Fast, dust-poor outflows in the local candidate dual AGN MCG-03-34-64 observed with VLT/ERIS

TL;DR

The study targets the nearby candidate dual AGN MCG-03-34-64, using VLT/ERIS J-band IFU data to map ionised gas kinematics and identify two fast outflows spatially coincident with proposed nuclei. Emission-line fitting with multiple Gaussians yields outflows with v10 ≈ −1.1–1.2×10^3 km s−1, vmax ≈ −1.6–1.8×10^3 km s−1, radii ≈ 67 pc, and masses ≈ (4±1)×10^5 M⊙, corresponding to dot M_out ≈ 20 M⊙ yr−1 per outflow; the outflows are blueshift-dominated and appear dust-poor, as inferred from coronal line behavior. Ancillary X-ray data reveal two Fe-Kα peaks whose comparable intensities strengthen the dual-AGN hypothesis, while optical coronal [Fe VII] emission suggests outflow-associated, dust-depleted gas. Although the ERIS results are consistent with a dual AGN picture, the paper notes that a single AGN with jet-ISM interactions could also explain some features, underscoring the need for deeper X-ray follow-up to reach a definitive conclusion.

Abstract

We present VLT/ERIS IFU J-band observations of MCG-03-34-64, a nearby (z = 0.0167) Seyfert galaxy hosting a candidate dual AGN system with a separation of ~100 pc between the nuclei. The observations cover, among others, the HeI1.083um, [FeII]1.257um and Pa$β$ emission lines, over a FoV of 3"x3"(~1x1 kpc$^2$). We analyse the ionised gas kinematics and identify two regions with enhanced velocity dispersion (W80~1500 km/s), suggestive of fast outflowing gas, spatially coincident with the position of the two candidate active nuclei. The spectra of the two outflows show a prominent blueshifted wing with velocities vmax ~ -1700 km/s corresponding to the highest 2-5 percentiles of samples of local AGN with similar bolometric luminosities. For the ionised phase of the two outflows, we derive comparable masses of $(4\pm1)\times 10^5$ $M_{\odot}$ and mass outflow rates of $20\pm5$ $M_{\odot}$/yr. The two distinct outflows could be associated with the two nuclei, or be generated by the interaction of the radio jet with the ISM. We also analyse the peculiar profile of the [Fe VII]6087A optical coronal line from an archival VLT/X-shooter spectrum. The comparison with the [NeV]3425A and [FeII]1.257um profiles indicates that [Fe VII] emission likely arises only from the outflow. The absence of the systemic component in [Fe VII] - unlike in [NeV], which has similar ionisation potential and critical density - suggests suppression of [Fe VII] due to iron depletion onto dust grains, while its detection in the outflow implies a lower dust content than in the host ISM. The additional information gained from the ERIS data are consistent with the scenario of a dual AGN, however further observations are required to confirm its nature.

Figures (18)

• Figure 1: HST, ERIS and Chandra images of MCG-03-34-64. Left: HST F647M continuum image, with contours at arbitrary flux levels. The grey rectangle shows the $3"\times3"$ ERIS FoV, while the green rectangle shows the size of the middle and right panels ($1"\times1"$). North is up and east to the left. Middle: Map of the total Pa$\beta$ flux from ERIS, showing the position of the sources detected at different wavelengths: the [O iii] peaks from HST are shown with blue crosses (+), the X-ray Chandra peaks with magenta circles indicating the position uncertainties, the HST continuum centroid (and ERIS continuum peak) with a lightblue triangle. Lavender contours show the radio emission at 33 GHz from VLA. Right: Map of the Fe-K$\alpha$ emission from Chandra. The image refers to the 6.2--6.6 keV rest-frame band at the 1/4 subpixel level, with a Gaussian smoothing with standard deviation of 1 image pixel.
• Figure 2: Integrated ERIS spectrum of MCG-03-34-64 extracted from an aperture of $r=0.5$ centred at the continuum peak. The blue-shaded regions show the part of the spectrum affected by telluric absorption. Vertical lines show the wavelength of the main emission lines. The best-fit model is shown in magenta, with individual Gaussian components (narrow, broad1, and broad2) shown in light blue, blue and orange, respectively.
• Figure 3: Fit of the optical X-shooter spectrum. Left: H$\beta$ and [O iii] lines. Right: H$\alpha$, [N ii] and [S ii] lines. Observed spectrum is in black; the magenta curve shows the best-fit total profile; the light-blue, blue and orange curves show the narrow, b1 and b2 components, respectively. The vertical dashed lines show the centroid positions of the difference components. The bottom panel shows the residuals.
• Figure 4: Map of the total flux, average velocity ($v50$) and line width $W80$ (width encompassing 80% of the flux) derived from total line profile fitted with three Gaussian components. From top to bottom: He i$\lambda1.083$$\mu$m, Pa$\beta$, [Fe ii]$\lambda1.257$$\mu$m. We show only spaxels with peak S/N in the total profile above 3. The blue $'+$' symbols show the positions of the [O iii] peaks; the purple circles show the position of the X-ray peaks. Velocity maps are shown with respect to the systemic redshift $z= 0.01677$. Contours in the first column show arbitrary flux levels, in the second column velocity contours are in intervals of 100 km s$^{-1}$.
• Figure 5: Velocity maps of the Pa$\beta$ emission line. From left to right: map of the percentiles velocities $v10$, the difference between $v10$ and the velocity at the peak of the line profile ($v_{peak}$), $v90$, and the difference $v90-v_{peak}$. We show only spaxels with peak S/N in the total profile above 3. The blue $'+$' symbols show the positions of the [O iii] peaks; the purple circles show the position of the X-ray peaks.Velocity maps are shown with respect to $z= 0.01677$.