J/ApJ/651/61    Optically thick absorbers near luminous quasars (Hennawi+, 2006)
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Quasars probing quasars. I. Optically thick absorbers near luminous quasars.
    Hennawi J.F., Prochaska J.X., Burles S., Strauss M.A., Richards G.T.,
    Schlegel D.J., Fan X., Schneider D.P., Zakamska N.L., Oguri M., Gunn J.E.,
    Lupton R.H., Brinkmann J.
   <Astrophys. J., 651, 61-83 (2006)>
   =2006ApJ...651...61H
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ADC_Keywords: QSOs ; Redshifts ; Photometry, SDSS
Keywords: cosmology: observations - cosmology: theory - intergalactic medium -
          quasars: absorption lines - quasars: general - surveys

Abstract:
    With close pairs of quasars at different redshifts, a background
    quasar sight line can be used to study a foreground quasar's
    environment in absorption. We search 149 moderate-resolution
    background quasar spectra from Gemini, Keck, the MMT, and the SDSS to
    survey Lyman limit systems (LLSs) and damped Ly{alpha} systems (DLAs)
    in the vicinity of 1.8<z<4.0 luminous foreground quasars. A sample of
    27 new quasar-absorber pairs is uncovered with column densities
    10^17.2^cm^-2^<NH<10^20.9^cm^-2^ and transverse (proper) distances of
    22h^-1^kpc<R<1.7h^-1^Mpc from the foreground quasars.

File Summary:
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 FileName  Lrecl  Records   Explanations
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ReadMe        80        .   This file
table1.dat    97       28   Optically thick absorption-line systems near
                             foreground quasars
table2.dat    97        7   Tentative optically thick absorption-line
                             systems near foreground quasars
table3.dat    91       54   Coordinates and photometry for projected quasar
                             pairs in table 1
table4.dat    91       12   Coordinates and photometry for projected quasar
                             pairs in table 2
table5.dat    91        5   Coordinates and photometry for the five quasars
                             in the projected group SDSS J0127+1507
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See also:
   II/282 : The SDSS Photometric Catalog, Release 6 (Adelman-McCarthy+, 2007)
   http://www.sdss.org : SDSS Home Page

Byte-by-byte Description of file: table1.dat table2.dat
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   Bytes Format Units    Label     Explanations
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   1- 15  A15   ---      System    System name (SDSS JHHMM+DDMM)
      16  A1    ---    n_System    [a-d] Note on System (1)
  18- 21  F4.2  ---      zbg       Background quasar redshift
  23- 27  F5.3  ---      zfg       Foreground quasar redshift
  29- 33  F5.1  arcsec   Dthe      Angular separation of the quasar pair
                                    sight lines (2)
  35- 38  I4    kpc      R         Radius (in (h^-1^kpc)
  40- 45  F6.4  ---      zabs      Absorber redshift
  47- 50  I4    km/s     |DV|      Velocity difference between the absorber
                                    redshift and our best estimate of the
                                    redshift of the foreground quasar
  52- 55  I4    km/s     DVfg      Estimated error on the foreground quasar
                                    redshift
      57  A1    ---    l_logNHI    Limit flag on logNHI
  58- 62  F5.2  [cm-2]   logNHI    ? Column density of the absorber from our fit
                                     to the HI profile
  64- 67  F4.2  [cm-2] e_logNHI    ? rms uncertainty on logNHI
  69- 72  I4    ---      gUV       Maximum enhancement of the quasar's ionizing
                                    photon flux over that of the extragalactic
                                    ionizing background, at the location of the
                                    background quasar sight line, assuming that
                                    gUV=1+F_QSO_/F_UVB_
                                    the quasar emission is isotropic
  74- 82  A9    ---    n_zfg       Emission line that was centered to determine
                                    foreground quasar redshift (zfg)
  84- 89  A6    ---      obs.fg    Instrument used to observed foreground quasar
  92- 97  A6    ---      obs.bg    Instrument used to observed background quasar
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Note (1): Individual notes as follows:
      a = In the systems SDSS J0127+1507 there are two distinct background
          quasars at z=2.38 and 2.60, which show absorption in the
          vicinity of the same foreground quasar at z=1.818.
      b = The foreground quasar for this system has large BAL troughs in
          the Ly{alpha} and CIV emission lines. The redshift was computed
          by comparing the peak of CIV, determined by eye, to the shifted
          wavelength lambda=1545.3{AA} We apply a conservative redshift
          uncertainty of +/-1500km/s.
      c = In the systems SDSS J2347+1501, there is a single background
          quasar at z=2.29 and two foreground quasars at z=2.157 and
          2.167, although the velocity separation is larger than our
          nominal 1500km/s cutoff for the former.
      d = Voigt profile fits to the Ly{alpha} absorption in the SDSS
          spectrum of the background quasar gave log(NHI)=19.55+/-0.3.
          An archive echelle spectrum of this quasar gives the smaller
          value that is listed in the table, logNHI=18.8+.-0.2.
Note (2): The angular separation of the quasar pair sight lines corresponds
     to a transverse proper separation of R at the foreground quasar
     redshift.
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Byte-by-byte Description of file: table[345].dat
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   Bytes Format Units   Label   Explanations
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   1- 15  A15   ---     Name    Quasar name (SDSS JHHMM+DDMM or 2QZ  JHHMM+DDMM)
      16  A1    ---   m_Name    [A-E] Multiplicity index on Name (1)
  18- 19  I2    h       RAh     Right ascension (J2000)
  21- 22  I2    min     RAm     Right ascension (J2000)
  24- 28  F5.2  s       RAs     Right ascension (J2000)
      30  A1    ---     DE-     Declination sign (J2000)
  31- 32  I2    deg     DEd     Declination (J2000)
  34- 35  I2    arcmin  DEm     Declination (J2000)
  37- 40  F4.1  arcsec  DEs     Declination (J2000)
  42- 45  F4.2  ---     z       Spectroscopic redshift
  47- 51  F5.2  mag     umag    Extinction-corrected SDSS u magnitude
  53- 57  F5.2  mag     gmag    Extinction-corrected SDSS g magnitude
  59- 63  F5.2  mag     rmag    Extinction-corrected SDSS r magnitude
  65- 69  F5.2  mag     imag    Extinction-corrected SDSS i magnitude
  71- 75  F5.2  mag     zmag    Extinction-corrected SDSS z magnitude
  77- 91  A15   ---     System  System name ((SDSS JHHMM+DDMM)
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Note (1): The background and foreground quasars are labeled A and B,
          respectively
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History:
    From electronic version of the journal
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(End)                                      Patricia Vannier [CDS]    23-Jul-2008