[en] The 1₁₀-1₁₁ formaldehyde (H₂CO) absorption line and H_110α radio recombination line (H RRL) are observed towards the giant HII region in cloud complex W43. The observations are obtained using the Nanshan 25 m single dish operated by Urumqi Observatory, National Astronomical Observatories of China. A region about 30' x 30' is observed, which covers the whole HII region in W43. Except for the central 10' region, all the other seven points are first observed with the H₂CO 1₁₀-1₁₁ absorption. The column density of the H₂CO is calculated, and the H₂CO density contours show some differences with the infrared image. Multiple features appear in the H₂CO and H RRL which indicate complex structure. The intensities of the H₂CO and the velocities of the H_110α seem to present a linear correlation, which illustrates that the sphere of influence of the central WR/OB cluster may be much more extended than presently known, since the size is nearly 50 pc. (research papers)

[en] We observed the H₂CO(1₁₀–1₁₁) absorption lines and H_110α radio recombination lines (RRL) toward 180 NH₃ sources using the Nanshan 25-m radio telescope. In our observation, 138 sources were found to have H₂CO lines and 36 have H_110α RRLs. Among the 138 detected H₂CO sources, 38 sources were first detected. The detection rates of H₂CO have a better correlation with extinction than with background continuum radiation. Line center velocities of H₂CO and NH₃ agree well. The line width ratios of H₂CO and NH₃ are generally larger than unity and are similar to that of ¹³CO. The correlation between column densities of H₂CO and extinction is better than that between NH₃ and extinction. These line width relation and column density relation indicate H₂CO is distributed on a larger scale than that of NH₃, being similar to the regions of ¹³CO. The abundance ratios between NH₃ and H₂CO were found to be different in local clouds and other clouds.

[en] We collect 3249 OH maser sources from the literature published up to April 2007, and compile a new catalog of OH masers. We look for the exciting sources of these masers and their infrared properties from IRAS and MSX data, and make a statistical study. MSX sources associated with stellar 1612 MHz OH masers are located mainly above the blackbody line; this is caused by the dust absorption of stellar envelopes, especially in the MSX_A band. The mid-IR sources associated with stellar OH masers are concentrated in a small region in an [A]-[D] vs. [A]-[E] diagram with a small fraction of contamination; this gives us a new criterion to search for new stellar OH masers and distinguish stellar masers from unknown types of OH masers. IR sources associated with 1612 MHz stellar OH masers show an expected result: the average flux of sources with F60 > F25 increases with increasing wavelength, while those with F60 < F25 vary little with wavelength, because the sources with F60 < F25 are much hotter than those with F60 > F25.

[en] We present large scale observations of C¹⁸O (1–0) towards four massive star forming regions: MON R2, S156, DR17/L906 and M17/M18. The transitions of H₂CO (1₁₀–1₁₁), C¹⁸O (1–0) and the 6 cm continuum are compared in these four regions. Our analysis of the observations and the results of the Non—LTE model shows that the brightness temperature of the formaldehyde absorption line is strongest in a background continuum temperature range of about 3 – 8 K. The excitation of the H₂CO absorption line is affected by strong background continuum emission. From a comparison of H₂CO and C¹⁸O maps, we found that the extent of H₂CO absorption is broader than that of C¹⁸O emission in the four regions. Except for the DR17 region, the maximum in H₂CO absorption is located at the same position as the C¹⁸O peak. A good correlation between intensities and widths of H₂CO absorption and C¹⁸O emission lines indicates that the H₂CO absorption line can trace the dense, warm regions of a molecular cloud. We find that N(H₂CO) is well correlated with N(C¹⁸O) in the four regions and that the average ratio of column densities is 〈N(H₂CO)/N(C¹⁸O)〉 ∼ 0.03. (research papers)

[en] We report results of the H₂CO and H110α survey toward 281 UCHII regions using the Urumqi 25m radio telescope. We obtained 37 new H₂CO detections, and H110α was simultaneously detected in eight of them. Only H110α was detected in another UCHII region. We calculated kinematic distances of nine UCHII regions with the detected H110α and resolved the kinematic distance ambiguity for six of them. The detection rate of H₂CO of our observation was 13.2%, which is low compared with one of the other authors. The possible reason is that the sensitivity of our telescope is relatively low.

