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

Hainline, Kevin

Malkan, Matthew A.

Spinoglio, Luigi

Tommasin, Silvia

English

arXiv

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

Malkan, Matthew A

eScholarship - University of California

UCLAUCLA Previously Published WorksTitleSpitzer Spectra of Seyfert GalaxiesPermalinkhttps://escholarship.org/uc/item/5rq5513sJournalSTARBURST-AGN CONNECTION, 408AuthorsSpinoglio, LuigiTommasin, SilviaMalkan, Matthew Aet al.Publication Date2009 Peer reviewedeScholarship.org Powered by the California Digital LibraryUniversity of CaliforniaarXiv:0902.3341v1  [astro-ph.GA]  19 Feb 2009**FULL TITLE**ASP Conference Series, Vol. **VOLUME**, **YEAR OF PUBLICATION****NAMES OF EDITORS**Spitzer spectra of Seyfert galaxiesLuigi Spinoglio & Silvia TommasinIstituto di Fisica dello Spazio Interplanetario, INAF, Via Fosso delCavaliere 100, I-00133, Roma, ItalyMatthew A. Malkan & Kevin HainlineAstronomy Division, University of California, Los Angeles, CA90095-1547, USAAbstract. The Spitzer IRS high resolution spectra of about 90 Seyfert galax-ies from the 12µm Galaxy Sample are presented and discussed. These representabout 70% of the total complete sample of local Seyfert galaxies. The presenceof starburst components in these galaxies can be quantified by powerful mid-IRdiagnostics tools (i.e. 11.25µm PAH feature equivalent width and the H2 emis-sion line intensity) as well as the AGN dominance can be measured by specificfine structure line ratios (e.g. [NeV]/[NeII], [NeV]/[SiII], etc.). The observedline ratios are compared to the results of semianalytical models, which can beused to compute the AGN and starburst contributions to the total luminosityof the galaxies. The results are also discussed in the light of unification andevolution models.1. Mid-IR spectroscopy with SpitzerWe briefly describe here some of the results of the mid-IR spectroscopic survey ofSeyfert galaxies belonging to the 12µm Galaxy sample (hereafter 12MGS)(Rush,Malkan & Spinoglio 1993).The first results of the Spitzer spectroscopic survey of the Seyfert galax-ies of the 12µm sample (Tommasin et al 2008) show a clear inverse trend be-tween the indicator of AGN dominance, the [NeV]14.3µm/[NeII]12.8µm lineratio, and the equivalent width of the 11.25µm PAH feature, which can be con-sidered as an indicator of the star formation dominance, as shown in Figure1a, where the sample objects increaed from 30 (Tommasin et al 2008) to 87(Tommasin et al 2009). This result confirms an early finding of the ISO-SWSspectrometer (Genzel et al 1998) with a much better statistics. Here the Seyfertgalaxies have been reclassified, following the results of spectropolarimetry (au-thor?) (Tran 2001, Tran 2003), in type 1’s (including the classical Seyfert 1’sand the hidden Broad Line Region Seyfert 2’s, as discovered through spectropo-larimetry) and ”pure” type 2’s (for which a BLR was not detected). Most of thetype 1 objects, including both Seyfert 1s and hidden Broad Line Region Seyfert2s, are located at high values of the [NeV]14.3µm/[NeII]12.8µm line ratio andvery low or absent PAH emission.Another diagnostic diagram using both spectroscopic and photometric re-sults is shown in Figure 1b: the spectral index between 25 and 60µm α(60µm−25µm)versus the [NeV]14.3µm/[NeII]12.8µm line ratio. A clear trend shows that when12 Spinoglio et al.Figure 1. a:(left) [NeV]14.3µm/[NeII]12.8µm line ratio versus the equiv-alent width of the 11.25µm PAH. b:(right) The mid-to-far-IR spec-tral index α(60µm−25µm) versus the [NeV]14.3µm/[NeII]12.8µm line ratio(Tommasin et al 2008; Tommasin et al 2009).the AGN dominance increases, the spectral index flattens. Most of type 1 ob-jects appear to be concentrated in the upper right part of the diagram, at