The relationship between radio power at 22 and 43 GHz and black hole properties of AGN in elliptical galaxies

Abstract

We investigate the relationship between radio power and properties related to active galactic nuclei (AGNs). Radio power at 1.4 or 5 GHz, which has been used in many studies, can be affected by synchrotron self-absorption and free-free absorption in a dense region. On the other hand, these absorption effects get smaller at higher frequencies. Thus, we performed simultaneous observations at 22 and 43 GHz using the Korean VLBI Network (KVN) radio telescope based on a sample of 305 AGN candidates residing in elliptical galaxies from the overlap between the Sloan Digital Sky Survey (SDSS) Data Release 7 and Faint Images of the Radio Sky at Twenty-Centimeters (FIRST). About 37% and 22% of the galaxies are detected at 22 and 43 GHz, respectively. Assuming no flux variability between the FIRST and KVN observations, spectral indices were derived from FIRST and KVN data and we found that over 70% of the detected galaxies have flat or inverted spectra, implying the presence of optically thick compact regions near the centres of the galaxies. Core radio power does not show a clear dependence on black hole mass at either low (1.4 GHz) or high (22 and 43 GHz) frequencies. However, we found that the luminosity of the [OIII] λ5007 emission line and the Eddington ratio correlate with radio power more closely at high frequencies than at low frequencies. This suggests that radio observation at high frequencies can be an appropriate tool for unveiling the innermost region. In addition, the luminosity of the [OIII] λ5007 emission line and the Eddington ratio can be used as a tracer of AGN activity. Our study suggests a causal connection between high frequency radio power and optical properties of AGNs.

Discovery of millimetre-wave excess emission in radio-quiet active galactic nuclei

“…A similar effect of 95 GHz excess emission (diminishing steepness with frequency, and in some cases even an inverted spectrum) was observed by Doi et al (2005Doi et al ( , 2011 and by Park et al (2013) in low luminosity AGN as well as in early type galaxies. Indeed, Doi et al (2011) conclude that this is indicative of core AGN emission.…”

Study of central light concentration in nearby galaxies

“…The relation between SMBH masses and nuclear radio emission of ETGs is not yet understood clearly. Some authors report that the two parameters are correlated (Nagar et al 2005) whereas others dispute the correlation (Park et al 2013). The current relation between optical concentration and the central radio luminosity might be indicating a co-evolution of ETGs and LLAGNs.…”

The atlas3DProject – XXXI. Nuclear radio emission in nearby early-type galaxies

“…As suggested by Ho & Peng (2001), a statistically-significant relationship between radio and optical emission line luminosity (or emission line equivalent width) may provide clues regarding the interplay between AGN fueling and the subsequent production of radio continuum emission. Previously, a number of authors have concluded that relationships between radio luminosity and optical emission lines are significant (e.g., Meurs & Wilson 1984;Baum & Heckman 1989;Tadhunter et al 1998;Ho & Peng 2001;Nagar et al 2005;Balmaverde & Capetti 2006;Kauffmann et al 2008;Park et al 2013), while others have reported the absence of any statistically significant relationships between these quantities (e.g., Sadler et al 1989;Best et al 2005). These discrepant results are likely due to differences in SMBH accretion regime (efficient or inefficient; for a review see Heckman & Best 2014) and spatial resolution probed by each survey.…”

“…The relationship between radio luminosity and SMBH mass has been the subject of much debate in the literature, with some studies finding evidence for the presence of a correlation (Franceschini et al 1998;Jarvis & McLure 2002;Nagar et al 2005) and others concluding that the two parameters are unrelated (Ho 2002;Balmaverde & Capetti 2006;Park et al 2013). In the left panel of Figure 11 we have plotted the 5 GHz radio luminosity vs. SMBH mass.…”