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
Brammer, G.; Dokkum, P.; Illingworth, G.; Bouwens, R.; Labbé, I.; Franx, M.; ... ; Oesch, P. 2013
We present deep WFC3 grism observations of the candidate z \~{} 12 galaxy UDFj-39546284 in the Hubble Space Telescope (HST) Ultra Deep Field (UDF), by combining spectroscopic data from the 3D-HST... Show moreWe present deep WFC3 grism observations of the candidate z \~{} 12 galaxy UDFj-39546284 in the Hubble Space Telescope (HST) Ultra Deep Field (UDF), by combining spectroscopic data from the 3D-HST and CANDELS surveys. The total exposure time is 40.5 ks and the spectrum covers 1.10 {\lt} {$λ$} {\lt} 1.65 {$μ$}m. We search for faint emission lines by cross-correlating the two-dimensional G141 spectrum with the observed H $_{160}$ morphology, a technique that is unique to slitless spectroscopy at HST resolution. We find a 2.7{$σ$} detection of an emission line at 1.599 {$μ$}m{\mdash}just redward of the JH $_{140}$ filter{\mdash}with flux 3.5 {\plusmn} 1.3 {\times} 10$^{-18}$ erg s$^{-1}$ cm$^{-2}$. Assuming that the line is real, it contributes 110\% {\plusmn} 40\% of the observed H $_{160}$ flux and has an observed equivalent width {\gt}7300 Å. If the line is confirmed, it could be Ly{$α$} at z = 12.12. However, a more plausible interpretation, given current results, could be a lower redshift feature such as [O III]{$λ$}4959,5007 at z = 2.19. We find two other 3D-HST [O III] emitters within 1000 km s$^{-1}$ of that redshift in the GOODS-South field. Additional support for this interpretation comes from the discovery of a bright ''[O III] blob'' with a secure G141 grism redshift of z = 1.605. This object has a strikingly large observed equivalent width of nearly 9000 Å that results in similar ''dropout'' colors as UDFj-39546284. Based on observations made with the NASA/ESA Hubble Space Telescope, programs GO-12099, 12177, and 12547, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. Show less
Szomoru, D.; Franx, M.; Dokkum, P.; Trenti, M.; Illingworth, G.; Labbé, I.F.L.; Oesch, P. 2013
We present stellar mass surface density profiles of a mass-selected sample of 177 galaxies at 0.5 {lt} z {lt} 2.5, obtained using very deep Hubble Space Telescope optical and near-infrared data... Show moreWe present stellar mass surface density profiles of a mass-selected sample of 177 galaxies at 0.5 {lt} z {lt} 2.5, obtained using very deep Hubble Space Telescope optical and near-infrared data over the GOODS-South field, including recent CANDELS data. Accurate stellar mass surface density profiles have been measured for the first time for a complete sample of high-redshift galaxies more massive than 10$^{10.7}$ M $_{⊙}$. The key advantage of this study compared to previous work is that the surface brightness profiles are deconvolved for point-spread function smoothing, allowing accurate measurements of the structure of the galaxies. The surface brightness profiles account for contributions from complex galaxy structures such as rings and faint outer disks. Mass profiles are derived using radial rest-frame ug color profiles and a well-established empirical relation between these colors and the stellar mass-to-light ratio. We derive stellar half-mass radii from the mass profiles, and find that these are on average ~{}25% smaller than rest-frame g-band half-light radii. This average size difference of 25% is the same at all redshifts, and does not correlate with stellar mass, specific star formation rate, effective surface density, Sérsic index, or galaxy size. Although on average the difference between half-mass size and half-light size is modest, for approximately 10% of massive galaxies this difference is more than a factor of two. These extreme galaxies are mostly extended, disk-like systems with large central bulges. These results are robust, but could be impacted if the central dust extinction becomes high. ALMA observations can be used to explore this possibility. These results provide added support for galaxy growth scenarios wherein massive galaxies at these epochs grow by accretion onto their outer regions. 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.; 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
