Search

We present the results from a spectroscopic survey using the MOSFIRE near-infrared spectrograph on the 10m Keck telescope to search for Ly$\alpha$ emission from candidate galaxies at z ~9-10 in four of the CANDELS fields (GOODS-N, EGS, UDS, and COSMOS). We observed 11 target galaxies, detecting Ly$\alpha$ from one object in ~8.1 hours of integration, at z = 8.665 +/- 0.001 with an integrated signal-to-noise > 7. This galaxy is in the CANDELS Extended Groth Strip (EGS) field, and lies physically close (3.5 physical Mpc [pMpc]) to another confirmed galaxy in this field with Ly$\alpha$ detected at z=8.683 (Zitrin et al. 2015). The detection of Ly$\alpha$ suggests the existence of large (~1 pMpc) ionized bubbles fairly early in the reionization process. We explore the ionizing output needed to create bubbles of this size at this epoch and find that such a bubble requires more than the ionizing power provided by the full expected population of galaxies (by integrating the UV Luminosity Function down to M_UV = -13). The Ly$\alpha$ we detect would be able to escape the predominantly-neutral intergalactic medium at this epoch if our galaxy is inhabiting an overdensity, which would be consistent with the photometric overdensity previously identified in this region by Finkelstein et al. 2021. This implies that the CANDELS EGS field is hosting an overdensity at z = 8.7 which is powering one (or more) ionized bubbles, a hypothesis that will be imminently testable with forthcoming James Webb Space Telescope observations in this field., Comment: 19 pages, 12 figures, 8 tables, Published in ApJ

In the next decade, deep galaxy surveys from telescopes such as the James Webb Space Telescope and Roman Space Telescope will provide transformational data sets that will greatly enhance the understanding of galaxy formation during the epoch of reionization (EoR). In this work, we present the Deep Realistic Extragalactic Model (DREaM) for creating synthetic galaxy catalogs. Our model combines dark matter simulations, subhalo abundance matching and empirical models, and includes galaxy positions, morphologies, and spectral energy distributions (SEDs). The resulting synthetic catalog extends to redshifts $z \sim 12 $, and galaxy masses $\log_{10}(M/M_{\odot}) = 5 $ covering an area of $1\, {\rm deg}^2$ on the sky. We use DREaM to explore the science returns of a $1\, {\rm deg}^2$ \emph{Roman} UDF, and to provide a resource for optimizing ultra-deep survey designs. We find that a \emph{Roman} UDF to $\sim 30\,m_{\rm AB}$ will potentially detect more than $10^6$ $M_{\rm UV}<-17$ galaxies, with more than $10^4$ at redshifts $z>7$, offering an unparalleled dataset for constraining galaxy properties during the EoR. Our synthetic catalogs and simulated images are made publicly available to provide the community with a tool to prepare for upcoming data., Comment: 39 pages, 27 figures. Submitted to ApJ. Comments welcome

The JWST MIRI instrument will revolutionize extragalactic astronomy with unprecedented sensitivity and angular resolution in mid-IR. Here, we assess the potential of MIRI photometry to constrain galaxy properties in the Cosmic Evolution Early Release Science (CEERS) survey. We derive estimated MIRI fluxes from the spectral energy distributions (SEDs) of real sources that fall in a planned MIRI pointing. We also obtain MIRI fluxes for hypothetical AGN-galaxy mixed models varying the AGN fractional contribution to the total IR luminosity ($\rm frac_{AGN}$). Based on these model fluxes, we simulate CEERS imaging (3.6-hour exposure) in 6 bands from F770W to F2100W using MIRISIM, and reduce these data using JWST PIPELINE. We perform PSF-matched photometry with TPHOT, and fit the source SEDs with X-CIGALE, simultaneously modeling photometric redshift and other physical properties. Adding the MIRI data, the accuracy of both redshift and $\rm frac_{AGN}$ is generally improved by factors of $\gtrsim 2$ for all sources at $z\lesssim 3$. Notably, for pure-galaxy inputs ($\rm frac_{AGN}=0$), the accuracy of $\rm frac_{AGN}$ is improved by $\sim 100$ times thanks to MIRI. The simulated CEERS MIRI data are slightly more sensitive to AGN detections than the deepest X-ray survey, based on the empirical $L_{\rm X}$-$L_{\rm 6\mu m}$ relation. Like X-ray observations, MIRI can also be used to constrain the AGN accretion power (accuracy $\approx 0.3$ dex). Our work demonstrates that MIRI will be able to place strong constraints on the mid-IR luminosities from star formation and AGN, and thereby facilitate studies of the galaxy/AGN co-evolution., Comment: 31 pages, 24 figures, 3 tables. Re-submitted to ApJS after revision

