A DEEP HUBBLE SPACE TELESCOPE SEARCH FOR ESCAPING LYMAN CONTINUUM FLUX AT z {approx} 1.3: EVIDENCE FOR AN EVOLVING IONIZING EMISSIVITY

Journal Article · Mon Nov 01 00:00:00 EDT 2010 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/723/1/241· OSTI ID:21467202

Siana, Brian; Bridge, Carrie R ^[1]; Teplitz, Harry I; Chary, Ranga-Ram; Colbert, James W; Scarlata, Claudia ^[2]; Ferguson, Henry C; Brown, Thomas M ^[3]; Giavalisco, Mauro ^[4]; Dickinson, Mark ^[5]; De Mello, Duilia F ^[6]; Conselice, Christopher J ^[7]; Gardner, Jonathan P ^[8]

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1. California Institute of Technology, MS 249-17, Pasadena, CA 91125 (United States)
2. Spitzer Science Center, California Institute of Technology, 220-6, Pasadena, CA 91125 (United States)
3. Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States)
4. Department of Astronomy, University of Massachusetts, Amherst, MA 01003 (United States)
5. National Optical Astronomy Observatory, 950 N. Cherry Avenue, Tucson, AZ 85719 (United States)
6. Department of Physics, Catholic University of America, 620 Michigan Avenue, Washington, DC 20064 (United States)
7. University of Nottingham, Nottingham, NG7 2RD (United Kingdom)
8. Astrophysics Science Division, Observational Cosmology Laboratory, Code 665, Goddard Space Flight Center, Greenbelt, MD 20771 (United States)

We have obtained deep Hubble Space Telescope far-UV images of 15 starburst galaxies at z {approx} 1.3 in the GOODS fields to search for escaping Lyman continuum (LyC) photons. These are the deepest far-UV images (m{sub AB} = 28.7, 3{sigma}, 1'' diameter) over this large an area (4.83 arcmin{sup 2}) and provide some of the best escape fraction constraints for any galaxies at any redshift. We do not detect any individual galaxies, with 3{sigma} limits to the LyC ({approx}700 A) flux 50-149 times fainter (in f{sub {nu}}) than the rest-frame UV (1500 A) continuum fluxes. Correcting for the mean intergalactic medium (IGM) attenuation (factor {approx}2), as well as an intrinsic stellar Lyman break (factor {approx}3), these limits translate to relative escape fraction limits of f{sub esc,rel} < [0.03, 0.21]. The stacked limit is f{sub esc,rel}(3{sigma}) < 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 {approx} 1.3 we find that, at the 95% confidence level, no more than 8% of star-forming galaxies at z {approx} 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 {approx} 3, we also stack sub-regions of our galaxies with different surface brightnesses and detect no significant LyC flux at the f{sub 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 {approx} 1.3 is significantly lower than has been observed in LBGs at z {approx} 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.

• OSTI ID: 21467202
• Journal Information: Astrophysical Journal, Vol. 723, Issue 1; Other Information: DOI: 10.1088/0004-637X/723/1/241; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
COMPUTERIZED SIMULATION
EMISSIVITY
GALAXIES
LYMAN LINES
MONTE CARLO METHOD
PHOTOIONIZATION
RED SHIFT
STARS
TELESCOPES
ULTRAVIOLET RADIATION
CALCULATION METHODS
ELECTROMAGNETIC RADIATION
IONIZATION
OPTICAL PROPERTIES
PHYSICAL PROPERTIES
RADIATIONS
SIMULATION
SURFACE PROPERTIES