Browsing by Author "Schneider, DP"

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    A catalog of broad absorption line quasars from the Sloan Digital Sky Survey Early Data Release
    (2003) Reichard, TA; Richards, GT; Schneider, DP; Hall, PB; Tolea, A; Krolik, JH; Tsvetanov, Z; Vanden Berk, DE; York, DG; Knapp, GR; Gunn, JE; Brinkmann, J
    We present a catalog of 224 broad absorption line quasars (BALQSOs) from the Sloan Digital Sky Survey's Early Data Release Quasar Catalog, including a relatively complete and homogeneous subsample of 131 BALQSOs. Since the identification of BALQSOs is subject to considerable systematic uncertainties, we attempt to create a complete sample of SDSS BALQSOs by combining the results of two automated selection algorithms and a by-eye classification scheme. One of these automated algorithms finds broad absorption line troughs by comparing with a composite quasar spectrum. We present the details of this algorithm and compare this method with one that uses a power-law fit to the continuum. The BALQSOs in our sample are further classified as high-ionization BALQSOs (HiBALs), low-ionization BALQSOs (LoBALs), and BALQSOs with excited iron absorption features (FeLoBALs); composite spectra of each type are presented. We further present a study of the properties of the BALQSOs in terms of the balnicity distribution, which rises with decreasing balnicity. This distribution of balnicities suggests that the fraction of quasars with intrinsic outflows may be significantly underestimated.
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    A large, uniform sample of X-ray-emitting AGNs
    (2003) Anderson, SF; Voges, W; Margon, B; Trümper, J; Agüeros, MA; Boller, T; Collinge, MJ; Homer, L; Stinson, G; Strauss, MA; Annis, J; Gómez, P; Hall, PB; Nichol, RC; Richards, GT; Schneider, DP; Vanden Berk, DE; Fan, XH; Ivezic, Z; Munn, JA; Newberg, HJ; Richmond, MW; Weinberg, DH; Yanny, B; Bahcall, NA; Brinkmann, J; Fukugita, M; York, DG
    Many open questions in X-ray astronomy are limited by the relatively small number of objects in uniform optically identified and observed samples, especially when rare subclasses are considered or when subsets are isolated to search for evolution or correlations between wavebands. We describe the initial results of a new program aimed to ultimately yield similar to10(4) fully characterized X-ray source identifications-a sample about an order of magnitude larger than earlier efforts. The technique is detailed and employs X-ray data from the ROSAT All-Sky Survey (RASS) and optical imaging and spectroscopic follow-up from the Sloan Digital Sky Survey (SDSS); these two surveys prove to be serendipitously very well matched in sensitivity. As part of the SDSS software pipelines, optical objects in the SDSS photometric catalogs are automatically positionally cross-correlated with RASS X-ray sources. Then priorities for follow-on SDSS optical spectra of candidate counterparts are automatically assigned using an algorithm based on the known ratios of f(x)/f(opt) for various classes of X-ray emitters at typical RASS fluxes of similar to10(-13) ergs cm(-2) s(-1). SDSS photometric parameters for optical morphology, magnitude, and colors, plus FIRST radio information, serve as proxies for object class. Initial application of this approach to RASS/SDSS data from 1400 deg(2) of sky provides a catalog of more than 1200 spectroscopically confirmed quasars and other AGNs that are probable RASS identifications. Most of these are new identifications, and only a few percent of the AGN counterparts are likely to be random superpositions. The magnitude and redshift ranges of the counterparts are very broad, extending over 15
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    A Lyα-only active galactic nucleus from the Sloan Digital Sky Survey
    (2004) Hall, PB; Hoversten, EA; Tremonti, CA; Vanden Berk, DE; Schneider, DP; Strauss, MA; Knapp, GR; York, DG; Hutsemékers, D; Newman, PR; Brinkmann, J; Frye, B; Fukugita, M; Glazebrook, K; Harvanek, M; Heckman, TM; Ivezic, Z; Kleinman, S; Krzesinski, J; Long, DC; Neilsen, E; Niederste-Ostholt, M; Nitta, A; Schlegel, DJ; Snedden, S
    The Sloan Digital Sky Survey has discovered a z = 2.4917 radio-loud active galactic nucleus (AGN) with a luminous, variable, low-polarization UV continuum, H I two-photon emission, and a moderately broad Lyalpha line (FWHM similar or equal to 1430 km s(-1)) but without obvious metal-line emission. SDSS J113658.36+024220.1 does have associated metal-line absorption in three distinct, narrow systems spanning a velocity range of 2710 km s(-1). Despite certain spectral similarities, SDSS J1136+0242 is not a Lyman break galaxy. Instead, the Lyalpha and two-photon emission can be attributed to an extended, low-metallicity narrow-line region. The unpolarized continuum argues that we see SDSS J1136+0242 very close to the axis of any ionization cone present. We can conceive of two plausible explanations for why we see a strong UV continuum but no broad-line emission in this "face-on radio galaxy'' model for SDSS J1136+0242: the continuum could be relativistically beamed synchrotron emission that swamps the broad-line emission, or more likely, SDSS J1136+0242 could be similar to PG 1407+265, a quasar in which for some unknown reason the high-ionization emission lines are very broad, very weak, and highly blueshifted.
