ATLASGAL-selected massive clumps in the inner Galaxy: VI. Kinetic temperature and spatial density measured with formaldehyde

We aim to directly determine the kinetic temperature and spatial density with formaldehyde for the $\sim$100 brightest ATLASGAL-selected clumps at 870 $\mu$m representing various evolutionary stages of high-mass star formation. Ten transitions ($J$ = 3-2 and 4-3) of ortho- and para-H$_2$CO near 211, 218, 225, and 291 GHz were observed with the APEX 12 m telescope. Using non-LTE models with RADEX, we derive the gas kinetic temperature and spatial density using the measured p-H$_2$CO 3$_{21}$-2$_{20}$/3$_{03}$-2$_{02}$, 4$_{22}$-3$_{21}$/4$_{04}$-3$_{03}$, and 4$_{04}$-3$_{03}$/3$_{03}$-2$_{02}$ ratios. The gas kinetic temperatures derived from the p-H$_2$CO 3$_{21}$-2$_{20}$/3$_{03}$-2$_{02}$ and 4$_{22}$-3$_{21}$/4$_{04}$-3$_{03}$ line ratios are high, ranging from 43 to $>$300 K with an unweighted average of 91 $\pm$ 4 K. Deduced $T_{\rm kin}$ values from the $J$ = 3-2 and 4-3 transitions are similar. Spatial densities of the gas derived from the p-H$_2$CO 4$_{04}$-3$_{03}$/3$_{03}$-2$_{02}$ line ratios yield 0.6-8.3 $\times$ 10$^6$ cm$^{-3}$ with an unweighted average of 1.5 ($\pm$0.1) $\times$ 10$^6$ cm$^{-3}$. A comparison of kinetic temperatures derived from p-H$_2$CO, NH$_3$, and the dust emission indicates that p-H$_2$CO traces a distinctly higher temperature than the NH$_3$ (2,2)/(1,1) transitions and the dust, tracing heated gas more directly associated with the star formation process. The H$_2$CO linewidths are found to be correlated with bolometric luminosity and increase with the evolutionary stage of the clumps, which suggests that higher luminosities tend to be associated with a more turbulent molecular medium. It seems that the spatial densities measured with H$_2$CO do not vary significantly with the evolutionary stage of the clumps. However, averaged gas kinetic temperatures derived from H$_2$CO increase with time through the evolution of the clumps.Comment: Accepted for publication in A&

Investigating Cold Dust Properties of 12 Nearby Dwarf Irregular Galaxies by Hierarchical Bayesian Spectral Energy Distribution Fitting

Combining infrared and submillimeter observations and applying a two-temperature modified blackbody (TMBB) model with a hierarchical Bayesian technique, we model the spectral energy distribution of 12 nearby dwarf irregular (dIrr) galaxies. We aim to probe potential submillimeter excess emission at 350, 500, and 850 μm and investigate the properties of cold dust parameters. Based on the TMBB model with cold dust emissivity index (βc) fixed to 2, one galaxy shows 500 μm excess emission and nine galaxies show excess at 850 μm (five of them still show 850 μm excess in the case of free βc). We find that the 850 μm excess emission is easily detected in the dIrr galaxies with low star formation activity. The 850 μm excess is more frequent and more prominent in dIrr galaxies with low molecular hydrogen gas mass fraction or low ratios between cold dust mass and gas mass. As galaxies evolve, the ratios between atomic hydrogen gas mass and stellar mass decrease and the 850 μm excess emission tends to decrease or even disappear. Our results suggest that the cold dust temperature may increase, as the dIrr galaxies have more intense star formation or richer metallicity. There is a weak anticorrelation between the cold dust-to-stellar mass ratio and the specific star formation rate for our galaxies

The infrared dust bubble N22: an expanding HII region and the star formation around it

