Shooting for the stars: Jet-mode feedback and AGN jet deceleration from stellar mass-loading

TL;DR

This work develops a simple, momentum-conserving model to quantify jet deceleration by stellar wind mass-loading and the resulting direct feedback within galaxies. By combining MS and evolved-star mass-loss rates—derived from X-ray proxies and MIST evolutionary tracks—with a plane-fit model of radio AGN incidence, the authors predict the fraction of jets that decelerate inside hosts and the kinetic power made available for feedback. They find that mass-loading can decelerate at least about $\gtrsim 25\%$ of local jet power, with MS winds being more important in younger populations and AGB winds dominating the total mass loss in older populations; importantly, the decelerated power fraction is largely independent of host mass. The model reproduces the observed FR-II fraction in local samples for a reasonable range of jet parameters but cannot readily explain FR-II HERGs, likely due to geometric and host-morphology effects not captured in the current framework. These results imply that stellar winds provide a robust, age-dependent channel for direct jet feedback in galaxies and offer a tractable correction factor for global energetics calculations in galaxy evolution models.

Abstract

AGN jets are thought to be vital ingredients in galaxy evolution through the action of kinetic feedback; however, how narrow, relativistic outflows couple to galaxies remains an open question. Jet deceleration, which is often attributed to the entrainment of material, such as stellar winds, is thought to be necessary for efficient coupling. We present a simple model of jet deceleration due to stellar mass-loading to investigate the energy budget of direct jet feedback in the local Universe. To this end, we produce models of stellar mass-loss, including deriving a prescription for main sequence mass-loss rates as a function of stellar population age. We pair this mass-loss data with a parametric fit for radio AGN incidence, predicting that a majority of jets are decelerated within their hosts, and generally replicate the expected FR-II fraction in LERGs. We calculate that $\gtrsim$25\% of the jet power in the local Universe is efficiently decelerated and available for direct feedback within galaxies for any stellar population age. This fraction is largely invariant to the shape of the radio AGN incidence function at low jet Eddington fractions. The stellar mass-loss rate evolves significantly over time, approximately following $τ^{-1.1}$, leading to corresponding decreases in decelerated jet power in older stellar populations. Although asymptotic giant branch (AGB) stars dominate mass-loss at all ages, we find that their stochasticity is important in low-mass galaxies, and derive a critical jet power below which main sequence stars alone are sufficient to decelerate the jet.

Figures (9)

• Figure 1: Edge-on view of our planar fit (dashed line) to log incidence $\eta$ (normalized per dex in jet Eddington ratio) of radio AGN, as a function of log($\lambda$) and stellar mass.
• Figure 2: X-ray flux through the stellar surface as a function of stellar age. The black points show young open cluster data from Nunez2016, and the purple points show stars measured by Booth2017. Thin teal lines display the bootstraps as described in the text. The dark blue line and shaded region show median and 1$\sigma$ distribution of the bootstrapped data. The Sun is shown in yellow, at an age of 4.5 billion years, and the pink points show data from SanzForcada2010 for reference.
• Figure 3: Mass loss rate (scaled by galaxy stellar mass) as a function of stellar population age for a variety of stellar types. Low-mass main sequence stars (blue line) account for G-, K-, and M-type stars, while the cyan line shows mass loss from main sequence O- and B-type stars. The contribution of evolved stars are shown, including red giants (pink dotted), and AGB stars (purple dashed). Finally, the black curve shows mass loss leaving the IMF.
• Figure 4: Fraction of jets not decelerated by mass loading. The top panel shows the escape fraction of jets above the Igo2024 jet Eddington fraction range, for a range of opening angles. The horizontal dashed lines represent the FR-II fraction found in Igo2024 for varying stellar mass bins, though note that these measurements have large errors Igo2024. In the bottom panel, we use the extrapolated sample, for a ${\sim}2$ dex range of stellar masses. The bottom panel assumes $\theta=3\degree$, and both panels adopt $\Gamma_j=3$.
• Figure 5: Feedback power in decelerated jets. The top panel shows the mean kinetic power decelerated per stellar mass (i.e. specific feedback power) as a function of stellar population age, for selected stellar masses. The bottom panel shows the fraction of kinetic power in jets that is affected (i.e. the top panel divided by the total mean jet power for a given stellar mass). Throughout we use our fiducial model of $\theta=3\degree$, and $\Gamma_j=3$.