We present the detection of multiple CO line transitions with ALMA in a few tens of infrared-selected galaxies on and above the main sequence at z=1.1-1.7. We reliably detected the emission of CO(5-4), CO(2-1), and CO(7-6)+[CI](2-1) in 50, 33, and 13 galaxies, respectively, and we complemented this information with available CO(4-3) and [CI](1-0) fluxes for part of the sample, and modeling of the optical-to-mm SEDs. We retrieve a quasi-linear relation between LIR and CO(5-4) or CO(7-6) for main-sequence galaxies and starbursts, corroborating the hypothesis that these transitions can be used as SFR tracers. We find the CO excitation to steadily increase as a function of the star formation efficiency, the mean intensity of the radiation field warming the dust, the surface density of SFR, and, less distinctly, with the distance from the main sequence. This adds to the tentative evidence for higher excitation of the CO+[CI] SLED of starbursts relative to that for main-sequence objects, where the dust opacities play a minor role in shaping the high-J CO transitions in our sample. However, the distinction between the average SLED of upper main-sequence and starburst galaxies is blurred, driven by a wide variety of intrinsic shapes. LVG radiative transfer modeling demonstrates the existence of a highly excited component that elevates the CO SLED of high-redshift main-sequence and starbursting galaxies above the typical values observed in the disk of the Milky Way. This excited component is dense and it encloses ~50% of the total molecular gas mass in main-sequence objects. We interpret the observed trends involving the CO excitation as mainly driven by a combination of large SFRs and compact sizes, naturally connected with enhanced dense molecular gas fractions and higher dust and gas temperatures, due to increasing UV radiation fields, cosmic ray rates, and dust/gas coupling. [Abridged], Comment: 18 pages, 9 figures + Appendix, accepted in A&A. The data compilation will be released as a .fits table on the journal's website. For an early access, please contact the corresponding author. The plots of spectra and far-infrared SEDs will be available on the journal's website and temporarily at this link: https://bit.ly/spectra_and_seds_valentino_2020c

Star formation depends critically on cooling mechanisms in the interstellar medium (ISM); however, thermal properties of gas in galaxies at the peak epoch of star formation (z ~ 2) remain poorly understood. A limiting factor in understanding the multiphase ISM is the lack of multiple tracers detected in the same galaxies, such as Polycyclic Aromatic Hydrocarbon (PAH) emission, a tracer of a critical photoelectric heating mechanism in interstellar gas, and [C II] 158{\mu}m fine-structure emission, a principal coolant. We present ALMA Band 9 observations targeting [C II] in six z ~ 2 star-forming galaxies with strong Spitzer IRS detections of PAH emission. All six galaxies are detected in dust continuum and marginally resolved. We compare the properties of PAH and [C II] emission, and constrain their relationship as a function of total infrared luminosity (LIR) and IR surface density. [C II] emission is detected in one galaxy at high signal-to-noise (34{\sigma}), and we place a secure upper limit on a second source. The rest of our sample are not detected in [C II] likely due to redshift uncertainties and narrow ALMA bandpass windows. Our results are consistent with the deficit in [C II]/LIR and PAH/LIR observed in the literature. However, the ratio of [C II] to PAH emission at z ~ 2 is possibly much lower than what is observed in nearby dusty star-forming galaxies. This could be the result of enhanced cooling via [O I] at high-z, hotter gas and dust temperatures, and/or a reduction in the photoelectric efficiency, in which the coupling between interstellar radiation and gas heating is diminished., Comment: Accepted to The Astrophysical Journal, 22 pages, 11 figures

We present a robust method, weighted von Mises kernel density estimation, along with boundary correction to reconstruct the underlying number density field of galaxies. We apply this method to galaxies brighter than $\rm HST/F160w\le 26$ AB mag at the redshift range of $0.4\leq z \leq 5$ in the five CANDELS fields (GOODS-N, GOODS-S, EGS, UDS, and COSMOS). We then use these measurements to explore the environmental dependence of the star formation activity of galaxies. We find strong evidence of environmental quenching for massive galaxies ($\rm M \gtrsim 10^{11} \rm {M}_\odot$) out to $z\sim 3.5$ such that an over-dense environment hosts $\gtrsim 20\%$ more massive quiescent galaxies compared to an under-dense region. We also find that environmental quenching efficiency grows with stellar mass and reaches $\sim 60\%$ for massive galaxies at $z\sim 0.5$. The environmental quenching is also more efficient in comparison to the stellar mass quenching for low mass galaxies ($\rm M \lesssim 10^{10} \rm {M}_\odot$) at low and intermediate redshifts ($z\lesssim 1.2$). Our findings concur thoroughly with the "over-consumption" quenching model where the termination of cool gas accretion (cosmological starvation) happens in an over-dense environment and the galaxy starts to consume its remaining gas reservoir in depletion time. The depletion time depends on the stellar mass and could explain the evolution of environmental quenching efficiency with the stellar mass., Comment: 17 pages, 10 figures, 3 tables, accepted for publication in the ApJ. Catalogs of the environment measurements and the density maps will be available with the final published paper in ApJ

