We have used the JVLA at the 1 cm band to map five highly-excited metastable inversion transitions of ammonia, (J,K)=(6,6), (7,7), (9,9), (10,10), and (13,13), in W51 IRS2 with ~0.2 angular resolution. We present detections of both thermal (extended) ammonia emission in the five inversion lines, with rotational states ranging in energy from about 400 to 1700 K, and point-like ammonia maser emission in the (6,6), (7,7), and (9,9) lines. The thermal ammonia emits around a velocity of 60 km/s, near the clouds systemic velocity, is elongated in the east-west direction across 4 and is confined by the HII regions W51d, W51d1, and W51d2. The ammonia masers are observed in the eastern tip of the dense clump traced by thermal ammonia, offset by 0.65 to the East from its emission peak, and have a peak velocity at ~47.5 km/s. No maser components are detected near the systemic velocity. The ammonia masers are separated by 0.65 (3500 AU) from the (rare) vibrationally-excited SiO masers, excited by the deeply-embedded YSO W51-North. This excludes that the two maser species are excited by the same object. Interestingly, the ammonia masers originate at the same sky position as a peak in a submm line of SO2 imaged with the SMA, tracing a face-on circumstellar disk/ring around W51-North. In addition, the thermal emission from the most highly excited ammonia lines, (10,10) and (13,13), shows two main condensations, the dominant one towards W51-North with the SiO/H2O masers, and a weaker peak at the ammonia maser position. We propose a scenario where the ring seen in SO2 emission is a circumbinary disk surrounding (at least) two high-mass YSOs, W51-North (exciting the SiO masers) and a nearby companion (exciting the ammonia masers), separated by 3500 AU. This finding indicates a physical connection (in a binary) between the two rare SiO and ammonia maser species.
With a goal toward deriving the physical conditions in external galaxies, we present a study of the ammonia (NH$_3$) emission and absorption in a sample of star forming systems. Using the unique sensitivities to kinetic temperature afforded by the excitation characteristics of several inversion transitions of NH$_3$, we have continued our characterization of the dense gas in star forming galaxies by measuring the kinetic temperature in a sample of 23 galaxies and one galaxy offset position selected for their high infrared luminosity. We derive kinetic temperatures toward 13 galaxies, 9 of which possess multiple kinetic temperature and/or velocity components. Eight of these galaxies exhibit kinetic temperatures $>100$ K, which are in many cases at least a factor of two larger than kinetic temperatures derived previously. Furthermore, the derived kinetic temperatures in our galaxy sample, which are in many cases at least a factor of two larger than derived dust temperatures, point to a problem with the common assumption that dust and gas kinetic temperatures are equivalent. As previously suggested, the use of dust emission at wavelengths greater than 160 $mu$m to derive dust temperatures, or dust heating from older stellar populations, may be skewing derived dust temperatures in these galaxies to lower values. We confirm the detection of high-excitation OH $^2Pi_{3/2}$ J=9/2 absorption toward Arp220 (Ott et. al. 2011). We also report the first detections of non-metastable NH$_3$ inversion transitions toward external galaxies in the (2,1) (NGC253, NGC660, IC342, and IC860), (3,1), (3,2), (4,3), (5,4) (all in NGC660) and (10,9) (Arp220) transitions.
(abridged) We present ATCA and GBT observations of ammonia (NH3) toward the ultraluminous infrared galaxy (ULIRG) merger Arp220. We detect the NH3 (1,1), (2,2), (3,3), (4,4), (5,5), and (6,6) inversion lines in absorption against the unresolved, (62+/-9)mJy continuum source at 1.2cm. The peak apparent optical depths of the NH3 lines range from ~0.05 to 0.18. The absorption depth of the NH3 (1,1) line is significantly shallower than expected based on the depths of the other transitions, which might be caused by contamination from emission by a hypothetical, cold (<~20K) gas layer with an estimated column density of <~ 2x10^14 cm^-2. The widths of the NH3 absorption lines are ~120-430 km s^-1, in agreement with those of other molecular tracers. We cannot confirm the extremely large linewidths of up to ~1800km s^-1 previously reported. We determine a rotational temperature of (124+/-19)K, corresponding to a kinetic temperature of T_kin=(186+/-55)K. NH3 column densities depend on the excitation temperature. For an excitation temperature of 50K, we estimate (8.4+/-0.5)x10^16cm^-2. The relation scales linearly for possible higher excitation temperatures. In the context of a model with a molecular ring that connects the two nuclei in Arp220, we estimate the H2 gas density to be ~f_V^-0.5 x (1-4)x10^3, (f_V: volume filling factor). In addition to NH3, our ATCA data show an absorption feature adjacent in frequency to the NH3 (3,3) line. If we interpret the line to be from the OH ^2Pi_3/2 J=9/2 F=4-4 transition, it would have a linewidth, systemic velocity, and apparent optical depth similar to what we detect in the NH3 lines. If this association with OH is correct, it marks the first detection of the highly excited (~511K above ground state) ^2Pi_3/2 J=9/2 F=4-4 OH line in an extragalactic object.
