Tol 2240-384 - a new low-metallicity AGN candidate
  Active galactic nuclei (AGNs) have typically been discovered in massive
galaxies of high metallicity. We attempt to increase the number of AGN
candidates in low metallicity galaxies. We present VLT/UVES and archival
VLT/FORS1 spectroscopic and NTT/SUSI2 photometric observations of the
low-metallicity emission-line galaxy Tol 2240-384 and perform a detailed study
of its morphology, chemical composition, and emission-line profiles. We
determine abundances of nitrogen, O, Ne, S, Cl, Ar, and Fe by analyzing the
fluxes of narrow components of the emission lines using empirical methods. We
verify with a photoionisation model that the physics of the narrow-line
component gas is similar to that in common metal-poor galaxies. Image
deconvolution reveals two high-surface brightness regions in Tol 2240-384
separated by 2.4 kpc.The brightest southwestern region is surrounded by intense
ionised gas emission on a spatial scale of ~5 kpc. The profiles of the strong
emission lines in the UVES spectrum are asymmetric and all these lines apart
from Halpha and Hbeta can be fitted by two Gaussians of FWHM ~75-92 km/s
separated by ~80 km/s implying that there are two regions of ionised gas
emitting narrow lines. The shapes of the Halpha and Hbeta lines are more
complex. In particular, the Halpha emission line consists of two broad
components of FWHM ~700 km/s and 2300 km/s, in addition to narrow components of
two regions revealed from profiles of other lines. The extraordinarily high
luminosity of the broad Halpha line of 3x10e41 erg/s cannot be accounted for by
massive stars at different stages of their evolution. The broad Halpha emission
persists over a period of 7 years, which excludes supernovae as a powering
mechanism of this emission. This emission most likely arises from an accretion
disc around a black hole of mass ~10e7 Msun.
