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Register a new userMillimeter Spectral Line Mapping Observations Toward Four Massive Star Forming HII Regions
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We present spectral line mapping observations toward four massive star-forming regions (Cepheus A, DR21S, S76E and G34.26+0.15), with the IRAM 30 meter telescope at 2 mm and 3 mm bands. Totally 396 spectral lines from 51 molecules, one helium recombination line, ten hydrogen recombination lines, and 16 unidentified lines were detected in these four sources. An emission line of nitrosyl cyanide (ONCN, 14$_{0,14}$-13$_{0,13}$) was detected in G34.26+0.15, as first detection in massive star-forming regions. We found that the $c$-C$_{3}$H$_{2}$ and NH$_{2}$D show enhancement in shocked regions as suggested by evidences of SiO and/or SO emission. Column density and rotational temperature of CH$_{3}$CN were estimated with the rotational diagram method for all four sources. Isotope abundance ratios of $^{12}$C/$^{13}$C were derived using HC$_{3}$N and its $^{13}$C isotopologue, which were around 40 in all four massive star-forming regions and slightly lower than the local interstellar value ($sim$65). $^{14}$N/$^{15}$N and $^{16}$O/$^{18}$O abundance ratios in these sources were also derived using double isotopic method, which were slightly lower than that in local interstellar medium. Except for Cep A, $^{33}$S/$^{34}$S ratio in the other three targets were derived, which were similar to that in the local interstellar medium. The column density ratios of N(DCN)/N(HCN) and N(DCO$^{+}$)/N(HCO$^{+}$) in these sources were more than two orders of magnitude higher than the elemental [D]/[H] ratio, which is 1.5$times$10$ ^{-5}$. Our results show the later stage sources, G34.26+0.15 in particular, present more molecular species than earlier stage ones. Evidence of shock activity is seen in all stages studied.
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We have identified 453 compact dense cores in 3 mm continuum emission maps in the ATOMS (ALMA Three-millimeter Observations of Massive Star-forming regions) survey, and compiled three catalogues of high-mass star forming cores. One catalogue, referred to as H/UC-HII catalogue, includes 89 cores that enshroud hyper/ultra compact (H/UC) HII regions as characterized by associated compact H40alpha emission. A second catalogue, referred to as pure s-cHMC, includes 32 candidate Hot Molecular Cores (HMCs) showing rich spectra (N>20lines) of complex organic molecules (COMs) but not associated with H/UC-HII regions. The third catalogue, referred to as pure w-cHMC, includes 58 candidate HMCs with relatively low levels of COM richness and not associated with H/UC-HII regions. These three catalogues of dense cores provide an important foundation for future studies of the early stages of high-mass star formation across the Milky Way. We also find that nearly half of H/UC-HII cores are candidate HMCs. From the number counts of COM-containing and H/UC-HII cores, we suggest that the duration of high-mass protostellar cores showing chemically rich features is at least comparable to the lifetime of H/UC-HII regions. For cores in the H/UC-HII catalogue, the width of the H40alpha line increases as the core size decreases, suggesting that the non-thermal dynamical and/or pressure line-broadening mechanisms dominate on the smaller scales of the H/UC-HII cores.
We observed radio recombination lines (RRLs) toward the W51 molecular cloud complex, one of the most active star forming regions in our Galaxy. The UV radiation from young massive stars ionizes gas surrounding them to produce HII regions. Observations of the W51 IRS1 HII region were made with the Arecibo 305 m telescope. Of the full 1-10 GHz database, we have analyzed the observations between 4.5 and 5 GHz here. The steps involved in the analysis were: a) bandpass calibration using on-source/off-source observations; b) flux density calibration; c) removing spectral baselines due to errors in bandpass calibration and d) Gaussian fitting of the detected lines. We detected alpha, beta and gamma transitions of hydrogen and alpha transitions of helium. We used the observed line parameters to 1) measure the source velocity (56.6 $pm$ 0.3 km s$^{-1}$) with respect to the Local Standard of Rest (LSR); 2) estimate the electron temperature (8500 $pm$ 1800 K) of the HII region and 3) derive the emission measure (5.4 $pm$ 2.7 $times$ 10$^{6}$ pc cm$^{-6}$) of the ionized gas.
