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Register a new userSemi-empirical metallicity calibrations based on ultraviolet emission lines of type-2 AGNs
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We derived two semi-empirical calibrations between the metallicity of the Narrow Line Region (NLR) of type-2 Active Galactic Nuclei and the rest-frame of the N V$lambda$1240/He II$lambda1640$, C43=log[(C IV$lambda1549$+C III]$lambda1909$)/HeII$lambda1640$] and C III]$lambda1909$/C IV$lambda1549$ emission-line intensity ratios. A metallicity-independent calibration between the ionization parameter and the C III]$lambda1909$/C IV$lambda1549$ emission-lines ratio was also derived. These calibrations were obtained comparing ratios of measured UV emission-line intensities, compiled from the literature, for a sample of 77 objects (redshift $0 : < : z : < : 3.8$) with those predicted by a grid of photoionization models built with the Cloudy code. Using the derived calibrations, it was possible to show that the metallicity estimations for NLRs are lower by a factor of about 2-3 than those for Broad Line Regions (BLRs). Besides we confirmed the recent result of the existence of a relation between the stellar mass of the host galaxy and its NLR metallicity. We also derived a $M-Z$ relation for the objects in our sample at $1.6 : < : z : < : 3.8$. This relation seems to follow the same trend as the ones estimated for Star Forming galaxies of similar high redshifts but for higher masses.
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We present a semi-empirical calibration between the metallicity ($Z$) of Seyfert 2 Active Galactic Nuclei and the $N2$=log([N II]$lambda$6584/H$alpha$) emission-line intensity ratio. This calibration was derived through the [O III]$lambda$5007/[O II]$lambda$3727 versus $N2$ diagram containing observational data and photoionization model results obtained with the Cloudy code. The observational sample consists of 463 confirmed Seyfert 2 nuclei (redshift $z < 0.4$) taken from the Sloan Digital Sky Survey DR7 dataset. The obtained $Z$-$N2$ relation is valid for the range $0.3 < (Z/Z_{odot}) < 2.0$ which corresponds to $-0.7 < : (N2) < 0.6$. The effects of varying the ionization parameter ($U$), electron density and the slope of the spectral energy distribution on the $Z$ estimations are of the order of the uncertainty produced by the error measurements of $N2$. This result indicates the large reliability of our $Z-N2$ calibration. A relation between $U$ and the [O III]/[O II] line ratio, almost independent of other nebular parameter, was obtained.
We derive new empirical calibrations for strong-line diagnostics of gas phase metallicity in local star forming galaxies by uniformly applying the Te method over the full metallicity range probed by the Sloan Digital Sky Survey (SDSS). To measure electron temperatures at high metallicity, where the auroral lines needed are not detected in single galaxies, we stacked spectra of more than 110,000 galaxies from the SDSS in bins of log[O II]/H$beta$ and log[O III]/H$beta$. This stacking scheme does not assume any dependence of metallicity on mass or star formation rate, but only that galaxies with the same line ratios have the same oxygen abundance. We provide calibrations which span more than 1 dex in metallicity and are entirely defined on a consistent absolute Te metallicity scale for galaxies. We apply our calibrations to the SDSS sample and find that they provide consistent metallicity estimates to within 0.05 dex.
Type 2 active galactic nuclei (AGN) represent the majority of the AGN population. However, due to the difficulties in measuring their black hole (BH) masses, it is still unknown whether they follow the same BH mass-host galaxy scaling relations valid for quiescent galaxies and type 1 AGN. Here we present the locus of type 2 AGN having virial BH mass estimates in the $M_{BH}-sigma_star$ plane. Our analysis shows that the BH masses of type 2 AGN are $sim0.9$ dex smaller than type 1 AGN at $sigma_starsim 185$ km s$^{-1}$, regardless of the (early/late) AGN host galaxy morphology. Equivalently, type 2 AGN host galaxies have stellar velocity dispersions $sim 0.2$ dex higher than type 1 AGN hosts at $M_{BH}sim10^7$ M$_odot$.
Using integral field spectroscopic data of 24 nearby spiral galaxies obtained with the Multi-Unit Spectroscopic Explorer (MUSE), we derive empirical calibrations to determine the metallicity of the diffuse ionized gas (DIG) and/or of the low-ionisation emission region (LI(N)ER) in passive regions of galaxies. To do so, we identify a large number of HII--DIG/LIER pairs that are close enough to be chemically homogeneous and we measure the metallicity difference of each DIG/LIER region relative to its HII region companion when applying the same strong line calibrations. The O3N2 diagnostic ($=$log [([O III]/H$beta$)/([N II]/H$alpha$)]) shows a minimal offset (0.01--0.04 dex) between DIG/LIER and HII regions and little dispersion of the metallicity differences (0.05 dex), suggesting that the O3N2 metallicity calibration for HII regions can be applied to DIG/LIER regions and that, when used on poorly resolved galaxies, this diagnostic provides reliable results by suffering little from DIG contamination. We also derive second-order corrections which further reduce the scatter (0.03--0.04 dex) in the differential metallicity of HII-DIG/LIER pairs. Similarly, we explore other metallicity diagnostics such as O3S2 ($=$log([O III]/H$beta$+[S II]/H$alpha$)) and N2S2H$alpha$ ($=$ log([N II]/[S II]) + 0.264log([N II]/H$alpha$)) and provide corrections for O3S2 to measure the metallicity of DIG/LIER regions. We propose that the corrected O3N2 and O3S2 diagnostics are used to measure the gas-phase metallicity in quiescent galaxies or in quiescent regions of star-forming galaxies.
Accurately weigh the masses of SMBH in AGN is currently possible for only a small group of local and bright broad-line AGN through reverberation mapping (RM). Statistical demographic studies can be carried out considering the empirical scaling relation between the size of the BLR and the AGN optical continuum luminosity. However, there are still biases against low-luminosity or reddened AGN, in which the rest-frame optical radiation can be severely absorbed/diluted by the host and the BLR emission lines could be hard to detect. Our purpose is to widen the applicability of virial-based SE relations to reliably measure the BH masses also for low-luminosity or intermediate/type 2 AGN that are missed by current methodology. We achieve this goal by calibrating virial relations based on unbiased quantities: the hard X-ray luminosities, in the 2-10 keV and 14-195 keV bands, that are less sensitive to galaxy contamination, and the FWHM of the most important rest-frame NIR and optical BLR emission lines. We built a sample of RM AGN having both X-ray luminosity and broad optical/NIR FWHM measurements available in order to calibrate new virial BH mass estimators. We found that the FWHM of the H$alpha$, H$beta$ and NIR lines (i.e. Pa$alpha$, Pa$beta$ and HeI$lambda$10830) all correlate each other having negligible or small offsets. This result allowed us to derive virial BH mass estimators based on either the 2-10 keV or 14-195 keV luminosity. We took also into account the recent determination of the different virial coefficients $f$ for pseudo and classical bulges. By splitting the sample according to the bulge type and adopting separate $f$ factors we found that our virial relations predict BH masses of AGN hosted in pseudobulges $sim$0.5 dex smaller than in classical bulges. Assuming the same average $f$ factor for both populations, a difference of $sim$0.2 dex is still found.
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