Observations of AGN-driven feedback: dynamics and ionization of the filaments in M87

Abstract

We present a comprehensive kinematic and ionization analysis of the warm ionized filaments ($10^4$ K) in M87, the central galaxy of the Virgo cluster, using new integral field spectroscopy from MEGARA (GTC) and SITELLE (CFHT). MEGARA targets the southeastern (SE) filaments (3 kpc from the nucleus), coincident with the only known molecular gas clump, and the far eastern (FE) filament (15 kpc), spatially isolated within an old radio lobe. SITELLE fully maps the filaments, offering the first complete views of their kinematics and excitation. Combined with archival ALMA, MUSE and Chandra data, these observations offer a multi-phase view of gas dynamics. The filaments display complex motions inconsistent with simple rotation. Velocity structure functions (VSFs) of the warm and cold gas in the central and SE filaments show consistent steep slopes (2/3) and flattening on small scales of a few hundred parsecs, possibly suggesting energy injection from Type Ia supernovae, though interpretation is method-limited. The FE filament shows a lower VSF amplitude, suggesting less active driving. ALMA CO emission is co-spatial and kinematically aligned with the ionized gas, the latter showing broader velocity dispersions. Ionization diagnostics indicate AGN-related processes (e.g., shocks) dominate, with higher-energy excitation near the radio lobes and lower-energy fossil feedback signatures in the FE filament. Finally, the filaments follow the same strong H$α$-X-ray surface brightness correlation seen in other clusters, supporting local thermal coupling between phases. However, the FE filament deviates from this trend, possibly due to uplift from past AGN outbursts or limitations in the analysis method.

Figures (17)

• Figure 1: Composite image of M87 combining SDSS optical data SDSS2022 with VESTIGE H$\alpha$ + [Nii] emission (in red), obtained with MegaCam/CFHT Boselli2018Boselli2019. The image reveals the central filamentary network and two isolated plumes extending northeastward at projected distances of $\sim$15 kpc and $\sim$18 kpc from the galaxy center. Previous MUSE WFM observations is outline in pink, the MEGARA pointings toward the SE and FE filaments are shown in cyan. The blue contour highlights the only known CO(2-1) molecular gas, detected in the SE filaments. Dotted grey contours indicate the 90 cm VLA radio continuum Owen2000. The field correspond to the full width and 60% of the height of the SITELLE FOV, centered on the galaxy.
• Figure 2: (A) MEGARA emission maps of [NII]$\lambda$6583 + H$\alpha$ for the first and second kinematic components of the SE filaments (continuum-subtracted), with North at the top and East to the left, as well as for the FE filament. The blue-shaded region outlines the area where the presence of two components if confirmed. Only spaxels with SNR$_{\text{H}\alpha} > 3$ are shown. CO(2-1) flux contours from ALMA (above the 3$\sigma$ level) are overlaid on the SE filament maps, ranging from $\sim$1 to $\sim$6 mJy beam$^{-1}$. All scale bars correspond to 5$\arcsec$. (B) Representative MEGARA spectra from selected spaxels: from left to right, one from the SE filament with a single component, one with two components, and one from the FE filament. A broken axis has been applied to better visualize the main spectral lines, which are marked by red dotted lines. For each spectrum, the fitted line profile (in red) is shown, along with individual components where applicable (blue dashed curves). The bottom panel displays the residuals of the fits, with the shaded region indicating the $\pm \epsilon_c$ interval.
• Figure 3: (A) SITELLE continuum-subtracted [NII] + H$\alpha$ emission map showing only spaxels with SNR$_{\text{H}\alpha} > 3$ and velocity error $\leq$ 30 km s$^{-1}$. (B) Corresponding [OII]$\lambda\lambda$3727-3729 emission map. The main panel displays all spaxels, while the inset shows a zoomed-in view of the central region with only spaxels satisfying SNR$_{\text{[OII]}} > 3$. In both panels, the MEGARA FOVs targeting the SE and FE filaments are outlined in blue. The displayed maps represent approximately 10% of SITELLE's full FOV. All scale bars correspond to 1$\arcmin$. Maps are shown with 2 $\times$ 2 binning and a logarithmic color scale to enhance contrast between bright and faint emission.
• Figure 4: (A) SITELLE velocity map showing spaxels with SNR$_{\text{H}\alpha} > 3$ and velocity uncertainties $\leq$ 30 km s$^{-1}$ (2 $\times$ 2 binning). (B) Rotating thin-disk model computed for the combined gravitational potential of the central SMBH and the stellar bulge, based on the best-fit model from Osorno2023. (C) Residual map showing the difference between the observed velocities and the rotation model. For each panel, faint solid white/black lines centered on the nucleus mark the disk's kinematic P.A. (45) and its perpendicular axis. MEGARA FOVs targeting the SE and FE filaments are outlined in blue, and the existing MUSE WFM observations is outlined with a white/black dashed box. The color scale is consistent across all panels and each scale bar corresponds to 1$\arcmin$.
• Figure 5: (A) Velocity dispersion maps and (B) velocity maps of the SE (top) and FE (bottom) filaments, obtained with MEGARA (left) and SITELLE (right), showing only spaxels with SNR$_{\text{H}\alpha} > 3$. North is up and East is to the left. For the SE filaments in MEGARA, the main maps display the first component, while separate maps display the second component and, for the velocity map, the single-component fit within the two-component region (outlined). SITELLE maps include only a single velocity component. Color scales are consistent across maps of the same type. All scale bars correspond to 5$\arcsec$. (C) VSFs for both pointings, derived from SITELLE and MEGARA data. Shaded areas indicates bins with an insufficient number of pairs ($< 20\%$ of the maximum pair count). Two reference slopes are shown: 1/3 (Kolmogorov turbulence) and 2/3 (steeper slope). Error bars are displayed, although in some cases they are smaller than the symbol size. The vertical dotted and solid lines indicate the SITELLE seeing limit ($\sim$1.2$\arcsec$) and the half the height of the MEGARA FOV, respectively.