The Square Kilometre Array (SKA)

Abstract:

An analysis of large-area CO J = 3-2 maps from the James Clerk Maxwell Telescope for 12 nearby spiral galaxies reveals low velocity dispersions in the molecular component of the interstellar medium. The three lowest luminosity galaxies show a relatively flat velocity dispersion as a function of radius while the remaining nine galaxies show a central peak with a radial fall-off within 0.2-0.4r25. Correcting for the average contribution due to the internal velocity dispersions of a population of giant molecular clouds, the average cloud-cloud velocity dispersion across the galactic discs is 6.1 ± 1.0 kms-1 (standard deviation of 2.9 kms-1), in reasonable agreement with previous measurements for the Galaxy and M33. The cloud-cloud velocity dispersion derived from the CO data is on average two times smaller than the HI velocity dispersion measured in the same galaxies. The low cloud-cloud velocity dispersion implies that the molecular gas is the critical component determining the stability of the galactic disc against gravitational collapse, especially in those regions of the disc which are H2 dominated. The cloud-cloud velocity dispersion shows a significant positivecorrelation with both the far-infrared luminosity, which traces the star formation activity, and the K-band absolute magnitude, which traces the total stellar mass. For three galaxies in the Virgo cluster, smoothing the data to a resolution of 4.5 kpc (to match the typical resolution of high-redshift CO observations) increases the measured velocity dispersion by roughly a factor of 2, comparable to the dispersion measured recently in a normal galaxy at z = 1. This comparison suggests that the mass and star formation rate surface densities may be similar in galaxies from z = 0 to 1 and that the high star formation rates seen at z = 1 may be partly due to the presence of physically larger molecular gas discs. © 2010 The Authors. Journal compilation © 2010 RAS.

Abstract:

We present deep spectroscopic data for a 24-object subsample of our full 41-object z~ 0.5 radio galaxy sample in order to investigate the evolution of the Fundamental Plane of radio galaxies. We find that the low-luminosity, Fanaroff-Riley type I (FRI), radio galaxies in our sample are consistent with the local Fundamental Plane of radio galaxies defined by Bettoni et al. when corrected for simple passive evolution of their stellar populations. However, we find that the higher luminosity, Fanaroff-Riley type II (FRII), radio galaxies are inconsistent with the local Fundamental Plane if only passive evolution is considered, and find evidence for a rotation in the Fundamental Plane at z~ 0.5 when compared with the local relation. We show that neither passive evolution, nor a mass-dependent evolution in the mass-to-light ratio, nor an evolution in the size of the host galaxies can, by themselves, plausibly explain the observed tilt. However, we suggest that some combination of all three effects, with size evolution as the dominant factor, may be sufficient to explain the difference between the planes.We also find evidence for a correlation between host galaxy velocity dispersion and radio luminosity at the 97 per cent significance level within our subsample, although further observations are required in order to determine whether this is different for the FRI and FRII radio sources. Assuming that the MBH-σ relation still holds at z~ 0.5, this implies that radio luminosity scales with black hole mass, in agreement with previous studies. © 2010 The Authors. Journal compilation © 2010 RAS.

Abstract:

In previous work, we have described novel smoothwalled multiple flare-angle horns designed using a genetic algorithm. A key feature of these horns is that they can be manufactured very rapidly and cheaply in large numbers, by repeated direct drilling into a single plate of aluminium using a shaped machine tool. The rapid manufacturing technique will enable the construction of very low cost focal-plane arrays, offering an alternative to conventional electroformed corrugated horn arrays. In order to experimentally demonstrate the new technology, we constructed a 230 GHz focal-plane array comprising 37 smooth-walled horns fabricated by direct drilling. We present the measured beam patterns for a large sample of these horns across the array, demonstrating the suitability of our manufacturing techniques for large format arrays. We have measured the cross coupling between adjacent feeds and have shown that it is negligible. We also present high quality beam patterns measured for a much smaller 700 GHz horn, showing the promise of extending this technology to THz frequencies.

Abstract:

We present the results of a ∼3yr campaign to monitor the low-luminosity active galactic nucleus (LLAGN) NGC 7213 in the radio (4.8 and 8.4GHz) and X-ray bands (2-10keV). With a reported X-ray Eddington ratio of 7 × 10-4LEdd, NGC 7213 can be considered to be comparable to a hard-state black hole X-ray binary. We show that a weak correlation exists between the X-ray and radio light curves. We use the cross-correlation function to calculate a global time-lag between events in the X-ray and radio bands to be 24 ± 12 d lag (8.4 GHz radio lagging X-ray) and 40 ± 13d lag (4.8GHz radio lagging X-ray), respectively. The radio-radio light curves are extremely well correlated with a lag of 20.5 ± 12.9d (4.8GHz lagging 8.4 GHz). We explore the previously established scaling relationship between core radio and X-ray luminosities and black hole mass LR∝M0.6-0.8L0.6X, known as the 'Fundamental Plane of black hole activity', and show that NGC 7213 lies very close to the best-fitting 'global' correlation for the plane as one of the most-luminous LLAGNs. With a large number of quasi-simultaneous radio and X-ray observations, we explore for the first time the variations of a single AGN with respect to the Fundamental Plane. Although the average radio and X-ray luminosities for NGC 7213 are in good agreement with the Plane, we show that there is intrinsic scatter with respect to the Plane for the individual data points. © 2010 The Authors Monthly Notices of the Royal Astronomical Society © 2010 RAS.

Abstract:

A recent detection of the peculiar neutron star X-ray binary Circinus X-1 with electronic very long baseline interferometry (e-VLBI) prompted the suggestion that compact, non-variable radio emission persists through the entire 16.6-d orbit of the binary system. We present the results of a high angular resolution monitoring campaign conducted with the Australian Long Baseline Array in real-time e-VLBI mode. e-VLBI observations of Circinus X-1 were made on alternate days over a period of 20 d covering the full binary orbit. A compact radio source associated with Circinus X-1 was clearly detected at orbital phases following periastron passage, but no compact radio emission was detected at any other orbital phase, ruling out the presence of a persistent, compact emitting region at our sensitivity levels. The jet was not resolved at any epoch of our 1.4-GHz monitoring campaign, suggesting that the ultrarelativistic flow previously inferred to exist in this source is likely to be dark. We discuss these findings within the context of previous radio monitoring of Circinus X-1. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.