University of Hertfordshire Research Archive

        JavaScript is disabled for your browser. Some features of this site may not work without it.

        Browse

        All of UHRABy Issue DateAuthorsTitlesThis CollectionBy Issue DateAuthorsTitles

        Arkivum Files

        My Downloads
        View Item 
        • UHRA Home
        • University of Hertfordshire
        • Research publications
        • View Item
        • UHRA Home
        • University of Hertfordshire
        • Research publications
        • View Item

        Cosmic rays and the magnetic field in the nearby starburst galaxy NGC 253 III.Helical magnetic fields in the nuclear outflow

        View/Open
        906060.pdf (PDF, 870Kb)
        Author
        Heesen, V.
        Beck, R.
        Krause, M.
        Dettmar, R.-J.
        Attention
        2299/7758
        Abstract
        Context.Magnetic fields are good tracers of gas compression by shock waves in the interstellar medium. These can be caused by the interaction of star-formation driven outflows from individual star formation sites as described in the chimney model. Integration along the line-of-sight and cosmic-ray diffusion may hamper detection of compressed magnetic fields in many cases. Aims. We study the magnetic field structure in the central part of the nuclear starburst galaxy NGC253 with spatial resolutions between 40 and 150 pc to detect any filamentary emission associated with the nuclear outflow. As the nuclear region is much brighter than the rest of the disc we can distinguish this emission from that of the disc. ethods.We used radio polarimetric observations with the VLA. New observations at λ3 cm with 7.' 5 resolution were combined with archive data at λ λ 20 and 6 cm. We created a map of the rotation measure distribution between λ λ 6 and 3 cm and compared it with a synthetic polarization map. Results. We find filamentary radio continuum emission in a geometrical distribution, which we interpret as the boundary of the NW nuclear outflow cone seen in projection. The scaleheight of the continuum emission is 150 ± 20 pc, regardless of the observing frequency. The equipartition magnetic field strength is 46±10 μG for the total field and 21±5 μG for the regular field in the filaments. We find that the ordered magnetic field is aligned along the filaments, in agreement with amplification due to compression. The perpendicular diffusion coefficient across the filaments is ? = 1.5 × 10 cm s • E(GeV) . In the SE part of the nuclear outflow cone the magnetic field is pointing away from the disc in form of a helix, with an azimuthal component increasing up to at least 1200 pc height, where it is about equal to the total component. The ordered magnetic field in the disc is anisotropic within a radius of 2.2 kpc. At larger radii, the large-scale field is regular and of even parity. Conclusions. The magnetic filaments indicate an interaction of the nuclear outflow with the interstellar medium. The magnetic field is able to collimate the outflow, which can explain the observed small opening angle of ≈26°. Owing to the conservation of angular momentum by the plasma in the nuclear outflow, the field lines are frozen into the plasma, and they wind up into a helix. Strong adiabatic losses of the cosmic-ray electrons in the accelerated outflow can partly explain why the radio luminosity of the nucleus lies below the radio-FIR correlation.
        Publication date
        2011-01-01
        Published in
        Astronomy and Astrophysics
        Published version
        https://doi.org/10.1051/0004-6361/201117618
        Other links
        http://hdl.handle.net/2299/7758
        Metadata
        Show full item record
        Keep in touch

        © 2019 University of Hertfordshire

        I want to...

        • Apply for a course
        • Download a Prospectus
        • Find a job at the University
        • Make a complaint
        • Contact the Press Office

        Go to...

        • Accommodation booking
        • Your student record
        • Bayfordbury
        • KASPAR
        • UH Arts

        The small print

        • Terms of use
        • Privacy and cookies
        • Criminal Finances Act 2017
        • Modern Slavery Act 2015
        • Sitemap

        Find/Contact us

        • T: +44 (0)1707 284000
        • E: ask@herts.ac.uk
        • Where to find us
        • Parking
        • hr
        • qaa
        • stonewall
        • AMBA
        • ECU Race Charter
        • disability confident
        • AthenaSwan