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Automated Selection and Characterization of Emission-Line Sources in Advanced Camera for Surveys Wide Field Camera Grism Data

Meurer, Gerhardt R. and Tsvetanov, Z. I. and Gronwall, C. and Capak, P. and Blakeslee, J. P. and Benítez, N. and Ford, H. C. and Illingworth, G. D. and Bradley, L. D. and Pirzkal, N. and Walsh, J. and Bouwens, R. J. and Srinivasan, S. (2007) Automated Selection and Characterization of Emission-Line Sources in Advanced Camera for Surveys Wide Field Camera Grism Data. Astronomical Journal, 134 (1). pp. 77-95. ISSN 0004-6256. http://resolver.caltech.edu/CaltechAUTHORS:20091118-152456295

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Abstract

We present complementary techniques to find emission-line targets and measure their properties in a semi-automated fashion from grism observations obtained with the Advanced Camera for Surveys aboard the Hubble Space Telescope (HST). The first technique is to find all likely sources in a direct image, extract their spectra, and search them for emission lines. The second method is to look for emission-line sources as compact structures in an unsharp masked version of the grism image. Using these methods we identify 46 emission-line targets in the Hubble Deep Field-North using a modest (three-orbit) expenditure of HST observing time. Grism spectroscopy is a powerful tool for efficiently identifying interesting low-luminosity, moderate-redshift emission-line field galaxies. The sources found here have a median i-band (F775W) flux 1.5 mag fainter than the spectroscopic redshift catalog of Cohen et al. They have redshift z ≤ 1.42, and high equivalent widths (typically >100 Å) and are usually less luminous than the characteristic luminosity at the same redshift. The chief obstacle in interpreting the results is line identification, since the majority of sources have a single emission line and the spectral resolution is low. Photometric redshifts are useful for providing a first-guess redshift. However, even at the depth of the state-of-the-art ground-based and HST data used here, photometric errors can result in uncertainties in line identifications, especially for sources with i magnitudes fainter than 24.5 ABmag. Reliable line identification for the faintest emission-line galaxies requires additional ground-based spectroscopy for confirmation. Of particular concern are the faint high-EW [O II] emitters, which could represent a strongly evolving galaxy population if the possibility that they are misidentified lower redshift interlopers can be ruled out.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1086/518228DOIUNSPECIFIED
http://www.iop.org/EJ/abstract/1538-3881/134/1/77/PublisherUNSPECIFIED
Additional Information:© 2007 The American Astronomical Society. Received 2006 May 30; accepted 2007 March 9. ACS was developed under NASA contract NAS 5-32865, and this research has been supported by NASA grant NAG5-7697 and by an equipment grant from Sun Microsystems, Inc. The Space Telescope Science Institute is operated by Association of Universities for Research in Astronomy (AURA), Inc., under NASA contract NAS5-26555.We are grateful to K. Anderson, J. McCann, S. Busching, A. Framarini, S. Barkhouser, and T. Allen for their invaluable contributions to the ACS project at Johns Hopkins University. G. R. M. acknowledges useful conversations with Anna Pasquali, Marco Sirianni, James Rhoads, Sangeeta Malhotra, Chun Xu, and Søren Larsen. We thank the anonymous referee for suggestions that improved the science and readability of this paper.
Group:COSMOS
Funders:
Funding AgencyGrant Number
NASANAS 5-32865
NASANAG5-7697
Sun Microsystems, IncUNSPECIFIED
NASANAS5-26555
Subject Keywords:galaxies : distances and redshifts; galaxies : high-redshift; methods : data analysis; surveys; techniques : spectroscopic
Record Number:CaltechAUTHORS:20091118-152456295
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20091118-152456295
Official Citation:Automated Selection and Characterization of Emission-Line Sources in Advanced Camera for Surveys Wide Field Camera Grism Data Gerhardt R. Meurer, Z. I. Tsvetanov, C. Gronwall, P. Capak, J. P. Blakeslee, N. Benítez, H. C. Ford, G. D. Illingworth, L. D. Bradley, N. Pirzkal, J. Walsh, R. J. Bouwens, and S. Srinivasan 2007 The Astronomical Journal 134 77-95 doi: 10.1086/518228
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:16754
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:07 Dec 2009 18:59
Last Modified:06 Jul 2015 21:23

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