J/ApJ/607/810 Companions to isolated elliptical galaxies (Madore+, 2004)
Companions to isolated elliptical galaxies: revisiting the Bothun-Sullivan
sample.
Madore B.F., Freedman W.L., Bothun G.D.
<Astrophys. J., 607, 8100 (2004)>
=2004ApJ...607..810M 2004ApJ...607..810M (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, galaxy ; Radial velocities
Keywords: Galaxies: Elliptical and Lenticular, cD - Galaxies: Statistics
Abstract:
We investigate the number of physical companion galaxies for a sample
of relatively isolated elliptical galaxies. The NASA/IPAC
Extragalactic Database (NED) has been used to reinvestigate the
incidence of satellite galaxies for a sample of 34 elliptical
galaxies, first investigated by Bothun & Sullivan (1977PASP...89....5B 1977PASP...89....5B)
using a visual inspection of Palomar Sky Survey prints out to a projected
search radius of 75 kpc. We have repeated their original investigation
using data cataloged in NED. Nine of these elliptical galaxies appear
to be members of galaxy clusters; the remaining sample of 25 galaxies
reveals an average of +1.0±0.5 apparent companions per galaxy within
a projected search radius of 75 kpc, in excess of two equal-area
comparison regions displaced by 150-300 kpc. This is significantly
larger than the +0.12±0.42 companions/galaxy found by Bothun & Sullivan
(1977PASP...89....5B 1977PASP...89....5B) for the identical sample. Making use of published
radial velocities, mostly available since the completion of the
Bothun-Sullivan study, identifies the physical companions and gives a
somewhat lower estimate of +0.4 companions per elliptical galaxy. This
is still 3 times larger than the original statistical study, but given
the incomplete and heterogeneous nature of the survey redshifts in NED,
it still yields a firm lower limit on the number (and identity) of
physical companions. An expansion of the search radius out to 300 kpc,
again restricted to sampling only those objects with known redshifts
in NED, gives another lower limit of 4.5 physical companions per galaxy.
(Excluding five elliptical galaxies in the Fornax Cluster, this
average drops to 3.5 companions per elliptical.) These physical companions
are individually identified and listed, and the ensemble-averaged
radial density distribution of these associated galaxies is presented.
For the ensemble, the radial density distribution is found to have a
falloff consistent with ρ∝R-0.5 out to approximately 150 kpc.
For non-Fornax Cluster companions the falloff continues out to the 300 kpc
limit of the survey. The velocity dispersion of these companions is found
to reach a maximum of 350 km/s at around 120 kpc, after which they fall
at a rate consistent with Keplerian falloff. This falloff may then
indicate the detection of a cut-off in the mass-density distribution
in the elliptical galaxies' dark matter halo at ∼100 kpc.
Description:
We start by repeating the Bothun & Sullivan (1977PASP...89....5B 1977PASP...89....5B)
(BS77) experiment as closely as can be reconstructed from their
published procedures. Their sample consisted of 34 elliptical galaxies
originally drawn from the Reference Catalogue of Bright Galaxies
(de Vaucouleurs & de Vaucouleurs 1964, Cat. VII/16), falling north of
DE=-45, and having expansion velocities V=<3000 km/s. This yielded a
master list of 90 elliptical galaxies, which was narrowed down to a
sample of 34 after applying the aforementioned isolation criterion.
Again, as in BS77, a projected search radius of 75 kpc was initially
adopted (assuming H0=75 km/s/Mpc and using the expansion velocities,
corrected for solar motion, as originally tabulated in BS77). For this
sample, the search radii ranged from 9 arcmin to 14 arcmin. To assess
the field-galaxy contamination rate around each target galaxy, we
searched two equivalent circular areas 20 arcmin-40 arcmin; to the
north and south of the primary position. The version of NED searched
had a public release date of 2003 June 19.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table2.dat 44 34 Companion-Galaxy Counts within R=75 kpc
of Isolated Ellipticals
table3.dat 57 211 Velocity-confirmed Companions within R=300 kpc
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See also:
VII/16 : Reference Catalogue of Bright Galaxies
(RC1; de Vaucouleurs+ 1964)
VII/112 : RC2 Catalogue (de Vaucouleurs+ 1976)
VII/155 : Third Reference Cat. of Bright Galaxies (RC3)
(de Vaucouleurs+ 1991)
J/A+AS/113/151 : Velocity dispersions for elliptical galaxies
(Di Nella+, 1995)
J/AJ/110/1032 : APM elliptical galaxies radial velocities (Muriel+ 1995)
J/other/Sci/348.418 : Isolated compact elliptical galaxies
(Chilingarian+, 2015)
Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 A4 --- --- [NGC ]
5- 8 I4 --- NGC [0584/6958] Central elliptical galaxy name
10- 12 I3 --- N75 [0/134] Total counts in the 75 kpc circular area
14- 15 I2 --- N [0/85] Field counts to the north
17- 18 I2 --- S [0/96] Field counts to the south
20- 24 F5.1 --- Excess Statistical excess
26- 29 F4.1 --- e_Excess Uncertainty in Excess
31- 34 F4.1 --- BS77 Number quoted on a galaxy-by-galaxy basis
by BS77 (Bothun & Sullivan 1977PASP...89....5B 1977PASP...89....5B)
36- 39 I4 km/s Vgsr [1141/2960] Galactic standard of rest velocity
41 I1 --- S75 [0/2] Number of radial velocity-confirmed
companions inside 75 kpc search radius
43- 44 I2 --- L150 [0/28] Number of radial velocity-confirmed
companions inside 150 kpc search radius
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Byte-by-byte Description of file: table3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 A4 --- --- [NGC ]
5- 8 I4 --- NGC [0584/6958] Central elliptical galaxy name
10- 12 I3 km/s sigma Radial-velocity dispersion
13 A1 --- n_NGC [n] Note on NGC (1)
15- 44 A30 --- Name Confirmed galaxy companion name
46- 47 A2 --- n_Name Flag on Name (2)
49- 52 F4.1 arcmin Rad ? Projected radial separation from elliptical
54- 57 I4 km/s DRV ? Differential radial velocity (3)
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Note (1): Note as follows:
n = Indicates no galaxy companions.
Note (2): Flag as follows:
* = Indicates an object that is within the Rad=75 kpc sample;
** = Indicates an object that is within a one-degree search radius, but
beyond the 300 kpc cut-off radius analyzed in this paper.
Note (3): In the sense of companion minus central elliptical.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Tiphaine Pouvreau [CDS] 16-Feb-2018