%0 Journal Article
%T High-velocity hot CO emission close to Sgr A* - Herschel/HIFI submillimeter spectral survey toward Sgr A*
%A D. Teyssier
%A J. Cernicharo
%A J. Pety
%A J. R. Goicoechea
%A M. G. Santa-Maria
%A M. Gerin
%J -
%D 2018
%R 10.1051/0004-6361/201833684
%X The properties of molecular gas, the fuel that forms stars, inside the cavity of the circumnuclear disk (CND) are not well constrained. We present results of a velocity-resolved submillimeter scan (~480¨C1250 GHz) and [C£¿II] 158 <i>¦Ì<i/>m line observations carried out with <i>Herschel<i/>/HIFI toward Sgr A<sup>*<sup/>; these results are complemented by a ~2¡ä ¡Á 2¡ä <sup>12<sup/>CO (<i>J<i/> = 3£¿2) map taken with the IRAM 30 m telescope at ~7¡å resolution. We report the presence of high positive-velocity emission (up to about +300 km s<sup>£¿1<sup/>) detected in the wings of <sup>12<sup/>CO <i>J<i/> = 5£¿4 to 10£¿9 lines. This wing component is also seen in H<sub>2<sub/>O (1<sub>1,0<sub/>£¿1<sub>0,1<sub/>), a tracer of hot molecular gas; in [C£¿II]158 <i>¦Ì<i/>m, an unambiguous tracer of UV radiation; but not in [C£¿I] 492, 806 GHz. This first measurement of the high-velocity <sup>12<sup/>CO rotational ladder toward Sgr A<sup>*<sup/> adds more evidence that hot molecular gas exists inside the cavity of the CND, relatively close to the supermassive black hole (<1 pc). Observed by ALMA, this velocity range appears as a collection of <sup>12<sup/>CO (<i>J<i/> = 3£¿2) cloudlets lying in a very harsh environment that is pervaded by intense UV radiation fields, shocks, and affected by strong gravitational shears. We constrain the physical conditions of the high positive-velocity CO gas component by comparing with non-LTE excitation and radiative transfer models. We infer <i>T<i/><sub>k<sub/> £¿ 400 K¨C2000 K for <i>n<i/><sub>H<sub/> £¿ (0.2£¿1.0) ¡Á 10<sup>5<sup/> cm<sup>£¿3<sup/>. These results point toward the important role of stellar UV radiation, but we show that radiative heating alone cannot explain the excitation of this ~10£¿60 <i>M<i/><sub>¡Ñ<sub/> component of hot molecular gas inside the central cavity. Instead, strongly irradiated shocks are promising candidates
%U https://www.aanda.org/articles/aa/full_html/2018/08/aa33684-18/aa33684-18.html