The first detection of ammonia (NH3) is reported from the Magellanic Clouds. Using the Australia Telescope Compact Array, we present a targeted search for the (J,K) = (1,1) and (2,2) inversion lines towards seven prominent star-forming regions in the Large Magellanic Cloud (LMC). Both lines are detected in the massive star-forming region N159W, which is located in the peculiar molecular ridge south of 30 Doradus, a site of extreme star formation strongly influenced by an interaction with the Milky Way halo. Using the ammonia lines, we derive a kinetic temperature of ~16K, which is 2-3 times below the previously derived dust temperature. The ammonia column density, averaged over ~17 is ~6x10^{12} cm^{-2} <1.5x10^{13} cm^{-2} over 9 in the other six sources) and we derive an ammonia abundance of ~4x10^{-10} with respect to molecular hydrogen. This fractional abundance is 1.5-5 orders of magnitude below those observed in Galactic star-forming regions. The nitrogen abundance in the LMC (~10% solar) and the high UV flux, which can photo-dissociate the particularly fragile NH3 molecule, must both contribute to the low fractional NH3 abundance, and we likely only see the molecule in an ensemble of the densest, best shielded cores of the LMC.
We report a search for H2O megamasers in 274 SDSS type-2 AGNs (0.3 < z < 0.83), half of which can be classified as type-2 QSOs from their [OIII] 5007 luminosity, using the Robert C. Byrd Green Bank Telescope (GBT) and the Effelsberg 100-m radio telescope. Apart from the detection of the extremely luminous water vapor megamaser SDSS J080430.99+360718.1, already reported by Barvainis & Antonucci (2005), we do not find any additional line emission. This high rate of non-detections is compared to the water maser luminosity function created from the 78 water maser galaxies known to date and its extrapolation towards the higher luminosities of gigamasers that we would have been able to detect given the sensitivity of our survey. The properties of the known water masers are summarized and discussed with respect to the nature of high-z type-2 AGNs and megamasers in general. In the appendix, we list 173 additional objects (mainly radio galaxies, but also QSOs and galaxies) that were observed with the GBT, the Effelsberg 100-m radio telescope, or Arecibo Observatory without leading to the detection of water maser emission.
Using the IRAM 30 m telescope, a mapping survey in optically thick and thin lines was performed towards 46 high mass star-forming regions. The sample includes UC H{sc ii} precursors and UC H{sc ii} regions. Seventeen sources are found to show blue profiles, the expected signature of collapsing cores. The excess of sources with blue over red profiles ([$N_{rm blue}$ -- $N_{rm red}$]/$N_{rm total}$) is 29% in the HCO$^+$ $J$=1--0 line, with a probability of 0.6% that this is caused by random fluctuations. UC H{sc ii} regions show a higher excess (58%) than UC H{sc ii} precursors (17%), indicating that material is still accreted after the onset of the UC H{sc ii} phase. Similar differences in the excess of blue profiles as a function of evolutionary state are not observed in low mass star-forming regions. Thus, if confirmed for high mass star-forming sites, this would point at a fundamental difference between low- and high-mass star formation. Possible explanations are inadequate thermalization, stronger influence of outflows in massive early cores, larger gas reserves around massive stellar objects or different trigger mechanisms between low- and high- mass star formation.
