J/ApJ/806/268 Cheshire Cat galaxies: redshifts and magnitudes (Irwin+, 2015)
The Cheshire Cat gravitational lens: the formation of a massive fossil group.
Irwin J.A., Dupke R., Carrasco E.R., Maksym W.P., Johnson L.,
White III R.E.
<Astrophys. J., 806, 268 (2015)>
=2015ApJ...806..268I 2015ApJ...806..268I (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, galaxy ; Gravitational lensing ; Photometry, SDSS ;
Redshifts
Keywords: galaxies: clusters: individual: SDSS J1038+4849 -
gravitational lensing: strong - X-rays: galaxies: clusters
Abstract:
The Cheshire Cat is a relatively poor group of galaxies dominated by
two luminous elliptical galaxies surrounded by at least four arcs from
gravitationally lensed background galaxies that give the system a
humorous appearance. Our combined optical/X-ray study of this system
reveals that it is experiencing a line of sight merger between two
groups with a roughly equal mass ratio with a relative velocity of
∼1350 km/s. One group was most likely a low-mass fossil group, while
the other group would have almost fit the classical definition of a
fossil group. The collision manifests itself in a bimodal galaxy velocity
distribution, an elevated central X-ray temperature and luminosity
indicative of a shock, and gravitational arc centers that do not
coincide with either large elliptical galaxy. One of the luminous
elliptical galaxies has a double nucleus embedded off-center in the
stellar halo. The luminous ellipticals should merge in less than a
Gyr, after which observers will see a massive 1.2-1.5x1014 M☉
fossil group with an Mr=-24.0 brightest group galaxy at its center.
Thus, the Cheshire Cat offers us the first opportunity to study a
fossil group progenitor. We discuss the limitations of the classical
definition of a fossil group in terms of magnitude gaps between the
member galaxies. We also suggest that if the merging of fossil (or
near-fossil) groups is a common avenue for creating present-day fossil
groups, the time lag between the final galactic merging of the system
and the onset of cooling in the shock-heated core could account for
the observed lack of well-developed cool cores in some fossil groups.
Description:
The optical observations (imaging and spectroscopy) were performed
with the Gemini Multi-Object Spectrograph (hereafter GMOS; Hook et al.
2004PASP..116..425H 2004PASP..116..425H) at the Gemini North Telescope in Hawaii, in queue
mode, as part of the program GN-2011A-Q-25. The direct images were
recorded through the r' and i' filters during the night of 2011 January 4,
in dark time, with seeing median values of 0.8" and 0.9" for the r'
and i' filters, respectively. The night was not photometric. Three 300 s
exposures (binned by two in both axes, with pixel scale of 0.146")
were observed in each filter. Offsets between exposures were used to
take into account the gaps between the CCDs (37 un-binned pixels) and
for cosmic ray removal.
Objects:
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RA (ICRS) DE Designation(s)
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10 38 43.58 +48 49 17.7 Cheshire Cat = [KAA2009] SDSS J1038+4849
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 87 98 Redshifts and Magnitudes of the Observed
Galaxies
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See also:
V/147 : The SDSS Photometric Catalogue, Release 12 (Alam+, 2015)
J/AJ/137/3942 : Fossil galaxy groups (La Barbera+, 2009)
J/ApJ/833/194 : Group of galaxies in gravitational lens fields (Wilson+, 2016)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1 A1 --- Group [ABC] Galaxy's group (1)
3- 6 A4 --- ID Source Extractor galaxy identifier (2)
8- 9 A2 --- Other Other ID
11- 12 I2 h RAh Hour of the Right Ascension (J2000)
14- 15 I2 min RAm Minute of the Right Ascension (J2000)
17- 22 F6.3 s RAs Second of the Right Ascension (J2000)
24 A1 --- DE- Sign of the Declination (J2000)
25- 26 I2 deg DEd Degree of Declination (J2000)
28- 29 I2 arcmin DEm Arcminute of Declination (J2000)
31- 36 F6.3 arcsec DEs Arcsecond of Declination (J2000)
38- 42 F5.2 mag r'mag ? Total magnitude in r'-band
44- 48 F5.2 mag i'mag ? Total magnitude in i'-band
50- 53 F4.2 mag r'-i ? Sloan r'-i color measured inside a fixed
aperture of 1.2"
55- 62 F8.6 --- z Redshift, corrected to the heliocentric system
64- 71 F8.6 --- e_z Uncertainty in z
73- 77 F5.2 --- R ? R value (Tonry & Davis 1979AJ.....84.1511T 1979AJ.....84.1511T)
79 I1 --- NEm [2/8]? Number of emission lines used to
calculate the redshift
81- 87 A7 --- Memb Membership flag (3)
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Note (1): Group as follows:
A = Galaxy within 0.5 r200 of the X-ray centroid of the Cheshire Cat;
B = Galaxy within 0.5-1.0 r200 of the X-ray centroid of the Cheshire Cat;
C = Galaxy within 1.0-1.5 r200 of the X-ray centroid of the Cheshire Cat.
Where r200 approximates the virial radius where the average mass density
inside this radius is 200 times the critical density of the universe.
Note (2): With B1-B23 from Bayliss et al. (2014ApJ...783...41B 2014ApJ...783...41B).
Note (3): Flag as follows:
Y/G1 = Member galaxy of G1, the eastern eye group;
Y/G1(E) = The G1 central galaxy;
Y/G2 = Member galaxy of G2, the western eye group;
Y/G2(W) = The G2 central galaxy;
N = Background/foreground galaxy.
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History:
From electronic version of the journal
(End) Prepared by Tiphaine Pouvreau [CDS] 19-Sep-2017