J/MNRAS/499/89 Identifying galaxy groups at high redshift I (Wang+, 2020)
Identifying galaxy groups at high redshift from incomplete spectroscopic data
I. The group finder and application to zCOSMOS.
Wang K., Mo H.J., Li C., Meng J., Chen Y.
<Mon. Not. R. Astron. Soc., 499, 89-105 (2020)>
=2020MNRAS.499...89W 2020MNRAS.499...89W (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies, group ; Redshifts ; Galaxy catalogs ; Optical
Keywords: methods: statistical - galaxies: groups: general - dark matter -
large-scale structure of Universe
Abstract:
Identifying galaxy groups from redshift surveys of galaxies plays an
important role in connecting galaxies with the underlying dark matter
distribution. Current and future high-z spectroscopic surveys, usually
incomplete in redshift sampling, present both opportunities and
challenges to identifying groups in the high-z Universe. We develop a
group finder that is based on incomplete redshift samples combined
with photometric data, using a machine learning method to assign halo
masses to identified groups. Test using realistic mock catalogues
shows that ≳90 per cent of true groups with halo masses
Mh≳1012M☉_h-1 are successfully identified, and that the
fraction of contaminants is smaller than 10 per cent. The standard
deviation in the halo mass estimation is smaller than 0.25dex at all
masses. We apply our group finder to zCOSMOS-bright and describe basic
properties of the group catalogue obtained.
Description:
In this paper, we have developed a group finder that is suitable for
identifying galaxy groups from incomplete redshift samples combined
with photometric data. A machine learning method is adopted to assign
halo masses to the identified groups. To test the impact of redshift
sampling effects, we have constructed realistic mock samples with
different redshift sampling schemes and applied our group finder to
them.
The zCOSMOS-bright is a spectroscopic galaxy survey obtained with the
ESO VLT (Lilly et al. 2007ApJS..172...70L 2007ApJS..172...70L, Cat. J/ApJS/172/70,
2009ApJS..184..218L 2009ApJS..184..218L, Cat. J/ApJS/184/218). It contains about 20000
galaxies with 15.0=<IAB=<22.5 in an area of about 1.7deg2 in the
COSMOS field and in the redshift range 0.1~<z~<1.2. The redshift
completeness, defined as the product of the redshift sampling rate and
the redshift success rate (Knobel et al. 2012ApJ...753..121K 2012ApJ...753..121K, Cat.
J/ApJ/753/121), is ∼48 per cent in the full zCOSMOS-bright area and
∼56 per cent in the central region. As discussed in de la Torre et al.
(2011MNRAS.412..825D 2011MNRAS.412..825D), the sampling effects for zCOSMOS, can be
modelled as a function of the right ascension (RA) and redshift. As an
application of our group finding pipeline, we identified galaxy groups
in the central region of the COSMOS area using both spectroscopic and
photometric galaxies at 0.1=<z=<1.0.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
galaxies.dat 68 30328 The galaxy catalogue
groups.dat 58 12002 The group catalogue
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See also:
J/ApJS/224/24 : The COSMOS2015 catalog (Laigle+, 2016)
J/ApJS/172/70 : zCOSMOS-bright catalog, DR3 (Lilly+, 2007)
Byte-by-byte Description of file: galaxies.dat
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Bytes Format Units Label Explanations
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1- 5 I5 --- ID [0/30327] Galaxy internal identifier
7- 12 I6 --- SID Galaxy identifier from the original survey
data release
14- 19 I6 --- L16ID Galaxy identifier in Laigle et al.
(2016ApJS..224...24L 2016ApJS..224...24L, Cat. J/ApJS/224/24)
21- 25 I5 --- Group ? Group internal identifier (1)
27- 35 F9.5 deg RAdeg Right ascension (J2000)
37- 43 F7.5 deg DEdeg Declination (J2000)
45- 51 F7.5 --- z Redshift (2)
53- 60 F8.5 [Msun] logMass Logarithm of the galaxy's stellar mass
62- 63 A2 --- tag Galaxy tag (3)
65- 68 F4.1 --- CC Redshift confidence flag (4)
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Note (1): -1 for photometric galaxy with no group assignment
Note (2): Photometric redshift if CC=-1 and spectroscopic redshift otherwise
Note (3): Galaxy tag as follows:
0 = satellite
1 = central
Note (4): Redshift confidence class, -1 for photometric redshift, others see
Lilly et al. (2007ApJS..172...70L 2007ApJS..172...70L, Cat. J/ApJS/172/70)
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Byte-by-byte Description of file: groups.dat
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Bytes Format Units Label Explanations
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1- 5 I5 --- Group ? Group internal identifier
7- 11 I5 --- ID Internal identifier of the central galaxy of
the group
13- 18 I6 --- L16ID Central galaxy identifier in Laigle et al.
(2016ApJS..224...24L 2016ApJS..224...24L, Cat. J/ApJS/224/24)
20- 28 F9.5 deg RAdeg Right ascension (J2000) of the group
centre (1)
30- 36 F7.5 deg DEdeg Declination (J2000) of the group centre (1)
38- 44 F7.5 --- z Redshift of the group (2)
46- 53 F8.5 [Msun] logMhalo Logarithm of the halo mass of the group
55 A1 --- tag [0/2] Group tag (3)
57- 58 I2 --- Richness Number of member galaxies in a group
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Note (1): The group's centre coordinates are defined as the average coordinates
of member galaxies weighted by the stellar mass
Note (2): The redshift of the group is defined as the average redshift of
member galaxies with spectroscopic redshift weighted by the stellar
mass
Note (3): Group tag as follows:
0 = group with only spectroscopic members
1 = group with photometric central and spectroscopic member
2 = group with only one photometric member
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History:
From electronic version of the journal
(End) Ana Fiallos [CDS] 14-Aug-2023