An Analysis of AGN Feedback in the Compact Galaxy Group Stephan's Quintet

TL;DR

This paper probes AGN feedback in the compact group Stephan's Quintet by disentangling rotation, AGN-driven outflows, and tidal flows around NGC 7319 using spatially resolved long-slit spectroscopy from APO KOSMOS and HST imaging. It introduces a first biconical outflow model for the NLR of NGC 7319, constrained by BEAT Gaussian decompositions and 2D kinematic maps, and anchors ionization conditions with BPT diagnostics. The results show AGN-driven ionized gas out to ~6.3 kpc, with a turnover in velocity at ~3.1 kpc and a transition to tidal flows between ~2.4 and 6.3 kpc, highlighting how feedback operates within a dense group environment and interacts with tidal dynamics. These findings provide a framework to quantify feeding and feedback processes in compact groups and inform future, higher-resolution, multi-phase studies (e.g., MIRI IFU data).

Abstract

Compact galaxy groups are ideal laboratories for studying the effects of interactions between AGN and multiple nearby galaxies. Recent JWST observations of the nearby compact group Stephan's Quintet highlight tidal flows between the interacting galaxies as well as outflows from the active galaxy NGC 7319. To study the kinematics on a large scale throughout the group, we obtained spatially-resolved long-slit spectra of Stephan's Quintet at multiple slit positions with Apache Point Observatory's Kitt Peak Ohio State Multi-Object Spectrograph. We fit multiple Gaussians to the H$α$ $λ$6563 Å and [N II] $λλ$6548, 6583 Å emission lines to isolate the different kinematic components. We used the kinematics to develop the first biconical outflow model of the narrow-line region of NGC 7319. Using a combination of galactic rotation models, biconical outflow models, and kinematic maps of the ionized gas, we disentangled the outflows, rotation, and tidal flows in the group. We found outflow radial velocities up to 550 km s$^{-1}$ peaking at 2.6 kpc from the central supermassive black hole, and a transition from AGN-powered outflows to gravitationally-powered tidal flows at a projected distance between 2.4 -- 6.3 kpc. We performed a line ratio analysis and determined the gas shows Seyfert-like ionization out to 6.3 kpc (projected), which supports our finding that gas outside this radius is predominantly powered by tidal flows. Our separation of kinematic components in Stephan's Quintet will enable future studies of the physical conditions and dynamical forces in the ionized gas to better quantify the feeding and feedback processes of AGN in compact groups.

Figures (13)

• Figure 1: Stephan's Quintet, as imaged by the James Webb Space Telescope (Image credit: NASA, ESA, CSA, and STScI. Created with data from [JWST ERO 2732]https://www.stsci.edu/jwst/science-execution/program-information?id=2732 (PI: Pontoppidan) with NIRCam F090W, F150W, F200W, F277W, F365W, F444W filters and MIRI F770W, F1000W filters). Cluster members and systemic redshift velocities provided by the NASA/IPAC Extragalactic Database (NED) are labeled. The bridge, a key feature seen later in the kinematic plots (Figure \ref{['fig:2D_kinematic']}), is also labeled. The curved, shocked ridge of ionized gas between NGC 7319 and NGC 7318B is also clearly evident. Scale provided in the image is for NGC 7319.
• Figure 2: Left: Stephan's Quintet with KOSMOS slits overlaid to scale (underlying image same as Figure \ref{['fig:SQ']}). Pink slits are observations taken along the major (slit PA 150) and minor (PA 60) axes of NGC 7319, and along the outflowing axis of the NLR (PA 18). Blue slits are observations along the minor axis but offset from the nucleus in increments of 2. In these observations, the slits are adjacent but not overlapping. We obtained four observations offset to the southeast of the nucleus and five to the northwest. Right: A continuum-subtracted H$\alpha$ image from HST WFC3 of the nuclear region of NGC 7319, with the nucleus-centered slits overlaid. The outflowing axis is still highlighted in pink, while the major and minor axes are in white.
• Figure 3: Examples of BEAT fitting the H$\alpha$$\lambda$6563 Å $+$ [N II] $\lambda\lambda$6548, 6583 Å emission lines near the nucleus of NGC 7319. The grey curve represents the data, while the black curve shows the composite fit. The green line marks the continuum level, and the grey shaded regions are those chosen to calculate the continuum. The vertical purple dashed line is the redshifted rest wavelength of H$\alpha$. Top Left: The zero component fit for the data, with key lines labeled. Top Right: The one component fit. Bottom: The two component fit. The pink and blue curves are the two individual component fits used to create the composite fit. In this case, BEAT finds the two-component fit to be the best model, as indicated by the difference in ln(Z) values. Not shown is the 3-component fit, which had a more negative ln(Z) than the 2-component fit, and was therefore not chosen.
• Figure 4: Example pPXF fits for NGC 7319 at a position of 1032 from the nucleus. Black is the log-rebinned spectrum. The blue vertical line is the rest wavelength of the line. Red is the initial best fit to the spectrum using the stellar templates. Green points are the residuals. Top: Ca II $\lambda$8542.0 Å. Middle: Na I $\lambda\lambda$5889.9, 5895.9 Å (blended). The masked region (grey) is the He I $\lambda$5876 Å emission line. Bottom: Mg I b $\lambda\lambda$5167.3, 5172.6 Å (blended), and $\lambda$5183.6 Å.
• Figure 5: Top: Rotation Curve of NGC 7319 along its major axis. The red points are the averaged velocities from the Ca II, Na I, and Mg I b fits, with propagated errors. The grey curve is an interpolated fit. The shaded area of the curve is the average error of $\pm$15 km s$^{-1}$. Bottom: Velocity Dispersions, averaged across the three lines.