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    A quasar without broad Lyα emission
    (2004) Hall, PB; Snedden, SA; Niederste-Ostholt, N; Eisenstein, DJ; Strauss, MA; York, DG; Schneider, DP
    The z = 3.02 quasar SDSS J095253.83+011421.9 exhibits broad metal-line emission ( C IV FWHM similar or equal to 9000 km s(-1)), but broad Lyalpha emission is not present. Instead, only a narrow Lyalpha line is observed ( FWHM similar or equal to 1140 km s(-1)). The large C IV/Lyalpha ratio in the broad-line region (BLR) emission from this object can be matched most closely by a BLR dominated by gas at very high densities (10(15) cm(-3)), which suppresses the Lyalpha emission, and illuminated by an incident power law extending to similar to200 mum, which yields increased emission from purely collisionally excited coolant lines (such as C IV, N v, and O VI) but not from recombination lines like Lyalpha. However, the strong C III emission predicted by this model is not observed, and the observed broad C III] emission must come from a lower density BLR component and should be accompanied by broad Lyalpha emission, which is not observed. The least unlikely explanation for this spectrum seems to be that any intrinsic broad Lyalpha emission is removed by smooth N v absorption in the red wing of the Lyalpha emission line and by smooth Lyalpha absorption in the blue wing of the Lyalpha emission line. This postulated smooth absorption would be in addition to the strong, associated, narrow absorption seen in numerous ions. Smooth absorption in Lyalpha, N v, and O vi, but not in C IV, would be unusual, but not impossible, although it is suspicious that the postulated absorption must almost exactly cancel the postulated intrinsic broad emission. We conclude that the spectrum of SDSS J0952+0114 appears unique ( among similar or equal to 3600 SDSS spectra of quasars at z > 2.12) because of some combination of unusual parameters, and we discuss possible observations to determine the combination of circumstances responsible for the spectrum.
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    An initial survey of white dwarfs in the Sloan Digital Sky Survey
    (2003) Harris, HC; Liebert, J; Kleinman, SJ; Nitta, A; Anderson, SF; Knapp, GR; Krzesinski, J; Schmidt, G; Strauss, MA; Berk, DV; Eisenstein, D; Hawley, S; Margon, B; Munn, JA; Silvestri, NM; Smith, JA; Szkody, P; Collinge, MJ; Dahn, CC; Fan, XH; Hall, PB; Schneider, DP; Brinkmann, J; Burles, S; Gunn, JE; Hennessy, GS; Hindsley, R; Ivezic, Z; Kent, S; Lamb, DQ; Lupton, RH; Nichol, RC; Pier, JR; Schlegel, DJ; SubbaRao, M; Uomoto, A; Yanny, B; York, DG
    An initial assessment is made of white dwarf and hot subdwarf stars observed in the Sloan Digital Sky Survey. In a small area of sky ( 190 square degrees), observed much like the full survey will be, 269 white dwarfs (WDs) and 56 hot subdwarfs are identified spectroscopically where only 44 white dwarfs and five hot subdwarfs were known previously. Most are ordinary DA ( hydrogen atmosphere) and DB ( helium) types. In addition, in the full survey to date, a number of WDs have been found with uncommon spectral types. Among these are blue DQ stars displaying lines of atomic carbon; red DQ stars showing molecular bands of C-2 with a wide variety of strengths; DZ stars where Ca and occasionally Mg, Na, and/or Fe lines are detected; and magnetic WDs with a wide range of magnetic field strengths in DA, DB, DQ, and ( probably) DZ spectral types. Photometry alone allows identification of stars hotter than 12,000 K, and the density of these stars for 15 < g < 20 is found to be similar to2.2 deg(-2) at Galactic latitudes of 29degrees - 62degrees. Spectra are obtained for roughly half of these hot stars. The spectra show that for 15 < g < 17, 40% of hot stars are WDs, and the fraction of WDs rises to similar to90% at g = 20. The remainder are hot sdB and sdO stars.
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    Broad absorption line quasars in the Sloan Digital Sky Survey with VLA first radio detections
    (2001) Menou, K; Vanden Berg, DE; Kim, RSJ; Knapp, GR; Richards, GT; Strateva, I; Fan, XH; Gunn, JE; Hall, PB; Heckman, T; Krolik, J; Lupton, RH; Schneider, DP; York, DG; Anderson, SF; Bahcall, NA; Brinkmann, J; Brunner, R; Csabai, I; Fukugita, M; Hennessy, GS; Kunszt, PZ; Lamb, DQ; Munn, JA; Nichol, RC; Szokoly, GP
    We present 13 broad absorption line (BAL) quasars, including 12 new objects, identified in the Sloan Digital Sky Survey (SDSS) and matched within 2 " to sources in the FIRST radio survey catalog. The surface density of this sample of radio-detected BAL quasars is 4.5 +/- 1.2 per 100 deg(2), i.e., approximately 4 times as high as previously found by the shallower FIRST Bright Quasar Survey (FBQS). A majority of these radio-detected BAL quasars are moderately radio-loud objects. The fraction of BAL quasars in the entire radio quasar sample, 4.8% +/- 1.3%, is comparable to the fraction of BAL quasars among the SDSS optical quasar sample (ignoring selection effects). We estimate that the true fraction of BAL quasars (mostly "HiBALs") in the radio sample is 9.2% +/- 2.6%, once selection effects are accounted for. We caution that the absorption troughs of four of the 13 radio-detected quasars considered do not strictly satisfy the standard BALnicity criteria. One or possibly two of the new radio-detected BAL quasars are of the rare "FeLoBAL" type. BAL quasars are generally redder than the median SDSS quasar at the same redshift.
