A deep, multi-epoch Chandra HETG study of the ionized outflow from NGC 4051

Actively accreting supermassive black holes significantly impact the evolution of their host galaxies, truncating further star formation by expelling large fractions of gas with wide-angle outflows. The X-ray band is key to understanding how these black hole winds affect their environment, as the outflows have high temperatures ($\sim$10$^{5-8}$K). We have developed a Bayesian framework for characterizing Active Galactic Nuclei (AGN) outflows with an improved ability to explore parameter space and perform robust model selection. We applied this framework to a new 700 ks and an archival 315 ks Chandra High Energy Transmission Gratings observation of the Seyfert galaxy NGC 4051. We have detected six absorbers intrinsic to NGC 4051. These wind components span velocities from 400 km s$^{-1}$ to 30,000 km s$^{-1}$. We have determined that the most statistically significant wind component is purely collisionally ionized, which is the first detection of such an absorber. This wind has $T\approx10^7$ K and $v\approx880$ km s$^{-1}$ and remains remarkably stable between the two epochs. Other slow components also remain stable across time. Fast outflow components change their properties between 2008 and 2016, suggesting either physical changes or clouds moving in and out of the line of sight. For one of the fast components we obtain one of the tightest wind density measurements to date, log $n/$[cm$^{-3}$]=13.0$^{+0.01}_{-0.02}$, and determine that it is located at $\sim$240 gravitational radii. The estimated total outflow power surpasses 5% of the bolometric luminosity (albeit with large uncertainties) making it important in the context of galaxy-black hole interactions.