We present a WFC3 F160W ($H$-band) selected catalog in the CANDELS/GOODS-N field containing photometry from the ultraviolet (UV) to the far-infrared (IR), photometric redshifts and stellar parameters derived from the analysis of the multi-wavelength data. The catalog contains 35,445 sources over the 171 arcmin$^{2}$ of the CANDELS F160W mosaic. The 5$\sigma$ detection limits (within an aperture of radius 0\farcs17) of the mosaic range between $H=27.8$, 28.2 and 28.7 in the wide, intermediate and deep regions, that span approximately 50\%, 15\% and 35\% of the total area. The multi-wavelength photometry includes broad-band data from UV (U band from KPNO and LBC), optical (HST/ACS F435W, F606W, F775W, F814W, and F850LP), near-to-mid IR (HST/WFC3 F105W, F125W, F140W and F160W, Subaru/MOIRCS Ks, CFHT/Megacam K, and \spitzer/IRAC 3.6, 4.5, 5.8, 8.0 $\mu$m) and far IR (\spitzer/MIPS 24$\mu$m, HERSCHEL/PACS 100 and 160$\mu$m, SPIRE 250, 350 and 500$\mu$m) observations. In addition, the catalog also includes optical medium-band data (R$\sim50$) in 25 consecutive bands, $\lambda=500$ to 950~nm, from the SHARDS survey and WFC3 IR spectroscopic observations with the G102 and G141 grisms (R$\sim210$ and 130). The use of higher spectral resolution data to estimate photometric redshifts provides very high, and nearly uniform, precision from $z=0-2.5$. The comparison to 1,485 good quality spectroscopic redshifts up to $z\sim3$ yields $\Delta z$/(1+$z_{\rm spec}$)$=$0.0032 and an outlier fraction of $\eta=$4.3\%. In addition to the multi-band photometry, we release added-value catalogs with emission line fluxes, stellar masses, dust attenuations, UV- and IR- based star formation rates and rest-frame colors., Comment: The catalogs, images and spectra are available in Rainbow-slicer (https://bit.ly/2OxKKx1 ), navigator (https://bit.ly/2GDS180 ) and MAST (https://bit.ly/2YtoBQ4 ). In addition to the photometry and other added-value catalogs we release UV+IR star formation rates based on Spitzer (MIPS) and Herschel (PACS and SPIRE) in the 5 CANDELS fields

The Large Synoptic Survey Telescope (LSST) will enable revolutionary studies of galaxies, dark matter, and black holes over cosmic time. The LSST Galaxies Science Collaboration has identified a host of preparatory research tasks required to leverage fully the LSST dataset for extragalactic science beyond the study of dark energy. This Galaxies Science Roadmap provides a brief introduction to critical extragalactic science to be conducted ahead of LSST operations, and a detailed list of preparatory science tasks including the motivation, activities, and deliverables associated with each. The Galaxies Science Roadmap will serve as a guiding document for researchers interested in conducting extragalactic science in anticipation of the forthcoming LSST era., Comment: For more information, see https://galaxies.science.lsst.org

We present a 0.4-8$\mu$m multi-wavelength photometric catalog in the Extended Groth Strip (EGS) field. This catalog is built on the Hubble Space Telescope (HST) WFC3 and ACS data from the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS), and it incorporates the existing HST data from the All-wavelength Extended Groth strip International Survey (AEGIS) and the 3D-HST program. The catalog is based on detections in the F160W band reaching a depth of F160W=26.62 AB (90% completeness, point-sources). It includes the photometry for 41457 objects over an area of $\approx 206$ arcmin$^2$ in the following bands: HST ACS F606W and F814W; HST WFC3 F125W, F140W and F160W; CFHT/Megacam $u^*$, $g'$, $r'$, $i'$ and $z'$; CFHT/WIRCAM $J$, $H$ and $K_\mathrm{S}$; Mayall/NEWFIRM $J1$, $J2$, $J3$, $H1$, $H2$, $K$; Spitzer IRAC $3.6\mu$m, $4.5\mu$m, $5.8\mu$m and $8.0\mu$m. We are also releasing value-added catalogs that provide robust photometric redshifts and stellar mass measurements. The catalogs are publicly available through the CANDELS repository., Comment: ApJS in press. Catalogs can be accessed through the MAST archive at https://archive.stsci.edu/prepds/candels/

In this paper we perform a comprehensive study of the main sources of random and systematic errors in stellar mass measurement for galaxies using their Spectral Energy Distributions (SEDs). We use mock galaxy catalogs with simulated multi-waveband photometry (from U-band to mid-infrared) and known redshift, stellar mass, age and extinction for individual galaxies. Given different parameters affecting stellar mass measurement (photometric S/N ratios, SED fitting errors, systematic effects, the inherent degeneracies and correlated errors), we formulated different simulated galaxy catalogs to quantify these effects individually. We studied the sensitivity of stellar mass estimates to the codes/methods used, population synthesis models, star formation histories, nebular emission line contributions, photometric uncertainties, extinction and age. For each simulated galaxy, the difference between the input stellar masses and those estimated using different simulation catalogs, $\Delta\log(M)$, was calculated and used to identify the most fundamental parameters affecting stellar masses. We measured different components of the error budget, with the results listed as follows: (1). no significant bias was found among different codes/methods, with all having comparable scatter; (2). A source of error is found to be due to photometric uncertainties and low resolution in age and extinction grids; (3). The median of stellar masses among different methods provides a stable measure of the mass associated with any given galaxy; (4). The deviations in stellar mass strongly correlate with those in age, with a weaker correlation with extinction; (5). the scatter in the stellar masses due to free parameters are quantified, with the sensitivity of the stellar mass to both the population synthesis codes and inclusion of nebular emission lines studied., Comment: 33 pages, 20 Figures, Accepted for publication in Astrophysical Journal

