- ID:
- ivo://CDS.VizieR/J/MNRAS/478/5579
- Title:
- Refined sample of Lyman excess H II regions
- Short Name:
- J/MNRAS/478/5579
- Date:
- 08 Feb 2022 11:53:49
- Publisher:
- CDS
- Description:
- A large number (67) of the compact/ultra-compact HII regions identified in the Coordinated Radio and Infrared Survey for High-Mass Star Formation catalogue were determined to be powered by a Lyman continuum flux in excess of what was expected given their corresponding luminosity. In this study we attempt to reasonably explain the Lyman excess phenomenon in as many of the 67 HII regions as possible through a variety of observational and astrophysical means including new luminosity estimates, new Herschel photometry, new distance determinations, the use of different models for dust and ionized gas covering factors, and the use of different stellar calibrations. This phenomenon has been observed before; however, the objects shown to exhibit this behaviour in the literature have decidedly different physical properties than the regions in our sample, and thus the origin of the excess is not the same. We find that the excess can be reproduced using OB stellar atmosphere models that have been slightly modified in the extreme ultraviolet. Though the exact mechanism producing the excess is still uncertain, we do find that a scaled up magnetospheric accretion model, often used to explain similar emission from T Tauri stars, is unable to match our observations. Our results suggest that the Lyman excess may be associated with younger HII regions, and that it is more commonly found in early B-type stars. Our refined sample of 24 Lyman excess HII regions provides an ideal sample for comparative studies with regular HII regions, and can act as the basis for the further detailed study of individual regions.
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402. RMC143 ALMA images
- ID:
- ivo://CDS.VizieR/J/A+A/626/A126
- Title:
- RMC143 ALMA images
- Short Name:
- J/A+A/626/A126
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The luminous blue variable (LBV) RMC143 is located in the outskirts of the 30~Doradus complex, a region rich with interstellar material and hot luminous stars. We report the 3{sigma} sub-millimetre detection of its circumstellar nebula with ALMA. The observed morphology in the sub-millimetre is different than previously observed with HST and ATCA in the optical and centimetre wavelength regimes. The spectral energy distribution (SED) of RMC suggests that two emission mechanisms contribute to the sub-mm emission: optically thin bremsstrahlung and dust. Both the extinction map and the SED are consistent with a dusty massive nebula with a dust mass of 0.055+/-0.018M_{sun}_ (assuming {kappa}_850_=1.7cm^2^/g). To date, RMC143 has the most dusty LBV nebula observed in the Magellanic Clouds. We have also re-examined the LBV classification of RMC143 based on VLT/X-shooter spectra obtained in 2015/16 and a review of the publication record. The radiative transfer code CMFGEN is used to derive its fundamental stellar parameters. We find an effective temperature of ~8500K, luminosity of log(L/L_{sun}_)=5.32, and a relatively high mass-loss rate of 1.0x10^-5^M_{sun}_/yr. The luminosity is much lower than previously thought, which implies that the current stellar mass of ~8M_{sun}_ is comparable to its nebular mass of ~5.5~M_{sun}_ (from an assumed gas-to-dust ratio of 100), suggesting that the star has lost a large fraction of its initial mass in past LBV eruptions or binary interactions. While the star may have been hotter in the past, it is currently not hot enough to ionize its circumstellar nebula. We propose that the nebula is ionized externally by the hot stars in the 30 Doradus star-forming region.
