Revealing the Physics and Evolution of Galaxies and Galaxy Clusters with SKA Continuum Surveys

Abstract

In this chapter we provide an overview of the science enabled by radio continuum surveys in the SKA era, focusing on galaxy/galaxy cluster physics and evolution studies, and other relevant continuum science in the > 2020 scientific framework. We outline a number of reference radio-continuum surveys for SKA1 that can address such topics, and comprehensively discuss the most critical science requirements that we have identified. We highlight what should be achieved by SKA1, to guarantee a major leap forwards with respect to the pre-SKA era, considering the science advances expected in the coming years with existing and upcoming telescopes (JVLA, LOFAR, eMERLIN, and the three SKA precursors: MWA, ASKAP and MeerKAT). In this exercise we take in due account also the other waveband facilities coming online at the same time (e.g. Euclid, LSST, etc.), which tackle overlapping scientific goals, but in a different manner. In this respect particular attention has been payed to ensure that the proposed reference surveys are able to exploit the existing synergies with such facilities, so as to generate strong involvement from all astronomical communities, and leave a lasting legacy value. It is clear that a certain degree of freedom is allowed to some of the observational parameters. We believe it is very important to best fine-tune such parameters taking into proper account existing commensalities with SKA1 surveys addressing other science areas (HI galaxy science, magnetism, cosmology).

The VLA-COSMOS 3 GHz Large Project: Multiwavelength counterparts and the composition of the faint radio population

“…14 we show the faint end of our source counts with two different definitions for nonoverlapping populations (left and right panels) and extrapolations down to radio fluxes of ∼10 nJy, encompassing the detection limits of SKA1 Ultra Deep, Deep, and Wide surveys (Prandoni & Seymour 2015). In a zero-order attempt to extrapolate the counts, not intended to be related to any physical model, we use a simple linear fit to the four faintest data points (S 1.4 GHz < 80 µJy) for each of the various radio-detected subpopulations.…”

“…This makes the VLA-COSMOS 3 GHz Large Project to-date the deepest radio continuum survey over a relatively large field. Combined with the rich COSMOS multiwavelength data this survey, thus, yields a unique data set to test the composition (i.e., fractions of various galaxy types) of the faintest radio source populations that can currently be probed; it also allows us to use these findings to make predictions for the populations to be detected by future surveys, such as those planned with the Square Kilometre Array (SKA), and its precursors (Prandoni & Seymour 2015).…”

“…Given the onset of upcoming revolutionary radio facilities, such as the Square Kilometre Array (SKA) 2 (Norris et al 2013;Prandoni & Seymour 2015) and the Next Generation Very Large Array (ngVLA) 3 (Hughes et al 2015), scheduled to be operational at the same time as the Large Synoptic Survey Telescope (LSST) 4 and Euclid 5 , it becomes even more important i) to study the composition of the radio source population as a function of radio flux density, probing the to-date faintest achievable flux limits over significant areas and accounting for the possibility of a composite nature of galaxies containing both AGN and star formation activity; and ii) to make predictions that are applicable to future radio surveys, facilitating the identification of the various galaxy populations within these surveys. The COSMOS project ) is optimal for such research as it is currently one of the most advanced panchromatic surveys covering a 2 square degree area and sampling galaxies and AGN out to high (z 6) redshift.…”

“…This project incorporates one of the deepest radio data sets ever obtained with the VLA at 3 GHz detecting 10 830 sources down to ≈11.5 µJy (≈5σ at an angular resolution of 0.75 ; Smolčić et al 2017a). Here we combine these radio data with the COSMOS X-ray to FIR multiwavelength data sets to search for counterparts of the radio sources and analyze the composition of the faint microJansky radio population, extrapolating this down to the flux limits that will be achieved with the SKA in Phase 1 (SKA1; Prandoni & Seymour 2015).…”

The VLA-COSMOS 3 GHz Large Project: Continuum data and source catalog release

“…These past surveys have shown that deep observations at high angular resolution ( 1 ) with exquisite panchromatic coverage are critical to comprehensively study the radio properties of the main galaxy populations, avoiding cosmic variance with large area coverage (e.g., Padovani et al 2009;Padovani 2011;Smolčić et al 2008Smolčić et al , 2009bSmolčić 2009;Smolčić & Riechers 2011;Seymour et al 2008;Bonzini et al 2012Bonzini et al , 2013. In this context, large area surveys down to unprecedented depths are planned with new and upgraded facilities (e.g., VLA, Westerbork, Australian Square Kilometre Array Pathfinder, MeerKAT, and Square Kilometre Array; e.g., Jarvis 2012; Norris et al 2011Norris et al , 2013Norris et al , 2015Prandoni & Seymour 2015). Figure 1 shows the 1σ sensitivity of each survey as a function of the area covered for past, current, and future radio continuum surveys.…”