highvalues of AGN dominance and flat mid-to-far-IR slopes.Figure 2. a:(left) [NeII]12.8µm line equivalent width as a function of thesource extendedness. b:(right) [NeV]14.3µm line EW versus source extend-edness (Tommasin et al 2008; Tommasin et al 2009).The two channels of the Spitzer high-resolution spectrometer: SH 9.6-19.5µm with slit size 4.7′′ × 11.3′′ and LH 19-39µm with slit size 11.1′′ × 22.3′′ allow multi-aperture photometry in the overlapping parts (19.0-19.5µm). Theratio of the flux measured in LH to that measured in SH gives the extended-ness of the source. We used this measure of the extendedness of the source toestimate the line emitting regions (Tommasin et al 2008). In Figure 2a we plotSpitzer spectra of Seyfert galaxies 3the [NeII]12.8µm line equivalent width as a function of the source extendedness.We notice that those sources showing a significant mid-IR extendedness aremostly type 2 objects or non-Seyfert galaxies and have the highest [NeII]12.8µmline equivalent width, with only two exceptions of very nearby Seyfert 1’s. Anhigh [NeII]12.8µm line equivalent width is a measure of a strong star formationcomponent. This is not the case for the high excitation lines, originated fromthe AGN, such as [NeV], for which no apparent trend appears between sourceextendedness and line EWs , as can be seen in Figure 2b (Tommasin et al 2008).2. Semianalytical models to estimate AGN and Starburst compo-nentsTo estimate the percentage of the contribution of AGN and Starburst in theobserved emission in a galaxy at 19µm, we computed an analytical model, foreach of the observed quantities as a function of R, which is defined as the ratioof the Starburst flux at 19µm to the AGN flux at the same wavelength. R variesfrom zero - emission totally from the AGN - to infinity - emission totally from theStarburst. The chosen observed quantities are: the extendedness of the source,the equivalent width of PAH at 11.25µm and [NeII] at 12.81µm, the line ratio[NeV]14.32µ/[NeII]12.81µm, the spectral index α at (60-25)µm.In Fig.3a and 3b the diagrams of [NeV]/[NeII] vs α(60-25)µ m and EW[NeII] vs EW PAH, are shown as examples, where the black curves representthe models. By inverting the models, i.e. solving the analytical expressions withthe true values of the observed quantities, we obtained a value of R for each ofthe five observed quantities of every source. We then computed the mean valueof R to estimate the relative percentage of AGN and Starburst emissions.The sample of sources to which we apply this analysis is reduced becausethe models depend on the extendedness and the PAH equivalent width, whichare not detected (for the PAH) or measurable (for the extendedness) for all thesources(from 86 to 59 objects). We found that the model can disentangle theAGN and the Starburst emission for 16 of 20 Seyfert 1’s, 14 of 16 HBLR’s, 13of 14 nonHBLR’s, 7 of 9 objects re-classified as not Seyferts. The details of thisapproach will appear in Tommasin et al. (2009).3. Analysis of the 12µm sample multi-frequency datasetThe 12MGS has been observed extensively from the radio to the X-rays andwe can use the large set of data to search for correlations between differentobserved quantities. To show an example, we want to relate the X-ray luminosity,measuring the accretion, to the bolometric luminosity, as given by the 12µmluminosity. We plot in Figure 4 the unabsorbed 2-10keV luminosity and the12µm luminosity.Following the finding of Spinoglio & Malkan (1989) and Spinoglio et al(1995) that the 12µm luminosity is linearly proportional to the bolometric lumi-nosity, at a given Lbol in Figure 4a a sequence can be identified with decreasingaccretion luminosity: from Seyfert 1’s → HBLR-Seyfert 2’s → pure Seyfert 2’s.Although these results