Ian Heywood

Radio Detections During Two State Transitions of the Intermediate-Mass Black Hole HLX-1

Big Black Holes Black holes come in two sizes: stellar-mass black holes, with masses just above that of the Sun, and supermassive black holes, with masses up to a billion times that of the Sun. The hyperluminous x-ray source HLX-1 in the spiral galaxy ESO 243-49 is the best candidate to host a black hole of intermediate mass. Webb et al. (p. 554, published online 5 July) now report the detection of transient radio emission from this source, which may represent a jet ejection event. The radio flares indicate a mass that is consistent with that of an intermediate mass black hole. Jets have been seen to emanate from both supermassive and stellar-mass black holes. Intermediate mass black holes thus seem to behave like other black holes. Observations of a candidate intermediate-mass black hole support the scale invariance of jets in black holes. Relativistic jets are streams of plasma moving at appreciable fractions of the speed of light. They have been observed from stellar-mass black holes (~3 to 20 solar masses, M☉) as well as supermassive black holes (~106 to 109 M☉) found in the centers of most galaxies. Jets should also be produced by intermediate-mass black holes (~102 to 105 M☉), although evidence for this third class of black hole has, until recently, been weak. We report the detection of transient radio emission at the location of the intermediate-mass black hole candidate ESO 243-49 HLX-1, which is consistent with a discrete jet ejection event. These observations also allow us to refine the mass estimate of the black hole to be between ~9 × 103 M☉ and ~9 × 104 M☉.

A VIRTUAL SKY WITH EXTRAGALACTIC H I AND CO LINES FOR THE SQUARE KILOMETRE ARRAY AND THE ATACAMA LARGE MILLIMETER/SUBMILLIMETER ARRAY*

We present a sky simulation of the atomic HI-emission line and the first 10 rotational CO emission lines of molecular gas in galaxies beyond the Milky Way. The simulated sky field has a comoving diameter of 500 Mpc/h; hence, the actual field-of-view depends on the (user-defined) maximal redshift zmax; e. g., for zmax=10, the field of view yields 4x4 deg^2. For all galaxies, we estimate the line fluxes, line profiles, and angular sizes of the Hi and CO-emission lines. The galaxy sample is complete for galaxies with cold hydrogen masses above 10^8 Msun. This sky simulation builds on a semi-analytic model of the cosmic evolution of galaxies in a Lambda-cold dark matter (Lambda CDM) cosmology. The evolving CDM distribution was adopted from the Millennium Simulation, an N-body CDM-simulation in a cubic box with a side length of 500 Mpc/h. This side length limits the coherence scale of our sky simulation: it is long enough to allow the extraction of the baryon acoustic oscillations in the galaxy power spectrum, yet the position and amplitude of the first acoustic peak will be imperfectly defined. This sky simulation is a tangible aid to the design and operation of future telescopes, such as the Square Kilometre Array, Large Millimeter Telescope, and Atacama Large Millimeter/submillimeter Array. The results presented in this paper have been restricted to a graphical representation of the simulated sky and fundamental dN/dz-analyses for peak flux density limited and total flux limited surveys of Hi and CO. A key prediction is that HI will be harder to detect at redshifts z>2 than predicted by a no-evolution model. The future verification or falsification of this prediction will allow us to qualify the semi-analytic models.We present a sky simulation of the atomic HI emission line and the first ten CO rotational emission lines of molecular gas in galaxies beyond the Milky Way. The simulated sky field has a comoving diameter of 500/h Mpc, hence the actual field-of-view depends on the (user-defined) maximal redshift zmax; e.g. for zmax=10, the field of view yields ~4x4 sqdeg. For all galaxies, we estimate the line fluxes, line profiles, and angular sizes of the HI and CO emission lines. The galaxy sample is complete for galaxies with cold hydrogen masses above 10^8 Msun. This sky simulation builds on a semi-analytic model of the cosmic evolution of galaxies in a Lambda-cold dark matter (LCDM) cosmology. The evolving CDM-distribution was adopted from the Millennium Simulation, an N-body CDM-simulation in a cubic box with a side length of 500/h Mpc. This side length limits the coherence scale of our sky simulation: it is long enough to allow the extraction of the baryon acoustic oscillations (BAOs) in the galaxy power spectrum, yet the position and amplitude of the first acoustic peak will be imperfectly defined. This sky simulation is a tangible aid to the design and operation of future telescopes, such the SKA, the LMT, and ALMA. The results presented in this paper have been restricted to a graphical representation of the simulated sky and fundamental dN/dz-analyzes for peak flux density limited and total flux limited surveys of HI and CO. A key prediction is that HI will be harder to detect at redshifts z>2 than predicted by a no-evolution model. The future verification or falsification of this prediction will allow us to qualify the semi-analytic models.

