Deep multi-frequency radio imaging in the Lockman Hole using the GMRT and VLA

By E. Ibar, R. Ivison, P. Best, K. Coppin, Adrian Pope, I. Smail, J. Dunlop. 2009

137 citations recorded by the source corpus.

In the run up to routine observations with the upcoming generation of radio facilities, the nature of sub-mJy radio population has been hotly debated. In this talk, we describe multi-frequency radio data designed to probe the emission mechanism that dominates in these faint radio sources. Our analysis is based on observations of the Lockman Hole using the Giant Metre-wave Radio Telescope (GMRT) – the deepest 610-MHz imaging yet reported – together with 1.4-GHz imaging from the Very Large Array (VLA), well matched in resolution and sensitivity to the GMRT data (σ610MHz ∼ 15μJy/beam, σ1.4GHz ∼ 6μJy/beam, FWHM∼5 arcsec). The GMRT and VLA data are cross-matched to obtain the radio spectral indices for the faint radio emitters. Statistical analyses show no clear evolution for the median spectral index, α1.4GHz 610MHz (where Sν ∝ ν α ), which is found to be approximately −0.6 to −0.7 based on an almost unbiased 10-sigma criterion, down to a flux level of S1.4GHz ≥ 100μJy. The fraction of inverted spectrum sources, α1.4GHz 610MHz ≥ 0, is less than 10%. The results suggest that the most prevalent emission mechanism in the sub-mJy regime is optically-thin synchrotron, ruling out a dominant flat spectrum or an aged ultra-steep spectrum radio population. The spectral index distribution has a significant scatter, ∆α ∼ 0.4–0.5, suggesting a mixture of different populations at all flux levels. This is supported by spectroscopic classifications of radio sources with X-ray emission, which has allowed us to estimate that the fraction of radio-quiet (type 1 and 2) active galactic nuclei (AGN) at 30 μJy

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/f28a93da2bacdd634b8eb9dba0de721b9bb60971

How researchers see this paper

The researchers whose trusted networks rank it highest, strongest advocate first. Every researcher gets a different order.

In Astronomy and Astrophysics

1. D. Narayanan
2. D. M. Alexander
3. C. Casey
4. A. Cooray
5. R. Ivison
6. L. Hernquist
7. I. Smail
8. F. Walter

In Nuclear and High Energy Physics

1. I. Smail
2. D. M. Alexander
3. R. Ivison
4. Mark Dickinson
5. P. Padovani
6. D. Narayanan
7. C. Casey
8. A. Cooray

Citations in the corpus

• VERY LARGE ARRAY 1.4 GHz OBSERVATIONS OF THE GOODS-NORTH FIELD: DATA REDUCTION AND ANALYSIS (2010, methodology): “This is why we prefer to perform theoretical corrections, as explained in OM08, rather than a simple Monte-Carlo approach as was in Ibar et al. (2009).”
• Dusty Star Forming Galaxies at High Redshift (2014, background): “4 < 1 mJy Bondi et al., 2007; Garn and Alexander, 2008) between −0.6 and −0.7 (Ibar et al., 2009); Ivison et al. (2010a,b) adopt α = −0.75± 0.06 with little evidence of evolution from 0 < z < 3 (i.e. the redshift dependence they measure is α ∝ (1 + z)0.14±0.20).”
• EMU: Evolutionary Map of the Universe (2011, background): “Position-dependent bandwidth smearing (chromatic aberration) over the mosaicked image due to the finite bandwidth of frequency channels (Condon et al. 1998; Ibar et al. 2009).”
• An Extreme Protocluster of Luminous Dusty Starbursts in the Early Universe (2017, background): “For a DSFG, its radio spectrum is relatively flat (e.g., Ibar et al. 2010; Murphy et al. 2017).”