We study for the first time the complete sub-millimeter spectra (450 GHz to
1550 GHz) of a sample of nearby active galaxies observed with the SPIRE Fourier
Transform Spectrometer (SPIRE/FTS) onboard Herschel. The CO ladder (from Jup =
4 to 12) is the most prominent spectral feature in this range. These CO lines
probe warm molecular gas that can be heated by ultraviolet photons, shocks, or
X-rays originated in the active galactic nucleus or in young star-forming
regions. In these proceedings we investigate the physical origin of the CO
emission using the averaged CO spectral line energy distribution (SLED) of six
Seyfert galaxies. We use a radiative transfer model assuming an isothermal
homogeneous medium to estimate the molecular gas conditions. We also compare
this CO SLED with the predictions of photon and X-ray dominated region (PDR and
XDR) models.Comment: Proceedings of the Torus Workshop 2012 held at the University of
  Texas at San Antonio, 5-7 December 2012. C. Packham, R. Mason, and A.
  Alonso-Herrero (eds.); 6 pages, 3 figure

Baes, M.

Barlow, M. J.

Boselli, A.

Busquet, G.

Cooray, A.

Cormier, D.

Glenn, J.

Isaak, K.

Kamenetzky, J.

Pereira-Santaella, M.

Rangwala, N.

Schirm, M. R. P.

Spinoglio, L.

English

arXiv

We study for the first time the complete sub-millimeter spectra (450 GHz to 1550 GHz) of a sample of nearby active galaxies observed with the SPIRE Fourier Transform Spectrometer (SPIRE/FTS) onboard Herschel. The CO ladder (from Jup = 4 to 12) is the most prominent spectral feature in this range. These CO lines probe warm molecular gas that can be heated by ultraviolet photons, shocks, or X-rays originated in the active galactic nucleus or in young star-forming regions. In these proceedings we investigate the physical origin of the CO emission using the averaged CO spectral line energy distribution (SLED) of six Seyfert galaxies. We use a radiative transfer model assuming an isothermal homogeneous medium to estimate the molecular gas conditions. We also compare this CO SLED with the predictions of photon and X-ray dominated region (PDR and XDR) models

