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

Abstract

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.

LABOCA 870 μm dust continuum mapping of selected infrared-dark cloud regions in the Galactic plane

“…In any case, EGOs appear to be related to outflow activity. Finding EGOs among our sources is unsurprising, because they often appear to be associated with IRDCs and 6.7-GHz Class II CH 3 OH masers (Chen et al 2010).…”

A molecular line study of the filamentary infrared dark cloud G304.74+01.32

“…These are comparable to the values 0.14 km s −1 and 3 × 10 −5 M yr −1 found by Hennemann et al (2009) towards J18364 SMM 1 South, which is a massive clump within an IRDC. Chen et al (2010) measured higher infall velocities and rates of ∼0.7−4.6 km s −1 and ∼1−28×10 −3 M yr −1 , respectively, for their sample of MYSOs associated with extended green objects (EGOs) and IRDCs. Typically, the mass infall rates in MYSOs are ∼10 −4 −10 −2 M yr −1 (e.g., Klaassen & Wilson 2007;Zapata et al 2008;Beltrán et al 2011).…”

First detections of FS Canis Majoris stars in clusters

“…Very close to this cloud, two nearby observational signs of ongoing star formation are present: a SiO maser (object "Onsala 100" from Harju et al 1998) and a EGO (G044.01-0.03; Cyganowski et al 2008). Chen et al (2010) gave a kinematic distance of 5.3 kpc for the EGO assuming the "near" option; this assumption is probably erroneous and this object is spatially coincident with the molecular clouds in the Mc20 wide field. In any way, none of the small clouds we refer in this paragraph are within a 7 radius, therefore we can discard them as either the origin of Mc20-16 or a sign of continuous star formation in the Mc20 field.…”