2015A&A...574A..93L


Query : 2015A&A...574A..93L

2015A&A...574A..93L - Astronomy and Astrophysics, volume 574A, 93-93 (2015/2-1)

Dark matter deprivation in the field elliptical galaxy NGC 7507.

LANE R.R., SALINAS R. and RICHTLER T.

Abstract (from CDS):

Previous studies have shown that the kinematics of the field elliptical galaxy NGC 7507 do not necessarily require dark matter. This is troubling because, in the context of ΛCDM cosmologies, all galaxies should have a large dark matter component. Our aims are to determine the rotation and velocity dispersion profile out to larger radii than do previous studies, and, therefore, more accurately estimate of the dark matter content of the galaxy. We use penalised pixel-fitting software to extract velocities and velocity dispersions from GMOS slit mask spectra. Using Jeans and MONDian modelling, we then produce models with the goal of fitting the velocity dispersion data. NGC 7507 has a two-component stellar halo, with the outer halo counter rotating with respect to the inner halo, with a kinematic boundary at a radius of ∼110" (∼12.4kpc). The velocity dispersion profile exhibits an increase at ∼70" (∼7.9kpc), reminiscent of several other elliptical galaxies. Our best fit models are those under mild anisotropy, which include ∼100 times less dark matter than predicted by ΛCDM, although mildly anisotropic models that are completely dark matter free fit the measured dynamics almost equally well. Our MONDian models, both isotropic and anisotropic, systematically fail to reproduce the measured velocity dispersions at almost all radii. The counter-rotating outer halo implies a merger remnant, as does the increase in velocity dispersion at ∼70". From simulations it seems plausible that the merger that caused the increase in velocity dispersion was a spiral-spiral merger. Our Jeans models are completely consistent with a no dark matter scenario, however, some dark matter can be accommodated, although at much lower concentrations than predicted by ΛCDM simulations. This indicates that NGC 7507 may be a dark matter free elliptical galaxy. Regardless of whether NGC 7507 is completely dark matter free or very dark matter poor, it is at odds with predictions from current ΛCDM cosmological simulations. It may be possible that the observed velocity dispersions could be reproduced if the galaxy is significantly flattened along the line of sight (e.g. due to rotation); however, invoking this flattening is problematic.

Abstract Copyright:

Journal keyword(s): galaxies: individual: NGC 7507 - galaxies: kinematics and dynamics - galaxies: elliptical and lenticular, cD - galaxies: halos

Simbad objects: 9

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Number of rows : 9
N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2023
#notes
1 NGC 157 EmG 00 34 46.7879913696 -08 23 47.273597952   11.0 19.00 10.03 10.7 ~ 341 0
2 NGC 821 G 02 08 21.1358498040 +10 59 41.832436704   12.210 11.310 10.739 9.744 ~ 556 0
3 ACO S 373 ClG 03 38 30 -35 27.3           ~ 1717 0
4 NGC 3115 GiG 10 05 13.9270507008 -07 43 06.982712292   11   9.37   ~ 978 2
5 M 105 LIN 10 47 49.600 +12 34 53.87   10.56 9.76 9.12 8.18 ~ 1428 0
6 NGC 4278 LIN 12 20 06.8253868 +29 16 50.713486 11.54 11.09 10.16     ~ 917 2
7 NAME Virgo Cluster ClG 12 26 32.1 +12 43 24           ~ 6355 0
8 NGC 4494 GiP 12 31 24.0391348536 +25 46 30.071664120   10.55 9.74     ~ 462 0
9 NGC 7507 GiG 23 12 07.595 -28 32 22.70   11.60   9.98   ~ 171 0

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2022.11.28-12:25:38

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