Dense gas in nearby galaxies

et al. 2010

A&A

Aims. Our aim is to confirm the interstellar detection of cyanic acid, HOCN, in the Galactic center clouds. It has previously been tentatively detected only in Sgr B2(OH). Methods. We used a complete line survey of the hot cores Sgr B2(N) and (M) in the 3 mm range, complemented by additional observations carried out with the IRAM 30 m telescope at selected frequencies in the 2 mm band and towards four additional positions in the Sgr B2 cloud complex in the 2 and 3 mm bands. The spectral survey was analysed in the local thermodynamical equilibrium approximation (LTE) by modeling the emission of all identified molecules simultaneously. This allowed us to distinguish weak features of HOCN from the rich line spectrum observed in Sgr B2(N) and (M). Lines of the more stable (by 1.1 eV) isomer isocyanic acid, HNCO, in these sources, as well as those of HOCN and HNCO towards the other positions, were analysed in the LTE approximation as well. Results. Four transitions of HOCN were detected in a quiescent molecular cloud in the Galactic center at a position offset in (RA, Dec) by (20 , 100 ) from the hot core source Sgr B2(M), confirming its previous tentative interstellar detection. Up to four transitions were detected toward five other positions in the Sgr B2 complex, including the hot cores Sgr B2(M), (S), and (N). A fairly constant abundance ratio of ∼0.3−0.8% for HOCN relative to HNCO was derived for the extended gas components, suggesting a common formation process of these isomers.

Section: Introductionmentioning

confidence: 95%

Interstellar HOCN in the Galactic center region

Brünken¹,

Беллоче

et al. 2010

A&A

“…), and the targeted observations towards NGC 4945 (Wang et al 2004). These studies have characterized the chemical complexity of starburst galaxies.…”

Section: Conclusion: Agn Vs Sb Driven Chemistrymentioning

confidence: 99%

The Submillimeter Array 1.3 mm line survey of Arp 220

Krips

Martı́n-Pintado

et al. 2011

A&A

159

Context. Though Arp 220 is the closest and by far the most studied ULIRG, a discussion is still ongoing on the main power source driving its huge infrared luminosity. Aims. To study the molecular composition of Arp 220 in order to find chemical fingerprints associated with the main heating mechanisms within its nuclear region. Methods. We present the first aperture synthesis unbiased spectral line survey toward an extragalactic object. The survey covered the 40 GHz frequency range between 202 and 242 GHz of the 1.3 mm atmospheric window. Results. We find that 80% of the observed band shows molecular emission, with 73 features identified from 15 molecular species and 6 isotopologues. The 13 C isotopic substitutions of HC 3 N and transitions from H 18 2 O, 29 SiO, and CH 2 CO are detected for the first time outside the Galaxy. No hydrogen recombination lines have been detected in the 40 GHz window covered. The emission feature at the transition frequency of H31α line is identified to be an HC 3 N molecular line, challenging the previous detections reported at this frequency. Within the broad observed band, we estimate that 28% of the total measured flux is due to the molecular line contribution, with CO only contributing 9% to the overall flux. We present maps of the CO emission at a resolution of 2.9 × 1.9 which, though not enough to resolve the two nuclei, recover all the single-dish flux. The 40 GHz spectral scan has been modelled assuming LTE conditions and abundances are derived for all identified species. Conclusions. The chemical composition of Arp 220 shows no clear evidence of an AGN impact on the molecular emission but seems indicative of a purely starburst-heated ISM. The overabundance of H 2 S and the low isotopic ratios observed suggest a chemically enriched environment by consecutive bursts of star formation, with an ongoing burst at an early evolutionary stage. The large abundance of water (∼10 −5 ), derived from the isotopologue H 18 2 O, as well as the vibrationally excited emission from HC 3 N and CH 3 CN are claimed to be evidence of massive star forming regions within Arp 220. Moreover, the observations put strong constraints on the compactness of the starburst event in Arp 220. We estimate that such emission would require ∼2−8 × 10 6 hot cores, similar to those found in the Sgr B2 region in the Galactic center, concentrated within the central 700 pc of Arp 220.

“…Their value of the 32 S/ 34 S ratio of 8 ± 2 would be doubled up to a value >16, closer to the value of ∼24 measured in the Galactic disk (Chin et al 1996). The ratio of 32 S/ 34 S ∼ 13.5 toward NGC 4945 (Wang et al 2004) might also be underestimated because it was based on the CS/C 34 S ratio assuming no significant saturation of the CS lines.…”

Section: The Sulfur 32 S/ 34 S Ratiomentioning

confidence: 99%

A large¹²C/¹³C isotopic ratio in M 82 and NGC 253

Aladro

Martı́n-Pintado

et al. 2010

A&A

Self Cite

Aims. Our aim is to derive carbon isotopic ratios from optically thin tracers in the central regions of the starburst galaxies M 82 and NGC 253. Methods. We present high-sensitivity observations of CCH and two of its 13 C isotopologues, C 13 CH and 13 CCH, as well as the optically thin emission from C 18 O and 13 C 18 O. We assume the column density ratio between isotopologues is representative of the 12 C/ 13 C isotopic ratio. Results. From CCH, lower limits to the 12 C/ 13 C isotopic ratio of 138 in M 82, and 81 in NGC 253, are derived. Lower limits to the 12 C/ 13 C ratios from CO isotopologues support these. 13 C 18 O is tentatively detected in NGC 253, which is the first reported detection in the extragalactic ISM. Based on these limits, we infer ratios of 16 O/ 18 O > 350 and >300 in M 82 and NGC 253, respectively, and 32 S/ 34 S > 16 in NGC 253. The derived CCH fractional abundances toward these galaxies of < ∼ 1.1 × 10 −8 agree well with those of molecular clouds in the Galactic disk. Conclusions. Our lower limits to the 12 C/ 13 C ratio from CCH are a factor of 2−3 larger than previous limits. The results are discussed in the context of molecular and nucleo-chemical evolution. The high 12 C/ 13 C isotopic ratio of the molecular ISM in these starburst galaxies suggest that the gas has been recently accreted toward their nuclear regions.