The Polytropic Equation of State of Interstellar Gas Clouds

Models are presented for the polytropic equation of state of self-gravitating, quiescent interstellar gas clouds. A detailed analysis, including chemistry, thermal balance, and radiative transfer, is performed for the physical state of the gas as a function of density, metallicity, velocity field, and background radiation field. It is found that the stiffness of the equation of state strongly depends on all these physical parameters, and the adiabatic index varies between 0.2-1.4. The implications for star formation, in particular at high redshift and in starburst galaxies, and the initial stellar mass function are discussed.Comment: Accepted by Ap

Molecular Lines as Diagnostics of High Redshift Objects

Models are presented for CO rotational line emission by high redshift starburst galaxies. The influence of the cosmic microwave background on the thermal balance and the level populations of atomic and molecular species is explicitly included. Predictions are made for the observability of starburst galaxies through line and continuum emission between z=5 and z=30. It is found that the Millimeter Array could detect a starburst galaxy with ~10^5 Orion regions, corresponding to a star formation rate of about 30 Mo yr^{-1}, equally well at z=5 or z=30 due to the increasing cosmic microwave background temperature with redshift. Line emission is a potentially more powerful probe than dust continuum emission of very high redshift objects.Comment: 15 pages LaTex, uses aasms4.sty, Accepted by ApJ

Star formation near an obscured AGN: Variations in the initial mass function

The conditions that affect the formation of stars in radiatively and mechanically active environments are quite different than the conditions that apply to our local interstellar neighborhood. In such galactic environments, a variety of feedback processes can play a significant role in shaping the initial mass function (IMF). Here, we present a numerical study on the effects of an accreting black hole and the influence of nearby massive stars to a collapsing, 800 M_sun, molecular cloud at 10 pc distance from the black hole. We parametrize and study radiative feedback effects of hard X-rays emanating from the black hole broad line region, increased cosmic ray rates due to supernovae in starbursts, and strong UV radiation produced by nearby massive stars. We also investigate the importance of shear from the supermassive, 10^6-10^8 M_sun, black hole as the star-forming cloud orbits around it. We find that thermal pressure from X-rays compresses the cloud, which induces a high star formation rate early on, but reduces the overall star formation efficiency to about 7% due to gas depletion by evaporation. We see that the turn-over mass of the IMF increases up to a factor of 2.3, M_turn = 1-1.5 M_sun, for the model with the highest X-ray flux (160 erg s^-1 cm^-2), while the high-mass slope of the IMF becomes Gamma > -1. This results in more high mass stars and a non-Salpeter IMF. Cosmic rays penetrate deeply into the cloud and increase the gas temperature (50-200 K), which leads to a reduced formation efficiency of low mass stars. High cosmic ray rates increase the average mass of stars, thereby shifting the turn-over mass to higher values, i.e., up to several solar masses. Due to this process, the onset of star formation is also delayed. We conclude that the IMF inside active galaxies is different than the one obtained from local environments.Comment: 25 pages, 17 figure