. The Formation of Catastrophically Cooling Outflows in Star-forming Regions via Non-equilibrium Radiative Cooling Ashkbiz Danehkar, M. S. Oey, and William J. Gray Department of Astronomy, University of Michigan, 1085 S. University Ave, Ann Arbor, MI 48109, USA Supported by NASA HST-GO-14080.002-A and HST-GO-15088.001-A. E-mail: danehkar@umich.edu ABSTRACT Multiwavelength surveys of star-forming regions suggest the presence of catastrophically cooling outflows. Mechanical feedback from super star clusters in starburst regions can produce cooling galactic-scale outflows, but outflows predicted by the adiabatic models cannot lead to strong cooling seen in several star-forming galaxies such as M82 and NGC 2366. We simulate starburst- driven outflows using the MAIHEM non-equilibrium cooling package built on the hydrodynamics code FLASH to determine the existence domains of catastrophic cooling, in the parameter space of the metallicity, mass-loading, kinetic heating efficiency, and ambient density. Although the metallicity has a major role in cooling, radiative cooling is significantly enhanced by increasing mass- loading and decreasing kinetic heating efficiency. Our results demonstrate the significance of radiative cooling for star-forming regions, where coolants could be responsible for the build-up of cold molecular hydrogen (H2) clumps leading to the star formation. Chevalier R. A. and Clegg A. W. 1985 Natur 317 44 Danehkar A., Oey M. S. and Gray W. J. 2021 ApJ, arXiv:2106.10854 Ferland G. J., Chatzikos M., Guzmán F. et al 2017 RMxAA 53 385 Fryxell B., Olson K., Ricker P. et al 2000 ApJS 131 273 Gray W. J., Oey M. S., Silich S. and Scannapieco E. 2019 ApJ 887 161 Heckman T. M., Armus L. and Miley G. K. 1990 ApJS 74 833 Leitherer C., Ekström S., Meynet G. et al 2014 ApJS 212 14 Oey M. S., Herrera C. N., Silich S. et al 2017 ApJL 849 L1 Oey M. S. and Massey P. 1995 ApJ 452 210 Silich S., Tenorio-Tagle G. and Rodríguez-González A. 2004 ApJ 610 226 Smith L. J., Westmoquette M. S., Gallagher J. S. et al 2006 MNRAS 370 513 Turner J. L., Consiglio S. M., Beck S. C. et al 2017 ApJ 846 73 Weaver R., McCray R., Castor J., Shapiro P. and Moore R. 1977 ApJ 218 377 REFERENCES CONCLUSION INTRODUCTION Starburst-driven galactic-scale outflows usually appear in starburst regions, which are created by stellar winds from OB associations in super star clusters (e.g., Heckman et al. 1990; Oey & Massey 1995). The physical properties of starburst-driven outflows have been modeled using the adiabatic assumptions (Weaver et al. 1977; Chevalier & Clegg 1985). According to Weaver et al. (1977), this type of outflows has four regions: (1) freely expanding wind, (2) hot bubble, (3) shell, and (4) ambient medium (see Fig. 1). The adiabatic solutions of the fluid model obtained by Chevalier & Clegg (1985) indicate that the density and temperature profiles in the freely expanding wind region decline with radius r as see Fig. 1. The semi-analytic radiative solutions studied by Silich et al. (2004) imply that there are departures from the adiabatic solutions (Fig. 1), i.e. catastrophic cooling. Observations of some starburst galaxies such as M82 and NGC 2366 support the presence of catastrophic cooling in some regions (Smith et al. 2006; Oey et al. 2017; Turner et al. 2017). FIG 1. From Left to Right, a schematic view an galactic-scale starburst-driven outflow, temperature and density profiles with 4 different regions refined by Weaver el al. (1997), followed by the analytic adiabatic and radiative solutions from Silich et al. (2004). HYDRODYNAMIC SIMULATIONS We conducted hydrodynamic simulations of starburst-driven outflows generated by feedback from a spherically symmetric super star cluster (SSC) characterized by the cluster radius (Rsc), mass deposition rate (Ṁ), wind terminal velocity (V∞), and stellar ionizing fields described by ionizing luminosity (Lion) and spectral energy distribution (SED) surrounded by ambient medium (density namb and temperature