Jonathan P. Gardner

The Great Observatories Origins Deep Survey: Initial Results from Optical and Near-Infrared Imaging

This special issue of the Astrophysical Journal Letters is dedicated to presenting initial results from the Great Observatories Origins Deep Survey (GOODS) that are primarily, but not exclusively, based on multiband imaging data obtained with the Hubble Space Telescope and the Advanced Camera for Surveys (ACS). The survey covers roughly 320 arcmin2 in the ACS F435W, F606W, F814W, and F850LP bands, divided into two well-studied fields. Existing deep observations from the Chandra X-Ray Observatory and ground-based facilities are supplemented with new, deep imaging in the optical and near-infrared from the European Southern Observatory and from the Kitt Peak National Observatory. Deep observations with the Space Infrared Telescope Facility are scheduled. Reduced data from all facilities are being released worldwide within 3-6 months of acquisition. Together, this data set provides two deep reference fields for studies of distant normal and active galaxies, supernovae, and faint stars in our own Galaxy. This Letter serves to outline the survey strategy and describe the specific data that have been used in the accompanying letters, summarizing the reduction procedures and sensitivity limits.

The James Webb Space Telescope

The James Webb Space Telescope (JWST) is a large (6.6 m), cold (<50 K), infrared (IR)-optimized space observatory that will be launched early in the next decade into orbit around the second Earth–Sun Lagrange point. The observatory will have four instruments: a near-IR camera, a near-IR multiobject spectrograph, and a tunable filter imager will cover the wavelength range, 0.6 < ; < 5.0 μ m, while the mid-IR instrument will do both imaging and spectroscopy from 5.0 < ; < 29 μ m.The JWST science goals are divided into four themes. The key objective of The End of the Dark Ages: First Light and Reionization theme is to identify the first luminous sources to form and to determine the ionization history of the early universe. The key objective of The Assembly of Galaxies theme is to determine how galaxies and the dark matter, gas, stars, metals, morphological structures, and active nuclei within them evolved from the epoch of reionization to the present day. The key objective of The Birth of Stars and Protoplanetary Systems theme is to unravel the birth and early evolution of stars, from infall on to dust-enshrouded protostars to the genesis of planetary systems. The key objective of the Planetary Systems and the Origins of Life theme is to determine the physical and chemical properties of planetary systems including our own, and investigate the potential for the origins of life in those systems. Within these themes and objectives, we have derived representative astronomical observations.To enable these observations, JWST consists of a telescope, an instrument package, a spacecraft, and a sunshield. The telescope consists of 18 beryllium segments, some of which are deployed. The segments will be brought into optical alignment on-orbit through a process of periodic wavefront sensing and control. The instrument package contains the four science instruments and a fine guidance sensor. The spacecraft provides pointing, orbit maintenance, and communications. The sunshield provides passive thermal control. The JWST operations plan is based on that used for previous space observatories, and the majority of JWST observing time will be allocated to the international astronomical community through annual peer-reviewed proposal opportunities.

The Herschel ATLAS

The Herschel ATLAS is the largest open-time key project that will be carried out on the Herschel Space Observatory. It will survey 570 deg2 of the extragalactic sky, 4 times larger than all the other Herschel extragalactic surveys combined, in five far-infrared and submillimeter bands. We describe the survey, the complementary multiwavelength data sets that will be combined with the Herschel data, and the six major science programs we are undertaking. Using new models based on a previous submillimeter survey of galaxies, we present predictions of the properties of the ATLAS sources in other wave bands.