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    Broad emission-line shifts in quasars: An orientation measure for radio-quiet quasars?
    (2002) Richards, GT; Berk, DEV; Reichard, TA; Hall, PB; Schneider, DP; SubbaRao, M; Thakar, AR; York, DG
    Using a sample of 3814 quasars from the Early Data Release of the Sloan Digital Sky Survey, we confirm that high-ionization, broad emission lines, such as C IV are significantly blueshifted with respect to low-ionization, broad emission lines, such as Mg II which are thought to be close to the systemic redshift. We examine the velocity shifts of the Mg II and C iv emission lines with respect to [O III and Mg II respectively. C iv emission-line peaks have a range of shifts from a redshift of 500 km s(-1) to blueshifts well in excess of 2000 km s(-1) as compared with Mg II We confirm previous results that suggest an anticorrelation between the shift of the C iv emission-line peak and the rest equivalent width of the C iv emission line. Furthermore, by creating composite quasar spectra as a function of C iv shift, we are able to study in detail the profiles of the line as a function of velocity shift. We find that the apparent shift of the C iv emission-line peak is not a shift so much as it is a lack of flux in the red wing for the composite with the largest apparent shift. This observation should strongly constrain models for the broad emission-line region in quasars. The emission-line blueshift and equivalent width of C iv are also discussed in light of the well-known anticorrelation between the equivalent width of C iv emission and continuum luminosity, otherwise known as the Baldwin effect. We further discuss the C iv emission-line shift as a function of other quasar properties, such as spectral index, radio and X-ray detection. We find a possible correlation between the C iv emission-line shifts and the radio properties of the quasars, which is suggestive of orientation as the cause of the C iv velocity shifts. Finally, we explore whether the C iv emission-line blueshifts correlate with the presence of broad absorption line absorption troughs or with narrow, associated absorption, and how these might be related to orientation.
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    Composite quasar spectra from the Sloan Digital Sky Survey
    (2001) Vanden Berk, DE; Richards, GT; Bauer, A; Strauss, MA; Schneider, DP; Heckman, TM; York, DG; Hall, PB; Fan, XH; Knapp, GR; Anderson, SF; Annis, J; Bahcall, NA; Bernardi, M; Briggs, JW; Brinkmann, J; Brunner, R; Burles, S; Carey, L; Castander, FJ; Connolly, AJ; Crocker, JH; Csabai, I; Doi, M; Finkbeiner, D; Friedman, S; Frieman, JA; Fukugita, M; Gunn, JE; Hennessy, GS; Ivezic, Z; Kent, S; Kunszt, PZ; Lamb, DQ; Leger, RF; Long, DC; Loveday, J; Lupton, RH; Meiksin, A; Pier, JR; Pope, A; Rockosi, CM; Schlegel, DJ; Siegmund, WA; Smee, S; Snir, Y; Stoughton, C; Stubbs, C; SubbaRao, M; Szalay, AS; Szokoly, GP; Tremonti, C; Uomoto, A; Waddell, P; Yanny, B; Zheng, W
    We have created a variety of composite quasar spectra using a homogeneous data set of over 2200 spectra from the Sloan Digital Sky Survey (SDSS). The quasar sample spans a redshift range of 0.044 less than or equal to z less than or equal to 4.789 and an absolute r' magnitude range of -18.0 to -26.5. The input spectra cover an observed wavelength range of 3800-9200 Angstrom at a resolution of 1800. The median composite covers a rest-wavelength range from 800 to 8555 Angstrom and reaches a peak signal-to-noise ratio of over 300 per 1 Angstrom resolution element in the rest frame. We have identified over 80 emission-line features in the spectrum. Emission-line shifts relative to nominal laboratory wavelengths are seen for many of the ionic species. Peak shifts of the broad permitted and semiforbidden lines are strongly correlated with ionization energy, as previously suggested, but we find that the narrow forbidden lines are also shifted by amounts that are strongly correlated with ionization energy. The magnitude of the forbidden line shifts is less than or similar to 100 km s(-1), compared with shifts of up to 550 km s(-1) for some of the permitted and semiforbidden lines. At wavelengths longer than the Ly alpha emission, the continuum of the geometric mean composite is well fitted by two power laws, with a break at approximate to 5000 Angstrom. The frequency power-law index, alpha (v), is -0.44 from approximate to 1300 to 5000 and -2.45 redward of approximate to 5000 The abrupt change in slope can be accounted for partly by host-galaxy contamination at low redshift. Stellar absorption lines, including higher order Balmer lines, seen in the composites suggest that young or intermediate-age stars make a significant contribution to the light of the host galaxies. Most of the spectrum is populated by blended emission lines, especially in the range 1500-3500 Angstrom, which can make the estimation of quasar continua highly uncertain unless large ranges in wavelength are observed. An electronic table of the median quasar template is available.
