Kavli Affiliate: Sarah Church
| First 5 Authors: Gaspar Galaz, David T. Frayer, Matias Blaña, J. Christopher Howk, Thomas Puzia
| Summary:
We report on results from GBT/ARGUS $^{12}$CO(1-0) observations for the giant
low surface brightness galaxy Malin 1, which allow us to determine an upper
limit for its CO mass, and hence its molecular gas mass and molecular gas mass
surface density $Sigma_{H_2}$. Although we performed very deep observations
through 17 hours on source integration time, reaching a noise level of $sim
0.2$ mK (T$^{*}_{A}$) with a corresponding extended source CO limit (3$sigma$)
of 0.09 K km s$^{-1}$, 19 times more sensitive than previous works, we do not
detect the $^{12}$CO(1-0) emission line. However, the observations allow us to
estimate an upper limit (3$sigma$) for the CO mass of about $7.4 times 10^9$
M$_odot$ for the extended emission, and $1.4 times 10^8$ M$_odot$ for the
central part of the galaxy. With these figures we conclude that the molecular
gas surface density is lower than 0.3 M$_odot$ pc$^{-2}$, and the
corresponding molecular to atomic gas mass ratio is lower than 0.13. The
evidence suggests a quite different physical conditions for the interstellar
medium in Malin 1 compared to that of normal, high surface brightness spirals.
This, in one way to another, keeps an usual molecular gas tracer as CO hidden
from our observations, in spite of the diverse stellar and structural
properties of Malin 1 observed by several authors since more than 30 years.
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