- ID:
- ivo://CDS.VizieR/J/A+A/587/A152
- Title:
- Rotational spectrum of ^13^C methylamine
- Short Name:
- J/A+A/587/A152
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Methylamine (CH_3_NH_2_) is a light molecule of astrophysical interest, which has an intensive rotational spectrum that extends in the submillimeter wave range and far beyond, even at temperatures characteristic for the interstellar medium. It is likely for ^13^C isotopologue of methylamine to be identified in astronomical surveys, but there is no information available for the ^13^CH_3_NH_2_ millimeter and submillimeter wave spectra. In this context, to provide reliable predictions of ^13^CH_3_NH_2_ spectrum in millimeter and submillimeter wave ranges, we have studied rotational spectra of the 13C methylamine isotopologue in the frequency range from 48 to 945GHz. The spectrum of ^13^C methylamine was recorded using conventional absorption spectrometers in Lille and Kharkov. The analysis of the rotational spectrum of ^13^C methylamine in the ground vibrational state was performed on the basis of the group- theoretical high-barrier tunneling Hamiltonian that was developed for methylamine by Ohashi and Hougen. The available multiple observations of the parent methylamine species toward Sgr B2(N) at 1, 2, and 3mm using the Submillimeter Telescope and the 12 m antenna of the Arizona Radio Observatory were used to make a search for interstellar ^13^CH_3_NH_2_. In the recorded spectra, we have assigned 2721 rotational transitions that belong to the ground vibrational state of the ^13^CH_3_NH_2_. These measurements were fitted to the Hamiltonian model that uses 75 parameters to achieve an overall weighted rms deviation of 0.73. On the basis of these spectroscopic results, predictions of transition frequencies in the frequency range up to 950GHz with J<50 and Ka<20 are presented. The search for interstellar ^13^C methylamine in available observational data was not successful and therefore only an upper limit of 6.5x10^14^cm^-2^ can be derived for the column density of ^13^CH_3_NH_2_ toward Sgr B2(N), assuming the same source size, temperature, linewidth, and systemic velocity as for parent methylamine isotopic species.
- ID:
- ivo://CDS.VizieR/J/A+A/559/A44
- Title:
- Rotational spectrum of MAAN (CH_2_NCH_2_CN)
- Short Name:
- J/A+A/559/A44
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Aminoacetonitrile has been detected in the interstellar medium and the Strecker-type synthesis is considered as one of its possible mechanisms of formation in this medium. Methyleneaminoacetonitrile (CH_2_=N-CH_2_-CN, MAAN) is one of the by-products of the Strecker reaction and a good candidate for astrophysical detection. Rotational spectrum of MAAN has never been studied before. To provide the basis for the detection of MAAN in the interstellar medium we studied its millimeter and submillimeter-wave spectrum. The rotational spectrum of MAAN was measured in the frequency range 120-600GHz. The spectroscopic study was supported by theoretical calculations of the molecular structure and harmonic force field. The ground and two lowest excited vibrational states of the most stable synperiplanar conformation of MAAN were assigned and analyzed. Obtained sets of rotational constants allows us to make accurate predictions of transition frequencies of MAAN in the frequency range up to 900GHz.
- ID:
- ivo://CDS.VizieR/J/ApJS/169/28
- Title:
- Rotational transitions of Methyl carbamate
- Short Name:
- J/ApJS/169/28
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The rotational-torsional spectrum of the syn conformer of methyl carbamate [CH_3_OC(:O)NH_2_], an isomer of the essential amino acid glycine [NH_2_CH_2_C(:O)OH], has been recorded at room temperature in the spectral region from 79 to 371GHz. Methyl carbamate possesses a methyl group internal rotor, which gives rise to A and E torsional substates, and associated splittings in the rotational spectrum. Almost 6000 new rotational transitions arising from the vibrational ground state have been assigned, about half of them belonging to the E torsional substate. The Fast Scan Submillimeter-wave Spectroscopic Technique (FASSST) spectrometer at the Ohio State University was used for the present measurements
- ID:
- ivo://CDS.VizieR/J/A+A/582/A66
- Title:
- SABOCA NGC 3603 IRS 9A images
- Short Name:
- J/A+A/582/A66
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The formation of massive stars and their arrival on the zero-age main-sequence occurs hidden behind dense clouds of gas and dust. In the giant HII region NGC 3603, the radiation of a young cluster of OB stars has dispersed dust and gas in its vicinity. At a projected distance of 2.5pc from the cluster, a bright mid-infrared (mid-IR) source (IRS 9A) was identified as a massive young stellar object (MYSO), located on the side of a molecular clump (MM2) of gas facing the cluster. We investigated the physical conditions in MM2, based on APEX sub-mm observations using the SABOCA and SHFI instruments, and archival ATCA 3mm continuum and CS spectral line data. We resolved MM2 into several compact cores, one of them closely associated with IRS 9A. These are likely to be infrared dark clouds because they do not show the typical hot-core emission lines and are mostly opaque against the mid-IR background. The compact cores have masses of up to several hundred times the solar mass and gas temperatures of about 50K, without evidence of internal ionizing sources. We speculate that IRS 9A is younger than the cluster stars, but is in an evolutionary state after the compact cores.
