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We present observations in CO(3-2) that, combined with previous observations in CO(2-1), constrain the physical properties of the filamentary molecular gas in the central $\sim$6.5 kpc of NGC 1275, the central giant elliptical galaxy of the Perseus cluster. We find this molecular gas to have a temperature $\gtrsim 20$ K and a density $\sim$$10^2$-$10^4 {\rm \ cm^{-3}}$, typically warmer and denser than the bulk of Giant Molecular Clouds (GMCs) in the Galaxy. Bathed in the harsh radiation and particle field of the surrounding intracluster X-ray gas, the molecular gas likely has a much higher ionization fraction than that of GMCs. For an ionization fraction of $\sim$$10^{-4}$, similar to that of Galactic diffuse ($\lesssim 250 {\rm \ cm^{-3}}$) partially-molecular clouds that emit in HCN(1-0) and HCO$^+$(1-0), we show that the same gas traced in CO can produce the previously reported emissions in HCN(3-2), HCO$^+$(3-2), and CN(2-1) from NGC 1275; the dominant source of excitation for all the latter molecules is collisions with electrons. To prevent collapse, as evidenced by the lack of star formation in the molecular filaments, they must consist of thin strands that have cross-sectional radii $\lesssim$0.2-2 pc if supported solely by thermal gas pressure; larger radii are permissible if turbulence or poloidal magnetic fields provide additional pressure support. We point out that the conditions required to relate CO luminosities to molecular gas masses in our Galaxy are unlikely to apply in cluster central elliptical galaxies. Rather than being virialized structures analogous to GMCs, we propose that the molecular gas in NGC 1275 comprises pressure-confined structures created by turbulent flows., Comment: 41 pages, 1 table, 12 figures; accepted by ApJ

The circumstellar envelope of the hypergiant star IRC+10420 has been traced as far out in SiO J=2-1 as in CO J = 1-0 and CO J = 2-1, in dramatic contrast with the centrally condensed (thermal) SiO- but extended CO-emitting envelopes of giant and supergiant stars. Here, we present an observation of the circumstellar envelope in SiO J=1-0 that, when combined with the previous observation in {\sioii}, provide more stringent constraints on the density of the SiO-emitting gas than hitherto possible. The emission in SiO peaks at a radius of $\sim$2\arcsec\ whereas that in SiO J=2-1 emission peaks at a smaller radius of $\sim$1\arcsec, giving rise to their ring-like appearances. The ratio in brightness temperature between SiO J=1-0 and SiO J=2-1 decreases from a value well above unity at the innermost measurable radius to about unity at radius of $\sim$2\arcsec, beyond which this ratio remains approximately constant. Dividing the envelope into three zones as in models for the CO J = 1-0 and CO J = 2-1 emission, we show that the density of the SiO-emitting gas is comparable with that of the CO-emitting gas in the inner zone, but at least an order of magnitude higher by comparison in both the middle and outer zones. The SiO-emitting gas therefore originates from dense clumps, likely associated with the dust clumps seen in scattered optical light, surrounded by more diffuse CO-emitting interclump gas. We suggest that SiO molecules are released from dust grains due to shock interactions between the dense SiO-emitting clumps and the diffuse CO-emitting interclump gas., Comment: Accepted for publication in ApJ

A single dish monitoring of millimeter maser lines SiS J=14-13 and HCN nu_2 = 1^f J=3-2 and several other rotational lines is reported for the archetypal carbon star IRC+10216. Relative line strength variations of 5%~30% are found for eight molecular line features with respect to selected reference lines. Definite line-shape variation is found in limited velocity intervals of the SiS and HCN line profiles. The asymmetrical line profiles of the two lines are mainly due to the varying components. Their dominant varying components of the line profiles have similar periods and phases as the IR light variation, although both quantities show some degree of velocity dependence; there is also variability asymmetry between the blue and red line wings of both lines. Combining the velocities and amplitudes with a wind velocity model, we suggest that the line profile variations are due to SiS and HCN masing lines emanating from the wind acceleration zone. The possible link of the variabilities to thermal, dynamical and/or chemical processes within or under this region is also discussed., Comment: 22 pages, 14 figures, accepted to publish in ApJ

We present high angular resolution observations of the HCN(1-0) emission (at ~1" or ~34 pc), together with CO J = 1-0, 2-1, and 3-2 observations, toward the Seyfert 2 nucleus of M51 (NGC 5194). The overall HCN(1-0) distribution and kinematics are very similar to that of the CO lines, which have been indicated as the jet-entrained molecular gas in our past observations. In addition, high HCN(1-0)/CO(1-0) brightness temperature ratio of about unity is observed along the jets, similar to that observed at the shocked molecular gas in our Galaxy. These results strongly indicate that both diffuse and dense gases are entrained by the jets and outflowing from the AGN. The channel map of HCN(1-0) at the systemic velocity shows a strong emission right at the nucleus, where no obvious emission has been detected in the CO lines. The HCN(1-0)/CO(1-0) brightness temperature ratio at this region reaches >2, a value that cannot be explained considering standard physical/chemical conditions. Based on our calculations, we suggest infrared pumping and possibly weak HCN masing, but still requiring an enhanced HCN abundance for the cause of this high ratio. This suggests the presence of a compact dense obscuring molecular gas in front of the nucleus of M51, which remains unresolved at our ~1" (~34 pc) resolution, and consistent with the Seyfert 2 classification picture., Comment: 10 pages, 7 figures, accepted by ApJ

We report the first extragalactic detection of chloronium (H2Cl+), in the z=0.89 absorber in front of the lensed blazar PKS1830-211. The ion is detected through its 1_11-0_00 line along two independent lines of sight toward the North-East and South-West images of the blazar. The relative abundance of H2Cl+ is significantly higher (by a factor ~7) in the NE line of sight, which has a lower H2/H fraction, indicating that H2Cl+ preferably traces the diffuse gas component. From the ratio of the H2^35Cl+ and H2^37Cl+ absorptions toward the SW image, we measure a 35Cl/37Cl isotopic ratio of 3.1 (-0.2; +0.3) at z=0.89, similar to that observed in the Galaxy and the solar system., Comment: Accepted for publication in A&A Letter

