The Extraordinary Outburst in the Massive Protostellar System NGC 6334I-MM1: Flaring of the Water Masers in a North–South Bipolar Outflow Driven by MM1B

Abstract

We compare multi-epoch sub-arcsecond VLA imaging of the 22 GHz water masers toward the massive protocluster NGC 6334I observed before and after the recent outburst of MM1B in (sub)millimeter continuum. Since the outburst, the water maser emission toward MM1 has substantially weakened. Simultaneously, the strong water masers associated with the synchrotron continuum point source CM2 have flared by a mean factor of 6.5 (to 4.2 kJy) with highly-blueshifted features (up to 70 km s −1 from LSR) becoming more prominent. The strongest flaring water masers reside 3000 au north of MM1B and form a remarkable bow shock pattern whose vertex coincides with CM2 and tail points back to MM1B. Excited OH masers trace a secondary bow shock located ∼120 au downstream. ALMA images of CS (6-5) reveal a highly-collimated north-south structure encompassing the flaring masers to the north and the non-flaring masers to the south seen in projection toward the MM3-UCHII region. Proper motions of the southern water masers over 5.3 years indicate a bulk projected motion of 117 km s −1 southward from MM1B with a dynamical time of 170 yr. We conclude that CM2, the water masers, and many of the excited OH masers trace the interaction of the high velocity bipolar outflow from MM1B with ambient molecular gas. The previously-excavated outflow cavity has apparently allowed the radiative energy of the current outburst to propagate freely until terminating at the northern bow shock where it strengthened the masers. Additionally, water masers have been detected toward MM7 for the first time, and a highly collimated CS (6-5) outflow has been detected toward MM4.

NGC6334I - Tracing the Gas Motion During A Contemporaneous Maser Flare Event

“…We obtained ten dozens of the proper motion vectors for the maser features associated with maser groups A -E (see Figure 2. Overall gas motion traced by the maser kinematics is consistent with the north-south bipolar outflow reported by Brogan et al (2018).…”

“…Our 3-epoch observations covered the peak of the H 2 O maser outburst and interferometric observations with JVLA confirmed the bursting masers to be located in CM2 object corresponding to the cluster A of out map (Brogan et al 2018). We were able to capture the gas motion at the shocked interface that resulted in the enhancement of the flux densities of the masers.…”

“…These gas motion is driven by a young stellar object in MM1 (see Brogan et al 2018;Hunter et al 2017Hunter et al , 2018. There clear evidence of multiplicity of protostars in MM1 as suggested by the presence of multiple cores and multiple outflows from the region.…”

Submillimeter-wave spectroscopy and the radio-astronomical investigation of propynethial (HC≡CCHS)

“…We searched for both propynethial and its oxygen-substituted counterpart propynal in a number of astronomically observed datasets, most of which are publicly available and all of which have previously been published elsewhere. These include ALMA observations of the high-mass star-forming region NGC 6334I (Brogan et al 2018;McGuire et al 2018aMcGuire et al , 2017, observations of the Sgr B2N high-mass star-forming region using the Green Bank Telescope (GBT) from the Prebiotic Interstellar Molecule Survey (PRIMOS) project (Neill et al 2012), as well as the datasets from the Astrochemical Surveys at IRAM (ASAI) Large Program, which was conducted with the IRAM 30 m telescope. The ASAI spectra cover a range of source types, from cold, dark clouds to class 0/1 protostars and shocked outflows, with observational details available in Lefloch et al (2018).…”

Studies of stellar evolution using masers

“…In many cases maser emission helps to unveil information from the interiors of dense regions. In NGC 6334I, an outburst of (sub)millimeter continuum in the protocluster MM1 was detected, along with multi-frequency maser emission from different species as water and methanol [7], [16]. Only some continuum sources are related to masers.…”