Search

Context. Star formation in the central molecular zone (CMZ) is suppressed with respect to that of the Galactic disk, and this is likely related to its high turbulent environment. This turbulence impedes the potential detection of prestellar cores. Aims. We present the temperature, density, and spatial structure of the CMZ molecular cloud G+0.693-0.027, which has been proposed to host a prestellar cluster in the Sgr B2 region. Methods. We analysed multiple HC3N rotational transitions that were observed with the IRAM 30m, APEX, Yebes 40m, and GBT radio telescopes, together with SMA+APEX spatially resolved maps. Results. The spectral shape of HC3N lines shows three distinct velocity components: a broad component with a line width of 23 km s−1 (C1), and two narrow components with line widths of 7.2 and 8.8 km s−1 (C2 and C3). This suggests that a fraction of the molecular gas in this cloud is undergoing turbulence dissipation. From an initial local thermodynamic equilibrium analysis, we found column densities of N = (6.54 ± 0.07) × 1014 cm−2, (9 ± 3) × 1014 cm−2, and (3.6 ± 0.7) × 1013 cm−2 for C1, C2, and C3, respectively. These values were used as input for a subsequent non-local thermodynamic equilibrium analysis, in which we found H2 densities of 2 × 104 cm−3, 5 × 104 cm−3, and 4 × 105 cm−3 and kinetic temperatures of 140 K, 30 K, and 80 K for C1, C2, and C3, respectively. The spatially resolved maps confirm that the colder and high-density condensations C2 and C3, which peak in the 70–85 km s−1 velocity range, have deconvolved sizes of 9″ (0.36 pc) and 7.6″ (0.3 pc), respectively, and are embedded in a more diffuse and warmer gas (C1). Conclusions. The larger-scale structure of the Sgr B2 region, consistently with previous works, shows a hole at 40–50 km s−1 that is likely due to a small cloud that shocked the Sgr B2 region and is spatially related with a massive cloud at 60–80 km s−1. We propose that the impacting small cloud sequentially triggered the formation of Sgr B2(M), (N), and (S) and the condensations in G+0.693-0.027 during its passage. The two condensations are in a post-shocked environment that has undergone internal fragmentation. Based on the analysis of their masses and the virial parameters, C2 might expand, while C3 might further fragment or collapse. [ABSTRACT FROM AUTHOR]

The presence in the interstellar medium of several imines suggests that other molecules of the same family could be present as well. The propargylimine molecule (HCCCHNH), which arises from CCH substitution on the C atom of methanimine (H2CNH), the simplest imine, has been recently detected in space. Therefore, the analogous CCH derivative substituted on the N atom, known as N-ethynylmethanimine (H2CNCCH), is a good candidate to be observed as well. To allow for its astronomical detection we have investigated its laboratory rotational spectra. The species has been produced by an electric discharge of acetonitrile (CH3CN) and acetylene (HCCH) in argon, and its rotational spectrum between 9 and 40 GHz has been characterized using a Balle–Flygare narrow band-type Fourier-transform microwave spectrometer. The spectral analysis allowed us to derive accurate spectroscopic parameters to obtain reliable frequency predictions for astronomical searches in different sources. We searched for H2CNCCH in several molecular clouds, G+0.693−0.027, L483, and TMC-1, but did not detect it. The upper limits to its abundance derived are consistent with a preference of the CCH substitution of H2CNH on the C atom rather than on the N atom, in line with quantum chemical calculations on the reaction between CCH and H2CNH. [ABSTRACT FROM AUTHOR]

The H2NC radical is the high-energy metastable isomer of H2CN radical, which has been recently detected for the first time in the interstellar medium towards a handful of cold galactic sources, besides a warm galaxy in front of the PKS 1830−211 quasar. These detections have shown that the H2CN/H2NC isomeric ratio, likewise the HCN/HNC ratio, might increase with the kinetic temperature (T kin), but the shortage of them in warm sources still prevents us from confirming this hypothesis and shedding light on their chemistry. In this work, we present the first detection of H2CN and H2NC towards a warm galactic source, the G+0.693−0.027 molecular cloud (with T kin > 70 K), using IRAM 30-m telescope observations. We have detected multiple hyperfine components of the |$N_{K_\text{a}K_\text{c}} =$| 101–000 and 202–101 transitions. We derived molecular abundances with respect to H2 of (6.8 ± 1.3) × 10−11 for H2CN and of (3.1 ± 0.7) × 10−11 for H2NC, and an H2CN/H2NC abundance ratio of 2.2 ± 0.5. These detections confirm that the H2CN/H2NC ratio is ≳2 for sources with T kin > 70 K, larger than the ∼1 ratios previously found in colder cores (T kin ∼ 10 K). This isomeric ratio dependence on temperature cannot be fully explained with the currently proposed gas-phase formation and destruction pathways. Grain surface reactions, including the H2NC → H2CN isomerization, deserve consideration to explain the higher isomeric ratios and H2CN abundances observed in warm sources, where the molecules can be desorbed into the gas phase through thermal and/or shock-induced mechanisms. [ABSTRACT FROM AUTHOR]

Methylamine has been the only simple alkylamine detected in the interstellar medium for a long time. With the recent secure and tentative detections of vinylamine and ethylamine, respectively, dimethylamine has become a promising target for searches in space. Its rotational spectrum, however, has been known only up to 45 GHz until now. Here we investigate the rotation-tunnelling spectrum of dimethylamine in selected regions between 76 and 1091 GHz using three different spectrometers in order to facilitate its detection in space. The quantum number range is extended to J  = 61 and  Ka  = 21, yielding an extensive set of accurate spectroscopic parameters. To search for dimethylamine, we refer to the spectral line survey ReMoCA carried out with the Atacama Large Millimeter/submillimeter Array towards the high-mass star-forming region Sagittarius B2(N) and a spectral line survey of the molecular cloud G+0.693–0.027 employing the IRAM 30 m and Yebes 40 m radio telescopes. We report non-detections of dimethylamine towards the hot molecular cores Sgr B2(N1S) and Sgr B2(N2b) as well as G+0.693−0.027 which imply that dimethylamine is at least 14, 4.5, and 39 times less abundant than methylamine towards these sources, respectively. The observational results are compared to computational results from a gas-grain astrochemical model. The modelled methylamine to dimethylamine ratios are compatible with the observational lower limits. However, the model produces too much ethylamine compared with methylamine which could mean that the already fairly low levels of dimethylamine in the models may also be too high. [ABSTRACT FROM AUTHOR]