We present the first results of an ALMA spectral survey of strong absorption lines for common interstellar species in the z=0.89 molecular absorber toward the lensed blazar PKS1830-211. The dataset brings essential information on the structure and composition of the absorbing gas in the foreground galaxy. In particular, we find absorption over large velocity intervals (gtrsim 100 km/s) toward both lensed images of the blazar. This suggests either that the galaxy inclination is intermediate and that we sample velocity gradients or streaming motions in the disk plane, that the molecular gas has a large vertical distribution or extraplanar components, or that the absorber is not a simple spiral galaxy but might be a merger system. The number of detected species is now reaching a total of 42 different species plus 14 different rare isotopologues toward the SW image, and 14 species toward the NE line-of-sight. The abundances of CH, H2O, HCO+, HCN, and NH3 relative to H2 are found to be comparable to those in the Galactic diffuse medium. Of all the lines detected so far toward PKS1830-211, the ground-state line of ortho-water has the deepest absorption. We argue that ground-state lines of water have the best potential for detecting diffuse molecular gas in absorption at high redshift., Comment: Accepted for publication in A&A

The launching mechanism of the jets of active galactic nuclei is observationally poorly constrained, due to the large distances to these objects and the very small scales (sub-parsec) involved. In order to better constrain theoretical models, it is especially important to get information from the region close to the physical base of the jet, where the plasma acceleration takes place. In this paper, we report multi-epoch and multi-frequency continuum observations of the z=2.5 blazar PKS1830-211 with ALMA, serendipitously coincident with a strong $\gamma$-ray flare reported by Fermi-LAT. The blazar is lensed by a foreground z=0.89 galaxy, with two bright images of the compact core separated by 1". Our ALMA observations individually resolve these two images (although not any of their substructures), and we study the change of their relative flux ratio with time (four epochs spread over nearly three times the time delay between the two lensed images) and frequency (between 350 and 1050 GHz, rest-frame of the blazar), during the $\gamma$-ray flare. In particular, we detect a remarkable frequency-dependent behaviour of the flux ratio, which implies the presence of a chromatic structure in the blazar (i.e., a core-shift effect). We rule out the possiblity of micro- and milli-lensing effects and propose instead a simple model of plasmon ejection in the blazar's jet to explain the time and frequency variability of the flux ratio. We suggest that PKS1830-211 is likely one of the best sources to probe the activity at the base of a blazar's jet at submillimeter wavelengths, thanks to the peculiar geometry of the system. The implications of the core-shift in absorption studies of the foreground z=0.89 galaxy (e.g., constraints on the cosmological variations of fundamental constants) are discussed., Comment: Accepted for publication in A&A

We present a spectral line survey of the proto-planetary nebula AFGL 2688 in the frequency ranges of 71-111 GHz, 157-160 GHz, and 218-267 GHz using the Arizona Radio Observatory 12m telescope and the Heinrich Hertz Submillimeter Telescope. A total of 143 individual spectral features associated with 32 different molecular species and isotopologues were identified. The molecules C3H, CH3CN, H2CO, H2CS, and HCO+ were detected for the first time in this object. By comparing the integrated line strengths of different transitions, we are able to determine the rotation temperatures, column densities, and fractional abundances of the detected molecules. The C, O, and N isotopic ratios in AFGL 2688 are compared with those in IRC+10216 and the Sun, and were found to be consistent with stellar nucleosynthesis theory. Through comparisons of molecular line strengths in asymptotic giant branch stars, proto-planetary nebulae, and planetary nebulae, we discuss the evolution in circumstellar chemistry in the late stages of evolution., Comment: 41 pages, 10 figures. Accepted for publication in ApJ

We present preliminary results from a multi-wavelength study of a merger candidate, NGC3801, hosting a young FR I radio galaxy, with a Z-shaped structure. Analysing archival data from the VLA, we find two HI emission blobs on either side of the host galaxy, suggesting a 30 kpc sized rotating gas disk aligned with stellar rotation, but rotating significantly faster than the stars. Broad, faint, blue-shifted absorption wing and an HI absorption clump associated with the shocked shell around the eastern lobe are also seen, possibly due to an jet-driven outflow. While 8.0 um dust and PAH emission, from Spitzer and near and far UV emission from GALEX is seen on a large scale in an S-shape, partially coinciding with the HI emission blobs, it reveals a ~2 kpc radius ring-like, dusty, starforming structure in the nuclear region, orthogonal to the radio jet axis. Its similarities with Kinematically Decoupled Core galaxies and other evidences have been argued for a merger origin of this young, bent jet radio galaxy., Comment: Presented in "The Low-Frequency Radio Universe" ASP Conference Series, Vol. 407, proceedings of the conference held 8-12 December 2008, at National Centre for Radio Astrophysics (NCRA), TIFR, Pune, India. Edited by D. J. Saikia, D. A. Green, Y. Gupta, and T. Venturi. San Francisco: Astronomical Society of the Pacific, p.104

In this paper we investigate the polarization property of the radiation amplified by astronomical masers in the presence of a strong magnetic field. Our model explicitly takes into account the broadband nature of the radiation field and the interaction of the radiation with the maser transition J=1--0. The amplification of different realisations of the background continuum radition by the maser is directly simulated and the Stokes parameters of the radiation field are then obtained by averaging over the ensemble of emerging maser radiation. For isotropic pumping and partially saturated masers we find that the maser radiation is linearly polarized in two representative cases where the magnetic field {\bf B} makes an angle $\theta$=30$^0$ and $\theta$=90$^0$ to the maser axis. The linear polarization for maser radiation obtained in our simulations for both cases are in agreement with the results of the standard model. Furthermore, no instability during amplification is seen in our simulations. Therefore, we conclude that there is no problem with the previous numerical investigations of maser polarization in the unsaturated and partially saturated regime., Comment: 17 pages, 7 figures, to appear on MNRAS