We present an analysis of the deepest Herschel images in four major extragalactic fields GOODS-North, GOODS-South, UDS and COSMOS obtained within the GOODS-Herschel and CANDELS-Herschel key programs. The picture provided by 10497 individual far-infrared detections is supplemented by the stacking analysis of a mass-complete sample of 62361 star-forming galaxies from the CANDELS-HST H band-selected catalogs and from two deep ground-based Ks band-selected catalogs in the GOODS-North and the COSMOS-wide fields, in order to obtain one of the most accurate and unbiased understanding to date of the stellar mass growth over the cosmic history. We show, for the first time, that stacking also provides a powerful tool to determine the dispersion of a physical correlation and describe our method called "scatter stacking" that may be easily generalized to other experiments. We demonstrate that galaxies of all masses from z=4 to 0 follow a universal scaling law, the so-called main sequence of star-forming galaxies. We find a universal close-to-linear slope of the logSFR-logM* relation with evidence for a flattening of the main sequence at high masses (log(M*/Msun) > 10.5) that becomes less prominent with increasing redshift and almost vanishes by z~2. This flattening may be due to the parallel stellar growth of quiescent bulges in star-forming galaxies. Within the main sequence, we measure a non varying SFR dispersion of 0.3 dex. The specific SFR (sSFR=SFR/M*) of star-forming galaxies is found to continuously increase from z=0 to 4. Finally we discuss the implications of our findings on the cosmic SFR history and show that more than 2/3 of present-day stars must have formed in a regime dominated by the main sequence mode. As a consequence we conclude that, although omnipresent in the distant Universe, galaxy mergers had little impact in shaping the global star formation history over the last 12.5 Gyr., Comment: 30 pages, 26 figures, accepted for publication in A&A

We use deep panchromatic datasets in the GOODS-N field, from GALEX to the deepest Herschel far-infrared and VLA radio continuum imaging, to explore, using mass-complete samples, the evolution of the star formation activity and dust attenuation of star-forming galaxies to z~4. Our main results can be summarized as follows: i) the slope of the SFR-M correlation is consistent with being constant, and equal to ~0.8 at least up to z~1.5, while its normalization keeps increasing with redshift; ii) for the first time here we are able to explore the FIR-radio correlation for a mass-selected sample of star-forming galaxies: the correlation does not evolve up to z~4; iii) we confirm that galaxy stellar mass is a robust proxy for UV dust attenuation in star-forming galaxies, with more massive galaxies being more dust attenuated, strikingly we find that this attenuation relation evolves very weakly with redshift, the amount of dust attenuation increasing by less than 0.3 magnitudes over the redshift range [0.5-4] for a fixed stellar mass, as opposed to a tenfold increase of star formation rate; iv) the correlation between dust attenuation and the UV spectral slope evolves in redshift, with the median UV spectral slope of star-forming galaxies becoming bluer with redshift. By z~3, typical UV slopes are inconsistent, given the measured dust attenuation, with the predictions of commonly used empirical laws. Finally, building on existing results, we show that gas reddening is marginally larger (by a factor of around 1.3) than stellar reddening at all redshifts probed, and also that the amount of dust attenuation at a fixed ISM metallicity increases with redshift. We speculate that our results support evolving ISM conditions of typical star-forming galaxies such that at z~1.5 Main Sequence galaxies have ISM conditions getting closer to those of local starbursts., Comment: 19 pages, 12 figure, accepted for publication in ApJ

We derive physical properties of 10 submillimeter galaxies located in the CANDELS coverage of the GOODS-S field. The galaxies were first identified as submillimeter sources with the LABOCA bolometer and subsequently targeted for 870um continuum observation with ALMA. The high angular resolution of the ALMA imaging allows secure counterparts to be identified in the CANDELS multiband dataset. The CANDELS data provide deep photometric data from UV through near-infrared wavelengths. Using synthetic spectral energy distributions, we derive photometric redshifts, stellar masses, extinction, ages, and the star formation history. The redshift range is z=1.65-4.76, with two of the galaxies located at z>4. Two SMG counterparts have stellar masses 2-3 orders of magnitude lower than the rest. The remaining SMG counterparts have stellar masses around 1x10^11 Msun. The stellar population in the SMGs is typically older than the expected duration of the submillimeter phase, suggesting that the star formation history of submillimeter galaxies is more complex than a single burst. Non-parametric morphology indices suggest that the SMG counterparts are among the most asymmetric systems compared with galaxies of the same stellar mass and redshift. The HST images shows that 3 of the SMGs are associated with on-going mergers. The remaining counterparts are isolated. Estimating the dust and molecular gas mass from the submm fluxes, and comparing with our stellar masses shows that the molecular gas mass fraction of SMGs is ~28% and that the final stellar mass is likely to be (1-2)x10^11 Msun., Comment: 51 pages, 9 figures, 5 tables; Submitted to ApJ

The Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) was a multi-cycle treasury program on the Hubble Space Telescope (HST) that surveyed a total area of ~0.25 deg^2 with ~900 HST orbits spread across 5 fields over 3 years. Within these survey images we discovered 65 supernovae (SN) of all types, out to z~2.5. We classify ~24 of these as Type Ia SN (SN Ia) based on host-galaxy redshifts and SN photometry (supplemented by grism spectroscopy of 6 SN). Here we present a measurement of the volumetric SN Ia rate as a function of redshift, reaching for the first time beyond z=2 and putting new constraints on SN Ia progenitor models. Our highest redshift bin includes detections of SN that exploded when the universe was only ~3 Gyr old and near the peak of the cosmic star-formation history. This gives the CANDELS high-redshift sample unique leverage for evaluating the fraction of SN Ia that explode promptly after formation (<500 Myr). Combining the CANDELS rates with all available SN Ia rate measurements in the literature we find that this prompt SN Ia fraction is fP=0.53 +0.09 -0.10 (stat) +0.10 -0.26 (sys), consistent with a delay time distribution that follows a simple t^{-1} power law for all times t>40 Myr. However, a mild tension is apparent between ground-based low-z surveys and space-based high-z surveys. In both CANDELS and the sister HST program CLASH, we find a low rate of SN Ia at z>1. This could be a hint that prompt progenitors are in fact relatively rare, accounting for only ~20% of all SN Ia explosions -- though further analysis and larger samples will be needed to examine that suggestion., Comment: 20 pages + 10-page appendix, 12 figures + 5 in appendix; Accepted to AJ ; latest version includes updates to discussion and figures, responding to referee and others

We present results from the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) photometric redshift methods investigation. In this investigation, the results from eleven participants, each using a different combination of photometric redshift code, template spectral energy distributions (SEDs) and priors, are used to examine the properties of photometric redshifts applied to deep fields with broad-band multi-wavelength coverage. The photometry used includes U-band through mid-infrared filters and was derived using the TFIT method. Comparing the results, we find that there is no particular code or set of template SEDs that results in significantly better photometric redshifts compared to others. However, we find codes producing the lowest scatter and outlier fraction utilize a training sample to optimize photometric redshifts by adding zero-point offsets, template adjusting or adding extra smoothing errors. These results therefore stress the importance of the training procedure. We find a strong dependence of the photometric redshift accuracy on the signal-to-noise ratio of the photometry. On the other hand, we find a weak dependence of the photometric redshift scatter with redshift and galaxy color. We find that most photometric redshift codes quote redshift errors (e.g., 68% confidence intervals) that are too small compared to that expected from the spectroscopic control sample. We find that all codes show a statistically significant bias in the photometric redshifts. However, the bias is in all cases smaller than the scatter, the latter therefore dominates the errors. Finally, we find that combining results from multiple codes significantly decreases the photometric redshift scatter and outlier fraction. We discuss different ways of combining data to produce accurate photometric redshifts and error estimates., Comment: 26 pages, 15 figures, ApJ in press

We present a UV-to-mid infrared multi-wavelength catalog in the CANDELS/GOODS-S field, combining the newly obtained CANDELS HST/WFC3 F105W, F125W, and F160W data with existing public data. The catalog is based on source detection in the WFC3 F160W band. The F160W mosaic includes the data from CANDELS deep and wide observations as well as previous ERS and HUDF09 programs. The mosaic reaches a 5$\sigma$ limiting depth (within an aperture of radius 0.17 arcsec) of 27.4, 28.2, and 29.7 AB for CANDELS wide, deep, and HUDF regions, respectively. The catalog contains 34930 sources with the representative 50% completeness reaching 25.9, 26.6, and 28.1 AB in the F160W band for the three regions. In addition to WFC3 bands, the catalog also includes data from UV (U-band from both CTIO/MOSAIC and VLT/VIMOS), optical (HST/ACS F435W, F606W, F775W, F814W, and F850LP), and infrared (HST/WFC3 F098M, VLT/ISAAC Ks, VLT/HAWK-I Ks, and Spitzer/IRAC 3.6, 4.5, 5.8, 8.0 $\mu$m) observations. The catalog is validated via stellar colors, comparison with other published catalogs, zeropoint offsets determined from the best-fit templates of the spectral energy distribution of spectroscopically observed objects, and the accuracy of photometric redshifts. The catalog is able to detect unreddened star-forming (passive) galaxies with stellar mass of 10^{10}M_\odot at a 50% completeness level to z$\sim$3.4 (2.8), 4.6 (3.2), and 7.0 (4.2) in the three regions. As an example of application, the catalog is used to select both star-forming and passive galaxies at z$\sim$2--4 via the Balmer break. It is also used to study the color--magnitude diagram of galaxies at 0

