be used to constrain mass profiles in clusters.
    The Astrophysical Journal 03/2012; 748(2):128. · 6.73 Impact Factor
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    ABSTRACT: We present and describe a catalog of galaxy photometric redshifts (photo-z) for the Sloan Digital Sky Survey (SDSS) Co-add Data. We use the artificial neural network (ANN) technique to calculate the photo-z and the nearest neighbor error method to estimate photo-z errors for ~13 million objects classified as galaxies in the co-add with r < 24.5. The photo-z and photo-z error estimators are trained and validated on a sample of ~83,000 galaxies that have SDSS photometry and spectroscopic redshifts measured by the SDSS Data Release 7 (DR7), the Canadian Network for Observational Cosmology Field Galaxy Survey, the Deep Extragalactic Evolutionary Probe Data Release 3, the VIsible imaging Multi-Object Spectrograph-Very Large Telescope Deep Survey, and the WiggleZ Dark Energy Survey. For the best ANN methods we have tried, we find that 68% of the galaxies in the validation set have a photo-z error smaller than σ68 = 0.031. After presenting our results and quality tests, we provide a short guide for users accessing the public data.
    The Astrophysical Journal 02/2012; 747(1):59. · 6.73 Impact Factor
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    ABSTRACT: We present and describe a catalog of galaxy photometric redshifts (photo-z's) for the Sloan Digital Sky Survey (SDSS) Coadd Data. We use the Artificial Neural Network (ANN) technique to calculate photo-z's and the Nearest Neighbor Error (NNE) method to estimate photo-z errors for $\sim$ 13 million objects classified as galaxies in the coadd with $r < 24.5$. The photo-z and photo-z error estimators are trained and validated on a sample of $\sim 83,000$ galaxies that have SDSS photometry and spectroscopic redshifts measured by the SDSS Data Release 7 (DR7), the Canadian Network for Observational Cosmology Field Galaxy Survey (CNOC2), the Deep Extragalactic Evolutionary Probe Data Release 3(DEEP2 DR3), the VIsible imaging Multi-Object Spectrograph - Very Large Telescope Deep Survey (VVDS) and the WiggleZ Dark Energy Survey. For the best ANN methods we have tried, we find that 68% of the galaxies in the validation set have a photo-z error smaller than $\sigma_{68} =0.031$. After presenting our results and quality tests, we provide a short guide for users accessing the public data.
    11/2011;
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    ABSTRACT: Stripe 82 in the Sloan Digital Sky Survey was observed multiple times, allowing deeper images to be constructed by coadding the data. Here we analyze the ellipticities of background galaxies in this 275 square degree region, searching for evidence of distortions due to cosmic shear. The E-mode is detected in both real and Fourier space with $>5$-$\sigma$ significance on degree scales, while the B-mode is consistent with zero as expected. The amplitude of the signal constrains the combination of the matter density $\Omega_m$ and fluctuation amplitude $\sigma_8$ to be $\Omega_m^{0.7}\sigma_8 = 0.252^{+0.032}_{-0.052}$.
    The Astrophysical Journal 11/2011; · 6.73 Impact Factor
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    ABSTRACT: We present details of the construction and characterization of the coaddition of the Sloan Digital Sky Survey Stripe 82 \ugriz\ imaging data. This survey consists of 275 deg$^2$ of repeated scanning by the SDSS camera of $2.5\arcdeg$ of $\delta$ over $-50\arcdeg \le \alpha \le 60\arcdeg$ centered on the Celestial Equator. Each piece of sky has $\sim 20$ runs contributing and thus reaches $\sim2$ magnitudes fainter than the SDSS single pass data, i.e. to $r\sim 23.5$ for galaxies. We discuss the image processing of the coaddition, the modeling of the PSF, the calibration, and the production of standard SDSS catalogs. The data have $r$-band median seeing of 1.1\arcsec, and are calibrated to $\le 1%$. Star color-color, number counts, and psf size vs modelled size plots show the modelling of the PSF is good enough for precision 5-band photometry. Structure in the psf-model vs magnitude plot show minor psf mis-modelling that leads to a region where stars are being mis-classified as galaxies, and this is verified using VVDS spectroscopy. As this is a wide area deep survey there are a variety of uses for the data, including galactic structure, photometric redshift computation, cluster finding and cross wavelength measurements, weak lensing cluster mass calibrations, and cosmic shear measurements.