In this paper we re-analyse the amplification process of broadband continuum radiation by astronomical masers in one-dimensional case. The basic equations appropriate for the scalar maser and the random nature of the maser radiation field are derived from basic physical principles. Comparision with the standard radiation transfer equation allows us to examine the underlying assumptions involved in the current theory of astronomical masers. Simulations are carried out to follow the amplification of different realisations of the broadband background radiation by the maser. The observable quantities such as intensity, spectral line profile are obtained by averaging over an ensemble of the emerging radiation corresponding to the amplified background radiation field. Our simulations show that the fluctuations of the radiation field inside the astronomical maser deviates significantly from Gaussian statistics even when the maser is only partially saturated. Coupling between different frequency modes and the population pulsing are shown to have increasing importance in the transport of maser radiation as the maser approaches saturation. Our results suggest that the standard formulation of radiation transfer provides a satisfactory description of the intensity and the line narrowing effect in the unsaturated and partially saturated masers within the framework of one-dimensional model. Howerver, the application of the same formulation to the strong saturation regime should be considered with caution., Comment: 16 pages, 4 figures, to appear on MNRAS

We present high angular resolution observations of the NH$_3$(1,1), (2,2) and (3,3) inversion transitions from the Egg Nebula, the archetypical proto-planetary nebula. The spatial distribution and kinematics of the emission in all three lines show four distinct components or lobes that are aligned with the polar and equatorial directions. The kinematics of the NH$_3$ emission is also found to follow a clear pattern: redshifted emission in the South and West and blueshifted emission in the North and East. The morphology and spatial kinematics of NH$_3$ emission are shown to have strong similarity to that observed previously in molecular hydrogen emission and CO emission which arise from the shocked molecular gas. We also find that the higher lying inversion transition NH$_3$ (2,2) and (3,3) are stronger in the polar direction in comparison to the lower transition NH$_3$ (1,1). We conclude that the NH$_3$ emission traces the warm molecular gas, which is shocked and heated by the interaction between the high velocity outflows and the surrounding envelope. The presence of strong ammonia emission associated with the shock fronts and the lack of the emission at the center of the nebula indicate that the abundance of ammonia is significantly enhanced by shocks, a situation very similar to that found in outflows from protostars., Comment: 21 pages, 9 figures. Accepted for publication in The Astrophysical Journal

We have extended our previous observation (Lim et al. 2008) of NGC1275 covering a central radius of ~10kpc to the entire main body of cool molecular gas spanning ~14kpc east and west of center. We find no new features beyond the region previously mapped, and show that all six spatially-resolved features on both the eastern and western sides (three on each side) comprise radially aligned filaments. Such radial filaments can be most naturally explained by a model in which gas deposited "upstream" in localized regions experiencing an X-ray cooling flow subsequently free falls along the gravitational potential of PerA, as we previously showed can explain the observed kinematics of the two longest filaments. All the detected filaments coincide with locally bright Halpha features, and have a ratio in CO(2-1) to Halpha luminosity of ~1e-3; we show that these filaments have lower star formation efficiencies than the nearly constant value found for molecular gas in nearby normal spiral galaxies. On the other hand, some at least equally luminous Halpha features, including a previously identified giant HII region, show no detectable cool molecular gas with a corresponding ratio at least a factor of ~5 lower; in the giant HII region, essentially all the pre-existing molecular gas may have been converted to stars. We demonstrate that all the cool molecular filaments are gravitationally bound, and without any means of support beyond thermal pressure should collapse on timescales ~< 1e6yrs. By comparison, as we showed previously the two longest filaments have much longer dynamical ages of ~1e7yrs. Tidal shear may help delay their collapse, but more likely turbulent velocities of at least a few tens km/s or magnetic fields with strengths of at least several ~10uG are required to support these filaments., Comment: 52 pages, 11 figures. Accepted to ApJ

Powerful radio-AGN are normally hosted by massive elliptical galaxies which are usually very poor in molecular gas. Nevertheless the gas is needed in the very center to feed the nuclear activity. Thus it is important to study the origin, the distribution and the kinematics of the molecular gas in such objects. We have performed at the IRAM-30m telescope a survey of the CO(1-0) and CO(2-1) emission in the most powerful radio galaxies of the Local Universe, selected only on the basis of their radio-continuum fluxes. The main result of this survey is the very low content in molecular gas of such galaxies compared to FIR selected galaxies. The median value of the molecular gas mass, taking into account the upper limits, is 1x10^8 Msun; if we calculate it for all the galaxies together, and if we separate them into FR-I and FR-II type galaxies, an important difference is found between them. Moreover, the CO spectra indicates the presence of a central molecular gas disk in these radio galaxies. Our results contrast with previous surveys, mainly selected through the FIR emission, with a larger mass of molecular gas observed. The first results indicate that minor mergers are good candidates to fuel the central part of the radio galaxies of our sample., Comment: Oral Presentation - "The Starburst-AGN Connection Conference", Shanghai, P.R.China. October 27-31, 2008

