Bulletin of Taras Shevchenko National University of Kyiv. Astronomy, no. 59, p. 9-12 (2019)

STUDY OF THE THERMAL EMISSION IN THE RADIO CONTINUUM AT 1.4 GHZ IN SELECTED COMPACT GALAXIES WITH ACTIVE STAR FORMATION 

S. Parnovsky, Dr.Sci., professor
I. Izotova, PhD

Taras Shevchenko National University of Kyiv, Kyiv, Ukraine   


Abstract

The fraction of thermal (free-free) emission in the radio continuum at the frequency of 1.4 GHz is derived in subsample of 92 compact star-forming galaxies (CSFGs). These galaxies with detected radio emission and selected with a more strong compactness criterion represent the subsample of a larger sample of 193 galaxies (Parnovsky, S., & Izotova, I.: 2018, BTSNU, 57(1), 41). We use the 1.4 GHz fluxes from the FIRST (Becker R.H.,White R.L., & Helfand D.J.: 1995, ApJ, 450, 559). The fluxes of the thermal component at 1.4 GHz are derived from the extinction- and aperture-corrected fluxes of the Hβ emission line in the SDSS spectra following to (Caplan, J., & Deharveng, L.: 1986, A&A, 155, 297) and are compared with the total fluxes in radio continuum. As well as for a complete sample of 193 galaxies, the distribution of the fraction of thermal emission A in the radio continuum at 1.4 GHz in subsample of 92 CSFGs is similar to the log-normal one with a median value of about 15%. We find that the fraction of thermal emission at 1.4 GHz is lower for the older starbursts. However, the results of the statistical analysis of the dependence of A on various parameters have been changed. For the complete sample, correlations of A with the equivalent width EW(Hβ) of the Hβ emission line and the g – r colour index are revealed. For the subsample of 92 galaxies, the statistical significance of the correlation A with the colour index becomes negligible, and it corresponds to a confidence level of 92% for dependence of A on the equivalent width EW(Hβ). The reasons for the differences in the properties of these samples are discussed.

Key words
Star-forming galaxies, continuum radio emission, thermal emission

References

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DOI: https://doi.org/10.17721/BTSNUA.2019.59.09-12