Circumnuclear regions of different BPT types in star-forming MaNGA galaxies: AGN detectability

Abstract

We consider the circumnuclear regions of star-forming MaNGA galaxies. The spaxels spectra are classified as active-galactic-nucleus-like (AGN-like), H II-region-like (or SF-like), and intermediate (INT) spectra according to their positions on the Baldwin-Phillips-Terlevich (BPT) diagram. There are the following four configurations of the radiation distributions in the circumnuclear regions in (massive) galaxies: (1) AGN+INT, the innermost region of the AGN-like radiation is surrounded by a ring of radiation of the intermediate type; (2) INT, the central area of radiation of the intermediate type; (3) SF+INT, the inner region of the H II-region-like radiation is surrounded by a ring of radiation of the intermediate type; and (4) SF, the central area of the H II-region-like radiation only. The low ionization nuclear emission line regions (LINERs) of configurations 1 and 2 are examined. The spaxel spectra of the LINERs form a sequences on the BPT diagram, that is, they lie along the known AGN-SF mixing line trajectories. The diagnostic line ratios of the spaxels spectra change smoothly with radius, from AGN-like (or INT) line ratios at the galactic center to H II-region-like at larger galactocentric distances. This is in agreement with the paradigm that the LINERs are excited by AGN activity. We found that the AGN and INT radiation in the circumnuclear region is accompanied by an enhanced gas velocity dispersion σgas. The radius of the area of the AGN and INT radiation is similar to the radius of the area with enhanced σgas, and the central σgas, c correlates with the luminosity of the AGN+INT area. We assume that the gas velocity dispersion can serve as an indicator of the AGN activity. An appreciable enhancement of σgas, c was also measured in the SF-type centers of massive galaxies. The values of σgas, c for the SF-type centers partly overlap with those of the AGN-type centers. This suggests that the manifestation of the circumnuclear region as AGN or as SF on the BPT diagram depends not only on the value of σgas, c (the level of the AGN activity) but it is also governed by an additional parameter(s). We find that there is a demarcation line between the positions of the AGN-type and SF-type objects on the central gas velocity dispersion – central Hα surface brightness diagram, in the sense that an object with a given value of σgas, c is an AGN-type only if the central Hα surface brightness is lower than some value.

Physical Drivers of Emission Line Diversity of SDSS Seyfert 2s and LINERs After Removal of Contributions by Star Formation

“…It should be noted that we are not focused here on spatially resolved individual galaxies and the mixing sequences which may be observed as a function of distance in IFU studies (e.g.,Davies et al (2016); D'Agostino et al (2019a,b);Pilyugin et al (2020)). …”

MaNGA galaxies with off-centered spots of enhanced gas velocity dispersion

“…The publicly available spectroscopic observations from the Sloan Digital Sky Survey Data Release 15 (SDSS DR15) MaNGA survey (Bundy et al 2015;Albareti et al 2017) are at the base of this investigation. The same data was also used in our previous studies (Pilyugin et al 2020b(Pilyugin et al , 2021, and the data reduction is described in Zinchenko et al (2016) and Sakhibov et al (2018). Briefly, we used LOGCUBE datacubes, which have logarithmic wavelength sampling.…”

“…There is a variation in the values of σ across the image of each galaxy. The variation of σ can form a global structure: the σ distribution can show a band of enhanced σ along the minor axis in the image (Pilyugin et al 2021), and the value of the gas velocity dispersion is usually enhanced at the center of the galaxy (Pilyugin et al 2020b). There is a chaotic variation in the σ in addition to the global variation.…”

“…This is the third paper of series devoted to the investigation of the distribution of the gas velocity dispersion σ in star-forming (SF) galaxies from the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey (Bundy et al 2015;Albareti et al 2017). In the first paper, we considered the circumnuclear regions of 161 galaxies from the Sloan Digital Sky Survey Data Release 15 (SDSS DR15) MaNGA survey (Pilyugin et al 2020b). The spaxel spectra were classified as active galactic nucleus-like (AGN-like), H II-regionlike (or SF-like), and intermediate (INT) spectra according to their positions in the Baldwin-Phillips-Terlevich (BPT, Baldwin, Phillips, Terlevich 1981) diagnostic diagram.…”

Metal-THINGS: On the metallicity and ionization of ULX sources in NGC 925

“…To further explore the possibility of shocks in the ULX-1 spaxels and their impact on the gas metallicity, we use the MANGA sample of Pilyugin et al (2020). From this sample, we examine the gas metallicity, using the S-calibration, of SF-type regions with gas velocity dispersions of ∼100 km/s, and spaxels with sizes of ∼300 pc.…”