We have used the sub-millimeter array to image the molecular envelope around IRC+10420. Our observations reveal a large and clumpy expanding envelope around the star. The molecular envelope shows a clear asymmetry in $^{12}$CO J=2--1 emission in the South-West direction. The elongation of the envelope is found even more pronounced in the emission of $^{13}$CO J=2--1 and SO J$_{\rm K}$=6$_5$--5$_4$. A small positional velocity gradient across velocity channels is seen in these lines, suggesting the presence of a weak bipolar outflow in the envelope of IRC+10420. In the higher resolution $^{12}$CO J=2--1 map, we find that the envelope has two components: (1) an inner shell (shell I) located between radius of about 1"-2"; (2) an outer shell (shell II) located between 3" to 6" in radius. These shells represent two previous mass-loss episodes from IRC+10420. We attempt to derive in self-consistent manner the physical conditions inside the envelope by modelling the dust properties, and the heating and cooling of molecular gas. We estimate a mass loss rate of $\sim$9 10$^{-4}$ M$_\odot$ yr$^{-1}$ for shell I and 7 10$^{-4}$ M$_\odot$ yr$^{-1}$ for shell II. The gas temperature is found to be unusually high in IRC+10420 in comparison with other oxygen-rich envelopes. The elevated gas temperature is mainly due to higher heating rate, which results from the large luminosity of the central s tar. We also derive an isotopic ratio $^{12}$C/$^{13}$C = 6., Comment: 30 pages, 14 figures. Accepted for publication in The Astrophysical Journal

We have investigated the presence of dense gas toward the radio source Cen A by looking at the absorption of the HCO+ and HCN (3-2) lines in front of the bright continuum source with the Submillimeter Array. We detect narrow HCO+ (3-2) absorption, and tentatively HCN (3-2), close to the systemic velocity. For both molecules, the J=3-2 absorption is much weaker than for the J=1-0 line. From simple excitation analysis, we conclude that the gas density is on the order of a few 10^4 cm^-3 for a column density N(HCO+)/dV of 3x10^12 cm^-2 km^-1 s and a kinetic temperature of 10 K. In particular, we find no evidence for molecular gas density higher than a few 10^4 cm^-3 on the line of sight to the continuum source. We discuss the implications of our finding on the nature of the molecular gas responsible for the absorption toward Cen A., Comment: Accepted for publication in ApJ

We present high resolution images of the 12CO(2-1) emission in the central 1' (1 kpc) of NGC 5128 (Centaurus A), observed using the SMA. We elucidate for the first time the distribution and kinematics of the molecular gas in this region with a resolution of 6'.0 x 2'.4 (100 pc x 40 pc). We spatially resolve the circumnuclear molecular gas in the inner 24'' x 12'' (400 pc x 200 pc), which is elongated along a position angle P.A. = 155 deg and perpendicular to the radio/X-ray jet. The SE and NW components of the circumnuclear gas are connected to molecular gas found at larger radii. This gas appears as two parallel filaments at P.A. = 120 deg, which are coextensive with the long sides of the 3 kiloparsec parallelogram shape of the previously observed dust continuum, as well as ionized and pure rotational H2 lines. Spatial and kinematical asymmetries are apparent in both the circumnuclear and outer gas, suggesting non-coplanar and/or non-circular motions. We extend to inner radii (r < 200 pc) previously studied warped disk models built to reproduce the central parallelogram-shaped structure. Adopting the warped disk model we would confirm a gap in emission between the radii r = 200 - 800 pc (12'' - 50''), as has been suggested previously. Although this model explains this prominent feature, however, our 12CO(2-1) observations show relevant deviations from this model. Namely, the physical connection between the circumnuclear gas and that at larger radii, brighter SE and NW sides on the parallelogram-shaped feature, and an outer curvature of its long sides. Overall it resembles more closely an S-shaped morphology, a trend that is also found in other molecular species. Hence, we explore qualitatively the possible contribution of a weak bi-symmetric potential which would naturally explain these peculiarities., Comment: 26 Pages, 14 Figures. Accepted for publication in ApJ

We present high angular resolution observations of the HC$_3$N J=5--4 line from the Egg nebula, which is the archetype of protoplanetary nebulae. We find that the HC$_{\rm 3}$N emission in the approaching and receding portion of the envelope traces a clumpy hollow shell, similar to that seen in normal carbon rich envelopes. Near the systemic velocity, the hollow shell is fragmented into several large blobs or arcs with missing portions correspond spatially to locations of previously reported high--velocity outlows in the Egg nebula. This provides direct evidence for the disruption of the slowly--expanding envelope ejected during the AGB phase by the collimated fast outflows initiated during the transition to the protoplanetary nebula phase. We also find that the intersection of fast molecular outflows previously suggested as the location of the central post-AGB star is significantly offset from the center of the hollow shell. From modelling the HC$_3$N distribution we could reproduce qualitatively the spatial kinematics of the HC$_3$N J=5--4 emission using a HC$_3$N shell with two pairs of cavities cleared by the collimated high velocity outflows along the polar direction and in the equatorial plane. We infer a relatively high abundance of HC$_3$N/H$_2$ $\sim$3x10$^{-6}$ for an estimated mass--loss rate of 3x10$^{-5}$ M$_\odot$ yr$^{-1}$ in the HC$_3$N shell. The high abundance of HC$_3$N and the presence of some weaker J=5--4 emission in the vicinity of the central post-AGB star suggest an unusually efficient formation of this molecule in the Egg nebula., Comment: 22 pages, 6 figures, submitted to the Astrophysical Journal

We present high angular resolution observations of HC$_3$N J=5--4 line and 7 mm continumm emission from the extreme carbon star CIT 6. We find that the 7 mm continuum emission is unresolved and has a flux consistent with black-body thermal radiation from the central star. The HC$_3$N J=5--4 line emission originates from an asymmetric and clumpy expanding envelope comprising two separate shells of HC$_3$N J=5--4 emission: (i) a faint outer shell that is nearly spherical which has a radius of 8\arcsec; and (ii) a thick and incomplete inner shell that resembles a one-arm spiral starting at or close to the central star and extending out to a radius of about 5\arcsec. Our observations therefore suggest that the mass loss from CIT 6 is strongly modulated with time and highly anisotropic. Furthermore, a comparison between the data and our excitation modelling results suggests an unusually high abundance of HC$_3$N in its envelope. We discuss the possibility that the envelope might be shaped by the presence of a previously suggested possible binary companion. The abundance of HC$_3$N may be enhanced in spiral shocks produced by the interaction between the circumstellar envelope of CIT 6 and its companion star., Comment: 23 pages, 5 figures, submitted to the Astrophysical Journal

