S. A. Wright

Publications (10)4.03 Total impact

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  Available from: Phil Marshall

  Article: Dark Matter Structures in the Universe: Prospects for Optical Astronomy in the Next Decade

  P. J. Marshall, M. Auger, J. G. Bartlett, M. Bradac, A. Cooray, N. Dalal, G. Dobler, C. D. Fassnacht, B. Jain, C. R. Keeton, R. Mandelbaum, L. A. Moustakas, M. A. Strauss, J. A. Tyson, D. Wittman, S. A. Wright
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  ABSTRACT: The Cold Dark Matter theory of gravitationally-driven hierarchical structure formation has earned its status as a paradigm by explaining the distribution of matter over large spans of cosmic distance and time. However, its central tenet, that most of the matter in the universe is dark and exotic, is still unproven; the dark matter hypothesis is sufficiently audacious as to continue to warrant a diverse battery of tests. While local searches for dark matter particles or their annihilation signals could prove the existence of the substance itself, studies of cosmological dark matter in situ are vital to fully understand its role in structure formation and evolution. We argue that gravitational lensing provides the cleanest and farthest-reaching probe of dark matter in the universe, which can be combined with other observational techniques to answer the most challenging and exciting questions that will drive the subject in the next decade: What is the distribution of mass on sub-galactic scales? How do galaxy disks form and bulges grow in dark matter halos? How accurate are CDM predictions of halo structure? Can we distinguish between a need for a new substance (dark matter) and a need for new physics (departures from General Relativity)? What is the dark matter made of anyway? We propose that the central tool in this program should be a wide-field optical imaging survey, whose true value is realized with support in the form of high-resolution, cadenced optical/infra-red imaging, and massive-throughput optical spectroscopy.
  03/2009;
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  Available from: ArXiv

  Article: Triggered or Self-Regulated Star Formation within Intermediate Redshift Luminous Infrared Galaxies (I). Morphologies and Spatially Resolved Spectral Energy Distributions

  J. Melbourne, M. Ammons, S. A. Wright, A. Metevier, E. Steinbring, C. Max, D. C. Koo, J. E. Larkin, M. Barczys
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  ABSTRACT: We imaged a set of 15 intermediate redshift (z~0.8) luminous infrared galaxies (LIRGs) with the Keck Laser Guide Star (LGS) AO facility. These galaxies were selected from the GOODS-S field, allowing us to combine the high spatial resolution HST optical (B, V, i, and z-bands) images with our near-infrared (K'-band) images to study the LIRG morphologies and spatially resolved spectral energy distributions (SEDs). Two thirds of the LIRGs are disk galaxies, with only one third showing some evidence for interactions, minor, or major mergers. In contrast with local LIRG disks (which are primarily barred systems), only 10% of the LIRG disks in our sample contain a prominent bar. While the optical bands tend to show significant point-like substructure, indicating distributed star formation, the AO K-band images tend to be smooth. The SEDs of the LIRGs are consistent with distributed dusty star formation, as exhibited by optical to IR colors redder than allowed by old stellar populations alone. This effect is most pronounced in the galaxy cores, possibly indicating central star formation. We also observed a set of 11 intermediate redshift comparison galaxies, selected to be non-ellipticals with apparent K-band magnitudes comparable to the LIRGs. The "normal" (non-LIRG) systems tended to have lower optical luminosity, lower stellar mass, and more irregular morphology than the LIRGs. Half of the "normal" galaxies have SEDs consistent with intermediate aged stellar populations and minimal dust. The other half show evidence for some dusty star formation, usually concentrated in their cores. Our work suggests that the LIRG disk galaxies are similar to large disk systems today, undergoing self regulated star formation, only at 10 - 20 times higher rates. (Abridged) Comment: Accepted for Publication in AJ. 27 pages, 21 figures, 3 tables
  01/2008;
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  Available from: K. S. Dawson

  Article: Rest-Frame R-band Light Curve of a z ~ 1.3 Supernova Obtained with Keck Laser Adaptive Optics