Interstellar amides have attracted significant attentions as they are potential precursors for a wide variety of organics essential to life. However, our current understanding of their formation in space is heavily based on observations in star-forming regions and hence the chemical networks lack the constraints on their early origin. In this work, unbiased sensitive spectral surveys with IRAM 30 m and Yebes 40 m telescopes are used to systematically study a number of amides towards a quiescent Galactic centre molecular cloud, G+0.693−0.027. We report the first detection of acetamide (CH3C(O)NH2) and trans-N-methylformamide (CH3NHCHO) towards this cloud. In addition, with the wider frequency coverage of the survey, we revisited the detection of formamide (NH2CHO) and urea (carbamide; NH2C(O)NH2), which had been reported previously towards G+0.693−0.027. Our results are compared with those present in the literature including recent laboratory experiments and chemical models. We find constant abundance ratios independently of the evolutionary stages, suggesting that amides related chemistry is triggered in early evolutionary stages of molecular cloud and remain unaffected by the warm-up phase during the star formation process. Although a correlation between more complex amides and NH2CHO have been suggested, alternative formation routes involving other precursors such as acetaldehyde (CH3CHO), methyl isocyanate (CH3NCO), and methylamine (CH3NH2) may also contribute to the production of amides. Observations of amides together with these species towards a larger sample of sources can help to constrain the amide chemistry in the interstellar medium. [ABSTRACT FROM AUTHOR]

Recent observations of the pre-stellar core L1544 and the younger starless core L1498 have revealed that complex organic molecules (COMs) are enhanced in the gas phase towards their outer and intermediate-density shells. Our goal is to determine the level of chemical complexity towards the starless core L1517B, which seems younger than L1498, and compare it with the other two previously studied cores to see if there is a chemical evolution within the cores. We have carried out 3 mm high-sensitivity observations towards two positions in the L1517B starless core: the core's centre and the position where the methanol emission peaks (at a distance of ∼5000 au from the core's centre). Our observations reveal that a lower number of COMs and COM precursors are detected in L1517B with respect to L1498 and L1544, and also show lower abundances. Besides methanol, we only detected CH3O, H2CCO, CH3CHO, CH3CN, CH3NC, HCCCN, and HCCNC. Their measured abundances are ∼3 times larger towards the methanol peak than towards the core's centre, mimicking the behaviour found towards the more evolved cores L1544 and L1498. We propose that the differences in the chemical complexity observed between the three studied starless cores are a consequence of their evolution, with L1517B being the less evolved one, followed by L1498 and L1544. Chemical complexity in these cores seems to increase over time, with N-bearing molecules forming first and O-bearing COMs forming at a later stage as a result of the catastrophic depletion of CO. [ABSTRACT FROM AUTHOR]

We have used ALMA imaging (resolutions 0.1–0.4 arcsec) of ground and vibrationally excited lines of HCN and HC3N toward the nucleus of NGC 4945 to trace the protostellar phase in super star clusters (proto-SSC). Out of the 14 identified SSCs, we find that eight are in the proto-SSC phase showing vibrational HCN emission with five of them also showing vibrational HC3N emission. We estimate proto-SSC ages of 5–9.7 × 104 yr. The more evolved ones, with only HCN emission, are close to reach the zero-age main sequence (ZAMS; ages ≳105 yr). The excitation of the parental cloud seems to be related to the SSC evolutionary stage, with high (∼65 K) and low (∼25 K) rotational temperatures for the youngest proto and ZAMS SSCs, respectively. Heating by the H  ii regions in the SSC ZAMS phase seems to be rather local. The youngest proto-SSCs are located at the edges of the molecular outflow, indicating SSC formation by positive feedback in the shocked regions. The proto-SSCs in NGC 4945 seem to be more evolved than in the starburst galaxy NGC 253. We propose that sequential SSC formation can explain the spatial distribution and different ages of the SSCs in both galaxies. [ABSTRACT FROM AUTHOR]

Using high angular resolution ALMA observations (0.02 arcsec ≈ 0.34 pc), we study the thermal structure and kinematics of the proto-super star cluster 13 in the central region of NGC 253 through their continuum and vibrationally excited HC3N emission from J  = 24−23 and J  = 26−25 lines arising from vibrational states up to v 4 = 1. We have carried 2D-LTE and non-local radiative transfer modelling of the radial profile of the HC3N and continuum emission in concentric rings of 0.1 pc width. From the 2D-LTE analysis, we found a Super Hot Core (SHC) of 1.5 pc with very high vibrational temperatures (>500 K), and a jump in the radial velocity (21 km s−1) in the SE-NW direction. From the non-local models, we derive the HC3N column density, H2 density, and dust temperature (T dust) profiles. Our results show that the thermal structure of the SHC is dominated by the greenhouse effect due to the high dust opacity in the IR, leading to an overestimation of the LTE T dust and its derived luminosity. The kinematics and T dust profile of the SHC suggest that star formation was likely triggered by a cloud–cloud collision. We compare proto-SSC 13 to other deeply embedded star-forming regions, and discuss the origin of the |$L_\text{IR}/M_{\text{H}_2}$| excess above ∼100 L⊙ M |$_\odot ^{-1}$| observed in (U)LIRGs. [ABSTRACT FROM AUTHOR]

We report here the first detection in the interstellar medium of the cyanomidyl radical (HNCN). Using the Yebes 40m and the IRAM 30m telescopes, we have targeted the doublets of the N  = 2–1, 4–3, 5–4, 6–5, and 7–6 transitions of HNCN towards the molecular cloud G+0.693-0.027. We have detected three unblended lines of HNCN, these are the N  = 6–5 doublet and one line of the N  = 4–3 transition. Additionally, we present one line of the N  = 5–4 transition partially blended with emission from other species. The local thermodynamic equilibrium best fit to the data gives a molecular abundance of (0.91 ± 0.05) × 10−10 with respect to H2. The relatively low abundance of this species in G+0.693-0.027 and its high reactivity suggest that HNCN is possibly produced by gas-phase chemistry. Our work shows that this highly reactive molecule is present in interstellar space, and thus it represents a plausible precursor of larger prebiotic molecules with the nitrogen–carbon–nitrogen backbone such as cyanamide (NH2CN), carbodiimide (HNCNH), and formamidine (NH2CHNH). [ABSTRACT FROM AUTHOR]

Using the ALMA data, we have studied the HC3N and continuum emission in the starburst pseudo-ring (SB pseudo-ring) and the circumnuclear disc (CND) of the SB/active galactic nucleus (AGN) composite galaxy NGC 1068. We have detected emission from vibrationally excited HC3N (HC3N*) only towards one star-forming region of the SB pseudo-ring. Remarkably, HC3N* was not detected towards the CND despite its large HC3N v = 0 column density. From local thermodynamic equilibrium (LTE) and non-LTE modelling of HC3N*, we obtained a dust temperature (T dust) of ∼250 K and a density |$(n_{\text{H}_2}) \text{ of }6\times 10^5$|  cm−3 for this star-forming region. The estimated infrared (IR) luminosity of 5.8 × 108 L⊙ is typical of proto-superstar clusters (proto-SSCs) observed in the SB galaxy NGC 253. We use the continuum emissions at 147 and 350 GHz, along with CO and Pa α, to estimate the ages of other 14 SSCs in the SB pseudo-ring. We find the SSCs to be associated with the region connecting the nuclear bar with the SB pseudo-ring, supporting the inflow scenario. For the CND, our analysis yields T dust ≤ 100 K and |$n_{\text{H}_2}\sim (3\!-\!6)\times 10^5$|  cm−3. The very different dust temperatures found for the CND and the proto-SSC indicate that, while the dust in the proto-SSC is being efficiently heated from the inside by the radiation from massive protostars, the CND is being heated externally by the AGN, which in the IR optically thin case can only heat the dust to 56 K. We discuss the implications of the non-detection of HC3N* near the luminous AGN in NGC 1068 on the interpretation of the HC3N* emission observed in the SB/AGN composite galaxies NGC 4418 and Arp 220. [ABSTRACT FROM AUTHOR]