A spectral-line survey of IRC+10216 in the 345 GHz band has been undertaken with the Submillimeter Array. Although not yet completed, it has already yielded a fairly large sample of narrow molecular emission lines with line-widths indicating expansion velocities of ~4 km/s, less than 3 times the well-known value of the terminal expansion velocity (14.5 km/s) of the outer envelope. Five of these narrow lines have now been identified as rotational transitions in vibrationally excited states of previously detected molecules: the v=1, J=17--16 and J=19--18 lines of Si34S and 29SiS and the v=2, J=7--6 line of CS. Maps of these lines show that the emission is confined to a region within ~60 AU of the star, indicating that the narrow-line emission is probing the region of dust-formation where the stellar wind is still being accelerated., Comment: 5 pages, 5 figures, Accepted for publication in ApJ

Circumbinary disks have been hypothesized to exist around a number of binary post-AGB stars. Although most of the circumbinary disks have been inferred through the near IR excess, a few of them are strong emitters of molecular emission. Here we present high angular resolution observations of the emission of $^{12}$CO and its isotopomer $^{13}$CO J=2--1 line from the circumstellar envelope around the binary post-AGB star IRAS 08544$-$4431, which is one of the most prominent members of this class of objects. We find that the envelope is resolved in our observations and two separate components can be identified: (a) a central extended and strong component with very narrow linewidth between 2 - 6 \kms; (b) a weak bipolar outflow with expansion velocity up to 8 \kms. The central compact component possesses low and variable $^{12}$CO/$^{13}$CO J=2--1 line ratio, indicating optically thick emission of the main isotope. We estimate a molecular gas mass of 0.0047 M$_\odot$ for this component based on the optically thinner $^{13}$CO J=2--1 line. We discuss the relation of the molecular envelope and the circumbinary disk inferred from near IR excess and compare with other known cases where the distribution of molecular gas has been imaged at high angular resolution., Comment: 14 pages, 4 figures. Accepted for publication in Astrophysical Journal

We present a spectral line survey of the C-rich envelope CIT 6 in the 2mm and 1.3mm bands carried out with the Arizona Radio Observatory (ARO) 12m telescope and the Heinrich Hertz Submillimeter Telescope (SMT). The observations cover the frequency ranges of 131--160 GHz, 219--244 GHz, and 252--268 GHz with typical sensitivity limit of T_R<10 mK. A total of 74 individual emission features are detected, of which 69 are identified to arise from 21 molecular species and isotopologues, with 5 faint lines remaining unidentified. Two new molecules (C4H and CH3CN) and seven new isotopologues (C17O, 29SiC2, 29SiO, 30SiO, 13CS, C33S, and CS) are detected in this object for the first time. The column densities, excitation temperatures, and fractional abundances of the detected molecules are determined using rotation diagram analysis. Comparison of the spectra of CIT 6 to that of IRC+10216 suggests that the spectral properties of CIT 6 are generally consistent with those of IRC+10216. For most of the molecular species, the intensity ratios of the lines detected in the two objects are in good agreement with each other. Nevertheless, there is evidence suggesting enhanced emission from CN and HC3N and depleted emission from HCN, SiS, and C4H in CIT 6. Based on their far-IR spectra, we find that CIT 6 probably has a lower dust-to-molecular gas ratio than IRC+10216. To investigate the chemical evolution of evolved stars, we compare the molecular abundances in the AGB envelopes CIT 6 and IRC+10216 and those in the bright proto-planetary nebula CRL 618. The implication on the circumstellar chemistry is discussed., Comment: 39 pages, 9 figures, accepted for publication in ApJ

We report high angular resolution observations of the HCN (3-2) line emission in the circumstellar envelope of the O-rich star W Hya with the Submillimeter Array. The proximity of this star allows us to image its molecular envelope with a spatial resolution of just ~40 AU, corresponding to about 10 times the stellar diameter. We resolve the HCN (3-2) emission and find that it is centrally peaked and has a roughly spherically symmetrical distribution. This shows that HCN is formed in the innermost region of the envelope (within ~10 stellar radii), which is consistent with predictions from pulsation-driven shock chemistry models, and rules out the scenario in which HCN forms through photochemical reactions in the outer envelope. Our model suggests that the envelope decreases steeply in temperature and increases smoothly in velocity with radius, inconsistent with the standard model for mass-loss driven by radiative pressure on dust grains. We detect a velocity gradient of ~5 km/s in the NW--SE direction over the central 40 AU. This velocity gradient is reminescent of that seen in OH maser lines, and could be caused by the rotation of the envelope or by a weak bipolar outflow., Comment: accepted for publication in ApJL

We present the Submillimeter Array observation of the CO J=2-1 transition towards the northern galaxy, ARP 302N, of the early merging system, ARP 302. Our high angular resolution observation reveals the extended spatial distribution of the molecular gas in ARP 302N. We find that the molecular gas has a very asymmetric distribution with two strong concentrations on either side of the center together with a weaker one offset by about 8 kpc to the north. The molecular gas distribution is also found to be consistent with that from the hot dust as traced by the 24 micro continuum emission observed by the Spitzer. The line ratio of CO J=2-1/1-0 is found to vary strongly from about 0.7 near the galaxy center to 0.4 in the outer part of the galaxy. Excitation analysis suggests that the gas density is low, less than 10$^3$ cm$^{-3}$, over the entire galaxy. By fitting the SED of ARP 302N in the far infrared we obtain a dust temperature of $T\rm_d$=26-36 K and a dust mass of M$\rm _{dust}$=2.0--3.6$\times10^8$ M$\rm_\odot$. The spectral index of the radio continuum is around 0.9. The spatial distribution and spectral index of the radio continuum emission suggests that most of the radio continuum emission is synchrotron emission from the star forming regions at the nucleus and ARP302N-cm. The good spatial correspondance between the 3.6 cm radio continuum emission, the Spitzer 8 & 24 $\mu$m data and the high resolution CO J=2-1 observation from the SMA shows that there is the asymmetrical star forming activities in ARP 302N., Comment: 19 pages, 8 figures, accepted by AJ

