Information on Service 'CARS source catalogue query'

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Further access options are discussed below

Images and data from from the CFHTLS archive research survey, a multi-band dataset spanning 37 square degrees of sky in high galactic latitudes.

For a list of all services and tables belonging to this service's resource, see Information on resource 'CARS survey data'

Service Documentation

These services deliver products from the CFHTLS-Archive-Research Survey (CARS). The survey currently offers derived products from 37 sq. degrees of the Wide part from the Canada-France-Hawaii Telescope Legacy Survey (CFHTLS). The main documentation for the products, its creation and its content is the publication 2009A&A...493.1197E. Here, we discuss some points which are not evident from this publication.

AVAILABLE DATA PRODUCTS

For each 1 sq. deg. CARS pointing we currently offer the following products (we discuss them on the example of the CARS pointing W1m0p1); a typical file is named W1m0p1_izrgu.V1.7A.final.cat. The name contains the following information:

The individual files we offer are:

W1m0p1_izrgu.V1.7A.final.cat
object catalogue in FITS binary format; beware that they are very big and cumbersome to handle if you do not have efficient tools to work on big FITS binary tables! (typical file size per field: 0.5GB!)
W1m0p1_izrgu.V1.7A.final.asc.gz
An ASCII version of W1m0p1_izrgu.V1.7A.final.cat containing a subset of the most important catalogue quantities. This catalogue should be sufficient for most users. The main content of the catalogue can also be queried in the cat service. (typical gzipped file size per field: 20MB)
W1m0p1_izrgu.V1.7A.final.reg.gz

An ASCII ds9 region file containing saoimage/ds9 polygon entries (in pixel coordinates). They represent the CARS image masks described in Sect. 3.4 of 2009A&A...493.1197E. Polygons originating from different masking procedures are encoded with different colours (look at expressions such as '# color=yellow' at the end of each line). We offer this file so that interested users can construct own masks containing only parts of our global MASK key. (typical gzipped file size per field: 1MB)

The colour coding in these files is as follows:

  • yellow: masks from our object density analysis and stars identified in the USNO-A2 catalogue
  • green: stars identified in the GSC1 and GSC2 cataogues
  • magenta: masks around extended haloes of bright stars
  • red: masks from our asteroid track analysis

W1m0p1_irg.V1.7A.truecol.jpg

low resolution true colour i', r' and g' JPG image of the CARS field. These images allow a quick look at the data but they are probably not suitable for high-quality poster print-outs. (typical file size per field: 10MB)
W1m0p1_izrgu.V1.7A.masks.obj.jpg

low resolution JPG image showing object positions and object masks overlayed on the i'-band image. It allows a quick-look at field-layout and object positions. (typical file size per field: 3MB)

The colour coding in this is:

  • green: areas excluded from scientific analysis by our MASK key
  • yellow: stellar sources (SExtractor CLASS_STAR >=0.95)
  • red: galaxies with high-confidence photo-z estimates: (SExtractor CLASS_STAR < 0.95; reliable object photometry in five bands; BPZ ODDS quality parameter > 0.9); see also Sect. 4 of 2009A&A...493.1197E
  • blue: all other galaxies (SExtractor CLASS_STAR < 0.95)

CATALOGUE QUANTITIES

See 2009A&A...493.1197E, in particular Sect. 4, and the SExtractor Users manual for a description of most catalogue entries. Also see the table notes.

CURRENT COVERAGE

CARS coverage

Overview

You can access this service using:

This service is published as follows:

local means it is listed on our front page, ivo_managed means it has a record in the VO registry.

Other services provided on the underlying data include:

Input Fields

The following fields are available to provide input to the service (with some renderers, some of these fields may be unavailable):

NameTable Head DescriptionUnitUCD
DEC Delta (ICRS) Declination (ICRS decimal) deg pos.eq.dec
hscs_pos Position/Name Coordinates (as h m s, d m s or decimal degrees), or SIMBAD-resolvable object N/A N/A
hscs_sr Search radius Search radius in arcminutes N/A N/A
magAuto Auto. mag. Kron-like elliptical aperture magnitude mag phot.mag
RA Alpha (ICRS) Right Ascension (ICRS decimal) deg pos.eq.ra
sgclass S/G S/G classifier output (0..1) N/A src.class.starGalaxy
SR Search Radius Search radius deg N/A

Default Output Fields

The following fields are contained in the output by default. More fields may be available for selection; these would be given below in the VOTable output fields.

