- ID:
- ivo://CDS.VizieR/J/other/ApSS/361.191
- Title:
- High-mass star forming clumps from MALT90
- Short Name:
- J/other/ApSS/361
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A total of 197 relatively isolated high-mass star-forming clumps were selected from the Millimeter Astronomy Legacy Team 90GHz (MALT90) survey data and their global chemical evolution investigated using four molecular lines, N_2_H^+^(1-0), HCO^+^(1-0), HCN(1-0), and HNC(1-0). The results suggest that the global averaged integrated intensity ratios I(HCO^+^)/I(HNC), I(HCN)/I(HNC), I(N_2_H^+^)/I(HCO^+^), and I(N_2_H^+^)/ I(HCN) are promising tracers for evolution of high-mass star-forming clumps. The global averaged column densities and abundances of N_2_H^+^, HCO^+^, HCN, and HNC increase as clumps evolve. The global averaged abundance ratios X(HCN)/X(HNC) could be used to trace evolution of high-mass star forming clumps, X(HCO^+^)/X(HNC) is more suitable for distinguishing high-mass star-forming clumps in prestellar (stage A) from those in protostellar (stage B) and HII/PDR region (stage C). These results suggest that the global averaged integrated intensity ratios between HCN(1-0), HNC(1-0), HCO^+^(1-0) and N_2_H^+^(1-0) are more suitable for tracing the evolution of high-mass star forming clumps. We also studied the chemical properties of the target high-mass star-forming clumps in each spiral arm of the Galaxy, and got results very different from those above. This is probably due to the relatively small sample in each spiral arm. For high-mass star-forming clumps in Sagittarius arm and Norma-Outer arm, comparing two groups located on one arm with different Galactocentric distances, the clumps near the Galactic Center appear to be younger than those far from the Galactic center, which may be due to more dense gas concentrated near the Galactic Center, and hence more massive stars being formed there.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/ApJS/231/11
- Title:
- High-mass starless clump candidates from ATLASGAL
- Short Name:
- J/ApJS/231/11
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report a sample of 463 high-mass starless clump (HMSC) candidates within -60{deg}<l<60{deg} and -1{deg}<b<1{deg}. This sample has been singled out from 10861 ATLASGAL clumps. None of these sources are associated with any known star-forming activities collected in SIMBAD and young stellar objects identified using color-based criteria. We also make sure that the HMSC candidates have neither point sources at 24 and 70{mu}m nor strong extended emission at 24{mu}m. Most of the identified HMSCs are infrared dark, and some are even dark at 70{mu}m. Their distribution shows crowding in Galactic spiral arms and toward the Galactic center and some well-known star-forming complexes. Many HMSCs are associated with large-scale filaments. Some basic parameters were attained from column density and dust temperature maps constructed via fitting far-infrared and submillimeter continuum data to modified blackbodies. The HMSC candidates have sizes, masses, and densities similar to clumps associated with Class II methanol masers and H II regions, suggesting that they will evolve into star-forming clumps. More than 90% of the HMSC candidates have densities above some proposed thresholds for forming high-mass stars. With dust temperatures and luminosity-to-mass ratios significantly lower than that for star-forming sources, the HMSC candidates are externally heated and genuinely at very early stages of high-mass star formation. Twenty sources with equivalent radii r_eq_<0.15pc and mass surface densities {Sigma}>0.08g/cm^2^ could be possible high-mass starless cores. Further investigations toward these HMSCs would undoubtedly shed light on comprehensively understanding the birth of high-mass stars.
- ID:
- ivo://CDS.VizieR/J/AJ/125/277
- Title:
- High proper motions in central Orion nebula
- Short Name:
- J/AJ/125/277
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The brightest portion of the Orion Nebula has been reimaged with the Hubble Space Telescope in H{alpha}, [N II], and [O III]. Comparison with earlier Wide Field Planetary Camera 2 images going back as much as 8yr has allowed determination of tangential velocities (proper motions) down to about 10km/s for a variety of sources. Multiple outflow systems are found associated with individual proplyds in the ionized portion of the nebula (HH 518, HH 624, possibly HH 507). The Orion-S complex of radio and infrared sources is the source of multiple outflows. A new outflow system (HH 625) has been identified as coming from the blueshifted portion of the imbedded high velocity CO flow coming from the Orion-S region, this object having CO, H2, and low ionization optical components. The low velocity CO outflow originating from or near FIR 4 is the likely source of HH 530. A new imbedded source is inferred from this optical data to lie in Orion-S. This optical outflow source (OOS) clearly feeds the systems HH 269 and HH 529, which lie along a straight line. There is evidence that this is also the source for HH 528, HH 202, and HH 203/204, all of which are blueshifted (except possibly HH 528 whose radial velocity is unknown). There is no strong radio, infrared, or X-ray source within the positional ellipse of the OOS.
