Aims. We study the origin of large abundances of complex organic molecules in the Galactic center (GC). Methods. We carried out a systematic study of the complex organic molecules CH 3 OH, C 2 H 5 OH, (CH 3 ) 2 O, HCOOCH 3 , HCOOH, CH 3 COOH, H 2 CO, and CS toward 40 GC molecular clouds. Using the LTE approximation, we derived the physical properties of GC molecular clouds and the abundances of the complex molecules. The abundances of complex organic molecules in the GC are compared with those measured in hot cores and hot corinos, in which these complex molecules are also abundant. Results. The CH 3 OH abundance between clouds varies by nearly two orders of magnitude from 2.4×10 −8 to 1.1×10 −6 . The abundance of the other complex organic molecules relative to that of CH 3 OH is basically independent of the CH 3 OH abundance, with variations of only a factor 4-8. We find that both the abundance and the abundance ratios of the complex molecules relative to CH 3 OH in hot cores are similar to those found in the GC clouds. However, hot corinos show different abundance ratios than observed in hot cores and in GC clouds. The rather constant abundance of all the complex molecules relative to CH 3 OH suggests that all complex molecules are ejected from grain mantles by shocks. Frequent (∼10 5 years) shocks with velocities >6 km s −1 are required to explain the high abundances in gas phase of complex organic molecules in the GC molecular clouds. The rather uniform abundance ratios in the GC clouds and in Galactic hot cores indicate a similar average composition of grain mantles in both kinds of regions. The Sickle and the Thermal Radio Arches, affected by UV radiation, show different relative abundances in the complex organic molecules due to the differentially photodissociation of these molecules.

M 87 is one of the nearest radio galaxies with a prominent jet extending from sub-pc to kpc-scales. Because of its proximity and large mass of the central black hole, it is one of the best radio sources to study jet formation. We aim at studying the physical conditions near the jet base at projected separations from the BH of ∼ 7 − 100 Schwarzschild radii (R sch ). Global mm-VLBI Array (GMVA) observations at 86 GHz (λ = 3.5 mm) provide an angular resolution of ∼ 50µas, which corresponds to a spatial resolution of only 7 R sch and reach the small spatial scale. We use five GMVA data sets of M 87 obtained during 2004-2015 and present new high angular resolution VLBI maps at 86 GHz. In particular, we focus on the analysis of the brightness temperature, the jet ridge lines, and the jet to counter-jet ratio. The imaging reveals a parabolically expanding limb-brightened jet which emanates from a resolved VLBI core of ∼ (8 − 13)R sch size. The observed brightness temperature of the core at any epoch is ∼ (1 − 3) × 10 10 K, which is below the equipartition brightness temperature and suggests magnetic energy dominance at the jet base. We estimate the diameter of the jet at its base to be ∼ 5R sch assuming a self-similar jet structure. This suggests that the sheath of the jet may be anchored in the very inner portion of the accretion disk. The image stacking reveals faint emission at the center of the edge-brightened jet on sub-pc scales. We discuss its physical implication within the context of the spine-sheath structure of the jet.

We report the detection for the first time in space of three new pure hydrocarbon cycles in TMC-1: c-C3HCCH (ethynyl cyclopropenylidene), c-C5H6 (cyclopentadiene), and c-C9H8 (indene). We derive a column density of 3.1 × 1011 cm−2 for the first cycle and similar values, in the range (1−2) × 1013 cm−2, for the second and third. This means that cyclopentadiene and indene, in spite of their large size, are exceptionally abundant, only a factor of five less abundant than the ubiquitous cyclic hydrocarbon c-C3H2. The high abundance found for these two hydrocarbon cycles together with the high abundance previously found for the propargyl radical (CH2CCH) and other hydrocarbons, such as vinyl and allenyl acetylene (Agúndez et al. 2021, A&A, 647, L10; Cernicharo et al. 2021a, A&A, 647, L2; Cernicharo et al. 2021b, A&A, 647, L3), start to allow us to quantify the abundant content of hydrocarbon rings in cold dark clouds and to identify the intermediate species that are probably behind the in situ bottom-up synthesis of aromatic cycles in these environments. While c-C3HCCH is most likely formed through the reaction between the radical CCH and c-C3H2, the high observed abundances of cyclopentadiene and indene are difficult to explain through currently proposed chemical mechanisms. Further studies are needed to identify how five- and six-membered rings are formed under the cold conditions of a cloud such as TMC-1.

Abstract. We present ISO observations of several H2 pure-rotational lines (from S(0) to S(5)) towards a sample of 16 molecular clouds distributed along the central ∼ 500 pc of the Galaxy. We also present C 18 O and 13 CO J = 1 → 0 and J = 2 → 1 observations of these sources made with the IRAM-30 m telescope. With the CO data we derive H2 densities of 10 3.5−4.0 cm −3 and H2 column densities of a few 10 22 cm −2 . We have corrected the H2 data for ∼ 30 magnitudes of visual extinction using a self-consistent method. In every source, we find that the H2 emission exhibits a large temperature gradient. The S(0) and S(1) lines trace temperatures (T ) of ∼ 150 K while the S(4) and S(5) lines indicate temperatures of ∼ 600 K. The warm H2 column density is typically ∼ 1-2 10 22 cm −2 , and is predominantly gas with T = 150 K. This is the first direct estimate of the total column density of the warm molecular gas in the Galactic center region. These warm H2 column densities represent a fraction of ∼ 30% of the gas traced by the CO isotopes emission. The cooling by H2 in the warm component is comparable to that by CO. Comparing our H2 and CO data with available ammonia (NH3) observations from literature one obtains relatively high NH3 abundances of a few 10 −7 in both the warm and the cold gas. A single shock or Photo-Dissociation Region (PDR) cannot explain all the observed H2 lines. Alternatives for the heating mechanisms are discussed.

We have mapped the J ϭ 1 3 0 line of SiO in a 1Њ ϫ 12Ј (l ϫ b) region around the Galactic center (GC) with an angular resolution of 2Ј (14 pc). In contrast to the spatial distribution of other high dipole moment molecules like CS, whose emission is nearly uniform, the SiO emission is very fragmented, and it is associated with some molecular clouds only. In particular, it is remarkable that the SiO emission follows closely the nonthermal radio arc in the GC. The SiO clouds are more extended than the beam, with typical sizes between 4 and 20 pc. High angular resolution (26Љ) mapping in the J ϭ 2 3 1 line of SiO toward the molecular clouds in Sgr B2 and Sgr A shows that the SiO emission is relatively smooth, with structures of typically 2 pc. From the line intensities of the J ϭ 2 3 1, J ϭ 3 3 2, and J ϭ 5 3 4 transitions of SiO, we derive H 2 densities for these clouds of a few 10 4 cm Ϫ3 . The SiO fractional abundances are 110 Ϫ9 for the SiO clouds and =10 Ϫ10 for the other molecular clouds in the GC. The characteristics (size and H 2 densities) of the SiO emission in the GC are completely different from those observed in the Galactic disk, where the SiO emission arises from much smaller regions with larger H 2 densities. We discuss briefly the implications of the SiO emission in the molecular clouds of the GC. We conclude that the particular chemistry in these clouds is probably related to large-scale fast shocks occurring in the Galactic center region.