Context. The nearby Sy 1 galaxy NGC 1097 represents an ideal laboratory for exploring the molecular chemistry in the surroundings of an active galactic nucleus (AGN). Aims. Exploring the distribution of different molecular species allows us to understand the physical processes affecting the interstellar medium both in the AGN vicinity and in the outer star forming molecular ring. Methods. We carried out 3 mm ALMA observations that include seven different molecular species, namely HCN, HCO + , CCH, CS, HNCO, SiO, HC 3 N, and SO, as well as the 13 C isotopologues of the first two. Spectra were extracted from selected positions and all species were imaged over the central 2 kpc (∼30 ) of the galaxy at a resolution of ∼2.2 × 1.5 (150 pc × 100 pc). Results. HCO + and CS appear to be slightly enhanced in the star forming ring. CCH shows the largest variations across NGC 1097 and is suggested to be a good tracer of both obscured and early stage star formation. HNCO, SiO, and HC 3 N are significantly enhanced in the inner circumnuclear disk surrounding the AGN. Conclusions. Differences in the molecular abundances are observed between the star forming ring and the inner circumnuclear disk. We conclude that the HCN/HCO + and HCN/CS differences observed between AGN-dominated and starburst (SB) galaxies are not due to a HCN enhancement due to X-rays, but rather this enhancement is produced by shocked material at distances of 200 pc from the AGN. Additionally, we claim that lower HCN/CS is a combination of a small underabundance of CS in AGNs, together with excitation effects, where a high density gas component (∼10 6 cm −3 ) may be more prominent in SB galaxies. However, the most promising are the differences found among the dense gas tracers that, at our modest spatial resolution, seem to outline the physical structure of the molecular disk around the AGN. In this picture, HNCO probes the well-shielded gas in the disk, surrounding the dense material moderately exposed to the X-ray radiation traced by HC 3 N. Finally SiO might be the innermost molecule in the disk structure.

Context. The interstellar medium is the locus of physical processes affecting the evolution of galaxies which drive or are the result of star formation activity, supermassive black hole growth, and feedback. The resulting physical conditions determine the observable chemical abundances that can be explored through molecular emission observations at millimeter and submillimeter wavelengths. Aims. Our goal is to unveiling the molecular richness of the central region of the prototypical nearby starburst galaxy NGC 253 at an unprecedented combination of sensitivity, spatial resolution, and frequency coverage. Methods. We used the Atacama Large Millimeter/submillimeter Array (ALMA), covering a nearly contiguous 289 GHz frequency range between 84.2 and 373.2 GHz, to image the continuum and spectral line emission at 1.6″(∼28 pc) resolution down to a sensitivity of 30 − 50 mK. This article describes the ALMA Comprehensive High-resolution Extragalactic Molecular Inventory (ALCHEMI) large program. We focus on the analysis of the spectra extracted from the 15″ (∼255 pc) resolution ALMA Compact Array data. Results. We modeled the molecular emission assuming local thermodynamic equilibrium with 78 species being detected. Additionally, multiple hydrogen and helium recombination lines are identified. Spectral lines contribute 5 to 36% of the total emission in frequency bins of 50 GHz. We report the first extragalactic detections of C2H5OH, HOCN, HC3HO, and several rare isotopologues. Isotopic ratios of carbon, oxygen, sulfur, nitrogen, and silicon were measured with multiple species. Concluison. Infrared pumped vibrationaly excited HCN, HNC, and HC3N emission, originating in massive star formation locations, is clearly detected at low resolution, while we do not detect it for HCO+. We suggest high temperature conditions in these regions driving a seemingly “carbon-rich” chemistry which may also explain the observed high abundance of organic species close to those in Galactic hot cores. The Lvib/LIR ratio was used as a proxy to estimate a 3% contribution from the proto super star cluster to the global infrared emission. Measured isotopic ratios with high dipole moment species agree with those within the central kiloparsec of the Galaxy, while those derived from 13C/18O are a factor of five larger, confirming the existence of multiple interstellar medium components within NGC 253 with different degrees of nucleosynthesis enrichment. The ALCHEMI data set provides a unique template for studies of star-forming galaxies in the early Universe.

The Serpens South infrared dark cloud consists of several filamentary ridges, some of which fragment into dense clumps. On the basis of CCS (J N = 4 3 − 3 2 ), HC 3 N (J = 5 − 4), N 2 H + (J = 1 − 0), and SiO (J = 2 − 1, v = 0) observations, we investigated the kinematics and chemical evolution of these filamentary ridges. We find that CCS is extremely abundant along the main filament in the protocluster clump. We emphasize that Serpens South is the first cluster-forming region where extremely-strong CCS

Sensitive observations with the Atacama Large Millimeter/submillimeter Array (ALMA) allow astronomers to observe and discuss the detailed distributions of molecules with relatively weak intensity in nearby galaxies. In particular, we report distributions of several molecular transitions including shock and dust related species ( 13 CO J = 1-0, C 18 O J = 1-0, 13 CN N = 1-0, CS J = 2-1, SO J N = 3 2 -2 1 , HNCO J Ka,Kc = 5 0,5 -4 0,4 , HC 3 N J = 11-10, 12-11, CH 3 OH J K = 2 K -1 K , and CH 3 CN J K = 6 K -5 K ) in the nearby Seyfert 2 galaxy NGC 1068. This is the first paper reporting our study of molecular distributions in NGC 1068 with the ALMA early science program. The central ∼1 arcmin (∼4.3 kpc) of this galaxy was observed in the 100 GHz region (band 3) covering ∼96-100 GHz and ∼108-111 GHz with an angular resolution of ∼ 4 ′′ × 2 ′′ (290 pc×140 pc). These observations were motivated to study the effects of an active galactic nucleus and its surrounding starburst ring on molecular abundances. In this article, we present images and report a classification of 1 molecular distributions into three main categories, defined as follows: (1) Molecules concentrated in the circumnuclear disk (CND) (SO J N = 3 2 -2 1 , HC 3 N J = 11-10, 12-11, and CH 3 CN J K = 6 K -5 K ), (2) Molecules distributed both in the CND and the starburst ring (CS J = 2-1 and CH 3 OH J K = 2 K -1 K ), (3) Molecules distributed mainly in the starburst ring ( 13 CO J = 1-0 and C 18 O J = 1-0). Since most of the molecules such as HC 3 N observed in the CND are easily dissociated by UV photons and X-rays, our results indicate that these molecules must be effectively shielded. In the starburst ring, the distribution of CH 3 OH is similar to those of 13 CO, C 18 O, and CS on the whole, but the relative intensity of methanol at each clumpy region is not consistent with those of 13 CO, C 18 O, and CS. This difference is probably caused by the unique formation and destruction mechanisms of CH 3 OH in the environment of the starburst ring.

No abstract