UV CONTINUUM SLOPE AND DUST OBSCURATION FROM z approx 6 TO z approx 2: THE STAR FORMATION RATE DENSITY AT HIGH REDSHIFT
- Astronomy Department, University of California, Santa Cruz, CA 95064 (United States)
- Leiden Observatory, University of Leiden, Postbus 9513, 2300 RA Leiden (Netherlands)
- Divison of Physics, Mathematics, and Astronomy, California Institute of Technology, Pasadena, CA 91125 (United States)
- Department of Physics and Astronomy, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218 (United States)
- University of Nottingham, School of Physics and Astronomy, Nottinghm NG7 2RD (United Kingdom)
- Department of Astronomy, University of Massachusetts, Amherst, MA (United States)
- Department of Astronomy, Yale University, New Haven, CT (United States)
We provide a systematic measurement of the rest-frame UV continuum slope beta over a wide range in redshift (z approx 2-6) and rest-frame UV luminosity (0.1 L* {sub z} {sub =} {sub 3} to 2 L* {sub z={sub 3}}) to improve estimates of the star formation rate (SFR) density at high redshift. We utilize the deep optical and infrared data (Advanced Camera for Surveys/NICMOS) over the Chandra Deep Field-South and Hubble Deep Field-North Great Observatories Origins Deep Survey fields, as well as the UDF for our primary UBVi 'dropout' Lyman Break Galaxy sample. We also use strong lensing clusters to identify a population of very low luminosity, high-redshift dropout galaxies. We correct the observed distributions for both selection biases and photometric scatter. We find that the UV-continuum slope of the most luminous galaxies is substantially redder at z approx 2-4 than it is at z approx 5-6 (from approx-2.4 at z approx 6 to approx-1.5 at z approx 2). Lower luminosity galaxies are also found to be bluer than higher luminosity galaxies at z approx 2.5 and z approx 4. We do not find a large number of galaxies with beta's as red as -1 in our dropout selections at z approx 4, and particularly at z approx> 5, even though such sources could be readily selected from our data (and also from Balmer Break Galaxy searches at z approx 4). This suggests that star-forming galaxies at z approx> 5 almost universally have very blue UV-continuum slopes, and that there are not likely to be a substantial number of dust-obscured galaxies at z approx> 5 that are missed in 'dropout' searches. Using the same relation between UV-continuum slope and dust extinction as has been found to be appropriate at both z approx 0 and z approx 2, we estimate the average dust extinction of galaxies as a function of redshift and UV luminosity in a consistent way. As expected, we find that the estimated dust extinction increases substantially with cosmic time for the most UV luminous galaxies, but remains small (approx<2 times) at all times for lower luminosity galaxies. Because these same lower luminosity galaxies dominate the luminosity density in the UV continuum, the overall dust extinction correction remains modest at all redshifts and the evolution of this correction with redshift is only modest. We include the contribution from ultra-luminous IR galaxies in our SFR density estimates at z approx 2-6, but find that they contribute only approx20% of the total at z approx 2.5 and approx<10% at z approx> 4.
- OSTI ID:
- 21378307
- Journal Information:
- Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 705; ISSN ASJOAB; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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