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Peculiar Broad Absorption Line Quasars Found in DPOSS

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Peculiar Broad Absorption Line Quasars Found in DPOSS Accepted by the Astronomical Journal Peculiar Broad Absorption Line Quasars found in DPOSS1 Robert J. Brunner1 Palomar Observatory, California Institute of Technology, Pasadena, CA 91125 [email protected] Patrick B. Hall Pontificia Universidad Cat´olica de Chile, Departamento de Astronom´ıa y Astrof´ısica, Facultad de F´ısica, Casilla 306, Santiago 22, Chile, and Princeton University Observatory, Princeton, NJ 08544-1001 S. George Djorgovski, R.R. Gal2, A.A. Mahabal, P.A.A. Lopes, R.R. de Carvalho3, S.C. Odewahn4, S. Castro5, D. Thompson Palomar Observatory, California Institute of Technology, Pasadena, CA 91125 F. Chaffee W.M. Keck Observatory, 65-1120 Mamalahoa Highway, Kamuela, HI 96743 J. Darling6, and V. Desai7 Palomar Observatory, California Institute of Technology, Pasadena, CA 91125 ABSTRACT arXiv:astro-ph/0304166v1 9 Apr 2003 With the recent release of large (i.e., & hundred million objects), well-calibrated photometric surveys, such as DPOSS, 2MASS, and SDSS, spectroscopic identification of important targets is no longer a simple issue. In order to enhance the returns from a 1Current address: Department of Astronomy, University of Illinois, Urbana, IL, 61801 2Current address: Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218 3Current address: Observatorio Nacional, CNPq, Rio de Janeiro, Brasil 4Current address: Department of Physics and Astronomy, Arizona State University, Tempe, AZ 85287 5Current address: Infrared Processing and Analysis Center, 770 S. Wilson Ave, Pasadena, CA, 91125 6Current address: Department of Astronomy, Cornell University, Ithaca, NY 14853 7Current address: Department of Astronomy, University of Washington, Seattle, WA 98195 – 2 – spectroscopic survey, candidate sources are often preferentially selected to be of interest, such as brown dwarfs or high redshift quasars. This approach, while useful for targeted projects, risks missing new or unusual species. We have, as a result, taken the alternative path of spectroscopically identifying interesting sources with the sole criterion being that they are in low density areas of the g − r and r − i color-space defined by the DPOSS survey. In this paper, we present three peculiar broad absorption line quasars that were discovered during this spectroscopic survey, demonstrating the efficacy of this approach. PSS J0052+2405 is an Iron LoBAL quasar at a redshift z = 2.4512 ± 0.0001 with very broad absorption from many species. PSS J0141+3334 is a reddened LoBAL quasar at z = 3.005±0.005 with no obvious emission lines. PSS J1537+1227 is a Iron LoBAL at a redshift of z = 1.212±0.007 with strong narrow Mg ii and Fe ii emission. Follow-up high resolution spectroscopy of these three quasars promises to improve our understanding of BAL quasars. The sensitivity of particular parameter spaces, in this case a two- color space, to the redshift of these three sources is dramatic, raising questions about traditional techniques of defining quasar populations for statistical analysis. Subject headings: quasars: absorption lines, quasars: surveys, quasars: general, quasars: emission lines 1. Introduction Quasars have been studied for forty years now (e.g., Sandage 1965), but our understanding of them is still sketchy in many ways. The currently accepted paradigm is that quasars derive their luminosity from accretion onto supermassive black holes (see, e.g., Small & Blandford 1992). However, the detailed structure of the central engine is a mystery: we do not know exactly how matter accretes onto the black hole, though an accretion disk seems likely; we do not know why some quasars have strong jets (or how they are formed); and we do not know exactly how broad absorption line (BAL) outflows fit into the overall quasar model, even though the mass loss rates in such outflows could be comparable to the overall accretion rates (e.g., Scoville & Norman 1995). BAL quasars show absorption from gas with blueshifted outflow velocities of typically 0.1c (for a good overview of BAL quasars see Weymann 1995). Most known BAL quasars are HiBALs, with absorption only from high-ionization species like C iv, but about 15% are LoBALs, which also show absorption from low-ionization species like Mg ii. The rare Iron LoBALs, or FeLoBALs, also show absorption from excited fine-structure levels or excited atomic terms of Fe ii or Fe iii. 1Some of the data presented herein were obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W.M. Keck Foundation. – 3 – Recent spectroscopic surveys for quasars, such as the two degree field survey (2DFQRS; Boyle et al. 1999) and the Sloan Digital Sky Survey (SDSS; Schneider et al. 2002), have dramatically increased the number of spectroscopically confirmed quasars. As a direct result, the number of known BALs, and in