Physical properties and gas kinematics of massive star forming region G328.24$-$0.55

TL;DR

This paper analyzes ALMA data of the G328.24-0.55 star forming region, revealing multiple protostars with diverse physical and kinematic properties, including evidence of a massive protostar actively accreting and driving outflows.

Contribution

It provides detailed physical and kinematic characterization of multiple protostars in G328.24-0.55, highlighting the presence of a massive protostar with active accretion and outflow processes.

Findings

Identification of five protostellar objects with varying excitation temperatures.

Detection of a rotating gas envelope around MM1a.

Evidence of bipolar outflow from MM1a.

Abstract

This study presents the results of ALMA band 6 archival data of G328.24$-$0.55, with the aim to pin down the physical and kinematic properties of young stellar objects (YSOs) in G328.24$-$0.55 star forming region. The dust continuum image reveals 5 protostellar objects (MM1a, MM1b, MM1c, MM2 and MM3), with MM1a dominating the region. The dust continuum peaks do not coincide with the strongest radio continuum peak previously detected in the region in a MeerKAT observation, but coincide with the weaker MeerKAT peak. The dust continuum objects are associated with faint unresolved infrared emission. We detected 70, 49, 26, 7 and 8 molecular transitions toward MM1a, MM1b, MM1c, MM2 and MM3, respectively. This variation in the number of detected molecular transitions supports different excitation conditions in these objects. The excitation temperatures estimated toward MM1a, MM1b and MM1c are $\sim$ 183, 168 and 110\,K, respectively. MM2 and MM3 lack multiple transitions of molecular lines to determine their excitation temperatures. The masses of MM1a, MM1b, MM1c, MM2 and MM3 were calculated to be 23.2, 16.1, 12.0, 9.8 and 14.9$M_{\odot}$, respectively. The velocity gradient of CH$_{3}$OH ($10_{2,8}-9_{3,7}$) emission traces a rotating structure, probably an envelope of gas around MM1a. Bipolar outflow traced by CO emission is seen towards MM1a. The properties of MM1a clearly point to the existence of a massive protostellar object that is still undergoing accretion and outflow in its early formative stage.