We present an 8 pc × 5 pc resolution view of the central ∼ 200 pc region of the nearby starburst galaxy NGC 253, based on ALMA Band 7 (λ 0.85 mm or ν ∼ 350 GHz) observations covering 11 GHz. We resolve the nuclear starburst of NGC 253 into eight dusty star-forming clumps, 10 pc in scale, for the first time. These clumps, each of which contains (4-10) ×10 4 M of dust (assuming that the dust temperature is 25 K) and up to 6 × 10 2 massive (O5V) stars, appear to be aligned in two parallel ridges, while they have been blended in previous studies. Despite the similarities in sizes and dust masses of these clumps, their line spectra vary drastically from clump to clump although they are separated by only ∼ 10 pc. Specifically, one of the clumps, Clump 1, exhibits line confusion-limited spectra with at least 36 emission lines from 19 molecules (including CH 3 OH, HNCO, H 2 CO, CH 3 CCH, H 2 CS, and H 3 O + ) and a hydrogen recombination line (H26α), while much fewer kinds of molecular 3 lines are detected in some other clumps where fragile species, such as complex organic molecules and HNCO, completely disappear from their spectra. We demonstrate the existence of hot molecular gas (T rot (SO 2 ) = 90 ± 11 K) in the former clump, which suggests that the hot and chemically rich environments are localized within a 10-pc scale star-forming clump.

We report on Atacama Large Millimeter/submillimeter Array (ALMA) detections of molecular absorption lines in Bands 3, 6 and 7 toward four radio-loud quasars, which were observed as the bandpass and complex gain calibrators. The absorption systems, three of which are newly detected, are found to be Galactic origin. Moreover, HCO absorption lines toward two objects are detected, which almost doubles the number of HCO absorption samples in the Galactic diffuse medium. In addition, high HCO to H 13 CO + column density ratios are found, suggesting that the interstellar media (ISM) observed toward the two calibrators are in photodissociation regions, which observationally illustrates the chemistry of diffuse ISM driven by ultraviolet (UV) radiation. These results demonstrate that calibrators in the ALMA Archive are potential sources for the quest for new absorption systems and for detailed investigation of the nature of the ISM.

We report Atacama Large Millimeter/submillimeter Array (ALMA) observations of 243–263 GHz absorption lines from Galactic diffuse molecular gas seen against three extragalactic radio-loud objects, J1717-337, J1625-254, and NRAO530. No significant absorption features were detected in our new sensitive ALMA Band 6 (λ ≃ 1.2 mm) spectra (1σ ≃ 2–4 mJy beam−1 with a velocity resolution of 1 km s−1), despite the fact that the obtained spectra cover the line frequencies of c-C3H2, CS, H13CN, HCO, H13CO+, SiO, and C2H, and that the lower transition absorption lines of these molecular species have been detected in ALMA Band 3 (λ ≃ 3 mm) observations toward these three Galactic molecular absorption systems. By combining the upper limits of the higher transitions that we obtain in this study and the archival detections of the lower transitions, we constrain the excitation temperatures of these species in the Galactic diffuse medium to be below 10 K, in spite of their PDR-like chemical states, where elevated column density ratios of HCO to H13CO+ are previously reported. These constraints are in line with the widely accepted view of the diffuse molecular clouds, where the molecular excitation is almost in equilibrium with the cosmic microwave background, although its kinetic temperature can be a few tens of Kelvin. Molecular abundance patterns seem to be similar in the Galactic diffuse gas and nearby active galaxies observed with a kpc-scale beam, suggesting the importance of observations with a parsec-scale resolution, which can resolve individual molecular clouds.

Abstract. In the central regions of active galaxies, dense molecular medium are exposed to various types of radiation and energy injections, such as UV, X-ray, cosmic ray, and shock dissipation. With the rapid progress of chemical models and implementation of new-generation mm/submm interferometry, we are now able to use molecules as powerful diagnostics of the physical and chemical processes in galaxies. Here we give a brief overview on the recent ALMA results to demonstrate how molecules can reveal underlying physical and chemical processes in galaxies. First, new detections of Galactic molecular absorption systems with elevated HCO/H 13 CO + column density ratios are reported, indicating that these molecular media are irradiated by intense UV fields. Second, we discuss the spatial distributions of various types of shock tracers including HNCO, CH3OH and SiO in NGC 253 and NGC 1068. Lastly, we provide an overview of proposed diagnostic methods of nuclear energy sources using ALMA, with an emphasis on the synergy with sensitive mid-infrared spectroscopy, which will be implemented by JWST and SPICA to disentangle the complex nature of heavily obscured galaxies across the cosmic time.