Astronomy and Astrophysics – Astronomy
Scientific paper
Mar 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996aj....111.1227p&link_type=abstract
Astronomical Journal v.111, p.1227
Astronomy and Astrophysics
Astronomy
11
Ism: Jets And Outflows, Ism: Individual: Ngc 6210
Scientific paper
We have acquired low- and intermediate-resolution spectroscopy at 11 positions across the nucleus of NGC 6210. As a consequence, we are able to map the variation of velocity, temperature, line excitation, and density over the projected core and halo of this source. Temperatures reach a peak value Te≌1.1×104K close to the nucleus, and thereafter decline by ˜24% towards the periphery of the core, some 7.5 arcsec from the central star. By contrast, density peaks towards the north, achieving maximal values ne≌6.1×103, and subsequently falls by ˜72% towards the southern limits of the region; a distribution which is reminiscent of (and presumably causally related to) the observed radio structure. Line excitation is highly variable, with low-excitation lines particularly enhanced to the NW, along arms extending NW and (to a lesser degree) SE into the halo, and close to a bright condensation located some ˜17 arcsec outside of the primary shell. These low-excitation extensions, and the associated NW condensation, appear also to be the location of a significant kinematic disturbance; a feature which is narrowly focused, and possesses characteristics reminiscent of a highly collimated jet. it is apparent, in brief, that the nucleus of NGC 6210 is ejecting material along two, and possibly four opposing directions, with curvature of this outflow indicating possible rotation of the collimating source. The kinematics of the halo appear to be similarly disturbed, with evidence for at least three circularly symmetric, low-amplitude ripples extending through the exterior velocity field. Halo linewidths appear also to be appreciable, of order 50 km s-1, although the precise origin of this broadening remains far from clear. Finally, and in keeping with the maps of density and line excitation, it is clear that the velocity structure of the core is by no means straightforward. Detailed consideration of our results suggests, however, that we may be observing a partially disrupted shell, of type recently proposed in the cases of NGC 6905 and NGC 7026. In particular, the kinematic trends for locations close to P.A.=335° are reminiscent of spheroidal expanding shells-although with notable disparities which may suggest some elongation or fragmentation of the outflow. Alternatively, orthogonal axes reveal strongly variable, and more-or-less parallel velocity trends between front and rear shells, resulting in positive velocities to the west, and corresponding negative velocities to the east. Such a tendency can be reasonably modeled in terms of a pseudocylindrical outflow structure, provided we assume appreciable ionization stratification, substantial radial velocity gradients, and that the exterior has appreciable nonradial asymmetries arising from localized fragmentation.
Cuesta Luis
Phillips J. P.
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