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    Continuum and emission-line properties of broad absorption line quasars
    (2003) Reichard, TA; Richards, GT; Hall, PB; Schneider, DP; Vanden Berk, DE; Fan, XH; York, DG; Knapp, GR; Brinkmann, J
    We investigate the continuum and emission-line properties of 224 broad absorption line quasars (BALQSOs) with 0.9less than or similar tozless than or similar to4.4 drawn from the Sloan Digital Sky Survey Early Data Release, which contains 3814 bona. de quasars. We find that low-ionization BALQSOs (LoBALs) are significantly reddened as compared with normal quasars, in agreement with previous work. High-ionization BALQSOs (HiBALs) are also more reddened than the average non-BALQSO. Assuming SMC-like dust reddening at the quasar redshift, the amount of reddening needed to explain HiBALs is E(B-V)similar to0.023 and LoBALs is E( B-V)similar to0.077 (compared with the ensemble average of the entire quasar sample). We find that there are differences in the emission-line properties between the average HiBAL, LoBAL, and non-BAL quasar. These differences, along with differences in the absorption-line troughs, may be related to intrinsic quasar properties such as the slope of the intrinsic (unreddened) continuum; more extreme absorption properties are correlated with bluer intrinsic continua. Despite the differences among BALQSO subtypes and non-BALQSOs, BALQSOs appear to be drawn from the same parent population as non-BALQSOs when both are selected by their UV/optical properties. We find that the overall fraction of traditionally defined BALQSOs, after correcting for color-dependent selection effects due to different SEDs of BALQSOs and non-BALQSOs, is 13.4%+/-1.2% and shows no significant redshift dependence for 1.7less than or equal tozless than or equal to3.45. After a rough completeness correction for the effects of dust extinction, we find that approximately one in every six quasars is a BALQSO.
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    Double-peaked low-ionization emission lines in active galactic nuclei
    (2003) Strateva, IV; Strauss, MA; Hao, L; Schlegel, DJ; Hall, PB; Gunn, JE; Li, LX; Ivezic, Z; Richards, GT; Zakamska, NL; Voges, W; Anderson, SF; Lupton, RH; Schneider, DP; Brinkmann, J; Nichol, RC
    We present a new sample of 116 double-peaked Balmer line active galactic nuclei (AGNs) selected from the Sloan Digital Sky Survey. Double-peaked emission lines are believed to originate in the accretion disks of AGNs, a few hundred gravitational radii (R-G) from the supermassive black hole. We investigate the properties of the candidate disk emitters with respect to the full sample of AGNs over the same redshifts, focusing on optical, radio, and X-ray flux, broad-line shapes and narrow-line equivalent widths, and line flux ratios. We find that the disk emitters have medium luminosities (similar to10(44) ergs s(-1)) and FWHM on average 6 times broader than the AGNs in the parent sample. The double-peaked AGNs are 1.6 times more likely to be radio sources and are predominantly (76%) radio-quiet, with about 12% of the objects classified as LINERs. Statistical comparison of the observed double-peaked line profiles with those produced by axisymmetric and nonaxisymmetric accretion disk models allows us to impose constraints on accretion disk parameters. The observed Halpha line profiles are consistent with accretion disks with inclinations smaller than 50degrees, surface emissivity slopes of 1.0-2.5, outer radii larger than similar to2000R(G), inner radii of (200-800) R-G, and local turbulent broadening of 780-1800 km s(-1). The comparison suggests that 60% of accretion disks require some form of asymmetry ( e. g., elliptical disks, warps, spiral shocks, or hot spots).
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    Faint high-latitude carbon stars discovered by the Sloan Digital Sky Survey: Methods and initial results
    (2002) Margon, B; Anderson, SF; Harris, HC; Strauss, MA; Knapp, GR; Fan, XH; Schneider, DP; Berk, DEV; Schlegel, DJ; Deutsch, EW; Ivezic, Z; Hall, PB; Williams, BF; Davidsen, AF; Brinkmann, J; Csabai, I; Hayes, JJE; Hennessy, G; Kinney, EK; Kleinman, SJ; Lamb, DQ; Long, D; Neilsen, EH; Nichol, R; Nitta, A; Snedden, SA; York, DG
    We report the discovery of 39 faint high-latitude carbon stars (FHLCs) from Sloan Digital Sky Survey (SDSS) commissioning data. The objects, each selected photometrically and verified spectroscopically, range over 16.6 < r* < 20.0 and show a diversity of temperatures as judged by both colors and NaD line strengths. Although a handful of these stars were previously known, these objects are, in general, too faint and too warm to be effectively identified in other modern surveys such as the Two Micron All Sky Survey, nor are their red/near-IR colors particularly distinctive. The implied surface density of FHLCs in this magnitude range is uncertain at this preliminary stage of the survey because of completeness corrections but is clearly greater than 0.05 deg(-2). At the completion of the Sloan survey, there will be many hundred homogeneously selected and observed FHLCs in this sample. We present proper-motion measures for each object, indicating that the sample is a mixture of extremely distant (greater than 100 kpc) halo giant stars, useful for constraining halo dynamics, and members of the recently recognized exotic class of very nearby dwarf carbon (dC) stars. The broadband colors of the two populations are indistinguishable. Motions, and thus dC classification, are inferred for 40%-50% of the sample, depending on the level of statistical significance invoked. The new list of dC stars presented here, although selected from only a small fraction of the final SDSS, doubles the number of such objects found by all previous methods. The observed kinematics suggest that the dwarfs occupy distinct halo and disk populations. The coolest FHLCs with detectable proper motions in our sample also display multiple CaH bands in their spectra. It may be that CaH is another long-sought, low-resolution, spectroscopic luminosity discriminant between dC's and distant faint giants, at least for the cooler stars.
