Infrared spectroscopic diagnostics for Active Galactic Nuclei

Infrared spectroscopy in the mid- and far-infrared provides powerful diagnostics for studying the emission regions in active galaxies. The large variety of ionic fine structure lines can probe gas conditions in a variety of physical conditions, from highly ionized gas excited by photons originated by black hole accretion to gas photoionized by young stellar systems. The critical density and the ionization potential of these transitions allow to fully cover the density-ionization parameter space. Some examples of line ratios diagrams using both mid-infrared and far-infrared ionic fine structure lines are presented. The upcoming space observatory Herschel will be able to observe the far-infrared spectra of large samples of local active galaxies. Based on the observed near-to-far infrared emission line spectrum of the template galaxy NGC1068, are presented the predictions for the line fluxes expected for galaxies at high redshift. To observe spectroscopically large samples of distant galaxies, we will have to wait fot the future space missions, like SPICA and, ultimately, FIRI.Comment: Proc. of the Winter School "Astronomy in the submillimeter and far infrared domains with the Herschel Space Observatory", Centre de Physique des Houches 23 april - 04 may 200

How many active galaxies and QSOs will future Space Missions detect?

Averaged spectral energy distributions (SEDs) of active and starburst galaxies from the 12 micron sample in the Local Universe and Quasars, from an optically selected sample at a mean redshift =0.7, are built from optical/near-IR/far-IR (IRAS & ISO) photometric observations. These SEDs are then used to predict at various redshifts the number of Seyfert type 1 and type 2, starburst, normal galaxies, and quasars, that will be detected by future Space Missions dedicated to far-infrared and submillimeter astronomy, like SIRTF and Herschel. These predictions are then compared with the expected capabilities and detection limits of future deep far-IR surveys. Possible ways to identify AGN candidates on far-IR colour-colour plots for follow-up observations are then explored.Comment: accepted in Ap

Spitzer spectra of Seyfert galaxies

The Spitzer IRS high resolution spectra of about 90 Seyfert galaxies from the 12um Galaxy Sample are presented and discussed. These represent about 70% of the total complete sample of local Seyfert galaxies. The presence of starburst components in these galaxies can be quantified by powerful mid-IR diagnostics tools (i.e. 11.25um PAH feature equivalent width and the H_2 emission line intensity) as well as the AGN dominance can be measured by specific fine structure line ratios (e.g. [NeV]/[NeII], [NeV]/[SiII], etc.). The observed line ratios are compared to the results of semianalytical models, which can be used to compute the AGN and starburst contributions to the total luminosity of the galaxies. The results are also discussed in the light of unification and evolution models.Comment: to appear in the proceedings of "The Starburst-AGN Connection Conference", Shanghai, China, 27 Oct - 1 Nov 2008, ASP Conference Serie

Seyfert Galaxies in the Local Universe: Analysis of Spitzer Spectra of a Complete Sample

The Spitzer high resolution spectra of 72 Seyfert galaxies from the 12$\mu$m Galaxy Sample are presented and discussed. The presence of starburst components in these galaxies can be quantified by powerful mid-IR diagnostics tools (i.e. 11.25$\mu$m PAH feature equivalent width and the H$_2$ emission line intensity), as well as the AGN dominance can be measured by specific fine structure line ratios (e.g. [NeV]/[NeII], [NeV]/[SiII], etc.). The two types of Seyfert galaxies do not show any statistical difference in our diagnostic tools. However, the Seyfert 2's showing hidden Broad Line Regions in spectro-polarimetric observations have on average an higher AGN dominance, a weaker star formation component and a warmer [60 - 25] spectral index than those without broad emission lines.Comment: Proceedings of the Conference "The central kiloparsec. Active Galactic Nuclei and their hosts, 4-6 June 2008, Ierapetra, Crete, Greec

Emission Line Properties of Seyfert Galaxies in the 12 Micron Sample

We present spectroscopy of emission lines for 81 Seyfert 1 and 104 Seyfert 2 galaxies in the IRAS 12$\mu$m galaxy sample. We analyzed the emission-line luminosity functions, reddening, and other gas diagnostics. The narrow-line regions (NLR) of Sy1 and 2 galaxies do not significantly differ from each other in most of these diagnostics. Combining the H$\alpha$/H$\beta$ ratio with a new reddening indicator-the [SII]6720/[OII]3727 ratio, we find the average $E(B-V)=0.49\pm0.35$ for Sy1s and $0.52\pm0.26$ for Sy2s. The NLR of Sy1 galaxies has only marginally higher ionization than the Sy2s. Our sample includes 22 Sy1.9s and 1.8s. In their narrow lines, these low-luminosity Seyferts are more similar to the Sy2s than the Sy1s. We construct a BPT diagram, and include the Sy1.8s and 1.9s. They overlap the region occupied by the Sy2s. The C IV equivalent width correlates more strongly with [O III]/H$\beta$ than with UV luminosity. The Sy1 and Sy2 luminosity functions of [OII]3727 and [OIII]5007 are indistinguishable. Unlike the LF's of Seyfert galaxies measured by SDSS, ours are nearly flat at low L. The larger number of faint Sloan "AGN" is attributable to their inclusion of weakly emitting LINERs and H II+AGN "composite" nuclei, which do not meet our classification criteria for Seyferts. An Appendix investigates which emission line luminosities provide the most reliable measures of the total non-stellar luminosity. The hard X-ray or near-ultraviolet continuum luminosity can be crudely predicted from either the [O III]5007 luminosity, or the combination of [O III]+H$\beta$, or [N II]+H$\alpha$ lines, with a scatter of $\pm\,4$ times for the Sy1s and $\pm\,10$ times for the Sy2s. The latter two hybrid (NLR+BLR) indicators have the advantage of predicting the same HX luminosity independent of Seyfert type.Comment: 70 pages, including 15 Figures and 10 Tables. Accepted for publication in The Astrophysical Journa