- ID:
- ivo://CDS.VizieR/J/A+A/631/A72
- Title:
- SABOCA 350um view of ATLASGAL-selected massive clumps
- Short Name:
- J/A+A/631/A72
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The structure formation of the dense interstellar material and the fragmentation of clumps into cores is a fundamental step to understand how stars and stellar clusters form. We aim to establish a statistical view of clump fragmentation at sub-parsec scales based on a large sample of massive clumps selected from the ATLASGAL survey. We used the APEX/SABOCA camera at 350um to image clumps at a resolution of 8.5", corresponding to physical scales of <0.2pc at a distance <5kpc. The majority of the sample consists of massive clumps that are weak or in absorption at 24um. We resolve spherical and filamentary structures and identify the population of compact sources. Complemented with archival Herschel data, we derive the physical properties, such as dust temperature, mass and bolometric luminosity of clumps and cores. We use association with mid-infrared 22-24 m and 70 m point sources to pin down the star formation activity of the cores. We then statistically assess their physical properties, and the fragmentation characteristics of massive clumps. We detect emission at 350um towards all targets and find that it typically exhibits a filamentary(-like) morphology and hosts a population of compact sources. Using Gaussclumps we identify 1120 compact sources and derive the physical parameters and star formation activity for 971 of these, 874 of which are associated with 444 clumps. We find a moderate correlation between the clump fragmentation levels with the clump gas density and the predicted number of fragments with pure Jeans fragmentation scenario. We find a strong correlation between the mass of the most massive fragment and the total clump mass, suggesting that the self-gravity may play an important role in the clumps' small scale structure formation. Finally, due to the improved angular resolution compared to ATLASGAL, we are able to identify 27 massive quiescent cores with M_core_>100M_{sun}_ within 5kpc; these are massive enough to be self-gravitating but do not yet show any sign of star-formation. This sample comprises, therefore, promising candidates of massive pre-stellar cores, or deeply embedded high-mass protostars. The submillimeter observations of the massive clumps that are weak or completely dark at 24um reveal rich filamentary structures and an embedded population of compact cores. The maximum core mass is likely determined by the self-gravity of the clump. The rarity of massive pre-stellar core candidates implies short collapse time-scales for dense structures.
- ID:
- ivo://CDS.VizieR/J/ApJ/820/82
- Title:
- S2CLS: multiwavelength counterparts to SMGs
- Short Name:
- J/ApJ/820/82
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present multiwavelength identifications for the counterparts of 1088 submillimeter sources detected at 850{mu}m in the SCUBA-2 Cosmology Legacy Survey (S2CLS) study of the UKIRT Infrared Deep Sky Survey-Ultra-Deep Survey (UDS) field. By utilizing an Atacama Large Millimeter Array (ALMA) pilot study on a subset of our bright SCUBA-2 sample as a training set, along with the deep optical-near-infrared (OIR) data available in this field, we develop a novel technique, Optical-IR Triple Color (OIRTC), using z-K, K-[3.6], [3.6]-[4.5] colors to select the candidate submillimeter galaxy (SMG) counterparts. By combining radio identification and the OIRTC technique, we find counterpart candidates for 80% of the Class = 1 >=4{sigma} SCUBA-2 sample, defined as those that are covered by both radio and OIR imaging and the base sample for our scientific analyses. Based on the ALMA training set, we expect the accuracy of these identifications to be 82%+/-20%, with a completeness of 69%+/-16%, essentially as accurate as the traditional p-value technique but with higher completeness. We find that the fraction of SCUBA-2 sources having candidate counterparts is lower for fainter 850{mu}m sources, and we argue that for follow-up observations sensitive to SMGs with S_850_>~1mJy across the whole ALMA beam, the fraction with multiple counterparts is likely to be >40% for SCUBA-2 sources at S_850_>~4mJy. We find that the photometric redshift distribution for the SMGs is well fit by a lognormal distribution, with a median redshift of z=2.3+/-0.1. After accounting for the sources without any radio and/or OIRTC counterpart, we estimate the median redshift to be z=2.6+/-0.1 for SMGs with S_850_>1mJy. We also use this new large sample to study the clustering of SMGs and the far-infrared properties of the unidentified submillimeter sources by stacking their Herschel SPIRE far-infrared emission.