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    Magnetic white dwarfs from the Sloan Digital Sky Survey: The first data release
    (2003) Schmidt, GD; Harris, HC; Liebert, J; Eisenstein, DJ; Anderson, SF; Brinkmann, J; Hall, PB; Harvanek, M; Hawley, S; Kleinman, SJ; Knapp, GR; Krzesinski, J; Lamb, DQ; Long, D; Munn, JA; Neilsen, EH; Newman, PR; Nitta, A; Schlegel, DJ; Schneider, DP; Silvestri, NM; Smith, JA; Snedden, SA; Szkody, P; Berk, DV
    Beyond its goals related to the extragalactic universe, the Sloan Digital Sky Survey (SDSS) is an effective tool for identifying stellar objects with unusual spectral energy distributions. Here we report on the 53 new magnetic white dwarfs discovered during the first two years of the survey, including 38 whose data are made public in the 1500 deg(2) First Data Release. Discoveries span the magnitude range 16.3 less than or equal to g less than or equal to 20.5, and based on the recovery rate for previously known magnetic white dwarfs, the completeness of the SDSS appears to be high for reasonably hot stars with B greater than or similar to 3 MG and g greater than or similar to 15. The new objects nearly double the total number of known magnetic white dwarfs and include examples with polar field strengths B-p > 500 MG, as well as several with exotic atmospheric compositions. The improved sample statistics and uniformity indicate that the distribution of magnetic white dwarfs has a broad peak in the range similar to5-30 MG and a tail extending to nearly 10(9) G. Degenerates with polar fields B-p greater than or similar to 50 MG are consistent with being descendents of magnetic Ap/Bp main-sequence stars, but low- and moderate-field magnetic white dwarfs appear to imply another origin. Yet-undetected magnetic F-type stars with convective envelopes that destroy the ordered underlying field are attractive candidates.
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    Optical and radio properties of extragalactic sources observed by the first survey and the Sloan Digital Sky Survey
    (2002) Ivezic, Z; Menou, K; Knapp, GR; Strauss, MA; Lupton, RH; Vanden Berk, DE; Richards, GT; Tremonti, C; Weinstein, MA; Anderson, S; Bahcall, NA; Becker, RH; Bernardi, M; Blanton, M; Eisenstein, D; Fan, XH; Finkbeiner, D; Finlator, K; Frieman, J; Gunn, JE; Hall, PB; Kim, RSJ; Kinkhabwala, A; Narayanan, VK; Rockosi, CM; Schlegel, D; Schneider, DP; Strateva, I; SubbaRao, M; Thakar, AR; Voges, W; White, RL; Yanny, B; Brinkmann, J; Doi, M; Fukugita, M; Hennessy, GS; Munn, JA; Nichol, RC; York, DG
    We discuss the optical and radio properties of similar to30,000 FIRST (radio, 20 cm, sensitive to 1 mJy) sources positionally associated within 1."5 with a Sloan Digital Sky Survey (SDSS) (optical, sensitive to r*similar to22.2) source in 1230 deg(2) of sky. The matched sample represents similar to30% of the 108,000 FIRST sources and 0.1% of the 2.5x10(7) SDSS sources in the studied region. SDSS spectra are available for 4300 galaxies and 1154 quasars from the matched sample and for a control sample of 140,000 galaxies and 20, 000 quasars in 1030 deg(2) of sky. Here we analyze only core sources, which dominate the sample; the fraction of SDSS-FIRST sources with complex radio morphology is determined to be less than 10%. This large and unbiased catalog of optical identifications provides much firmer statistical footing for existing results and allows several new findings. The majority (83%) of the FIRST sources identified with an SDSS source brighter than r*=21 are optically resolved; the fraction of resolved objects among the matched sources is a function of the radio flux, increasing from similar to50% at the bright end to similar to90% at the FIRST faint limit. Nearly all optically unresolved radio sources have nonstellar colors indicative of quasars. We estimate an upper limit of similar to5% for the fraction of quasars with broadband optical colors indistinguishable from those of stars. The distribution of quasars in the radio flux optical flux plane suggests the existence of the "quasar radio dichotomy" 8%+/-1% of all quasars with i*<18.5 are radio-loud, and this fraction seems independent of redshift and optical luminosity. The radio-loud quasars have a redder median color by 0.08±0.02 mag, and show a 3 times larger fraction of objects with extremely red colors. FIRST galaxies represent 5% of all SDSS galaxies with r*<17.5, and 1% for r*<20, and are dominated by red (u*-r*>2.22) galaxies, especially those with r*>17.5. Magnitude- and redshift-limited samples show that radio galaxies have a different optical luminosity distribution than nonradio galaxies selected by the same criteria; when galaxies are further separated by their colors, this result remains valid for both blue and red galaxies. For a given optical luminosity and redshift, the observed optical colors of radio galaxies are indistinguishable from those of all SDSS galaxies selected by identical criteria. The distributions of radio-to-optical flux ratio are similar for blue and red galaxies in redshift-limited samples; this similarity implies that the difference in their luminosity functions and resulting selection effects are the dominant cause for the preponderance of red radio galaxies in flux-limited samples. The fraction of radio galaxies whose emission-line ratios indicate an AGN(30%), rather than starburst, origin is 6 times larger than the corresponding fraction for all SDSS galaxies (r*<17.5). We confirm that the AGN-to-starburst galaxy number ratio increases with radio flux and find that radio emission from AGNs is more concentrated than radio emission from starburst galaxies.
