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.
