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

        A search for hypercompact HII regions in the Galactic Plane

        View/Open
        1809.00404v1_cs.pdf (PDF, 705Kb)
        Author
        Yang, A. Y.
        Thompson, M. A.
        Tian, W. W.
        Bihr, S.
        Beuther, H.
        Hindson, L.
        Attention
        2299/20948
        Abstract
        We have carried out the largest and most unbiased search for hypercompact (HC) H II regions. Our method combines four interferometric radio continuum surveys (THOR, CORNISH, MAGPIS, and White2005) with far-infrared and sub-mm Galactic Plane surveys to identify embedded H II regions with positive spectral indices; 120 positive spectrum H II regions have been identified from a total sample of 534 positive spectral index radio sources. None of these H II regions, including the known HC H II regions recovered in our search, fulfills the canonical definition of an HC H II region at 5 GHz. We suggest that the current canonical definition of HC H II regions is not accurate and should be revised to include a hierarchical structure of ionized gas that results in an extended morphology at 5 GHz. Correlating our search with known ultracompact (UC) H II region surveys, we find that roughly half of detected UC H II regions have positive spectral indices, instead of more commonly assumed flat and optically thin spectra. This implies a mix of optically thin and thick emission and has important implications for previous analyses which have so far assumed optically thin emission for these objects. Positive spectrum H II regions are statistically more luminous and possess higher Lyman continuum fluxes than H II regions with flat or negative indices. Positive spectrum H II regions are thus more likely to be associated with more luminous and massive stars. No differences are found in clump mass, linear diameter, or luminosity-to-mass ratio between positive spectrum and non-positive spectrum H II regions.
        Publication date
        2019-01-11
        Published in
        Monthly Notices of the Royal Astronomical Society
        Published version
        https://doi.org/10.1093/mnras/sty2811
        Other links
        http://hdl.handle.net/2299/20948
        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