We have selected an all-sky (|b| ≥ 25°) 12 μm flux-limited sample of 893 galaxies from the IRAS Faint Source Catalog, Version 2 (FSC-2). This new sample contains 2.3 times as many objects as an earlier selection by Spinoglio & Malkan based on the IRAS Point Source Catalog, Version 2. We have obtained accurate total fluxes in the IRAS wavebands by using the ADDSCAN procedure for all objects with FSC-2 12 μm fluxes greater than 0.15 Jy and increasing flux densities from 12 to 60 μm, and denned the sample by imposing a survey limit of 0.22 Jy on the total 12 μm flux. Its completeness is verified, by means of the classical log N - log S and V/Vmax tests, down to 0.30 Jy, below which we have measured the incompleteness down to the survey limit, using the log N -log S plot, for our statistical analysis. We have obtained redshifts (mostly from catalogs) for virtually all (98.4%) the galaxies in the sample. Using existing catalogs of active galaxies, we defined a subsample of 118 objects consisting of 53 Seyfert 1s and quasars, 63 Seyfert 2s, and two blazars (∼13% of the full sample), which is the largest unbiased sample of Seyfert galaxies ever assembled. Since the 12 μm flux has been shown to be about one-fifth of the bolometric flux for Seyfert galaxies and quasars, the subsample of Seyferts (including quasars and blazars) is complete not only to 0.30 Jy at 12 μm but also with respect to a bolometric flux limit of ∼2.0 × 10-10 ergs s-1 cm-2. The average value of V/Vmax for the full sample, corrected for incompleteness at low fluxes, is 0.51 ± 0.04, expected for a complete sample of uniformly distributed galaxies, while the value for the Seyfert galaxy subsample is 0.46 ± 0.10, suggesting that several of the more distant galaxies remain to be identified as Seyferts in our sample. We have derived 12 μm and far-infrared luminosity functions for the AGNs, as well as for the entire sample. The AGN luminosity functions are more complete than those of the optically selected CfA Seyfert galaxies for all luminosities and AGN types. We extracted from our sample a complete subsample of 235 galaxies flux-limited (8.3 Jy) at 60 μm. The 60 μm luminosity function computed for this subsample is in satisfactory agreement with the ones derived from the bright galaxy sample (BGS) and the deep high-galactic latitude sample, both selected at 60 μm. Over the high-luminosity range where our sample and the BGS overlap, however, our space densities are systematically lower by a factor of ∼1.5, whereas at low luminosities our space densities are higher by about the same amount. Comparable results are obtained when comparing the far-IR luminosity function of our entire sample with the one derived from the BGS. This is not unexpected, because of the bias toward high-luminosity spirals caused by selection at 60 μm.

Averaged spectral energy distributions (SEDs) of active and starburst galaxies, from the 12 μm sample in the local universe, and QSOs, from an optically selected sample at a mean redshift (z) = 0.7, are built from optical, near-IR, and far-IR (FIR; IRAS and Infrared Space Observatory) photometric observations. These SEDs are then used to predict at various redshifts the number of Seyfert type 1 and type 2, starburst, and normal galaxies and QSOs that will be detected by future space missions dedicated to FIR and submillimeter astronomy, such as SIRTF and Herschel. These predictions are then compared with the expected capabilities and detection limits of future deep FIR surveys. Possible ways to identify active galactic nucleus candidates on FIR color-color plots for follow-up observations are then explored.

New far-infrared photometry with ISOPHOT aboard the Infrared Space Observatory (ISO) is presented for 58 galaxies with homogeneous published data for another 32 galaxies, all belonging to the 12 μm galaxy sample - in total, 29 Seyfert 1 galaxies, 35 Seyfert 2 galaxies, and 12 starburst galaxies, or about half of the 12 μm active galaxy sample, plus 14 normal galaxies for comparison. ISO and Infrared Astronomical Satellite (IRAS) data are used to define color-color diagrams and spectral energy distributions (SEDs). Thermal dust emission at two temperatures (one cold at 15-30 K and one warm at 50-70 K) can fit the 60-200 μm SED, with a dust emissivity law proportional to the inverse square of the wavelength. Seyfert 1 galaxies and Seyfert 2 galaxies are indistinguishable longward of 100 μm, while, as already seen by IRAS, the former have flatter SEDs shortward of 60 μm. A mild anticorrelation is found between the [200-100] color and the "60 μm excess." We infer that this is due to the fact that galaxies with a strong starburst component and thus a strong 60 μm flux have a steeper far-infrared turnover. In non-Seyfert galaxies, increasing the luminosity corresponds to increasing the star formation rate, which enhances the 25 and 60 μm emission. This shifts the peak emission from around 150 μm in the most quiescent spirals to shorter than 60 μm in the strongest starburst galaxies. To quantify these trends further, we identified with the IRAS colors three idealized infrared SEDs: pure quiescent disk emission, pure starburst emission, and pure Seyfert nucleus emission. Even between 100 and 200 μm, the quiescent disk emission remains much cooler than the starburst component. Seyfert galaxies have 100-200 μm SEDs ranging from pure disks to pure starbursts, with no apparent contribution from their active nuclei at those wavelengths.

