Abstract
Abstract Molecular emission was imaged with ALMA from numerous components near and within bright H2-emitting knots and absorbing dust globules in the Crab Nebula. These observations provide a critical test of how energetic photons and particles produced in a young supernova remnant interact with gas, cleanly differentiating between competing models. The four fields targeted show contrasting properties but within them, seventeen distinct molecular clouds are identified with CO emission; a few also show emission from HCO+, SiO, and/or SO. These observations are compared with Cloudy models of these knots. It has been suggested that the Crab filaments present an exotic environment in which H2 emission comes from a mostly neutral zone probably heated by cosmic rays produced in the supernova surrounding a cool core of molecular gas. Our model is consistent with the observed CO J = 3 − 2 line strength. These molecular line emitting knots in the Crab Nebula present a novel phase of the ISM representative of many important astrophysical environments.
Highlights
Massive stars explode via core collapse and ejection of surrounding layers
Physical properties of the H2-emitting knots, including the density, temperature, and mass? What is the physics that governs molecular emission? What excites the molecular emission and what is its chemistry? What are the dust properties in this very young SN remnant? Is there a component of cooler molecular gas? What is the connection between the dust blobs, the H2 knots, and other molecular species such as CO? We address these issues with new data obtained with ALMA reported here
Spurred by Richardson et al (2013) who present a range of models for knots observed in the Crab, the “fully molecular core” model of Knot 51, we have undertaken a small survey
Summary
Massive stars explode via core collapse and ejection of surrounding layers. ALMA has identified CO, 28SiO, and 29SiO (Kamenetzky et al 2013; Matsuura et al 2017) as well as copious amounts of dust (∼0.7 Me) in the core-collapse supernova 1987A inner ejecta; the mass of molecular material continues to increase as the remnant evolves. Dust (0.1–0.6 Me; Barlow et al 2010; De Looze et al 2017) and molecules (Wallström et al 2013) have been observed in the more evolved (330 yr old) remnant Cas A, the remnant of a Type IIb supernova of a massive supergiant. Dust has been measured in G54.1+0.3, which appears to have at least ∼0.3 Me in the more evolved (1500–3000 yr old) remnant of its 16–27 Me progenitor (Rho et al 2018; Temim et al 2017). We investigate the chemistry of a remnant of intermediate age, the Tau A remnant, the Crab, which appeared in the year 1054
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