Sample variance, source clustering and their influence on the counts of faint radio sources

The shape of the curves defined by the counts of radio sources per unit area as a function of their flux density was one of the earliest cosmological probes. Radio source counts continue to be an area of astrophysical interest as they can be used to study the relative populations of galaxy types in the Universe (as well as investigate any cosmological evolution in their respective luminosity functions). They are also a vital consideration for determining how source confusion may limit the depth of a radio interferometer observation, and are essential for characterizing the extragalactic foregrounds in cosmic microwave background experiments. There is currently no consensus as to the relative populations of the faintest (sub-mJy) source types, where the counts show a turn-up. Most of the source count data in this regime are gathered from multiple observations that each use a deep, single pointing with an interferometric radio telescope. These independent count measurements exhibit large amounts of scatter (factors of the order of a few) that significantly exceeds their respective stated uncertainties. In this paper, we use a simulation of the extragalactic radio continuum emission to assess the level at which sample variance may be the cause of the scatter. We find that the scatter induced by sample variance in the simulated counts decreases towards lower flux density bins as the raw source counts increase. The field-to-field variations make significant contributions to the scatter in the measurements of counts derived from deep observations that consist of a single pointing, and could even be the sole cause at >100 µJy. We present a method for evaluating the flux density limit that a radio survey must reach in order to reduce the count uncertainty induced by sample variance to a specific value. We also derive a method for correcting Poisson errors on source counts from existing and future deep radio surveys in order to include the uncertainties due to the cosmological clustering of sources. A conclusive empirical constraint on the effect of sample variance at these low luminosities is unlikely to arise until the completion of future large-scale radio surveys with next-generation radio telescopes.

Herschel-ATLAS: far-infrared properties of radio-selected galaxies

We use the Herschel-Astrophysical Terahertz Large Area Survey (ATLAS) science demonstration data to investigate the star formation properties of radio-selected galaxies in the GAMA-9h field as a function of radio luminosity and redshift. Radio selection at the lowest radio luminosities, as expected, selects mostly starburst galaxies. At higher radio luminosities, where the population is dominated by active galactic nuclei (AGN), we find that some individual objects are associated with high far-infrared luminosities. However, the far-infrared properties of the radio-loud population are statistically indistinguishable from those of a comparison population of radio-quiet galaxies matched in redshift and K-band absolute magnitude. There is thus no evidence that the host galaxies of these largely low-luminosity (Fanaroff-Riley class I), and presumably low-excitation, AGN, as a population, have particularly unusual star formation histories. Models in which the AGN activity in higher luminosity, high-excitation radio galaxies is triggered by major mergers would predict a luminosity-dependent effect that is not seen in our data (which only span a limited range in radio luminosity) but which may well be detectable with the full Herschel-ATLAS data set.

Radio Galaxy Zoo: Host galaxies and radio morphologies derived from visual inspection

We present results from the first twelve months of operation of Radio Galaxy Zoo, which upon completion will enable visual inspection of over 170,000 radio sources to determine the host galaxy of the radio emission and the radio morphology. Radio Galaxy Zoo uses

The closest black holes

1.4\,

Multiwavelength study of Cygnus A – III. Evidence for relic lobe plasma

GHz radio images from both the Faint Images of the Radio Sky at Twenty Centimeters (FIRST) and the Australia Telescope Large Area Survey (ATLAS) in combination with mid-infrared images at

V723 Cas (Nova Cassiopeiae 1995): MERLIN observations from 1996 to 2001

3.4\,\mu

The Australian Square Kilometre Array Pathfinder: Performance of the Boolardy Engineering Test Array

m from the {\it Wide-field Infrared Survey Explorer} (WISE) and at

Evolution of the Milky Way in Semi-Analytic Models: Detecting Cold Gas at z=3 with ALMA and SKA

3.6\,\mu