STAR FORMATION RATES AND STELLAR MASSES OF z = 7-8 GALAXIES FROM IRAC OBSERVATIONS OF THE WFC3/IR EARLY RELEASE SCIENCE AND THE HUDF FIELDS

Journal Article · Sun Jun 20 00:00:00 EDT 2010 · Astrophysical Journal Letters

DOI:https://doi.org/10.1088/2041-8205/716/2/L103· OSTI ID:21451086

Labbe, I ^[1]; Gonzalez, V; Bouwens, R J; Illingworth, G D; Magee, D ^[2]; Franx, M ^[3]; Trenti, M ^[4]; Oesch, P A; Carollo, C M ^[5]; Van Dokkum, P G ^[6]; Stiavelli, M ^[7]; Kriek, M ^[8]

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1. Carnegie Observatories, Pasadena, CA 91101 (United States)
2. UCO/Lick Observatory, University of California, Santa Cruz, CA 95064 (United States)
3. Leiden Observatory, Leiden University, NL-2300 RA Leiden (Netherlands)
4. Center for Astrophysics and Space Astronomy, University of Colorado, 389-UCB, Boulder, CO 80309 (United States)
5. Institute for Astronomy, ETH Zurich, 8092 Zurich (Switzerland)
6. Department of Astronomy, Yale University, New Haven, CT 06520 (United States)
7. Space Telescope Science Institute, Baltimore, MD 21218 (United States)
8. Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544 (United States)

We investigate the Spitzer/IRAC properties of 36 z {approx} 7 z{sub 850}-dropout galaxies and three z {approx} 8 Y{sub 098} galaxies derived from deep/wide-area WFC3/IR data of the Early Release Science, the ultradeep HUDF09, and wide-area NICMOS data. We fit stellar population synthesis models to the spectral energy distributions to derive mean redshifts, stellar masses, and ages. The z {approx} 7 galaxies are best characterized by substantial ages (>100 Myr) and M/L{sub V} {approx} 0.2. The main trend with decreasing luminosity is that of bluing of the far-UV slope from {beta} {approx} -2.0 to {beta} {approx} -3.0. This can be explained by decreasing metallicity, except for the lowest luminosity galaxies (0.1L*{sub z{sub ={sub 3}}}), where low metallicity and smooth star formation histories (SFHs) fail to match the blue far-UV and moderately red H - [3.6] color. Such colors may require episodic SFHs with short periods of activity and quiescence ('on-off' cycles) and/or a contribution from emission lines. The stellar mass of our sample of z {approx} 7 star-forming galaxies correlates with star formation rate (SFR) according to log M* = 8.70({+-}0.09) + 1.06({+-}0.10)log SFR, implying that star formation may have commenced at z > 10. No galaxies are found with SFRs much higher or lower than the past averaged SFR suggesting that the typical star formation timescales are probably a substantial fraction of the Hubble time. We report the first IRAC detection of Y{sub 098}-dropout galaxies at z {approx} 8. The average rest-frame U - V {approx} 0.3 (AB) of the three galaxies are similar to faint z {approx} 7 galaxies, implying similar M/L. The stellar mass density to M{sub UV,AB} < -18 is {rho}*(z = 8) = 1.8{sup +0.7}{sub -1.0} x 10{sup 6} M{sub sun} Mpc{sup -3}, following log {rho}*(z) = 10.6({+-}0.6) - 4.4({+-}0.7) log(1 + z) [M{sub sun} Mpc{sup -3}] over 3 < z < 8.

• OSTI ID: 21451086
• Journal Information: Astrophysical Journal Letters, Vol. 716, Issue 2; Other Information: DOI: 10.1088/2041-8205/716/2/L103; ISSN 2041-8205
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
COLOR
ENERGY SPECTRA
GALACTIC EVOLUTION
GALAXIES
LUMINOSITY
MASS
RED SHIFT
STARS
EVOLUTION
OPTICAL PROPERTIES
ORGANOLEPTIC PROPERTIES
PHYSICAL PROPERTIES
SPECTRA