Near-Infrared K-Band Imaging of a Sample of Ultra-Steep-Spectrum Radio Sources Selected at 74 MHz
NAVAL RESEARCH LAB WASHINGTON DC
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In this paper we present near-infrared K-band imaging of a sample of ultra-steep-spectrum USS radio sources selected at 74 MHz. The dual selection criteria of low frequency and USS mean that we should be sensitive to the highest-redshift z 5 radio galaxies. We have obtained K-band magnitudes for all of the objects in our sample of 26 and discuss the properties of each. There is a pronounced bias in this sample towards fainter magnitudes and thus higher redshifts when compared to complete unfiltered samples such as the 7CRS of Willott et al., implying that the steep-spectrum technique is still viable at 74 MHz. However, there are more bright K 17 sources in the 74-MHz sample than in a similar sample selected at 151 MHz, namely 6C. This is principally due to the additional selection criterion of a small angular size for the radio sources in 6C four of the six sources in the 74-MHz USS sample with K 17 have angular sizes 15 arcsec the angular size cut-off of 6C. We find that the distribution of K-band magnitudes from a sample selected at 74 MHz is statistically indistinguishable from the 6C sample, when similar angular size filtering is applied to the 74-MHz sample.
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