  J. Melbourne, K. S. Dawson, D. C. Koo, C. Max, J. E. Larkin, S. A. Wright, E. Steinbring, M. Barczys, G. Aldering, K. Barbary, [......], M. Kowalski, N. Kuznetsova, C. Lidman, T. Morokuma, S. Perlmutter, D. Rubin, D. J. Schlegel, A. L. Spadafora, N. Takanashi, and N. Yasuda
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  ABSTRACT: We present Keck diffraction-limited H-band photometry of a z ~ 1.3 Type Ia supernova (SN) candidate, first identified in a Hubble Space Telescope search for SNe in massive high-redshift galaxy clusters. The adaptive optics (AO) data were obtained with the Laser Guide Star facility during four observing runs from 2005 September to November. In the analysis of data from the observing run nearest to maximum SN brightness, the SN was found to have a magnitude H = 23.9 ± 0.14 (Vega). We present the H-band (approximately rest-frame R) light curve and provide a detailed analysis of the AO photometric uncertainties. By constraining the aperture correction with a nearby (4'' separation) star we achieve 0.14 mag photometric precision, despite the spatially varying AO point-spread function.
  The Astronomical Journal 12/2007; 133(6):2709. · 4.03 Impact Factor
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  Available from: Phil Marshall

  Article: Super-resolving distant galaxies with gravitational telescopes: Keck-LGSAO and Hubble imaging of the lens system SDSSJ0737+3216

  P. J. Marshall, T. Treu, J. Melbourne, R. Gavazzi, K. Bundy, S. M. Ammons, A. S. Bolton, S. Burles, J. E. Larkin, D. Le Mignant, D. C. Koo, L. V. E. Koopmans, C. E. Max, L. A. Moustakas, E. Steinbring, S. A. Wright
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  ABSTRACT: We combine high-resolution images in four optical/infra-red bands, obtained with the laser guide star adaptive optics system on the Keck Telescope and with the Hubble Space Telescope, to study the gravitational lens system SDSSJ0737+3216 (lens redshift 0.3223, source redshift 0.5812). We show that (under favorable observing conditions) ground-based images are comparable to those obtained with HST in terms of precision in the determination of the parameters of both the lens mass distribution and the background source. We also quantify the systematic errors associated with both the incomplete knowledge of the PSF, and the uncertain process of lens galaxy light removal, and find that similar accuracy can be achieved with Keck LGSAO as with HST. We then exploit this well-calibrated combination of optical and gravitational telescopes to perform a multi-wavelength study of the source galaxy at 0.01" effective resolution. We find the Sersic index to be indicative of a disk-like object, but the measured half-light radius (0.59+-0.007+-0.1 kpc) and stellar mass (2.0+-1.0+-0.8e9Msun) place it more than three sigma away from the local disk size-mass relation. The SDSSJ0737+3216 source has the characteristics of the most compact faint blue galaxies studied, and has comparable size and mass to dwarf early-type galaxies in the local universe. With the aid of gravitational telescopes to measure individual objects' brightness profiles to 10% accuracy, the study of the high-redshift size-mass relation may be extended by an order of magnitude or more beyond existing surveys at the low-mass end, thus providing a new observational test of galaxy formation models. Comment: ApJ, in press; 17 pages, 8 figures
  10/2007;
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  Available from: arxiv.org

  Article: Integral Field Spectroscopy of a Candidate Disk Galaxy at z~1.5 using Laser Guide Star Adaptive Optics

  S. A. Wright, J. E. Larkin, M. Barczys, D. K. Erb, C. Iserlohe, A. Krabbe, D. R. Law, M. W. McElwain, A. Quirrenbach, C. C. Steidel, J. Weiss
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  ABSTRACT: We present 0.1" resolution near-infrared integral field spectroscopy of Halpha in a z=1.4781 star forming galaxy, Q2343-BM133. These observations were obtained with OSIRIS (OH Suppressing Infra-Red Imaging Spectrograph) using the W.M. Keck Observatory Laser Guide Star Adaptive Optics system. Halpha emission is resolved over a 0.8" (6.8 kpc) x 0.5" (4.3 kpc) region with a 0.1" spatial resolution. We find a global flux of 4.2+/-0.6x10^{-16} ergs s^{-1} cm^{-2}, and detect a spatially resolved velocity gradient of ~134 km s^{-1} across the galaxy and a global velocity dispersion of 73+/-9 km s^{-1}. An upper limit of NII/Halpha < 0.12 is inferred, which implies that this galaxy is not dominated by an active galactic nucleus and has a metallicity at or below 1/2 solar metallicity. We derive a star formation rate (SFR) of 47+/-6 Msun yr^{-1}, and a dereddened SFR of 66+/-9 Msun yr^{-1}. Two-dimensional kinematics for Q2343-BM133 fit well with an inclined-disk model, with which we estimate an enclosed mass of 4.3x10^{9} Msun within 5.5 kpc. A possible merger scenario is also presented, and can not be fully ruled out. We derive a virial mass of 1.1x10^{10} Msun for a disk geometry, using the observed velocity dispersion. We propose that Q2343-BM133 is currently at an early stage of disk formation at a look-back time of 9.3 Gyr.
  01/2007;
• Article: Diffraction Limited Imaging Spectroscopy of a Sgr A* Flare with OSIRIS

