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        The sub-stellar birth rate from UKIDSS

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        Author
        Day-Jones, A. C.
        Marocco, F.
        Pinfield, D.J.
        Zhang, Z. H.
        Burningham, B.
        Deacon, Niall
        Ruiz, M. T.
        Gallardo, J.
        Jones, H.R.A.
        Lucas, P.W.
        Jenkins, J. S.
        Gomes, J.
        Folkes, S. L.
        Clarke, J. R. A.
        Attention
        2299/13870
        Abstract
        We present a new sample of mid-L to mid-T dwarfs with effective temperatures of 11001700 K selected from the UKIDSS Large Area Survey (LAS) and confirmed with infrared spectra from X-shooter/Very Large Telescope. This effective temperature range is especially sensitive to the formation history of Galactic brown dwarfs and allows us to constrain the form of the sub-stellar birth rate, with sensitivity to differentiate between a flat (stellar like) birth rate and an exponentially declining form. We present the discovery of 63 new L and T dwarfs from the UKIDSS LAS DR7, including the identification of 12 likely unresolved binaries, which form the first complete sub-set from our programme, covering 495 square degrees of sky, complete to J = 18.1. We compare our results for this sub-sample with simulations of differing birth rates for objects of masses 0.10-0.03 M-circle dot and ages 1-10 Gyr. We find that the more extreme birth rates (e. g. a halo type form) can likely be excluded as the true form of the birth rate. In addition, we find that although there is substantial scatter we find a preference for a mass function, with a power-law index a in the range -1 <alpha <0 that is consistent (within the errors) with the studies of late T dwarfs.
        Publication date
        2013-04
        Published in
        Monthly Notices of the Royal Astronomical Society
        Published version
        https://doi.org/10.1093/mnras/sts685
        Other links
        http://hdl.handle.net/2299/13870
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