J/MNRAS/435/1198    z∼6 QSOs CIV doublet absorption systems  (D'Odorico+, 2013)
Metals in the IGM approaching the re-ionization epoch:
results from X-shooter at the VLT.
    D'Odorico V., Cupani G., Cristiani S., Maiolino R., Molaro P., Nonino M.,
    Centurion M., Cimatti A., Di Serego Alighieri S., Fiore F., Fontana A.,
    Gallerani S., Giallongo E., Mannucci F., Marconi A., Pentericci L.,
    Viel M., Vladilo G.
   <Mon. Not. R. Astron. Soc., 435, 1198-1232 (2013)>
   =2013MNRAS.435.1198D
ADC_Keywords: QSOs ; Spectroscopy

Keywords: galaxies: abundances - intergalactic medium -
          quasars: absorption lines - cosmology: observations

Abstract:
    We present the results of observations taken with the X-shooter
    spectrograph devoted to the study of quasars at z∼6. This paper
    focuses on the properties of metals at high redshift traced, in
    particular, by the CIV doublet absorption systems. Six objects were
    observed with resolutions ≃27 and 34km/s in the visual, and 37.5 and
    53.5km/s in the near-infrared. We detected 102 CIV lines in the
    range: 4.35<z<6.2 of which 27 are above z∼5. Thanks to the
    characteristics of resolution and spectral coverage of X-shooter, we
    could also detect 25 SiIV doublets associated with the CIV at z≳5.
    The column density distribution function of the CIV line sample is
    observed to evolve in redshift for z≳5.3, with respect to the
    normalization defined by low-redshift (1.5<z<4) CIV lines. This
    behaviour is reflected in the redshift evolution of the CIV cosmic
    mass density, ΩCIV, of lines with column density in the range
    13.4<logN(CIV)<15, which is consistent with a drop of a factor of ∼2
    for z≳5.3. Considering only the stronger CIV lines
    (13.8<logN(CIV)<15), ΩCIV gently rises by a factor of ∼10
    between z≃6.2 and z≃1.5 with a possible flattening towards z∼0. The
    increase is well fitted by a power law:
    Ω_CIV=(2±1)x10-8[(1+z)/4]-3.1±0.1. An insight into the
    properties of the CIV absorbers and their evolution with redshift is
    obtained by comparing the observed column densities of associated CIV,
    SiIV and CII absorptions with the output of a set of cloudy
    photoionization models. As already claimed by cosmological
    simulations, we find that CIV is a good tracer of the metallicity in
    the low-density intergalactic medium (IGM) gas at z∼5-6 while at z∼3
    it arises in gas with overdensity δ∼100.

Description:
    We present the spectra obtained in a Guaranteed Timed Observation
    (GTO) programme (PI: V. D'Odorico) carried out with the X-shooter
    spectrograph at the European Southern Observatory (ESO) Very Large
    Telescope (VLT) between 2010 January and 2011 June.

    The spectra were acquired with a binning of two pixels in the
    dispersion direction and adopting two sets of slit apertures for the
    blue, visual (VIS) and near-infrared (NIR) arms, respectively:
    1.0/0.9/0.9 and 0.8/0.7/0.6 arcsec depending on the seeing conditions
    at the moment of the observations.
Objects:
  -----------------------------------------------------------------------------
       RA   (ICRS)   DE        Designation(s)                     (files)
  -----------------------------------------------------------------------------
   08 18 27.4    +17 22 52     SDSS J0818+1722  = QSO J0818+1722  (tablea1.dat)
   08 36 43.9    +00 54 53     SDSS J0836+0054  = QSO J0836+0054  (tablea2.dat)
   10 30 27.09   +05 24 55.1   SDSS J1030+0524  = QSO J1030+0524  (tablea3.dat)
   13 06 08.2    +03 56 26     SDSS J1306+0356  = QSO J1306+0356  (tablea4.dat)
   13 19 11.28   +09 50 51.4   SDSS J1319+0950  = QSO J1319+0950  (tablea5.dat)
   15 09 41.8    -17 49 27     CFHQS J1509-1749 = QSO J1509-1749  (tablea6.dat)
   ----------------------------------------------------------------------------

File Summary:

       FileName      Lrecl  Records   Explanations

ReadMe            80        .   This file
table1.dat        72        6   X-shooter spectroscopic observations
tablea1.dat       68       62   CIV absorption systems in SDSS J0818+1722
tablea2.dat       68       47   CIV absorption systems in SDSS J0836+0054
tablea3.dat       68       45   CIV absorption systems in SDSS J1030+0524
tablea4.dat       68       44   CIV absorption systems in SDSS J1306+0356
tablea5.dat       68       46   CIV absorption systems in ULAS J1319+0950
tablea6.dat       68       21   CIV absorption systems in CFHQS J1509-1749


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

   Bytes Format Units   Label     Explanations

   1- 10  A10   ---     QSO       Quasar name
  13- 17  F5.3  ---     zem       [5.8/6.4] Redshift of emission lines
  19- 23  F5.2  mag     Jmag      [17/19] J-band (near-IR) magnitude
  25- 29  I5    s       Tvis      Exposure time in visible (optical)
  31- 35  I5    s       Tnir      Exposure time in near-infrared
  37- 39  I3    ---     SNRv      [50/125] Signal-to-noise ratio at 0.9µm
  41- 42  I2    ---     SNRi      [7/24] Signal-to-noise ratio at 1.035µm
  44- 48  F5.3  ---     zC.min    Lower value of CIV absoption redshift
      49  A1    ---     ---       [-]
  50- 54  F5.3  ---     zC.max    Upper value of CIV absoption redshift
  56- 60  F5.3  ---     DX        CIV redshift absorption path ΔXCIV
  62- 66  F5.3  ---     zSi.min   Lower value of SiIV absoption redshift
      67  A1    ---     ---       [-]
  68- 72  F5.3  ---     zSi.max   Upper value of SiIV absoption redshift


Byte-by-byte Description of file: tablea?.dat

   Bytes Format Units   Label   Explanations

   1-  2  I2    ---     Sys     [1/22] System number (in QSO)
       3  A1    --      m_Sys   [abcdefghi] Multiplicity index on System
   5- 13  A9    ---     Ion     Ion (CII, CIV, or SiIV)
  14- 15  A2    ---     n_Ion   [asbmlS ] Note on line (1)
  17- 23  F7.5  ---     z       [4.4/6.0]? Redshift
  25- 31  F7.5  ---     e_z     ? rms uncertainty on z
      33  A1    ---     l_W0    Limit flag on W0
  34- 39  F6.3  0.1nm   W0      [0/1.6]? Rest-frame equivalent width (Å)
  41- 45  F5.3  0.1nm   e_W0    ? rms uncertainty on W0
  48- 51  F4.1  km/s    b       [7/94]? Doppler velocity width
  53- 56  F4.1  km/s    e_b     ? rms uncertainty on b
      58  A1    ---     l_logN  Limit flag on logN
  59- 63  F5.2  [cm-2]  logN    [12/14.6]? Abundance (column density)
  65- 68  F4.2  [cm-2]  e_logN  ? rms uncertainty on logN

Note (1): Notes as follows:
   b = line blended with another absorption line
   m = multiple components
   s = line contaminated by a sky emission line
   l = feature below 3σ detection.
   a = We found an alternative identification for this line:
       it could be AlIII at zabs~=3.71
   S = The line could be saturated


History:
    From electronic version of the journal