Max Planck Institute for Astronomy - Annual Report 2007

60 II. Highlights
V [km s –1 ] V c [km s –1 ]
V [km s –1 ] V c [km s –1 ]
150
100
50
0
–50
100
50
0
–50
NGC2403
0
0
V5
IC2574
V5
200 400 600
r
200
800 1000 1200
It is still unclear today whether all galaxies or at least
each galaxy type follows a universal “Schmidt Law” or
whether varying external conditions significantly influence
the relationship between star formation rate and gas
density. This question is of great significance for theories
and models of galaxy evolution.
If one experimentally pursues the question, then it
turns out to be useful to distinguish between the density
of atomic (HI) and molecular gas (H 2 ). tH i N g s is
especially suitable because of the high spatial resolution
that it can achieve and its homogenous sensitivity. An
astronomer team with Frank Bigiel, Adam Leroy, and
Fabian Walter discussed this question by using data from
the ga l e x Nearby Galaxy Survey and si N g s. From these
the star formation rate could be derived. In addition, CO
observations with the 30 m ir a m telescope were available
r
400 600
Fig. II.8.3: These rotation curves (blue) demonstrate how strongly
the derived radial velocities vary depending on the method
applied; above: the rotation-dominated galaxy, NGC 2403;
below: IC 2574, in which strongly asymmetrical line profiles
appear.
log(V halo / km s –1 )
2.5
2
1.5
1
0
0.5
log (V/km s –1 )
3
2
1
0
–22
–20 –18
M B [mag]
log(r) = 1
–16 –14
Fig. II.8.4: The rotation curves of all galaxies, sorted by absolute
luminosities of the galaxies with a logarithmic representation
of the rotation velocity.
which permitted the derivation of the molecular hydrogen’s
(H 2 ) density.
Fig. II.8.6 shows the results (above) for spiral galaxies
with H 2 -dominated central areas as well as (below) for
late spiral and dwarf galaxies. The values are listed in relation
to averaged radius and azimuth. One sees how star
formation rates and H 2 -density decrease in spiral galaxies
with growing distance, while the HI density does not follow
this trend. In Fig. II.8.7, these measurements for the
spiral galaxies were then plotted such that the SFR can
Fig. II.8.5: The studied galaxies’ rotation curves. tH i N g s measurements
(red), their averages (blue squares), cosmological
models (dotted curves), as well as a theoretical result by S. S.
McGaugh et al. from 2007 (upper dotted curve).
1
log(R/kpc)
1.5 2