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    Photometric redshifts from reconstructed quasar templates
    (2001) Budavári, T; Csabai, I; Szalay, AS; Connolly, AJ; Szokoly, GP; Vanden Berk, DE; Richards, GT; Weinstein, MA; Schneider, DP; Benítez, N; Brinkman, J; Brunner, R; Hall, PB; Hennessy, GS; Ivezic, Z; Kunszt, PZ; Munn, JA; Nichol, RC; Pier, JR; York, DG
    From Sloan Digital Sky Survey (SDSS) commissioning photometric and spectroscopic data, we investigate the utility of photometric redshift techniques in the task of estimating QSO redshifts. We consider empirical methods (e.g., nearest neighbor searches and polynomial fitting), standard spectral template fitting, and hybrid approaches (i.e., training spectral templates from spectroscopic and photometric observations of QSOs). We find that in all cases, because of the presence of strong emission lines within the QSO spectra, the nearest neighbor and template-fitting methods are superior to the polynomial-fitting approach. Applying a novel reconstruction technique, we can, from the SDSS multicolor photometry, reconstruct a statistical representation of the underlying SEDs of the SDSS QSOs. Although the reconstructed templates are based on only broadband photometry, the common emission lines present within the QSO spectra can be recovered in the resulting spectral energy distributions. The technique should be useful in searching for spectral differences among QSOs at a given redshift, in searching for spectral evolution of QSOs, in comparing photometric redshifts for objects beyond the SDSS spectroscopic sample with those in the well-calibrated photometric redshifts for objects brighter than 20th magnitude, and in searching for systematic and time-variable effects in the SDSS broadband photometric and spectral photometric calibrations.
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    Photometric redshifts of quasars
    (2001) Richards, GT; Weinstein, MA; Schneider, DP; Fan, XH; Strauss, MA; Vanden Berk, DE; Annis, J; Burles, S; Laubacher, EM; York, DG; Frieman, JA; Johnston, D; Scranton, R; Gunn, JE; Nichol, RC; Ivezic, Z; Nichol, RC; Budavári, T; Csabai, I; Szalay, AS; Connolly, AJ; Szokoly, GP; Bahcall, NA; Benítez, N; Brinkmann, J; Brunner, R; Fukugita, M; Hall, PB; Hennessy, GS; Knapp, GR; Kunszt, PZ; Lamb, DQ; Munn, JA; Newberg, HJ; Stoughton, C
    We demonstrate that the design of the Sloan Digital Sky Survey (SDSS) filter system and the quality of the SDSS imaging data are sufficient for determining accurate and precise photometric redshifts of quasars. Using a sample of 2625 quasars, we show that "photo-z" determination is even possible for z less than or equal to2.2 despite the lack of a strong continuum break, which robust photo-z techniques normally require. We find that, using our empirical method on our sample of objects known to be quasars, approximately 70% of the photometric redshifts are correct to within Deltaz = 0.2; the fraction of correct photometric redshifts is even better for z >3. The accuracy of quasar photometric redshifts does not appear to be dependent upon magnitude to nearly 21st magnitude in i'. Careful calibration of the color-redshift relation to 21st magnitude may allow for the discovery of similar to 10(6) quasar candidates in addition to the 10(5) quasars that the SDSS will confirm spectroscopically. We discuss the efficient selection of quasar candidates from imaging data for use with the photometric redshift technique and the potential scientific uses of a large sample of quasar candidates with photometric redshifts.
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    Red and reddened quasars in the Sloan Digital Sky Survey
    (2003) Richards, GT; Hall, PB; Berk, DEV; Strauss, MA; Schneider, DP; Weinstein, MA; Reichard, TA; York, DG; Knapp, GR; Fan, XH; Ivezic, Z; Brinkmann, J; Budavári, T; Csabai, I; Nichol, RC
    We investigate the overall continuum and emission-line properties of quasars as a function of their optical/ UV spectral energy distributions. Our sample consists of 4576 quasars from the Sloan Digital Sky Survey (SDSS) that were chosen using homogeneous selection criteria. Expanding on our previous work, which demonstrated that the optical/ UV color distribution of quasars is roughly Gaussian but with a red tail, here we distinguish between ( 1) quasars that have intrinsically blue ( optically. at) power-law continua, ( 2) quasars that have intrinsically red ( optically steep) power-law continua, and ( 3) quasars whose colors are inconsistent with a single power-law continuum. We find that 273 (6.0%) of the quasars in our sample fall into the latter category and appear to be redder because of SMC-like dust extinction and reddening rather than because of synchrotron emission. Even though the SDSS quasar survey is optically selected and flux-limited, we demonstrate that it is sensitive to dust reddened quasars with E( B - V) less than or similar to 0.5, assuming a classical SMC extinction curve. The color distribution of our SDSS quasar sample suggests that the population of moderately dust reddened, but otherwise normal (i.e., type 1) quasars is smaller than the population of unobscured quasars: we estimate that a further 10% of the quasar population with M(i) < - 25.61 is missing from the SDSS sample because of extinction, bringing the total fraction of dust-reddened quasars to 15% of broad-line quasars. We also investigate the emission- and absorption-line properties of these quasars as a function of color and comment on how some of these results relate to Boroson-Green- type eigenvectors. Quasars with intrinsically red ( optically steep) power-law continua tend to have narrower Balmer lines and weaker C IV, C III], He II, and 3000 angstrom bump emission as compared with bluer ( optically flatter) quasars. The change in strength of the 3000 angstrom bump appears to be dominated by the Balmer continuum and not by Fe II emission. The dust-reddened quasars have even narrower Balmer lines and weaker 3000 angstrom bumps, in addition to having considerably larger equivalent widths of [O II] and [ O III] emission. The fraction of broad absorption line quasars (BALQSOs) increases from similar to 3.4% for the bluest quasars to perhaps as large as 20% for the dust-reddened quasars, but the intrinsic color distribution will be much bluer if all BALQSOs are affected by dust reddening.