- ID:
- ivo://CDS.VizieR/J/A+A/632/L7
- Title:
- High-redshift molecular outflow
- Short Name:
- J/A+A/632/L7
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the discovery of a high-redshift, massive molecular outflow in the starburst galaxy SPT 0346-52 (z=5.656) via the detected absorption of high-excitation water transitions (H_2_O 4_2,3_-4_1,4_ and H_2_O 3_3,0_-3_2,1_) with the Atacama Large Millimeter/submillimeter Array (ALMA). The host galaxy is one of the most powerful starburst galaxies at high redshift (star formation rate; SFR~3600M_{sun}_/yr), with an extremely compact (~320pc) star formation region and a SFR surface density ({SIGMA}_SFR_~5500M_{sun}_/yr/kpc^2^) five times higher than "maximum" (i.e. Eddington-limited) starbursts, implying a highly transient phase. The estimated outflow rate is ~500M_{sun}_/yr, which is much lower than the SFR, implying that in this extreme starburst the outflow capabilities saturate and the outflow is no longer capable of regulating star formation, resulting in a runaway process in which star formation will use up all available gas in less than 30Myr. Finally, while previous kinematic investigations of this source revealed possible evidence for an ongoing major merger, the coincidence of the hyper-compact starburst and high-excitation water absorption indicates that this is a single starburst galaxy surrounded by a disc.
- ID:
- ivo://CDS.VizieR/J/A+A/469/207
- Title:
- High-resolution images in Cep-A HW2 region
- Short Name:
- J/A+A/469/207
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Due to its relatively small distance (725pc), the Cepheus A East star-forming region is an ideal laboratory to study massive star formation processes. Based on its morphology, it has been suggested that the flattened molecular gas distribution around the YSO HW2 may be a 350-AU-radius massive protostellar disk. The goal of our work is to ascertain the nature of this structure. We have employed the Plateau de Bure Interferometer to acquire (sub-)arcsecond-resolution imaging of high-density and shock tracers, such as methyl cyanide (CH3CN) and silicon monoxide (SiO), towards the HW2 position. On the 1" scale, the flattened distribution of molecular gas around HW2 appears to be due to the projected superposition, on the plane of the sky, of at least three protostellar objects, of which at least one is powering a molecular outflow at a small angle with respect to the line of sight. The presence of a protostellar disk around HW2 is not ruled out.
- ID:
- ivo://CDS.VizieR/J/AJ/154/156
- Title:
- High resolution survey of Galactic plane at 408 MHz
- Short Name:
- J/AJ/154/156
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The interstellar medium is a complex "ecosystem" with gas constituents in the atomic, molecular and ionized states, dust, magnetic fields, and relativistic particles. The Canadian Galactic Plane Survey has imaged these constituents at multiple radio and infrared frequencies with angular resolution of the order of arcminutes. This paper presents radio continuum data at 408 MHz over the area of 52{deg}=<l=<193{deg}, -6.5{deg}=<b=<8.5{deg}, with an extension to b=21{deg} in the range of 97{deg}=<l=<120{deg}, with angular resolution 2.8'x2.8' cosec{delta}. Observations were made with the Synthesis Telescope at the Dominion Radio Astrophysical Observatory as part of the Canadian Galactic Plane Survey. The calibration of the survey using existing radio source catalogs is described. The accuracy of 408 MHz flux densities from the data is 6%. Information on large structures has been incorporated into the data using the single-antenna survey of Haslam et al. (1982A&AS...47....1H). The paper presents the data, describes how it can be accessed electronically, and gives examples of applications of the data to ISM research.
- ID:
- ivo://CDS.VizieR/J/MNRAS/444/757
- Title:
- HII complexes optical and IR emissions
- Short Name:
- J/MNRAS/444/757
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an analysis of optical spectroscopy and infrared aperture photometry of more than 100 HII complexes in nine galaxies. Spectra obtained with the 6-m telescope of Special Astrophysical Observatory of the Russian Academy of Sciences are used along with archival data from Spitzer and several ground-based telescopes to infer a strength of polycyclic aromatic hydrocarbon (PAH) emission, age, properties of the UV radiation field, and metallicity of studied HII complexes. Physical properties (age, radiation field parameters, metallicity) are related to the F_8_/F_24_ ratio used as a proxy for the PAH abundance in order to reveal factors that may influence the PAH evolution in HII complexes. The well-known correlation between the F_8_/F_24_ ratio and metallicity is confirmed in the studied complexes. The infrared flux ratio also correlates with the [Oiii]{lambda}5007/H{beta} ratio which is often considered as an indicator of the radiation field hardness, but this correlation seems to be a mere reflection of a correlation between [Oiii]{lambda}5007/H{beta} and metallicity. In separate metallicity bins, the F_8_/F_24_ ratio is found to correlate with an age of an Hii complex, which is estimated from the equivalent width of H{beta} line. The correlation is positive for low-metallicity complexes and negative for high-metallicity complexes. Analysing various mechanisms of PAH formation and destruction in the context of found correlations, we suggest that PAH abundance is likely altered by the UV radiation within HII complexes, but this is not necessarily due to their destruction. If PAHs can also form in Hii complexes due to some processes like aromatization, photodestruction, shattering and sputtering of very small grains, the net F_8_/F_24_ ratio is determined by a balance between all these processes that can be different at different metallicities.
