LOWER-LUMINOSITY GALAXIES COULD REIONIZE THE UNIVERSE: VERY STEEP FAINT-END SLOPES TO THE UV LUMINOSITY FUNCTIONS AT z {>=} 5-8 FROM THE HUDF09 WFC3/IR OBSERVATIONS
Abstract
The HUDF09 data are the deepest near-IR observations ever, reaching to 29.5 mag. Luminosity functions (LFs) from these new HUDF09 data for 132 z {approx} 7 and z {approx} 8 galaxies are combined with new LFs for z {approx} 5-6 galaxies and the earlier z {approx} 4 LF to reach to very faint limits (<0.05 L*{sub z=3}). The faint-end slopes {alpha} are steep: -1.79 {+-} 0.12 (z {approx} 5), -1.73 {+-} 0.20 (z {approx} 6), -2.01 {+-} 0.21 (z {approx} 7), and -1.91 {+-} 0.32 (z {approx} 8). Slopes {alpha} {approx}< -2 lead to formally divergent UV fluxes, though galaxies are not expected to form below {approx} - 10 AB mag. These results have important implications for reionization. The weighted mean slope at z {approx} 6-8 is -1.87 {+-} 0.13. For such steep slopes, and a faint-end limit of -10 AB mag, galaxies provide a very large UV ionizing photon flux. While current results show that galaxies can reionize the universe by z {approx} 6, matching the Thomson optical depths is more challenging. Extrapolating the current LF evolution to z > 8, taking {alpha} to be -1.87 {+-} 0.13 (the mean value at z {approx} 6-8), and adopting typical parameters,more »
- Authors:
-
- Leiden Observatory, Leiden University, NL-2300 RA Leiden (Netherlands)
- UCO/Lick Observatory, University of California, Santa Cruz, CA 95064 (United States)
- Center for Astrophysics and Space Astronomy, University of Colorado, 389-UCB, Boulder, CO 80309 (United States)
- Space Telescope Science Institute, Baltimore, MD 21218 (United States)
- Institute for Astronomy, ETH Zurich, 8092 Zurich (Switzerland)
- Department of Astronomy, Yale University, New Haven, CT 06520 (United States)
- Publication Date:
- OSTI Identifier:
- 22047768
- Resource Type:
- Journal Article
- Journal Name:
- Astrophysical Journal Letters
- Additional Journal Information:
- Journal Volume: 752; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 2041-8205
- Country of Publication:
- United States
- Language:
- English
- Subject:
- 79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ASTRONOMY; ASTROPHYSICS; COSMIC PHOTONS; COSMIC RAY FLUX; EVOLUTION; GALAXIES; HYPOTHESIS; LUMINOSITY; NEAR INFRARED RADIATION; RED SHIFT; ULTRAVIOLET RADIATION; UNIVERSE
Citation Formats
Bouwens, R J, Labbe, I, Franx, M, Illingworth, G D, Oesch, P A, Magee, D, Trenti, M, Stiavelli, M, Carollo, C M, and Van Dokkum, P. LOWER-LUMINOSITY GALAXIES COULD REIONIZE THE UNIVERSE: VERY STEEP FAINT-END SLOPES TO THE UV LUMINOSITY FUNCTIONS AT z {>=} 5-8 FROM THE HUDF09 WFC3/IR OBSERVATIONS. United States: N. p., 2012.
Web. doi:10.1088/2041-8205/752/1/L5.
Bouwens, R J, Labbe, I, Franx, M, Illingworth, G D, Oesch, P A, Magee, D, Trenti, M, Stiavelli, M, Carollo, C M, & Van Dokkum, P. LOWER-LUMINOSITY GALAXIES COULD REIONIZE THE UNIVERSE: VERY STEEP FAINT-END SLOPES TO THE UV LUMINOSITY FUNCTIONS AT z {>=} 5-8 FROM THE HUDF09 WFC3/IR OBSERVATIONS. United States. https://doi.org/10.1088/2041-8205/752/1/L5
Bouwens, R J, Labbe, I, Franx, M, Illingworth, G D, Oesch, P A, Magee, D, Trenti, M, Stiavelli, M, Carollo, C M, and Van Dokkum, P. 2012.
"LOWER-LUMINOSITY GALAXIES COULD REIONIZE THE UNIVERSE: VERY STEEP FAINT-END SLOPES TO THE UV LUMINOSITY FUNCTIONS AT z {>=} 5-8 FROM THE HUDF09 WFC3/IR OBSERVATIONS". United States. https://doi.org/10.1088/2041-8205/752/1/L5.
@article{osti_22047768,
title = {LOWER-LUMINOSITY GALAXIES COULD REIONIZE THE UNIVERSE: VERY STEEP FAINT-END SLOPES TO THE UV LUMINOSITY FUNCTIONS AT z {>=} 5-8 FROM THE HUDF09 WFC3/IR OBSERVATIONS},
author = {Bouwens, R J and Labbe, I and Franx, M and Illingworth, G D and Oesch, P A and Magee, D and Trenti, M and Stiavelli, M and Carollo, C M and Van Dokkum, P},
abstractNote = {The HUDF09 data are the deepest near-IR observations ever, reaching to 29.5 mag. Luminosity functions (LFs) from these new HUDF09 data for 132 z {approx} 7 and z {approx} 8 galaxies are combined with new LFs for z {approx} 5-6 galaxies and the earlier z {approx} 4 LF to reach to very faint limits (<0.05 L*{sub z=3}). The faint-end slopes {alpha} are steep: -1.79 {+-} 0.12 (z {approx} 5), -1.73 {+-} 0.20 (z {approx} 6), -2.01 {+-} 0.21 (z {approx} 7), and -1.91 {+-} 0.32 (z {approx} 8). Slopes {alpha} {approx}< -2 lead to formally divergent UV fluxes, though galaxies are not expected to form below {approx} - 10 AB mag. These results have important implications for reionization. The weighted mean slope at z {approx} 6-8 is -1.87 {+-} 0.13. For such steep slopes, and a faint-end limit of -10 AB mag, galaxies provide a very large UV ionizing photon flux. While current results show that galaxies can reionize the universe by z {approx} 6, matching the Thomson optical depths is more challenging. Extrapolating the current LF evolution to z > 8, taking {alpha} to be -1.87 {+-} 0.13 (the mean value at z {approx} 6-8), and adopting typical parameters, we derive Thomson optical depths of 0.061{sup +0.009}{sub -0.006}. However, this result will change if the faint-end slope {alpha} is not constant with redshift. We test this hypothesis and find a weak, though uncertain, trend to steeper slopes at earlier times (d{alpha}/dz {approx} -0.05 {+-} 0.04) that would increase the Thomson optical depths to 0.079{sup +0.063}{sub -0.017}, consistent with recent WMAP estimates ({tau} = 0.088 {+-} 0.015). It may thus not be necessary to resort to extreme assumptions about the escape fraction or clumping factor. Nevertheless, the uncertainties remain large. Deeper WFC3/IR+ACS observations can further constrain the UV ionizing flux from faint galaxies.},
doi = {10.1088/2041-8205/752/1/L5},
url = {https://www.osti.gov/biblio/22047768},
journal = {Astrophysical Journal Letters},
issn = {2041-8205},
number = 1,
volume = 752,
place = {United States},
year = {Sun Jun 10 00:00:00 EDT 2012},
month = {Sun Jun 10 00:00:00 EDT 2012}
}