2016/06/21 by Leah K. Morabito, L. K. Morabito, Adam T. Deller +17 · 32 citations
Physics and Astronomy · #Astronomy #Astrophysics #Astrophysics and Cosmic Phenomena #Galaxies: Formation, Evolution, Phenomena #Galaxy #LOFAR #Physics #Radio Astronomy Observations and Technology #Radio frequency #Radio galaxy #Radio spectrum #Radio telescope #Redshift #Spectral index #Spectral line #Telecommunications #Very-long-baseline interferometry #astro-ph.GA
paper · pdf · doi:10.1093/mnras/stw1501
published in Monthly Notices of the Royal Astronomical Society 461(3), 2676-2687 (Oxford University Press) · 14 pages; 9 figures; 4 tables; Accepted for publication in MNRAS
arxiv created 2016/06/21 · arxiv updated 2016/06/23 · openalex publication_date 2016/06/29 · openalex created_date 2016/07/22 · openalex updated_date 2026/08/06
The correlation between radio spectral index and redshift has been exploited to discover high-redshift radio galaxies, but its underlying cause is unclear. It is crucial to characterize the particle acceleration and loss mechanisms in high-redshift radio galaxies to understand why their radio spectral indices are steeper than their local counterparts. Low-frequency information on scales of ∼1 arcsec are necessary to determine the internal spectral index variation. In this paper we present the first spatially resolved studies at frequencies below 100 MHz of the z = 2.4 radio galaxy 4C 43.15 which was selected based on its ultrasteep spectral index (α < −1; Sν ∼ να) between 365 MHz and 1.4 GHz. Using the International Low Frequency Array Low Band Antenna we achieve subarcsecond imaging resolution at 55 MHz with very long baseline interferometry techniques. Our study reveals low-frequency radio emission extended along the jet axis, which connects the two lobes. The integrated spectral index for frequencies <500 MHz is −0.83. The lobes have integrated spectral indices of −1.31 ± 0.03 and −1.75 ± 0.01 for frequencies ≥1.4 GHz, implying a break frequency between 500 MHz and 1.4 GHz. These spectral properties are similar to those of local radio galaxies. We conclude that the initially measured ultrasteep spectral index is due to a combination of the steepening spectrum at high frequencies with a break at intermediate frequencies.