Objects with Ultra Steep Spectra in the Central Section of the RATAN Zenith Field (RZF) Catalog
September 29, 2022
December 14, 2022
Objects with ultra-steep spectra (USS) are the main indicator in the search for distant radio galaxies. A study of an updated sample of 73 objects with ultra-steep spectra (spectral indices α ≤ -1.1, Sν ~ ν α) from the the central section ± 2′ of the RATAN-600 Zenith Field deep survey (RZF, 40°.5 ≤ Dec ≤ 42°.5) in the centimeter wavelength range (λ = 7.6 cm) is presented. The considered sample of USS sources turned out to be rather weak: the median flux densities S3.94 = 6.8 mJy and S1.4 = 34.5 mJy at 3.94 GHz and 1.4 GHz respectively. For 31 radio sources photometric redshifts (zph) were determined and optical identifications were carried out using the
SDSS (DR7, DR12). Twenty-three objects turned out to be galaxies, and 8 are star-forming objects. The radio luminosity of the considered sources at a frequency of 1.4 GHz varies in the range of 1.51 × 1024 ≤ L1.4 ≤ 5.17 × 1027 W/Hz, with median L1.4 ≈ 4.25 × 1026 W/Hz. Fifteen galaxies, judging by their radio luminosities L1.4 > 1026 W/Hz, belong to the FR II type, 6 objects are mixed objects of the FR I − FR II types. Two galaxies with L1.4 < 1025 W/Hz and zph < 0.5 turned out to be rare nearby galaxies of the FR I type. Nearly all these sources can be observed with the SAO 6-m telescope. The galaxies with L 1.4 ≥ 1026 W/Hz (FR II) have r magnitudes in the range 18 ≤ mr ≤ 23. According to their activity indices, all but one of the objects are active (Rr > 1) with the main contribution to their integrated radio emission coming from an active nucleus.
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