Publications (8)24.1 Total impact
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Article: The Great Observatories Origins Deep Survey: Initial Results from Optical and Near-Infrared Imaging
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ABSTRACT: 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 Astrophysical Journal 12/2008; 600(2):L93. · 6.02 Impact Factor -
Article: The Evolution of Disk Galaxies in the GOODS-South Field: Number Densities and Size Distribution
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ABSTRACT: 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 z ~ 1.25. In order to minimize the effect of selection biases, we confine our 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 0.25 ≤ z ≤ 1.25. We 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 σ uncertainties.The Astrophysical Journal 12/2008; 604(1):L9. · 6.02 Impact Factor -
Chapter: Probing the High Redshift Universe with Extreme X-Ray/Optical Sources (EXOs)
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ABSTRACT: Extreme X-ray/Optical ratio sources (EXOs) are a class of source that are robustly detected in our Chandra Deep Field X-ray data, while being completely undetected in our deep multi-band GOODS HST/ACS data, including the long-wavelength z-band data, yet are detected in the deep GOODS near-IR VLT imaging. These sources have values of Fx/Fopt that are factors of 10–100 times higher than those generally found for other AGN. We thus infer two plausible scenarios: (1) if these sources lie at moderately high redshifts (z ~ 3 – 5) then their hosts need to be exceedingly underluminous and/or excessively reddened compared with other AGN hosts; (2) if they lie above z ~ 6 – 7, such that their Lyman-alpha emission is redshifted out of the z-band filter, then their K-band and X-ray properties can be accounted for in terms of relatively normal hosts and moderate-luminosity AGN. In this case, these objects can serve as an invaluable probe of black hole growth and accretion activity in the early universe.01/2006: pages 88-93; -
Article: AGN Host Galaxies at z~0.4-1.3 : Bulge-dominated and Lacking Merger-AGN Connection
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ABSTRACT: We investigate morphological structure parameters and local environments of distant moderate-luminosity active galactic nucleus (AGN) host galaxies in the overlap between the HST/ACS observations of the Great Observatories Origins Deep Survey (GOODS) and the two Chandra Deep Fields. We compute near-neighbor counts and BViz asymmetry (A) and concentration (C) indices for ~35,500 GOODS/ACS galaxies complete to z_850 ~ 26.6, including the resolved hosts of 322 X-ray-selected AGNs. Distributions of (1) z_850 asymmetry for 130 AGN hosts at z_850 < 23 and (2) near-neighbor counts for 173 AGN hosts at z_850 < 24 are both consistent with non-AGN control samples. This implies no close connection between recent galaxy mergers and moderate-luminosity AGN activity out to appreciable look-back times (z < 1.3), approaching the epoch of peak AGN activity in the universe. The distribution of z_850 concentrations for the AGN hosts is offset by +0.5 compared to the non-AGN, a 6.4-sigma discrepancy much larger than can be explained by the possible influence of unresolved emission from the AGN or a circumnuclear starburst. The local universe association between AGN and bulge-dominated galaxies thus persists to substantial look-back time. We discuss implications in the context of the low-redshift supermassive central black hole mass correlation with host galaxy properties, including concentration. Comment: Astrophysical Journal Letters, in press. Figure 1 available at full resolution upon requestThe Astrophysical Journal 07/2005; · 6.02 Impact Factor -
Article: Obscured Active Galactic Nuclei and the X-Ray, Optical, and Far-Infrared Number Counts of Active Galactic Nuclei in the GOODS Fields
apj. 11/2004; 616:123-135. -
Article: Obscured AGN and the X-ray, Optical and Far-Infrared Number Counts of AGN in the GOODS Fields
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ABSTRACT: The deep X-ray, optical, and far-infrared fields that constitute GOODS are sensitive to obscured AGN (N_H>10^{22} cm^{-2}) at the quasar epoch (z~2-3), as well as to unobscured AGN as distant as z~7. Luminous X-ray emission is a sign of accretion onto a supermassive black hole and thus reveals all but the most heavily obscured AGN. We combine X-ray luminosity functions with appropriate spectral energy distributions for AGN to model the X-ray, optical and far-infrared flux distributions of the X-ray sources in the GOODS fields. A simple model based on the unified paradigm for AGN, with ~3 times as many obscured AGN as unobscured, successfully reproduces the z-band flux distributions measured in the deep HST ACS observations on the GOODS North and South fields. This model is also consistent with the observed spectroscopic and photometric redshift distributions once selection effects are considered. The previously reported discrepancy between observed spectroscopic redshift distributions and the predictions of population synthesis models for the X-ray background can be explained by bias against the most heavily obscured AGN generated both by X-ray observations and the identification of sources via optical spectroscopy. We predict the AGN number counts for Spitzer MIPS 24 um and IRAC 3.6-8 um observations in the GOODS fields, which will verify whether most AGN in the early Universe are obscured in the optical. Such AGN should be very bright far-infrared sources and include some obscured AGN missed even by X-ray observations. Comment: Accepted by ApJ; 39 pages, 13 figures08/2004; -
Article: A Possible New Population of Sources with Extreme X-Ray / Optical Ratios
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ABSTRACT: We describe a possible new class of X-ray sources that have robust detections in ultra-deep Chandra data, yet have no detections at all in our deep multi-band GOODS Hubble Space Telescope (HST) ACS images, which represent the highest quality optical imaging obtained to date on these fields. These extreme X-ray / Optical ratio sources ("EXO"s) have values of Fx/Fopt at least an order of magnitude above those generally found for other AGN, even those that are harbored by reddened hosts. We thus infer two possible scenarios: (1) if these sources lie at redshifts z < 6, then their hosts need to be exceedingly underluminous, or more reddened, compared with other known sources; (2) if these sources lie above z ~ 6-7, such that even their Lyman-alpha emission is redshifted out of the bandpass of our ACS z(850) filter, then their optical and X-ray fluxes can be accounted for in terms of relatively normal L* hosts and moderate-luminosity AGN. Comment: AASTEX-Latex, 12 pages, 3 figures, including 1 jpg figure. Accepted by the Astrophysical Journal LettersThe Astrophysical Journal 06/2003; · 6.02 Impact Factor -
Article: Evolution of Structural Parameters of Galaxies in the GOODS-South field
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ABSTRACT: The structural parameters of galaxies reflect the effects of physical processes related to their formation and evolution. The high spatial resolution (0.1 " ) HST ACS images obtained in the B, V, i, and z bands by the Great Observatories Origins Deep Survey (GOODS) over a large survey area (320 sq. arcmin), provides a unique opportunity to quantify the morphological evolution of galaxies out to redshifts z = 1. We present the preliminary results from an analysis based on two-dimensional modeling of the surface brightness distributions of galaxies in the GOODS-South field. The decomposition of multiple galaxy components (such as the bulge, inner and outer disks, bars, and central compact sources) is performed using multiple Sérsic profiles. The observed scale lengths, bulge magnitudes, bulge-to-disk ratios, Sérsic indices, and the correlations among these structural parameters are used to examine the evolution of the bulge and disk properties of the galaxies with redshift.11/2002; 201:611.
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Institutions
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2003–2008
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Yale University
- Department of Astronomy
New Haven, CT, USA
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