S. Martín, J. Martín-Pintado, M. Montero-Castaño, P. T. P. Ho, R. Blundell
The interstellar region within the few central parsecs around the
super-massive black hole, Sgr A* at the very Galactic center is composed by a
number of overlapping molecular structures which are subject to one of the most
hostile physical environments in the Galaxy. We present high resolution
(4"x3"~0.16x0.11 pc) interferometric observations of CN, 13CN, H2CO, SiO,
c-C3H2 and HC3N emission at 1.3 mm towards the central ~4 pc of the Galactic
center region. Strong differences are observed in the distribution of the
different molecules. The UV resistant species CN, the only species tracing all
previously identified circumnuclear disk (CND) structures, is mostly
concentrated in optically thick clumps in the rotating filaments around Sgr A*.
H2CO emission traces a shell-like structure that we interpret as the expansion
of Sgr A East against the 50 km/s and 20 km/s giant molecular clouds (GMCs). We
derive isotopic ratios 12C/13C~15-45 across most of the CND region. The densest
molecular material, traced by SiO and HC3N, is located in the southern CND. The
observed c-C3H2/HC3N ratio observed in the region is more than an order of
magnitude lower than in Galactic PDRs. Toward the central region only CN was
detected in absorption. Apart from the known narrow line-of-sight absorptions,
a 90 km/s wide optically thick spectral feature is observed. We find evidences
of an even wider (>100 km/s) absorption feature. Around 70-75% of the gas mass,
concentrated in just the 27% densest molecular clumps, is associated with
rotating structures and show evidences of association with each of the arcs of
ionized gas in the mini-spiral structure. Chemical differentiation has been
proven to be a powerful tool to disentangle the many overlapping molecular
components in this crowded and heavily obscured region.
View original:
http://arxiv.org/abs/1112.0566
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