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    SDSS J090334.92+502819.2: A new gravitational lens
    (2003) Johnston, DE; Richards, GT; Frieman, JA; Keeton, CR; Strauss, MA; Knapp, GR; Becker, RH; White, RL; Johnson, ET; Ma, ZM; SubbaRao, M; Bahcall, NA; Bernardi, M; Brinkmann, J; Eisenstein, DJ; Fukugita, M; Hall, PB; Inada, N; Pindor, B; Schlegel, DJ; Scranton, R; Sheldon, ES; Schneider, DP; Szalay, AS; York, DG
    We report the discovery of a new gravitationally lensed quasar from the Sloan Digital Sky Survey, SDSS J090334.92+502819.2. This object was targeted for SDSS spectroscopy as a luminous red galaxy, but manual examination of the spectrum showed the presence of a quasar at zsimilar or equal to3.6 in addition to a red galaxy at z=0.388, and the SDSS image showed a second possible quasar image nearby. Follow-up imaging and spectroscopy confirmed the lensing hypothesis. In images taken at the Astrophysical Research Consortium 3.5 m telescope, two quasars are separated by 2".8; the lensing galaxy is clearly seen and is blended with one of the quasar images. Spectroscopy taken at the Keck II telescope shows that the quasars have identical redshifts of zsimilar or equal to3.6, and both show the presence of the same broad absorption line-like troughs. We present simple lens models that account for the geometry and magnifications. The lens galaxy lies near two groups of galaxies and may be a part of them. The models suggest that the groups may contribute considerable shear that has a strong effect on the lens configuration.
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    SDSS J092455.87+021924.9: An interesting gravitationally lensed quasar from the Sloan Digital Sky Survey
    (2003) Inada, N; Becker, RH; Burles, S; Castander, FJ; Eisenstein, D; Hall, PB; Johnston, DE; Pindor, B; Richards, GT; Schechter, PL; Sekiguchi, M; White, RL; Brinkmann, J; Frieman, JA; Kleinman, SJ; Krzesinski, J; Long, DC; Neilsn, EH; Newman, PR; Nitta, A; Schneider, DP; Snedden, S; York, DG
    We report the discovery of a new gravitationally lensed quasar from the Sloan Digital Sky Survey, SDSS J092455.87+021924.9 (SDSS J0924+0219). This object was selected from among known SDSS quasars by an algorithm that was designed to select another known SDSS lensed quasar (SDSS J1226-0006A,B). Five separate components, three of which are unresolved, are identified in photometric follow-up observations obtained with the Magellan Consortium's 6.5 m Walter Baade Telescope at Las Campanas Observatory. Two of the unresolved components (designated A and B) are confirmed to be quasars with z = 1.524; the velocity difference is less than 100 km s(-1) according to spectra taken with the W. M. Keck Observatory's Keck II Telescope at Mauna Kea, Hawaii. A third stellar component, designated C, has the colors of a quasar with redshift similar to components A and B. The maximum separation of the point sources is 1."78. The other two sources, designated G and D, are resolved. Component G appears to be the best candidate for the lensing galaxy. Although component D is near the expected position of the fourth lensed component in a four-image lens system, its properties are not consistent with being the image of a quasar at z similar to 1.5. Nevertheless, the identical redshifts of components A and B and the presence of component C strongly suggest that this object is a gravitational lens. Our observations support the idea that a foreground object reddens the fourth lensed component and that another unmodeled effect (such as micro- or millilensing) demagnifies it, but we cannot rule out the possibility that SDSS J0924+0219 is an example of the relatively rare class of "three-component'' lens systems.
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    SDSS white dwarfs with spectra showing atomic oxygen and/or carbon lines
    (2003) Liebert, J; Harris, HC; Dahn, CC; Schmidt, GD; Kleinman, SJ; Nitta, A; Krzesinski, J; Eisenstein, D; Smith, JA; Szkody, P; Hawley, S; Anderson, SF; Brinkmann, J; Collinge, MJ; Fan, XH; Hall, PB; Knapp, GR; Lamb, DQ; Margon, B; Schneider, DP; Silvestri, N
    We discuss 18 white dwarfs, one of which (G227-5) was previously known, whose SDSS spectra show lines of neutral and/or singly ionized carbon. At least two and perhaps four show lines of neutral or singly ionized oxygen. Apart from the extremely hot "PG 1159'' stars, these are the first white dwarfs with photospheric oxygen detected in their optical spectra. The photometry strongly suggests that these stars lie in the 11,000-30,000 K temperature range of the helium-atmosphere DB white dwarfs, though only one of them shows weak neutral helium lines in the spectrum. Trigonometric parallaxes are known for G227-5 and another, previously known white dwarf (G35-26) showing atomic carbon lines, and they indicate that both are massive stars. Theoretical arguments suggest that all members of this class of rare white dwarfs are massive (similar to1 M.), and this finding could explain the paucity of massive DB white dwarfs.
