A newborn active galactic nucleus in a star-forming galaxy
Salvato, M.; Merloni, A.; Arévalo, P.; Lira, P.; López-Navas, E.; Ricci, C.; Bernal, S.; Hernández-García, L.; Krumpe, M.; Sánchez-Sáez, P.; Martínez-Aldama, M. L.
Chile, Germany
Abstract
Aims: We report on the finding of a newborn active galactic nucleus (AGN), based on the observation of current AGN activity in a galaxy previously classified as non-active. We subsequently characterize the AGN's evolution.
Methods: Black hole ignition event candidates were selected from a parent sample of spectrally classified non-active galaxies (2 394 312 objects), which currently show optical flux variability indicative of a type I AGN, according to the ALeRCE light curve classifier. A second epoch spectrum for a sample of candidate newborn AGNs was obtained with the SOAR telescope to search for new AGN features.
Results: We present the spectral results for the most convincing case of new AGN activity for a galaxy with a prior star-forming optical classification, where the second epoch spectrum shows the appearance of prominent, broad Balmer lines, without any significant changes seen in the narrow line flux ratios. The long-term optical light curves show a steady increase in luminosity starting 1.5 years after the SDSS spectrum was taken and continuing for at least 7 years. Mid-infrared (MIR) colors from the WISE catalog have also evolved from typical non-active galaxy colors to AGN-like colors. Recent X-ray flux detections confirm its nature as an AGN.