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VIPERS PDR-1 data release: Spectroscopic catalogs
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Columns description
===================
An extensive explanation of all quantities and their meaning can be
found in the PDR-1 presentation paper Garilli et al. 2013
(http://arxiv.org/abs/1310.1008). For further details please refer
to the VIPERS survey description paper Guzzo et al. 2013
(http://arxiv.org/abs/1303.2623).
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
attxxxxxx
where
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. 2013.
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. A conventional zpsec value of 9.9999 is assigned
in case a redshift could not be measured.
zflg
~~~~
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.
0 no reliable spectroscopic redshift measurement was
possible. Redshift is set to the conventional value of 9.9999.
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
20 a second object with flag 0
And similarly for BLAGN (214, 213, 212, ...).
Suffix in form of decimal digit has the following meaning:
.5 the spectroscopic redshift is compatible within 1 sigma with
photometric redshift, i.e
zphot_min < zspec < zphot_max
.4 the spectroscopic redshift is compatible with photometric
redshift at the 2 sigma level, i.e.
minvalue < zspec < maxvalue
where
minvalue = min[ zphot-(1+zphot)*0.05, zphot_min ]
maxvalue = max[ zphot+(1+zphot)*0.05, zphot_max ]
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
epoch
~~~~~
Observing epoch. epoch=1 objects have been observed before VIMOS
refurbishing in summer 2010, epoch=2 objects have been observed after
summer 2010.
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 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 bins of apparent magnitude to take into account
the possible dependence of the sampling rate on the clustering of bright
objects (possibly causing slit collision) and the higher fraction of
observed bright objects for which a spectrum has not been extracted (see
Garilli et al. 2013).
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 Garilli et al. 2013 for details
TSR is = -1 for serendipitous targets (flags 2*.*), and observed objects
not fulfilling the selection criterion for z>0.5 galaxies (i.e. AGN);
TSR = -99 for objects outside the considered area and selection
magnitude range (i.e. either i<17.5 or i>22.5).
ssr
~~~
The 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), and of redshift (because the spectral
features visible in the observed spectral range can change). Therefore
SSR has been computed in bins of redshift and apparent magnitude.
SSR is = -1 for stars (z=0.0000), non measured objects (flag 0), low
confidence redshift measurements (flags 1.*), spectroscopic BLAGN (flags
1*.*), serendipitous targets (flags=2*.*), and hight redshift galaxies
(zspec>3);
SSR = -99 for objects outside the considered area and selection
magnitude range (i.e. either i<17.5 or i>22.5).
Colour Sampling Rate
====================
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 (CSR)
=========================
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 = 5.347
deg^2; Area_W4 = 4.968 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.
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03/10/2013