Polarized CO emission from molecular clouds

J. S. Greaves; W. S. Holland; P. Friberg; W. R. F. Dent

doi:10.1086/311888

Home/Archive/arXiv

arXiv · astro-ph/9812428

Polarized CO emission from molecular clouds

J. S. Greaves·W. S. Holland·P. Friberg·W. R. F. Dent

View original source ↗Read source document ↗Export metadata ↓

Abstract

Linearly polarized, non-masing, rotational lines have been detected for the first time in the interstellar medium. This effect occurs in molecular clouds with a magnetic field, and traces the field direction, offering an alternative technique to dust emission polarimetry. The line polarization mechanism is similar to that in masers, but with lower degrees of polarization (~1%). We have detected the effect towards the Galactic Centre and its surrounding `2 pc ring', and in the molecular clouds S140 and DR21 (tentatively), in the lines CO J=2-1 and J=3-2, and 13CO J=2-1. The deduced magnetic field directions agree well with previous dust polarimetry results, confirming that the line polarization is a real effect. This new technique will be useful in sources that are too faint for dust polarimetry, and can also be used to investigate 3-dimensional morphology of magnetic fields, where the velocity structure of the clouds is known.

Explore related subjects

astro-ph

Keep this discovery

Explore connections, maps & timelines

BibTeX RIS

J. S. Greaves, W. S. Holland, P. Friberg, W. R. F. Dent. 1998-12-23. Polarized CO emission from molecular clouds. https://doi.org/10.1086/311888

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related papers

arXiv2020

Cosmic Variance and Its Effect on the Luminosity Function Determination in Deep High z Surveys

We study cosmic variance in deep high redshift surveys and its influence on the determination of the luminosity function for high redshift galaxies. For several survey geometries relevant for HST and JWST instruments, we characterize the distribution of the galaxy number counts. This is obtained by means of analytic estimates via the two point correlation function in extended Press-Schechter theory as well as by using synthetic catalogs extracted from N-body cosmological simulations of structure formation. We adopt a simple luminosity - dark halo mass relation to investigate the environment effects on the fitting of the luminosity function. We show that in addition to variations of the normalization of the luminosity function, a steepening of its slope is also expected in underdense fields, similarly to what is observed within voids in the local universe. Therefore, to avoid introducing artificial biases, caution must be taken when attempting to correct for field underdensity, such as in the case of HST UDF i-dropout sample, which exhibits a deficit of bright counts with respect to the average counts in GOODS. A public version of the cosmic variance calculator based on the two point correlation function integration is made available on the web.

astro-ph↗

arXiv2020

Receiver control for the Submillimeter Array

Efficient operation of a submillimeter interferometer requires remote (preferably automated) control of mechanically tuned local oscillators, phase-lock loops, mixers, optics, calibration vanes and cryostats. The present control system for these aspects of the Submillimeter Array (SMA) will be described. Distributed processing forms the underlying architecture and the software is split between hardware platforms in a leader/follower arrangement. In each antenna cabin, a serial network of up to ten independent 80C196 microcontroller boards attaches to the real-time PowerPC computer (running LynxOS). A multi-threaded, gcc-compiled leader program on the PowerPC accepts top-level requests via remote procedure calls (RPC), subsequently dispatches tuning commands to the relevant follower microcontrollers, and regularly reports the system status to optical-fiber-based reflective memory for common access by the telescope monitor and error reporting system. All serial communication occurs asynchronously via encoded, variable-length packets. The microcontrollers respond to the requested commands and queries by accessing non-volatile, rewriteable lookup-tables (when appropriate) and executing embedded software that operates additional electronic devices (DACs, ADCs, etc.). Since various receiver hardware components require linear or rotary motion, each microcontroller also implements a position servo via a one-millisecond interrupt service routine which drives a DC-motor/encoder combination that remains standard across each subsystem.

astro-ph↗

arXiv2019

Classical analysis of the rotational dynamic of spiral galaxies: Quo Vadis Dark Matter?

In this paper we study a stellar dynamic model for the stars' rotational-dynamics, with a distribution of its own mass, rotating around its center with a higher density, like spiral galaxies happen, by means of a classical calculus of the rotation velocities of a particle around its rotational axis, inside a smoothed distribution of matter. The stars are supposed to be particles and their distribution in the galaxy is modelled as a matter distribution inversely proportional to its distance from its center. Two kinds of matter distribution are supposed: one with constant density, and other with radial distribution. Two types of galaxy symmetry are also considered: spherical and oblate ellipsoidal. Using only classical mechanics arguments it is shown that the calculated velocity distribution inside the galaxy is similar to that obtained from astronomical observations, without the necessity of suppose the existence of dark matter or other phenomena.

astro-ph↗