The Square Kilometre Array (SKA)

Abstract:

Published by Oxford University Press on behalf of the Royal Astronomical Society. We have combined spectroscopic and photometric data from the Sloan Digital Sky Survey with 1.4 GHz radio observations, conducted as part of the Stripe 82 1-2 GHz Snapshot Survey using the Karl G. Jansky Very Large Array, which covers ~100 sq deg, to a flux limit of 88 μJy rms. Cross-matching the 11 768 radio source components with optical data via visual inspection results in a final sample of 4794 cross-matched objects, of which 1996 have spectroscopic redshifts and 2798 objects have photometric redshifts. Three previously undiscovered giant radio galaxies were found during the cross-matching process, which would have been missed using automated techniques. For the objects with spectroscopy, we separate radio-loud active galactic nuclei (AGN) and star-forming galaxies (SFGs) using three diagnostics and then further divide our radio-loud AGN into the high and low excitation radio galaxy (HERG and LERG) populations. A control-matched sample of HERGs and LERGs, matched on stellar mass, redshift, and radio luminosity, reveals that the host galaxies of LERGs are redder and more concentrated than HERGs. By combining with near-infrared data, we demonstrate that LERGs also follow a tight K - z relationship. These results imply the LERG populations are hosted by population ofmassive, passively evolving early-type galaxies. We go on to show that HERGs, LERGs, quasars, and SFGs in our sample all reside in different regions of aWide-field Infrared Survey Explorer colour-colour diagram. This cross-matched sample bridges the gap between previous 'wide but shallow' and 'deep but narrow' samples and will be useful for a number of future investigations.

Abstract:

A sample of 1161 radio galaxies with 0.01 <z< 0.7 and 1021 < L1.4 GHz/W ˜Hz−1 < 1027 is selected from the Stripe 82 1–2 GHz Karl G. Jansky Very Large Array Snapshot Survey, which covers 100 sq. deg. and has a 1σ noise level of 88 μJy beam−1. Optical spectra are used to classify these sources as high excitation and low excitation radio galaxies (HERGs and LERGs), resulting in 60 HERGs, 149 LERGs, and 600 ‘probable LERGs’. The host galaxies of the LERGs have older stellar populations than those of the HERGs, in agreement with previous results in the literature. We find that the HERGs tend to have higher Eddington-scaled accretion rates than the LERGs but that there is some overlap between the two distributions. We show that the properties of the host galaxies vary continuously with accretion rate, with the most slowly accreting sources having the oldest stellar populations, consistent with the idea that these sources lack a supply of cold gas. We find that 84 per cent of our sample releases more than 10 per cent of their accretion power in their jets, showing that mechanical active galactic nucleus (AGN) feedback is significantly underestimated in many hydrodynamical simulations. There is a scatter of ∼2 dex in the fraction of the accreted AGN power deposited back into the interstellar medium in mechanical form, showing that the assumption in many simulations that there is a direct scaling between accretion rate and radio-mode feedback does not necessarily hold. We also find that mechanical feedback is significant for many of the HERGs in our sample as well as the LERGs.

Abstract:

The Compact High Energy Camera (CHEC) is a camera design for the Small-Sized Telescopes (SSTs; 4 m diameter mirror) of the Cherenkov Telescope Array (CTA). The SSTs are focused on very-high-energy γ-ray detection via atmospheric Cherenkov light detection over a very large area. This implies many individual units and hence cost-effective implementation, as well as shower detection at large impact distance, and hence large field of view (FoV), and efficient image capture in the presence of large time gradients in the shower image detected by the camera. CHEC relies on dual-mirror optics to reduce the plate-scale and make use of 6 × 6 mm2pixels, leading to a low-cost (∼150 k€), compact (0.5 m × 0.5 m), and light (∼45 kg) camera with 2048 pixels providing a camera FoV of ∼9 degrees. The CHEC electronics are based on custom TARGET (TeV array readout with GSa/s sampling and event trigger) application-specific integrated circuits (ASICs) and field programmable gate arrays (FPGAs) sampling incoming signals at a gigasample per second, with flexible camera-level triggering within a single backplane FPGA. CHEC is designed to observe in the γ-ray energy range of 1–300 TeV, and at impact distances up to ∼500 m. To accommodate this and provide full flexibility for later data analysis, full waveforms with 96 samples for all 2048 pixels can be read out at rates up to ∼900 Hz. The first prototype, CHEC-M, based on multi-anode photomultipliers (MAPMs) as photosensors, was commissioned and characterised in the laboratory and during two measurement campaigns on a telescope structure at the Paris Observatory in Meudon. In this paper, the results and conclusions from the laboratory and on-site testing of CHEC-M are presented. They have provided essential input on the system design and on operational and data analysis procedures for a camera of this type. A second full-camera prototype based on Silicon photomultipliers (SiPMs), addressing the drawbacks of CHEC-M identified during the first prototype phase, has already been built and is currently being commissioned and tested in the laboratory.