Astron. Astrophys. Suppl. Ser. 131, 105-114

Mixed early and late-type properties in the bar of NGC 6221: Evidence for evolution along the Hubble sequence?

J.C. Vega Beltrán¹ - W.W. Zeilinger² - P. Amico³ - M. Schultheis² - E.M. Corsini⁴ - J.G. Funes, S.J.⁵ - J. Beckman⁶ - F. Bertola⁵

Send offprint request: J.C. Vega Beltrán, jvega@astrpd.pd.astro.it, jvega@ll.iac.es

1 - Telescopio Nazionale Galileo, Osservatorio Astronomico di Padova, Padova, Italy
2 - Institut für Astronomie, Universität Wien, Wien, Austria
3 - European Southern Observatory, Garching bei München, Germany
4 - Osservatorio Astrofisico di Asiago, Dipartimento di Astronomia, Università di Padova, Asiago, Italy
5 - Dipartimento di Astronomia, Università di Padova, Padova, Italy
6 - Instituto de Astrofísica de Canarias, La Laguna, Spain

Received January 13; accepted February 18, 1998

Abstract:

Rotation curves and velocity dispersion profiles are presented for both the stellar and gaseous components along five different position angles ($\rm PA =5^{\circ}$, $50^{\circ}$, $95^{\circ}$, $125^{\circ}$, and $155^{\circ}$)of the nearby barred spiral NGC 6221. The observed kinematics extends out to about 80'' from the nucleus. Narrow and broad-band imaging is also presented. The radial profiles of the fluxes ratio [$\rm N \;{\scriptsize II}$] ($\lambda$ 6583.4 Å)/H$\alpha$ reveal the presence of a ring-like structure of ionized gas, with a radius of about 9'' and a deprojected circular velocity of about 280 $\rm km\;s^{-1}$.The analysis of the dynamics of the bar indicates this ring is related to the presence of an inner Lindblad resonance (ILR) at 1.3 kpc. NGC 6221 is found to exhibit intermediate properties between those of the early-type barred galaxies: the presence of a gaseous ring at an ILR, the bar edge located between the ILR's and the corotation radius beyond the steep rising portion of the rotation curve, the dust-lane pattern, and those of the late-type galaxies: an almost exponential surface brightness profile, the presence of H$\alpha$ regions along all the bar, the spiral-arm pattern. It is consistent with scenarios of bar-induced evolution from later to earlier-type galaxies.

Key words: galaxies: individual: NGC 6221 -- galaxies: kinematics and dynamics -- galaxies: structure -- galaxies: evolution -- galaxies: spiral