Supernovae and AGN driven galactic outflows

TL;DR

This paper derives analytical models for galactic winds driven by supernovae and black hole radiation, revealing how wind speeds and gas loss depend on galaxy mass, black hole influence, and star formation activity.

Contribution

It introduces new analytical solutions for galaxy wind dynamics considering both supernovae and AGN effects, highlighting the mass-dependent transition in outflow properties.

Findings

Winds from quiescent galaxies in the 10^{11.5} to 10^{12.5} Msun range cannot escape.

Wind speeds in low to intermediate mass galaxies are 400-1000 km/s, matching observations.

Massive galaxies with AGN have winds exceeding 1000 km/s.

Abstract

We present analytical solutions for winds from galaxies with NFW dark matter halo. We consider winds driven by energy and mass injection from multiple supernovae, as well as momentum injection due to radiation from a central black hole. We find that the wind dynamics depends on three velocity scales: (a) v_star \sim (\dot{E} / 2 \dot{M})^{1/2} describes the effect of starburst activity, with \dot{E}, \dot{M} as energy and mass injection rate in a central region of radius R; (b) \vbh ~ (G\mbh / 2 R)^{1/2} for the effect of a central black hole of mass \mbh on gas at distance R and (c) v_{s} =(GM_h/ 2Cr_s)^{1/2} which is closely related to the galaxy circular velocity, with C as a function of halo concentration parameter. We find the wind terminal speed to be 2 (v_star^2 +1.5(\Gamma -1) \vbh^2 -v_s^2)^{1/2}, where \Gamma is the ratio of force due to radiation pressure to gravity of the central black hole. We also find that: (a) winds from quiescent star forming galaxies cannot escape from 10^{11.5} \le M_h \le 10^{12.5}Msun galaxies, (b) circumgalactic gas at large distances should be present for galaxies in this mass range, (c) for an escaping wind, the wind speed in low to intermediate mass galaxies is ~ 400--1000 km/s, consistent with observed X-ray temperatures; (d) winds from massive galaxies with AGN have speeds \gtrsim 1000 km/s. We also find that the ratio [2 v_star ^2 -(1 -\Gamma) \vbh^2]/ v_c^2 dictates the amount of gas lost. Used in conjunction with an appropriate relation between \mbh and M_h, and an appropriate opacity of dust grains in IR (K band), this ratio becomes minimum at a certain halo mass scale (M_h ~ 10^{12--12.5} Msun) that signifies the cross-over of AGN domination in outflow properties from starburst activity at lower masses. We find that stellar mass for massive galaxies scales as M_star \propto M_h^{0.26},and for low mass galaxies, M_star \propto M_h^{5/3}.