Powerful radio-AGN are hosted by massive elliptical galaxies which are usually very poor in molecular gas. Nevertheless the central Black Hole (BH) needs molecular gas for the nuclear activity. Thus it is important to study the origin, the distribution and the kinematics of the molecular gas in such objects. We have performed at the IRAM-30m telescope a survey of the CO(1-0) and CO(2-1) emission in the most powerful radio galaxies of the Local Universe, selected only on the basis of their radio continuum fluxes. The main result of that survey is the low content in molecular gas of such galaxies compared to Seyfert galaxies. The median value of the molecular gas mass is 4x10^8 Msun. Moreover, the CO spectra indicate the presence of a central molecular gas disk in some of these radio galaxies. We complemented this survey with photometric data of SPITZER and IRAS fluxes with the purpose to study the dust and its relation with the molecular gas and AGN., Comment: 3 pages and 2 figures. Conference of "The Evolution of Galaxies through the Neutral Hydrogen Window" February 1-3, 2008 Arecibo Observatory, Puerto Rico

We report on a recent spectral line survey of the planetary nebula (PN) NGC 7027 using the Arizona Radio Observatory (ARO) 12m telescope and the Heinrich Hertz Submillimeter Telescope (SMT) at millimeter wavelengths. The spectra covering the frequency ranges 71--111GHz, 157--161GHz, and 218--267GHz were obtained with a typical sensitivity of rms<8mK. A total of 67 spectral lines are detected, 21 of which are identified with 8 molecular species, 32 with recombination lines from hydrogen and helium, and 14 remains unidentified. As the widths of emission lines from CO, other neutral molecules, molecular ions, as well as recombination of H+ and He+ are found to be different with each other, the line strengths and profiles are used to investigate the physical conditions and chemical processes of the neutral envelope of NGC 7027. The column densities and fractional abundances relative to H2 of the observed molecular species are calculated and compared with predictions from chemical models. We found evidence for overabundance of N2H+ and underabundance of CS and HNC in NGC 7027, suggesting that X-ray emission and shock wave may play an important role in the chemistry of the hot molecular envelope of the young PN., Comment: 62 pages, 8 figures, accepted for publication in ApJ

We present the results of our spectral line surveys in the 2 mm and 1.3 mm windows toward the carbon rich envelope of IRC +10216. Totally 377 lines are detected, among which 360 lines are assigned to 57 known molecules (including 29 rare isotopomers and 2 cyclic isomers). Only 17 weak lines remain unidentified. Rotational lines of isotopomers 13CCH and HN13C are detected for the first time in IRC +10216. The detection of the formaldehyde lines in this star is also confirmed. Possible abundance difference among the three 13C substituted isotopic isomers of HC3N is reported. Isotopic ratios of C and O are confirmed to be non-solar while those of S and Si to be nearly solar. Column densities have been estimated for 15 molecular species. Modified spectroscopic parameters have been calculated for NaCN, Na13CN, KCN and SiC2. Transition frequencies from the present observations were used to improve the spectroscopic parameters of Si13CC, 29SiC2 and 30SiC2., Comment: 17 pages of text, 18 pages of 14 tables, 35 pages of 4 figures, a typo corrected in Abstract

We have imaged in CO(2-1) the molecular gas in NGC 1275 (Perseus A), the cD galaxy at the center of the Perseus Cluster, at a spatial resolution of $\sim$1 kpc over a central region of radius $\sim$ 10 kpc. Per A is known to contain $\sim$1.3x10$^{10}$ M$_\odot$ of molecular gas, which has been proposed to be captured from mergers with or ram-pressure stripping of gas-rich galaxies, or accreted from a X-ray cooling flow. The molecular gas detected in our image has a total mass of $\sim$4x10$^9$ M$_\odot$, and for the first time can be seen to be concentrated in three radial filaments with lengths ranging from at least 1.1-2.4 kpc all lying in the east-west directions spanning the center of the galaxy to radii of $\sim$8 kpc. The eastern and outer western filaments exhibit larger blueshifted velocities with decreasing radii, whereas the inner western filament spans the systemic velocity of the galaxy. The molecular gas shows no signature of orbital motion, and is therefore unlikely to have been captured from gas-rich galaxies. Instead, we are able to reproduce the observed kinematics of the two outer filaments as free-fall in the gravitational potential of Per A, as would be expected if they originate from a X-ray cooling flow. Indeed, all three filaments lie between two prominent X-ray cavities carved out by radio jets from Per A, and closely resembles the spatial distribution of the coolest X-ray gas in the cluster core. The inferred mass-deposition rate into the two outermost filaments alone is roughly 75 M$_odot$ yr$^{-1}$. This cooling flow can provide a nearly continuous supply of molecular gas to fuel the active nucleus in Per A., Comment: 40 pages, 10 figures, accepted for publication in ApJ

We report high angular-resolution VLA observations of cyanopolyyne molecules HC$_3$N and HC$_5$N from the carbon rich circumstellar envelope of IRC+10216. The observed low-lying rotational transitions trace a much more extended emitting region than seen in previous observations at higher frequency transitions. We resolve the hollow quasi-spherical distribution of the molecular emissions into a number of clumpy shells. These molecular shells coincide spatially with dust arcs seen in deep optical images of the IRC+10216 envelope, allowing us to study for the first time the kinematics of these features. We find that the molecular and dust shells represent the same density enhancements in the envelope separated in time by $\sim$120 to $\sim$360 yrs. From the angular size and velocity spread of the shells, we estimate that each shell typically covers about 10% of the stellar surface at the time of ejection. The distribution of the shells seems to be random in space. The good spatial correspondance between HC$_3$N and HC$_5$N emissions is in qualitative agreement with a recent chemical model that takes into account the presence of density-enhanced shells. The broad spatial distribution of the cyanopolyyne molecules, however, would necessitate further study on their formation., Comment: 16 pages, 5 figures, accepted for publication in ApJ