We present SiO J = 2–1 maps of the Sgr B2 molecular cloud, which show shocked gas with a turbulent substructure comprising at least three cavities at velocities of |$[10,40]\, \rm km\, s^{-1}$| and an arc at velocities of |$[-20,10]\, \rm km\, s^{-1}$|⁠. The spatial anticorrelation of shocked gas at low and high velocities, and the presence of bridging features in position-velocity diagrams suggest that these structures formed in a cloud–cloud collision. Some of the known compact H  ii regions spatially overlap with sites of strong SiO emission at velocities of |$[40,85]\, \rm km\, s^{-1}$|⁠ , and are between or along the edges of SiO gas features at |$[100,120]\, \rm km\, s^{-1}$|⁠ , suggesting that the stars responsible for ionizing the compact H  ii regions formed in compressed gas due to this collision. We find gas densities and kinetic temperatures of the order of |$n_{\rm H_2}\sim 10^5\, \rm cm^{-3}$| and |$\sim 30\, \rm K$|⁠ , respectively, towards three positions of Sgr B2. The average values of the SiO relative abundances, integrated line intensities, and line widths are ∼10−9, |$\sim 11\, \rm K\, km\, s^{-1}$|⁠ , and |$\sim 31\, \rm km\, s^{-1}$|⁠ , respectively. These values agree with those obtained with chemical models that mimic grain sputtering by C-type shocks. A comparison of our observations with hydrodynamical simulations shows that a cloud–cloud collision that took place |$\lesssim 0.5\, \rm Myr$| ago can explain the density distribution with a mean column density of |$\bar{N}_{\rm H_2}\gtrsim 5\times 10^{22}\, \rm cm^{-2}$|⁠ , and the morphology and kinematics of shocked gas in different velocity channels. Colliding clouds are efficient at producing internal shocks with velocities |$\sim 5\!-\!50\, \rm km\, s^{-1}$|⁠. High-velocity shocks are produced during the early stages of the collision and can readily ignite star formation, while moderate- and low-velocity shocks are important over longer time-scales and can explain the widespread SiO emission in Sgr B2. [ABSTRACT FROM AUTHOR]

Context. Understanding the dominant heating mechanism in the nuclei of galaxies is crucial to understanding star formation in starbursts (SBs), active galactic nuclei (AGN) phenomena, and the relationship between star formation and AGN activity in galaxies. Analysis of the carbon monoxide (12CO) rotational ladder versus the infrared continuum emission (hereafter, 12CO/IR) in galaxies with different types of activity reveals important differences between them. Aims. We aim to carry out a comprehensive study of the nearby composite AGN-SB galaxy, NGC 4945, using spectroscopic and photometric data from the Herschel satellite. In particular, we want to characterize the thermal structure in this galaxy using a multi-transition analysis of the spatial distribution of the 12CO emission at different spatial scales. We also want to establish the dominant heating mechanism at work in the inner region of this object at smaller spatial scales (≲200 pc). Methods. We present far-infrared (FIR) and sub-millimeter (sub-mm) 12CO line maps and single spectra (from Jup = 3 to 20) using the Heterodyne Instrument for the Far Infrared (HIFI), the Photoconductor Array Camera and Spectrometer (PACS), and the Spectral and Photometric Imaging REceiver (SPIRE) onboard Herschel, and the Atacama Pathfinder EXperiment (APEX). We combined the 12CO/IR flux ratios and the local thermodynamic equilibrium (LTE) analysis of the 12CO images to derive the thermal structure of the interstellar medium (ISM) for spatial scales raging from ≲200 pc to 2 kpc. In addition, we also present single spectra of low- (12CO, 13CO and [CI]) and high-density (HCN, HNC, HCO+, CS and CH) molecular gas tracers obtained with APEX and HIFI applying LTE and non-LTE (NLTE) analyses. Furthermore, the spectral energy distribution of the continuum emission from the FIR to sub-mm wavelengths is also presented. Results. From the NLTE analysis of the low- and high-density tracers, we derive gas volume densities (103–106 cm−3) for NGC 4945 that are similar to those found in other galaxies with different types of activity. From the 12CO analysis we find a clear trend in the distribution of the derived temperatures and the 12CO/IR ratios. It is remarkable that at intermediate scales (360 pc–1 kpc, or 19″–57″) we see large temperatures in the direction of the X-ray outflow while at smaller scales (≲200 pc–360 pc, or ∼9″–19″), the highest temperature, derived from the high-J lines, is not found toward the nucleus but toward the galaxy plane. The thermal structure derived from the 12CO multi-transition analysis suggests that mechanical heating, like shocks or turbulence, dominates the heating of the ISM in the nucleus of NGC4945 located beyond 100 pc (≳5″) from the center of the galaxy. This result is further supported by published models, which are able to reproduce the emission observed at high-J (PACS) 12CO transitions when mechanical heating mechanisms are included. Shocks and/or turbulence are likely produced by the barred potential and the outflow observed in X–rays. [ABSTRACT FROM AUTHOR]

G+0.693-0.03 is a quiescent molecular cloud located within the Sagittarius B2 (Sgr B2) star-forming complex. Recent spectral surveys have shown that it represents one of the most prolific repositories of complex organic species in the Galaxy. The origin of such chemical complexity, along with the small-scale physical structure and properties of G+0.693-0.03, remains a mystery. In this paper, we report the study of multiple molecules with interferometric observations in combination with single-dish data in G+0.693-0.03. Despite the lack of detection of continuum source, we find small-scale (0.2 pc) structures within this cloud. The analysis of the molecular emission of typical shock tracers such as SiO, HNCO, and CH3OH unveiled two molecular components, peaking at velocities of 57 and 75 km s−1. They are found to be interconnected in both space and velocity. The position–velocity diagrams show features that match with the observational signatures of a cloud–cloud collision. Additionally, we detect three series of class I methanol masers known to appear in shocked gas, supporting the cloud–cloud collision scenario. From the maser emission we provide constraints on the gas kinetic temperatures (∼30–150 K) and H2 densities (104–105 cm−2). These properties are similar to those found for the starburst galaxy NGC 253 also using class I methanol masers, suggested to be associated with a cloud–cloud collision. We conclude that shocks driven by the possible cloud–cloud collision is likely the most important mechanism responsible for the high level of chemical complexity observed in G+0.693-0.03. [ABSTRACT FROM AUTHOR]

