NCSA Astronomy Digital Image Library
Project Abstract and Description
BIMA Observations of CO, HCN, and 13CO in NGC 1068
Tamara T. Helfer and Leo Blitz
Contact: Tamara T. Helfer
Email: thelfer@astro.berkeley.edu
Number of images in project: 4
References: 1995ApJ...450...90H
Abstract
We present high-resolution CO, HCN, and 13CO maps of the inner
arcminute of NGC 1068. The maps were made by combining observations
from the Berkeley-Illinois-Maryland Association (BIMA) interferometer
with single-dish data from the NRAO 12 m telescope; the maps therefore
do not suffer the usual interferometric problems associated with the
lack of small spatial frequency visibilities. Several features appear
in the CO map which have not previously been observed: (1) a firm
detection of CO line emission from a compact region centered on the
nucleus of the galaxy; (2) the detection of a triplet velocity
structure characteristic of kinematically independent regions shown on
the spectrum of the unresolved nuclear emission; and (3) the detection
of a molecular bar, the extent and position angle of which are in good
agreement with the 2 micron stellar bar. As seen in previous
high-resolution images, the most intense CO emission is nonnuclear at a
typical distance of 15 arcseconds from the center of NGC 1068. The
structure and kinematics of this emission imply that this gas is
distributed along the inner spiral arms and not in a ring. The bar's
kinematic influence on the molecular gas in the spiral arms is modest,
with typical ordered noncircular motions of < 30 km/s in the
plane of the galaxy. Interior to the spiral arms, the bar's influence
is more dramatic, as reflected by the twisted isovelocity contours in
the CO and HCN velocity fields. We derive pattern speed for the bar of
150--170 km/s/kpc. The position angle of the bar, ~63 degrees, is
close to that of the jet emanating from the nucleus, ~33 degrees.
The surface density of molecular gas within the central 100 pc
radius of NGC 1068 is the same as that in the central 200 pc radius in
the Milky Way to within the uncertainties. There is evidence for an
m = 1 kinematic mode in NGC 1068; we find the kinematic center of
rotation to be displaced from the radio continuum center by about
2.9\arcsec, or 200 pc. The HCN image, in agreement with recent results
from other interferometers and in contrast to the CO map, shows a
strong concentration of emission centered on the nucleus. The ratio of
integrated intensities of the HCN emission to that of CO is about 0.6
and is the highest ratio measured in the central region of any galaxy.
The 13CO emission follows the general distribution of the CO
emissio The average CO/13CO ratio of integrated intensities in the
spiral arms is about 13; this is similar to what is observed in the
centers of other nearby galaxies.
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