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A deep hubble space telescope search for escaping lymna continuum flux at z ~ 1.3: evidence for an evolving ionizing emissivity

Siana, Brian and Teplitz, Harry I. and Ferguson, Henry C. and Brown, Thomas M. and Giavalisco, Mauro and Dickinson, Mark and Chary, Ranga-Ram and de Mello, Duilia F. and Conselice, Christopher J. and Bridge, Carrie R. and Gardner, Jonathan P. and Colbert, James W. and Scarlata, Claudia (2010) A deep hubble space telescope search for escaping lymna continuum flux at z ~ 1.3: evidence for an evolving ionizing emissivity. Astrophysical Journal, 723 (1). pp. 241-250. ISSN 0004-637X.

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We have obtained deep Hubble Space Telescope far-UV images of 15 starburst galaxies at z ~ 1.3 in the GOODS fields to search for escaping Lyman continuum (LyC) photons. These are the deepest far-UV images (m_(AB) = 28.7, 3σ, 1" diameter) over this large an area (4.83 arcmin^2) and provide some of the best escape fraction constraints for any galaxies at any redshift. We do not detect any individual galaxies, with 3σ limits to the LyC (~700 Å) flux 50–149 times fainter (in f_ν) than the rest-frame UV (1500 Å) continuum fluxes. Correcting for the mean intergalactic medium (IGM) attenuation (factor ~2), as well as an intrinsic stellar Lyman break (factor ~3), these limits translate to relative escape fraction limits of f_(esc,rel) < [0.03, 0.21]. The stacked limit is f_(esc,rel)(3σ) < 0.02. We use a Monte Carlo simulation to properly account for the expected distribution of line-of-sight IGM opacities. When including constraints from previous surveys at z ~ 1.3 we find that, at the 95% confidence level, no more than 8% of star-forming galaxies at z ~ 1.3 can have relative escape fractions greater than 0.50. Alternatively, if the majority of galaxies have low, but non-zero, escaping LyC, the escape fraction cannot be more than 0.04. In light of some evidence for strong LyC emission from UV-faint regions of Lyman break galaxies (LBGs) at z ~ 3, we also stack sub-regions of our galaxies with different surface brightnesses and detect no significant LyC flux at the f_(esc,rel) < 0.03 level. Both the stacked limits and the limits from the Monte Carlo simulation suggest that the average ionizing emissivity (relative to non-ionizing UV emissivity) at z ~ 1.3 is significantly lower than has been observed in LBGs at z ~ 3. If the ionizing emissivity of star-forming galaxies is in fact increasing with redshift, it would help to explain the high photoionization rates seen in the IGM at z > 4 and reionization of the IGM at z > 6.

Item Type:Article
Related URLs:
URLURL TypeDescription
Siana, Brian0000-0002-4935-9511
Teplitz, Harry I.0000-0002-7064-5424
Ferguson, Henry C.0000-0001-7113-2738
Brown, Thomas M.0000-0002-1793-9968
Giavalisco, Mauro0000-0002-7831-8751
Dickinson, Mark0000-0001-5414-5131
Chary, Ranga-Ram0000-0001-7583-0621
Conselice, Christopher J.0000-0003-1949-7638
Scarlata, Claudia0000-0002-9136-8876
Additional Information:© 2010 American Astronomical Society. Received 2009 November 6; accepted 2010 August 28; published 2010 October 8. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with program 10872. Facilities: HST.
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
NASANAS 5-26555
Subject Keywords:intergalactic medium – galaxies: high-redshift – galaxies: starburst – ultraviolet: galaxies
Issue or Number:1
Classification Code:PACS: 98.54.Ep; 98.62.Py; 95.85.Mt; 98.62.Ra
Record Number:CaltechAUTHORS:20101217-094158383
Persistent URL:
Official Citation:Brian Siana et al 2010 ApJ 723 241 doi: 10.1088/0004-637X/723/1/241
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:21420
Deposited By: Benjamin Perez
Deposited On:17 Dec 2010 18:17
Last Modified:23 Nov 2019 00:35

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