2009/12/18 by Xi Chen, Zhi-Qiang Shen, Jingjing Li +4
Chemical Engineering · Physics and Astronomy · #Advanced Combustion Engine Technologies #Astronomy #Astrophysics #Astrophysics and Star Formation Studies #Galaxy #Green Bank Telescope #Infrared #Line (geometry) #Maser #Meteorology #Northern Hemisphere #Observatory #Outflow #Physics #Star formation #Stellar, planetary, and galactic studies #Telescope #astro-ph.SR
paper · pdf · doi:10.1088/0004-637x/710/1/150
published as Astrophys.J.710:150-169,2010 · 44 pages, 4 figures, accepted for publication in ApJ
arxiv created 2009/12/18 · openalex publication_date 2010/01/15 · arxiv updated 2014/11/20 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
We report the first systematic survey of molecular lines (including HCO + (1–0) and 12 CO, 13 CO, C 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 + for 69 of 72 EGOs with HCO + 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.