Susanne Hüttemeister

The effect of violent star formation on the state of the molecular gas in M 82

We present the results of a high angular resolution, multi-transition analysis of the molecular gas in M 82. The analysis is based on the two lowest transitions of

Warm H

^{12}{\rm CO}

_\mathsf{2}

and the ground transition of the rare isotopes

in the Galactic center region

^{13}{\rm CO}

The Interaction between the Interstellar Medium and Star Formation in the Dwarf Starburst Galaxy NGC 4214

and

Radio Recombination Lines

{\rm C}^{18}{\rm O}

Line Radiation from Atoms

measured with the PdBI, the BIMA array and the IRAM 30 m telescope. In order to address the question of how the intrinsic molecular cloud properties are influenced by massive star formation we have carried out radiative transfer calculations based on the observed CO line ratios. The calculations suggest that the kinetic temperature of the molecular gas is high in regions with strong star formation and drops towards the outer molecular lobes with less ongoing star formation. The location of the highest kinetic temperature is coincident with that of the mid infrared (MIR) peaks which trace emission from hot dust. The hot gas is associated with low H 2 densities while the cold gas in the outer molecular lobes has high H 2 densities. We find that CO intensities do not trace H 2 , column densities well. Most of the molecular gas is distributed in a double-lobed distribution which surrounds the starburst. A detailed analysis of the conversion factor from CO intensity to H 2 column density shows that X CO depends on the excitation conditions. We find

Solutions for Chapter 16: Molecules in Interstellar Space

X_{\rm CO} \sim T_{\rm kin}^{-1} n(H_2)^{1/2}

Solutions for Chapter 4: Signal Processing and Receivers: Theory

, as expected for virialized clouds.

Solutions for Chapter 2: Electromagnetic Wave Propagation Fundamentals

We present ISO observations of several H2 pure-rotational lines (from S(0) to S(5)) towards a sample of 16 molecular clouds distributed along the central ~ 500 pc of the Galaxy. We also present C18O and 13CO J=1->0 and J=2->1 observations of these sources made with the IRAM-30m telescope. With the CO data we derive H2 densities of 10e(3.5-4.0) cm-3 and H2 column densities of a few 10e22 cm-2. We have corrected the H2 data for ~ 30 magnitudes of visual extinction using a self-consistent method. In every source, we find that the H2 emission exhibits a large temperature gradient. The S(0) and S(1) lines trace temperatures (T) of ~150 K while the S(4) and S(5) lines indicate temperatures of ~ 600K. The warm H2 column density is typically ~1-2 x 10e22 cm-2, and is predominantly gas with T=150 K. This is the first direct estimate of the total column density of the warm molecular gas in the Galactic center region. These warm H2 column densities represent a fraction of ~ 30 % of the gas traced by the CO isotopes emission. The cooling by H2 in the warm component is comparable to that by CO. Comparing our H2 and CO data with available ammonia NH3 observations from literature one obtains relatively high NH3 abundances of a few 10e(-7) in both the warm and the cold gas. A single shock or Photo-Dissociation Region (PDR) cannot explain all the observed H2 lines. Alternatives for the heating mechanisms are discussed.