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J/ApJ/697/1842      zCOSMOS 10K sample group catalog to z=1      (Knobel+, 2009)

An optical group catalog to z = 1 from the zCOSMOS 10 K sample. Knobel C., Lilly S.J., Iovino A., Porciani C., Kovac K., Cucciati O., Finoguenov A., Kitzbichler M.G., Carollo C.M., Contini T., Kneib J.-P., Le Fevre O., Mainieri V., Renzini A., Scodeggio M., Zamorani G., Bardelli S., Bolzonella M., Bongiorno A., Caputi K., Coppa G., de la Torre S., de Ravel L., Franzetti P., Garilli B., Kampczyk P., Lamareille F., Le Borgne J.-F., Le Brun V., Maier C., Mignoli M., Pello R., Peng Y., Montero E.P., Ricciardelli E., Silverman J.D., Tanaka M., Tasca L., Tresse L., Vergani D., Zucca E., Abbas U., Bottini D., Cappi A., Cassata P., Cimatti A., Fumana M., Guzzo L., Koekemoer A.M., Leauthaud A., Maccagni D., Marinoni C., McCracken H.J., Memeo P., Meneux B., Oesch P., Pozzetti L., Scaramella R. <Astrophys. J., 697, 1842-1860 (2009)> =2009ApJ...697.1842K
ADC_Keywords: Galaxy catalogs ; Redshifts Keywords: catalogs - galaxies: clusters: general - galaxies: high-redshift - methods: data analysis Abstract: We present a galaxy group catalog spanning the redshift range 0.1≲z≲1 in the ∼1.7deg2 COSMOS field, based on the first ∼10000 zCOSMOS spectra. The performance of both the Friends-of-Friends (FOF) and Voronoi-Delaunay method (VDM) approaches to group identification has been extensively explored and compared using realistic mock catalogs. We find that the performance improves substantially if groups are found by progressively optimizing the group-finding parameters for successively smaller groups, and that the highest fidelity catalog, in terms of completeness and purity, is obtained by combining the independently created FOF and VDM catalogs. The final completeness and purity of this catalog, both in terms of the groups and of individual members, compares favorably with recent results in the literature. The current group catalog contains 102 groups with N≥5 spectroscopically confirmed members, with a further ∼700 groups with 2≤N≤4. Most of the groups can be assigned a velocity dispersion and a dark-matter mass derived from the mock catalogs, with quantifiable uncertainties. The fraction of zCOSMOS galaxies in groups is about 25% at low redshift and decreases toward ∼15% at z∼0.8. The zCOSMOS group catalog is broadly consistent with that expected from the semianalytic evolution model underlying the mock catalogs. Description: zCOSMOS is a spectroscopic redshift survey (Lilly et al. 2007, cat. J/ApJS/172/70; S. J. Lilly et al. 2009, Cat. J/ApJS/184/218) covering the ∼1.7 deg2 COSMOS field (Scoville et al. 2007ApJS..172....1S). The redshifts are measured with the VLT using the VIMOS spectrograph. The mocks we use to calibrate and test our groupfinders are adapted from the COSMOS mock light cones (Kitzbichler & White 2007MNRAS.376....2K). File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table3.dat 48 800 Group catalog table4.dat 38 2310 Group galaxies
See also: VII/256 : Groups of Galaxies from CfA2 Redshift Survey (Mahtessian++, 2010) VII/86 : Groups of Galaxies. I. Nearby Groups (Huchra+ 1982) J/A+A/520/A42 : Galaxy groups in the VIMOS-VLT Deep Survey (Cucciati+, 2010) J/ApJS/184/218 : The zCOSMOS 10k-bright spectroscopic sample (Lilly+, 2009) J/ApJS/172/70 : zCOSMOS-bright catalog (Lilly+, 2007) J/ApJ/625/6 : Galaxy groups in the DEEP2 Galaxy Redshift Survey (Gerke+, 2005) Byte-by-byte Description of file: table3.dat
Bytes Format Units Label Explanations
1- 3 I3 --- GrpID Running identification number 5- 6 I2 --- N Group richness 8- 15 F8.4 deg RAdeg Right Ascension in decimal degrees (J2000) 17- 22 F6.4 deg DEdeg Declination in decimal degrees (J2000) 24- 29 F6.4 --- z Group redshift 31- 34 I4 km/s sigma Final velocity dispersion estimate σ 36- 43 E8.2 Msun Mfudge The "fudge" mass (1) 45- 48 F4.2 --- GRP1 [0,1] First Group purity parameter (2)
Note (1): The mass for a group with observed richness N and redshift z is simply given by: Mfudge=<Mhalo(N~,z)> where Mhalo(N~,z) denotes the mass of a halo at redshift z containing N∼ galaxies, N∼ is the observed richness of the group corrected for sampling and redshift success rate, and the angle brackets denote the average over the halos in the 24 mocks. We will denote this mass as "fudge mass" to indicate that it is calibrated with the mocks. See section 4.4 for further details. Note (2): The group purity parameter (GRPi) for i=1,2 is defined by the fraction of FOF members having a galaxy purity parameter GAP≥i (see Note (1) of table 4). For i=1 this is the fraction of FOF members that are also 1WM ("one-way-matched") members, and for i=2 that are also 2WM ("two-way-matched") members. See section 4.1 for further details.
Byte-by-byte Description of file: table4.dat
Bytes Format Units Label Explanations
1- 6 I6 --- zCOSMOS Galaxy identification 8- 10 I3 --- GrpID Group identification; see Table 3 12- 13 I2 --- N Group richness 15- 22 F8.4 deg RAdeg Right Ascension in decimal degrees (J2000) 24- 29 F6.4 deg DEdeg Declination in decimal degrees (J2000) 31- 36 F6.4 --- z zCOSMOS 10k-bright spectroscopic redshift (Lilly et al. 2009, Cat. J/ApJS/184/218) 38 I1 --- GAP [0,2] Galaxy purity parameter (1)
Note (1): GAP is a flag indicating if a certain group galaxy is contained simultaneously in catalogs from FOF (Friends-of-Friends algorithm; (Huchra & Geller 1982, Cat. VII/86)) and from VDM (Voronoi-Delaunay method adapted by Gerke et al. (2005, Cat. J/ApJ/625/6). For a certain FOF group galaxy GAP is defined as follows: 0 = If there is no VDM group containing this galaxy. 1 = If it is also contained in a VDM group, and the FOF group has a one-way match to this VDM group or this VDM group exhibits a one-way match to the FOF group. 2 = If it is contained in a VDM group, and the FOF group has a two-way match to this VDM group. See section 3.3.2 for further details.
History: From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 03-Jun-2011
The document above follows the rules of the Standard Description for Astronomical Catalogues.From this documentation it is possible to generate f77 program to load files into arrays or line by line

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