Aims. To increase the observational samples of star formation around expanding Hii regions, we analyzed the interstellar medium and star formation around N22. Methods. We used data extracted from the seven large-scale surveys from infrared to radio wavelengths. In addition we used the JCMT observations of the J = 3-2 line of 12CO emission data released on CADC and the 12CO J = 2-1 and J =3-2 lines observed by the KOSMA 3 m telescope. We performed a multiwavelength study of bubble N22. Results. A molecular shell composed of several clumps agrees very well with the border of N22, suggesting that its expansion is collecting the surrounding material. The high integrated 12CO line intensity ratio (ranging from 0.7 to 1.14) implies that shocks have driven into the molecular clouds. We identify eleven possible O-type stars inside the Hii region, five of which are located in projection inside the cavity of the 20 cm radio continuum emission and are probably the exciting-star candidates of N22. Twenty-nine YSOs (young stellar objects) are distributed close to the dense cores of N22. We conclude that star formation is indeed active around N22; the formation of most of YSOs may have been triggered by the expanding of the Hii region. After comparing the dynamical age of N22 and the fragmentation time of the molecular shell, we suggest that radiation-driven compression of pre-existing dense clumps may be ongoing.Comment: accepted in A&A 30/05/2012. arXiv admin note: text overlap with arXiv:1010.5430 by other author

Polarisation Observations of VY Canis Majoris Water Vapour 5{32}-4{41} 620.701 GHz Maser Emission with HIFI

CONTEXT: Water vapour maser emission from evolved oxygen-rich stars remains poorly understood. Additional observations, including polarisation studies and simultaneous observation of different maser transitions may ultimately lead to greater insight. AIMS: We have aimed to elucidate the nature and structure of the VY CMa water vapour masers in part by observationally testing a theoretical prediction of the relative strengths of the 620.701 GHz and the 22.235 GHz maser components of ortho water vapour. METHODS: In its high-resolution mode (HRS) the Herschel Heterodyne Instrument for the Infrared (HIFI) offers a frequency resolution of 0.125 MHz, corresponding to a line-of-sight velocity of 0.06 km/s, which we employed to obtain the strength and linear polarisation of maser spikes in the spectrum of VY CMa at 620.701 GHz. Simultaneous ground based observations of the 22.235 GHz maser with the Max-Planck-Institut f\"ur Radioastronomie 100-meter telescope at Effelsberg, provided a ratio of 620.701 GHz to 22.235 GHz emission. RESULTS:We report the first astronomical detection to date of water vapour maser emission at 620.701 GHz. In VY CMa both the 620.701 and the 22.235 GHz polarisation are weak. At 620.701 GHz the maser peaks are superposed on what appears to be a broad emission component, jointly ejected asymmetrically from the star. We observed the 620.701 GHz emission at two epochs 21 days apart, both to measure the potential direction of linearly polarised maser components and to obtain a measure of the longevity of these components. Although we do not detect significant polarisation levels in the core of the line, they rise up to approximately 6% in its wings

Observations of multiple NH3 transitions in W33

Stars and planetary system

Kinetic temperature of massive star-forming molecular clumps measured with formaldehyde IV. The ALMA view of N113 and N159W in the LMC

We mapped the kinetic temperature structure of two massive star-forming regions, N113 and N159W, in the Large Magellanic Cloud (LMC). We have used ~1.′′6 (~0.4 pc) resolution measurements of the para-H2CO JKaKc = 303–202, 322–221, and 321–220 transitions near 218.5 GHz to constrain RADEX non local thermodynamic equilibrium models of the physical conditions. The gas kinetic temperatures derived from the para-H2CO line ratios 322–221/303–202 and 321–220/303–202 range from 28 to 105 K in N113 and 29 to 68 K in N159W. Distributions of the dense gas traced by para-H2CO agree with those of the 1.3 mm dust and Spitzer 8.0 μm emission, but they do not significantly correlate with the Hα emission. The high kinetic temperatures (Tkin ≳ 50 K) of the dense gas traced by para-H2CO appear to be correlated with the embedded infrared sources inside the clouds and/or young stellar objects in the N113 and N159W regions. The lower temperatures (Tkin < 50 K) were measured at the outskirts of the H2CO-bearing distributions of both N113 and N159W. It seems that the kinetic temperatures of the dense gas traced by para-H2CO are weakly affected by the external sources of the Hα emission. The non thermal velocity dispersions of para-H2CO are well correlated with the gas kinetic temperatures in the N113 region, implying that the higher kinetic temperature traced by para-H2CO is related to turbulence on a ~0.4 pc scale. The dense gas heating appears to be dominated by internal star formation activity, radiation, and/or turbulence. It seems that the mechanism heating the dense gas of the star-forming regions in the LMC is consistent with that in Galactic massive star-forming regions located in the Galactic plane

