Large Area Survey

7-year plan

The LAS will image an area of 3792 sq. degs at high Galactic latitudes in the YJHK filters to a depth K=18.2 (the Y filter covers the wavelength range 0.97 to 1.07µm - see the filters description in the technical pages). Additionally a second pass in J will be executed over 2000 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 Steve Warren.

Final plan Filter Area
sq. degs
Mag. limit
t(exp.) t(total) Nights
Large Area Survey
Y379220.240s 367h262
J20.040x2s 734h
H18.840s 367h
K18.240s 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 3792 sq. degs is a subsection of the Sloan survey. The footprint has changed substantially since the original proposal. Originally a large spring northern block was planned, and the lowest Dec parts were started, but the block was then abandoned. The area was shifted to the autumn for scheduling regions. The revised regions are described below. In estimating the final areas an allowance has been made for slight overfilling by the tiling algorithm. The 5 regions are as follows.

Total area: 3792deg2. Because the boundaries of L1 are defined by the coordinate eta they cut slightly inside the SDSS stripe boundaries, as explained below.

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.