Aims. Future astrophysics and cosmic microwave background space missions operating in the far-infrared to millimetre part of the spectrum will require very large arrays of ultra-sensitive detectors in combination with high multiplexing factors and efficient lownoise and low-power readout systems. We have developed a demonstrator system suitable for such applications. Methods. The system combines a 961 pixel imaging array based upon Microwave Kinetic Inductance Detectors (MKIDs) with a readout system capable of reading out all pixels simultaneously with only one readout cable pair and a single cryogenic amplifier. We evaluate, in a representative environment, the system performance in terms of sensitivity, dynamic range, optical efficiency, cosmic ray rejection, pixel-pixel crosstalk and overall yield at an observation centre frequency of 850 GHz and 20% fractional bandwidth. Results. The overall system has an excellent sensitivity, with an average detector sensitivity NEP det = 3 × 10 −19 W/ √ Hz measured using a thermal calibration source. At a loading power per pixel of 50 fW we demonstrate white, photon noise limited detector noise down to 300 mHz. The dynamic range would allow the detection of ∼1 Jy bright sources within the field of view without tuning the readout of the detectors. The expected dead time due to cosmic ray interactions, when operated in an L2 or a similar far-Earth orbit, is found to be <4%. Additionally, the achieved pixel yield is 83% and the crosstalk between the pixels is <−30 dB. Conclusions. This demonstrates that MKID technology can provide multiplexing ratios on the order of a 1000 with state-of-the-art single pixel performance, and that the technology is now mature enough to be considered for future space based observatories and experiments.

Low luminosity radio-loud active galactic nuclei (AGN) are generally found in massive red elliptical galaxies, where they are thought to be powered through gas accretion from their surrounding hot halos in a radiatively inefficient manner. These AGN are often referred to as "low-excitation" radio galaxies (LERGs). When radio-loud AGN are found in galaxies with a young stellar population and active star formation, they are usually high-power radiatively-efficient radio AGN ("high-excitation", HERG). Using a sample of low-redshift radio galaxies identified within the Sloan Digital Sky Survey (SDSS), we determine the fraction of galaxies that host a radio-loud AGN, f RL , as a function of host galaxy stellar mass, M * , star formation rate, color (defined by the 4000 Å break strength), radio luminosity and excitation state (HERG/LERG). We find the following: 1. LERGs are predominantly found in red galaxies. 2. The radio-loud AGN fraction of LERGs hosted by galaxies of any color follows a f LE RL ∝ M 2.5 * power law. 3. The fraction of red galaxies hosting a LERG decreases strongly for increasing radio luminosity. For massive blue galaxies this is not the case. 4. The fraction of green galaxies hosting a LERG is lower than that of either red or blue galaxies, at all radio luminosities. 5. The radio-loud AGN fraction of HERGs hosted by galaxies of any color follows a f LE RL ∝ M 1.5 * power law. 6. HERGs have a strong preference to be hosted by green or blue galaxies. 7. The fraction of galaxies hosting a HERG shows only a weak dependence on radio luminosity cut. 8. For both HERGs and LERGs, the hosting probability of blue galaxies shows a strong dependence on star formation rate. This is not observed in galaxies of a different color. Our interpretation of these results is that the presence of cold gas in a LERG enhances the probability that its SMBH becomes a luminous radio-loud AGN compared to the typical "model" LERG in a red elliptical galaxy. If enough cold gas can be transported to the SMBH a HERG can be created. However, the presence of cold gas does not automatically imply a HERG will be created. We speculate that feedback of the enhanced AGN activity in blue galaxies is responsible for the reduced probability of green galaxies to host a LERG.

We demonstrate photon noise limited performance in both phase and amplitude readout in microwave kinetic inductance detectors (MKIDs) consisting of NbTiN and Al, down to 100 fW of optical power. We simulate the far field beam pattern of the lens-antenna system used to couple radiation into the MKID and derive an aperture efficiency of 75%. This is close to the theoretical maximum of 80% for a single-moded detector. The beam patterns are verified by a detailed analysis of the optical coupling within our measurement setup. V C 2013 AIP Publishing LLC.[http://dx.doi.org/10.1063/1.4829657]In the next decades millimeter and sub-mm astronomy require 1 large format imaging arrays to complement the high spatial resolution of the Atacama Large Millimeter/ submillimeter Array.2 The desired sensors should have a background limited sensitivity and a high optical efficiency and enable arrays of up to megapixels in size. The most promising candidates to fulfill these requirements are microwave kinetic inductance detectors (MKIDs) 3 due to their inherent potential for frequency domain multiplexing. MKIDs are superconducting resonators, thousands of which can be coupled to a single feedline. Each resonator is sensitive to changes in the Cooper pair density induced by absorption of sub-mm radiation. By monitoring the change in either phase or amplitude of the complex feedline transmission at the MKID resonance one can measure the absorbed photon power. Using amplitude readout photon noise limited performance has been shown. 4 However, for practical applications two key properties need to be demonstrated: (1) Photon noise limited operation in phase readout. (2) A measurement of the aperture efficiency, 5 which describes the absolute optical coupling of a MKID imaging array to a plane wave.In this letter we present antenna coupled hybrid NbTiNAl MKIDs designed for groundbased sub-mm astronomy. We show that these devices achieve photon noise limited performance in both amplitude and phase readout. Through a detailed analysis of the optical coupling within our setup we validate the simulation of the lens-antenna far field beam pattern. From this we derive an aperture efficiency of 75%. This is close to the theoretical maximum of 80% for a single-moded detector.The device design, shown in Fig. 1, aims to simultaneously maximize the phase response and minimize the two-level system (TLS) noise contribution. 8 The device is a L % 5 mm long quarter wavelength coplanar waveguide (CPW) resonator consisting of two sections. The first section ($4 mm), at the open end of the resonator, is a wide CPW made entirely from 200 nm thick NbTiN. NbTiN has 10 dB lower TLS noise than conventional superconductors such as Al. 9 The TLS noise is further reduced by the width of the CPW, 9 23.7 lm and 5.4 lm for the CPW gap and central line, respectively.The second section (1 mm), at the shorted end of the resonator, is a narrow CPW with NbTiN groundplanes and a 48 nm thick Al central line. The Al is galvanically connected to the NbTiN central line (Fig. 1...