- ID:
- ivo://CDS.VizieR/J/ApJ/880/43
- Title:
- S2COSMOS: bright SCUBA-2 submm sources in COSMOS
- Short Name:
- J/ApJ/880/43
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present sensitive 850{mu}m imaging of the Cosmological Evolution Survey (COSMOS) field using 640hr of new and archival observations taken with SCUBA-2 at the East Asian Observatory's James Clerk Maxwell Telescope. The SCUBA-2 COSMOS survey (S2COSMOS) achieves a median noise level of {sigma}_850{mu}m_=1.2mJy/beam over an area of 1.6deg^2^ (MAIN; Hubble Space Telescope/Advanced Camera for Surveys footprint), and {sigma}_850{mu}m_=1.7mJy/beam over an additional 1deg^2^ of supplementary (supp) coverage. We present a catalog of 1020 and 127 sources detected at a significance level of >4{sigma} and >4.3{sigma} in the main and supp regions, respectively, corresponding to a uniform 2% false-detection rate. We construct the single-dish 850{mu}m number counts at S_850_>2mJy and show that these S2COSMOS counts are in agreement with previous single-dish surveys, demonstrating that degree-scale fields are sufficient to overcome the effects of cosmic variance in the S_850_=2-10mJy population. To investigate the properties of the galaxies identified by S2COSMOS sources we measure the surface density of near-infrared-selected galaxies around their positions and identify an average excess of 2.0+/-0.2 galaxies within a 13" radius (~100kpc at z~2). The bulk of these galaxies represent near-infrared-selected submillimeter galaxies and/or spatially correlated sources and lie at a median photometric redshift of z=2.0+/-0.1. Finally, we perform a stacking analysis at submillimeter and far-infrared wavelengths of stellar-mass-selected galaxies (M_*_=10^10^-10^12^M_{sun}_) from z=0-4, obtaining high-significance detections at 850{mu}m in all subsets (signal-to-noise ratio, S/N=4-30), and investigate the relation between far-infrared luminosity, stellar mass, and the peak wavelength of the dust spectral energy distribution. The publication of this survey adds a new deep, uniform submillimeter layer to the wavelength coverage of this well-studied COSMOS field.
- ID:
- ivo://CDS.VizieR/J/MNRAS/468/250
- Title:
- SCUBA-2 Ambitious Sky Survey
- Short Name:
- J/MNRAS/468/250
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The SCUBA-2 Ambitious Sky Survey (SASSy) is composed of shallow 850-{mu}m imaging using the Submillimetre Common-User Bolometer Array 2 (SCUBA-2) on the James Clerk Maxwell Telescope. Here we describe the extraction of a catalogue of beam-sized sources from a roughly 120deg^2^ region of the Galactic plane mapped uniformly (to an rms level of about 40mJy), covering longitude 120{deg}<l<140{deg} and latitude |b|<2.9{deg}. We used a matched-filtering approach to increase the signal-to-noise ratio (S/N) in these noisy maps and tested the efficiency of our extraction procedure through estimates of the false discovery rate, as well as by adding artificial sources to the real images. The primary catalogue contains a total of 189 sources at 850{mu}m, down to an S/N threshold of approximately 4.6. Additionally, we list 136 sources detected down to S/N=4.3, but recognize that as we go lower in S/N, the reliability of the catalogue rapidly diminishes. We perform follow-up observations of some of our lower significance sources through small targeted SCUBA-2 images and list 265 sources detected in these maps down to S/N=5. This illustrates the real power of SASSy: inspecting the shallow maps for regions of 850-{mu}m emission and then using deeper targeted images to efficiently find fainter sources. We also perform a comparison of the SASSy sources with the Planck Catalogue of Compact Sources and the IRAS Point Source Catalogue, to determine which sources discovered in this field might be new, and hence potentially cold regions at an early stage of star formation.
