J/A+A/704/A163 Galaxies in the area of Abell 267 (Zarattini+, 2025)
Fossil group origins. XIV: The radial orbits of A267.
Zarattini S., Biviano A., Bartalucci I., Aguerri J.A.L., Haines C.P.,
Girardi M.
<Astron. Astrophys. 704, A163 (2025)>
=2025A&A...704A.163Z 2025A&A...704A.163Z (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, galaxy ; Galaxies, photometry
Keywords: galaxies: star clusters: individual: A267
Abstract:
Fossil groups (FGs) are groups or clusters of galaxies with a single,
massive, central galaxy dominating their luminosity distribution, and
with a clear lack of L* galaxies. The physical reason for the large
magnitude gap ({DELTA}m12) in these systems is still a matter for
investigation. It could originate in an early formation of FGs,
followed by passive evolution in which all L* galaxies merged with the
central one, and/or it could be related to the fact that galaxies
accreting on the FGs move on very radial orbits, reach small
pericentric radii, and are merged on shorter timescales than regular
cluster galaxies. The latter properties could be linked with the
peculiar position of FGs within the cosmic web.
To shed light on the origin of FGs, we determine the velocity
anisotropy profile β(r) of the fossil cluster A267, which is
related to the orbital distribution of cluster galaxies. This is the
first individual FG for which the orbital distribution of its galaxies
is determined. We aim to confirm previous findings based on stack
samples that indicate that FGs, on average, host galaxies on more
radial orbits than normal clusters.
We started with a sample of 2315 redshifts for galaxies in the field
of A267 and we determined the membership for 329 of them. Of these,
174 are located within the virial radius of the cluster, and we used
them as tracers of the gravitational potential of the cluster to solve
the Jeans equation for dynamical equilibrium using the MAMPOSSt
algorithm. As a result, we obtained the cluster mass profile M(r) and
β(r). We also estimated M(r) from the X-ray data by applying the
hydrostatic equilibrium.
A comparison of the MAMPOSSt and X-ray-determined M(r)s allows us to
estimate the cluster hydrostatic mass bias, which we find to be
consistent with previous findings. The anisotropy parameter β(r)
indicates tangential orbits for the galaxies near the cluster centre
and increasingly radial orbits in the external regions. We checked
that our results are not affected by the presence of subclusters and
by the choice of the models for M(r) and β(r). Conclusions. The
A267 β(r) is very similar to that previously determined for a
stack of large {DELTA}m12 systems. Our analysis therefore confirms
that FGs are characterized by more radial orbits for their member
galaxies than the average cluster population. We speculate that this
different orbital distribution might be an important element in
creating a large {DELTA}m12.
Description:
Our sample was built by cross matching and merging different
catalogues available in the literature. The starting point was the
catalogue of redshifts obtained as part of the Local Cluster
Substructure Survey (LoCuSS). Three configurations were taken with the
Hectospec spectrograph on the 6.5m Multi-Mirror Telescope (MMT) in
Arizona in 2009, obtaining 504 redshifts. A267 was one of 30 galaxy
clusters at 0.15<z<0.30 that were observed with the Hectospec
instrument as part of the Arizona Cluster Redshift Survey (ACReS).
These data were used in Haines et al. (2013ApJ...775..126H 2013ApJ...775..126H,
2015ApJ...806..101H 2015ApJ...806..101H). Targets were selected using near-infrared
photometry obtained with the NEWFIRM imager on the 4m Mayall telescope
at the Kitt Peak Observatory in Arizona, as being located along the
J-K versus K-band colour-magnitude relation of galaxies at the
cluster redshift (see Haines et al. 2009ApJ...704..126H 2009ApJ...704..126H, for details).
The 504 redshifts in this catalogue reach a maximum distance of about
2.5 r200 from the centre of A267.
We then merged this first catalogue with the data obtained by Rines et
al. (2013), who used the same Hectospec instrument to get 1198
redshifts out to about 3.8 r200. A total of 251 galaxies from the
LoCuSS catalogue also have a redshift in the Rines et al.
(2013ApJ...767...15R 2013ApJ...767...15R, Cat. J/ApJ/767/15) catalogue. We were thus able
to add 947 redshift from the Rines et al. (2013ApJ...767...15R 2013ApJ...767...15R, Cat.
J/ApJ/767/15) catalogue to the LoCuSS one, getting a total of 1451
redshifts.