  A Krabbe, C Iserlohe, J E Larkin, M Barczys, M McElwain, J Weiss, S A Wright, A Quirrenbach
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  ABSTRACT: We present diffraction limited K-band integral field spectroscopy of a flare associated with Sgr A*. Prom the spectrum we determined the K-band spectral index of the pure flare emission to be (F(ν) να) of α = −2.6 ± 0.9. If we do not subtract the quiet state emission of SgrA*, then our spectral index is consistent with earlier observations of Ghez et al. (2005, ApJ, 635, in print). We compare our observations with other data already published and discuss the implications.
  Journal of Physics Conference Series 12/2006; 54(1):406.
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  Available from: arxiv.org

  Article: Diffraction Limited Imaging Spectroscopy of the SgrA* Region using OSIRIS, a new Keck Instrument

  A. Krabbe, C. Iserlohe, J. E. Larkin, M. Barczys, M. McElwain, J. Weiss, S. A. Wright, A. Quirrenbach
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  ABSTRACT: We present diffraction limited spectroscopic observations of an infrared flare associated with the radio source SgrA*. These are the first results obtained with OSIRIS, the new facility infrared imaging spectrograph for the Keck Observatory operated with the laser guide star adaptive optics system. After subtracting the spectrum of precursor emission at the location of Sgr A*, we find the flare has a spectral index of -2.6 +- 0.9. If we do not subtract the precursor light, then our spectral index is consistent with earlier observations by Ghez et al. (2005). All observations published so far suggest that the spectral index is a function of the flare's K-band flux. Comment: paper accepted for publication in ApJ Letters
  05/2006;
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  Available from: arxiv.org

  Article: Merging Galaxies in Goods-s: First Extragalactic Results from Keck Laser Adaptive Optics

  J. Melbourne, S. A. Wright, M. Barczys, A. H. Bouchez, J. Chin, M. A. van Dam, S. Hartman, E. Johansson, D. C. Koo, R. Lafon, J. Larkin, D. Le Mignant, J. Lotz, C. E. Max, D. M. Pennington, P. J. Stomski, D. Summers, P. L. Wizinowich
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  ABSTRACT: The Center for Adaptive Optics Treasury Survey (CATS) aims to combine deep HST images in the optical with deep Keck adaptive optics (AO) data in the near-infrared (NIR) to study distant galaxies, AGN, and supernovae. We recently achieved an important new milestone by securing the first Keck laser guide star AO image of faint galaxies. Six galaxies with redshifts ranging from 0.3-1.0 were targeted in one pointing in the GOODS-S field. Two are Chandra Deep Field South sources, XID-56 and XID-536, with complex morphologies suggestive of recent merger activity. Substructures seen in the NIR AO image (FWHM ~ 0.1"), including multiple tight knots in XID-56 and a double nucleus in XID-536, are confirmed in the optical HST images. These structures are unresolved in the best seeing-limited (FWHM ~ 0.5") NIR images. Stellar population synthesis models of the substructures indicate that XID-56 is a gas rich merger with a recent burst of star formation and significant amounts of dust. XID-536 appears to be a merger of two evolved stellar populations. Comment: 6 pages, 4 figures, 1 table, accepted ApJL 2005
  04/2005;
• Article: CATS: Center for Adaptive Optics Treasury Survey of Distant Galaxies Supernovae, and Active Galactic Nuclei

  D. C. Koo, S. M. Ammons, M. Barczys, J. E. Larkin, C. E. Max, J. Melbourne, A. J. Metevier, Eric Steinbring, S. A. Wright
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  Available from: arxiv.org

  Article: Triggered or Self-Regulated Star Formation Within Intermediate Redshift Luminous Infrared Galaxies. I. Morphologies and Spectral Energy Distributions

  J. Melbourne, M. Ammons, S. A. Wright, A. Metevier, Eric Steinbring, C. Max, D. C. Koo, J. E. Larkin, M. Barczys