Molecular gas in the warped galaxy NGC 4013
Ana I. Gómez de Castro 1 and
S. García-Burillo 2
Received 2 May 1996 / Accepted 7 November 1996
The edge-on spiral galaxy NGC4013 has been mapped in the J=2-1 and 1-0 lines of 12 CO with the IRAM 30m telescope (HPBW and ). CO emission is detected within a galactocentric radius, R (5.5 Kpc). The radial molecular gas distribution consists of a ring-like source (of radius 1.5 kpc), and a fast rotating nuclear disk (of radius 500 pc).
The CO velocity field, derived from the position-velocity diagram taken along the galaxy major axis, reveals the existence of a compact nuclear disk rotating at high velocities which has no HI counterpart. The derived rotation curve reaches 130 kms-1 in less than 250 pc. This high velocity regime for molecular gas is satisfactorily explained by an inner bar scenario. The bulge of NGC4013 is box-shaped at optical wavelengths, which suggests the existence of a non-axisymmetric potential in the inner disk. The distribution of CO emissivity itself towards the center suggests that the orbits of some molecular clouds are inclined with respect to the plane of the galaxy.
NGC4013 presents a distorted vertical distribution of matter (stars and gas): it has a box-shaped bulge, a thick optical disk with a warped plane, and a spectacular HI warp in the outer disk. The molecular gas disk vertical structure is not resolved in the 2-1 line. The slight inclination of the galaxy allows us to detect non-axisymmetric structures that are probably spiral arms. If so the estimated inclination angle is i= 5, in excellent agreement with the derived by Guthrie (1992) from optical data. We show that the warp of the stellar disk reported from optical measurements might be an artifact due to spiral arms seen in projection. We have not detected a CO counterpart of the HI warp.
Key words: galaxies: individual: NGC 4013 galaxies: ISM galaxies: kinematics and dynamics galaxies: structure radio lines: galaxies
Send offprint requests to: Ana I. Gómez de Castro
© European Southern Observatory (ESO) 1997
Online publication: June 5, 1998