SASSy

SCUBA-2 "All Sky" Survey

Summary

One of the most successful and ground-breaking survey missions in the last 20 years has been the IRAS mid and far-infrared sky survey. Even almost 2 decades after the survey ended, IRAS data are still in active use in a wide range of astronomical disciplines. In contrast to the wide sky coverage of IRAS, the sub-millimetre wavelength regime lying longward of the IRAS 100 痠 band remains the most poorly observed to date, but is one of the most high-impact areas in observational astronomy. To address this we propose a novel large-area survey of the sub-mm sky using the SCUBA-2 instrument on the JCMT. Our aims are:

To determine the number and distribution of Infrared Dark Clouds (IRDCs) in the Galaxy
To determine the relation between IRDCs and Galactic structure
To search for and identify unknown populations of star formation in IRDCs, high-latitude clouds and isolated star-forming regions outside known clouds
To determine the fraction of clustered versus isolated star formation
To identify the origin of field T-Tauris by answering the distributed T-Tauri problem
To search for new populations of extreme luminosity galaxies and determine their redshifts with ASTRO-F FIR data
To determine the number counts of bright sub-mm galaxies
To investigate the lensing fraction of sub-mm galaxies
To provide high-resolution foreground maps at 850 痠 for Planck
To search for and identify cold local galaxies
To provide compact pointing and flux calibrators for ALMA, Planck, Herschel & JCMT.

We propose to map the entire sky visible to JCMT over a 2–5 year span, with staged breakpoints as the
survey progresses. The “All” sky referred to is a declination band in the range −30^◦≤ δ ≤ +70^◦, encompassing some 18,000 square degrees. Such an ambitious survey will require a large amount of time to complete and in order to achieve our goals with the minimum impact on other survey programmes we have designed SASSy so that we may take advantage of the substantially improved capability of SCUBA-2 to operate in poor weather. As such, we will run SASSy in Grade 4 weather conditions.

There is a separate SASSy web site available with further information as well as a pdf document.

The priority survey areas that will be covered by SASSy overlaid on an IRAS 100 痠 survey image. The red strip outlines the GP-wide region and the black strip the Pole-to-Pole or P2P region (see below). For comparison the black central square represents the 25 square degrees of sky that were mapped by SCUBA over its entire 8 year life span.

The 2-year programme

In the 2 year pilot phase of SASSy we will map two 10-degree wide strips, one centred on the Galactic Plane (GP-Wide) and one perpendicular to the plane and centred on the North Ecliptic Pole (Pole to Pole or P2P). Both strips are terminated by a declination limit of -30� to avoid regions of perpetually high airmass. The target 1-sigma depth of each strip is 30 mJy at 850 μm.

SASSy will observe in weather grade 4 and so will not obtain any 450 μm data. Following the 2 year pilot our intention is to map the remaining sky to the same target depth of 30 mJy, concentrating first on the ALMA accessible portion of the sky (-30� < δ < +40�), then on the northern cap > +40�. We will re-examine this proposed strategy in the light of the results from the 2-year programme.