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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 (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) 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) 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) (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
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) 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
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)
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.
History: From electronic version of the journal
(End) Prepared by [AAS], Tiphaine Pouvreau [CDS] 16-Feb-2018
The document above follows the rules of the Standard Description for Astronomical Catalogues.From this documentation it is possible to generate f77 program to load files into arrays or line by line

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