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J/ApJ/718/392       SDSS Lyman limit systems at z∼3.5         (Prochaska+, 2010)
A definitive survey for Lyman limit systems at z ∼ 3.5 with the Sloan Digital
Sky Survey.
    Prochaska J.X., O'Meara J.M., Worseck G.
   <Astrophys. J., 718, 392-416 (2010)>
   =2010ApJ...718..392P
ADC_Keywords: Redshifts ; QSOs ; Spectroscopy

Keywords: diffuse radiation - intergalactic medium


Abstract:
    We perform a semi-automated survey for τ912≥2 Lyman limit
    systems (LLSs) in quasar spectra from the Sloan Digital Sky Survey,
    Data Release 7. From a starting sample of 2473 quasars with
    zem=3.6-5.0, we analyze 429 spectra meeting strict selection
    criteria for a total redshift path Δz=93.8 and identify 190
    intervening systems at zLLS≥3.3. We also perform a survey for
    proximate LLSs (PLLSs) and find that lPLLS(z) is systematically
    lower (∼25%) than intervening systems.

Description:
    To assess uncertainties (statistical and systematic) of surveying LLSs
    in the SDSS quasar spectra, we obtained independent, higher quality
    spectra using the LRIS spectrometer on the Keck I telescope. All
    observations were obtained using a 1 arcsec slit which provides an
    ∼4pix FWHM corresponding to ∼290km/s and ∼220km/s for the blue
    (3100-5600Å) and red (5600-8200Å) data, respectively, during a
    four night run in 2008 October.

File Summary:

       FileName      Lrecl  Records   Explanations

ReadMe            80        .   This file
table1.dat        69     3759   SDSS-DR7 quasar sample
table2.dat        54      607   SDSS-DR7 intervening τ912≥2 LLS survey
table3.dat        41     2593   SDSS-DR7 non-statistical LLS systems and candidates
table6.dat        31      468   SDSS-DR7 proximate τ912≥2 LLS survey
table8.dat        55       32   SDSS-DR7 quasars with KECK+LRIS comparison spectra


See also:
   VII/260 : The SDSS-DR7 quasar catalog (Schneider+, 2010)
   II/294  : The SDSS Photometric Catalog, Release 7 (Adelman-McCarthy+, 2009)
   J/ApJ/736/42  : HST QSO Catalog (Ribaudo+, 2011)
   J/ApJS/195/16 : HST survey for Lyman limit systems. I. (O'Meara+, 2011)
   J/ApJ/648/L97 : 2 SDSS QSOs supersolar super-Lyman limit systems (Prochaska+
                   2006)
   http://www.ucolick.org/~xavier/SDSSLLS/ : SDSS LLS survey home page
   http://www.sdss.org/ : SDSS home page


Byte-by-byte Description of file: table1.dat

   Bytes Format Units   Label     Explanations

   1-  4  I4    ---     Plate     Plate number
   6- 10  I5    d       MJD       Modified Julian Date of observation
  12- 14  I3    ---     Fiber     Fiber identification
  16- 34  A19   ---     SDSS      Object name (JHHMMSS.ss+DDMMSS.s)
  36- 40  F5.3  ---     z         Emission line derived redshift (1)
      42  I1    ---     f_z       Flag on z (0=normal) (2)
  44- 49  F6.2  ---     A         ? Absorbed continuum fitting parameter A (3)
  51- 57  F7.2  ---     B         ? Absorbed continuum fitting parameter B (3)
  59- 62  F4.2  ---     Scale     ? Additional scaling factor (4)
  64- 67  F4.1  ---     S/N       ? Estimated signal-to-noise (5)
      69  A1    ---     f_S/N     [I] I: indicates an infinity value for S/N

Note (1): List of all objects tagged as QSO or HIZ_QSO in the SDSS Data
          Release 7 with estimated redshift 5≥z≥3.4.
Note (2): Redshift flag as follows:
    0 = Normal;
    1 = Not at SDSS reported redshift and/or not a quasar (excluded);
    2 = Too low S/N for evaluation (excluded);
    3 = Strong BAL (excluded).
Note (3): Absorbed continuum fitting parameters of the form:
          C=A+Blog10(λ/Å). We caution the reader that these
          models are not meant to describe the intrinsic spectral energy
          distributions of the quasars (see the text).
Note (4): Imposed by the authors on the best-fit absorbed quasar continuum.