particular, LoBALs and FeLoBALs, has increased as well, enabling the iden- tification of peculiar quasars, whose BAL outflows show properties never before seen. Due to their peculiar nature, detailed studies of these quasars often provide important insight into the physical characteristics of BAL outflows, and quasar models in general. Before high-resolution spectroscopy can be employed on these systems, however, these peculiar quasars must be found. Due to their rare nature, identifying candidates of such objects requires large photometric surveys, such as the FIRST radio survey (Becker et al. 1997), the SDSS (York et al. 2000), and the Digitized Palomar Observatory Sky Survey (DPOSS; Djorgovski et al. 2001). From the catalogs that are generated from these surveys, different selection criteria have been employed to pick suitable candidates for spectroscopic follow-up. In this paper we present three peculiar BAL quasars that were discovered during a spectroscopic follow-up of color-space outliers from the DPOSS survey. We outline the observations used in § 2, analyze the spectra in § 3, discuss some implications of these objects in § 4, and summarize our conclusions in § 5. 2. Observations The quasars presented in this paper were initially targeted due to their location in the g − r and r − i color space as quantified by the Digitized Palomar Observatory Sky Survey. The DPOSS survey is detailed extensively elsewhere (Djorgovski et al. 2001, and references therein). In order to clarify the selection of these three sources, however, the rest of this section provides a brief overview of DPOSS. DPOSS is based on the POSS-II photographic survey (Reid et al. 1991), which covers the Northern sky (δ > −3◦). The POSS-II plates were obtained at the 48-inch Oschin Scmidt telescope at Palomar in three bands: blue-green, IIIa-J + GC395, red, IIIa-F + RG610, and near-IR, IV-N + RG9. The plates were obtained following a strategy based on 897 fields, where each field is approximately 6.5◦ on a side (i.e., the size of an individual plate) while the individual field centers are spaced 5◦ apart. As a result, nearly half of the total survey area is covered by more than one plate, improving the overall calibration. The photographic plates were digitized using a modified PDS scanner at STScI (Lasker et al. 1996) producing a digital image that is 23,040 pixels square, with 1′′ pixels. Each image file is approximately one Gigabyte in size, and the total survey is nearly three Terabytes. The digital image files for all scans δ > 15◦ were processed using the SKICAT software (Weir et al. 1995), producing a catalog of approximately 60 parameters for each object. Object classification was performed using a subset of these parameters as described in Odewahn et al. (2003). – 4 – The photographic catalog data was calibrated using CCD calibration data in the g, r, and i filters (Gal et al. 2003). A second correction was applied to the catalog to correct for plate vignetting (Mahabal et al. 2003). Finally, extinction corrections were applied using the Schlegel, Finkbeiner, & Davis (1998) prescription. The typical limiting magnitudes for the calibrated catalog data are m m m gJ ∼ 20.5 , rF ∼ 20.7 , and iN ∼ 20.3 . The three sources presented in this paper are shown in Figure 1, along with random stellar sources with similar magnitudes to the quasars presented herein. In addition, the coordinates, magnitudes and measured redshifts for these sources are provided in Table 1. 2.1. Optical Spectroscopy Discovery spectra of all three objects were obtained at the Palomar Observatory 200-inch Hale telescope, using the Double Spectrograph (DBSP) instrument (Oke & Gunn 1982). All observations used a 2′′ wide, long slit, and in all cases the slit PA was close to the parallactic. Exposures of standard stars from Oke & Gunn (1983) were used to remove the instrument response function and provide at least a rough flux calibration, and exposures of arc lamps were used to derive the wavelength solutions. All data were processed using standard techniques. Observations of PSS J0052+2405 were made on 02 and 04 September 1997 UT, in non- photometric conditions. A set of exposures with integration times of 200, 400, and 1200 s were obtained. We used a 300 l/mm grating on the blue side of the DBSP, giving a dispersion of 2.17 A/pixel˚ and a FWHM resolution of 11 A,˚ covering the wavelength range from ∼ 3360 A˚ to 6860 A.˚ On the red side we used a 316 l/mm grating giving a dispersion of 3.06 A/pixel˚ and a resolution of 11 A,˚ covering the wavelength range ∼ 6760 A˚ to 9290 A.˚ A dichroic with a split wavelength near 6800 A˚ was used. Observations of PSS J0141+3334 were obtained on 10 November 1999 UT, in good conditions; exposure times were 120 and 800 s. We used gratings with 600 l/mm (blue) and 158 l/mm (red), covering the wavelength ranges ∼ 3400 to 5200 A˚ (blue), and ∼ 5120 to 10100 A˚ (red), and a 5200 A˚ dichroic.
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