Tasca Morphology Catalog v1.1 Definitions

COSMOS Overview

The COSMOS Archive serves data taken for the Cosmic Evolution Survey (COSMOS) project. COSMOS is an astronomical survey designed to probe the formation and evolution of galaxies as a function of cosmic time (redshift) and large scale structural environment. The survey covers a 2 square degree equatorial field with imaging by most of the major space-based telescopes (Hubble, Spitzer, GALEX, XMM, Chandra) and a number of large ground based telescopes (Subaru, VLA, ESO-VLT, UKIRT, NOAO, CFHT, and others).

IRSA serves the COSMOS archive using the following search methods:

Morphology Classification Overview

This catalog contains morphological information for 237,912 objects in the ACS catalog (Leauthaud et al. 2007, ApJS, 172, 219). Morphological parametric quantities have been computer using Morpheus 2005 (Abraham, R. G. et al. 2007, ApJ, 669, 184). SExtractor (Bertin & Arnouts) is used in a hot/cold configuration to optimize the deblending.

Morphological types are estimated in three different ways. Please acknowledge the proper paper according to the classification you use:

The morphological study is performed on HST-ACS images 0.03"/pix. Particular attention has been put in the tuning of the SExtractor parameters used to produce segmentation images. The reason is that Morpheus (Bob's code) computes morphological measurements starting from SExtractor segmentation images. It is therefore fundamental to reduce cases where galaxies are not deblended. Since this morphological catalog is HST-ACS selected we used the same hot/cold method as Leauthaud et al. (2007) in order to provide a one-one match with the official HST/ACS catalog.

To transform morphological parameters into morphological classes is not a trivial job. To help the user we provide three different morphological classification all obtained starting from structural parameters measured with Morpheus. Our preference is for the class named "class_int". This method has already been used in Cassata et al. (2007) and optimised for this release. The method is explained in Tasca et al. (2009) and Cassata et al. (in prep). Another classification based on a support vector machine is the parameter named "class_SVM". We refer to Huertas-Company et al.(2008) for further details. The parameter "class_linee" is the morphological class obtained with an optimisation of the standard and widely used Abraham et al. (1996) technique of subdividing the galaxy population into classes on the basis of position on an asymmetry versus concentration diagram.

Tasca Morphology Catalog v1.1 Overview

Objects in this catalog were selected from the 2005 release of the ground-based photometry catalog, with the criterion that their I-band (auto) magnitude had to be <= 23. The IDs, ra and dec provided in this catalog correspond to those of that 2005 release.

The catalog was cleared from stars and point sources as well as from all sources for which the morphology code did not run to completion. Objects that could have been rejected in that way include: objects close to the edge of the image, objects in dense tight groups and objects situated in the proximity of a bright source.


Further information can be found in Tasca et al. 2009, A&A, 503, 379

Tasca Morphology Catalog v1.1 Column Definitions

Gator serves the Tasca Morphology Catalog v1.1 (17 columns [12 delivered + 5 IRSA-created], 237,912 data rows). The column descriptions can be found below.

Column Name Data Type Units Description
ID int   Identification number
RA float degrees Right ascension
DEC float degrees Declination
ACS_MAG_AUTO float mag Auto magnitutde
AxialRatio float   Ratio of minor to major axis
R_HALF float pixels Half light radius
GINI float   Gini coefficient
CONC float   Concentration
ASYMMETRY float   Asymmetry
CLASS_INT int   Morphological class by Tasca and Cassata (1=Early type, 2=Spirals, 3=Irregulars)
CLASS_LINEE int   Morphological class based on CON and ASYMMETRY as used by Abraham 1996 (1=Early type, 2=Spirals, 3=Irregulars)
CLASS_SVM int   Morphological class based on support vector machine by Huertas-Company 2008 (1=Early type, 2=Spirals, 3=Irregulars)