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    Sloan Digital Sky Survey
    (2002) Stoughton, C; Lupton, RH; Bernardi, M; Blanton, MR; Burles, S; Castander, FJ; Connolly, AJ; Eisenstein, DJ; Frieman, JA; Hennessy, GS; Hindsley, RB; Ivezic, Z; Kent, S; Kunszt, PZ; Lee, BC; Meiksin, A; Munn, JA; Newberg, HJ; Nichol, RC; Nicinski, T; Pier, JR; Richards, GT; Richmond, MW; Schlegel, DJ; Smith, JA; Strauss, MA; SubbaRao, M; Szalay, AS; Thakar, AR; Tucker, DL; Vanden Berk, DE; Yanny, B; Adelman, JK; Anderson, JE; Anderson, SF; Annis, J; Bahcall, NA; Bakken, JA; Bartelmann, M; Bastian, S; Bauer, A; Berman, E; Böhringer, H; Boroski, WN; Bracker, S; Briegel, C; Briggs, JW; Brinkmann, J; Brunner, R; Carey, L; Carr, MA; Chen, B; Christian, D; Colestock, PL; Crocker, JH; Csabai, IN; Czarapata, PC; Dalcanton, J; Davidsen, AF; Davis, JE; Dehnen, W; Dodelson, S; Doi, M; Dombeck, T; Donahue, M; Ellman, N; Elms, BR; Evans, ML; Eyer, L; Fan, XH; Federwitz, GR; Friedman, S; Fukugita, M; Gal, R; Gillespie, B; Glazebrook, K; Gray, J; Grebel, EK; Greenawalt, B; Greene, G; Gunn, JE; de Haas, E; Haiman, Z; Haldeman, M; Hall, PB; Hamabe, M; Hansen, B; Harris, FH; Harris, H; Harvanek, M; Hawley, SL; Hayes, JJE; Heckman, TM; Helmi, A; Henden, A; Hogan, CJ; Hogg, DW; Holmgren, DJ; Holtzman, J; Huang, CH; Hull, C; Ichikawa, SI; Ichikawa, T; Johnston, DE; Kauffmann, G; Kim, RSJ; Kimball, T; Kinney, E; Klaene, M; Kleinman, SJ; Klypin, A; Knapp, GR; Korienek, J; Krolik, J; Kron, RG; Krzesinski, J; Lamb, DQ; Leger, RF; Limmongkol, S; Lindenmeyer, C; Long, DC; Loomis, C; Loveday, J; MacKinnon, B; Mannery, EJ; Mantsch, PM; Margon, B; McG'hee, P; Mckay, TA; McLean, B; Menou, K; Merelli, A; Mo, HJ; Monet, DG; Nakamura, O; Narayanan, VK; Nash, T; Neilsen, EH; Newman, PR; Nitta, A; Odenkirchen, M; Okada, N; Okamura, S; Ostriker, JP; Owen, R; Pauls, AG; Peoples, J; Peterson, RS; Petravick, D; Pope, A; Pordes, R; Postman, M; Prosapio, A; Quinn, TR; Rechenmacher, R; Rivetta, CH; Rix, HW; Rockosi, CM; Rosner, R; Ruthmansdorfer, K; Sandford, D; Schneider, DP; Scranton, R; Sekiguchi, M; Sergey, G; Sheth, R; Shimasaku, K; Smee, S; Snedden, SA; Stebbins, A; Stubbs, C; Szapudi, I; Szkody, P; Szokoly, GP; Tabachnik, S; Tsvetanov, Z; Uomoto, A; Vogeley, MS; Voges, W; Waddell, P; Walterbos, R; Wang, SI; Watanabe, M; Weinberg, DH; White, RL; White, SDM; Wilhite, B; Wolfe, D; Yasuda, N; York, DG; Zehavi, I; Zheng, W
    The Sloan Digital Sky Survey (SDSS) is an imaging and spectroscopic survey that will eventually cover approximately one-quarter of the celestial sphere and collect spectra of 10 6 galaxies, 100,000 quasars, 30,000 stars, and 30,000 serendipity targets. In 2001 June, the SDSS released to the general astronomical community its early data release, roughly 462 deg(2) of imaging data including almost 14 million detected objects and 54,008 follow-up spectra. The imaging data were collected in drift-scan mode in five bandpasses (u, g, r, i, and z); our 95% completeness limits for stars are 22.0, 22.2, 22.2, 21.3, and 20.5, respectively. The photometric calibration is reproducible to 5%, 3%, 3%, 3%, and 5%, respectively. The spectra are flux- and wavelength-calibrated, with 4096 pixels from 3800 to 9200 Angstrom at R approximate to 1800. We present the means by which these data are distributed to the astronomical community, descriptions of the hardware used to obtain the data, the software used for processing the data, the measured quantities for each observed object, and an overview of the properties of this data set.