We explore the relationship between gas, dust and star formation in a sample of 12 ultra-luminous infrared galaxies (ULIRGs) at high redshift compared to a similar sample of local galaxies. We present new CO observations and/or Spitzer mid-IR spectroscopy for 6 70 micron selected galaxies at z~1 in order to quantify the properties of the molecular gas reservoir, the contribution of an active galactic nuclei (AGN) to the mid-IR luminosity and the star formation efficiency (SFE=LIR/L'CO). The mid-IR spectra show strong polycyclic aromatic hydrocarbon (PAH) emission and our spectral decomposition suggests that the AGN makes a minimal contribution (<25%) to the mid-IR luminosity. The 70 micron selected ULIRGs which we find to be spectroscopic close pairs, are observed to have high SFE, similar to local ULIRGs and high redshift submillimeter galaxies, consistent with enhanced IR luminosity due to an ongoing major merger. Combined with existing observations of local and high redshift ULIRGs, we further compare the PAH, IR and CO luminosities. We show that the ratio LPAH6.2/LIR decreases with increasing IR luminosity for both local and high redshift galaxies but the trend for high redshift galaxies is shifted to higher IR luminosities; the average LPAH6.2/LIR ratio at a given LIR is ~3 times higher at high redshift. When we normalize by the molecular gas, we find this trend to be uniform for galaxies at all redshifts and that the molecular gas is correlated with the PAH dust emission.The similar trends seen in the [CII] to molecular gas ratios in other studies suggests that PAH emission, like [CII], continues to be a good tracer of photodissociation regions even at high redshift. Together the CO, PAH and far-IR fine structure lines should be useful for constraining the interstellar medium conditions in high redshift galaxies., Comment: 16 pages, 6 figures, 5 tables, accepted for publication in ApJ

We investigate how star-forming galaxies typically assemble their masses at high redshift. Using the deep multi-wavelength coverage of the GOODS dataset, we measure stellar mass of a large sample of star-forming galaxies at z~4 and 5, and make a robust determination of stellar mass function (SMF). We report a broad correlation between stellar mass and UV luminosity, such that more UV-luminous galaxies are, on average, more massive. However, the correlation has a substantial intrinsic scatter evidenced by a non-negligible number of UV-faint but massive galaxies. Furthermore, the low-mass end of the SMF does not rise as steeply as the UV luminosity function (alpha_UVLF} -(1.7-1.8), alpha_SMF -(1.3-1.4)) of the same galaxies. In a smooth formation scenario where star formation (SF) is sustained at the observed rates for a long time, these galaxies would have accumulated more mass (by a factor of ~3) than observed and therefore the SMF would mirror more closely that of the UVLF. The relatively shallow slope of the SMF is due to the fact that many of the UV-selected galaxies are not massive enough, and therefore are too faint in their rest-frame optical bands, to be detected in the current observations. Our results favor a episodic formation history in which SF in low-mass galaxies vary significantly over time, a scenario favored by galaxy clustering. Our findings for the UV-faint galaxies are in contrast with those found for more UV-luminous galaxies, which exhibit tighter SFR-M_star correlations. The discrepancy may suggest that galaxies at different luminosities may have different evolutionary paths., Comment: 24 pages, 9 figures, 2 tables, Accepted for publication in Astrophysical Journal

We use deep far-IR, submm, radio and X-ray imaging and mid-IR spectroscopy to explore the nature of a sample of Spitzer-selected dust-obscured galaxies (DOGs) in GOODS-N. A sample of 79 galaxies satisfy the criteria R-[24]>14 (Vega) down to S24>100 microJy. Twelve of these galaxies have IRS spectra available which we use to measure redshifts and classify these objects as being dominated by star formation or active galactic nuclei (AGN) activity in the mid-IR. The IRS spectra and Spitzer photometric redshifts confirm that the DOGs lie in a tight redshift distribution around z~2. Based on mid-IR colors, 80% of DOGs are likely dominated by star formation; the stacked X-ray emission from this sub-sample of DOGs is also consistent with star formation. Since only a small number of DOGs are individually detected at far-IR and submm wavelengths, we use a stacking analysis to determine the average flux from these objects and plot a composite IR (8-1000 microns) spectral energy distribution (SED). The average luminosity of these star forming DOGs is LIR~1e12 Lsun. We compare the average star forming DOG to the average bright (S850>5 mJy) submillimeter galaxy (SMG); the S24>100 microJy DOGs are 3 times more numerous but 8 times less luminous in the IR. The far-IR SED shape of DOGs is similar to that of SMGs (average dust temperature of around 30 K) but DOGs have a higher mid-IR to far-IR flux ratio. The average star formation-dominated DOG has a star formation rate of 200 Msun/yr which, given their space density, amounts to a contribution of 0.01 Msun/yr/Mpc3 (or 5-10%) to the star formation rate density at z~2. We use the composite SED to predict the average flux of DOGs in future Herschel/PACS 100 micron and SCUBA-2 450 micron surveys and show that the majority of them will be detected., Comment: 7 pages, 5 figures; accepted for publication in ApJ

