Evidence for axisymmetric halos: The case of IC 2006

Abstract

view Abstract Citations (157) References (26) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Evidence for Axisymmetric Halos: The Case of IC 2006 Franx, Marijn ; van Gorkom, J. H. ; de Zeeuw, Tim Abstract We present a new method to derive the shape of the potential from the velocity field of a gas ring, or a gas disk With a flat rotation curve. The method is an extension of previous work by Binney and Teuben, and it can detect deviations from axisymmetry at the level of a few percent. The velocity field of the ring or disk is expanded into harmonics, and we present analytic expressions which relate these harmonic terms to the intrinsic parameters, and the viewing angles. We show that both the velocity field and the geometry of the ring are necessary to give complete information on the shape of the potential in the plane of the ring. The velocity field alone gives incomplete information for small ellipticities. We present new neutral hydrogen data on the H I ring around the early-type galaxy IC 2006, which was discovered by Schweizer, van Gorkom, & Seitzer (1989). The new data show that the ring is filled and has a remarkably regular velocity field. Application of our method to this gas ring shows that the halo must be close to perfectly axisymmetric. We detect a nonsignificant ellipticity of the potential of 0.012 +/- 0.026. The 95% confidence limit on the ellipticity is 0.05. This implies that the potential is nearly circular in the plane of the ring. The analysis indicates that the circular velocity is nearly constant from 0.5 R_e_ to 6.5R_e_. We confirm that the M/L ratio in the outer parts increases (Schweizer et al. 1989). The stellar component probably has a strong disk. The data demonstrate that galaxies other than spiral galaxies have massive halos. The inferred shape of the halo can be contrasted to the strongly triaxial halos found in simulations of dissipationless halo formation. As suggested by Katz & Gunn (1991), the inclusion of baryonic matter in the simulations may be necessary to resolve this issue. Publication: The Astrophysical Journal Pub Date: December 1994 DOI: 10.1086/174939 Bibcode: 1994ApJ...436..642F Keywords: Astrodynamics; Astronomical Models; Disk Galaxies; Galactic Halos; Galactic Structure; Kinematics; Ring Galaxies; Computerized Simulation; Galactic Mass; H I Regions; Line Spectra; Mass Distribution; Mathematical Models; Radio Astronomy; Radio Spectra; Astrophysics; GALAXIES: INDIVIDUAL ALPHANUMERIC: IC 2006; GALAXIES: KINEMATICS AND DYNAMICS; GALAXIES: STRUCTURE; RADIO LINES: GALAXIES full text sources ADS | data products SIMBAD (2) NED (1)