A Cross‐Match of 2MASS and SDSS: Newly Found L and T Dwarfs and an Estimate of the Space Density of T Dwarfs

Metchev, Stanimir; Kirkpatrick, J. Davy; Berriman, G. Bruce; Looper, Dagny L.

doi:10.1086/524721

Cited by 140 publications

(178 citation statements)

References 73 publications

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“…Our results agree with others. For early-T-dwarfs, they agree with the lower value found by Metchev et al (2008). The most important aim in deriving the luminosity function for ultracool dwarfs is setting constraints on the mass function.…”

Section: The Luminosity Function Of Systemssupporting

confidence: 82%

“…However, first estimates of the substellar mass function have been obtained in the L-dwarf domain: Reid et al (1999) with 1 < α < 2, Burgasser (2002) Recently, Metchev et al (2008) derived a T dwarf space density that was mostly consistent with α = 0 and the comparison of the observed number of T4-T8.5 dwarfs by Pinfield et al (2008) favoured α < 0. The analysis of 47 T-dwarfs found in the Large Area Survey (LAS) of UKIDSS also suggests that the substellar mass function is declining at lower masses (Burningham et al 2010b).…”

Section: Discussionmentioning

confidence: 99%

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The ultracool-field dwarf luminosity-function and space density from the Canada-France Brown Dwarf Survey

Reylé

Delorme

Willott

et al. 2010

A&A

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Context. Thanks to recent and ongoing large scale surveys, hundreds of brown dwarfs have been discovered in the last decade. The Canada-France Brown Dwarf Survey is a wide-field survey for cool brown dwarfs conducted with the MegaCam camera on the Canada-France-Hawaii Telescope. Aims. Our objectives are to find ultracool brown dwarfs and to constrain the field brown-dwarf luminosity function and the mass function from a large and homogeneous sample of L and T dwarfs. Methods. We identify candidates in CFHT/MegaCam i and z images and follow them up with pointed near infrared (NIR) imaging on several telescopes. Halfway through our survey we found ∼50 T dwarfs and ∼170 L or ultra cool M dwarfs drawn from a larger sample of 1400 candidates with typical ultracool dwarfs i − z colours, found in 780 square degrees. Results. We have currently completed the NIR follow-up on a large part of the survey for all candidates from mid-L dwarfs down to the latest T dwarfs known with utracool dwarfs' colours. This allows us to draw on a complete and well defined sample of 102 ultracool dwarfs to investigate the luminosity function and space density of field dwarfs. Conclusions. We found the density of late L5 to T0 dwarfs to be 2.0 +0.8 −0.7 × 10 −3 objects pc −3 , the density of T0.5 to T5.5 dwarfs to be 1.4 +0.3 −0.2 × 10 −3 objects pc −3 , and the density of T6 to T8 dwarfs to be 5.3 +3.1 −2.2 × 10 −3 objects pc −3 . We found that these results agree better with a flat substellar mass function. Three latest dwarfs at the boundary between T and Y dwarfs give the high density 8.3 +9.0 −5.1 × 10 −3 objects pc −3 . Although the uncertainties are very large this suggests that many brown dwarfs should be found in this late spectral type range, as expected from the cooling of brown dwarfs, whatever their mass, down to very low temperature.

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Section: The Luminosity Function Of Systemssupporting

confidence: 82%

Section: Discussionmentioning

confidence: 99%

The ultracool-field dwarf luminosity-function and space density from the Canada-France Brown Dwarf Survey

Reylé

Delorme

Willott

et al. 2010

A&A

View full text Add to dashboard Cite

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“…This predicted value remains mostly indicative, because the initial mass function and scale heights of late L-and T-type dwarfs are still uncertain. Interestingly, Caballero et al (2008a) assume a rising mass function in the planetary mass regime and predict spatial densities of T0-8 dwarfs that are a factor of two higher than those derived from observations (Metchev et al 2008;Lodieu et al 2009a). …”