We present the Spitzer 10-37um IRS high resolution (R~600) spectroscopic survey of the Seyfert galaxies of the 12 micron Galaxy Sample. The new spectra of 61 galaxies, with those already published, gives us a total of 91 12micron Seyfert galaxies observed, out of 112. We use an improved AGN classification for Seyfert galaxies: instead of the type 1 and 2 classes, we use the spectropolarimetric data to divide them into "AGN 1" and "AGN 2", where AGN 1's include all broad-line objects, including the Seyfert 2's showing hidden broad lines in polarized light, while AGN 2's contains only Seyferts with no detectable broad lines at all. We present various mid-IR observables and we find that these properties characterize the AGN 1's objects as a single family, with strongly AGN-dominated spectra. In contrast, the AGN 2's can be divided in two groups, the first one with properties similar to the AGN 1's and the second similar to the non-Seyfert galaxies, such as LINERs or starburst galaxies. We computed a semianalytical model to estimate the AGN and the starburst contributions to the mid-IR galaxy emission at 19um. We find that AGN 1 have an AGN contribution >73% and AGN 2 >45% of their total emission at 19um. The detection of [NeV] lines is an almost perfect signature of energy production by an AGN. We present mean spectra of the various AGN categories. We derive the first local luminosity functions for the mid-infrared lines and the PAH feature. No statistical difference is found in the space densities for Seyfert 1's and 2's, nor for the new classes of AGN 1's and 2's. The global output of accretion-powered galactic nuclei in the local universe is derived from the correlation between [NeV] line and the nonstellar IR continuum luminosity.

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.

We investigated the 65$\mu$m, 71$\mu$m, 79$\mu$m, 84$\mu$m, 119$\mu$m, and 163$\mu$m OH doublets of 178 local (0 < $z$ < 0.35) galaxies. They were observed using the $Herschel$/PACS spectrometer, including Seyfert galaxies, LINERs, and star-forming galaxies. We observe these doublets exclusively in absorption (OH71), primarily in absorption (OH65, OH84), mostly in emission (OH79), only in emission (OH163) and an approximately even mix of the both (OH119). In 19 galaxies we find P-Cygni or reverse P-Cygni line profiles in the OH doublets. We use several galaxy observables to probe spectral classification, brightness of a central AGN/starburst component, and radiation field strength. We find that OH79, OH119, and OH163 are more likely to display strong emission for bright, unobscured AGN. For less luminous, obscured AGN and non-active galaxies, we find populations of strong absorption (OH119), weaker emission (OH163), and a mix of weak emission and weak absorption (OH79). For OH65, OH71 and OH84, we do not find significant correlations with the observables listed above. We do find relationships between OH79 and OH119 with both the 9.7$\mu$m silicate feature and Balmer decrement dust extinction tracers in which more dust leads to weaker emission / stronger absorption. The origin of emission for the observed OH doublets, whether from collisional excitation, or from radiative pumping by infrared photons, is discussed.

We present a coherent database of spectroscopic observations of far-IR fine-structure lines from the Herschel/PACS archive for a sample of 170 local AGN, plus a comparison sample of 20 starburst galaxies and 43 dwarf galaxies. Published Spitzer/IRS and Herschel/SPIRE line fluxes are included to extend our database to the full 10-600 $\mu m$ spectral range. The observations are compared to a set of CLOUDY photoionisation models to estimate the above physical quantities through different diagnostic diagrams. We confirm the presence of a stratification of gas density in the emission regions of the galaxies, which increases with the ionisation potential of the emission lines. The new [OIV]25.9$\mu m$/[OIII]88$\mu m$ vs [NeIII]15.6$\mu m$/[NeII]12.8$\mu m$ diagram is proposed as the best diagnostic to separate: $i)$ AGN activity from any kind of star formation; and $ii)$ low-metallicity dwarf galaxies from starburst galaxies. Current stellar atmosphere models fail to reproduce the observed [OIV]25.9$\mu m$/[OIII]88$\mu m$ ratios, which are much higher when compared to the predicted values. Finally, the ([NeIII]15.6$\mu m$ + [NeII]12.8$\mu m$)/([SIV]10.5$\mu m$ + [SIII]18.7$\mu m$) ratio is proposed as a promising metallicity tracer to be used in obscured objects, where optical lines fail to accurately measure the metallicity. The diagnostic power of mid- to far-infrared spectroscopy shown here for local galaxies will be of crucial importance to study galaxy evolution during the dust-obscured phase at the peak of the star formation and black-hole accretion activity ($1 < z < 4$). This study will be addressed by future deep spectroscopic surveys with present and forthcoming facilities such as JWST, ALMA, and SPICA.