The Hubble Ultra Deep Field source JD2 presented in Mobasher et al. (2005) is an unusual galaxy that is very faint at all wavelengths shortward of 1.1 micron. Photometric redshift fits to data at 0.4 to 8 microns yield a significant probability that it is an extremely massive galaxy at z~6.5. In this paper we present new photometry at 16 microns and 22 micron from Spitzer Infrared Spectrograph (IRS) peak-up imaging of the Great Observatories Origins Deep Survey (GOODS) fields. We find that the spectral energy distribution shows a factor of ~4 rise in flux density between the 16 micron and 22 micron bandpass which is most likely due to the entrance of polycyclic aromatic hydrocarbon emission features into the 22 micron and 24 micron passbands. The flux ratio between these bandpasses can be best fit by a z~1.7 luminous infrared galaxy with a bolometric luminosity of (2-6)\times10^{11} L_sun corresponding to a star-formation rate of 80 M_sun/yr. The predicted flux density values at other longer wavelengths are below the detection limits of current instrumentation but such sources could potentially be detected in lensed submillimeter surveys. Re-evaluation of the optical/near-infrared photometry continues to favor z>6 photometric redshift solutions, but we argue that the consistency of the multiwavelength parameters of this galaxy with other dusty starbursts favor the z~2 mid-infrared photometric redshift. The data presented here provide evidence that optically undetected near-infrared sources which are detected at 24 microns are most likely dusty, starburst galaxies at a redshift of z~2 with stellar masses >10^{10} M_sun., Comment: 20 pages, 6 figures (color), 3 tables, 2007, ApJ, 665 vol.1 (10 August)

We have detected likely z~7-8 galaxies in the 144"x144" NICMOS observations of the Hubble Ultra Deep Field. Objects are required to be >3 sigma detections in both NICMOS bands, J and H. The selection criteria for this sample are (z-J)>0.8, (z-J) > 0.66 (J-H)+0.8, (J-H)<1.2, and no detection at <8500 Angstroms. The 5 selected sources have total magnitudes H~27. Four of the five sources are quite blue compared to typical lower-redshift dropout galaxies and are clustered within a 1 arcmin**2 region. Because all 5 sources are near the limit of the NICMOS data, we have carefully evaluated their reality. Each of the candidates is visible in different splits of the data and a median stack. We analyzed several noise images and estimate the number of spurious sources to be 1+/-1. A search using an independent reduction of this same data set clearly revealed 3 of the 5 candidates and weakly detected a 4th candidate, suggesting the contamination could be higher. For comparison with predictions from lower redshift samples we take a conservative approach and adopt four z~7-8 galaxies as our sample. With the same detection criteria on simulated datasets, assuming no-evolution from z~3.8, we predict 10 sources at z~7-8, or 14 if we use a more realistic (1+z)^{-1} size scaling. We estimate that the rest-frame continuum UV (~1800 Angstroms) luminosity density at z~7.5 (integrated down to 0.3L*) is just 0.20_{-0.08}^{+0.12}x that found at z~3.8. Effectively this sets an upper limit on the luminosity density down to 0.3 L*. This result is consistent with significant evolution at the bright end of the luminosity function from z~7.5 to z~3.8. Even with the lower UV luminosity density at z~7.5, it appears that galaxies could still play an important role in reionization at these redshifts, though definitive measurements remain to be made. [abridged], Comment: 12 pages, 3 figures, 1 table, accepted for publication in the Astrophysical Journal Letters (modulo some minor editting to reduce the overall length)

Using U'- through Ks-band imaging data in the GOODS-South field, we construct a large, complete sample of 275 ``extremely red objects'' (EROs; K_s<22.0, R-K_s>3.35; AB), all with deep HST/ACS imaging in B_435, V_606, i_775, and z_850, and well-calibrated photometric redshifts. Quantitative concentration and asymmetry measurements fail to separate EROs into distinct morphological classes. We therefore visually classify the morphologies of all EROs into four broad types: ``Early'' (elliptical-like), ``Late'' (disk galaxies), ``Irregular'' and ``Other'' (chain galaxies and low surface brightness galaxies), and calculate their relative fractions and comoving space densities. For a broad range of limiting magnitudes and color thresholds, the relative number of early-type EROs is approximately constant at 33-44%, and the comoving space densities of Early- and Late-type EROs are comparable. Mean rest-frame spectral energy distributions (SEDs) at wavelengths between 0.1 and 1.2 um are constructed for all EROs. The SEDs are extremely similar in their range of shapes, independent of morphological type. The implication is that any differences between the broad-band SEDs of Early-type EROs and the other types are relatively subtle, and there is no robust way of photometrically distinguishing between different morphological types with usual optical/near-infrared photometry., Comment: Submitted to the ApJL. A version with full-resolution figures, all GOODS data and all GOODS collaboration papers may be found at http://www.stsci.edu/science/goods/

As part of the Hubble Deep Field South program, a set of shorter 2-orbit observations were obtained of the area adjacent to the deep fields. The WFPC2 flanking fields cover a contiguous solid angle of 48 square arcminutes. Parallel observations with the STIS and NICMOS instruments produce a patchwork of additional fields with optical and near-infrared (1.6 micron) response. Deeper parallel exposures with WFPC2 and NICMOS were obtained when STIS observed the NICMOS deep field. These deeper fields are offset from the rest, and an extended low surface brightness object is visible in the deeper WFPC2 flanking field. In this data paper, which serves as an archival record of the project, we discuss the observations and data reduction, and present SExtractor source catalogs and number counts derived from the data. Number counts are broadly consistent with previous surveys from both ground and space. Among other things, these flanking field observations are useful for defining slit masks for spectroscopic follow-up over a wider area around the deep fields, for studying large-scale structure that extends beyond the deep fields, for future supernova searches, and for number counts and morphological studies, but their ultimate utility will be defined by the astronomical community., Comment: 46 pages, 15 figures. Images and full catalogs available via the HDF-S at http://www.stsci.edu/ftp/science/hdfsouth/hdfs.html at present. The paper is accepted for the February 2003 Astronomical Journal. Full versions of the catalogs will also be available on-line from AJ after publication