NameTable Head DescriptionUnitUCD
_r Dist. Distance to cone center deg pos.distance
cutout Aladin View the generating images in Aladin. The applet version of aladin might run out of memory for these links. The script links gives you an Aladin script for cut'n'paste. N/A N/A
dej2000 Dec Declination of barycenter (J2000) deg pos.eq.dec;meta.main
fieldKey Field CARS field designation N/A meta.id
fwhm FWHM Full width half max assuming a gaussian core deg phys.angSize
magaprG F.a. mag. g' Fixed aperture magnitude in the g' band Note 1 mag phot.mag;em.opt
magaprI F.a. mag. i' Fixed aperture magnitude in the i' band Note 1 mag phot.mag;em.opt
magaprR F.a. mag. r' Fixed aperture magnitude in the r' band Note 1 mag phot.mag;em.opt
magaprU F.a. mag. u* Fixed aperture magnitude in the u* band Note 1 mag phot.mag;em.opt
magaprZ F.a. mag. z' Fixed aperture magnitude in the z' band Note 1 mag phot.mag;em.opt
magAuto Auto. mag. Kron-like elliptical aperture magnitude Note 1 mag phot.mag
magErrAuto Err. Auto. mag. Error in Kron-like elliptical aperture magnitude mag stat.error;phot.mag
raj2000 RA Right ascension of barycenter (J2000) deg pos.eq.ra;meta.main
sgclass S/G S/G classifier output (0..1) N/A src.class.starGalaxy

VOTable Output Fields

The following fields are available in VOTable output. The verbosity level is a number intended to represent the relative importance of the field on a scale of 1 to 30. The services take a VERB argument. A field is included in the output if their verbosity level is less or equal VERB*10.

NameTable Head DescriptionUnitUCD Verb. Level
raj2000 RA Right ascension of barycenter (J2000) deg pos.eq.ra;meta.main 1
dej2000 Dec Declination of barycenter (J2000) deg pos.eq.dec;meta.main 1
carsid Id CARS object ID N/A meta.id;meta.main 5
magaprU F.a. mag. u* Fixed aperture magnitude in the u* band Note 1 mag phot.mag;em.opt 9
magaprG F.a. mag. g' Fixed aperture magnitude in the g' band Note 1 mag phot.mag;em.opt 9
magaprR F.a. mag. r' Fixed aperture magnitude in the r' band Note 1 mag phot.mag;em.opt 9
magaprI F.a. mag. i' Fixed aperture magnitude in the i' band Note 1 mag phot.mag;em.opt 9
magaprZ F.a. mag. z' Fixed aperture magnitude in the z' band Note 1 mag phot.mag;em.opt 9
magisoU Iso. mag. u* Isophotal magnitude in the u* band Note 1 mag phot.mag;em.opt 9
magisoG Iso. mag. g' Isophotal magnitude in the g' band Note 1 mag phot.mag;em.opt 9
magisoR Iso. mag. r' Isophotal magnitude in the r' band Note 1 mag phot.mag;em.opt 9
magisoI Iso. mag. i' Isophotal magnitude in the i' band Note 1 mag phot.mag;em.opt 9
magisoZ Iso. mag. z' Isophotal magnitude in the z' band Note 1 mag phot.mag;em.opt 9
_r Dist. Distance to cone center deg pos.distance 10
sgclass S/G S/G classifier output (0..1) N/A src.class.starGalaxy 15
fwhm FWHM Full width half max assuming a gaussian core deg phys.angSize 15
SeqNr No Running object number (in field) N/A meta.id 15
majorAxis RMS major Profile RMS along major axis deg phys.angSize.smajAxis 15
minorAxis RMS minor Profile RMS along minor axis deg phys.angSize.sminAxis 15
theta Pos. Ang. Position angle (east of north) (J2000) deg pos.posAng 15
mask In mask True if object is within an object mask N/A meta.code 15
magisoErrU Err. iso. mag. u* RMS error of isophotal magnitude in the u* band mag stat.error;phot.mag;em.opt 19
magaprErrU Err. F.a. mag. u* RMS error of fixed aperture magnitude in the u* band mag stat.error;phot.mag;em.opt 19
magisoErrG Err. iso. mag. g' RMS error of isophotal magnitude in the g' band mag stat.error;phot.mag;em.opt 19
magaprErrG Err. F.a. mag. g' RMS error of fixed aperture magnitude in the g' band mag stat.error;phot.mag;em.opt 19
magisoErrR Err. iso. mag. r' RMS error of isophotal magnitude in the r' band mag stat.error;phot.mag;em.opt 19
magaprErrR Err. F.a. mag. r' RMS error of fixed aperture magnitude in the r' band mag stat.error;phot.mag;em.opt 19
magisoErrI Err. iso. mag. i' RMS error of isophotal magnitude in the i' band mag stat.error;phot.mag;em.opt 19
magaprErrI Err. F.a. mag. i' RMS error of fixed aperture magnitude in the i' band mag stat.error;phot.mag;em.opt 19
magisoErrZ Err. iso. mag. z' RMS error of isophotal magnitude in the z' band mag stat.error;phot.mag;em.opt 19
magaprErrZ Err. F.a. mag. z' RMS error of fixed aperture magnitude in the z' band mag stat.error;phot.mag;em.opt 19
fieldKey Field CARS field designation N/A meta.id 20
fluxRadius Flux rad. Fraction-of-light radius pix N/A 21
magAuto Auto. mag. Kron-like elliptical aperture magnitude Note 1 mag phot.mag 25
magErrAuto Err. Auto. mag. Error in Kron-like elliptical aperture magnitude mag stat.error;phot.mag 25
xpos X Object position on exposure along x pix pos.cartesian.x;instr.det 25
ypos Y Object position on exposure along y pix pos.cartesian.y;instr.det 25
maglimU Lim. mag. u* Limiting magnitude at object's position in u* band Note 4 mag N/A 25
maglimG Lim. mag. g' Limiting magnitude at object's position in g' band Note 4 mag N/A 25
maglimR Lim. mag. r' Limiting magnitude at object's position in r' band Note 4 mag N/A 25
maglimI Lim. mag. i' Limiting magnitude at object's position in i' band Note 4 mag N/A 25
maglimZ Lim. mag. z' Limiting magnitude at object's position in z' band Note 4 mag N/A 25
goodFilters Good Filters with faint photometry for BPZ Note 3 N/A N/A 25
badFilters Bad Filters with bad photometry for BPZ Note 3 N/A N/A 25
faintFilters Faint Filters with faint photometry for BPZ Note 3 N/A N/A 25
extflags Ext. Flags Extraction Flags N/A N/A 29
z_b Z_B Photometric redshift N/A N/A 29
t_b T_B Mask value N/A N/A 29
odds z odds Confidence parameter for photometric redshift N/A N/A 29
NgoodFilters #Good Number of filters with good photometry for BPZ Note 2 N/A meta.code.qual 29
NbadFilters #Bad Number of filters with bad photometry for BPZ Note 2 N/A meta.code.qual 29
NfaintFilters #Faint Number of filters with faint photometry for BPZ Note 2 N/A meta.code.qual 29

