New observations of multiple molecular gas tracers in nearby early- and late-types
galaxies are presented and are used to study the physical conditions of the gas
within different morphological structures. The CO Tully-Fisher relation is also
constructed for a sample of star-forming galaxies at z = 0:05 - 0:3, probing their
mass and size evolution.
First, using single-dish observations of multiple locations within the nearby spiral
galaxy NGC 6946, extensive CO ladders are generated. The molecular line ratios
reveal a large variety of physical conditions across the molecular gas complexes,
depending primarily on the presence of current or recent star formation, itself
compared with that in the centre of the galaxy and other galaxies.
Second, interferometric observations of CO and high density molecular tracers in
the nearby edge-on early-type galaxies NGC 4710 and NGC 5866 are presented.
The gas kinematics reveals that the galaxies are barred, with most of the gas
contained within a nuclear disc and a distinct inner ring. Using the molecular
line ratios to probe the physical conditions of the gas, the nuclear discs appear
to have a more diffuse and hotter molecular medium than the inner rings, with
more embedded dense clumps. This suggests that the conditions in the nuclear
discs are similar to those in photo-dissociation regions, with intense UV radiation
from young stars and few cosmic rays. Indeed, the observed molecular line ratios
are also intermediate between those of spiral galaxies and starbursts, with even
milder star formation in the inner rings.
Third, homogeneously measuring the line widths in the CO spectra of star-forming
disc galaxies at z = 0:05 - 0:3, their Ks-band CO Tully-Fisher relation is constructed.
A comparison to local star-forming galaxy TFRs from the literature
provides mild evidence that our sample galaxies are ≈ 0:89 mag brighter than
local ones at a given rotational velocity, a result entirely consistent with our stellar
mass TFR, suggesting that our sample galaxies are more massive than local
ones by ≈ 0:35 dex. While they deserve further scrutiny, we suspect that these
results are due to our sample galaxies being more heavily star-forming (and thus
brighter at a given mass) than the comparison sample galaxies.</p