Browsing by Subject "wfc3/ir observations"

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The Colors Of Galaxies At 4 < Z < 8 And Their Contribution To Reionization
(2012-09) Finkelstein, S. L.; Finkelstein, Steven L.
We present recent results on the rest-frame ultraviolet (UV) colors of galaxies at high-redshift, and the contribution of these galaxies to the reionization of the intergalactic medium (IGM). Using a combination of deep and wide data from the CANDELS, HUDF09 and ERS programs, we find that galaxies at z = 7 appear to be dust free, and they become substantially dustier by z = 4. Faint galaxies at z = 7 appear very blue, but they are consistent with the colors of very blue local galaxies, thus there is no evidence for the presence of exotic stellar populations. We find that the observable galaxy population can sustain a fully ionized IGM at z = 6 if the escape fraction of ionizing photons (f(esc)) is 30%. If the luminosity function extends much fainter, then the required f(esc) is lowered to similar to 10%. Examining the constraint on the emission rate of ionizing photons from Ly alpha forest measurements, we find that if the luminosity function extends to M-UV = -13, f(esc) must be less than 13% at z = 6. This escape fraction can still sustain a reionized IGM at z = 6, and even at z = 7, but unless it rises substantially at z > 6, the IGM may be similar to 20 - 50% neutral by z = 8.
Luminous And High Stellar Mass Candidate Galaxies At Z Approximate To 8 Discovered In The Cosmic Assembly Near-Infrared Deep Extragalactic Legacy Survey
(2012-12) Yan, Haojing; Finkelstein, Steven L.; Huang, Kuang-Han; Ryan, Russell E.; Ferguson, Henry C.; Koekemoer, Anton M.; Grogin, Norman A.; Dickinson, Mark; Newman, Jeffrey A.; Somerville, Rachel S.; Dave, Romeel; Faber, S. M.; Papovich, Casey; Guo, Yicheng; Giavalisco, Mauro; Lee, Kyoung-soo; Reddy, Naveen; Cooray, Asantha R.; Siana, Brian D.; Hathi, Nimish P.; Fazio, Giovanni G.; Ashby, Matthew; Weiner, Benjamin J.; Lucas, Ray A.; Dekel, Avishai; Pentericci, Laura; Conselice, Christopher J.; Kocevski, Dale D.; Lai, Kamson; Finkelstein, Steven L.
One key goal of the Hubble Space Telescope Cosmic Assembly Near-Infrared Deep Extragalactic Legacy Survey is to track galaxy evolution back to z approximate to 8. Its two-tiered "wide and deep" strategy bridges significant gaps in existing near-infrared surveys. Here we report on z approximate to 8 galaxy candidates selected as F105W-band dropouts in one of its deep fields, which covers 50.1 arcmin(2) to 4 ks depth in each of three near-infrared bands in the Great Observatories Origins Deep Survey southern field. Two of our candidates have J < 26.2 mag, and are >1 mag brighter than any previously known F105W-dropouts. We derive constraints on the bright end of the rest-frame ultraviolet luminosity function of galaxies at z approximate to 8, and show that the number density of such very bright objects is higher than expected from the previous Schechter luminosity function estimates at this redshift. Another two candidates are securely detected in Spitzer Infrared Array Camera images, which are the first such individual detections at z approximate to 8. Their derived stellar masses are on the order of a few x 10(9) M-circle dot, from which we obtain the first measurement of the high-mass end of the galaxy stellar mass function at z approximate to 8. The high number density of very luminous and very massive galaxies at z approximate to 8, if real, could imply a large stellar-to-halo mass ratio and an efficient conversion of baryons to stars at such an early time.