Planck Galactic Cold Clumps at High Galactic Latitude-a Study with CO Lines

Gas at high Galactic latitude is a relatively little noticed component of the interstellar medium. In an effort to address this, 41 Planck Galactic Cold Clumps at high Galactic latitude (HGal; divide b divide > 25 degrees) were observed in (CO)-C-12, (CO)-C-13, and (CO)-O-18 J = 1-0 lines, using the Purple Mountain Observatory 13.7 m telescope. (CO)-C-12 (1-0) and (CO)-C-13 (1-0) emission was detected in all clumps, while (CO)-O-18 (1-0) emission was only seen in 16 clumps. The highest and average latitudes are 71.degrees 4 and 37.degrees 8, respectively. Fifty-one velocity components were obtained, and then each was identified as a single clump. Thirty-three clumps were further mapped at 1 ' resolution, and 54 dense cores were extracted. Among dense cores, the average excitation temperature T (ex) of (CO)-C-12 is 10.3 K. The average line widths of thermal and nonthermal velocity dispersions are 0.19 and 0.46 km s(-1), respectively, suggesting that these cores are dominated by turbulence. Distances of the HGal clumps given by Gaia dust reddening are about 120-360 pc. The ratio of X (13)/X (18) is significantly higher than that in the solar neighborhood, implying that HGal gas has a different star formation history compared to the gas in the Galactic disk. HGal cores with sizes from 0.01 to 0.1 pc show no notable Larson's relation, and the turbulence remains supersonic down to a scale of slightly below 0.1 pc. None of the HGal cores that bear masses from 0.01 to 1 M (circle dot) are gravitationally bound, and all appear to be confined by outer pressure.Peer reviewe

ATLASGAL-selected massive clumps in the inner Galaxy. VI. Kinetic temperature and spatial density measured with formaldehyde

Context: Formaldehyde (H2CO) is a reliable tracer to accurately measure the physical parameters of dense gas in star-forming regions. Aim: We aim to determine directly the kinetic temperature and spatial density with formaldehyde for the ~100 brightest ATLASGAL-selected clumps (the TOP100 sample) at 870 ?m representing various evolutionary stages of high-mass star formation. Methods: Ten transitions (J = 3–2 and 4–3) of ortho- and para-H2CO near 211, 218, 225, and 291 GHz were observed with the Atacama Pathfinder EXperiment (APEX) 12 m telescope. Results: Using non-LTE models with RADEX, we derived the gas kinetic temperature and spatial density with the measured para-H2CO 321–220/303–202, 422–321/404–303, and 404–303/303–202 ratios. The gas kinetic temperatures derived from the para-H2CO 321–220/303–202 and 422–321/404–303 line ratios are high, ranging from 43 to >300 K with an unweighted average of 91 ± 4 K. Deduced Tkin values from the J = 3–2 and 4–3 transitions are similar. Spatial densities of the gas derived from the para-H2CO 404–303/303–202 line ratios yield 0.6–8.3 × 106 cm?3 with an unweighted average of 1.5 (±0.1) × 106 cm?3. A comparison of kinetic temperatures derived from para-H2CO, NH3, and dust emission indicates that para-H2CO traces a distinctly higher temperature than the NH3 (2, 2)/(1, 1) transitions and the dust, tracing heated gas more directly associated with the star formation process. The H2CO line widths are found to be correlated with bolometric luminosity and increase with the evolutionary stage of the clumps, which suggests that higher luminosities tend to be associated with a more turbulent molecular medium. It seems that the spatial densities measured with H2CO do not vary significantly with the evolutionary stage of the clumps. However, averaged gas kinetic temperatures derived from H2CO increase with time through the evolution of the clumps. The high temperature of the gas traced by H2CO may be mainly caused by radiation from embedded young massive stars and the interaction of outflows with the ambient medium. For Lbol/Mclump ? 10 L?/M?, we find a rough correlation between gas kinetic temperature and this ratio, which is indicative of the evolutionary stage of the individual clumps. The strong relationship between H2CO line luminosities and clump masses is apparently linear during the late evolutionary stages of the clumps, indicating that LH_2CO does reliably trace the mass of warm dense molecular gas. In our massive clumps H2CO line luminosities are approximately linearly correlated with bolometric luminosities over about four orders of magnitude in Lbol, which suggests that the mass of dense molecular gas traced by the H2CO line luminosity is well correlated with star formation

A H

Context. Accurate distances are necessary for determining the physical properties of massive star-formation regions and the structure of our Galaxy. One way to approach these studies is by determining the kinematic distances of H i