J/ApJ/954/36 Keck/DEIMOS redshifts for galaxies in ACO 56 (Wittman+, 2023)
A new galaxy cluster merger capable of probing dark matter: A56.
Wittman D., Stancioli R., Finner K., Bouhrik F., van Weeren R.,
Botteon A.
<Astrophys. J., 954, 36 (2023)>
=2023ApJ...954...36W 2023ApJ...954...36W
ADC_Keywords: Clusters, galaxy; X-ray sources; Radio sources; Galaxies, spectra;
Optical; Redshifts
Keywords: Galaxy clusters ; Dark matter ; Galaxy spectroscopy ;
Weak gravitational lensing ; Hubble Space Telescope
Abstract:
We report the discovery of a binary galaxy cluster merger via a search
of the redMaPPer optical cluster catalog, with a projected separation
of 535kpc between the brightest cluster galaxies (BCGs). Archival
XMM-Newton spectro-imaging reveals a gas peak between the BCGs,
suggesting a recent pericenter passage. We conduct a galaxy redshift
survey to quantify the line-of-sight velocity difference
(153±281km/s) between the two subclusters. We present weak-lensing
mass maps from archival Hubble Space Telescope Advanced Camera for
Surveys (HST/ACS) imaging, revealing masses of M200=4.5±0.8x1014
and 2.8±0.7x1014M☉ associated with the southern and northern
galaxy subclusters, respectively. We also present deep GMRT 650MHz
data revealing extended emission, 420kpc long, which may be an active
galactic nucleus (AGN) tail but is potentially also a candidate radio
relic. We draw from cosmological n-body simulations to find analog
systems, which imply that this system is observed fairly soon
(60-271Myr) after pericenter, and that the subcluster separation
vector is within 22° of the plane of the sky, making it suitable
for an estimate of the dark matter scattering cross section. We find
σDM/m=1.1±0.6cm2/g, suggesting that further study of this
system could support interestingly tight constraints.
Description:
The ACO 56 cluster was observed with the XMM-Newton European Photon
Imaging Camera (EPIC) in 2010 (Obs.ID 0650380401, PI: Allen). The
exposure times were 7121, 7127, and 5533 s for the MOS1, MOS2, and PN
instruments, respectively.
We observed A56 with the DEIMOS multi-object spectrograph at the W. M.
Keck Observatory on 2022 July 1 (UT). The 1200 line/mm grating was
tilted to observe the wavelength range ∼4200-6900Å. The total
exposure time was 45 (77) minutes on the first (second) mask, divided
into three (four) exposures.
We found 54 and 48 secure redshifts in the two masks, respectively,
for a total of 102. These are listed in Table 1. See Section 3 for
further details.
The Hubble Space Telescope Advanced Camera for Surveys (HST/ACS) F814W
archival observations analyzed (see Section 4 and Figure 1) can be
accessed via MAST doi:10.17909/d922-3v11
We were granted 15hr on the upgraded Giant Metrewave Radio Telescope
(uGMRT) for Band 4 (550-900MHz) observations of A56 (proposal code
42_069) with a much smaller synthesized beam size (4"). Observations
were taken on 2022 June 20 and 2022 June 24. See Section 6.
Objects:
----------------------------------------------------------
RA (ICRS) DE Designation(s)
----------------------------------------------------------
00 33 53.1 -07 52 10 A56 = ACO 56
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 36 102 Galaxy redshifts
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See also:
B/hst : HST Archived Exposures Catalog (STScI, 2007)
B/xmm : XMM-Newton Observation Log (XMM-Newton Science Operation Center, 2012-)
VII/110 : Rich Clusters of Galaxies (Abell+ 1989)
II/357 : The Dark Energy Survey (DES): Data Release 1 (Abbott+, 2018)
VII/292 : DESI Legacy Imaging Surveys DR8 photometric redshifts (Duncan, 2022)
J/ApJ/785/104 : redMaPPer. I. Algorithm applied to SDSS DR8 (Rykoff+, 2014)
J/A+A/594/A27 : Planck Sunyaev-Zeldovich sources (PSZ2) (Planck+, 2016)
J/A+A/598/A78 : The GMRT 150MHz all-sky radio survey (Intema+, 2017)
J/MNRAS/468/3322 : CoMaLit. V. Mass forecasting with proxies (Sereno+, 2017)
J/ApJ/882/69 : Radio relic merging cluster substructures (Golovich+, 2019)
J/A+A/647/A50 : Radio halos in mass selected clusters (Cuciti+, 2021)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 8 F8.6 deg RAdeg [8.4/8.6] Right ascension (J2000)
10- 18 F9.6 deg DEdeg [-8/-7.7] Declination (J2000)
20- 27 F8.6 --- z [0.12/0.8] Redshift
29- 36 F8.6 --- e_z [0.0001/0.0009] z uncertainty
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History:
From electronic version of the journal
(End) Emmanuelle Perret [CDS] 26-Sep-2025