A Well-Deep EAO Survey Observing Most Of The EBL

AWESOME is a new band-1 SCUBA-2 large program starting 2020 to observe a sample of carefully selected massive lensing clusters, which will allow us to integrate the images down to a noise level of 0.8-0.9 mJy/beam at 450 micron. The ultimate objective is to construct number counts down to 0.1 mJy level so below the 450 micron confusion limit by roughly an order of magnitude, by exploiting the power of gravitational lensing. With simulations we show that the proposed observations will allow us to determine the shape of the faint-end number counts, the point of turnover, and by integrating the counts the extragalactic background light to a precision of ~20%, a ~35% improvement over the widely adopted measurements from the COBE satellite.

Figure 1. Left panels show the current state-of-the-art deep surveys that allow construction of counts down to ~1 mJy level. The two best-fit models (Schechter and Power-Law) are shown in green and red, with their cumulative contribution to the CIB plot in the lower panel. The two horizontal lines are measurements of COBE. While the two models fit equally well to the data, it is clear that there is up to 50% of the CIB that is hidden below ~1 mJy, and there is yet any evidence of a turnover. The predicted outcome of number counts from AWESOME are shown in the right panels. Our proposed program is designed to robustly determine the counts shape at sub-mJy and obtain new determination of CIB at 450 micron with a precision that is ~35% better than that measured by COBE. Moreover, AWESOME will have the power to test the model predictions, shown in blue curves, which appear to be under predicting the faint-end counts by a factor of 2-10.


In addition, driven by the main objective the data offer two exciting opportunities. The first is that together with the excellent ancillary millimeter data from NIKA and Bolocam we will be able to measure the Sunyaev-Zeldovich Effects (SZE) on the targeted galaxy clusters, including the integrated tSZ, kSZ, as well as the spatially resolved kSZ which will allow us to measure the two- dimensional velocity fields on cluster scales. The data will allow us to make the first kSZ measurements at >5 sigma, superseding the “gold standard” which will make it an important benchmark. The second is that we expect to roughly double the number of faint 450 micron sources discovered by STUDIES. While a majority of these robust detections would closely follow the flux distribution of STUDIES, a significant fraction is expected to be fainter than the faintest STUDIES source thanks to lensing (Figure 2). Together with the deep infrared, millimeter, and radio data obtained from Spitzer, Herschel, and now the ALMA large program (ALCS), we will be able to characterise the physical properties of faint dusty galaxies that dominate the EBL. By including STUDIES sample we aim to improve the statistics of the properties of dusty galaxies with characteristic infrared luminosity by root two.

This new program builds on the existing deep 450 micron SCUBA-2 surveys such as S2CLS and STUDIES and pushes the frontier of the deep sub-THz surveys by exploiting the cosmic magnifier – gravitational lensing. Because we plan to target the cluster fields the additional science goals to conduct cluster science with SZE is unique to this survey, in addition to all the possible science cases that can be done in the blank fields. The results of this survey will serve as a critical reference for the design of the future surveys by large single-dish submillimeter telescopes such as AtLAST. This program is now partially approved as a pilot to target one of the selected lensing cluster, with the aim to demonstrate the feasibility of the above science goals.

Figure 2. Histogram of the 450 micron flux density from sources detected by STUDIES. Also plotted are the predicted flux distribution of AWESOME, considering two counts models shown in Figure 1. The flux distribution of AWESOME sources is expected to follow closely of that of STUDIES, with an extra extension to the fainter end thanks to lensing. With rich ancillary data including the key MIR, FIR, and radio bands, we will be able to improve the statistics regarding the properties of the high-z (U)LIRGs by roughly root two, including their contribution to the cosmic star formation rate density.

Coordinators: Chian-Chou Chen (TW) Scott Chapman (CA), Woong-Seob Jeong (KR), Kotaro Kohno (JP), Xinwen Shu (CN), Ian Smail (UK).

– JCMT Program code: M20AL020

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