THE MASSIVE PROTOSTELLAR CLUSTER NGC 6334I AT 220 au RESOLUTION: DISCOVERY OF FURTHER MULTIPLICITY, DIVERSITY, AND A HOT MULTI-CORE

Abstract

We present VLA and ALMA imaging of the deeply-embedded protostellar cluster NGC6334I from 5 cm to 1.3 mm at angular resolutions as fine as 0.′′ 17 (220 AU). The dominant hot core MM1 is resolved into seven components at 1.3 mm, clustered within a radius of 1000 AU. Four of the components have brightness temperatures > 200 K, radii ∼ 300 AU, minimum luminosities ∼ 10 4 L ⊙ , and must be centrally heated. We term this new phenomenon a "hot multi-core". Two of these objects also exhibit compact free-free emission at longer wavelengths, consistent with a hypercompact HII region (MM1B) and a jet (MM1D). The spatial kinematics of the water maser emission centered on MM1D are consistent with it being the origin of the highvelocity bipolar molecular outflow seen in CO. The close proximity of MM1B and MM1D (440 AU) suggests a proto-binary or a transient bound system. Several components of MM1 exhibit steep millimeter SEDs indicative of either unusual dust spectral properties or time variability. In addition to resolving MM1 and the other hot core (MM2) into multiple components, we detect five new millimeter and two new centimeter sources. Water masers are detected for the first time toward MM4A, confirming its membership in the protocluster. With a 1.3 mm brightness temperature of 97 K coupled with a lack of thermal molecular line emission, MM4A appears to be a highly optically-thick 240 L ⊙ dust core, possibly tracing a transient stage of massive protostellar evolution. The nature of the strongest water maser source CM2 remains unclear due to its combination of non-thermal radio continuum and lack of dust emission.

ALMA Detection of Interstellar Methoxymethanol (CH3OCH2OH)

“…Figure 1 shows the detections of CH 3 OCH 2 OH in the 0.2 Band 7 data (black) toward MM1 convolved to the spectral resolution of the observations, and with a 2.4 km s −1 linewidth (red). The position chosen for analysis (J2000 17:20:53.373, −35:46:58.14) lies ∼400 au west of the brightest continuum peak, denoted MM1b by Brogan et al (2016). The spectra were converted from Jy/beam to K intensity scale in each spectral window using the beam sizes listed in Table 1.…”

“…The ring-like appearance of the molecular emission toward MM1 is due to the high dust continuum opacity (> 1) and brightness temperature of the 1 mm dust continuum emission toward the dust peaks (> 100 K Brogan et al 2016). Toward the continuum peaks, the high dust opacity attenuates the line emission from the backside of the region, and the high background continuum brightness temperature compared to the line excitation temperature of the transitions shown here (of order 100-200 K) leads to weaker line emission (lower excitation lines are seen in absorption against the continuum peaks).…”

“…Here, we present the first interstellar detection of CH 3 OCH 2 OH using ALMA data in Bands 6 and 7 toward NGC 6334I, a massive protocluster (Hunter et al 2006) currently forming numerous massive stars and harboring two distinct regions of hot core line emission (MM1 and MM2, Brogan et al 2016;Zernickel et al 2012) at a distance of 1.3 kpc (Reid et al 2014). The observations are detailed in §2, and the spectroscopy in §3.…”

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

“…The other 12 new 1.3 cm detections, with a median peak intensity of 0.42 mJy beam −1 , are sufficiently weak that these are the first (published) data with the sensitivity to detect them. Sub-mJy emission at 1.3 cm (at kiloparsec distances) can be due to either free-free emission from protostellar winds/jets or hypercompact H II regions, or alternatively the Rayleigh-Jeans tail of dust emission (see, for example, Brogan et al 2016). In Section 3.3, we discuss the morphology of the 1.3 cm continuum emission and its relationship to the target EGO for individual sources, and compare with other cm-λ data where possible.…”

The Highly Collimated Radio Jet of HH 80–81: Structure and Nonthermal Emission

“…In past decades, radio emission with negative spectral indices at centimeter wavelengths has been reported in several YSO jets, such as the triple radio source in Serpens (Rodríguez et al 1989, Rodríguez-Kamenetzky et al 2016, HH 80-81 (Martí et al 1993), IRAS 16547−4247 (Garay et al 1996;Rodríguez et al 2005), W3(H 2 O) (Wilner et al 1999), L778-VLA6 (Girart et al 2002), DG Tau (Ainsworth et al 2014), NGC6334I-CM2 (Brogan et al 2016), and OMC-2 FIR 3 (Osorio et al 2017) suggesting a non-thermal origin for the emission. In a recent radio survey of the southern hemisphere, Purser et al (2017) found at least 10 new candidates to present non-thermal emission.…”