25 research outputs found
Theoretical modelling of two-component molecular discs in spiral galaxies
As recent observations of the molecular discs in spiral galaxies point to the
existence of a diffuse, low-density thick molecular disc along with the
prominent thin one, we investigate the observational signatures of this thick
disc by theoretically modelling two-component molecular discs in a sample of
eight nearby spiral galaxies. Assuming a prevailing hydrostatic equilibrium, we
set up and solved the joint Poisson's-Boltzmann equation to estimate the
three-dimensional distribution of the molecular gas and the molecular scale
height in our sample galaxies. The molecular scale height in a two-component
molecular disc is found to vary between pc, which is higher than what
is found in a single-component disc. We find that this scale height can vary
significantly depending on the assumed thick disc molecular gas fraction. We
also find that the molecular gas flares as a function of the radius and follows
a tight exponential law with a scale length of . We used the density solutions to produce the column density maps and
spectral cubes to examine the ideal observing conditions to identify a thick
molecular disc in galaxies. We find that unless the molecular disc is an
edge-on system and imaged with a high spatial resolution ( pc),
it is extremely hard to identify a thick molecular disc in a column density
map. The spectral analysis further reveals that at moderate to high inclination
(), spectral broadening can fictitiously introduce the
signatures of a two-component disc into the spectral cube of a single-component
disc. Hence, we conclude that a low inclination molecular disc imaged with high
spatial resolution would serve as the ideal site for identifying the thick
molecular disc in galaxies.Comment: Accepted for publication in A&
A slow bar in the dwarf irregular galaxy NGC 3741
Using the Tremaine-Weinberg method, we measure the speed of the HI bar seen
in the disk of NGC 3741. NGC 3741 is an extremely gas rich galaxy with an
{H\,{\sc i}} disk which extends to about 8.3 times its Holmberg radius. It is
also highly dark matter-dominated. Our calculated value of the pattern speed
is 17.1 3.4 km . We also
find the ratio of the co-rotation radius to the bar semi-major axis to be (1.6
0.3), indicating a slow bar. This is consistent with bar models in which
dynamical friction results in a slow bar in dark matter dominated galaxies.Comment: 7 pages, 4 figures, 2 tables Accepted for publlication in MNRA