The massive protostar W43-MM1 as seen by Herschel-HIFI water spectra: high turbulence and accretion luminosity

TL;DR

This study uses Herschel-HIFI water spectra to analyze the gas dynamics, turbulence, and accretion processes in the massive protostar W43-MM1, revealing high turbulence, rapid infall, and high accretion rates consistent with turbulent core models.

Contribution

First detailed water spectral analysis of a massive protostar W43-MM1, linking turbulence, accretion, and water abundance to star formation models.

Findings

High turbulence increases with distance from the center.

Accretion rate is high enough to surpass radiation pressure.

Water abundance varies between core and envelope.

Abstract

We present Herschel/HIFI observations of fourteen water lines in W43-MM1, a massive protostellar object in the luminous star cluster-forming region W43. We analyze the gas dynamics from the line profiles using Herschel-HIFI observations (WISH-KP) of fourteen far-IR water lines (H2O, H217O, H218O), CS(11-10), and C18O(9-8) lines, and using our modeling of the continuum spectral energy distribution. As for lower mass protostellar objects, the molecular line profiles are a mix of emission and absorption, and can be decomposed into 'medium', and 'broad' velocity components. The broad component is the outflow associated with protostars of all masses. Our modeling shows that the remainder of the water profiles can be well fitted by an infalling and passively heated envelope, with highly supersonic turbulence varying from 2.2 km/s in the inner region to 3.5 km/s in the outer envelope. Also, W43-MM1 has a high accretion rate, between 4.0 x 10^{-4} and 4.0 x 10^{-2} \msun /yr, derived from the fast (0.4-2.9 km/s) infall observed. We estimate a lower mass limit of gaseous water of 0.11 \msun and total water luminosity of 1.5 \lsun (in the 14 lines presented here). The central hot core is detected with a water abundance of 1.4 x 10^{-4} while the water abundance for the outer envelope is 8 x10^{-8}. The latter value is higher than in other sources, most likely related to the high turbulence and the micro-shocks created by its dissipation. Examining water lines of various energies, we find that the turbulent velocity increases with the distance to the center. While not in clear disagreement with the competitive accretion scenario, this behavior is predicted by the turbulent core model. Moreover, the estimated accretion rate is high enough to overcome the expected radiation pressure.