Using 0.2 arcsec (∼3 pc) ALMA images of vibrationally excited HC3N emission (HC3N*) we reveal the presence of eight unresolved Super Hot Cores (SHCs) in the inner 160 pc of NGC 253. Our LTE and non-LTE modelling of the HC3N* emission indicate that SHCs have dust temperatures of 200–375 K, relatively high H2 densities of (1−6) × 106 cm−3 and high IR luminosities of (0.1–1) × 108 L⊙. As expected from their short-lived phase (∼104 yr), all SHCs are associated with young super star clusters (SSCs). We use the ratio of luminosities from the SHCs (protostar phase) and from the free–free emission (ZAMS star phase), to establish the evolutionary stage of the SSCs. The youngest SSCs, with the larges ratios, have ages of a few 104 yr (proto-SSCs) and the more evolved SSCs are likely between 105 and 106 yr (ZAMS-SSCs). The different evolutionary stages of the SSCs are also supported by the radiative feedback from the UV radiation as traced by the HNCO/CS ratio, with this ratio being systematically higher in the young proto-SSCs than in the older ZAMS-SSCs. We also estimate the SFR and the SFE of the SSCs. The trend found in the estimated SFE (⁠|$\sim 40{{\ \rm per\ cent}}$| for proto-SSCs and |$\gt 85{{\ \rm per\ cent}}$| for ZAMS-SSCs) and in the gas mass reservoir available for star formation, one order of magnitude higher for proto-SSCs, suggests that star formation is still going on in proto-SSCs. We also find that the most evolved SSCs are located, in projection, closer to the centre of the galaxy than the younger proto-SSCs, indicating an inside-out SSC formation scenario. [ABSTRACT FROM AUTHOR]

Context. The increase in bandwidth and sensitivity of state-of-the-art radio observatories is providing a wealth of molecular data from nearby star-forming regions up to high-z galaxies. Analysing large data sets of spectral cubes requires efficient and user-friendly tools optimised for astronomers with a wide range of backgrounds. Aims. In this paper we present the detailed formalism at the core of Spectral Line Identification and Modelling (SLIM) within the MAdrid Data CUBe Analysis (MADCUBA) package and their main data-handling functionalities. These tools have been developed to visualise, analyse, and model large spectroscopic data cubes. Methods. We present the highly interactive on-the-fly visualisation and modelling tools of MADCUBA and SLIM, which includes a stand-alone spectroscopic database. The parameters stored therein are used to solve the full radiative transfer equation under local thermodynamic equilibrium (LTE). The SLIM package provides tools to generate synthetic LTE model spectra based on input physical parameters of column density, excitation temperature, velocity, line width, and source size. It also provides an automatic fitting algorithm to obtain the physical parameters (with their associated errors) better fitting the observations. Synthetic spectra can be overlayed in the data cubes/spectra to ease the task of multi-molecular line identification and modelling. Results. We present the Java-based MADCUBA and its internal module SLIM packages which provide all the necessary tools for manipulation and analysis of spectroscopic data cubes. We describe in detail the spectroscopic fitting equations and make use of this tool to explore the breaking conditions and implicit errors of commonly used approximations in the literature. Conclusions. Easy-to-use tools like MADCUBA allow users to derive physical information from spectroscopic data without the need for simple approximations. The SLIM tool allows the full radiative transfer equation to be used, and to interactively explore the space of physical parameters and associated uncertainties from observational data. [ABSTRACT FROM AUTHOR]

We present interferometric observations with the Atacama Large Millimeter Array (ALMA) of the free–free continuum and recombination line emission at 1 and 3 mm of the Red Square Nebula surrounding the B[e]-type star MWC 922. The distance to the source, which is unknown, is usually taken to be d = 1.7–3 kpc. The unprecedented angular resolution (up to ~0.′′02) and exquisite sensitivity of these data reveal for the first time the structure and kinematics of the nascent compact ionized region at its center. We imaged the line emission of H30α and H39α, previously detected with single-dish observations, and of H51ɛ, H55γ, and H63δ, detected for the first time in this work. The line emission is seen over a full velocity range of ~180 km s−1 arising in a region of diameter <0.′′14 (less than a few hundred au) in the maser line H30α, which is the most intense transition reported here. We resolve the spatio-kinematic structure of a nearly edge-on disk rotating around a central mass of ~10 M⊙ (d = 1.7 kpc) or ~18 M⊙ (d = 3 kpc), assuming Keplerian rotation. Our data also reveal a fast (~100 km s−1) bipolar ejection (possibly a jet) orthogonal to the disk. In addition, a slow (<15 km s−1) wind may be emanating from the disk. Both, the slow and the fast winds are found to be rotating in a similar manner to the ionized layers of the disk. This represents the first empirical proof of rotation in a bipolar wind expanding at high velocity (~100 km s−1). The launching radius of the fast wind is found to be <30–51 au (i.e., smaller than the inner rim of the ionized disk probed by our observations). We believe that the fast wind is actively being launched, probably by a disk-mediated mechanism in a (possibly accretion) disk around a possible compact companion. We have modeled our observations using the radiative transfer code MORELI. This enables us to describe with unparalleled detail the physical conditions and kinematics in the inner layers of MWC 922, which has revealed itself as an ideal laboratory for studying the interplay of disk rotation and jet-launching. Although the nature of MWC 922 remains unclear, we believe it could be a ~15 M⊙ post-main sequence star in a mass-exchanging binary system. If this is the case, a more realistic value of the distance may be d ~ 3 kpc. [ABSTRACT FROM AUTHOR]

Aims. We study the spatial distribution and kinematics of water emission in a ~8 × 8 pc2 region of the Galactic center (GC) that covers the main molecular features around the supermassive black hole Sagittarius A* (Sgr A*). We also analyze the water excitation to derive the physical conditions and water abundances in the circumnuclear disk (CND) and the "quiescent clouds". Methods. We presented the integrated line intensity maps of the ortho 110 − 101, and para 202 − 111 and 111 − 000 water transitions observed using the On the Fly mapping mode with the Heterodyne Instrument for the Far Infrared (HIFI) on board Herschel. To study the water excitation, we used HIFI observations of the ground state ortho and para H 218 $_2^{18}$ 2 18 O transitions toward three selected positions in the vicinity of Sgr A*. In our study, we also used dust continuum measurements of the CND, obtained with the Spectral and Photometric Imaging REceiver (SPIRE) instrument. Using a non-local thermodynamical equilibrium (LTE) radiative transfer code, the water line profiles and dust continuum were modeled, deriving H2O abundances (XH2O $X_{\textrm{H}_2\textrm{O}}$ X H 2 O ), turbulent velocities (Vt), and dust temperatures (Td). We also used a rotating ring model to reproduce the CND kinematics represented by the position velocity (PV) diagram derived from para 202 − 111 H2O lines. Results. In our H2O maps we identify the emission associated with known features around Sgr A*: CND, the Western Streamer, and the 20 and 50 km s−1 clouds. The ground-state ortho water maps show absorption structures in the velocity range of [−220,10] km s−1 associated with foreground sources. The PV diagram reveals that the 202 − 111 H2O emission traces the CND also observed in other high-dipole molecules such as SiO, HCN, and CN. Using the non-LTE code, we derive high XH2O $X_{\textrm{H}_2\textrm{O}}$ X H 2 O of ~(0.1–1.3) × 10−5, Vt of 14–23 km s−1 , and Td of 15–45 K for the CND, and the lower XH2O $X_{\textrm{H}_2\textrm{O}}$ X H 2 O of 4 × 10−8 and Vt of 9 km s−1 for the 20 km s−1 cloud. Collisional excitation and dust effects are responsible for the water excitation in the southwest lobe of the CND and the 20 km s−1 cloud, whereas only collisions can account for the water excitation in the northeast lobe of the CND. We propose that the water vapor in the CND is produced by grain sputtering by shocks of 10–20 km s−1, with some contribution of high temperature and cosmic-ray chemistries plus a photon-dominated region chemistry, whereas the low XH2O $X_{\textrm{H}_2\textrm{O}}$ X H 2 O derived for the 20 km s−1 cloud could be partially a consequence of the water freeze-out on grains. [ABSTRACT FROM AUTHOR]