Aperture photometry from our own observations and the literature is presented for the 12 μm galaxies in the near-infrared J, H, and K bands and, in some cases, in the L band. These data are corrected to "total" near-infrared magnitudes (with a typical uncertainty of 0.3 mag) for a direct comparison with our IRAS fluxes which apply to the entire galaxy. The corrected data are used to derive integrated total near-infrared and far-infrared luminosities. We then combine these with blue photometry and an estimate of the flux contribution from cold dust at wavelengths longward of 100 μm to derive the first bolometric luminosities for a large sample of galaxies. The presence of nonstellar radiation at 2-3 μm correlates very well with nonstellar IRAS colors. This enables us to identify a universal Seyfert nuclear continuum from near- to far-infrared wavelengths. Thus, there is a sequence of infrared colors which runs from a pure "normal galaxy" to a pure Seyfert/quasar nucleus. Seyfert 2 galaxies fall close to this same sequence, although only a few extreme narrow-line Seyfert galaxies have quasar-like colors, and these show strong evidence of harboring an obscured broad-line region. A corollary is that the host galaxies of Seyfert nuclei have normal near- to far-infrared spectra on average. Starburst galaxies lie significantly off the sequence, having a relative excess of 60 μm emission probably as a result of stochastically heated dust grains. We use these correlations to identify several combinations of infrared colors which discriminate between Seyfert 1 and 2 galaxies, LINERs, and ultraluminous starbursts. In the infrared, Seyfert 2 galaxies are much more like Seyfert Is than they are like starbursts, presumably because both kinds of Seyferts are heated by a single central source, rather than a distributed region of star formation. Moreover, combining the [25-2.2 μm] color with the [60-12 μm] color, it appears that Seyfert 1 galaxies are segregated from Seyfert 2 galaxies and starburst galaxies in a well-defined region characterized by the hottest colors, corresponding to the flattest spectral slopes. Virtually no Seyfert 2 galaxy is present in such a region. To reconcile this with the "unified scheme" for Seyfert 1 and 2 galaxies would therefore require that the higher frequency radiation from the nuclei of Seyfert 2 galaxies to be absorbed by intervening dust and reemitted at lower frequencies. We find that bolometric luminosity is most closely proportional to 12 μm luminosity. The 60 and 25 μm luminosities rise faster than linearly with bolometric luminosity, while the optical flux rises less than linearly with bolometric luminosity. This result is a confirmation of the observation that more luminous disk galaxies have relatively more dust-enshrouded stars. Increases in the dust content shifts luminosity from the optical to 25-60 μm, while leaving a "pivot point" in the mid-IR essentially unchanged. Thus, 12 μm selection is the closest available approximation to selection by a limiting bolometric flux, which is approximately 14 times vLv at 12 μm for non-Seyfert galaxies. It follows that future deep surveys in the mid-infrared, at wavelengths of 8-12 μm, will simultaneously provide complete samples to different bolometric flux levels of normal and active galaxies, which will not suffer the strong selection effects present both in the optical-UV and far-infrared.

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.

The first high-resolution Spitzer 1RS 9-37 μm spectra of 29 Seyfert galaxies of the 12 μm Active Galaxy Sample are presented. The spectroscopy was obtained with off-source observations, allowing excellent background subtraction and thus accurate measurements of continuum levels and strengths of weak emission lines. Several new combinations of emission-line ratios and line/continuum ratios were identified as effective diagnostics of the strength of the AGN component in these galaxies. The line ratios [Ne v]/[Ne II], [O IV]/[Ne II], already known, but also [Ne III]/[Ne II] and [Ne v]/[Si II] can be used to measure the dominance of the AGN. The equivalent width of the 11.25 μm PAH feature, like that of the 6.2 μm PAH feature, already studied, also anticorrelates with the dominance of the AGN. Our measurements indicate that the 11.25 μm PAH feature has a constant ratio with H2 S(1) irrespective of Seyfert type, approximately 10 to 1. The ratio of the 19 μm fluxes observed with the two spectrometer channels, with aperture areas differing by a factor of 4, measures the source extendedness, giving another estimate of the AGN dominance, which correlates with both the EWs of [Ne n] and PAH emission. Using the rotational transitions of H2, we estimated temperatures (200-300 K) and masses (1 -10 × 106 M⊙) for the warm molecular component. Finally, we used the ratios of the doublets of [Ne v] and of [S III] to estimate the gas electron density, which appears to be of the order of ne ∼ 103-104 cm-3 for the highly ionized component and a factor 10 lower for the intermediate- ionization gas. © 2008. The American Astronomical Society. All rights reserved.