Modelling CN Zeeman effect observations of the envelopes of a low-mass protostellar disc and a massive protostar
[1];
[1];
[3];
- University of Virginia, Charlottesville, VA (United States)
- University of Virginia, Charlottesville, VA (United States); Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)
- Queen's University, Kingston, ON (Canada)
- Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States); University of California, Berkeley, CA (United States)
We use the POLARIS radiative transfer code to produce simulated circular polarization Zeeman emission maps of the cyanide (CN) J = 1–0 molecular line transition for two types of protostellar envelope magnetohydrodynamic simulations. Our first model is a low-mass disc envelope system (box length L = 200 au), and our second model is the envelope of a massive protostar (L = 104 au) with a protostellar wind and a CN-enhanced outflow shell. We compute the velocity-integrated Stokes I and V, as well as the implied V/I polarization percentage, for each detector pixel location in our simulated emission maps. Our results show that both types of protostellar environments are in principle accessible with current circular polarization instruments, with each containing swaths of envelope area that yield percentage polarizations that exceed the 1.8 percent nominal sensitivity limit for circular polarization experiments with the Atacama Large Millimeter/submillimeter Array. In both systems, high-polarization (≳1.8 percent) pixels tend to lie at an intermediate distance away from the central star and where the line-centre opacity of the CN emission is moderately optically thin (τLC ~ 0.1–1). Furthermore, our computed V/I values scale roughly with the density-weighted mean line-of-sight magnetic field strength, indicating that Zeeman observations can effectively diagnose the strength of envelope-scale magnetic fields. We also find that pixels with large V/I are preferentially co-located where the absolute value of the velocity-integrated V is also large, suggesting that locations with favourable percentage polarization are also favourable in terms of raw signal.
- Research Organization:
- Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)
- Sponsoring Organization:
- USDOE National Nuclear Security Administration (NNSA); National Aeronautics and Space Administration (NASA); Virginia Space Grant Consortium (VSGC); National Science Foundation (NSF); USDOE Office of Science (SC)
- Grant/Contract Number:
- AC52-07NA27344; 09-0117; 80NSSC20K0533; AST-2307199; RGPIN-2020-06266; NNX17AK39G; AC02-05CH11231; NP-ERCAP0023065
- OSTI ID:
- 2318778
- Report Number(s):
- LLNL-JRNL-855781; 1084677
- Journal Information:
- Monthly Notices of the Royal Astronomical Society, Vol. 527, Issue 3; ISSN 0035-8711
- Publisher:
- Oxford University PressCopyright Statement
- Country of Publication:
- United States
- Language:
- English
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