The Rest-Frame Ultraviolet Luminosity Density of Star-forming Galaxies at Redshifts z > 3.5*

We have measured the rest-frame λ ~ 1500 A comoving specific luminosity density of star-forming galaxies at redshift 3.5 < z < 6.5 (Lyman break galaxies [LBGs]) selected from deep, multiband images taken with the Hubble Space Telescope and the Advanced Camera for Surveys, obtained as part of the Great Observatories Origins Deep Survey (GOODS). The samples cover ~0.09 deg2 and are also relatively deep, reaching between 0.2L and 0.5L, depending on the redshift, where L is the characteristic UV luminosity of LBGs at z ~ 3. The specific luminosity density appears to be nearly constant with redshift over the range 3 < z < 6, although the measure at z ~ 6 remains relatively uncertain, because it depends on the accurate estimate of the faint counts of the z ~ 6 sample. If LBGs are fair tracers of the cosmic star formation activity, our results suggest that at z ~ 6, namely, at less than ~7% of the current cosmic age, the universe was already producing stars as vigorously as it did near its maximum several gigayears later, at 1 z 3.

The Size Evolution of High-Redshift Galaxies

Hubble Space Telescope images of high-redshift galaxies selected via color and photometric redshifts are used to examine the size and axial ratio distribution of galaxies as a function of redshift at look-back times t > 8 Gyr. These parameters are measured at rest-frame UV wavelengths (1200 A < λ < 2000 A) on images with a rest-frame resolution of less than 0.8 kpc. Galaxy radii are found to scale with redshift approximately as the Hubble parameter H-1(z). This is in accord with the theoretical expectation that the typical sizes of the luminous parts of galaxies should track the expected evolution in the virial radius of dark matter halos. The mean ratio of the semimajor axis to the semiminor axis for a bright well-resolved sample of galaxies at z ~ 4 is b/a = 0.65, suggesting that these Lyman break galaxies are not drawn from a spheroidal population. However, the median concentration index of this sample is C = 3.5, which is closer to the typical concentration indices of nearby elliptical galaxies (C ~ 4) than to the values for local disk galaxies of type Sb and later (C < 2).

Cosmic Variance in the Great Observatories Origins Deep Survey

Cosmic variance is the uncertainty in observational estimates of the volume density of extragalactic objects such as galaxies or quasars arising from the underlying large-scale density fluctuations. This is often a significant source of uncertainty, especially in deep galaxy surveys, which tend to cover relatively small areas. We present estimates of the relative cosmic variance for one-point statistics (i.e., number densities) for typical scales and volumes sampled by the Great Observatories Origins Deep Survey (GOODS). We use two approaches: (1) For objects with a known two-point correlation function that is well approximated by a power law, one can use the standard analytic formalism to calculate the cosmic variance (in excess of shot noise). We use this approach to estimate the cosmic variance for several populations that are being studied in the GOODS program (extremely red objects [EROs] at z ~ 1 and Lyman break galaxies [LBGs] at z ~ 3 and z ~ 4) using clustering information for similar populations in the literature. (2) For populations with unknown clustering, one can use predictions from cold dark matter theory to obtain a rough estimate of the variance as a function of number density. We present a convenient plot that allows one to use this approach to read off the cosmic variance for a population with a known mean redshift and estimated number density. We conclude that for the volumes sampled by GOODS, cosmic variance is a significant source of uncertainty for strongly clustered objects (~40%-60% for EROs) and less serious for less clustered objects (~10%-20% for LBGs).

The Evolution of Disk Galaxies in the GOODS-South Field: Number Densities and Size Distribution*

We examine the evolution of the sizes and number densities of disk galaxies using the high-resolution images obtained by the Great Observatories Origins Deep Survey (GOODS) with the Advanced Camera for Surveys on the Hubble Space Telescope. The multiwavelength images are used to classify galaxies based on their rest-frame B-band morphologies out to redshift . In order to minimize the effect of selection biases, we confine our z ∼ 1.25 analysis to galaxies that occupy the region of the magnitude-size plane where the survey is ∼90% complete at all redshifts. The observed size distribution is consistent with a lognormal distribution as seen for the disk galaxies in the local universe and does not show any significant evolution over the redshift range . We 0.25 ≤ z ≤ 1.25 find that the number densities of disk galaxies remains fairly constant over this redshift range, although a modest evolution by a factor of 4 may be possible within the 2 j uncertainties. Subject headings: galaxies: evolution — galaxies: formation — galaxies: fundamental parameters — galaxies: structure