Theories of a pre-RNA world suggest that glycolonitrile (HOCH2CN) is a key species in the process of ribonucleotide assembly, which is considered as a molecular precursor of nucleic acids. In this Letter, we report the first detection of this pre-biotic molecule in the interstellar medium by using ALMA data obtained at frequencies between 86.5 GHz and 266.5 GHz toward the Solar-type protostar IRAS16293–2422 B. A total of 15 unblended transitions of HOCH2CN were identified. Our analysis indicates the presence of a cold (T |$\rm _{ex}$|  = 24 ± 8 K) and a warm (T |$\rm _{ex}$|  = 158 ± 38 K) component meaning that this molecule is present in both the inner hot corino and the outer cold envelope of IRAS16293 B. The relative abundance with respect to H2 is (6.5 ± 0.6) × 10−11 and ≥(6 ± 2) × 10−10 for the warm and cold components, respectively. Our chemical modelling seems to underproduce the observed abundance for both the warm and cold component under various values of the cosmic ray ionization rate (ζ). Key gas phase routes for the formation of this molecule might be missing in our chemical network. [ABSTRACT FROM AUTHOR]

We report the first detection in the interstellar medium (ISM) of the Z-isomer of cyanomethanimine (HNCHCN), an HCN dimer proposed as precursor of adenine. We identified six transitions of Z-cyanomethanimine, along with five transitions of E-cyanomethanimine, using IRAM 30m observations towards the Galactic Centre quiescent molecular cloud G + 0.693. The Z-isomer has a column density of (2.0 ± 0.6) × 1014 cm−2 and an abundance of 1.5 × 10−9. The relative abundance ratio between the isomers is [Z/E]∼6. This value cannot be explained by the two chemical formation routes previously proposed (gas phase and grain surface), which predicts abundances ratios between 0.9 and 1.5. The observed [Z/E] ratio is in good agreement with thermodynamic equilibrium at the gas kinetic temperature (130−210 K). Since isomerization is not possible in the ISM, the two species may be formed at high temperature. New chemical models, including surface chemistry on dust grains and gas-phase reactions, should be explored to explain our findings. Whatever the formation mechanism, the high abundance of Z-HNCHCN shows that precursors of adenine are efficiently formed in the ISM. [ABSTRACT FROM AUTHOR]

We present an unbiased spectral line survey towards the Galactic Centre (GC) quiescent giant molecular cloud, G+0.693 using the GBT and IRAM 30  telescopes. Our study highlights an extremely rich organic inventory of abundant amount of nitrogen (N)-bearing species in a source without signatures of star formation. We report the detection of 17 N-bearing species in this source, of which eight are complex organic molecules. A comparison of the derived abundances relative to H2 is made across various Galactic and extragalactic environments. We conclude that the unique chemistry in this source is likely to be dominated by low-velocity shocks with X-rays/cosmic rays also playing an important role in the chemistry. Like previous findings obtained for O-bearing molecules, our results for N-bearing species suggest a more efficient hydrogenation of these species on dust grains in G+0.693 than in hot cores in the Galactic disc, as a consequence of the low-dust temperatures coupled with energetic processing by X-ray/cosmic ray radiation in the GC. [ABSTRACT FROM AUTHOR]

We present a study of diffuse extended ionized gas towards three clouds located in the Galactic Centre (GC). One line of sight (LOS) is towards the 20 km s-1 cloud (LOS-0.11) in the Sgr A region, another LOS is towards the 50 km s-1 cloud (LOS-0.02), also in Sgr A, while the third is towards the Sgr B2 cloud (LOS+0.693). The emission from the ionized gas is detected from Hnα and Hmβ radio recombination lines (RRLs). Henα and Hemβ RRL emission is detected with the same n and m as those from the hydrogen RRLs only towards LOS+0.693. RRLs probe gas with positive and negative velocities towards the two Sgr A sources. The Hmβ to Hnα ratios reveal that the ionized gas is emitted under local thermodynamic equilibrium conditions in these regions. We find a He to H mass fraction of 0.29±0.01 consistent with the typical GC value, supporting the idea that massive stars have increased the He abundance compared to its primordial value. Physical properties are derived for the studied sources. We propose that the negative velocity component of both Sgr A sources is part of gas streams considered previously to model the GC cloud kinematics. Associated massive stars with what are presumably the closest HII regions to LOS-0.11 (positive velocity gas), LOS-0.02, and LOS+0.693 could be the main sources of ultraviolet photons ionizing the gas. The negative velocity components of both Sgr A sources might be ionized by the same massive stars, but only if they are in the same gas stream. [ABSTRACT FROM AUTHOR]

Aims. We aim to reveal the morphology, chemical composition, kinematics, and to establish the main processes prevalent in the gas at the footpoints of the giant molecular loops (GMLs) in the Galactic center region. Methods. Using the 22-m Mopra telescope, we mapped the M-3.8+0.9 molecular cloud, placed at the footpoints of a GML, in 3-mm range molecular lines. To derive the molecular hydrogen column density, we also observed the 13CO(2 - 1) line at 1 mm using the 12-m APEX telescope. From the 3 mm observations 12 molecular species were detected, namely HCO+, HCN, H13CN, HNC, SiO, CS, CH3OH, N2H+, SO, HNCO, OCS, and HC3N. Results. Maps revealing the morphology and kinematics of the M-3.8+0.9 molecular cloud in different molecules are presented. We identify six main molecular complexes. We derive fractional abundances in 11 selected positions of the different molecules assuming local thermodynamical equilibrium. Conclusions. Most of the fractional abundances derived for the M-3.8+0.9 molecular cloud are very similar over the whole cloud. However, the fractional abundances of some molecules show significant difference with respect to those measured in the central molecular zone (CMZ). The abundances of the shock tracer SiO are very similar between the GMLs and the CMZ. The methanol emission is the most abundant species in the GMLs. This indicates that the gas is likely affected by moderate ~30 km s-1 or even high velocity (50 km s-1) shocks, consistent with the line profile observed toward one of the studied position. The origin of the shocks is likely related to the flow of the gas throughout the GMLs towards the footpoints. [ABSTRACT FROM AUTHOR]