Understanding how the physical properties of galaxies (e.g. their spectral type or age) evolve as a function of redshift relies on having an accurate representation of galaxy spectral energy distributions. While it has been known for some time that galaxy spectra can be reconstructed from a handful of orthogonal basis templates, the underlying basis is poorly constrained. The limiting factor has been the lack of large samples of galaxies (covering a wide range in spectral type) with high signal-to-noise spectrophotometric observations. To alleviate this problem we introduce here a new technique for reconstructing galaxy spectral energy distributions directly from samples of galaxies with broadband photometric data and spectroscopic redshifts. Exploiting the statistical approach of the Karhunen-Loeve expansion, our iterative training procedure increasingly improves the eigenbasis, so that it provides better agreement with the photometry. We demonstrate the utility of this approach by applying these improved spectral energy distributions to the estimation of photometric redshifts for the HDF sample of galaxies. We find that in a small number of iterations the dispersion in the photometric redshifts estimator (a comparison between predicted and measured redshifts) can decrease by up to a factor of 2., Comment: 25 pages, 9 figures, LaTeX AASTeX, accepted for publication in AJ

We have discovered a concentration of extremely red objects (EROs; R-K>6) in the field of the z=2.69 quasar QSO 1213-0017 (UM 485), which is significantly overabundant compared to the field ERO surface density. The optical/near-IR colors of the EROs and numerous other red galaxies in this field are consistent with elliptical galaxies at z=1-2. HST optical images for a subset of galaxies show regular morphologies, most of them being disky or diffuse and without any obvious evidence for interactions. Ground-based IR images show similar morphologies, indicating any dust reddening in these objects is spatially uniform. Optical spectroscopy with the W. M. Keck Telescope has found that four of the red galaxies lie at =1.31, and a fifth lies in the foreground at z=1.20. Of the =1.31 galaxies, one is a reddened AGN while the remaining three have rest-frame UV absorption-line spectra characteristic of old (few Gyr) stellar populations, similar to the old red galaxy LBDS 53W091 at z=1.55. Including the MgII absorber seen in the QSO spectrum, we find five galaxies at =1.31 spread over 1.5 h_50^{-1} Mpc on the sky. These results suggest we have discovered a coherent structure of old galaxies at high-redshift, possibly associated with a massive galaxy cluster., Comment: 37 pages including 11 Postscript figures. To appear in the June 2000 issue of the Astronomical Journal

We present a novel method capable of creating optimal eigenspectra from multicolor redshift surveys for photometric redshift estimation. Our iterative training algorithm modifies the templates to represent the photometric measurements better. We present a short description of our algorithm here. We show that the corrected templates give more precise photometric redshifts, essentially a ``free'' feature, since we were not fitting for the redshifts themselves., Comment: 6 pages, 5 figures, requires paspconf.sty. To be published in "Photometric Redshifts and High Redshift Galaxies", eds. R. Weymann, L. Storrie-Lombardi, M. Sawicki & R. Brunner, (San Francisco: ASP Conference Series)

We have measured the angular correlation function w(theta) for a sample of 871 Lyman-break galaxies (LBGs) at z=3. Fitting a power-law to a weighted average of w(theta) from 5 fields, we find the amplitude to be A_w=2 arcsec^{\beta} and the slope \beta=0.9. The slope is the same as in the local and moderate redshift universe. A slope \beta=0.25 or shallower is ruled out by the data at the 99.9% confidence level. Because N(z) of LBGs is well determined from 376 spectroscopic redshifts, the real-space correlation function can be derived from the angular one through the Limber transform. This inversion is rather insensitive to the still relatively large errors on A_w and \beta, and the spatial correlation length is much more tightly constrained than either of these parameters. We estimate r_0=3.3 -0.6 +0.7 (2.1 -0.5 +0.4) h^{-1} Mpc (comoving) for q_0=0.1 (0.5) at z=3.04 (h is in units of 100 km/s/Mpc). The correlation length of LBGs at z=3 is comparable to that of present-day spiral galaxies and is only about 50% smaller than that of the ellipticals; it is as large or larger than any measured in galaxy samples at 0.3

The Lyman decrement associated with the cumulative effect of HI in QSO absorption systems along the line of sight provides a distinctive feature for identifying galaxies at z>2.5. The Hubble Deep Field (HDF) observations offer the opportunity to exploit the ubiquitous effect of intergalactic absorption and obtain useful statistical constraints on the redshift distribution of galaxies considerably fainter than current spectroscopic limits. We model the HI cosmic opacity as a function of redshift, including scattering in resonant lines of the Lyman series and Lyman-continuum absorption, and use stellar population synthesis models with a wide variety of ages, metallicities, dust contents, and redshifts, to derive color selection criteria that provide a robust separation between high redshift and low redshift galaxies. From the HDF images we construct a sample of star-forming galaxies at 2