Abstract
In the last decade, using single epoch virial based techniques in the optical band, it has been possible to measure the central black hole mass on large AGN1 samples. However these measurements use the width of the broad line region as a proxy of the virial velocities and are therefore difficult to be carried out on those obscured (type 2) or low luminosity AGN where the nuclear component does not dominate in the optical. Here we present the optical and near infrared spectrum of the starburst/Seyfert galaxy NGC 6221, observed with X-shooter/VLT. Previous observations of NGC 6221 in the X-ray band show an absorbed (N_H=8.5 +/- 0.4 x 10^21 cm^-2) spectrum typical of a type 2 AGN with luminosity log(L_14-195 keV) = 42.05 erg/s, while in the optical band its spectrum is typical of a reddened (A_V=3) starburst. Our deep X-shooter/VLT observations have allowed us to detect faint broad emission in the H_alpha, HeI and Pa_beta lines (FWHM ~1400-2300 km/s) confirming previous studies indicating that NGC 6221 is a reddened starburst galaxy which hosts an AGN. We use the measure of the broad components to provide a first estimate of its central black hole mass (M_BH = 10^(6.6 +/- 0.3) Msol, lambda_Edd=0.01-0.03), obtained using recently calibrated virial relations suitable for moderately obscured (N_H<10^24 cm^-2) AGN.
Highlights
Nowadays there is robust evidence that every galaxy hosts a supermassive black hole (SMBH; MBH = 106–109 M⊙) whose mass scales with the hosting galaxy bulge properties
La Franca et al (2015) have calibrated a new virial relationship suitable for moderately absorbed/obscured AGN2, which is based on the measure of the Full Width at Half Maximum (FWHM) of the broad line region (BLR) component of the Paβ emission line together with the measure of the hard (14–195 keV) luminosity
NGC 6221 has been observed by SWIFT/BAT in the 14–195 keV band and a luminosity log(L14−195/erg s−1) = 42.05 was measured (70-month catalog; Baumgartner et al, 2013)
Summary
It has been possible to obtain some estimates of the SMBH mass function for large samples of type 1 AGN (AGN1) In this class of AGN the broad line region (BLR) is visible in the rest-frame optical band and this allows the use of virial methods to derive in a direct way the AGN BH mass (Greene and Ho, 2007; Kelly et al, 2009; Merloni et al, 2010; Bongiorno et al, 2014).
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
