Spectroscopic data for the VIPERS survey.

For further details please refer to the VIPERS survey description paper Guzzo et al. 2014, to the PDR-1 presentation paper Garilli et al. 2014 and to the PDR-2 presentation paper Scodeggio et al. 2016

id_IAU and num VIPERS object name, according to IAU standards. The name is composed of the prefix VIPERS plus the internal identification number. The internal id number (num) is in the form
a identifies the sky area (1 for W1 and 4 for W4),
tt identifies the CFHTLS tile number where the object is located,
xxxxxx is the original CFHTLS ID within the tile.
The correspondence between our tile identifier and the official CFHTLS tile name is provided in Guzzo et al 2014
alpha and delta J2000 equatorial coordinates in degrees
selmag and errselmag i_AB selection magnitude and error. The selection magnitude comes from CFHTLS T0005 catalogues
zspec Spectroscopic redshift.
zflg Redshift measurement quality flag

The integer part of the flag has the following meaning:
  • 4 a high-confidence, highly secure redshift, based on a high SNR spectrum and supported by obvious and consistent spectral features. The confidence level of Flag 4 measurements is estimated to be 99% secure.
  • 3 also a very secure redshift, comparable in confidence with Flag 4, supported by clear spectral features in the spectrum, but not necessarily with high SNR.
  • 2 a fairly secure, ~90% confidence redshift measurement, supported by cross-correlation results, continuum shape and some spectral features.
  • 9 a redshift based on only one single clear spectral emission feature.
  • 1 a reasonable redshift measurement, based on weak spectral features and/or continuum shape, for which there is roughly a 50% chance that the redshift is actually wrong.
In case of broad emission lines typical of broad line AGN, a prefix of 1 is added to zflag, i.e.
  • 14 secure AGN with a >95% secure redshift, at least 2 broad lines;
  • 13 secure AGN with good confidence redshift, based on one broad line and some faint additional feature;
  • 12 a >95% secure redshift measurement, but lines are not significantly broad, might not be an AGN;
  • 19 secure AGN with one single secure emission line feature, redshift based on this line only;
  • 11 a tentative redshift measurement, with spectral features not significantly broad.
Second objects in slit get a 2 as prefix to the flag, i.e.
  • 24 a second object with flag 4
  • 23 a second object with flag 3
  • 22 a second object with flag 2
  • 29 a second object with flag 9
  • 21 a second object with flag 1
And similarly for BLAGN (214, 213, 212, ...).

Suffix in form of decimal digit has the following meaning:
  • .5 the spectroscopic redshift is compatible within 1σ with photometric redshift, i.e
        zphotmin < zspec < zphotmax
  • .4 the spectroscopic redshift is compatible with photometric redshift at the 2σ level, i.e.
        minvalue < zspec < maxvalue
        minvalue=min[ zphot-(1+zphot)*0.05, zphotmin ]
        maxvalue=max[ zphot+(1+zphot)*0.05, zphotmax ]
    and 0.05 is twice the median scatter of the comparison between spectroscopic and photometric redshifts.
  • .2 spectroscopic redshift is NOT compatible with photometric redshift
  • .1 no photometric redshift available
norm Normalization factor. The spectrum has been multiplied by this value to be normalized to the selmag value.
epoch Observing epoch. epoch=1 objects have been observed before VIMOS refurbishing in summer 2010, epoch=2 objects have been observed after summer 2010
classFlag The VIPERS galaxy target selection flag, based on the CFHTLS T005 catalogue, where

1: VIPERS main galaxy target, i.e. galaxy with colors compatible with z > 0.5, according to the color criteria described in Guzzo et al. 2014

0: galaxy with colors compatible with z < 0.5, according to the color criteria described in Guzzo et al. 2014

-1: stellar like object according to the VIPERS star/galaxy separation criteria

-2: magnitude i > 22.5

-3: magnitude i < 17.5

-88: problematic object, possibly saturated image

-99: problematic object, missing photometric data

photoMask Flag indicating whether the object falls within the photometric mask. 1 if the object is inside the mask, 0 if it is outside. Objects outside the photometric mask have a less reliable photometry
tsr The Target Sampling Rate (TSR) is defined as the ratio of the observed objects over the number of possible targets: TSR=Nspec/Nparent, where Nspec is the number of detected targets and Nparent is the number of all the possible random targets.
TSR has been computed in small rectangular apertures to take into account the shadowing effect of MOS slits in the sampling of the galaxy distribution. TSR and is needed to take into account the fact that not all the possible targets can be observed in the single pass strategy adopted in VIPERS. See Scodeggio et al. 2016 for details
ssr The Spectroscopic Success Rate (SSR) is defined as the ratio of the galaxies with a successfully measured redshift (flag = 2.*,3.*,4.*,9.*) over the total sample of detected galaxies.
SSR is a function of the apparent magnitude (since to bright objects correspond spectra with high signal-to-noise, from which the redshift can be more easily measured), of the galaxy luminosity and rest-frame color and of the overall quadrant quality, quantified via the mean SSR for all galaxies in that quadrant. See Scodeggio et al. 2016 for detail

Colour Sampling Rate (CSR)
The CSR is defined as the fraction of objects we are missing in the parent sample of possible targets due to the uncertainties associated to the adopted colour selection. This incompleteness affects in particular the number of galaxies very near the nominal low redshift boundary of the survey, z=0.5, and it is a steep function of redshift, reaching values ~1 (corresponding to a complete sampling) at z~0.6. The user can estimate the CSR(z) by means of the following equation we used to model it:
   CSR = 1/2 - 1/2*erf[b*(zt-z)]
where erf is the error function, and the best fit parameters are b=10.8 and zt=0.444.

Statistical weights
The statistical sample is defined by the galaxies that have been observed as VIPERS targets (classFlag=1), have a high confidence redshift measure (flag=2.*,3.*,4.*,9.*), and reside in the sky regions specified by the spectroscopic and photometric masks (Area_W1 = 11.012 deg^2; Area_W4 = 5.312 deg^2).
The weight to be applied to each galaxy when computing statistical functions like Luminosity or Stellar Mass functions is defined as:
   w = w_TSR * w_SSR * w_CSR
where w_TSR=1/TSR, w_SSR=1/SSR and w_CSR=1/CSR.
N.B.: Objects for which at least one between TSR and SSR is negative should not be used in the statistical sample.

Spectra are provided as FITS tables containing 5 columns Also a multi-extension FITS file is provided (1D2D) containing, in addiction of the 1D table described above, the 2D linearly resampled and sky subtracted spectrum.