We report the detection of the pre-biotic molecule CH3Gerasimenko has been proposed, and it has recently been detected in hot cores around high-mass protostars. We observed IRAS16293-2422 B with the Atacama Large Millimeter Array in the 90 to 265 GHz range, and detected eight unblended transitions of CH3NCO. From our Local Thermodynamic Equilibrium analysis, we derived an excitation temperature of 110 ± 19 K and a column density of of (4.0 ± 0.3)×1015 c-2, which results in an abundance of ≤(1.4 ± 0.1)×10-10 with respect to molecular hydrogen. This implies a CHCH3NCO/HNCO and CHCH3NCO/NHCH2CHO column density ratios of ~0.08. Our modelling of the chemistry of CH3NCO suggests that both ice surface and gas phase formation reactions of this molecule are needed to explain the observations. [ABSTRACT FROM AUTHOR]

We present the first detection of the ortho-H2O 423 - 330 transition at 448 GHz in space. We observed this transition in the local (z = 0.010) luminous infrared (IR) galaxy ESO 320-G030 (IRAS F11506-3851) using the Atacama Large Millimeter/submillimeter Array (ALMA). The water 423 - 330 emission, which originates in the highly obscured nucleus of this galaxy, is spatially resolved over a region of ~65 pc in diameter and shows a regular rotation pattern compatible with the global molecular and ionized gas kinematics. The line profile is symmetric and well fitted by a Gaussian with an integrated flux of 37.0 ± 0.7 Jy km s-1. Models predict this water transition as a potential collisionally excited maser transition. On the contrary, in this galaxy, we find that the 423 - 330 emission is primarily excited by the intense far-IR radiation field present in its nucleus. According to our modeling, this transition is a probe of deeply buried galaxy nuclei thanks to the high dust optical depths (t100µm> 1, NH> 1024 cm-2) required to efficiently excite it. [ABSTRACT FROM AUTHOR]

Aims. We aim to better understand the imprints that the nuclear activity in galaxies leaves in the molecular gas. Methods. We used the IRAM 30m telescope to observe the frequency range ∼[86-116] GHz towards the central regions of the starburst galaxies M83, M82, and NGC253, the galaxies hosting an active galactic nucleus (AGN) M51, NGC1068, and NGC7469, and the ultra-luminous infrared galaxies (ULIRGs) Arp 220 and Mrk 231. Assuming local thermodynamic equilibrium (LTE), we calculated the column densities of 27 molecules and 10 isotopologues (or their upper limits in case of non-detections). Results. Among others, we report the first tentative detections of CH3CHO, HNCO, and NS in M82 and, for the first time in the extragalactic medium, HC5N in NGC253. Hα recombination lines were only found in M82 and NGC253. Vibrationally excited lines of HC3N were only detected in Arp 220. CH3CCH emission is only seen in the starburst-dominated galaxies. By comparison of the fractional abundances among the galaxies, we looked for the molecules that are best suited to characterise the chemistry of each group of galaxies (starbursts, AGNs and ULIRGs), as well as the differences among galaxies within the same group. Conclusions. Suitable species for characterising and comparing starburst galaxies are CH3OH and HNCO as tracers of large-scale shocks, which dominate early to intermediate starburst stages, and CH3CCH, c-C3H2, and HCO as tracers of UV fields, which control the intermediate-to-old or post starburst phases. M83 shows signs of a shock-dominated environment. NGC253 is characterised by both strong shocks and some UV fields. M82 stands out for its bright photo-dissociated region tracers, which indicate an UV fielddominated environment. Regarding AGNs, the abundances of HCN and CN (previously claimed as enhanced in AGNs) in M51 are similar to those in starburst galaxies, while the HCN/HCO+ ratio is high in M51 and NGC1068, but not in NGC7469.We did not find a correlation between the HCN/CS ratio (recently claimed as a possible starburst/AGN discriminator) and the AGN activity. However, a high enough spatial resolution to separate their circumnuclear disks from the surrounding star-forming regions is needed to find molecular abundance trends in AGNs. High abundances of H13CN and HC3N, as well as a similarity between the column densities of 13CO and C18O, are representative of the molecular interstellar medium in the ULIRGs. Furthermore, the chemistry of Arp 220 points towards a more starburst-dominated environment, while that of Mrk 231 more resembles the AGNs of our sample. [ABSTRACT FROM AUTHOR]

The UC-HII region of MWC 349A is the prototype of an ionized wind driven by a massive star surrounded by a disk. Recent high angular resolution observations of the millimeter recombination lines have shown that the disk rotates with a Keplerian law in its outer parts. However, the kinematics of innermost regions in the UC-HII region of MWC 349A is still unknown, in particular, the radius where the wind is launched from the disk. We performed hydrogen recombination line observations with the Heterodyne Instrument for the Far Infrared (HIFI) onboard the Herschel Space Observatory to study the kinematics of its innermost regions by studying their spectral features. In addition to the two laser peaks, we report the first detection of two new components that are blueshifted with respect to the laser peaks for all the recombination lines with principal quantum number n ⩽ 21. These new spectral features originate from the region where the wind is ejected from the disk.We used our 3D non-LTE radiative transfer model for recombination lines (MORELI) to show that these features are consistent with the wind being ejected at a radius of ∼24 AU from the star, which supports magnetohydrodynamic wind models. [ABSTRACT FROM AUTHOR]

We study the disk-halo interaction, in the context of orbits and Giant Molecular loops (GMLs) in the Galactic center (GC) region. From a large scale survey of the central kpc of the Galaxy, in SiO J = (2 − 1), HCO+J = (1 − 0) and H13CO+J = (1 − 0) molecular emission, we identify shock regions traced by the enhancement of the SiO. These positions were studied using the 12C/13C isotopic ratio to trace gas accretion/ejection. We found a systematically higher 12C/13C isotopic ratio (> 40) toward the GMLs and the x1 orbits than for the GC standard molecular clouds (20–25). The high isotopic ratios are consistent with the accretion of the gas from the halo and from the outskirts of the Galactic disk. From multi-transitional observations of NH3, we derive two kinetic temperature regimes (one warm at ∼150 K and one cold at ∼40 K) for all the positions, except for the GMLs positions where only the warm component is present. The fractional abundances derived from the different molecules support the shock origin for the heating mechanism in the GC. We also present a detailed study of one molecular cloud placed in the foot points of two giant molecular loops, where two of the previously selected positions are placed. Using the 22m Mopra telescope we mapped the molecular cloud M − 3.8 + 0.9 in 3-mm molecular lines. The data show structures at small scale in SiO emission, with narrower line profiles than those of, e.g, HCO+ or HCN, which indicate that the shocks are dynamically confined. The data also show clear differences between different molecular tracers, e.g., between the SiO and HCO+ emission, which would indicate differences in the physical properties and chemistry within the cloud. [ABSTRACT FROM PUBLISHER]

