Using new ultradeep Spitzer/InfraRed Array Camera (IRAC) photometry from the IRAC Ultra Deep Field program, we investigate the stellar populations of a sample of 63 Y-dropout galaxy candidates at z... Show moreUsing new ultradeep Spitzer/InfraRed Array Camera (IRAC) photometry from the IRAC Ultra Deep Field program, we investigate the stellar populations of a sample of 63 Y-dropout galaxy candidates at z \~{} 8, only 650 Myr after the big bang. The sources are selected from HST/ACS+WFC3/IR data over the Hubble Ultra Deep Field (HUDF), two HUDF parallel fields, and wide area data over the CANDELS/GOODS-South. The new Spitzer/IRAC data increase the coverage in [3.6] and [4.5] to \~{}120h over the HUDF reaching depths of \~{}28 (AB,1{$σ$}). The improved depth and inclusion of brighter candidates result in direct {\gt}=3{$σ$} InfraRed Array Camera (IRAC) detections of 20/63 sources, of which 11/63 are detected at {\gt}=5{$σ$}. The average [3.6]-[4.5] colors of IRAC detected galaxies at z \~{} 8 are markedly redder than those at z \~{} 7, observed only 130 Myr later. The simplest explanation is that we witness strong rest-frame optical emission lines (in particular [O III] {$λ$}{$λ$}4959, 5007 + H{$β$}) moving through the IRAC bandpasses with redshift. Assuming that the average rest-frame spectrum is the same at both z \~{} 7 and z \~{} 8 we estimate a rest-frame equivalent width of $\{$W$\}$\_$\{$[O$\backslash$,$\backslash$scriptsize$\{$III$\}$]$\backslash$ $\backslash$lambda $\backslash$lambda 4959,5007+H$\backslash$beta $\}$=670\^{}$\{$+260$\}$\_$\{$-170$\}$ Å contributing 0.56\^{}$\{$+0.16$\}$\_$\{$-0.11$\}$ mag to the [4.5] filter at z \~{} 8. The corresponding $\{$W$\}$\_$\{$H$\backslash$alpha $\}$=430\^{}$\{$+160$\}$\_$\{$-110$\}$ Å implies an average specific star formation rate of sSFR=11\_$\{$-5$\}$\^{}$\{$+11$\}$ Gyr$^{–1}$ and a stellar population age of 100\_$\{$-50$\}$\^{}$\{$+100$\}$ Myr. Correcting the spectral energy distribution for the contribution of emission lines lowers the average best-fit stellar masses and mass-to-light ratios by \~{}3 {\times}, decreasing the integrated stellar mass density to $\backslash$rho \^{}*(z=8,M\_$\{$$\backslash$rm$\{$UV$\}$$\}${\lt}-18)=0.6\^{}$\{$+0.4$\}$\_$\{$-0.3$\}$$\backslash$times 10\^{}6 $\backslash$,M\_$\backslash$odot Mpc$^{–3}$. Based on observations made with the NASA/ESA Hubble Space Telescope, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with programs \#11563, 9797. Based on observations with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under NASA contract 1407. Support for this work was provided by NASA through contract 125790 issued by JPL/Caltech. Based on service mode observations collected at the European Southern Observatory, Paranal, Chile (ESO Program 073.A-0764A). Based on data gathered with the 6.5{\nbsp}m Magellan Telescopes located at Las Campanas Observatory, Chile. Show less
Oesch, P.A.; Bouwens, R.J.; Illingworth, G.D.; Labbé, I.; Franx, M.; Dokkum, P.G. van; ... ; Magee, D. 2013
We present a comprehensive analysis of z {gt} 8 galaxies based on ultra-deep WFC3/IR data. We exploit all the WFC3/IR imaging over the Hubble Ultra-Deep Field from the HUDF09 and the new HUDF12... Show moreWe present a comprehensive analysis of z {gt} 8 galaxies based on ultra-deep WFC3/IR data. We exploit all the WFC3/IR imaging over the Hubble Ultra-Deep Field from the HUDF09 and the new HUDF12 program, in addition to the HUDF09 parallel field data, as well as wider area imaging over GOODS-South. Galaxies are selected based on the Lyman break technique in three samples centered around z ~{} 9, z ~{} 10, and z ~{} 11, with seven z ~{} 9 galaxy candidates, and one each at z ~{} 10 and z ~{} 11. We confirm a new z ~{} 