SDSS-IV MaNGA: Identification and multiwavelength properties of Type-1 AGN in the DR15 sample

Abstract

We present a method to identify type-1 active galactic nuclei (AGNs) in the central 3 arcsec integrated spectra of galaxies in the MaNGA DR15 sample. It is based on flux ratios estimates in spectral bands flanking the expected H α broad component H α_BC. The high signal-to-noise ratio obtained (mean S/N = 84) permits the identification of H α_BC without prior subtraction of the host galaxy (HG) stellar component. A final sample of 47 type-1 AGN is reported out of 4700 galaxies at z < 0.15. The results were compared with those from other methods based on the SDSS DR7 and MaNGA data. Detection of type-1 AGN in those works compared to our method goes from 26 per cent to 81 per cent. Spectral indexes were used to classify the type-1 AGN spectra according to different levels of AGN-HG contribution, finding 9 AGN-dominated, 14 intermediate, and 24 HG-dominated objects. Complementary data in NIR-MIR allowed us to identify type I AGN-dominated objects as blue and HG-dominated as red in the WISE colours. From NVSS and FIRST radio continuum data, we identify 5 HERGs (high-excitation radio galaxies) and 4 LERGs (low-excitation radio galaxies), three showing evidence of radio-jets in the FIRST maps. Additional X-ray data from ROSAT allowed us to build [O III] and H α_BC versus X-ray, NIR-MIR, and radio continuum diagrams, showing that L(H α_BC) and L([O III]) provide good correlations. The range in H α_BC luminosity is wide 38 < logL(H α_BC) < 44, with log FWHM(H α_BC) ~ 3-4, covering a range of Eddington ratios of -5.15 < log L_bol/L_Edd < 0.70. Finally, we also identify and report ten possible changing-look AGN candidates.