Despite many investigations, the physical characteristics of the molecular gas in the Galactic center circumnuclear disk (CND) remain a topic of debate. Its mass is highly uncertain, between 104 (from dust) and 105–6 M⊙ (derived from gas tracers), and depending on the probe, density estimates for the dense clumps are 105–8 cm−3 and gas temperatures run from 50 to a few hundred K. The range of physical parameters leaves open many questions about the nature and fate of the CND. Using several ground-based observatories, together with Herschel and SOFIA, we have studied the physical conditions of the dense clumps using CO, HCN and HCO+, finding that most of them are transient. Their densities are not large enough for them to be gravitationally bound in the tidal field in the center of our Galaxy. [ABSTRACT FROM PUBLISHER]

Aims. We study the molecular composition of the interstellar medium (ISM) surrounding an active galactic nucleus (AGN), by making an inventory of molecular species and their abundances, to establish a chemical differentiation between starburst galaxies and AGN. Methods. We used the IRAM-30m telescope to observe the central 1.5-2 kpc region of NGC 1068, covering the frequencies between 86.2 GHz and 115.6 GHz. Using Boltzmann diagrams, we calculated the column densities of the detected molecules. We used a chemical model to reproduce the abundances found in the AGN, to determine the origin of each detected species, and to test the influence of UV fields, cosmic rays, and shocks on the ISM. Results. We identified 24 different molecular species and isotopologues, among which HC3N, SO, N2H+, CH3CN, NS, 13CN, and HN13C are detected for the first time in NGC1068. A comparison of the abundances in the nuclear regions of NGC1068, M82, and NGC253 allowed us to establish a chemical differentiation between starburst galaxies and AGN. Two abundant species in starburst galaxies, H2CO and CH3CCH, are not detected in NGC1068, probably because they are destroyed by UV fields or shocks. On the other hand, species such as CN, SiO, HCO+, and HCN, are enhanced by cosmic ray radiation fields. We obtained the upper limits to the isotopic ratios 12C/13C = 49, 16O/18O = 177, and 32S/34S = 5. These ratios are much lower in this AGN than in starburst galaxies. Our chemical models suggest that the chemistry in the nucleus of NGC1068 is strongly influenced by cosmic rays, although high values of both cosmic rays and far ultraviolet (FUV) radiation fields also explain the observations well. C-shocks can explain the abundances of C2H and H2CO, but do not strongly affect the abundances of the other detected species. Conclusions. The gas in the nucleus of NGC 1068 has a different chemical composition than starburst galaxies. The distinct physical processes dominating galaxy nuclei (e.g. C-shocks, UV fields, X-rays, cosmic rays) leave clear imprints in the chemistry of the gas, which allow the nucleus activity to be characterised by its molecular abundances. [ABSTRACT FROM AUTHOR]

Context. It is well known that the kinetic temperatures, Tkin, of the molecular clouds in the Galactic center region are higher than in typical disk clouds. However, the Tkin of the molecular complexes found at higher latitudes towards the giant molecular loops in the central region of the Galaxy is so far unknown. The gas of these high-latitude molecular clouds (hereafter referred to as "halo clouds") is located in a region where the gas in the disk may interact with the gas in the halo in the Galactic center region. Aims. To derive Tkin in the molecular clouds at high latitude and understand the physical process responsible for the heating of the molecular gas both in the central molecular zone (the concentration of molecular gas in the inner ∼500 pc) and in the giant molecular loops. Methods. We measured the metastable inversion transitions of NH3 from (J, K) = (1, 1) to (6, 6) toward six positions selected throughout the Galactic central disk and halo. We used rotational diagrams and large velocity gradient (LVG) modeling to estimate the kinetic temperatures toward all the sources. We also observed other molecules like SiO, HNCO, CS, C34S, C18O, and 13CO, to derive the densities and to trace different physical processes (shocks, photodissociation, dense gas) expected to dominate the heating of the molecular gas. Results. We derive for the first time Tkin of the high-latitude clouds interacting with the disk in the Galactic center region. We find high rotational temperatures in all the observed positions. We derive two kinetic temperature components (∼150 K and ∼40 K) for the positions in the central molecular zone, and only the warm kinetic temperature component for the clouds toward the giant molecular loops. The fractional abundances derived from the different molecules suggest that shocks provide the main heating mechanism throughout the Galactic center, also at high latitudes. [ABSTRACT FROM AUTHOR]

The detection of very narrow SiO emission and the higher degree of excitation of the ion fluid compared to the neutral one towards the protostas L1448-mm have been interpreted as signatures of the magnetic precursor of C-shocks. Since this is the only source where these features have been observed together, we carried out a survey to map the J = 2 → 1 and 8 → 7 lines of SiO, and the J = 1 → 0 and 4 → 3 lines of H13CO+ (as the representative ion) and HN13C (as the representative neutral species) towards four class 0/I low-mass protostars known to have young outflows (L1448-IRS3, NOC 1333-IRAS 4A/B and SSV 13, VLA 1623 and IRAS 20353). As previously reported, towards L1448-IRS3 and NGC 1333 strong, narrow SiO 29→1 is detected, and we also find a velocity component towards each outflow which shows high a H13CO+ 4 → 3/1→0 integrated intensity ratio compared to that of HN13C. Towards VLA 1623, we find very weak, narrow SiO, and a component that is visible in H13CO+ but not at all in HN13C. For IRAS 20353, we find neither narrow SiO nor high H13CO+ 4 → 3/1 → 0 flux ratios. Previous work explained the higher degree of excitation of H13CO+ by the selective excitation of ions by electrons, whose abundance is expected to increase at the precursor stage. Here, however, by considering a range of kinetic temperatures for the gas, we find that it is possible to fit the observations with a single temperature and density, without an increased electron abundance, despite the large differences in 4 → 3/1 → 0 ratio between the two molecules. The high H13CO+ 4 → 3/1 → 0 flux ratios may simply be due to protostellar heating. However, the hypothesis that narrow SiO is formed at the precursor stage of shocks remains plausible, since other explanations require either the presence of shocks with larger dynamical timescales, or predict the narrow SiO to have a larger spatial extent than it appears to have towards the sources L1448-IRS3 and VLA 1623. Larger scale maps of the narrow SiO emission are needed to confirm that it is confined to the regions around protostars (as would be expected in the precursor scenario), and mapping of different ion and neutral species is necessary to confirm whether there are indeed precursor regions surrounding young outflows where the ion and neutral species behave as separate fluids. [ABSTRACT FROM AUTHOR]

We report SOFIA/GREAT, Herschel/HIFI, and ground-based velocity-resolved spectroscopy of carbon monoxide (CO) rotational transitions from J = 2-1 to J = 16-15 toward two positions in the circum-nuclear disk (CND) in our Galactic center. Radiative transfer models were used to derive information on the physical State of the gas traced by CO. The excitation of the CO gas cannot be explained by a single physical component, but is clearly the superposition of various warm gas phases. In a two-component approach, our large velocity gradient (LVG) analysis suggests high temperatures of -200 K with moderate gas densities of only ∼ 104.5 cm-1 for the bulk of the material. A higher excited phase, carrying ∼20-30% of the column densities, is warmer (∼300-500 K) but only slightly denser (∼105.3 cm-3). These densities are too low to self-stabilize the clumps against their high internal turbulence and fall below the Roche density (>107 cm-3) at 1.5 Pc galactocentric distance. We conclude that the bulk of the material in the CND is not organized by self-gravity nor stable against tidal disruption, and must be transient. [ABSTRACT FROM AUTHOR]