    11/2011;
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    ABSTRACT: We present measurements of two types of cluster galaxy alignments based on a volume limited and highly pure ($\ge$ 90%) sample of clusters from the GMBCG catalog derived from SDSS DR7. We detect a clear BCG alignment (the alignment of major axis of the BCG toward the distribution of cluster satellite galaxies). We find that the BCG alignment signal becomes stronger as the redshift and BCG absolute magnitude decrease, and becomes weaker as BCG stellar mass decreases. No dependence of the BCG alignment on cluster richness is found. We can detect a statistically significant ($\ge$ 3 sigma) satellite alignment (the alignment of the major axes of the cluster satellite galaxies toward the BCG) only when we use the isophotal fit position angles (PAs, hereafter), and the satellite alignment depends on the apparent magnitudes rather than the absolute magnitudes of the BCGs. This suggests the detected satellite alignment based on isophotoal PAs from the SDSS pipeline is possibly due to the contamination from the diffuse light of nearby BCGs. We caution that this should not be simply interpreted as non-existence of the satellite alignment, but rather that we cannot detect them with our current photometric SDSS data. We perform our measurements on both SDSS $r$ band and $i$ band data, but did not observe a passband dependence of the alignments.
    The Astrophysical Journal 03/2011; · 6.73 Impact Factor
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    ABSTRACT: We report the discovery of seven new, very bright gravitational lens systems from our ongoing gravitational lens search, the Sloan Bright Arcs Survey (SBAS). Two of the systems are confirmed to have high source redshifts z = 2.19 and z = 2.94. Three other systems lie at intermediate redshift with z = 1.33, 1.82, 1.93 and two systems are at low redshift z = 0.66, 0.86. The lensed source galaxies in all of these systems are bright, with i-band magnitudes ranging from 19.73 to 22.06. We present the spectrum of each of the source galaxies in these systems along with estimates of the Einstein radius for each system. The foreground lens in most systems is identified by a red sequence based cluster finder as a galaxy group; one system is identified as a moderately rich cluster. In total, SBAS has now discovered 19 strong lens systems in the SDSS imaging data, 8 of which are among the highest surface brightness z 2-3 galaxies known.
    The Astrophysical Journal Letters 11/2010; 724(2):L137. · 6.35 Impact Factor
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    ABSTRACT: Large mosaic multiCCD camera is the key instrument for modern digital sky survey. DECam is an extremely red sensitive 520 Megapixel camera designed for the incoming Dark Energy Survey (DES). It is consist of sixty two 4k$\times$2k and twelve 2k x 2k 250-micron thick fully-depleted CCDs, with a focal plane of 44 cm in diameter and a field of view of 2.2 square degree. It will be attached to the Blanco 4-meter telescope at CTIO. The DES will cover 5000 square-degrees of the southern galactic cap in 5 color bands (g, r, i, z, Y) in 5 years starting from 2011. To achieve the science goal of constraining the Dark Energy evolution, stringent requirements are laid down for the design of DECam. Among them, the flatness of the focal plane needs to be controlled within a 60-micron envelope in order to achieve the specified PSF variation limit. It is very challenging to measure the flatness of the focal plane to such precision when it is placed in a high vacuum dewar at 173 K. We developed two image based techniques to measure the flatness of the focal plane. By imaging a regular grid of dots on the focal plane, the CCD offset along the optical axis is converted to the variation the grid spacings at different positions on the focal plane. After extracting the patterns and comparing the change in spacings, we can measure the flatness to high precision. In method 1, the regular dots are kept in high sub micron precision and cover the whole focal plane. In method 2, no high precision for the grid is required. Instead, we use a precise XY stage moves the pattern across the whole focal plane and comparing the variations of the spacing when it is imaged by different CCDs. Simulation and real measurements show that the two methods work very well for our purpose, and are in good agreement with the direct optical measurements. Comment: Presented at SPIE Conference,Ground-based and Airborne Instrumentation for Astronomy III, San Diego, 2010
    Proc SPIE 10/2010;
