J/A+A/700/A98 AXES-SDSS galaxy groups catalog (Kosowski+, 2025)
AXES-SDSS. Solving the puzzle of X-ray emission of optical galaxy groups via a
modified Hausdorff distance.
Kosowski J., Finoguenov A., Tempel E., Mamon G.A.
<Astron. Astrophys. 700, A98 (2025)>
=2025A&A...700A..98K 2025A&A...700A..98K (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, galaxy ; Galaxy catalogs ; X-ray sources ; Redshifts
Keywords: methods: data analysis - catalogs - surveys -
large-scale structure of Universe - X-rays: galaxies: clusters
Abstract:
The identification of X-ray and CMB sources as galaxy groups and
clusters is a prerequisite for cluster cosmology. But the
identification of groups, especially nearby ones, suffers from
projection effects which in turn affect the purity of the sample. In
X-rays, the position of the cluster can be given either by the peak of
the emission, or by the full information content of the cluster image.
Similarly, the optical center, or its member galaxies, can describe
the optical counterpart. With the progress of numerical simulations,
it is currently feasible to reproduce both the optical group
membership assignment and the behavior of the group outskirts in
X-rays, and therefore there is an opportunity to define a reproducible
group identification procedure. We performed two-way matching between
X-ray contours, drawn at a fixed surface brightness level
corresponding to a baryonic overdensity of ∼500, to the projected
galaxy positions using a modified Hausdorff distance (MHD). We used
the volume-limited SDSS group catalog to evaluate the purity and
completeness of the procedure, maintaining the constant performance of
the optical group finder with redshift. We find that an MHD of 0.631
Mpc provides 90% purity. This is a clear improvement over the methods
that rely on the optical counterparts' distance and richness. We study
the purity versus MHD and the completeness versus redshift and
velocity dispersion. Over half of nearby groups have X-ray emission,
even those with velocity dispersions as low as 200km/s; this has
never previously been demonstrated. The bulk of these groups follow
the same scaling relations as the groups with a small separation
between the optical and X-ray centers, removing feedback as an
explanation for the lack of matches in previous studies. Instead, the
problem is caused by over-merging in the optical group catalog
construction and source confusion in X-rays.
Description:
Catalogs of X-ray properties of SDSS groups from the volume limited
catalogs of Tempel et al. (2014A&A...566A...1T 2014A&A...566A...1T, Cat. J/A+A/566/A1).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
v180mpc.dat 131 83 X-ray properties of the AXES-SDSS 180Mpc group
catalog
v195mpc.dat 131 173 X-ray properties of the AXES-SDSS 195Mpc group
catalog
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See also:
J/A+A/566/A1 : Flux- and volume-limited groups for SDSS galaxies
(Tempel+, 2014)
Byte-by-byte Description of file: v180mpc.dat v195mpc.dat
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Bytes Format Units Label Explanations
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1- 5 I5 --- GroupID SDSS group identification number
(GROUP_ID) (1)
7- 15 I9 --- XCID Extended X-ray contour ID (XC_ID)
17- 25 F9.5 deg RAdeg Median right ascension of the matched part
of X-ray contour (J2000) (RA_X)
27- 34 F8.5 deg DEdeg Median declination of the matched part
of X-ray contour (J2000) (DEC_X)
36- 44 F9.5 deg RAOdeg Median right ascension of the matched part
of the optical group (J20 (RA_OPT)
46- 53 F8.5 deg DEOdeg Median declination of the matched part
of the optical group (J2000) (DEC_OPT)
55- 57 I3 --- Nmemb Number of spectroscopic members in
SDSS group catalog (NMEM)
59- 63 F5.3 --- zspec SDSS group redshift (ZSPEC)
65- 70 F6.1 km/s CluVdispGap Gapper estimate of the cluster
velocity dispersion (CLUVDISP_GAP)
72- 83 E12.6 10-7W LX0.1-2.4 Luminosity in the (0.1-2.4)keV band
of the cluster, aperture R500c (LX0124)
85- 96 E12.6 10-7W e_LX0.1-2.4 Uncertainty on LX0124 (ELX0124)
98-109 E12.6 mW/m2 Flux0.5-2 Galaxy cluster X-ray flux in
the 0.5-2.0keV band (FLUX052)
111-122 E12.6 mW/m2 e_Flux0.5-2 Uncertainty on FLUX052 (EFLUX052)
124-131 F8.5 arcmin Rae Apparent radial extent of X-ray emission
at the contour level (RA_E)
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Note (1): from Tempel et al. (2014A&A...566A...1T 2014A&A...566A...1T, Cat. J/A+A/566/A1).
Acknowledgements:
Alexis Finoguenov, alexis.finoguenov(at)helsinki.fi
(End) Patricia Vannier [CDS] 11-Jul-2025