The imprint of AGN-driven outflows on the CGM: the case of Lyα nebulae around high-z quasars

TL;DR

This study tests the hypothesis that AGN-driven outflows help power and extend Lyα nebulae around high-redshift quasars by linking ISM-scale [OIII] outflow properties to CGM Lyα emission. Using VLT/ERIS and Gemini/GNIRS, the authors perform BLR-subtracted, spaxel-by-spaxel fits of [OIII] to map outflow extents, velocities, and energetics for six quasars at z ~ 2–3, and reanalyse existing Lyα nebulae data. They find that, once an outlier is removed, outflow kinetic power correlates with Lyα nebula size and aligns spatially with the brightest Lyα regions, supporting a scenario in which outflows create low-optical-depth channels or boost ionization in the CGM. They also show that for some systems photoionization of optically thin gas by the AGN can explain extended Lyα emission, indicating a mix of powering mechanisms. The work highlights the need for wider samples and future JWST wide-field observations to robustly establish ISM-CGM coupling and the role of AGN feedback in shaping Lyα halos.

Abstract

Some cosmological hydrodynamical simulations predict that outflows driven by active galactic nuclei (AGN) play a key role in powering the Ly$α$ nebulae observed around high-redshift quasars. In such simulations, AGN feedback seeded as powerful outflows leads to extended and luminous nebulae whose morphology and surface-brightness profiles accurately reproduce the observations, while suppressing AGN feedback leads to compact and faint nebulae. This link might arise from outflows opening up a channel for Ly$α$ photons to escape from the galactic nucleus to the circumgalactic medium (CGM). The main aim of this paper is to test this theoretical prediction using observations, by comparing the physical properties of outflows and Ly$α$ nebulae. We analyze integral-field unit data obtained with VLT/ERIS and GEMINI/GNIRS to trace the ionized gas in the interstellar medium (ISM) of a sample of six quasars at $z\sim2-3$, using the [O III] emission line. We detect powerful outflows in all the quasars of our sample, with velocities $>1500~\mathrm{km~s^{-1}}$ and kinetic energies $ \gtrsim 2\times10^{43}~\mathrm{erg~s^{-1}}$. Four of our quasars are spatially resolved and show signs of extended [O III] emission out to distances $>2$ kpc from the central supermassive black hole. When excluding one outlier, we find a positive monotonic correlation between the outflow power and the Ly$α$ nebulae size ($ρ=0.89$, $p=0.03$) and luminosity ($ρ=0.6$, $p=0.28$). Additionally, we find evidence of spatial alignment between the ionization cone and the inner and brightest regions of the Ly$α$ nebula. Our results provide tentative evidence in support of the theoretical prediction that AGN-driven outflows at ISM scales open a low-optical-depth path for central Ly$α$ photons to reach the CGM and create extended nebulae.

Figures (12)

• Figure 1: Distribution of the Ly$\alpha$ nebulae around the targets in our sample in the velocity dispersion–size plane. The gray dots represent the parent sample from which our sources were selected, namely arrigoni2019qso (FAB+19) and cai2019evolution. Triangular and diamond markers indicate the targets selected for our study at $z\sim2$ and $z\sim3$, respectively. The points are color-coded by the bolometric luminosity $L_{\mathrm{bol}}$.
• Figure 2: Top: Fit model for an integrated spectrum with an aperture of one pixel around the quasar center. The orange lines represent the [Oiii]$\lambda4959,5007$ NLR component. The green lines represent the outflowing component in the [Oiii]$\lambda4959,5007$ line. The H$\beta$ line is modeled with a broad component for the BLR shown in purple, a narrow component for the NLR shown in brown, and an additional broad component for the outflowing gas in pink. The FeII emission is shown in grey and the linear continuum in red. The total profile is shown as a solid blue line. Bottom: Residuals of the total fit. The gray-shaded bands in both panels correspond to remnant sky emission after applying the sigma-clipping algorithm mentioned in Sect. \ref{['sect:mod_BLR']}.
• Figure 3: Optimally extracted SB maps of the Ly$\alpha$ nebulae surrounding the quasars (see Sect. \ref{['sect:lya_props']}). The white, grey and black contours represent $2\sigma$, $5\sigma$ and $10\sigma$, respectively. The values of $\sigma$ are reported in Table \ref{['tab:Lya_props']}. The green cross in the center represents the position of the quasar, determined by estimating the photocentroid of a channel map in a wavelength where the Ly$\alpha$ line is not present. North is up and East is left.
• Figure 4: Ly$\alpha$ SB radial profiles. The red points show the average SB per radial annulus, while the grey line denotes the $2\sigma$ detection limit estimated for each annulus.
• Figure 5: COG of the [Oiii] (blue) and BLR normalized flux (red), in log scale. Targets Q0050+0051, Q0052+0140 and SDSSJ2319-1040 show evidence of spatially resolved [Oiii] emission.