Copyright, License, Acknowledgements

If you use the CARS products for your own research, please give proper acknowledgment to CADC, the CFHTLS project and the publication 2009A&A...493.1197E

VOResource XML (that's something exclusively for VO nerds)

Note 1

The fluxes and related quantities are the result of a statistical analysis that may yield three different results, viz.,

  • invalid measurement: value and error are both NULL

  • null detection (i.e., we are sure that nothing has been detected down to

    the local limit): value 99, error NULL

  • object detection: value anything but 99, valid error

This means that something like:

SELECT sum(magisoU)/count(*) FROM cars.srccat WHERE <whatever>

to estimate a mean magnitude will, in all likelihood, not give the correct result since values of 99 will be present in the sum.

Instead, use something like:

SELECT sum(magisoU)/count(*) FROM cars.srccat
        WHERE magisoErrU IS NOT NULL
        AND <whatever>
Note 2

The relation between NgoodFilters/NBPZ_GOODFILT, NbadFilters/NBPZ_BADFILT, NfaintFilters/NBPZ_LIMFILT is as follows:

The number of filters in which an object has 'reliable photometry' is given NgoodFilters. Reliable photometry means magnitude errors < 1 mag and an object brighter than the limiting magnitude.

NbadFilters is the number of filters in which an object has formal magnitude errors of 1 mag or larger.

NfaintFilters is the number of filters in which an object is fainter than the formal limiting magnitude.

If an object would fall into badFilters AND faintFilters it is listed under badFilters. Magnitude errors refer to isophotal magnitudes; the adopted limiting magnitude is defined in Sect. 2 of 2009A&A...493.1197E.

Note 3

For the meaning of good, bad, and faint, see note 2.

The goodFilters/BPZ_GOODFILT, badFilters/BPZ_BADFILT, and failtFilters/BPZ_LIMFILT columns contain a binary encoding of the filters:

Filter Bit Value
     

The columns contain the sum of the values of the filters fulfilling the corresponding criteria.

Note 4

For non-detected objects in a filter magnitude limit columns might contain an invalid value NaN (NULL in the database).