10 candidate (with z = 9.8 {plusmn} 0.6) that was not convincingly identified in our first z ~{} 10 sample. Using these candidates, we perform one of the first estimates of the z ~{} 9 UV luminosity function (LF) and improve our previous constraints at z ~{} 10. Extrapolating the lower redshift UV LF evolution should have revealed 17 z ~{} 9 and 9 z ~{} 10 sources, i.e., a factor ~{}3 { imes} and 9{ imes} larger than observed. The inferred star formation rate density (SFRD) in galaxies above 0.7 M $_{⊙}$ yr$^{-1}$ decreases by 0.6 {plusmn} 0.2 dex from z ~{} 8 to z ~{} 9, in excellent agreement with previous estimates. From a combination of all current measurements, we find a best estimate of a factor 10{ imes} decrease in the SFRD from z ~{} 8 to z ~{} 10, following (1 + z)$^{-11.4 ± 3.1}$. Our measurements thus confirm our previous finding of an accelerated evolution beyond z ~{} 8, and signify a very rapid build-up of galaxies with M $_{UV}$ {lt} -17.7 mag within only ~{}200 Myr from z ~{} 10 to z ~{} 8, in the heart of cosmic reionization. Based on data obtained with the Hubble Space Telescope operated by AURA, Inc., for NASA under contract NAS5-26555. Show less
Oesch, P.; Bouwens, R.J.; Illingworth, G.; Labbé, I.F.L.; Franx, M.; Dokkum, P.; ... ; Magee, D. 2013
We present a comprehensive analysis of z {gt} 8 galaxies based on ultra-deep WFC3/IR data. We exploit all the WFC3/IR imaging over the Hubble Ultra-Deep Field from the HUDF09 and the new HUDF12... Show moreWe present a comprehensive analysis of z {gt} 8 galaxies based on ultra-deep WFC3/IR data. We exploit all the WFC3/IR imaging over the Hubble Ultra-Deep Field from the HUDF09 and the new HUDF12 program, in addition to the HUDF09 parallel field data, as well as wider area imaging over GOODS-South. Galaxies are selected based on the Lyman break technique in three samples centered around z ~{} 9, z ~{} 10, and z ~{} 11, with seven z ~{} 9 galaxy candidates, and one each at z ~{} 10 and z ~{} 11. We confirm a new z ~{} 10 candidate (with z = 9.8 {plusmn} 0.6) that was not convincingly identified in our first z ~{} 10 sample. Using these candidates, we perform one of the first estimates of the z ~{} 9 UV luminosity function (LF) and improve our previous constraints at z ~{} 10. Extrapolating the lower redshift UV LF evolution should have revealed 17 z ~{} 9 and 9 z ~{} 10 sources, i.e., a factor ~{}3 { imes} and 9{ imes} larger than observed. The inferred star formation rate density (SFRD) in galaxies above 0.7 M $_{⊙}$ yr$^{-1}$ decreases by 0.6 {plusmn} 0.2 dex from z ~{} 8 to z ~{} 9, in excellent agreement with previous estimates. From a combination of all current measurements, we find a best estimate of a factor 10{ imes} decrease in the SFRD from z ~{} 8 to z ~{} 10, following (1 + z)$^{-11.4 ± 3.1}$. Our measurements thus confirm our previous finding of an accelerated evolution beyond z ~{} 8, and signify a very rapid build-up of galaxies with M $_{UV}$ {lt} -17.7 mag within only ~{}200 Myr from z ~{} 10 to z ~{} 8, in the heart of cosmic reionization. Based on data obtained with the Hubble Space Telescope operated by AURA, Inc., for NASA under contract NAS5-26555. Show less
Oesch, P.A.; Labbé, I.; Bouwens, R.J.; Illingworth, G.D.; Gonzalez, V.; Franx, M.; ... ; Magee, D. 2013