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    ABSTRACT: We present low-resolution, rest-frame ~ 5 - 12 micron Spitzer/IRS spectra of two lensed z ~ 2 UV-bright star-forming galaxies, SDSS J120602.09+514229.5 and SDSS J090122.37+181432.3. Using the magnification boost from lensing, we are able to study the physical properties of these objects in greater detail than is possible for unlensed systems. In both targets, we detect strong PAH emission at 6.2, 7.7, and 11.3 microns, indicating the presence of vigorous star formation. For J1206, we find a steeply rising continuum and significant [S IV] emission, suggesting that a moderately hard radiation field is powering continuum emission from small dust grains. The strength of the [S IV] emission also implies a sub-solar metallicity of ~ 0.5 Z_{Sun}, confirming published rest-frame optical measurements. In J0901, the PAH lines have large rest-frame equivalent widths (> 1 micron) and the continuum rises slowly with wavelength, suggesting that any AGN contribution to L_{IR} is insignificant, in contrast to the implications of optical emission-line diagnostics. Using [O III] line flux as a proxy for AGN strength, we estimate that the AGN in J0901 provides only a small fraction of its mid-infrared continuum flux. By combining the detection of [Ar II] with an upper limit on [Ar III] emission, we infer a metallicity of > 1.3 Z_{Sun}. This work highlights the importance of combining rest-frame optical and mid-IR spectroscopy in order to understand the detailed properties of star-forming galaxies at high redshift. Comment: 20 pages, 3 figures, 2 tables. ApJ accepted
    The Astrophysical Journal 09/2010; · 6.73 Impact Factor
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    ABSTRACT: Weak lensing tomography is a powerful new tool for constraining cosmology in a way that is independent of both the physics and systematics of other methods. By measuring the variation in the weak lensing shear as a function of background galaxy redshift, we make a purely geometric measurement of the expansion rate history. This has the ability to measure dark energy and even constrain deviations from general relativity. We apply this technique to 91 clusters for which we have Hubble Space Telescope data. This proposal, a continuation of a previous NOAO project, seeks to follow up these clusters and obtain ground-based photometry which will provide photometric redshifts, fully enabling the technique. In addition, we will provide a legacy data set of galaxy clusters with Hubble images and accurate photometric redshifts which will be of great value to the astronomical community.
    NOAO Proposal. 08/2010;
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    ABSTRACT: We report the discovery of four very bright, strongly lensed galaxies found via systematic searches for arcs in Sloan Digital Sky Survey Data Release 5 and 6. These were followed up with spectroscopy and imaging data from the Astrophysical Research Consortium 3.5 m telescope at Apache Point Observatory and found to have redshift z > 2.0. With isophotal magnitudes r = 19.2-20.4 and 3'' diameter magnitudes r = 20.0-20.6, these systems are some of the brightest and highest surface brightness lensed galaxies known in this redshift range. In addition to the magnitudes and redshifts, we present estimates of the Einstein radii, which range from 50 to 127, and use those to derive the enclosed masses of the lensing galaxies.
    The Astrophysical Journal 11/2009; 707(1):686. · 6.73 Impact Factor
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    ABSTRACT: This is the first in a series of papers on the weak lensing effect caused by clusters of galaxies in Sloan Digital Sky Survey. The photometrically selected cluster sample, known as MaxBCG, includes ~130,000 objects between redshift 0.1 and 0.3, ranging in size from small groups to massive clusters. We split the clusters into bins of richness and luminosity and stack the surface density contrast to produce mean radial profiles. The mean profiles are detected over a range of scales, from the inner halo (25 kpc h –1) well into the surrounding large-scale structure (30 Mpc h –1), with a significance of 15 to 20 in each bin. The signal over this large range of scales is best interpreted in terms of the cluster-mass cross-correlation function. We pay careful attention to sources of systematic error, correcting for them where possible. The resulting signals are calibrated to the ~10% level, with the dominant remaining uncertainty being the redshift distribution of the background sources. We find that the profiles scale strongly with richness and luminosity. We find that the signal within a given richness bin depends upon luminosity, suggesting that luminosity is more closely correlated with mass than galaxy counts. We split the samples by redshift but detect no significant evolution. The profiles are not well described by power laws. In a subsequent series of papers, we invert the profiles to three-dimensional mass profiles, show that they are well fit by a halo model description, measure mass-to-light ratios, and provide a cosmological interpretation.
