Hyron Spinrad

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 unusual afterglow of the γ-ray burst of 26 March 1998 as evidence for a supernova connection

Cosmic γ-ray bursts have now been firmly established as one of the most powerful phenomena in the Universe, releasing almost the rest-mass energy of a neutron star within the space of a few seconds (ref. 1). The two most popular models to explain γ-ray bursts are the coalescence of two compact objects such as neutron stars or black holes, or the catastrophic collapse of a massive star in a very energetic supernova-like explosion. Here we show that, about three weeks after the γ-ray burst of 26 March 1998, the transient optical source associated with the burst brightened to about 60 times the expected flux, based upon an extrapolation of the initial light curve. Moreover, the spectrum changed dramatically, with the colour becoming extremely red. We argue that the new source is an underlying supernova. If our hypothesis is true then this provides evidence linking cosmologically located γ-ray bursts with deaths of massive stars.Palomar Observatory 105-24, Caltech, Pasadena, CA 91125, USA National Radio Astronomy Observatory, P. O. Box O, Socorro, NM 87801, USA Department of Astronomy, University of California, Berkeley, CA 94720-3411 USA National Optical Astronomy Observatories, 950 N. Cherry, Ave. Tucson, AZ 85719, USA Institute of Geophysics and Planetary Physics, Lawrence Livermore National Laboratory, 7000 East Avenue, P. O. Box 808, L-413, Livermore, CA 94551-9900, USA Center for Particle Astrophysics, University of California, Berkeley, CA 94720 USA Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA European Southern Observatory, D-85748 Garching, Germany Istituto di Astrofisica Spaziale, CNR, via Fosso del Cavaliere, Roma I-00133, Italy

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.

TWO BRIGHT SUBMILLIMETER GALAXIES IN A z=4.05 PROTOCLUSTER IN GOODS-NORTH, AND ACCURATE RADIO-INFRARED PHOTOMETRIC REDSHIFTS

We present the serendipitous discovery of molecular gas CO emission lines with the IRAM Plateau de Bure interferometer coincident with two luminous submillimeter galaxies (SMGs) in the Great Observatories Origins Deep Survey North field (GOODS-N). The identification of the millimeter emission lines as CO[4-3] at z = 4.05 is based on the optical and near-IR photometric redshifts, radio-infrared photometric redshifts and Keck+DEIMOS optical spectroscopy. These two galaxies include the brightest submillimeter source in the field (GN20; S850µm = 20.3mJy, zCO = 4.055 ± 0.001) and its companion (GN20.2; S850µm = 9.9mJy, zCO = 4.051 ± 0.003). These are among the most distant submillimeter-selected galaxies reliably identified through CO emission and also some of the most luminous known. GN20.2 has a possible additional counterpart and a luminous AGN inside its primary counterpart revealed in the radio. Continuum emission of 0.3mJy at 3.3mm (0.65mm in the rest frame) is detected at 5� for GN20, the first dust continuum detection in an SMG at such long wavelength, unveiling a spectral energy distribution that is similar to local ultra luminous infrared galaxies. In terms of CO to bolometric luminosities, stella r mass and star formation rates (SFRs), these newly discovered z > 4 SMGs are similar to z ∼ 2 − 3 SMGs studied to date. These z ∼ 4 SMGs have much higher specific SFRs than typical B-band dropout Lyman break galaxi es at the same redshift. The stellar mass-SFR correlation for normal galaxies does not seem to evolve much further, between z ∼ 2 and z ∼ 4. A significant z = 4.05 spectroscopic redshift spike is observed in GOODS-N, and a strong spatial overdensity of B-band dropouts and IRAC selected z > 3.5 galaxies appears to be centered on the GN20 and GN20.2 galaxies. This suggests a proto-cluster structure with total mass ∼ 10 14 M⊙. Using photometry at mid-IR (24µm), submm (850µm) and radio (20cm) wavelengths, we show that reliable photometric redshifts (�z/(1+ z) ∼ 0.1) can be derived for SMGs over 1 < ∼ z < ∼ 4. This new photometric redshift technique has been used to provide a first estimate of the space density of 3.5 < z < 6 hyper-luminous starburst galaxies, and to show that they both contribute substantially to the SFR density at early epochs and that they can account for the presence of old galaxies at z ∼ 2 − 3. Many of these high-redshift starbursts will be within rea ch of Herschel. We find that the

LBDS 53W091: An Old, Red Galaxy at z = 1.552

The weak radio source LBDS 53W091 is associated with a very faint (R ? 24.5) red (R - K ? 5.8) galaxy. Long spectroscopic integrations with the W. M. Keck telescope have provided an absorption-line redshift, z = 1.552 ? 0.002. The galaxy has a rest frame ultraviolet spectrum very similar to that of an F6 V star, and a single-burst old stellar population that matches the IR colors, the optical energy distribution and the spectral discontinuities has a minimum age of 3.5 Gyr. We present detailed population synthesis analyses of the observed spectrum in order to estimate the time since the last major epoch of star formation. We discuss the discrepancies in these estimates resulting from using different models, subjecting the UV spectrum of M32 to the same tests as a measure of robustness of these techniques. The models most consistent with the data tend to yield ages at z = 1.55 of 3.5 Gyr, similar to that inferred for the intermediate-age population in M32. Depending upon the assumed Hubble constant and the value of ?0, only certain cosmological expansion times are consistent with the age of LBDS 53W091; in particular, for ?0 = 1, only models with H0 45 km s-1 Mpc-1 are permitted. For H0 = 50 km s-1 Mpc-1 and ?0 = 0.2, we derive a formation redshift, zf ? 5.

