Non-detection of Broad Hydrogen Radio Recombination Lines in Circinus Galaxy

Abstract

The line widths of broad line regions (BLRs) of AGNs are key parameters for understanding the central super massive black holes (SMBHs). However, due to obscuration from dusty torus, optical recombination lines from BLRs in type II AGNs can not be directly detected. Radio recombination lines (RRLs), with low extinction, can be ideal tracers to probe emission from BLRs in type II AGNs. We performed RRL observations for H35$\alpha$ and H36$\alpha$ toward the center of Circinus galaxy with ALMA. Narrow components of H35$\alpha$ and H36$\alpha$, which are thought to be mainly from star forming regions around the nuclear region, are detected. However, only upper limits are obtained for broad H35$\alpha$ and H36$\alpha$. Since Circinus galaxy is one of the nearest AGN, non-detection of broad RRLs in Circinus galaxy at this band tells us that it is hopeless to detect broad RRL emission in local AGNs with current facilities. Submillimetre RRLs, with flux densities that are dozens of times higher than those at the millimetre level, could be the tools to directly detect BLRs in type II AGNs with ALMA, once its backend frequency coverage has been upgraded to several times better than its current capabilities.

arXiv comment5 pages, 2 Figures, published in MNRAS Letters

References in corpus (15)

• The slope of the black-hole mass versus velocity dispersion correlation
• Central Masses and Broad-Line Region Sizes of Active Galactic Nuclei. II. A Homogeneous Analysis of a Large Reverberation-Mapping Database
• The Relationship Between Luminosity and Broad-Line Region Size in Active Galactic Nuclei
• A 4% Geometric Distance to the Galaxy NGC4258 from Orbital Motions in a Nuclear Gas Disk
• Resolving the complex structure of the dust torus in the active nucleus of the Circinus galaxy
• The Early Evolution of Massive Stars: Radio Recombination Line Spectra
• SINFONI adaptive optics integral field spectroscopy of the Circinus Galaxy
• Near-infrared spectroscopy of nearby Seyfert galaxies. I. First results
• How Much Mass do Supermassive Black Holes Eat in their Old Age?
• Hydrogen Masers. I: Theory and Prospects
• Circumnuclear Multi-phase Gas in Circinus Galaxy III: Structure of the Nuclear Ionized Gas
• Detection of the H92alpha recombination line from the starbursts in the Circinus galaxy and NGC 1808
• ALMA observations of the submillimetre hydrogen recombination line from the type 2 active nucleus of NGC 1068
• Inverted level populations of hydrogen atoms in ionized gas
• Second Epoch ALMA Observations of 321 GHz Water Maser Emission in NGC 4945 and the Circinus Galaxy

Cited by in corpus (1)

• Star formation in the centre of NGC 1808 as observed by ALMA