Large Area Survey

7-year plan

The LAS will image an area of 4000 sq. degs at high Galactic latitudes in the YJHK filters to a depth K=18.4, requiring 262 nights of UKIRT time over 7 years (the Y filter covers the wavelength range 0.97 to 1.07µm - see the filters description in the technical pages). The LAS will be completed in two stages. The first stage is a single pass in YJHK over the full 4000 sq. degs. The second stage is an additional pass in J over the same 4000 sq. degs, for proper motions, with a baseline of at least 2 years. The parameters of the survey are summarised in the table below. The LAS Survey Head is Richard Jameson.

7-year plan Filter Area
sq. degs
Mag. limit
(Vega)
t(exp.) t(total) Nights
Large Area Survey
LAS
Y400020.540s 367h262
J20.040x2s 734h
H18.840s 367h
K18.440s 367h

The principal goals of the LAS are 1: surveys for the coolest T+ dwarfs and the nearest lowest-mass dwarfs, 2: surveys for z>6 and KX quasars, 3: multiwavelength photometry of SDSS galaxies, 4: detection of cool stars with high proper motions (cool white dwarfs and Pop II brown dwarfs). The science goals are described in detail on the science case page (dated Nov. 2001).

The target 4000 sq. degs is a subsection of the Sloan survey, and is now fixed. The selected fields are shown in Fig. 1 below. We will cover 1. a part of the SDSS equatorial block, 2. a part of the SDSS northern block, 3. a section of the southern equatorial stripe. The details are as follows.

  1. LAS equatorial block 1907.6deg2: we will survey a region defined by the SDSS coordinates¹ -36.25o<eta<-16.25o, -60o<lambda<+53o. This includes most of SDSS stripes 9 to 16.
  2. LAS northern block 1907.6deg2: we will survey a region defined by the SDSS coordinates +6.25o<eta<+26.25o, -60o<lambda<+53o. This includes most of SDSS stripes 26 to 33.
  3. LAS southern stripe 212.5deg2: we will survey a section of SDSS stripe 82, extending over -25o<RA< +60o, -1.25o<Dec.<+1.25o. Stripe 82 has been repeatedly scanned by SDSS, and this section is the region of highest quality.
Total area: 4027.7deg2. Because the boundaries of the two large blocks are defined by the coordinate eta they will cut slightly inside the SDSS stripe boundaries, as explained below.

The footprint of the two large blocks is provided in a text file, listing the outline in coordinates RA, Dec, l, b, eta, lambda.


Figure 1. Planned final LAS sky coverage. The equatorial block corresponds to SDSS stripes 9 to 16, the northern block corresponds to SDSS stripes 26 to 33, and the southern stripe is part of SDSS stripe 82. The dashed line marks the Galactic plane, and the dotted line marks the ecliptic.


¹ The coordinate system of the SDSS stripes is explained in Stoughton et al. (2002, AJ, 123, 485). Briefly, each stripe is 2.5o wide, and follows a great circle through the pole located at RA 18h20m Dec 0o (J2000). The stripes therefore reach maximum or minimum declination at either RA 12h20m (northern Galactic hemisphere stripes) or at 0h20m (southern Galactic hemisphere stripes). For the northern Galactic hemisphere stripes the max./min. declination is 2.5(N-10)o, where N is the stripe number. For the southern Galactic hemisphere stripes the max./min. declination is -2.5(N-82)o. We have defined the boundaries of the two large LAS blocks by the coordinate eta given by eta(c)+/-1.25o, where eta(c) is eta of the stripe on the edge of the block (i.e. stripes 9, 16, 26, 33). A SDSS stripe edge is a constant 1.25o from the stripe centre, whereas our boundaries cut inside the stripe edge, and lie a distance 1.25ocos(lambda) from the stripe centre.

2-year plan

The UKIDSS plan for the first two years of operation is based around an allocation of 290 nights of observing, which is 31% of the 936 nights required to complete the surveys. The LAS will proceed more quickly in the first two years, receiving 105 nights or 40% of the total 262 nights required. The strategy is to cover 2000 sq. degs, or half the total area, in a single pass in YJHK, leaving the second pass in J (for proper motions) to later years. There is a proposal to survey this area with the ESO VST to depth 23.5 in i to enhance the selection of brown dwarfs and high-redshift quasars. The parameters of the 2-year plan are summarised in the table below.

2-year plan Filter Area
sq. degs
Mag. limit
(Vega)
Fraction
completed
NightsFraction
total nights
Large Area Survey
LAS
Y200020.50.50 1050.40
J19.70.25
H18.80.50
K18.40.50

The fields for the first two years are shown in Fig. 2 below. These are the LAS equatorial block and the LAS southern equatorial stripe. Note that the LAS equatorial block extends sufficiently far north to cover the Virgo galaxy cluster.


Figure 1. Planned final LAS sky coverage. The equatorial block corresponds to SDSS stripes 9 to 16,and the southern stripe is part of SDSS stripe 82. The dashed line marks the Galactic plane, and the dotted line marks the ecliptic.