Brown dwarfs in the UKIDSSExtragalactic Surveys

UKIDSS II workshop London, 17 December 2008

Nicolas Lodieu

Instituto de Astrofísica de Canarias (IAC)

Surveys: goals➔ The Deep Extragalactic Survey (DXS):

➔ The Ultra Deep Survey (UDS):

➢ Understanding galaxy formation at high redshift➢ Measure the abundance of galaxy clusters at z=1-1.5➢ Measure galaxy clustering at z>1 and the evolution of bias➢ Multi-wavelength census of the luminosity density in SF and AGN

➢ Determine the epoch of spheroid formation➢ Produce the first large-volume map of the z=3 universe➢ Measure the growth of structure and bias since z>3➢ and others...

=> finding the coolest brown dwarfs (late-T and Y dwarfs)

2 known examples: 1) ESO NTT deep field (Cuby et al. 1999)2) IfA deep field (Liu et al. 2002)

Cons: Small coverage

XMM-LSS: 0.77 deg2Lockman Hole: 0.77 deg2ELAIS N1: 1.54 deg2VIMOS 4: 3.08 deg2

}Total DR2:6.16 deg2 UDS = 1 WFCAM tilein XMM-LSS 0.77 square degree

Pros: depth (I)

XMM-LSS: J=22.0; K=20.4 magLockman Hole: J=21.0; K=20.3 magELAIS N1: J=21.4; K=20.3 magVIMOS 4: J=21.6; K=20.6 mag

DR2: J=21.0; K=20.3 magDR3: J=22.0; K=20.4 mag

UDS depths

Selection criteria✔ J ≥ 13 mag & K ≤ 21.1 mag (5σ limit of DXS DR2)✔ J-K ≤ -0.1 mag✔ ellipticity less than 0.333✔ mergedClass between -2 and -1✔ Xi and Eta parameters between -0.5 and +0.5✔ good quality detections: ppErrBits ≤ 256

==> query to DXS DR2 returned 54 sources

J KUDXS2216p0024

Optical photometry➔ Sloan Digital Sky Survey (SDSS)

➔ Surveys from the Canada-France-Hawaii Telescope (CFHT)

➔ Subaru Deep eXtragalactic Survey (SDXS)

==> Complementary optical surveys providing counterpart to DXS & UDS

➢ Extensive coverage in XMM-LSS➢ No data in others DXS fields

➢ CFHT Legacy Synoptic Surveys: Deep and Wide➢ Deep +wide surveys in XMM-LSS➢ Wide survey in VIMOS 4

➢ Coverage in Lockman Hole and ELAIS N1➢ No data in XMM-LSS and VIMOS 4➢ VIMOS 4 available in SDSS DR7

==> 2 candidates left after exploitation of optical surveys

Methane imaging: observationsGemini NIRI: CH4 short centered at 1.58 μm and CH4 long at 1.69 μm

CH4 short

CH4 long

➢ UDXS2216p0033: 24 min in CH4 short and 65 min in CH4 long ➢ UDXS2219p0024: 5 min in CH4 short and 45 min in CH4 long

Methane imaging: results

22:16:11.51

22:19:03.10

RA (J2000) dec (J2000)

+00:33:08.1

+00:24:18.2

J

20.193

19.000 19.183

20.908

K CH4 colour

-1.23±0.15-0.87±0.09

SpT

T7±1

T6±1

Field T dwarfs in the GCS

==> The GCS adds 1000 square degrees to the LAS area

✔ Y-J ≥ 0.7 mag✔ J-H ≤ -0.2 mag✔ ellipticity less than 0.333✔ mergedClass = -2 or -1✔ good quality: ppErrBits ≤ 256

Selection criteria:

==> Query returned 3 candidatesLodieu et al. (2009, MNRAS, accepted)

Conclusions and outlook

➔ Conclusions:

➔ Outlook

➢ 2 distant late-T dwarfs in the DXS DR2 (paper submitted)➢ Distances of the T dwarfs around 80-100 pc➢ No late-T dwarf found in the UDS DR2➢ 2 field dwarfs along the line of sight of clusters (paper accepted)

➢ Final depth of the DXS and UDS➢ Wait for UDS DR4 for deeper data in J+K➢ Proper motion code to be implemented in DXS (Nick Cross)➢ Combine LAS and GCS efforts to uncover the “Y” dwarfs➢ Extend this work to the Galactic Plane Survey