Section: Cluster Membershipmentioning

confidence: 86%

Candidate free-floating super-Jupiters in the young σ Orionis open cluster

Bihain

Rebolo

Osorio³

et al. 2009

A&A

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Context. Free-floating substellar candidates with estimated theoretical masses of as low as ∼5 Jupiter masses have been found in the ∼3 Myr old σ Orionis open cluster. As the overlap with the planetary mass domain increases, the question of how these objects form becomes important. The determination of their number density and whether a mass cut-off limit exists is crucial to understanding their formation. Aims. We propose to search for objects of yet lower masses in the cluster and determine the shape of the mass function at low mass. Methods. Using new-and (re-analysed) published IZJHK s [3.6]−[8.0]-band data of an area of 840 arcmin 2 , we performed a search for LT-type cluster member candidates in the magnitude range J = 19.5-21.5 mag, based on their expected magnitudes and colours. Results. Besides recovering the T type object S Ori 70 and two other known objects, we find three new cluster member candidates, S Ori 72-74, with J ≈ 21 mag and within 12 arcmin of the cluster centre. They have theoretical masses of 4 +3 −2 M Jup and are among the least massive free-floating objects detected by direct imaging outside the Solar System. The photometry in archival Spitzer [3.6]-[5.8]-band images infers that S Ori 72 is an L/T transition candidate and S Ori 73 a T-type candidate, following the expected cluster sequence in the mid-infrared. Finally, the L-type candidate S Ori 74 with lower quality photometry is located at 11.8 arcsec (∼4250 AU) of a stellar member of σ Orionis and could be a companion. After contaminant correction in the area complete to J = 21.1 mag, we estimate that there remain between zero and two cluster members in the mass interval 6-4 M Jup . Conclusions. We present S Ori 73, a new candidate T type and candidate σ Orionis member of a few Jupiter masses. Our result suggests a possible turnover in the substellar mass spectrum below ∼6 Jupiter masses, which could be investigated further by wider and deeper photometric surveys.

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“…The spectral energy distribution of 500 K brown dwarfs peaks in the in the J band in the near infrared (even colder objects should emit more energy in the mid-infrared), and they are therefore most easily detected in that wavelength range. Their NIR JHK colours are, however, not distinctive at a modest signal-to-noise ratio (see Metchev et al 2008, for instance), and brown dwarfs are more easily recognised by including at least one photometric band blueward of 1 μm. At those wavelengths the steep slope of their spectra stands out, and they have very distinctively red i − z and z − J colours.…”

Section: Far-red and Near Infrared Photometric Properties Of Brown Dwmentioning

confidence: 99%

Extending the Canada-France brown dwarfs survey to the near-infrared: first ultracool brown dwarfs from CFBDSIR

Delorme

Forveille

et al. 2010

A&A

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Aims. We present the first results of the ongoing Canada-France Brown Dwarfs Survey-InfraRed, hereafter CFBDSIR, a near infrared extension to the optical wide-field survey CFBDS. Our final objectives are to constrain ultracool atmosphere physics by finding a statistically significant sample of objects cooler than 650 K and to explore the ultracool brown dwarf mass function building on a well-defined sample of such objects. Methods. We identify candidates in CFHT/WIRCam J and CFHT/MegaCam z images using optimised psf-fitting, and follow them up with pointed, near-infrared imaging with SOFI at the NTT. We finally obtain low-resolution spectroscopy of the coolest candidates to characterise their atmospheric physics. Results. We have so far analysed and followed up all candidates on the first 66 square degrees of the 335 square degree survey. We identified 55 T-dwarfs candidates with z − J > 3.5 and have confirmed six of them as T-dwarfs, including 3 that are strong laterthan-T8 candidates, based on their far-red and NIR colours. We also present here the NIR spectra of one of these ultracool dwarfs, CFBDSIR1458+1013, which confirms it as one of the coolest brown dwarf known, possibly in the 550-600 K temperature range. Conclusions. From the completed survey we expect to discover 10 to 15 dwarfs later than T8, more than doubling the known number of such objects. This will enable detailed studies of their extreme atmospheric properties and provide a stronger statistical basis for studies of their luminosity function.

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A Cross‐Match of 2MASS and SDSS: Newly Found L and T Dwarfs and an Estimate of the Space Density of T Dwarfs

Cited by 140 publications

References 73 publications

The ultracool-field dwarf luminosity-function and space density from the Canada-France Brown Dwarf Survey

The ultracool-field dwarf luminosity-function and space density from the Canada-France Brown Dwarf Survey

Candidate free-floating super-Jupiters in the young σ Orionis open cluster

Extending the Canada-France brown dwarfs survey to the near-infrared: first ultracool brown dwarfs from CFBDSIR

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