Evidence for AGN Feedback in the Broad Absorption Lines and Reddening of Mrk 231

TL;DR

This paper presents evidence of active galactic nucleus (AGN) feedback in Mrk 231 through analysis of broad absorption lines and reddening, revealing complex interactions between quasar winds and nuclear starburst dust.

Contribution

It provides the first J-band spectrum of Mrk 231 and combines multi-wavelength data to demonstrate AGN-driven feedback affecting the nuclear starburst environment.

Findings

He I* and Na I broad absorption lines have similar profiles.

The absorber is approximately 100 pc from the central engine.

The data suggest AGN winds impact and accelerate dusty starburst material.

Abstract

We present the first J-band spectrum of Mrk 231, which reveals a large \ion{He}{1}*$\lambda 10830$ broad absorption line with a profile similar to that of the well-known \ion{Na}{1} broad absorption line. Combining this spectrum with optical and UV spectra from the literature, we show that the unusual reddening noted by \citet{veilleux13} is explained by a reddening curve like those previously used to explain low values of total-to-selective extinction in SNe Ia. The nuclear starburst may be the origin and location of the dust. Spatially-resolved emission in the broad absorption line trough suggests nearly full coverage of the continuum emission region. The broad absorption lines reveal higher velocities in the \ion{He}{1}* lines (produced in the quasar-photoionized \ion{H}{2} region) compared with the \ion{Na}{1} and \ion{Ca}{2} lines (produced in the corresponding partially-ionized zone). {\it Cloudy} simulations show that a density increase is required between the \ion{H}{2} and partially-ionized zones to produce ionic column densities consistent with the optical and IR absorption line measurements and limits, and that the absorber lies $\sim 100\rm \, pc$ from the central engine. These results suggest that the \ion{He}{1}* lines are produced in an ordinary quasar BAL wind that impacts upon, compresses, and accelerates the nuclear starburst's dusty effluent (feedback in action), and the \ion{Ca}{2} and \ion{Na}{1} lines are produced in this dusty accelerated gas. This unusual circumstance explains the rarity of \ion{Na}{1} absorption lines; without the compression along our line of sight, Mrk~231 would appear as an ordinary FeLoBAL.