Warm ISM in the Sagittarius A Complex

I. Mid-J CO, atomic carbon, ionized atomic carbon, and ionized nitrogen sub-mm/FIR line observations with the Herschel-HIFI and NANTEN2/SMART telescopes^⋆,⋆⋆

¹ I. Physikalisches Institut der Universität zu Köln, 50937 Cologne, Germany
e-mail: pablo@ph1.uni-koeln.de
² Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany

Received: 26 May 2015
Accepted: 22 September 2015

Abstract

Aims. We investigate the spatial and spectral distribution of the local standard of rest (LSR) velocity resolved submillimetre emission from the warm (25−90 K) gas in the Sgr A Complex, located in the Galactic centre.

Methods. We present large-scale submillimetre heterodyne observations towards the Sgr A Complex covering ~300 arcmin². These data were obtained in the frame of the Herschel EXtraGALactic guaranteed time key program (HEXGAL) with the Herschel-HIFI satellite and are complemented with submillimetre observations obtained with the NANTEN2/SMART telescope as part of the NANTEN2/SMART Central Nuclear Zone Survey. The observed species are CO(J = 4−3) at 461.0 GHz observed with the NANTEN2/SMART telescope, and [CI] ³P₁−³P₀ at 492.2 GHz, [CI] ³P₂−³P₁ at 809.3 GHz, [NII] ³P₁−³P₀ at 1461.1 GHz, and [CII] ²P_3/2−²P_1/2 at 1900.5 GHz observed with the Herschel-HIFI satellite. The observations are presented in a 1 km s^-1 spectral resolution and a spatial resolution ranging from 46 arcsec to 28 arcsec. The spectral coverage of the three lower frequency lines is ±200 km s^-1, while in the two high frequency lines, the upper LSR velocity limit is +94 km s^-1 and +145 km s^-1 for the [NII] and [CII] lines, respectively.

Results. The spatial distribution of the emission in all lines is very widespread. The bulk of the carbon monoxide emission is found towards Galactic latitudes below the Galactic plane, and all the known molecular clouds are identified. Both neutral atomic carbon lines have their brightest emission associated with the +50 km s^-1 cloud. Their spatial distribution at this LSR velocity describes a crescent-shape structure, which is probably the result of interaction with the energetic event (one or several supernovae explosions) that gave origin to the non-thermal Sgr A-East source. The [CII] and [NII] emissions have most of their flux associated with the thermal arched-filaments and the H region and bright spots in [CII] emission towards the central nuclear disk (CND) are detected. Warm Gas at very high (|V_lsr|> 100 km s^-1) LSR velocities is also detected towards the line of sight to the Sgr A Complex, and it is most probably located outside the region, in the X₁ orbits.