Low Frequency Analysis of Radio Sources

Abstract

Radio sources emit high luminosity radiations in the radio regime. There are two types of radio sources: normal galaxies & radio galaxies. The radio emission from these galaxies arises from synchrotron emission. Generally the power-law is followed at high frequencies (from 300 MHz to 30 GHz) given by Flux density (S)~ ν^α, where α is the spectral index, with a downward curvature (peak) in the spectrum below 300 MHz. Study of the spectra near this curvature helps us characterize the physical conditions in the plasma, both inside and outside the radio source. In our study we planned to compare the low frequency spectra of normal galaxies and radio galaxies. Due to unavailability of 150 MHz data, it is difficult to do our low frequency spectra analysis. So, we attempted one another problem, where we did a low frequency analysis (<1000 MHz in rest frame) of redshift dependence on spectral index in powerful radio galaxies, within a specified luminosity range. In our analysis we found that spectral index is primarily correlated with redshift (i.e. steeper spectra at higher redshifts) than with luminosity. We measured the spectral index difference between higher redshift (z>2) and lower redshift (0.85<z<1.7) sources at 300 MHz rest frame frequency, which came as 0.11. This value is 0.1, which was obtained at 1 GHz rest frame by Athreya & Kapahi (1998). Thus concluding that at least some of the difference in spectral index is due to steeper electron injection spectrum at high redshifts.