Abstract
Starburst-driven galactic outflows in star-forming galaxies have been observed to contain complex thermal structures and emission line features that are difficult to explain by adiabatic fluid models and plasmas in photoionization equilibrium (PIE) and collisional ionization equilibrium (CIE). We previously performed hydrodynamic simulations of starburst-driven outflows using the MAIHEM module for non-equilibrium atomic chemistry and radiative cooling functions in the hydrodynamics code FLASH, and calculated emission lines in combined CIE and PIE conditions. In the present study, we consider time-dependent non-equilibrium ionization (NEI) states produced by our MAIHEM simulations. Through extensive CLOUDY calculations made with the NEI states from our hydrodynamic simulations, we predict the UV and optical emission line profiles for starburst-driven outflows in time-evolving non-equilibrium photoionization conditions. Our hydrodynamic results demonstrate applications of non-equilibrium radiative cooling for H II regions in starburst galaxies hosting cool outflows.
Highlights
Starburst-driven galactic-scale outflows are typically seen in star-forming galaxies [1, 2, 3, 4, 5, 6], which have complex multi-temperature structures ranging from cold (100–1000 K) in radio and IR [7, 8] to warm (∼ 104 K) in optical [9, 10], and hot (∼ 107 K) in X-ray observations [11, 12]
In catastrophic cooling (CC) mode, the temperature profile of the free wind is radiatively cooled, but it is without any hot bubble
Our findings confirm that radiative cooling is increased by raising massloading rate and reducing wind terminal velocity [23]
Summary
Starburst-driven galactic-scale outflows are typically seen in star-forming galaxies [1, 2, 3, 4, 5, 6], which have complex multi-temperature structures ranging from cold (100–1000 K) in radio and IR [7, 8] to warm (∼ 104 K) in optical [9, 10], and hot (∼ 107 K) in X-ray observations [11, 12]. The adiabatic solution of a free expanding wind can produce a hot bubble and a shell for an outflow model surrounded by the ambient medium [16]. A starburst-driven outflow could have four regions: freely expanding wind, hot bubble, shell, and ambient medium [13] (see Figure 1). Starburst-driven outflows have been investigated using fluid models with radiative cooling functions [20, 21], implying that cooling depends on the metallicity, mass-loading, and wind terminal velocity. A large grid of hydrodynamic simulations indicate that radiative cooling is stronger with higher mass-loading rate, and lower wind terminal velocity [23]. Emission lines predicted by this large grid of models were calculated using photoionization equilibrium (PIE) and collisional ionization equilibrium (CIE) that do not allow us to clearly identify the parameter space with strong radiative cooling [23]
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