Context. The interstellar region within the few central parsecs around the super-massive black hole, Sgr A", at the very Galactic center is composed of a number of overlapping molecular structures that are subject to one of the most hostile physical environments in the Galaxy. Aims. Through the study of the morphology and kinematics of the emission from different molecular species as well as the variation of their line ratios we can attain a deeper understanding of the distribution and interaction between different gas structures and the energetic phenomena taking place in the surroundings of Sgr A" and of the physical processes responsible for the heating in this region. Methods. We performed high-resolution (4'' × 3'' ~ 0.16 × 0.11 pc) interferometric observations of CN, 13CN, H2CO, SiO, c-C3H2 and HC3N emission at 1.3 mm toward the central ~4 pc of the Galactic center region. Results. Strong differences are observed in the distribution of the different molecules. The UV resistant species CN, the only species tracing all previously identified circumnuclear disk (CND) structures, is mostly concentrated in optically thick clumps in the rotating filaments around Sgr A". H2CO emission traces a shell-like structure that we interpret as the expansion of Sgr A East against the 50 km s-1 and 20 kms-1 giant molecular clouds (GMCs). We derive isotopic ratios 12C/13C~ 15-45 across most of the CND region, except for the northeast arm, where the peak of H2CO is observed and ratios <10 are found. The densest molecular material, traced by SiO and HC3N, is located in the southern CND, likely because of shocked gas infalling from the 20 kms-1 GMC streamers, and the northeast arm, as a result of the expansion of SgrA East or a connecting point of the 50 kms-1 streamer east of the CND. The observed c-C3H2/HC3N ratio observed in the region is more than an order of magnitude lower than in Galactic PDRs. Toward the central region only CN was detected in absorption. In addition to the known narrow line-of-sight absorptions, a 90 kms-1 wide optically thick spectral feature is observed. We found evidence of an even wider (>100 km s-1) absorption feature. About 70-75% of the gas mass, concentrated in just the 27% densest molecular clumps, is associated with rotating structures and show evidence of an association with each of the arcs of ionized gas in the mini-spiral structure. Conclusions. These observations provide a combined chemical and kinematical picture of the very central region around Sgr A". Chemical differentiation has been proven to be a powerful tool to distinguish the many overlapping molecular components in this crowded and heavily obscured region. [ABSTRACT FROM AUTHOR]

ABSTRACT We have mapped 20 spectral lines in the Central Molecular Zone (CMZ) around the Galactic Centre, emitting from 85.3 to 93.3 GHz. This work used the 22-m Mopra radio telescope in Australia, equipped with the 8-GHz bandwidth University of New South Wales-Mopra Spectrometer (UNSW-MOPS) digital filter bank, obtaining ∼2 km s−1 spectral and ∼40 arcsec spatial resolution. The lines measured include emission from the c-C3H2, CH3CCH, HOCO+, SO, H13CN, H13CO+, SO, H13NC, C2H, HNCO, HCN, HCO+, HNC, HC3N, 13CS and N2H+ molecules. The area covered is Galactic longitude −07 to 18 and latitude −03 to 02, including the bright dust cores around Sgr A, Sgr B2, Sgr C and G1.6−0.025. We present images from this study and conduct a principal component analysis on the integrated emission from the brightest eight lines. This is dominated by the first component, showing that the large-scale distribution of all molecules is very similar. We examine the line ratios and optical depths in selected apertures around the bright dust cores, as well as for the complete mapped region of the CMZ. We highlight the behaviour of the bright HCN, HNC and HCO+ line emission, together with that from the 13C isotopologues of these species, and compare the behaviour with that found in extragalactic sources where the emission is unresolved spatially. We also find that the isotopologue line ratios (e.g. HCO+/H13CO+) rise significantly with increasing redshifted velocity in some locations. Line luminosities are also calculated and compared to that of CO, as well as to line luminosities determined for external galaxies. [ABSTRACT FROM AUTHOR]

Large-scale shocks propagate in the interstellar medium of starburst and active galaxies, driven by the same mechanisms that regulate the evolution of the star formation and AGN episodes. The imprints of shocks in the chemical composition of the molecular gas provide useful means to identify those mechanisms and to asses their effects. We review some recent and on-going studies of the molecular gas chemistry in the nearby star-forming galaxies IC 342, NGC 253 and M 82, based on the well known shock tracer silicon monoxide (SiO). When mapped at high-spatial resolution the SiO emission reveals substantial differences among these galaxies. In particular, the location of shocks and their dominant driver are in correspondence with the evolutionary stage of the starburst episode. Complementary observations of other tracers of shock chemistry, like methanol (CH3OH), help us to improve the characterization of the shock mechanisms. We also present the first high-resolution observations of the SiO emission in the Seyfert 2 galaxy NGC 1068. [ABSTRACT FROM AUTHOR]

Gaussian beam-mode expansion with only the fundamental mode does not work properly when the angular region of interest is wide. It is necessary to use higher-order mode for the expansion. A study of the convergence of these higher order modes is presented for the case of a corrugated conical horn. Conclusions about the number of modes necessary for good accuracy are given. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 45: 199–203, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20769 [ABSTRACT FROM AUTHOR]

Using the IRAM 30 m telescope, we perform a molecular line survey of the 3 and 2 mm wavelength ranges towards 5 selected positions in the Galactic center region, sampling shocked regions, ultraviolet (UV) and X-ray pervaded regions, and positions with rich organic chemistry. These surveys have the potential to be used as chemical templates for different types of activity, such as photodissociated regions (PDRs), shocks and X-ray dominated regions (XDRs). Complementary, molecular surveys done towards extragalactic nuclei, that are also dominated by these physical activities, were carried by our group. [ABSTRACT FROM PUBLISHER]

Spectral surveys provide the only way to determine the full molecular inventory of a source and hence to build a comprehensive view of the state of the molecular gas and its role in the star formation process. Systematic studies have opened the possibility of using chemistry as a diagnostic tool for star burst and AGN activities in the highly obscured galactic nuclear regions. [ABSTRACT FROM AUTHOR]

We have studied how the active nucleus of the Seyfert 2 galaxy NGC 1068 influences the chemistry of its 200 pc circumnuclear disk of molecular gas (CND). Results from new observations made with the IRAM 30m telescope have served for deriving abundances of molecular species such as SiO, CN, HCO+, HOC+, H13CO+ and HCO. These estimates are complemented with a re-evaluation of abundances of HCN, CS and CO, based on previously published observations. We report on the first detection of significant SiO emission in the CND of NGC 1068. We also report on the first extragalactic detection of the reactive ion HOC+. Our conclusions favour an overall scenario where the CND of NGC 1068 has become a giant X-ray Dominated Region (XDR).To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html [ABSTRACT FROM PUBLISHER]