Note (5): For the absorbed quasar continuum at
          λ=λ912(1+zem).


Byte-by-byte Description of file: table2.dat

   Bytes Format Units   Label     Explanations

   1-  5  A5    ---     ---       [zem]
   6- 10  A5    ---     Range     The z_em_ range (< 3.6 or ≥3.6) (1)
  12- 30  A19   ---     SDSS      Quasar name (JHHMMSS.ss+DDMMSS.s)
  32- 36  F5.3  ---     z         Emission line derived redshift
  38- 42  F5.3  ---     zS/N2     Starting redshift at S/N=2 (2)
  44- 48  F5.3  ---     zS/N3     ? Starting redshift at S/N=3 (2)
  50- 54  F5.3  ---     zLLS      ? Lyman Limit System redshift

Note (1): The quasars with zem<3.6 are not included in the final analysis.

Note (2): The starting redshifts correspond to the wavelength at which the
          absorbed continuum model, starting from zem, no longer exceeds the
          smoothed noise array by the specified S/NA912 threshold. This
          value is limited to a maximum offset from zem of δz=0.4.


Byte-by-byte Description of file: table3.dat

   Bytes Format Units   Label     Explanations

   1- 19  A19   ---     SDSS      Quasar name (JHHMMSS.ss+DDMMSS.s)
  21- 25  F5.3  ---     z         Emission line derived redshift
  27- 31  F5.3  ---     zLLS      Lyman Limit System redshift
  33- 36  F4.1  [cm-2]  logNHI    Log of HI column density (1)
  38- 41  A4    ---     S/N       Signal-to-noise (2)

Note (1): The logNHI values listed serve as a rough estimate. Typical
          uncertainties for systems with NHI<1017.5cm-2 are at
          least 0.2dex.
Note (2): Estimate of the S/N of the absorbed continuum (ignoring the effects
          of pLLS) at λ=λ912(1+zLLS).


Byte-by-byte Description of file: table6.dat

   Bytes Format Units   Label     Explanations

   1- 19  A19   ---     SDSS      Quasar name
  21- 25  F5.3  ---     z         Emission line derived redshift
  27- 31  F5.3  ---     zLLS      ? Lyman Limit System redshift


Byte-by-byte Description of file: table8.dat

   Bytes Format Units   Label     Explanations

   1- 19  A19   ---     SDSS      SDSS name (JHHMMSS.ss+DDMMSS.s)
  21- 24  F4.2  ---     z         Emission line redshift
  26- 29  F4.1  ---     S/N       Signal to noise of the absorbed continuum at
                                  the Lyman limit (S/NA912)
      31  I1    ---     f_SDSS    [1/3] Flag indication (1=no LLS,
                                  2=τ912≥2LLS, 3=τ912<2LLS) (1)
  33- 37  F5.3  ---     SLLS      ? SDSS LLS modeling result
  39- 43  F5.3  ---     SpLLS     ? SDSS proximate LLS modeling result
  45- 49  F5.3  ---     LLLS      ? LRIS LLS modeling result
  51- 55  F5.3  ---     LpLLS     ? LRIS proximate LLS modeling result

Note (1): τ912 being the optical depth at the Lyman Limit (912Å),
     we define a "standard" Lyman Limit System (LLS) to be 1 (LLS=1) when
     τ912≥2, i.e. N(HI)≥1017.5cm-2. A flag=2 therefore indicates
     a "strong" LLS, a flag=3 a partial LLS.


History:
    From electronic version of the journal
(End)                 Greg Schwarz [AAS], Emmanuelle Perret [CDS]    07-Jun-2012