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.
Original language | English |
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Pages (from-to) | 1171-1187 |
Number of pages | 17 |
Journal | Monthly Notices of the Royal Astronomical Society |
Volume | 430 |
Issue number | 2 |
DOIs | |
Publication status | Published - Apr 2013 |
Keywords
- brown dwarfs
- stars: low-mass
- stars: luminosity function, mass function
- ALL-SKY SURVEY
- DWARF/T-DWARF TRANSITION
- SUBSTELLAR MASS FUNCTION
- PROPER MOTION SURVEY
- SURVEY-EXPLORER WISE
- STAR-FORMING REGION
- YOUNG MOVING GROUPS
- LARGE-AREA SURVEY
- BROWN DWARFS
- T-DWARFS