X-Ray Properties of Lyman Break Galaxies in the Hubble Deep Field-North Region

We describe the X-ray properties of a large sample of z ~ 3 Lyman break galaxies (LBGs) in the region of the Hubble Deep Field-North, derived from the 1 Ms public Chandra observation. Of our sample of 148 LBGs, four are detected individually. This immediately gives a measure of the bright AGN fraction in these galaxies of ~3%, which is in agreement with that derived from the UV spectra. The X-ray color of the detected sources indicates that they are probably moderately obscured. Stacking of the remainder shows a significant detection (6 ?) with an average luminosity of 3.4 ? 1041 ergs s-1 per galaxy in the rest-frame 2-10 keV band. We have also studied a comparison sample of 95 z ~ 1 Balmer break galaxies. Eight of these are detected directly, with at least two clear AGNs based on their high X-ray luminosity and very hard X-ray spectra. The remainder are of relatively low luminosity (<1042 ergs s-1), and the X-rays could arise from either AGNs or rapid star formation. The X-ray colors and evidence from other wave bands favor the latter interpretation. Excluding the clear AGNs, we deduce a mean X-ray luminosity of 6.6 ? 1040 ergs s-1, a factor of ~5 lower than the LBGs. The average ratio of the UV and X-ray luminosities of these star-forming galaxies LUV/LX, however, is approximately the same at z = 1 as it is at z = 3. This scaling implies that the X-ray emission follows the current star formation rate, as measured by the UV luminosity. We use our results to constrain the star formation rate at z ~ 3 from an X-ray perspective. Assuming the locally established correlation between X-ray and far-IR luminosity, the average inferred star formation rate in each LBG is found to be approximately 60 M? yr-1, in excellent agreement with the extinction-corrected UV estimates. This provides an external check on the UV estimates of the star formation rates and on the use of X-ray luminosities to infer these rates in rapidly star-forming galaxies at high redshift.

Herschel-ATLAS: Dust Temperature and Redshift Distribution of SPIRE and PACS Detected Sources Using Submillimetre Colours

We present colour-colour diagrams of detected sources in the Herschel-ATLAS science demonstration field from 100 to 500 mu m using both PACS and SPIRE. We fit isothermal modified black bodies to the spectral energy distribution (SED) to extract the dust temperature of sources with counterparts in Galaxy And Mass Assembly (GAMA) or SDSS surveys with either a spectroscopic or a photometric redshift. For a subsample of 330 sources detected in at least three FIR bands with a significance greater than 3 sigma, we find an average dust temperature of (28 +/- 8) K. For sources with no known redshift, we populate the colour-colour diagram with a large number of SEDs generated with a broad range of dust temperatures and emissivity parameters, and compare to colours of observed sources to establish the redshift distribution of this sample. For another subsample of 1686 sources with fluxes above 35 mJy at 350 mu m and detected at 250 and 500 mu m with a significance greater than 3s, we find an average redshift of 2.2 +/- 0.6.

Herschel -ATLAS: extragalactic number counts from 250 to 500 microns

Aims. The Herschel-ATLAS survey (H-ATLAS) will be the largest area survey to be undertaken by the Herschel Space Observatory. It will cover 550 sq. deg. of extragalactic sky at wavelengths of 100, 160, 250, 350 and 500 μm when completed, reaching flux limits (5σ) from 32 to 145 mJy. We here present galaxy number counts obtained for SPIRE observations of the first ∼14 sq. deg. observed at 250, 350 and 500 μm. Methods. Number counts are a fundamental tool in constraining models of galaxy evolution. We use source catalogs extracted from the H-ATLAS maps as the basis for such an analysis. Correction factors for completeness and flux boosting are derived by applying our extraction method to model catalogs and then applied to the raw observational counts. Results. We find a steep rise in the number counts at flux levels of 100−200 mJy in all three SPIRE bands, consistent with results from BLAST. The counts are compared to a range of galaxy evolution models. None of the current models is an ideal fit to the data but all ascribe the steep rise to a population of luminous, rapidly evolving dusty galaxies at moderate to high redshift.