High-resolution ammonia mapping of the very young protostellar core Chamaeleon-MMS1

Abstract

Aims. The aim of this study is to investigate the structure and kinematics of the nearby candidate first hydrostatic core Cha-MMS1. Methods. Cha-MMS1 was mapped in the NH 3 (1, 1) line and the 1.2 cm continuum using the Australia Telescope Compact Array (ATCA). The angular resolution of the ATCA observations is 7 (∼1000 AU), and the velocity resolution is 50 m s −1 . The core was also mapped with the 64 m Parkes Telescope in the NH 3 (1, 1) and (2, 2) lines. Observations from Herschel Space Observatory and Spitzer Space Telescope were used to help interpretation. The ammonia spectra were analysed using Gaussian fits to the hyperfine structure. A two-layer model was applied in the central parts of the core where the ATCA spectra show signs of self-absorption. Results. A compact high column density core with a steep velocity gradient (∼20 km s −1 pc −1 ) is detected in ammonia. We derive a high gas density (∼10 6 cm −3 ) in this region, and a fractional ammonia abundance compatible with determinations towards other dense cores (∼10 −8 ). This suggests that the age of the high density core is comparable to the freeze-out timescale of ammonia in these conditions, on the order of 10 4 years. The direction of the velocity gradient agrees with previous single-dish observations, and the overall velocity distribution can be interpreted as rotation. The rotation axis goes through the position of a compact far-infrared source detected by Spitzer and Herschel. The specific angular momentum of the core, ∼10 −3 km s −1 pc, is typical for protostellar envelopes. A string of 1.2 cm continuum sources is tentatively detected near the rotation axis. The ammonia spectra suggest the presence of warm embedded gas in its vicinity. An hourglass-shaped structure is seen in ammonia at the cloud's average LSR velocity, also aligned with the rotation axis. Although this structure resembles a pair of outflow lobes the ammonia spectra show no indications of shocked gas. Conclusions. The observed ammonia structure mainly delineates the inner envelope around the central source. The velocity gradient is likely to originate in the angular momentum of the contracting core, although influence of the outflow from the neighbouring young star IRS4 is possibly visible on one side of the core. The tentative continuum detection and the indications of a warm background component near the rotation axis suggest that the core contains a deeply embedded outflow which may have been missed in previous single-dish CO surveys owing to beam dilution.

Kinematics of a Young Low-mass Star-forming Core: Understanding the Evolutionary State of the First-core Candidate L1451-mm

“…For instance, Tsitali et al (2013) studied the first core candidate Cham-MMS1 and found envelope infall velocities of ∼0.2 km s −1 , an average gradient of 3 km s −1 pc −1 at 1000 AU scales and no signs of a fast, large scale outflow. They concluded that the envelope kinematic properties of this source are consistent with either a first core or a very young Class 0 protostar (see also Väisälä et al 2014).…”

Synthetic observations of star formation and the interstellar medium

“…Their synthetic observations predicted that the flux of such objects was below the sensitivity of IRAS, even in the nearest star-forming regions, but that they should be detectable by the infrared space observatory (ISO) and Spitzer (at the time known as SIRTF). In reality, the complexity of core structure and fragmentation, coupled with the short lifetime and low flux from first hydrostatic cores made unambigous detection more difficult, though candidates have now been identified and studied in multiple wavelengths, such as B1-bN/B1-bS (Pezzuto et al, 2012), Per-Bolo 58 (Hatchell et al, 2005;Chen et al, 2010;Enoch et al, 2010) Chamaeleon-MMS1 (Belloche et al, 2006;Väisälä et al, 2014), CB17-MMS (Chen et al, 2012) and L1451-mm (Maureira et al, 2017). Tomida et al (2010b) computed radiation hydrodynamic models of low-mass cores with only a small natal envelope.…”

What can the SEDs of first hydrostatic core candidates reveal about their nature?

“…We attempt to fit model SEDs to the observed SEDs of B1-bN and B1-bS (Pezzuto et al 2012;Hirano & Liu 2014), Per-Bolo 58 (Hatchell et al 2005;Enoch et al 2006;Schnee et al 2010;Enoch et al 2010), Chamaeleon-MMS1 (Belloche et al 2006;Tsitali et al 2013;Väisälä et al 2014) and CB17-MMS (Chen et al 2012). Per-Bolo 58 and Chamaeleon-MMS1 are brighter in the infrared than the other FHSC candidates while their SEDs peak at longer wavelengths.…”

“…Chamaeleon-MMS1. Observational data from Väisälä et al (2014). After SED fits which did not use all six data points were discarded, 17 models fell within a factor of two of the χ 2 value of the best fitting SED.…”

“…The results of the SED fitting for Chamaeleon-MMS1 using the monochromatic fluxes presented in Väisälä et al (2014) and Tsitali et al (2013) are presented in Fig. 24.…”