Multi frequency interferometer studies of active and starburst galaxies
Doctoral thesis, 2009
We report the results of a multi-frequency study of three interacting
galaxies: NGC 5218, NGC 1614 and NGC 4194 (the Medusa merger). These sources
belong to different classes of active and starburst galaxies.
NGC 5218 is a spiral in an early phase of its gravitational interaction
with a nearby elliptical galaxy, and is classified as a
pure LINER (Low Ionization Nuclear Emission-line Region).
NGC 1614 is more luminous and classified as both starburst and LINER
where the starburst activity takes place in a nuclear ring.
It is in a later stage of its interaction than NGC 5218 and is suggested
a merger between two unequal-mass spirals. The Medusa (NGC 4194) is
a merger of one spiral and one elliptical galaxy. It exhibits intense
star formation activity, and is classified as a starburst. In contrast to
NGC 1614 the starburst in the Medusa occurs on scales of several kpc.
We have used interferometric techniques at millimeter and decimeter
to image the molecular and atomic components in these sources. The 3mm J=1-0
transition of CO was imaged in emission and the 21cm atomic hydrogen line was
imaged in absorption toward the radio continuum source. Radio continuum
were also used to map the synchrotron (and thermal) emission associated with
the activity - and to attempt to establish the nature of the nuclear
activity: starburst or AGN (Active Galactic Nucleus). In particular, the goal
has been to establish whether the LINER characteristics of the two first
NGC 5218 and NGC 1614 are caused by starburst or AGN activity.
Sources with LINER activity make up a rather
inhomogeneous, and not yet well understood class, although LINER activity
is found in one third of the galaxies in the local bright galaxy population.
The LINER spectrum at optical wavelengths has similarities with
spectra from both Starburst galaxies and galaxies with AGNs, which raises
the question whether LINERs are typically driven by starbursts, AGN,
a combination, or something else.
We also report single dish observations of CO, HCN and HCO+ in NGC 5218
and interpret this in terms of dense gas content and nuclear activity.
With our multi-frequency observations we have studied the distribution and
dynamics of the neutral gas on scales ranging from several kiloparsecs
into the central few hundred parsecs.
In the central regions, we have detected significant deviations from
rotation, caused by supernova-driven large-scale outflows and/or nuclear
arms and bars. We present detailed atomic and molecular maps combined with
images to show that these velocity deviations are associated with regions
of intense star formation,
past- or ongoing. In general we find that, on the observed scales, the
and atomic gas phases are well mixed and trace the same dynamics. The lack
high-brightness radio cores indicate that the two LINER sources are
Sal EE, Hörsalsvägen 11, Chalmers University of Technology
Opponent: Prof. John. S. Gallagher, III, Dept. of Astronomy, University of Wisconsin, Madison, USA