The fountain of the luminous infrared galaxy Zw049.057 as traced by its OH megamaser

Le résumé fourni par la source

High-resolution ($ 0{{\overset{\prime\prime}{.}}}037{-}0{{\overset{\prime\prime}{.}}}13 $ [10 − 35 pc]) e-MERLIN (λ6 − 18 cm) and ($ 0{{\overset{\prime\prime}{.}}}024 $ [6.5 pc]) ALMA (λ1.1 mm) observations have been used to image OH (hydroxyl) and H2CO (formaldehyde) megamaser emission, and HCN 3 → 2 emission toward the nuclear (< 100 pc) region of the luminous infrared galaxy Zw049.057. Zw049.057 hosts a compact obscured nucleus (CON), and thus represents a class of galaxies that are often associated with inflow and outflow motions. Formaldehyde megamaser emission has been detected toward the nuclear region, ≲30 pc ($ 0{{\overset{\prime\prime}{.}}}1 $), and traces a structure along the disk major axis. OH megamaser (OHM) emission has been detected along the minor axis of the disk, ∼30 pc ($ 0{{\overset{\prime\prime}{.}}}1 $) from the nucleus, where it exhibits a velocity gradient with extrema of −20 km s−1 southeast (SE) of the disk and −110 km s−1 northwest (NW) of the disk. HCN 3 → 2 emission reveals extended emission, along the disk minor axis out to ∼60 pc ($ 0{{\overset{\prime\prime}{.}}}2 $). Analysis of the minor axis HCN emission reveals high-velocity features extending out to 600 km s−1, redshifted on the SE side and blueshifted on the NW side. We propose that the high-velocity HCN emission traces a fast (> 250 km s−1) and collimated outflow that is enveloped by a wide-angle and slow (∼50 km s−1) outflow that is traced by the OHM emission. Analysis of the outflow kinematics suggests that the slow wide-angle outflow will not reach escape velocity and will instead fall back to the galaxy disk, evolving as a so-called fountain flow, while the fast collimated outflow traced by HCN emission will likely escape the nuclear region. We suggest that the absence of OHM emission in the nuclear region is due to high densities there. Even though OHMs associated with outflows are an exception to conventional OHM emission, we expect them to be common in CON sources that host both OHM and H2CO megamasers.

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