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

        Low CO luminosities in dwarf galaxies

        View/Open
        906105.pdf (PDF, 2Mb)
        Author
        Schruba, Andreas
        Leroy, Adam K.
        Walter, Fabian
        Bigiel, Frank
        Brinks, E.
        de Blok, W.J.G.
        Kramer, Carsten
        Rosolowsky, Erik
        Sandstrom, Karin
        Schuster, Karl
        Usero, Antonio
        Weiss, Axel
        Wiesemeyer, Helmut
        Attention
        2299/8807
        Abstract
        We present maps of (12)COJ = 2-1 emission covering the entire star-forming disks of 16 nearby dwarf galaxies observed by the IRAM HERACLES survey. The data have 13 '' angular resolution, similar to 250 pc at our average distance of D = 4 Mpc, and sample the galaxies by 10-1000 resolution elements. We apply stacking techniques to perform the first sensitive search for CO emission in dwarf galaxies outside the Local Group ranging from individual lines of sight, stacking over IR-bright regions of embedded star formation, and stacking over the entire galaxy. We detect five galaxies in CO with total CO luminosities of LCO2-1 = (3-28) x 10(6) K km s(-1) pc(2). The other 11 galaxies remain undetected in CO even in the stacked images and have LCO2-1 less than or similar to (0.4-8) x 10(6) K km s(-1) pc(2). We combine our sample of dwarf galaxies with a large sample of spiral galaxies from the literature to study scaling relations of L-CO with M-B and metallicity. We find that dwarf galaxies with metallicities of Z approximate to 1/2-1/10 Z(circle dot) have L-CO of 2-4 orders of magnitude smaller than massive spiral galaxies and that their L-CO per unit L-B is 1-2 orders of magnitude smaller. A comparison with tracers of star formation (FUV and 24 mu m) shows that L-CO per unit star formation rate (SFR) is 1-2 orders of magnitude smaller in dwarf galaxies. One possible interpretation is that dwarf galaxies form stars much more efficiently: we argue that the low L-CO/SFR ratio is due to the fact that the CO-to-H-2 conversion factor, alpha(CO), changes significantly in low-metallicity environments. Assuming that a constant H-2 depletion time of tau(dep) = 1.8 Gyr holds in dwarf galaxies (as found for a large sample of nearby spirals) implies alpha(CO) values for dwarf galaxies with Z approximate to 1/2-1/10 Z(circle dot) that are more than one order of magnitude higher than those found in solar metallicity spiral galaxies. Such a significant increase of alpha(CO) at low metallicity is consistent with previous studies, in particular those of Local Group dwarf galaxies that model dust emission to constrain H2 masses. Even though it is difficult to parameterize the dependence of aCO on metallicity given the currently available data, the results suggest that CO is increasingly difficult to detect at lower metallicities. This has direct consequences for the detectability of star-forming galaxies at high redshift, which presumably have on average sub-solar metallicity.
        Publication date
        2012-05-07
        Published in
        The Astronomical Journal
        Published version
        https://doi.org/10.1088/0004-6256/143/6/138
        Other links
        http://hdl.handle.net/2299/8807
        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