Properties of OH Megamaser Galaxies in the Radio Continuum. II. Data Analysis

Abstract

The properties of OH megamaser galaxies in the radio continuum are discussed. Many radio sources in OH megamaser galaxies exhibit relatively flat ( -0.5 ≥ α ) radio spectra between frequencies of 1.49 and 8.44 GHz along with high brightness temperatures ( 4 10 ≥ b T K). In these galaxies the line and radio continuum fluxes are not correlated. The continuum radio emission of OH megamasers is predominantly nonthermal and is associated either with an active nucleus or with compact star formation. The thermal component of the radio emission from these galaxies can be neglected. The observed flat radio spectra and high brightness temperatures imply the existence of an active galactic nucleus, although some megamasers may be associated with compact star formation.

Some Features of the X-Ray and Radio Emission from OH Megamaser Galaxies

“…Since the principle for selecting the galaxies in the present sample is their megamaser activity and many of them have relatively flat spectral indices and high brightness temperatures [1], we may assume that the megamaser activity and nuclear activity are interrelated. Furthermore, the observed correlations between the variables L 2-10keV , W, and L 1.49 (Table 2) suggest the presence of AGN in these galaxies.…”

“…) [1]. The observed flat radio spectra and high brightness temperatures suggest the presence of an active nucleus (AGN) in these galaxies, although some megamasers may be associated with active star formation (SB).…”

“…(5)). Thus, we believe that in OH megamaser galaxies the x-ray emission is mainly thermal in origin, while the radio emission is nonthermal [1], and their relationship exists via a central energy source of mass M, the inverse Compton effect, and bursts (jets) from the nucleus. Jets have been observed [18] from the OH megamasers Mkn 231 and UGC 5101 in association with the activity of the nuclei of these galaxies.…”

“…The correlation coefficients r and their significances p (p is the probability that the correlation between two variables is random), as well as the number N of galaxies, are given there. (Simultaneous data on the half width of the hydroxyl line and its intensity are given in the literature only for 87 megamaser galaxies, although more than 110 megamasers are known [1,10].) Table 2 shows that the line width and the x-ray emission are highly correlated.…”

Circumnuclear dense gas in OH-megamaser galaxies

“…Therefore, It is surprising that these entirely different methods of calculating the slope of L 2-10keV as a function of M c yield essentially the same result (1.27 and 1.28).Furthermore, Eq. (2) of Ref 23. can be used to calculate the expected widths of the lines for the four galaxies, for which the required parameters of their rotating disks have been measured by VLBI observations.…”