are to be considered preliminary, as no statistical methodhas yet been applied, most Seyfert 1’s have:4 Spinoglio et al.100% AGN70% AGN50% AGN100%Starburst100% AGN70% AGN50% AGN100% StarburstFigure 3. a:(left) The spectral index α(60µm−25µm) versus the[NeV]14.3µm/[NeII]12.8µm line ratio: the solid line fitting the data is themodel and the dashed lines separate the diagram in 3 regions with differentAGN contribution, (100% - 70%),(70% - 50%), (50% - 0%). b:(right) EW[NeII]12.8µm vs EW PAH 11.25µm: same notation as in Fig.3a.0.1 × L(12µm) < L(2 − 10keV ) < L(12µm)Most HBLR-Seyfert 2’s have:0.01 × L(12µm) < L(2 − 10keV ) < 0.1 × L(12µm)Most pure Seyfert 2’s and non-Seyfert’s have:L(2 − 10keV ) < 0.01 × L(12µm)We preminilarily suggest that black hole accretion, as measured by X-rays, isthe dominant mechanism determining the observational nature of a galaxy: whenaccretion is not an important energy source, we have galaxies without Seyfertnuclei, dominated by stellar evolution processes (called here non-Seyfert’s), thenwhen accretion increases we have a sequence from the pure Seyfert 2’s, to theHBLR-Seyfert 2’s and finally when accretion dominates the bolometric luminos-ity, we have the Seyfert 1’s.In an analogous way, we try to correlate the IRAS 60µm luminosity (mea-suring the integrated star formation activity) and the H2 S(1) line luminosity(typical star formation indicator) in Figure 4bMost Seyfert 1’s and HBLR-Seyfert 2’s have:L(H2) ∼ 5 × 10−4× L(60µm)Most pure Seyfert 2’s and non-Seyfert have:L(H2) ∼ 10−4× L(60µm)If we make least squares fits to the two extreme populations of Seyfert type1’s and non-Seyfert galaxies, we obtain a sequence of two almost parallel linesof the form Log(L(60µm)) = a × log(L(H2)) + b from the bottom to the top:- for Seyfert 1’s: a=0.905, b=7.325, with a regression coefficient of R=0.928;- for non-Seyfert’s: a=1.030, b=2.797, with R=0.925.There are two interpretations of this behavior: either the more active galax-ies (type 1’s) have enhanced H2 emission (Rigopoulou et al 2002), or at a givenSpitzer spectra of Seyfert galaxies 5 bona fide SY1 (RMS93,Tran’03) HBLR-SY2 (RMS93,Tran’03,Shu+’07) non-HBLR-SY2 (RMS93,Tran’03,Shu+’07) SY2 no-pol-data (RMS93,Tran’03,Shu+’07) non-SY (RMS93,Tran’03) bona fide SY1 (RMS93,Tran’03) HBLR-SY2 (RMS93,Tran’03,Shu+’07) non-HBLR-SY2 (RMS93,Tran’03,Shu+’07) SY2 no-pol-data(RMS93,Tran’03,Shu+’07) non-SY (RMS93,Tran’03)Figure 4. a:(left) Corrected (unabsorbed) X-ray (2-10 keV) luminosityas a function of the 12µm luminosity. The three lines from the top to thebottom indicate the loci of L(2-10keV) = L(12µm) (upper); L(2-10keV) = 0.1× L(12µm) (middle); and L(2-10keV) = 0.01 × L(12µm) (lower), which areused in the text to roughly separate the different objects. b:(right) Total60µm luminosity as a function of the H2 17µm line luminosity. The two linesfrom the top to the bottom are least squares fits of the non-Seyfert galaxiesand of the Seyfert 1’s, respectively (see the text)H2 luminosity, type 2’s (and non-Sy) have L(60µm) 5 times higher than type1’s, because of an enhanced star formation process.ReferencesGenzel, R. et al, 1998, ApJ, 498, 579Rigopoulou, D., Kunze, D., Lutz, D., Genzel, R., & Moorwood, A.F.M. 2002, A&A,389, 374Rush, B., Malkan, M.A., & Spinoglio, L. 1993, ApJS, 89, 1 (RMS).Spinoglio, L. & Malkan, M.A. 1989, ApJ, 342, 83Spinoglio, L., Malkan, M.A., Rush, B., Carrasco, L., Recillas-Cruz, E. 1995, ApJ, 453,616Tommasin, S., Spinoglio, L., Malkan, M.A., Smith, H., Gonzalez-Alfonso, E. & Char-mandaris, V. 2008, ApJ, 676, 836.Tommasin, S., Spinoglio, L., Malkan, M.A., Smith, H. 2009, in preparationTran, H.D., 2001, ApJ, 554, L19Tran, H.D., 2003, ApJ, 583, 632

Spitzer spectra of Seyfert galaxies

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