We present interferometric observations of $^{12}$CO and $^{13}$CO $J$=2$-$1 emission from the butterfly-shaped, young planetary nebula NGC 6302. The high angular resolution and high sensitivity achieved in our observations allow us to resolve the nebula into two distinct kinematic components: (1) a massive expanding torus seen almost edge-on and oriented in the North-South direction, roughly perpendicular to the optical nebula axis. The torus exhibits very complex and fragmentated structure; (2) high velocity molecular knots moving at high velocity, higher than 20 \kms, and located in the optical bipolar lobes. These knots show a linear position-velocity gradient (Hubble-like flow), which is characteristic of fast molecular outflow in young planetary nebulae. From the low but variable $^{12}$CO/$^{13}$CO $J$=2$-$1 line intensity ratio we conclude that the $^{12}$CO $J$=2$-$1 emission is optically thick over much of the nebula. Using the optically thinner line $^{13}$CO $J$=2$-$1 we estimate a total molecular gas mass of $\sim$ 0.1 M$_\odot$, comparable to the ionized gas mass; the total gas mass of the NGC 6302 nebula, including the massive ionized gas from photon dominated region, is found to be $\sim$ 0.5 M$_\odot$. From radiative transfer modelling we infer that the torus is seen at inclination angle of 75$^\circ$ with respect to the plane of the sky and expanding at velocity of 15 \kms. Comparison with recent observations of molecular gas in NGC 6302 is also discussed., Comment: 24 pages, 7 figures, accepted for publication in Astrophysical Journal

We have mapped the central region of NGC 4945 in the $J=2\to1$ transition of $^{12}$CO, $^{13}$CO, and C$^{18}$O, as well as the continuum at 1.3 mm, at an angular resolution of $5\farc \times 3\farc$ with the Submillimeter Array. The relative proximity of NGC 4945 (distance of only 3.8 Mpc) permits a detailed study of the circumnuclear molecular gas and dust in a galaxy exhibiting both an AGN (classified as a Seyfert 2) and a circumnuclear starburst in an inclined ring with radius $\sim$2\farcs5 ($\sim$50 pc). We find that all three molecular lines trace an inclined rotating disk with major axis aligned with that of the starburst ring and large-scale galactic disk, and which exhibits solid-body rotation within a radius of $\sim$5\farc ($\sim$95 pc). We infer an inclination for the nuclear disk of $62^{\circ} \pm 2^{\circ}$, somewhat smaller than the inclination of the large-scale galactic disk of $\sim$$78^{\circ}$. The continuum emission at 1.3 mm also extends beyond the starburst ring, and is dominated by thermal emission from dust. If it traces the same dust emitting in the far-infrared, then the bulk of this dust must be heated by star-formation activity rather than the AGN. We discover a kinematically-decoupled component at the center of the disk with a radius smaller than $1\farcs4$ (27 pc), but which spans approximately the same range of velocities as the surrounding disk. This component has a higher density than its surroundings, and is a promising candidate for the circumnuclear molecular torus invoked by AGN unification models., Comment: 13 pages, 10 figures,accepted by ApJ

We present millimeter interferometric observations of the molecular envelope around the red supergiant VY CMa with the SubMillimeter Array (SMA). The high angular resolution (< 2'') allows us to derive the structure of the envelope as observed in the 1.3 mm continuum, 12CO(2-1), 13CO(2-1) and SO(6,5-5,4) lines emission. The circumstellar envelope is resolved into three components: a dense, compact and dusty central component, embedded in a more diffuse and extended envelope plus a high velocity component. We construct a simple model, consisting of a spherically symmetric slowly expanding envelope and bipolar outflows with a wide opening angle (~ 120 deg.) viewed close to the line of sight (i = 15 deg.). Our model can explain the main features of the SMA data and previous single-dish CO multi-line observations. An episode of enhanced mass loss along the bipolar direction is inferred from our modelling. The SMA data provide a better understanding of the complicated morphology seen in the optical/IR high resolution observations., Comment: accepted for publication in ApJ

We present the first interferometric CO(J=3-2) observations (beam size of 3.9"x1.6" or 160pc x 65pc) with the Submillimeter Array (SMA) toward the center of the Seyfert 2 galaxy M51. The image shows a strong concentration at the nucleus and weak emission from the spiral arm to the northwest. The integrated intensity of the central component in CO(J=3-2) is almost twice as high as that in CO(J=1-0), indicating that the molecular gas within an ~80 pc radius of the nucleus is warm (>~100 K) and dense (~10^4 cm^-3). Similar intensity ratios are seen in shocked regions in our Galaxy, suggesting that these gas properties may be related to AGN or starburst activity. The central component shows a linear velocity gradient (~1.4 km/s/pc) perpendicular to the radio continuum jet, similar to that seen in previous observations and interpreted as a circumnuclear molecular disk/torus around the Seyfert 2 nucleus. In addition, we identify a linear velocity gradient (~0.7 km/s/pc) along the jet. Judging from the energetics, the velocity gradient can be explained by supernova explosions or energy and momentum transfer from the jet to the molecular gas via interaction, which is consistent with the high intensity ratio., Comment: 12 pages, 3 figures, accepted for publication in ApJL

