Large-scale molecular shocks in galaxies: the SiO interferometer map of IC 342 (original) (raw)
Related papers
2000
This paper presents the first high-resolution SiO map made in an external galaxy. The nucleus of the nearby barred spiral NGC253 has been observed simultaneously in the v=0, J=2-1 line of SiO and in the J=1-0 line of H13CO+ with the IRAM interferometer, with a resolution of 7.5"x2.6". Emission from SiO and H13CO+ is extended in the nucleus of NGC253. The bulk of the SiO/H13CO+ emission arises from a 600pcx250pc circumnuclear disk (CND) with a double ringed structure. The inner ring, of radius r=60pc, viewed edge-on along PA=51deg, hosts the nuclear starburst; the outer pseudo-ring opens out as a spiral-like arc up to r=300pc. The kinematics of the gaseous disk, characterized by strong non-circular motions, is interpreted in terms of the resonant response of the gas to the barred potential. The inner ring would correspond to the inner Inner Lindblad Resonance(iILR), whereas the outer region is linked to the onset of a trailing spiral wave across the outer ILR (oILR). Most notably, we report the detection of a molecular gas counterpart of the giant outflow of hot gas, previously seen in X-ray and optical lines, and tentatively identified as a dust chimney in the the 450mu continuum band.The SiO shows a high average fractional abundance in the CND of X(SiO)=1.5x10E-10. This is more than an order of magnitude above the predicted value of a PDR. Moreover, X(SiO) varies at least by an order of magnitude between the inner starburst region, which dominates the global emission, where we derive X(SiO)=1--2x10E-10, and the outer region, where X(SiO) reaches a few 10E-9. SiO abundance is also significantly enhanced in the outflow (X(SiO)=3--5x10E-10). Different mechanisms are explored to explain the unlike chemical processing of molecular gas within the nucleus.
2010
This paper is part of a multi-species survey of line emission from the molecular gas in the circum-nuclear disk (CND) of the Seyfert 2 galaxy NGC1068. Single-dish observations have provided evidence that the abundance of silicon monoxide(SiO) in the CND of NGC1068 is enhanced by 3-4 orders of magnitude with respect to the values typically measured in quiescent molecular gas in the Galaxy. We aim at unveiling the mechanism(s) underlying the SiO enhancement. We have imaged with the IRAM Plateau de Bure interferometer the emission of the SiO(2-1) and CN(2--1) lines in NGC1068 at 150pc and 60pc spatial resolution, respectively. We have also obtained complementary IRAM 30m observations of HNCO and methanol (CH3OH) lines. SiO is detected in a disk of 400pc size around the AGN. SiO abundances in the CND of (1-5)xE-09 are about 1-2 orders of magnitude above those measured in the starburst ring. The overall abundance of CN in the CND is high: (0.2-1)xE-07. The abundances of SiO and CN are en...
Spatially resolved chemistry in nearby galaxies. I. The center of IC 342
2008
We have imaged emission from the millimeter lines of eight molecules-C 2 H, C 34 S, N 2 H + , CH 3 OH, HNCO, HNC, HC 3 N, and SO-in the central half kiloparsec of the nearby spiral galaxy IC 342. The 5 ′′ (∼ 50 pc) resolution images were made with the Owens Valley Millimeter Array (OVRO). Using these and previously published CO and HCN images we obtain a picture of the chemistry within the nuclear region on the sizescales of individual giant molecular clouds. Bright emission is detected from all but SO. There are marked differences in morphology for the different molecules. A principal component analysis is performed to quantify similarities and differences among the images. This analysis reveals that while all molecules are to zeroth order correlated, that is, they are all found in dense molecular clouds, there are three distinct groups of molecules distinguished by the location of their emission within the nuclear region. N 2 H + , C 18 O, HNC and HCN are widespread and bright, good overall tracers of dense molecular gas. C 2 H and C 34 S, tracers of Photo-Dissociation Region chemistry, originate exclusively from the central 50-100 pc region, where radiation fields are high. The third group of molecules, CH 3 OH and HNCO, correlates well with the expected locations of bar-induced orbital shocks. The good correlation of HNCO with the established shock tracer molecule CH 3 OH is evidence that this molecule, whose chemistry has been uncertain, is indeed produced by processing of grains. HC 3 N is observed to correlate tightly with 3mm continuum emission, demonstrating that the young starbursts are the sites of the warmest and densest molecular gas. We compare our HNC images with the HCN images of Downes et al. (1992) to produce the first high resolution, extragalactic HCN/HNC map: the HNC/HCN ratio is near unity across the nucleus and the correlation of both of these gas tracers with the star formation is excellent. The ratio exhibits no obvious correlation with gas temperature or star formation strength.
