Evidence of Enhanced Ionization in Protostellar Envelopes

TL;DR

This study measures ionization rates in protostellar envelopes, revealing significantly higher ionization than in the diffuse interstellar medium, which impacts early chemical evolution.

Contribution

It provides observational evidence of enhanced ionization in Class 0 protostellar envelopes, highlighting its role in early chemical processing.

Findings

Ionization rates in envelopes range from 1e-16 to 1e-13 s$^{-1}$.

Ionization rates are several orders of magnitude higher than in the diffuse ISM.

Supports that ionization-driven chemistry is more efficient in early protostellar stages.

Abstract

Ionization is a major driver of both physical and chemical evolution in protostellar systems. Recent observations reveal substantial chemical processing in protoplanetary disks by the time the surrounding envelope has cleared. Thus, physical conditions during the preceeding phase, when an infalling envelope of material is still present, are crucial for determining the extent of chemical processing at early stages. We used observations of H13CO+ and C18O from the Northern Extended Millimeter Array (NOEMA) and IRAM 30m telescope to constrain the ionization rate in the envelopes of three Class 0 protostars: NGC-1333 IRAS4A, L1448-C, and L1157. We find ionization rates in the range zeta = 1e-16 - 1e-13 s$^{-1}$ , several orders of magnitude above the ionization rate of zeta = 6e-17 s$^{-1}$ in the diffuse interstellar medium. This supports the idea that ionization driven chemistry is more efficient at earlier stages (< 1e5 years) of protostellar evolution.