364 research outputs found
Wide-field 1-2 GHz research on galaxy evolution - synenergies with multi-wavelenght surveys
In these proceedings I discuss various extragalactic surveys which will be undertaken over the
next few years and which will be complementary to any HI and/or continuum surveys with the
SKA-precursor telescopes. I concentrate on the near-infrared public surveys which will be undertaken
with the Visible and Infrared Survey Telscope for Astronomy (VISTA), and in particular
the VISTA Deep Extragalactic Observations (VIDEO) survey which will provide the ideal data
set to combine with any deep SKA-precursor observations of the extragalactic sky. After highlighting
the links that the SKA precursors have with the various VISTA surveys, I briefly describe
two forthcoming Herschel surveys, Herschel-ATLAS survey and HerMES which have a large
scientific overlap with the SKA-precursor telescopes. Finally, I present a case study in combining
multi-wavelength data sets with radio-frequency surveys to find the highest redshift radio sources
with the aim of probing the epoch of reionization.
Radio Galaxy populations and the multi-tracer technique: pushing the limits on primordial non-Gaussianity
We explore the use of different radio galaxy populations as tracers of
different mass halos and therefore, with different bias properties, to
constrain primordial non-Gaussianity of the local type. We perform a Fisher
matrix analysis based on the predicted auto and cross angular power spectra of
these populations, using simulated redshift distributions as a function of
detection flux and the evolution of the bias for the different galaxy types
(Star forming galaxies, Starburst galaxies, Radio-Quiet Quasars, FRI and FRII
AGN galaxies). We show that such a multi-tracer analysis greatly improves the
information on non-Gaussianity by drastically reducing the cosmic variance
contribution to the overall error budget. By using this method applied to
future surveys, we predict a constraint of sigma_fnl=3.6 on the local
non-Gaussian parameter for a galaxy detection flux limit of 10 \muJy and
sigma_fnl=2.2 for 1 \muJy. We show that this significantly improves on the
constraints obtained when using the whole undifferentiated populations
(sigma_fnl=48 for 10 \muJy and sigma_fnl=12 for 1 \muJy). We conclude that
continuum radio surveys alone have the potential to constrain primordial
non-Gaussianity to an accuracy at least a factor of two better than the present
constraints obtained with Planck data on the CMB bispectrum, opening a window
to obtain sigma_fnl~1 with the Square Kilometer Array.Comment: 9 pages, 5 figures, submitted to MNRA
Herschel-atlas/Gama: a difference between star formation rates in strong-line and weak-line radio galaxies
We have constructed a sample of radio-loud objects with optical spectroscopy from the Galaxy
and Mass Assembly (GAMA) project over the Herschel Astrophysical Terahertz Large Area
Survey (Herschel-ATLAS) Phase 1 fields. Classifying the radio sources in terms of their
optical spectra, we find that strong-emission-line sources (‘high-excitation radio galaxies’)
have, on average, a factor of ∼4 higher 250-μm Herschel luminosity than weak-line (‘lowexcitation’)
radio galaxies and are also more luminous than magnitude-matched radio-quiet
galaxies at the same redshift. Using all five H-ATLAS bands, we show that this difference in
luminosity between the emission-line classes arises mostly from a difference in the average
dust temperature; strong-emission-line sources tend to have comparable dust masses to, but
higher dust temperatures than, radio galaxies with weak emission lines. We interpret this as
showing that radio galaxies with strong nuclear emission lines are much more likely to be
associated with star formation in their host galaxy, although there is certainly not a one-to-one
relationship between star formation and strong-line active galactic nuclei (AGN) activity. The
strong-line sources are estimated to have star formation rates at least a factor of 3–4 higher than those in the weak-line objects. Our conclusion is consistent with earlier work, generally carried
out using much smaller samples, and reinforces the general picture of high-excitation radio
galaxies as being located in lower-mass, less evolved host galaxies than their low-excitation
counterparts.Web of Scienc
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