The Astrophysical Journal, 2011
We present high angular resolution (0. 5-2. 0) observations of the millimeter continuum and the 12 CO(J = 3-2), 13 CO(J = 3-2), 13 CO(J = 2-1), C 18 O(J = 2-1), HCN(J = 3-2), HCO + (J = 4-3), and HCO + (J = 3-2) line emission in the circumnuclear disk (r 100 pc) of the prototypical Seyfert 2 galaxy NGC 1068, carried out with the Submillimeter Array. We also include in our analysis new 13 CO(J = 1-0) and improved 12 CO(J = 2-1) observations of NGC 1068 at high angular resolution (1. 0-2. 0) and sensitivity, conducted with the Institute de Radioastronomie Millimetrique Plateau de Bure Interferometer. Based on the complex dynamics of the molecular gas emission indicating non-circular motions in the central ∼100 pc, we propose a scenario in which part of the molecular gas in the circumnuclear disk of NGC 1068 is blown radially outward as a result of shocks. This shock scenario is further supported by quite warm (T kin 200 K) and dense (n(H 2) 10 4 cm −3) gas constrained from observed molecular line ratios. The HCN abundance in the circumnuclear disk is found to be [HCN]/[ 12 CO] ≈ 10 −3.5. This is slightly higher than the abundances derived for Galactic and extragalactic star-forming/starbursting regions. This result lends further support to X-ray-enhanced HCN formation in the circumnuclear disk of NGC 1068 as suggested by earlier studies. The HCO + abundance ([HCO + ]/[ 12 CO] ≈ 10 −5) appears to be somewhat lower than that of Galactic and extragalactic star-forming/starbursting regions. When trying to fit the centimeter-to-millimeter continuum emission by different thermal and non-thermal processes, it appears that electron-scattered synchrotron emission yields the best results while thermal free-free emission seems to overpredict the millimeter continuum emission.
SiO in G34.26: Outflows and shocks in a high mass star forming region
Astronomy and Astrophysics, 2001
We have looked for SiO emission as evidence of shocks in the high mass star formation region G34.26+0.15. JCMT, VLA and FCRAO observations show that SiO emission is widespread across the region. The SiO emission highlights a massive, collimated outflow and other regions where stellar winds are interacting with molecular clumps. As in other star forming regions, there is also SiO at ambient velocities which is related to the outflow activity. No strong SiO abundance enhancement was measured in either the outflow or the low velocity gas, though abundances up to 10 −8 are possible if the SiO is locally enhanced in clumps and optically thick. SiO emission is not detected from the hot core itself, indicating either that SiO is not strongly enhanced in the hot core or that column densities in the region where grain mantle evaporation has taken place are low. In line of sight spiral arm clouds, we measure a SiO abundance of 0.4-2 × 10 −10 , consistent with previous estimates for quiescent clouds.
Atomic and molecular gas in the starburst galaxy NGC 4945
Astronomy and Astrophysics, 2001
Spatial and kinematical correlations between the H i and 12 CO(2−1) emission of the southern spiral galaxy NGC 4945 are studied with a common angular resolution of ∼23 (corresponding to 750 pc at D = 6.7 Mpc) and a velocity resolution of ∼7 km s −1 . The 1.4 GHz continuum emission is also observed. The H i kinematics yield a galaxy mass of ∼1.4×10 11 M within radius R = 380 , with molecular and neutral atomic gas each contributing ∼2%, respectively. A central continuum source of size 7 . 6 × 3 . 4 (250 × 110 pc) is enveloped by a molecular cloud of mass 1.5 × 10 9 M for R ≤ 7 . 5, and is rapidly rotating with Vrot ∼ 160 km s −1 . H i emission from the central region at velocities |V −Vsys| > 200 km s −1 may be related to optically detected gas that is believed to trace an outflow directed towards the halo. Nuclear H i absorption at V -Vsys ∼ +80 km s −1 suggests inflow towards the centre, that was so far only seen in molecular lines. H i features at each end of the major axis (|R| ∼ 600 ) are interpreted as spiral arms that are viewed tangentially and that also cause prominent emission features in the radio continuum, H i, and CO further inside the galaxy. A central elongated region showing non-circular motions is interpreted as a bar which fuels the nuclear starburst. The H i and CO position-velocity data have been analysed using linear resonance theory, and possible locations of resonances are identified.
