High-Mass Protostellar Candidates. I. The Sample and Initial Results

By Sridharan T. K., H. Beuther, Peter Schilke, K. Menten, F. Wyrowski. 2001

362 citations recorded by the source corpus.

We describe a systematic program aimed at identifying and characterizing candidate high-mass protostellar objects (HMPOs). Our candidate sample consists of 69 objects selected by criteria based on those established by Ramesh & Sridharan using far-infrared, radio continuum, and molecular line data. IRAS and Midcourse Space Experiment data were used to study the larger scale environments of the candidate sources and determine their total luminosities and dust temperatures. To derive the physical and chemical properties of our target regions, we observed continuum and spectral line radiation at millimeter and radio wavelengths. We imaged the free-free and dust continuum emission at wavelengths of 3.6 cm and 1.2 mm, respectively, searched for H2O and CH3OH maser emission, and observed the CO J = 2 → 1 line and several NH3 lines toward all sources in our sample. Other molecular tracers were observed in a subsample. While dust continuum emission was detected in all sources, most of them show only weak or no emission at 3.6 cm. Where detected, the centimeter emission is frequently found to be offset from the millimeter emission, indicating that the free-free and dust emissions arise from different subsources possibly belonging to the same (proto)cluster. A comparison of the luminosities derived from the centimeter emission with bolometric luminosities calculated from the IRAS far-infrared fluxes shows that the centimeter emission very likely traces the most massive source, whereas the whole cluster contributes to the far-infrared luminosity. Estimates of the accretion luminosity indicate that a significant fraction of the bolometric luminosity is still due to accretion processes. The earliest stages of HMPO evolution we seek to identify are represented by dust cores without radio emission. Line wings due to outflow activity are nearly omnipresent in the CO observations, and the molecular line data indicate the presence of hot cores for several sources, where the abundances of various molecular species are elevated because of evaporation of icy grain mantles. Kinetic gas temperatures of 40 sources are derived from NH3 (1, 1) and (2, 2) data, and we compare the results with the dust temperatures obtained from the IRAS data. Comparing the amount of dust, and hence the gas, associated with the HMPOs and with ultracompact H II (UCH II) regions, we find that the two types of sources are clearly separated in mass-luminosity diagrams: for the same dust masses, the UCH II regions have higher bolometric luminosities than HMPOs. We suggest that this is an evolutionary trend, with the HMPOs being younger and reprocessing less (stellar) radiation in the IR than the more evolved UCH II regions. These results indicate that a substantial fraction of our sample harbors HMPOs in a pre-UCH II region phase, the earliest known stage in the high-mass star formation process.

Subfields: Astronomy and Astrophysics, Atmospheric Science

View Paper: https://www.semanticscholar.org/paper/5ae6563f8e8b313814e75934b461e626a625d19e

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In Astronomy and Astrophysics

1. N. Evans II
2. Ralf Klessen
3. Mark R. Krumholz
4. P. Caselli
5. E. Bergin
6. S. Glover
7. M. Tafalla
8. Simon Bruderer

In Atmospheric Science

1. P. Caselli
2. E. Bergin
3. M. Tafalla
4. N. Evans II
5. J. Jørgensen
6. Peter Schilke
7. Simon Bruderer
8. Y. Shirley

Citations in the corpus

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• A CATALOG OF EXTENDED GREEN OBJECTS IN THE GLIMPSE SURVEY: A NEW SAMPLE OF MASSIVE YOUNG STELLAR OBJECT OUTFLOW CANDIDATES (2008, methodology): “91-0.26 (W33a), for example), the mean angular separation between a catalogued EGO and the nearest IRAS point source is ∼85′′.”
• The simultaneous formation of massive stars and stellar clusters (2009, background): “…et al. 1998; Carey et al. 2000; Rathborne, Jackson & Simon 2006; Simon et al. 2006) and high-mass protostellar objects (HMPOs) (Beuther et al. 2002; Sridharan et al. 2002; Faúndez et al. 2004; Williams, Fuller & Sridharan 2004) have begun to probe the earliest stages of the massive clumps from…”
• Ammonia from cold high-mass clumps discovered in the inner Galactic disk by the ATLASGAL survey (2012, result): “%) were observed in previous ammonia surveys (Sridharan et al. 2002; Churchwell et al. 1990; Molinari et al. 1996; Pillai et al. 2006).”
• Parallaxes and proper motions of interstellar masers toward the Cygnus X star-forming complex. I. Membership of the Cygnus X region (2011, background): “All phases of star formation and stellar evolution are observed projected across the CygnusX region, including a population of dense, massive, and dusty cores with embedded protoclusters and high-mass protostellar objects (Sridharan et al. 2002; Beuther et al. 2002; Motte etal.”
• CH3OH and H2O masers in high-mass star-forming regions (2002, methodology): “Detailed analyzes of different sample properties (luminosities, density distributions, outflows) are presented in Sridharan et al. (2002) and Beuther et al. (2002a, b).”
• THE RED MSX SOURCE SURVEY: THE MASSIVE YOUNG STELLAR POPULATION OF OUR GALAXY (2013, result): “We can also compare with the earlier, IRAS-based, Chan, Henning & Schreyer (1996) and Sridharan et al. (2002) catalogs of high-mass protostellar candidates.”
• Water in Star-forming Regions with the Herschel Space Observatory (WISH). I. Overview of Key Program and First Results (2010, background): “The sources are nearby (less than a few kiloparsecs) and isolated, selected from surveys by Molinari et al. (1996), Sridharan et al. (2002), Wood & Churchwell (1989), and van der Tak et al. (2000b).”
• Hierarchical fragmentation and differential star formation in the Galactic ‘Snake’: infrared dark cloud G11.11−0.12 (2014, background): “Clumps with a similar mass but at a later evolutionarystage have a higher luminosity due to increased protostellar activity, resulting a higher luminosity-to-mass ratio (Sridharan et al. 2002; Molinari et al. 2008; Rathborne et al. 2010).”
• THE PROPERTIES OF MASSIVE, DENSE CLUMPS: MAPPING SURVEYS OF HCN AND CS (2010, background): “There have been many detailed studies of individual regions of massive star formation and surveys of likely regions in tracers of dense gas or dust (e.g., Plume et al. 1992, 1997; Zinchenko, Mattila, & Toriseva, 1995; Anglada et al. 1996; Sridharan et al. 2002; Beuther et al. 2002; Wu & Evans 2003).”
• EVOLUTION OF MASSIVE PROTOSTARS VIA DISK ACCRETION (2010, background): “However, a lot of HMPOs have high infrared luminosity exceeding 104 L⊙ without observable H II regions (e.g., Sridharan et al. 2002; Beltrán et al. 2006b; Beuther et al. 2007).”
• From Massive Protostars to a Giant H II Region: Submillimeter Imaging of the Galactic Ministarburst W43 (2002, positive): “As they are not coincident with any near- to mid-infrared sources, they likely represent even younger phases than the IRAS selected HMPOs (Brand et al. 2001; Sridharan et al. 2002).”
• The RMS survey - 6 cm continuum VLA observations towards candidate massive YSOs in the northern hemisphere (2009, methodology): “…2) we cross-matched our source list with previous high resolution surveys (i.e., Wood & Churchwell 1989; Kurtz et al. 1994; Walsh et al. 1998; Sridharan et al. 2002) eliminating sources for which data were already available; 3) conducted a nearest-neighbour search to identify small groups of…”