Astronomy and Astrophysics – Astronomy
Scientific paper
May 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001aj....121.2499s&link_type=abstract
The Astronomical Journal, Volume 121, Issue 5, pp. 2499-2514.
Astronomy and Astrophysics
Astronomy
8
Galaxies: Nuclei, Galaxies: Individual: Ngc Number: Ngc 615, Galaxies: Evolution, Galaxies: Structure, Galaxies: Kinematics And Dynamics
Scientific paper
The results of a complex photometric and spectral investigation of the regular Sb galaxy NGC 615 are presented. The observations were made with the 6 m, 1 m, and 0.6 m telescopes of the Special Astrophysical Observatory RAS (Nizhnij Arkhyz, Russia) and the 1.5 m ESO telescope (La Silla, Chile). The analysis of the radial brightness profiles reveals the existence of at least two decoupled exponential components; the parameters of the outer component are typical for the global disks of Sb galaxies, and the inner component seen in the radius range 9"-30" (1.0-3.5 kpc) is distinguished by compactness and high surface brightness. A combination of two-dimensional velocity fields for stars and ionized gas in the central part of the galaxy and of the long-slit velocity profiles along the major axis up to the optical border of NGC 615 provides some interesting findings. In the very center, R<3" (0.3 kpc), stars and gas rotate together, and the dynamical and photometric major axes are turned with respect to the global line of nodes; we conclude that an inclined circumnuclear disk is detected. In the bulge, R=3"-6" (0.35-0.75 kpc), the stellar velocity dispersion is more than 100 km s-1, the stars rotate twice as slowly as the ionized gas, and a counterrotating gaseous component is observed. In the inner exponential component the stars rotate together with the ionized gas, and the stellar velocity dispersion drops to about 50 km s-1. As the photometric major axis of this component is turned with respect to the line of nodes, we call it ``an oval inner disk.'' The mean age of the stellar populations in the nucleus and in the inner disk beyond its H II regions is 5 Gyr, while the bulge is much older. Both the chemically decoupled nucleus of NGC 615 and the inner disk probably formed the bulk of their more luminous stars in a secondary burst of star formation, perhaps provoked by the close passage of another galaxy some gigayears ago. Based on observations collected with the 6 m, 1 m, and 0.6 m telescopes of the Special Astrophysical Observatory (SAO) of the Russian Academy of Sciences (RAS) and with the 1.52 m ESO telescope at La Silla.
Alvarado Franklin
Sil'chenko Olga K.
Vlasyuk V. V.
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