Optical emission-line profiles were evaluated in order to explore the structure of galactic nuclei containing H _ { 2 } O megamaser sources .
Long-slit spectra of IC 2560 , NGC 1386 , NGC 1052 and Mrk 1210 were obtained at \sim 100 km/s spectral and \sim 2 \arcsec \times 2 \arcsec spatial resolution .
The following individual properties of the objects were found : The active nucleus of IC 2560 ( innermost \pm 2 \arcsec ) emits lines typical for a high-ionization Seyfert-2 spectrum albeit with comparatively narrow profiles ( FWHM \sim 200 km/s ) .
Line wings are stronger on the blue side than on the red side suggesting outflow .
The central velocity gradient fits into the general velocity curve of the galaxy .
Attributing it to a rotating disk coplanar with the galaxy leads to a Keplerian mass of \sim 10 ^ { 7 } M _ { \odot } inside a radius of 100 pc .
— The central 6″ sized structure seen on HST H \alpha and [ O iii ] images of NGC 1386 appears to be the inner part of a near-edge-on warped rotating spiral disk that is traced in H \alpha within a diameter of 17″ along p.a .
23° .
This interpretation is based on observed kinematic continuity and a typical S-shaped dust lane crossing the kinematical center .
The central velocity gradient yields a Keplerian mass estimate of \sim 10 ^ { 8 } M _ { \odot } inside R = 100 pc and 5 10 ^ { 9 } M _ { \odot } inside 0.8 kpc .
The total mass of the ionized gas of 10 ^ { 5 - 6 } M _ { \odot } is small compared to the dynamical mass of the spiral disk .
— The kinematical gradient of the rotating gas disk in the center of the elliptical galaxy NGC 1052 yields a mass of \sim 6 10 ^ { 8 } M _ { \odot } inside 166 pc .
Two components are found : component \cal A arises in a rotating disk , component \cal B is blueshifted by \sim 400 km/s relative to the disk . \cal B likely originates from outflowing gas distributed within a wide cone .
There is no need for a broad H \alpha component in unpolarized flux .
The peculiar polarization seen in [ O i ] \lambda 6300 by Barth et al .
( 1999 ) may be related to the outflow component .
— In Mrk 1210 , a redshifted component \cal R contributes to the exceptional width of [ O i ] \lambda 6300 .
An additional blueshifted component \cal B strong in [ O iii ] allows to fit the H \alpha + [ N ii ] blend without a broad component of H \alpha . \cal B and \cal R are likely to be outflow components .
The location of the brightness maximum BM is slightly ( \sim 1 \arcsec ) shifted relative to the kinematical center KC .
Locating the true obscured nucleus in KC makes it understandable that BM displays faint broad scattered H \alpha in polarized light .
— Galactic rotation and outflow of narrow-line gas are common features of this sample of water-megamaser galaxies .
All decomposed line-systems exhibit AGN typical line ratios .
Recent detections of H _ { 2 } O megamasers in starburst galaxies and the apparent asssociation of one megamaser with a Seyfert 1 AGN suggest that megamasers can possibly be triggered by optically detectable outflows .
The frequently encountered edge-on geometry favoring large molecular column densities appears to be verified for NGC 1386 and IC 2560 .
For NGC 1052 and Mrk 1210 , maser emission triggered by the optically detected outflow components can not be ruled out .