Using the partially completed Submillimeter Array with five antennas, we have observed the CO J=2-1 and 3-2 emission from the envelope surrounding the carbon star V Hya. The high-angular resolution (2"-4") maps show that V Hya is powering a bipolar molecular jet having an extreme velocity of 70-185 km/s. The axis of this high velocity jet is perpendicular to the major axis of the flattened disk-like envelope, which is expanding with a velocity of ~16 km/s.There is a third kinematic component, a medium-velocity wind having a deprojected velocity of 40-120 km/s moving along the disk plane. Both the high velocity jet and the medium velocity wind have a dynamical time scale of a few hundred years. The flattened structure and the collimated jet observed in V Hya suggests that the formation of asymmetrical structure proceeds while the central star is still in the AGB phase, Comment: 11 pages, 4 figures, accepted by the ApJL

We report a survey for molecular gas in 3C radio galaxies at redshifts z < 0.031. Four of the twenty-three galaxies observed were detected with molecular gas masses in the range 10^7--10^9 Msun. The remainder had typical upper limits in molecular gas masses of ~10^8 Msun., Comment: 2 pages, to appear in Active Galactic Nuclei: from Central Engine to Host Galaxy Abstract Book, meeting held in Meudon, France, July 23-27, 2002, Eds.: S. Collin, F. Combes and I. Shlosman (ASP)

We report a survey for molecular gas in nearby powerful radio galaxies. Eight of the eighteen radio galaxies observed were detected with molecular masses in the range 10^7--10^9 Msun, similar to the same survey we performed towards 3C radio galaxies. The upper limits of molecular gas in the remainder are typically of 10^8 Msun, indicating that very few radiogalaxies have molecular gas reservoir with more than 10^9 Msun., Comment: 2 pages, to appear in Active Galactic Nuclei: from Central Engine to Host Galaxy Abstract Book, meeting held in Meudon, France, July 23-27, 2002, Eds.: S. Collin, F. Combes and I. Shlosman (ASP)

In the complete sample of ultraluminous infrared galaxies (ULIRGs) compiled by Kim (1995) about 5% consists of widely separated galaxies which are presumably in the early phase of interaction. This fact is contrary to the conventional view that ULIRGs are in the final stages of the merger of two gas-rich disk galaxies. We have undertaken high resolution CO(J=1-0) observations for the ultraluminous infrared galaxies that have nuclear separations larger than 20 kpc. We have detected the CO emission in 5 out of 6 systems, but only in one component of the ULIRG pairs. 4 of them have LINER spectral type and 1 galaxy has Seyfert II spectral type. In K'-band images these components are also brighter than the other components which have either HII-region spectra or no detectable emission lines. Using the standard conversion factor, the molecular gas content is estimated to be a few times 10 $^{10}$ M$_\odot$, similar to that of the other ultraluminous galaxies. The result indicates that the galaxy containing the molecular gas is also the source of most, if not all, of the huge far-infrared luminosity of the system. The optical and K'-band imaging observations and optical spectra suggest multiple merger scenario for 1 system. If the remaining systems are in an early stage of a binary tidal interaction, the commonly accepted interpretation of the ULIRG phenomenon as the final merger stage of two disk galaxies may need to be re-examined., Comment: 26 pages, 03 figures, accepted for ApJ

We report the detection of $^{12}$CO~($1 \to 0$) and $^{12}$CO~($2 \to 1$) emission from the central regions ($\lesssim 5$--$10 {\rm kpc}$) of the two powerful radio galaxies 3C~31 and 3C~264. Their individual CO emission exhibits a double-horned line profile that is characteristic of an inclined rotating disk with a central depression at the rising part of its rotation curve. The inferred disk or ring distributions of the molecular gas is consistent with the observed presence of dust disks or rings detected optically in the cores of both galaxies. For a CO to H$_2$ conversion factor similar to that of our Galaxy, the corresponding total mass in molecular hydrogen gas is $(1.3 \pm 0.2) \times 10^9 {\rm M_{\odot}}$ in 3C~31 and $(0.31 \pm 0.06) \times 10^9 {\rm M_{\odot}}$ in 3C~264. Despite their relatively large molecular-gas masses and other peculiarities, both 3C~31 and 3C~264, as well as many other powerful radio galaxies in the (revised) 3C catalog, are known to lie within the fundamental plane of normal elliptical galaxies. We reason that if their gas originates from the mergers of two gas-rich disk galaxies, as has been invoked to explain the molecular gas in other radio galaxies, then both 3C~31 and 3C~264 must have merged a long time (a few billion years or more) ago but their remnant elliptical galaxies only recently (last tens of millions of years or less) become active in radio. Instead, we argue that the cannibalism of gas-rich galaxies provides a simpler explanation for the origin of molecular gas in the elliptical hosts of radio galaxies. Given the transient nature of their observed disturbances, these galaxies probably become active in radio soon after the accretion event when sufficient molecular gas agglomerates in their nuclei., Comment: 16 pages, 1 JPEG figure attached, accepted for publication in ApJL

We have searched for water vapor emission at 183 GHz, redshifted at 157 GHz and 161 GHz, in the two ultraluminous starburst galaxies Mrk1014 and VIIZw244. Due to the low energy level of the upper state of the 183 GHz transition (\approx 200K), it is expected that the emission regions are extended, as they are in the Orion or W49N molecular cloud cores. Since the warm and dense gas, typical of star-forming cores, is expected to have a large surface filling factor in ultraluminous starburst galaxies, the maser H_2O emission at 183 GHz could have been detected. In fact, no water line has been detected in Mrk1014 and VIIZw244 with an upper limit of \sigma = 1 mK. We compare the H_2O/CO emission ratio with that obtained towards the ultraluminous high-z object F10214+4724, which flux is amplified by a gravitationnal lens. We suggest that the amplification factor for the H_2O emitting cores in this galaxy should be higher than for the general CO emitting region. We conclude that the warm and dense H_2O cores are much less extended in the two observed starburst galaxies than in the Orion molecular cloud; this provides some information on the physical conditions and cooling processes of the interstellar medium in starburst galaxies., Comment: 7 pages, 5 figures, uses Latex, L-AA, psfig.tex, accepted in A&A