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


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

Taras Shevchenko National University of Kyiv, Kyiv, Ukraine   


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


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