Shock Excitation in Interacting Galaxies: Markarian 266
The Astrophysical Journal, 2000
We present near infrared data on the luminous interacting system Mkn 266 (NGC 5256), comprising 2 µm continuum, and Brγ and 1-0 S(1) emission line images, together with K-band spectra. We have fitted stellar templates to the continuum, allowing us to account for all the stellar features and hence detect even faint gas excitation emission lines, including 8 and 11 H 2 lines in the SW and NE nuclei respectively. Population diagrams for the excited H 2 molecules indicate that most of the 1-0 S(1) in each of the nuclei has a thermal origin. We discuss this with reference to the observed morphologies, especially that of the 1-0 S(1) line. In particular, the core of 1-0 S(1) in the NE nucleus is more compact than the 2 µm continuum; while in the SW nucleus the 1-0 S(1) is significantly offset by 500 pc from the continuum (and other) emission. Lastly we address the issue of the region midway between the two nuclei, where previously a strong source of radio continuum has been observed. These results are set in the context of interacting galaxies where shock excited emission might be expected to occur as a direct consequence of the interaction.
Molecular gas in NUclei of GAlaxies (NUGA)
Astronomy and Astrophysics, 2009
We present CO(1-0) and CO(2-1) maps of the LINER galaxy NGC 7217, obtained with the IRAM interferometer, at 2.4 ′′ ×1.9 ′′ and 1.2 ′′ ×0.8 ′′ resolution respectively. The nuclear ring (at r = 12 ′′ = 0.8kpc) dominates the CO maps, and has a remarkable sharp surface density gradient at its inner edge. The latter is the site of the stellar/Hα ring, while the CO emission ring extends farther or is broader (500-600pc). This means that the star formation has been more intense toward the inner edge of the CO ring, in a thin layer, just at the location of the high gas density gradient. The CO(2-1)/CO(1-0) ratio is close to 1, typical of warm optically thick gas with high density. The overall morphology of the ring is quite circular, with no evidence of non-circular velocities. In the CO(2-1) map, a central concentration might be associated with the circumnuclear ionized gas detected inside r=3" and interpreted as a polar ring in the literature. The CO(2-1) emission inside 3" coincides with a spiral dust lane, clearly seen in the HST V − I color image. N-body simulations including gas dissipation and star formation are performed to better understand the nature of the nuclear ring observed. The observed rotation curve of NGC 7217 allows two possibilities, according to the adopted mass for the disk:
Molecular Gas Kinematics and Line Diagnostics in Early-type Galaxies: NGC 4710 & NGC 5866
We present interferometric observations of CO lines (12CO(1-0, 2-1) and 13CO(1-0, 2-1)) and dense gas tracers (HCN(1-0), HCO+(1-0), HNC(1-0) and HNCO(4-3)) in two nearby edge-on barred lenticular galaxies, NGC~4710 and NGC~5866, with most of the gas concentrated in a nuclear disc and an inner ring in each galaxy. We probe the physical conditions of a two-component molecular interstellar medium in each galaxy and each kinematic component by using molecular line ratio diagnostics in three complementary ways. First, we measure the ratios of the position-velocity diagrams of different lines, second we measure the ratios of each kinematic component's integrated line intensities as a function of projected position, and third we model these line ratios using a non-local thermodynamic equilibrium radiative transfer code. Overall, the nuclear discs appear to have a tenuous molecular gas component that is hotter, optically thinner and with a larger dense gas fraction than that in the inner rings, suggesting more dense clumps immersed in a hotter more diffuse molecular medium. This is consistent with evidence that the physical conditions in the nuclear discs are similar to those in photo-dissociation regions. A similar picture emerges when comparing the observed molecular line ratios with those of other galaxy types. The physical conditions of the molecular gas in the nuclear discs of NGC4710 and NGC5866 thus appear intermediate between those of spiral galaxies and starbursts, while the star formation in their inner rings is even milder.