VLA Survey of Dense Gas in Extended Green Objects: Prevalence of 25 GHz Methanol Masers

Abstract

We present ∼1″-4″ resolution Very Large Array (VLA) observations of four CH 3 OH -J J 2 1 -E25 GHz transitions (J=3, 5, 8, 10) along with the 1.3 cm continuum toward 20 regions of active massive star formation containing Extended Green Objects (EGOs), 14 of which we have previously studied with the VLA in the ClassI 44 GHz and ClassII 6.7 GHz maser lines. Sixteen regions are detected in at least one 25 GHz line (J=5), with 13 of 16 exhibiting maser emission. In total, we report 34 new sites of CH 3 OH maser emission and 10 new sites of thermal CH 3 OH emission, significantly increasing the number of 25 GHz Class I CH 3 OH masers observed at high angular resolution. We identify probable or likely maser counterparts at 44 GHz for all 15 of the 25 GHz masers for which we have complementary data, providing further evidence that these masers trace similar physical conditions despite uncorrelated flux densities. The sites of thermal and maser emission of CH 3 OH are both predominantly associated with the 4.5 μm emission from the EGO, and the presence of thermal CH 3 OH emission is accompanied by 1.3 cm continuum emission in 9 out of 10 cases. Of the 19 regions that exhibit 1.3 cm continuum emission, it is associated with the EGO in 16 cases (out of a total of 20 sites), 13 of which are new detections at 1.3 cm. Twelve of the 1.3 cm continuum sources are associated with 6.7 GHz maser emission and likely trace deeply embedded massive protostars.

ALMA observations of the Extended Green Object G19.01−0.03 – I. A Keplerian disc in a massive protostellar system

“…Cragg et al 2005;Billington et al 2019;Jones et al 2020), and with collisionally-pumped 44 and 25 GHz Class I CH 3 OH masers (e.g. Cyganowski et al 2008Cyganowski et al , 2009Towner et al 2017). On the whole, EGOs can be inferred to contain one (or more) MYSOs that have active outflows and hence exist in a stage of ongoing accretion.…”

Analysis of bipolar outflow parameters, magnetic fields and maser activity relationship in EGO sources

“…• OH masers at 1665 and 1667 MHz were detected within ∼ 0.1 from the continuum source -ejector of bipolar outflow found in e.g. Cyganowski et al (2011), Towner et al (2017).…”

SOFIA FORCAST Photometry of 12 Extended Green Objects in the Milky Way

“…The causal link between accretion and ejection (Frank et al 2014) thus implies that these objects contain protostars undergoing active accretion, and the maser data indicate that these protostars are massive. The youth of the massive protostars within these EGOs was confirmed by deep (at that time) VLA continuum observations (Cyganowski et al 2011b), which yielded only a few 3.6 cm detections, and by later VLA 1.3 cm continuum observations (Towner et al 2017), which revealed primarily weak (<1 mJy beam −1 ), compact emission. The low detection rates and integrated flux densities of the centimeter continuum emission in these sources demonstrate that any free-free emission is weak, consistent with a stage prior to the development of ultracompact HII regions.…”