[en] We performed an H₂O maser survey towards 274 Bolocam Galactic Plane Survey (BGPS) sources with 85° < l < 193° using the Nanshan 25 m radio telescope. We detected 25 H₂O masers, and five of them are new detections. The detection rate of H₂O masers in our sample is 9% which is very low. The detection rate of H₂O masers increases as the 1.1 mm flux density of BGPS sources increases, and both the peak flux density and luminosity of H₂O masers increase as the sources evolve. The detection rate of H₂O masers toward BGPS sources without HCO⁺ emission is low. The BGPS sources associated with both H₂O and CH₃OH masers seem to be more compact than those only associated with H₂O masers. This indicates that the sources with both masers may be in a relatively later evolutionary stage. The strongest H₂O maser source G133.715+01.217, also well known as W3 IRS 5 which has a flux density of 2.9×10³ Jy, was detected at eight different nearby positions. By measuring the correlation between the flux densities of these H₂O masers and their angular distance from the true source location, we get the influence radius $r=\frac{1}{0.8}\log \left(\frac{F_0}{3\text{rms}}\right)$. For our observations, strong sources can be detected anywhere within this radius. It is helpful to determine whether or not a weak maser nearby the strong maser is a true detection. (paper)

[en] The bubble G15.684-0.29 has a radius of 15.7 pc. Its large size indicates that it may have enough time to trigger star formation. We identify 39 dense cold clumps around the bubble from the Hi-GAL survey. All of them satisfy the criteria for forming massive stars, and most of them lie in the bubble shell. We identify 19 molecular clumps around the bubble from the ¹²CO(3–2) survey, all of which are gravitationally bound. We found 9 Class I YSOs, 28 Class II YSOs, and 12 transition disks (TDs) around the bubble. For those young stellar objects (YSOs) located within the bubble boundary, 6 of 7 Class I YSOs lie in the shell, 15 of 22 Class II YSOs lie inside the bubble, and 3 of 5 TDs lie inside the bubble. The dynamical age of G15.684-0.29 in a turbulent medium is ∼4 Myr, which is much greater than the shell fragmentation time, ∼0.82–1.74 Myr. We suggest that triggered star formation may be ongoing in the shell of the bubble, and the collect and collapse model may work here. However, we cannot rule out the possibility that the radiation-driven implosion model may work on the formation of some YSOs. As we expected, the larger bubble has a much longer dynamical age, but we failed to find a clear age gradient for YSOs around the bubble.

[en] We mapped the kinetic temperature structure of Orion KL in a ∼20″ (∼8000 au) sized region with para-H₂CS 7₀₇ − 6₀₆, 7₂₆ − 6₂₅, and 7₂₅ − 6₂₄ making use of Atacama Large Millimeter/submillimeter Array Band 6 Science Verification data. The kinetic temperatures obtained with a resolution of 1.″65 × 1.″14 (∼550 au) are deduced by modeling the measured averaged velocity-integrated intensity ratios of para-H₂CS 7₂₆ − 6₂₅/7₀₇ − 6₀₆ and 7₂₅ − 6₂₄/7₀₇ − 6₀₆ with a RADEX non-LTE model. The kinetic temperatures of the dense gas, derived from the para-H₂CS line ratios at a spatial density of 10⁷ cm⁻³, are high, ranging from 43 to >500 K with an unweighted average of ∼170 K. There is no evidence for internal sources playing an important role in the heating of the various structures identified in previous work, namely the elongated ridge, the northwestern clump, and the eastern region of the compact ridge, while the high temperatures in the western region of the compact ridge may be dominated by internal massive star formation. Significant gradients of kinetic temperature along molecular filaments traced by H₂CS indicate that the dense gas is heated by the shocks induced by the enigmatic explosive event which occurred several hundred years ago and greatly affected the energetics of the Orion KL region. Thus, with the notable exception of the western region of the compact ridge, the high temperatures of the dense gas in Orion KL are probably caused by shocks from the explosive event, leading to a dominant component of externally heated dense gas.

[en] We have selected 43 southern massive star-forming regions to study the spatial distribution of HNCO 4₀₄–3₀₃, SiO 2–1, and HC₃N 10–9 line emission and to investigate their spatial association with the dust emission. The morphology of HNCO 4₀₄–3₀₃ and HC₃N 10–9 agrees well with the dust emission. HC₃N 10–9 tends to originate from more compact regions than HNCO 4₀₄–3₀₃ and SiO 2–1. We divided our sources into three groups: those in the Central Molecular Zone (CMZ), those associated with bubbles (Bubble), and the remaining sources, which are termed “normal star-forming regions” (NMSFR). These three groups, subdivided into three different categories with respect to line widths, integrated intensities, and column densities, hint at the presence of different physical and chemical processes. We find that the dust temperature T _d, and the abundance ratios N _HNCO/N _SiO and N _HNCO/N _HC3N show a decreasing trend toward the central dense regions of CMZ sources, while N _HC3N/N _SiO moves in the opposite direction. Moreover, a better agreement is found between T _d and N _HC3N/N _SiO in Bubble and NMSFR category sources. Both outflow and inflow activities have been found in eight of the 16 bubble and NMSFR sources. The low outflow detection rate indicates either that in these sources the SiO 2–1 line wing emission is below our sensitivity limit or that the bulk of the SiO emission may be produced by the expansion of an H ii region or supernova remnant, which has pushed molecular gas away, forming a shock and yielding SiO.

[en] 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 (β_c) 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 β_c). 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.