The sub-stellar birth rate from UKIDSS

Day-Jones, A. C.; Marocco, F.; Pinfield, D. J.; Zhang, Z. H.; Burningham, B.; Deacon, N.; Ruiz, M. T.; Gallardo, J.; Jones, H. R. A.; Lucas, P. W. L.; Jenkins, J. S.; Gomes, J.; Folkes, S. L.; Clarke, J. R. A.
Referencia bibliográfica

Monthly Notices of the Royal Astronomical Society, Volume 430, Issue 2, p.1171-1187

Fecha de publicación:
4
2013
Número de autores
14
Número de autores del IAC
0
Número de citas
60
Número de citas referidas
45
Descripción
We present a new sample of mid-L to mid-T dwarfs with effective temperatures of 1100-1700 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⊙ 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 α in the range -1 <α < 0 that is consistent (within the errors) with the studies of late T dwarfs.