A SEARCH FOR INFALL EVIDENCE IN EGOs. I. THE NORTHERN SAMPLE

Journal Article · Wed Feb 10 00:00:00 EST 2010 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/710/1/150· OSTI ID:21394524

Xi, Chen; Zhiqiang, Shen ^[1]; Jingjing, Li; Ye, Xu ^[2]; Jinhua, He ^[3]

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1. Key Laboratory for Research in Galaxies and Cosmology, Shanghai Astronomical Observatory, Chinese Academy of Sciences, Shanghai 200030 (China)
2. Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008 (China)
3. National Astronomical Observatories/Yunnan Observatory, Chinese Academy of Sciences, Kunming 650011 (China)

We report the first systematic survey of molecular lines (including HCO{sup +} (1-0) and {sup 12}CO, {sup 13}CO, C{sup 18}O (1-0) lines at the 3 mm band) toward a new sample of 88 massive young stellar object (MYSO) candidates associated with ongoing outflows (known as extended green objects or EGOs) identified from the Spitzer GLIMPSE survey in the northern hemisphere with the Purple Mountain Observatory 13.7 m radio telescope. By analyzing the asymmetries of the optically thick line HCO{sup +} for 69 of 72 EGOs with HCO{sup +} detection, we found 29 sources with 'blue asymmetric profiles' and 19 sources with 'red asymmetric profiles'. This results in a blue excess of 0.14, seen as a signature of collapsing cores in the observed EGO sample. We found that the sources not associated with infrared dark clouds (IRDCs) show a higher blue excess (0.41) than those associated with IRDCs (-0.08), and 'possible' outflow candidates show a higher blue excess (0.29) than 'likely' outflow candidates (0.05). A higher blue excess (0.19) and a lower blue excess (0.07) were also measured in ultracompact H II regions and 6.7 GHz class II methanol maser sources, respectively. These suggest that the relatively small blue excess (0.14) in our full sample is due to the fact that the observed EGOs are mostly dominated by outflows and at an earlier evolutionary phase associated with IRDCs and 6.7 GHz methanol masers. The physical properties of clouds surrounding EGOs derived from CO lines are similar to those of massive clumps wherein the massive star-forming cores associated with EGOs possibly embedded. The infall velocities and mass infall rates derived for 20 infall candidates are also consistent with the typical values found in MYSOs. Thus, our observations further support the speculation of Cyganowski et al. that EGOs trace a population with ongoing outflow activity and at the active rapid accretion stage of massive protostellar evolution from a statistical view, although there may be limitations due to a single-pointing survey with a large beam.

• OSTI ID: 21394524
• Journal Information: Astrophysical Journal, Vol. 710, Issue 1; Other Information: DOI: 10.1088/0004-637X/710/1/150; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
ASYMMETRY
CARBON MONOXIDE
GHZ RANGE 01-100
MASERS
METHANOL
NORTHERN HEMISPHERE
PHYSICAL PROPERTIES
RADIO TELESCOPES
STAR EVOLUTION
STARS
ALCOHOLS
AMPLIFIERS
ANTENNAS
CARBON COMPOUNDS
CARBON OXIDES
CHALCOGENIDES
EARTH PLANET
ELECTRICAL EQUIPMENT
ELECTRONIC EQUIPMENT
EQUIPMENT
EVOLUTION
FREQUENCY RANGE
GHZ RANGE
HYDROXY COMPOUNDS
MICROWAVE AMPLIFIERS
MICROWAVE EQUIPMENT
ORGANIC COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
PLANETS
RADIO EQUIPMENT
TELESCOPES