    The Astrophysical Journal 09/2009; 703(2):2217. · 6.73 Impact Factor
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    ABSTRACT: We describe and present initial results of a weak lensing survey of nearby (z 0.1) galaxy clusters in the Sloan Digital Sky Survey (SDSS). In this first study, galaxy clusters are selected from the SDSS spectroscopic galaxy cluster catalogs of Miller et al. and Berlind et al. We report a total of seven individual low-redshift cluster weak lensing measurements that include A2048, A1767, A2244, A1066, A2199, and two clusters specifically identified with the C4 algorithm. Our program of weak lensing of nearby galaxy clusters in the SDSS will eventually reach ~200 clusters, making it the largest weak lensing survey of individual galaxy clusters to date.
    The Astrophysical Journal 08/2009; 702(2):L110. · 6.73 Impact Factor
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    ABSTRACT: We report on the discovery of a very bright z = 2.00 star-forming galaxy that is strongly lensed by a foreground z = 0.422 luminous red galaxy (LRG), SDSS J120602.09+514229.5. This system, nicknamed the "Clone," was found in a systematic search for bright arcs lensed by LRGs and brightest cluster galaxies in the Sloan Digital Sky Survey Data Release 5 sample. Follow-up observations on the Subaru 8.2 m telescope on Mauna Kea and the Astrophysical Research Consortium 3.5 m telescope at Apache Point Observatory confirmed the lensing nature of this system. A simple lens model for the system, assuming a singular isothermal ellipsoid mass distribution, yields an Einstein radius of θEin = 3.82 ± 003 or 14.8 ± 0.1 h –1 kpc at the lens redshift. The total projected mass enclosed within the Einstein radius is 2.10 ± 0.03 × 1012 h –1 M ☉, and the magnification factor for the source galaxy is 27 ± 1. Combining the lens model with our gVriz photometry, we find a (unlensed) star formation rate (SFR) for the source galaxy of 32 h –1 M ☉ yr–1, adopting a fiducial constant SFR model with an age of 100 Myr and E(B – V) = 0.25. With an apparent magnitude of r = 19.8, this system is among the very brightest lensed z ≥ 2 galaxies, and provides an excellent opportunity to pursue detailed studies of the physical properties of an individual high-redshift star-forming galaxy.
    The Astrophysical Journal 06/2009; 699(2):1242. · 6.73 Impact Factor

Publication Stats

4k Citations
379.18 Total Impact Points

Institutions

  • 1999–2012
    • Fermi National Accelerator Laboratory (Fermilab)
      • Center for Particle Astrophysics
      Winfield, IL, United States
  • 2009
    • The University of Tokyo
      • Institute for Cosmic Ray Research
      Edo, Tōkyō, Japan
    • Harvard-Smithsonian Center for Astrophysics
      Cambridge, Massachusetts, United States
    • American Museum of Natural History
      New York City, New York, United States
  • 2008
    • Gemini Observatory
      Hilo, Hawaii, United States
  • 1999–2008
    • The University of Arizona
      • Department of Astronomy
      Tucson, Arizona, United States
  • 2007
    • French National Centre for Scientific Research
      Lutetia Parisorum, Île-de-France, France
  • 2006–2007
    • University of Chicago
      • • Department of Physics
      • • Department of Astronomy and Astrophysics
      Chicago, Illinois, United States
  • 2005
    • Academia Sinica
      • Institute of Astronomy and Astrophysics
      T’ai-pei, Taipei, Taiwan
  • 1996–1998
    • University of Toronto
      Toronto, Ontario, Canada
    • JVS Toronto
      Toronto, Ontario, Canada