Early results from the Herschel Space Observatory revealed the water cation H2O+ to be an abundant ingredient of the interstellar medium. Here we present new observations of the H2O and H2O+ lines at 1113.3 and 1115.2 GHz using the Herschel Space Observatory toward a sample of high-mass star-forming regions to observationally study the relation between H2O and H2O+ . Nine out of ten sources show absorption from H2O+ in a range of environments: the molecular clumps surrounding the forming and newly formed massive stars, bright high-velocity outflows associated with the massive protostars, and unrelated low-density clouds along the line of sight. Column densities per velocity component of H2 O+ are found in the range of 10^12 to a few 10^13 cm-2 . The highest N(H2O+) column densities are found in the outflows of the sources. The ratios of H2O+/H2O are determined in a range from 0.01 to a few and are found to differ strongly between the observed environments with much lower ratios in the massive (proto)cluster envelopes (0.01-0.1) than in outflows and diffuse clouds. Remarkably, even for source components detected in H2O in emission, H2O+ is still seen in absorption.
The shape of the OB-star spectral energy distribution is a critical component in many diagnostics of the ISM and galaxy properties. We use single-star HII regions from the LMC to quantitatively examine the ionizing SEDs from widely available CoStar, TLUSTY, and WM-basic atmosphere grids. We evaluate the stellar atmosphere models by matching the emission-line spectra that they predict from CLOUDY photoionization simulations with those observed from the nebulae. The atmosphere models are able to reproduce the observed optical nebular line ratios, except at the highest energy transitions > 40 eV, assuming that the gas distribution is non-uniform. Overall we find that simulations using WM-basic produce the best agreement with the observed line ratios. The rate of ionizing photons produced by the model SEDs is consistent with the rate derived from the Halpha luminosity for standard, log(g) = 4.0 models adopted from the atmosphere grids. However, there is a systematic offset between the rate of ionizing photons from different atmosphere models that is correlated with the relative hardness of the SEDs. In general WM-basic and TLUSTY atmosphere models predict similar effective temperatures, while CoStar predicts effective temperatures that are cooler by a few thousand degrees. We compare our effective temperatures, which depend on the nebular ionization balance, to conventional photospheric-based calibrations from the literature. We suggest that in the future, spectral type to effective temperature calibrations can be constructed from nebular data.
We report studies of the relationships between the total bolometric luminosity ($L_{rm bol}$ or $L_{rm TIR}$) and the molecular line luminosities of $J=1-0$ transitions of H$^{13}$CN, H$^{13}$CO$^+$, HCN, and HCO$^+$ with data obtained from ACA observations in the ATOMS survey of 146 active Galactic star forming regions. The correlations between $L_{rm bol}$ and molecular line luminosities $L_{rm mol}$ of the four transitions all appear to be approximately linear. Line emission of isotopologues shows as large scatters in $L_{rm bol}$-$L_{rm mol}$ relations as their main line emission. The log($L_{rm bol}$/$L_{rm mol}$) for different molecular line tracers have similar distributions. The $L_{rm bol}$-to-$L_{rm mol}$ ratios do not change with galactocentric distances ($R_{rm GC}$) and clump masses ($M_{rm clump}$). The molecular line luminosity ratios (HCN-to-HCO$^+$, H$^{13}$CN-to-H$^{13}$CO$^+$, HCN-to-H$^{13}$CN and HCO$^+$-to-H$^{13}$CO$^+$) all appear constant against $L_{rm bol}$, dust temperature ($T_{rm d}$), $M_{rm clump}$ and $R_{rm GC}$. Our studies suggest that both the main lines and isotopologue lines are good tracers of the total masses of dense gas in Galactic molecular clumps. The large optical depths of main lines do not affect the interpretation of the slopes in star formation relations. We find that the mean star formation efficiency (SFE) of massive Galactic clumps in the ATOMS survey is reasonably consistent with other measures of the SFE for dense gas, even those using very different tracers or examining very different spatial scales.
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