- ID:
- ivo://CDS.VizieR/J/ApJ/709/424
- Title:
- HII regions identified with WMAPS and GLIMPSE
- Short Name:
- J/ApJ/709/424
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We use the Wilkinson Microwave Anisotropy Probe (WMAP) maximum entropy method foreground emission map combined with previously determined distances to giant HII regions to measure the free-free flux at Earth and the free-free luminosity of the Galaxy. We find a total flux f_{nu}_=54211Jy and a flux from 88 sources of f_{nu}_=36043Jy. The bulk of the sources are at least marginally resolved, with mean radii ~60pc, electron density n_e_~9cm^-3^, and filling factor {Phi}HII~0.005 (over the Galactic gas disk). We use GLIMPSE and Midcourse Space Experiment (MSX) 8um images to show that the bulk of the free-free luminosity is associated with bubbles having radii r~5-100pc, with a mean of ~20pc. These bubbles are leaky, so that ionizing photons emitted inside the bubble escape and excite free-free emission beyond the bubble walls, producing WMAP sources that are larger than the 8um bubbles. We suggest that the WMAP sources are the counterparts of the extended low density HII regions described by Mezger (1978A&A....70..565M). The 18 most luminous WMAP sources emit half the total Galactic ionizing flux.
- ID:
- ivo://CDS.VizieR/J/AJ/104/92
- Title:
- HII Regions Properties in M101
- Short Name:
- J/AJ/104/92
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Spectrophotometrically calibrated CCD imagery of two overlapping 16 arc min fields in the SAB(rs)cdI galaxy M101 in the emission of H alpha, [O III] lambda 5007, H beta, and [S II] lambda 6723 are used to study various physical properties of the H II region population. Individual H II regions are identified and mapped using an automated algorithm, thus eliminating personal bias in the measurements. Characteristics of the population studied include the H II region luminosity function and radial variations in extinction, [O III]/H beta, O/H, [S II]/H alpha, ionization parameter, and numbers of ionizing photons. In addition, radial and azimuthal variations in the H II surface density are studied in comparison to that of H I and H_2 inferred from radio 21 cm and CO observations. It is demonstrated that the magnitude of trends and ``gradients'' found from such analyses depend on the surface brightness threshold set in defining the H II region boundaries; so results are presented for both low (log S(H alpha) = -15.7 ergs/s/cm^2/arcsec^2; 625 H II regions) and high (-15.0; 248 H II regions) thresholds. Radial gradients in both extinction, C(H beta), and O/H are seen in the H II region population -- with a distinct flattening in the O/H gradient seen in the outer disk beginning at about 10 kpc. The luminosity function of the H II region population found is similar to previous studies, though both the high and low ends are sensitive to the threshold levels set. Other parameters, such as the ionization parameters, luminosities, and size distribution, show no evidence for systematic variations with galactocentric distance. Current star formation processes active in the disk of M101 are analyzed two-dimensionally by comparison of the distribution of ionized and neutral hydrogen. The star formation efficiency shows considerable variation across the disk, suggesting significant spatial variation in the critical density for cloud collapse across the disk of M101 and thus departures from the simple Toomre model.
- ID:
- ivo://CDS.VizieR/J/MNRAS/387/954
- Title:
- H2 imaging of NGC 1333, L1455, L1448 and B1
- Short Name:
- J/MNRAS/387/954
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We discuss wide-field near-infrared (near-IR) imaging of the NGC 1333, L1448, L1455 and B1 star-forming regions in Perseus. The observations have been extracted from a much larger narrow-band imaging survey of the Taurus-Auriga-Perseus complex. These H_2_ 2.122um observations are complemented by broad-band K imaging, mid-IR imaging and photometry from the Spitzer Space Telescope, and published submillimetre CO J=3-2 maps of high-velocity molecular outflows. We detect and label 85 H_2_ features and associate these with 26 molecular outflows.
