Spatially Resolved UV Diagnostics of AGN Feedback: Radiation Pressure Dominates in a Prototypical Quasar-driven Superwind

Abstract

Galactic-scale winds driven by active galactic nuclei (AGN) are often invoked to suppress star formation in galaxy evolution models, but the mechanisms driving these outflows are hotly debated. Two key AGN feedback models are (1) radiation pressure accelerating cool gas and (2) a hot outflowing wind entraining the ISM. Highly ionized emission-line diagnostics represent a powerful means of differentiating these scenarios because of their sensitivity to the expected compression of the ISM clouds by the hot wind. Here, we report the first spatially resolved UV emission spectroscopy of a prototypical (radio-quiet) quasar-driven superwind around the obscured quasar SDSS J1356+1026 at z = 0.123. We observe ratios of O VI/C IV, N V/C IV, and C IV/He II that are remarkably similar for outflowing gas clouds 100 pc and ≈ 10 kpc from the nucleus. Such similarity is expected for clouds with AGN radiation pressure dominated dynamics. Comparing the observed line emission to models of clouds in balance with radiation pressure and/or a hot wind, we rule out the presence of a dynamically important hot wind and constrain the ratio of hot gas pressure to radiation pressure to P hot /P rad 0.25 both at 100 pc and ≈ 10 kpc from the nucleus. Moreover, the predictions of the radiation pressure confined cloud models that best fit observed UV line ratios are consistent with the observed diffuse X-ray spectrum. These results indicate that this AGN superwind is driven by radiation pressure or was driven by a hot wind that has since dissipated despite on-going AGN activity.

AGN-driven galactic outflows: comparing models to observations

“…2016). Spatially resolved UV emission spectroscopy of the outflow in the obscured quasar SDSS J1356+1026 indicates that the UV line ratios are very similar in the nuclear region (r 100 pc) and on galactic scales (r ∼ 10 kpc; Somalwar et al 2020). These observations constrain the ratio between hot gas pressure and radiation pressure to P hot /P rad 0.25 at all radial scales, suggesting that radiation pressure is likely at the origin of the observed outflowing gas in SDSS J1356+1026.…”

“…The relative importance of the hot wind and radiation pressure can also be empirically constrained by emission line diagnosis. The line ratios observed in quasar outflows suggest that radiation pressure can dominate hot gas pressure over a wide range of radii (Stern et al 2016;Somalwar et al 2020).…”

Radiation pressure confinement -- V. The predicted free-free absorption and emission in active galactic nuclei

“…The results above add to earlier evidence on that RPC sets the gas density in AGN. Specifically, the NLR density radial dependence and its ionization structure (Dopita et al 2002;Stern et al 2014a;Davies et al 2016), the BLR emission radial dependence (Baskin et al 2014a;Netzer 2020), the Broad Absorption Lines ionization structure (Baskin et al 2014b;Mas-Ribas & Mauland 2019), the X-ray lines absorption measure distribution (Stern et al 2014b), the X-ray lines emission measure distribution (Bianchi et al 2019), and galactic scale winds (Stern et al 2016;Mas-Ribas 2019;Somalwar et al 2020). These results suggest that generally there is no additional significant confining mechanism for ionized gas in AGN, such as ambient magnetic or thermal pressure.…”

Towards modelling ghostly damped Ly αs

“…Telfer et al (2002) indicates that the Lyman-and O blend has a flux of approximately 0.2 that of the Lyman-one. In Somalwar et al (2020), the authors present a quasar spectrum where the Lyman-and O doublet emissions are not blended and have a flux equal to 2.5% and twice 7.5% of the Lyman-emission, respectively. We use the latter numbers.…”