Hintze Centre for Astrophysical Surveys

Abstract:

We present a catalogue of ∼3,000 submillimetre sources detected (≥3.5σ) at 850μm over ∼5 deg2 surveyed as part of the James Clerk Maxwell Telescope (JCMT) SCUBA-2 Cosmology Legacy Survey (S2CLS). This is the largest survey of its kind at 850μm, increasing the sample size of 850-μm-selected submillimetre galaxies by an order of magnitude. The wide 850μm survey component of S2CLS covers the extragalactic fields: UKIDSS-UDS, COSMOS, Akari-NEP, Extended Groth Strip, Lockman Hole North, SSA22 and GOODS-North. The average 1σ depth of S2CLS is 1.2 mJy beam−1, approaching the SCUBA-2 850μm confusion limit, which we determine to be σc ≈ 0.8 mJy beam−1. We measure the 850μm number counts, reducing the Poisson errors on the differential counts to approximately 4% at S850 ≈ 3 mJy. With several independent fields, we investigate field-to-field variance, finding that the number counts on 0.5–1° scales are generally within 50% of the S2CLS mean for S850 > 3 mJy, with scatter consistent with the Poisson and estimated cosmic variance uncertainties, although there is a marginal (2σ) density enhancement in GOODS-North. The observed counts are in reasonable agreement with recent phenomenological and semi-analytic models, although determining the shape of the faint end slope (S850 < 3 mJy) remains a key test. The large solid angle of S2CLS allows us to measure the bright-end counts: at S850 > 10 mJy there are approximately ten sources per square degree, and we detect the distinctive up-turn in the number counts indicative of the detection of local sources of 850μm emission, and strongly lensed high-redshift galaxies. All calibrated maps and the catalogue are made publicly available.

Abstract:

We present a robust calibration of the 1.4 GHz radio continuum star formation rate (SFR) using a combination of the Galaxy And Mass Assembly (GAMA) survey and the Faint Images of the Radio Sky at Twenty-cm (FIRST) survey. We identify individually detected 1.4 GHz GAMA-FIRST sources and use a late-type, non-AGN, volume-limited sample from GAMA to produce stellar mass-selected samples. The latter are then combined to produce FIRST-stacked images. This extends the robust parametrisation of the 1.4 GHz-SFR relation to faint luminosities. For both the individually detected galaxies and our stacked samples, we compare 1.4 GHz luminosity to SFRs derived from GAMA to determine a new 1.4 GHz luminosity-to-SFR relation with well constrained slope and normalisation. For the first time, we produce the radio SFR-M⇤ relation over 2 decades in stellar mass, and find that our new calibration is robust, and produces a SFR-M⇤relation which is consistent with all other GAMA SFR methods. Finally, using our new 1.4 GHz luminosity-to-SFR calibration we make predictions for the number of star-forming GAMA sources which are likely to be detected in the upcoming ASKAP surveys, EMU and DINGO.