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).

SPECTROSCOPIC CONFIRMATION OF THREE z-DROPOUT GALAXIES AT z = 6.844-7.213: DEMOGRAPHICS OF Lyα EMISSION IN z ∼ 7 GALAXIES

We present the results of our ultra-deep Keck/DEIMOS spectroscopy of z-dropout galaxies in the Subaru Deep Field and Great Observatories Origins Deep Surveys northern field. For 3 out of 11 objects, we detect an emission line at ~1 ?m with a signal-to-noise ratio of ~10. The lines show asymmetric profiles with high weighted skewness values, consistent with being Ly?, yielding redshifts of z = 7.213, 6.965, and 6.844. Specifically, we confirm the z = 7.213 object in two independent DEIMOS runs with different spectroscopic configurations. The z = 6.965 object is a known Ly? emitter, IOK-1, for which our improved spectrum at a higher resolution yields a robust skewness measurement. The three z-dropouts have Ly? fluxes of 3 ? 10?17?erg?s?1?cm?2 and rest-frame equivalent widths EWLy? 0 = 33-43 ?. Based on the largest spectroscopic sample of 43 z-dropouts, which is the combination of our and previous data, we find that the fraction of Ly?-emitting galaxies (EWLy? 0 > 25 ?) is low at z ~ 7; 17% ? 10% and 24% ? 12% for bright (M UV ?21) and faint (M UV ?19.5) galaxies, respectively. The fractions of Ly?-emitting galaxies drop from z ~ 6 to 7 and the amplitude of the drop is larger for faint galaxies than for bright galaxies. These two pieces of evidence would indicate that the neutral hydrogen fraction of the intergalactic medium increases from z ~ 6 to 7 and that the reionization proceeds from high- to low-density environments, as suggested by an inside-out reionization model.

A Third Update of the Status of the 3CR Sources: Further New Redshifts and New Identifications of Distant Galaxies

We present the third major update of new optical and radio data for the strong sources in the Revised Third Cambridge Catalogue (hereafter 3CR). New positions, redshifts, magnitudes, and identifications have been included as well as some radio data for the sample of 298 extragalactic 3CR sources. A new and extended bibliography of optical and radio data is included. The 3CR sources have now reached an almost satisfactory state of optical identification; 91% of the sources at b > 10° now have firm identifications and we have spectra for most of them. The few remaining faint objects at high latitudes are, of course, important, as they tend to be the most luminous radio sources known. Full completion of the 3CR data will aid in reducing the residual uncertainties at the luminous end of the evolving radio luminosity ftinction. Finally, we present some new identifications and new spectroscopic data for 29 faint 3CR galaxies, and one quasar.

The peculiar Type IA SN 1991T - Detonation of a white dwarf?

SN 1991T was a peculiar object whose premaximum optical spectrum did not resemble that of any known supernova; it appears to have been dominated by lines of iron-group elements. Near maximum brightness, however, lines of intermediate-mass elements slowly appeared, and the spectrum began to resemble that of Type Ia supernovae (SNs Ia). With time, the spectral similarity to classical SNs Ia grew progressively stronger. Two months after the explosion, the spectrum was once again dominated by iron-group elements and appeared almost identical to that of typical SNs Ia

First Results from the Large-Area Lyman Alpha Survey

We report on a new survey for z ≈ 4.5 Lyα sources, the Large-Area Lyman Alpha (LALA) survey. Our survey achieves an unprecedented combination of volume and sensitivity by using narrowband filters on the new 81922 pixel CCD Mosaic camera at the 4 m Mayall telescope of Kitt Peak National Observatory. Well-detected sources with flux and equivalent width matching previously known high-redshift Lyα galaxies (i.e., observed equivalent width EW > 80 A; 2.6 × 10-17 ergs cm-2 s-1 < line + continuum flux < 5.2 × 10-17 ergs cm-2 s-1, and a small uncertainty on the equivalent width, δEW < EW/4) have an observed surface density corresponding to 11,000 ± 700 deg-2 per unit redshift at z = 4.5. Variations in this surface density are apparent on comparison between counts in 6561 ± 40 and 6730 ± 40 A filters. Early spectroscopic followup results from the Keck telescope included three sources meeting our criteria for good Lyα candidates. Of these, one is confirmed as a z = 4.52 source, another remains consistent with either z = 4.55 or z = 0.81, and the third is an [O III] λ5007 emitter at z = 0.34. These pilot spectroscopic results suggest that approximately one-third of our good candidates are bona fide Lyα emitters, implying a net density of ~4000 Lyα emitters per square degree per unit redshift.