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Register a new userSMA Observations of the Extended CO(6-5) Emission in the Starburst Galaxy NGC253
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We present observations of the $^{12}$CO(6-5) line and 686GHz continuum emission in NGC253 with the Submillimeter Array at an angular resolution of ~4arcsec. The $^{12}$CO(6-5) emission is clearly detected along the disk and follows the distribution of the lower $^{12}$CO line transitions with little variations of the line ratios in it. A large-velocity gradient analysis suggests a two-temperature model of the molecular gas in the disk, likely dominated by a combination of low-velocity shocks and the disk wide PDRs. Only marginal $^{12}$CO(6-5) emission is detected in the vicinity of the expanding shells at the eastern and western edges of the disk. While the eastern shell contains gas even warmer (T$_{rm kin}$>300~K) than the hot gas component (T$_{rm kin}$=300K) of the disk, the western shell is surrounded by gas much cooler (T$_{rm kin}$=60K) than the eastern shell but somewhat hotter than the cold gas component of the disk (for similar H$_2$ and CO column densities), indicative of different (or differently efficient) heating mechansisms. The continuum emission at 686GHz in the disk agrees well in shape and size with that at lower (sub-)millimeter frequencies, exhibiting a spectral index consistent with thermal dust emission. We find dust temperatures of ~10-30K and largely optically thin emission. However, our fits suggest a second (more optically thick) dust component at higher temperatures (T$_{rm d}$>60K), similar to the molecular gas. We estimate a global dust mass of ~10$^6$Msun for the disk translating into a gas-to-dust mass ratio of a few hundred consistent with other nearby active galaxies.
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We present moderate (${sim}5^{primeprime}$) and high angular resolution (${sim}1^{primeprime}$) observations of $^{12}rm{CO,}(J=2-1)$ emission toward nearby, interacting galaxy NGC 3627 taken with the Submillimeter Array (SMA). These SMA mosaic maps of NGC 3627 reveal a prominent nuclear peak, inter-arm regions, and diffuse, extended emission in the spiral arms. A velocity gradient of ${sim}400$-$450$ km s$^{-1}$ is seen across the entire galaxy with velocity dispersions ranging from $lesssim 80$ km s$^{-1}$ toward the nuclear region to $lesssim 15$ km s$^{-1}$ in the spiral arms. We also detect unresolved $^{13}rm{CO,}(J=2-1)$ line emission toward the nuclear region, southern bar end, and in a relatively isolated clump in the southern portion of the galaxy, while no $rm{C}^{18}O(J=2-1)$ line emission is detected at a $3sigma$ rms noise level of 42 mJy beam$^{-1}$ per 20 km s$^{-1}$ channel. Using RADEX modeling with a large velocity gradient approximation, we derive kinetic temperatures ranging from ${sim}5$-$10$ K (in the spiral arms) to ${sim}25$ K (at the center) and H$_2$ number densities from ${sim}$400-1000 cm$^{-3}$ (in the spiral arms) to ${sim}$12500 cm$^{-3}$ (at the center). From this density modeling, we find a total H$_2$ mass of $9.6times10^9 M_{odot}$, which is ${sim}50%$ higher than previous estimates made using a constant H$_2$-CO conversion factor but is largely dependent on the assumed vertical distribution of the CO gas. With the exception of the nuclear region, we also identify a tentative correlation between star formation efficiency and kinetic temperature. We derive a galactic rotation curve, finding a peak velocity of ${sim}207$ km s$^{-1}$ and estimate a total dynamical mass of $4.94 pm 0.70 times 10^{10} M_{odot}$ at a galactocentric radius of ${sim}6.2$ kpc ($121^{primeprime}$).
We present the first images of the 691.473 GHz CO J=6-5 line in a protoplanetary disk, obtained along with the 690 GHz dust continuum, toward the classical T Tauri star TW Hya using the Submillimeter Array. Imaging in the CO J=6-5 line reveals a rotating disk, consistent with previous observations of CO J=3-2 and 2-1 lines. Using an irradiated accretion disk model and 2D Monte Carlo radiative transfer, we find that additional surface heating is needed to fit simultaneously the absolute and relative intensities of the CO J=6-5, 3-2 and 2-1 lines. In particular, the vertical gas temperature gradient in the disk must be steeper than that of the dust, mostly likely because the CO emission lines probe nearer to the surface of the disk. We have used an idealized X-ray heating model to fit the line profiles of CO J=2-1 and 3-2 with Chi-square analysis, and the prediction of this model yields CO J=6-5 emission consistent with the observations.
NGC253 is one of the closest starburst galaxies to the Milky Way and as such it has been studied in detail across the electromagnetic spectrum. Recent observations have detected the first extragalactic class I methanol masers at 36 and 44 GHz and the first extragalactic HC$_3$N (cyanoacetylene) masers in this source. Here we discuss the location of the masers with respect to key morphological features within NGC253 and the association between the masers and the ongoing starburst.
We present the spatially-resolved near-infrared (2.5-5.0 um) spectra of the edge-on starburst galaxy NGC253 obtained with the Infrared Camera onboard AKARI. Near the center of the galaxy, we clearly detect the absorption features of interstellar ices (H_2O: 3.05 um, CO_2: 4.27 um, and XCN: 4.62 um) and the emission of polycyclic aromatic hydrocarbons (PAHs) at 3.29 um and hydrogen recombination line Br alpha at 4.05 um. We find that the distributions of the ices differ from those of the PAH and gas. We calculate the column densities of the ices and derive the abundance ratios of N(CO_2)/N(H_2O) = 0.17 +- 0.05. They are similar to those obtained around the massive young stellar objects in our Galaxy (0.17 +- 0.03), although much stronger interstellar radiation field and higher dust temperature are expected near the center of NGC253.
High resolution submm observations are important in probing the morphology, column density and dynamics of obscured active galactic nuclei (AGNs). With high resolution (0.06 x 0.05) ALMA 690 GHz observations we have found bright (TB >80 K) and compact (FWHM 10x7 pc) CO 6-5 line emission in the nucleus of the extremely radio-quiet galaxy NGC1377. The integrated CO 6-5 intensity is aligned with the previously discovered jet/outflow of NGC1377 and is tracing the dense (n>1e4 cm-3), hot gas at the base of the outflow. The velocity structure is complex and shifts across the jet/outflow are discussed in terms of jet-rotation or separate, overlapping kinematical components. High velocity gas (deltaV +-145 km/s) is detected inside r<2-3 pc and we suggest that it is emerging from an inclined rotating disk or torus of position angle PA=140+-20 deg with a dynamical mass of approx 3e6 Msun. This mass is consistent with that of a supermassive black hole (SMBH), as inferred from the M-sigma relation. The gas mass of the proposed disk/torus constitutes <3% of the nuclear dynamical mass. In contrast to the intense CO 6-5 line emission, we do not detect dust continuum with an upper limit of S(690GHz)<2mJy. The corresponding, 5 pc, H2 column density is estimated to N(H2)<3e23 cm-2, which is inconsistent with a Compton Thick (CT) source. We discuss the possibility that CT obscuration may be occuring on small (subparsec) or larger scales. From SED fitting we suggest that half of the IR emission of NGC1377 is nuclear and the rest (mostly the far-infrared (FIR)) is more extended. The extreme radio quietness, and the lack of emission from other star formation tracers, raise questions on the origin of the FIR emission. We discuss the possibility that it is arising from the dissipation of shocks in the molecular jet/outflow or from irradiation by the nuclear source along the poles.
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