Ashby, M.; Willner, S.; Fazio, G.; Huang, J.; Arendt, R.; Barmby, P.; ... ; Yan, H. 2013
The Spitzer Extended Deep Survey (SEDS) is a very deep infrared survey within five well-known extragalactic science fields: the UKIDSS Ultra-Deep Survey, the Extended Chandra Deep Field South,... Show moreThe Spitzer Extended Deep Survey (SEDS) is a very deep infrared survey within five well-known extragalactic science fields: the UKIDSS Ultra-Deep Survey, the Extended Chandra Deep Field South, COSMOS, the Hubble Deep Field North, and the Extended Groth Strip. SEDS covers a total area of 1.46 deg$^{2}$ to a depth of 26 AB mag (3{$σ$}) in both of the warm Infrared Array Camera (IRAC) bands at 3.6 and 4.5 {$μ$}m. Because of its uniform depth of coverage in so many widely-separated fields, SEDS is subject to roughly 25% smaller errors due to cosmic variance than a single-field survey of the same size. SEDS was designed to detect and characterize galaxies from intermediate to high redshifts (z = 2-7) with a built-in means of assessing the impact of cosmic variance on the individual fields. Because the full SEDS depth was accumulated in at least three separate visits to each field, typically with six-month intervals between visits, SEDS also furnishes an opportunity to assess the infrared variability of faint objects. This paper describes the SEDS survey design, processing, and publicly-available data products. Deep IRAC counts for the more than 300,000 galaxies detected by SEDS are consistent with models based on known galaxy populations. Discrete IRAC sources contribute 5.6 {plusmn} 1.0 and 4.4 {plusmn} 0.8 nW m$^{-2}$ sr$^{-1}$ at 3.6 and 4.5 {$μ$}m to the diffuse cosmic infrared background (CIB). IRAC sources cannot contribute more than half of the total CIB flux estimated from DIRBE data. Barring an unexpected error in the DIRBE flux estimates, half the CIB flux must therefore come from a diffuse component. Show less
Szomoru, D.; Franx, M.; Dokkum, P.; Trenti, M.; Illingworth, G.; Labbé, I.F.L.; Oesch, P. 2013
We present stellar mass surface density profiles of a mass-selected sample of 177 galaxies at 0.5 {lt} z {lt} 2.5, obtained using very deep Hubble Space Telescope optical and near-infrared data... Show moreWe present stellar mass surface density profiles of a mass-selected sample of 177 galaxies at 0.5 {lt} z {lt} 2.5, obtained using very deep Hubble Space Telescope optical and near-infrared data over the GOODS-South field, including recent CANDELS data. Accurate stellar mass surface density profiles have been measured for the first time for a complete sample of high-redshift galaxies more massive than 10$^{10.7}$ M $_{⊙}$. The key advantage of this study compared to previous work is that the surface brightness profiles are deconvolved for point-spread function smoothing, allowing accurate measurements of the structure of the galaxies. The surface brightness profiles account for contributions from complex galaxy structures such as rings and faint outer disks. Mass profiles are derived using radial rest-frame ug color profiles and a well-established empirical relation between these colors and the stellar mass-to-light ratio. We derive stellar half-mass radii from the mass profiles, and find that these are on average ~{}25% smaller than rest-frame g-band half-light radii. This average size difference of 25% is the same at all redshifts, and does not correlate with stellar mass, specific star formation rate, effective surface density, Sérsic index, or galaxy size. Although on average the difference between half-mass size and half-light size is modest, for approximately 10% of massive galaxies this difference is more than a factor of two. These extreme galaxies are mostly extended, disk-like systems with large central bulges. These results are robust, but could be impacted if the central dust extinction becomes high. ALMA observations can be used to explore this possibility. These results provide added support for galaxy growth scenarios wherein massive galaxies at these epochs grow by accretion onto their outer regions. Show less