Then, since A267 was also observed as part of the FOGO project, we
cross matched this catalogue with the one obtained in the previous
paragraph. The photometric observations were taken at the Nordic Optic
Telescope (NOT) in the period 2008-2011, whereas the spectroscopic
observations were taken at the Telescopio Nazionale Galileo (TNG)
telescope in the period 2008-2010. In Zarattini et al.
(2014A&A...565A.116Z 2014A&A...565A.116Z), these data were matched with the Sloan Digital
Sky Survey Data Release 7 (SDSS-DR7, Abazajian et al.,
2009ApJS..182..543A 2009ApJS..182..543A) with the aim of completing the photometric and
spectroscopic samples. The resulting FOGO catalogue consists of 6632
entries, with redshifts for galaxies in the magnitude range
14.5≲r≲21.5. According to Table 1 of Zarattini et al.
(2014A&A...565A.116Z 2014A&A...565A.116Z), there are 111 galaxies with measured redshifts
within r200 of the A267 centre, of which 42 are considered to be
cluster members. The virial radius of A267, which we assume to
coincide with r200, is estimated to be 1.85Mpc by Zarattini et al.
(2014A&A...565A.116Z 2014A&A...565A.116Z), which corresponds to 8.4 arcmin given the
cluster redshift zA267=0.23. These values are updated in our dynamical
analysis (see Sect. 3). When cross matching the FOGO catalogue with
the previous one, built on the Hectospec observations, we were able to
add 25 redshifts to the sample, reaching a total of 1476 redshifts.
Finally, we included the Dark Energy Spectroscopic Instrument Data
Release 1 (DESI-DR1) data (DESI Collaboration 2025, arXiv:2503.14745)
in the area of A267. The DESI-DR1 dataset consists of more than 18
million spectra of which 13 millions are galaxies. We used data out to
about 3.5 r200, for a total of 1629 redshifts. Of those, 839 are new
redshifts, not available in the catalogue built in the previous
passages. It is worth noting, however, that almost all of these new
redshifts are outside the virial radius of the cluster. The final
spectroscopic catalogue contains 2315 galaxies in a circular area of
radius ∼4 r200 around the cluster centre (defined by the X-ray
analysis described in Sect. 2.2).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
catalog.dat 41 2315 Position and velocity for Abell 267 galaxies
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See also:
J/ApJ/767/15 : Hectospec Cluster Survey (HeCS) (Rines+, 2013)
J/A+A/527/A143 : RX J105453.3+552102 cluster SDSS photometry (Aguerri+, 2011)
J/A+A/618/A172 : Stellar populations of fossil galaxy groups (Corsini+, 2018)
Byte-by-byte Description of file: catalog.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1 I1 --- Cat [0/3] Velocity source catalog (1)
4- 11 F8.5 deg RAdeg Right ascension (J2000.0)
15- 21 F7.5 deg DEdeg Declination (J2000.0)
25- 31 I7 km/s Vel Reccessional velocity
37- 41 F5.2 mag rmag r-band magnitude
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Note (1): Velocity source catalog code as follows:
0 = ACReS
1 = Rines et al., 2013ApJ...767...15R 2013ApJ...767...15R, Cat. J/ApJ/767/15
2 = FOGO
3 = DESI
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Acknowledgements:
Stefano Zarattini, szarattini(at)cefca.es
References:
Aguerri et al., Paper I 2011A&A...527A.143A 2011A&A...527A.143A, Cat. J/A+A/527/A143
Mendez-Abreu et al., Paper II 2012A&A...537A..25M 2012A&A...537A..25M
Girardi et al., Paper III 2014A&A...565A.115G 2014A&A...565A.115G
Zarattini et al., Paper IV 2014A&A...565A.116Z 2014A&A...565A.116Z
Zarattini et al., Paper V 2015A&A...581A..16Z 2015A&A...581A..16Z
Kundert et al., Paper VI 2015MNRAS.454..161K 2015MNRAS.454..161K
Zarattini et al., Paper VII 2016A&A...586A..63Z 2016A&A...586A..63Z
Aguerri et al., Paper VIII 2018A&A...609A..48A 2018A&A...609A..48A
Corsini et al. Paper IX 2018A&A...618A.172C 2018A&A...618A.172C, Cat. J/A+A/618/A172
Zarattini et al., Paper X 2019A&A...631A..16Z 2019A&A...631A..16Z
Zarattini et al., Paper XI 2021A&A...655A.103Z 2021A&A...655A.103Z
Zarattini et al., Paper XII 2022A&A...668A..38Z 2022A&A...668A..38Z
Zarattini et al., Paper XIII 2023A&A...676A.133Z 2023A&A...676A.133Z
(End) Patricia Vannier [CDS] 05-Nov-2025