Ian Heywood

Abstract:

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. © 2010 The Authors. Journal compilation © 2010 RAS.

Abstract:

We present new radio data of IRAS FSC10214, a gravitationally lensed starburst/AGN composite galaxy at z=2.3. Our Bayesian MCMC source plane reconstruction places what we argue to be the AGN core (VLA 8 GHz) and the scattered quasar light (HST rest-frame ultraviolet) at an angle perpendicular to the ultraviolet polarisation angle. The size of and projected distance to the dominant HST UV emission component is roughly consistent with the smooth polarisation angle variation observed with HST polarimetry, suggesting that the modelled offset between these two components is reasonably accurate. Both of these components lie inside a larger 1.6 GHz component (observed with MERLIN) thought to be dominated by a radio lobe based on its steep radio spectrum but very likely to include star formation as well given the substantial molecular mass (MH2 ~ 1012 µ−1 M) in this system. Our lens model finds the HST rest-frame UV component is preferentially magnified due to its closer proximity to the cusp of the caustic. A preferential magnification of the narrow line region dust clouds, where the ultraviolet scattering is assumed to occur, supports previous claims that differential magnification could mask the expected polycyclic aromatic hydrocarbon spectral features in the Spitzer mid-infrared spectrum which broadly trace the star forming regions. fu¨rther predictions will be tested with upcoming EVN and VLBA observations.

Abstract:

We study the particle energy distribution in the cocoon surrounding Cygnus A, using radio images between 151 MHz and 15 GHz and a 200 ks Chandra ACIS-I image. We show that the excess low frequency emission in the the lobe further from Earth cannot be explained by absorption or excess adiabatic expansion of the lobe or a combination of both. We show that this excess emission is consistent with emission from a relic counterlobe and a relic counterjet that are being re-energized by compression from the current lobe. We detect hints of a relic hotspot at the end of the relic X-ray jet in the more distant lobe. We do not detect relic emission in the lobe nearer to Earth as expected from light travel-time effects assuming intrinsic symmetry. We determine that the duration of the previous jet activity phase was slightly less than that of the current jet-active phase. Further, we explain some features observed at 5 and 15 GHz as due to the presence of a relic jet.

Abstract:

We predict the emission line luminosity functions (LFs) of the first 10 rotational transitions of 12C16O in galaxies at redshift z = 0 to z = 10. This prediction relies on a recently presented simulation of the molecular cold gas content in 3 × 107 evolving galaxies based on the Millennium Simulation. We combine this simulation with a model for the conversion between molecular mass and CO-line intensities, which incorporates the following mechanisms: (1) molecular gas is heated by the cosmic microwave background (CMB), starbursts (SBs), and active galactic nuclei (AGNs); (2) molecular clouds in dense or inclined galaxies can overlap; (3) compact gas can attain a smooth distribution in the densest part of disks; (4) CO luminosities scale with metallicity changes between galaxies; and (5) CO luminosities are always detected against the CMB. We analyze the relative importance of these effects and predict the cosmic evolution of the CO-LFs. The most notable conclusion is that the detection of regular galaxies (i.e., no AGN, no massive SB) at high z ≳ 7 in CO emission will be dramatically hindered by the weak contrast against the CMB, in contradiction to earlier claims that CMB heating will ease the detection of high-redshift CO. The full simulation of extragalactic CO lines and the predicted CO-LFs at any redshift can be accessed online (http://s-cubed.physics.ox.ac.uk/, go to "S3-SAX") and they should be useful for the modeling of CO-line surveys with future telescopes, such as the Atacama Large Millimeter/submillimeter Array or the Square Kilometre Array. © 2009 The American Astronomical Society. All rights reserved.

Abstract:

We present a sky simulation of the atomic H I-emission line and the first 10 12C16O rotational emission lines of molecular gas in galaxies beyond the Milky Way. The simulated sky field has a comoving diameter of 500 h -1 Mpc; hence, the actual field of view depends on the (user-defined) maximal redshift z max; e.g., for z max = 10, the field of view yields 4 × 4 deg2. For all galaxies, we estimate the line fluxes, line profiles, and angular sizes of the H I and CO-emission lines. The galaxy sample is complete for galaxies with cold hydrogen masses above 108 M. This sky simulation builds on a semi-analytic model of the cosmic evolution of galaxies in a Λ cold dark matter (ΛCDM) 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 -1 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 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 H I and CO. A key prediction is that H I 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. © 2009. The American Astronomical Society. All rights reserved.