We present a study of rest-frame UV-to-optical color distributions for z ~{} 4 galaxies based on the combination of deep HST/ACS+WFC3/IR data with Spitzer/IRAC imaging. In particular, we use new,... Show moreWe present a study of rest-frame UV-to-optical color distributions for z ~{} 4 galaxies based on the combination of deep HST/ACS+WFC3/IR data with Spitzer/IRAC imaging. In particular, we use new, ultra-deep data from the IRAC Ultradeep Field program (IUDF10), together with previous, public IRAC data over the GOODS fields. Our sample contains a total of ~{}2600 galaxies selected as B-dropout Lyman-break Galaxies in the HUDF and its deep parallel field HUDF09-2, as well as GOODS-North/South. This sample is used to investigate the UV continuum slopes {$β$} and Balmer break colors (J $_{125}$ - [4.5]) as a function of rest-frame optical luminosity (using [4.5] to avoid optical emission lines). We find that galaxies at M$_z$ {lt} -21.5 (roughly corresponding to L^{}*_${$z$ackslash$sim 4$}$) are significantly redder than their lower luminosity counterparts. The UV continuum slopes and the J $_{125}$ - [4.5] colors are well correlated, indicating that the dust reddening at these redshifts is better described by an SMC-like extinction curve, rather than the typically assumed Calzetti reddening. After dust correction, we find that the galaxy population shows mean stellar population ages in the range 10$^{8.5}$ to 10$^{9}$ yr, with a dispersion of ~{}0.5 dex, and only weak trends as a function of luminosity. Only a small fraction of galaxies shows Balmer break colors consistent with extremely young ages, younger than 100 Myr. Under the assumption of smooth star-formation histories, this fraction is 12%-19% for galaxies at M$_z$ {lt} -19.75. Our results are consistent with a gradual build-up of stars and dust in galaxies at z {gt} 4 with only a small fraction of stars being formed in short, intense bursts of star-formation. Based on data obtained with the Hubble Space Telescope operated by AURA, Inc. for NASA under contract NAS5-26555. Based on observations with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under NASA contract 1407. Show less
Oesch, P.; Bouwens, R.J.; Illingworth, G.; Labbé, I.F.L.; Franx, M.; Dokkum, P.; ... ; Magee, D. 2013
We present a comprehensive analysis of z {gt} 8 galaxies based on ultra-deep WFC3/IR data. We exploit all the WFC3/IR imaging over the Hubble Ultra-Deep Field from the HUDF09 and the new HUDF12... Show moreWe present a comprehensive analysis of z {gt} 8 galaxies based on ultra-deep WFC3/IR data. We exploit all the WFC3/IR imaging over the Hubble Ultra-Deep Field from the HUDF09 and the new HUDF12 program, in addition to the HUDF09 parallel field data, as well as wider area imaging over GOODS-South. Galaxies are selected based on the Lyman break technique in three samples centered around z ~{} 9, z ~{} 10, and z ~{} 11, with seven z ~{} 9 galaxy candidates, and one each at z ~{} 10 and z ~{} 11. We confirm a new z ~{} 10 candidate (with z = 9.8 {plusmn} 0.6) that was not convincingly identified in our first z ~{} 10 sample. Using these candidates, we perform one of the first estimates of the z ~{} 9 UV luminosity function (LF) and improve our previous constraints at z ~{} 10. Extrapolating the lower redshift UV LF evolution should have revealed 17 z ~{} 9 and 9 z ~{} 10 sources, i.e., a factor ~{}3 { imes} and 9{ imes} larger than observed. The inferred star formation rate density (SFRD) in galaxies above 0.7 M $_{⊙}$ yr$^{-1}$ decreases by 0.6 {plusmn} 0.2 dex from z ~{} 8 to z ~{} 9, in excellent agreement with previous estimates. From a combination of all current measurements, we find a best estimate of a factor 10{ imes} decrease in the SFRD from z ~{} 8 to z ~{} 10, following (1 + z)$^{-11.4 ± 3.1}$. Our measurements thus confirm our previous finding of an accelerated evolution beyond z ~{} 8, and signify a very rapid build-up of galaxies with M $_{UV}$ {lt} -17.7 mag within only ~{}200 Myr from z ~{} 10 to z ~{} 8, in the heart of cosmic reionization. Based on data obtained with the Hubble Space Telescope operated by AURA, Inc., for NASA under contract NAS5-26555. Show less