Pereira-Santaella, M

Spinoglio, L

Busquet, G

Glenn, J

Isaak, K

Kamenetzky, J

Rangwala, N

Schirm, MRP

Baes, M

Barlow, MJ

Boselli, A

Cooray, A

Cormier, D

UCL Discovery

Proceedings of the Torus Workshop 2012 held at the University of Texas at San Antonio, 5-7 December2012. C. Packham, R. Mason, and A. Alonso-Herrero (eds.).Mid-J CO Emission in Nearby Seyfert GalaxiesMiguel Pereira-Santaella1, Luigi Spinoglio1, Gemma Busquet1, Jason Glenn2,Kate Isaak3, Julia Kamenetzky2, Naseem Rangwala2, Maximilien R. P. Schirm4,Maarten Baes5, Michael J. Barlow6, Alessandro Boselli7, Asantha Cooray8, andDiane Cormier91 Istituto di Astrofisica e Planetologia Spaziali, INAF, Via Fosso del Cavaliere 100, I-00133 Roma,Italy. e-mail: miguel.pereira@ifsi-roma.inaf.it2 Center for Astrophysics and Space Astronomy, 389-UCB, University of Colorado, Boulder, CO80303, USA3 ESA Astrophysics Missions Division, ESTEC, PO Box 299, 2200 AG Noordwijk, The Netherlands4 Dept. of Physics & Astronomy, McMaster University, Hamilton, Ontario, L8S 4M1, Canada5 Sterrenkundig Observatorium, Universiteit Gent, Krijgslaan 281 S9, B-9000 Gent, Belgium6 Department of Physics and Astronomy, University College London, Gower Street, London WC1E6BT,UK7 Laboratoire d’Astrophysique de Marseille - LAM, Universitè d’Aix-Marseille & CNRS, UMR7326,38 rue F. Joliot-Curie, 13388, Marseille Cedex 13, France8 Center for Cosmology, Department of Physics and Astronomy, University of California, Irvine, CA92697, USA9 Laboratoire AIM, CEA/DSM-CNRS-Universitè Paris Diderot, Irfu/Service d’Astrophysique, CEASaclay, F-91191, Gif-sur-Yvette, FranceAbstractWe study for the first time the complete sub-millimeter spectra (450 GHz to 1550 GHz) of asample of nearby active galaxies observed with the SPIRE Fourier Transform Spectrometer(SPIRE/FTS) onboard Herschela. The CO ladder (from Jup = 4 to 12) is the most promi-nent spectral feature in this range. These CO lines probe warm molecular gas that can beheated by ultraviolet photons, shocks, or X-rays originated in the active galactic nucleusor in young star-forming regions. In these proceedings we investigate the physical originof the CO emission using the averaged CO spectral line energy distribution (SLED) of sixSeyfert galaxies. We use a radiative transfer model assuming an isothermal homogeneousmedium to estimate the molecular gas conditions. We also compare this CO SLED withthe predictions of photon and X-ray dominated region (PDR and XDR) models.aHerschel is an ESA space observatory with science instruments provided by European-ledPrincipal Investigator consortia and with important participation from NASA.arXiv:1301.3365v1  [astro-ph.GA]  15 Jan 20132 Mid-J CO Emission in Nearby Seyfert Galaxies1 IntroductionTo date, the sub-millimeter (sub-mm) spectrum of galaxies has not been fully explored,in part due to the low transparency of the atmosphere in this range. The SPIRE Fouriertransform spectrometer (SPIRE/FTS) [2, 6, 12] onboard the Herschel Space Observatory [8]fills this gap, covering the spectral range between 450 and 1440 GHz (210 and 670 µm).In the SPIRE/FTS spectra the most obvious spectral feature is the mid-J CO ladder(Jup = 4 to 13). CO is one of the most abundant molecules in the interstellar medium;therefore it is considered a good tracer of the molecular gas phase. Specifically, the mid-JCO line emission originate from warm molecular gas (upper-level energies ranging from 55to 500 K above the ground state) that can be excited by ultraviolet (UV) photons in photondominated regions (PDRs; e.g., [14]), X-rays in X-ray dominated regions (XDRs; e.g., [5]) orby shocks (e.g., [1]).In these proceedings we analyze the average CO spectral line energy distribution(SLED) of local Seyfert galaxies, including both low- and mid-J CO transitions, in orderto understand the physical conditions of the warm molecular gas and the dominant excita-tion mechanism in this class of galaxies.2 Sub-mm Spectra of Local Seyfert GalaxiesWe obtained sub-mm SPIRE/FTS spectra of eleven nearby (d = 12 − 160 Mpc) Seyfertgalaxies selected from the 12µm Galaxy Sample [10] through two guaranteed time projects:“Bright Seyfert Nuclei: FTS spectroscopy” (PI: L. Spinoglio) and “Physical Processes in theInterstellar Medium of Very Nearby Galaxies” (PI: C. D. Wilson). Our sample includesgalaxies with different nuclear activity classes in similar proportions. Their infrared (IR)luminosities1 range from 1010 to 1012 L and their hard X-ray luminosities1 from 1040 to1043 erg s−1. The SPIRE/FTS beam size is 20–40′′ that corresponds to 1.4–32 kpc at thedistance of our galaxies. More details on the sample and data reduction are given in [7].In the SPIRE/FTS spectra of these galaxies we detected transitions of several molecules.The brightest lines are those produced by CO, but lines from other molecules like H2O,OH+, and HF are often detected. In addition, atomic lines from neutral gas ([C I] at 492and 809 GHz) and ionized gas ([N II] at 1461 GHz) are bright in these galaxies [7]. In theseproceedings we focus on the mid-J CO emission.For six of these galaxies we detected more than three CO lines at >3σ level in theirSPIRE/FTS spectra (see Figure 1) that were used, together with ground observations ofthe low-J CO lines (Jup = 1 to 3), to construct the CO SLEDs for each galaxy. The COSLEDs of five of them (UGC 05101, NGC 3227, NGC 4388, NGC 7130, and NGC 7582)are remarkably similar. Therefore we averaged them (normalized by their CO luminosity)to construct an average SLED which we used to study the typical conditions in the warmmolecular gas in Seyfert galaxies. We note that the Seyfert type, the AGN luminosity, or the1The IR luminosity refers to the 8–1000µm galaxy integrated luminosity while the hard X-ray luminosityis the 2–10 keV luminosity.Pereira-Santaella et al. 3500 600 700 800 900-20246CO 4-3CO 5-4CO 6-5CO 7-6CO 8-7[CI][CI]1000 1100 1200 1300 1400 15000246810CO 9-8CO 10-9CO 11-10H2O 220-211[NII]NGC3227νobs [GHz]Fν [Jy]Figure 1: Observed SPIRE/FTS spectra of the Seyfert 1.5 NGC 3227. The dashed red linesmark the position of the detected lines. The error bars indicate the median 1σ uncertainty.total IR luminosity (mainly related to their star-formation rate) do not seem to affect theCO SLED shape in our sample of galaxies.3 CO Emission Modeling3.1 Radiative Transfer ModelWe used the non-LTE radiative transfer code RADEX, with the assumption that the mid-J CO emission originates from a homogeneous medium, to infer the physical conditions ofthe emitting regions. We produced a grid of models that was used to model the averageCO SLED. The best fit RADEX model is shown in Figure 2 (dotted red line). The derivedkinetic temperature is 500+500−250 K and the H2 density 103.7±1.0 cm−3. As expected, these valuesagree with those obtained from the individual galaxies (see [7]). Moreover, these conditionsare similar to those observed in the starburst M 82 [3]. Differently, in the ultra-luminousIR galaxy Arp 220 the gas temperature is higher (∼ 1300 K) [9], whereas in the Seyfert 2NGC 1068 it is lower (∼ 90 K) [11]. This is consistent with the mid-J CO emission fromour sub-sample of Seyfert galaxies being driven by star-formation activity rather than by theAGN.3.2 PDR ModelsIn star-forming regions where UV photons from young stars heat the ISM we expect PDRexcitation of the molecular gas. Therefore we compared the average CO SLED with the PDRmodels of [14]. In Figure 2 we plot the best-fit model (solid green line). The plotted model cor-responds to nH2 = 104.25 cm−3 and far-UV flux 105.5G0, where G0 = 1.6×10−3 erg cm−2 s−1.4 Mid-J CO Emission in Nearby Seyfert Galaxies2 4 6 8 10 12 14Jup0.0010.0100.100CO Norm. LuminosityRADEXPDRXDR AXDR BXDR CFigure 2: Average CO SLED of our sample of nearby Seyfert galaxies (gray squares) nor-malized by the total CO luminosity. The dotted red line represents the best-fit RADEXmodel. The solid green line is the best-fit PDR model [14]. XDR models of [5] are plottedwith purple, blue, and orange dashed lines (see Section 3.3).However, models with nH2 = 104.2 − 105.0 cm−3 and FFUV = 10 − 106.5G02 also provideequally good fits. These PDR models provide a good fit to the emission of CO lines withJup < 8, however emission from higher-J transitions is clearly underpredicted.Figure 3 shows the LCO/LIR3 ratio as a function of the incident far-UV flux and gasdensity. In our galaxies this ratio is ∼10−4, however this is a lower limit because not allthe IR luminosity have to be associated with the warm molecular gas emitting the mid-JCO lines. Consequently, from this figure we can constrain the far-UV radiation field to bebetween 10 and 104G0.3.3 XDR ModelsWe also fitted our averaged CO SLED using the XDR models of [5]. These authors modelthree possible scenarios for XDR emission: high-density (nH2 ∼ 104 − 106.5 cm−3) compactmolecular clouds close to the AGN (XDR A); “traditional” mid-range density (nH2 ∼ 103 −104 cm−3) molecular clouds (XDR B); and diffuse molecular gas (nH2 ∼ 102−103 cm−3) whereXDR B type clouds are usually embedded (XDR C). The best-fit models are plotted in Figure2 with dashed lines. The XDR models better reproduce the CO emission for Jup > 8 thando the PDR models. The best one is the XDR B, although it systematically underpredictsthe CO luminosities for Jup > 8. Conversely, the XDR A model underpredict CO lines withJup < 6, but agrees with the observed higher-J emission.2FFUV = 106.5G0 is the upper limit of the grid of PDR models, so higher FFUV could be compatible aswell.3LCO is defined as the integrated luminosity of the CO lines from Jup = 4 to Jup = 12.Pereira-Santaella et al. 50 1 2 3 4 5 6log FUV [G0]123456log n [cm-3]-10-8-6-6-4-4-2 -2Figure 3: The black contours represent the logarithm of the LCO/LIR ratio as a functionof the incident far-UV flux and gas density. The models capable of fitting the observed COSLED (up to Jup = 7) are marked with a shaded green area. We assumed LIR = 2×LFUV [4].The LCO/LX4 ratio, for these two XDR models is ∼10−4; therefore for our Seyfertgalaxies the observed LCO implies X-ray luminosities 100 − 10 000 times higher than thoseobserved. Other XDR models in these grids have higher LCO/LX ratios (up to ∼10−2) thatwould be compatible with the AGN luminosities although they produce worse fits to the COSLED. On the other hand we can reject the extended diffuse XDR emission (C model) sincethe observed CO surface brightness in our galaxies (>10−6 erg cm−2 s−1 sr−1) is almost twoorder of magnitude higher than that of the best-fit model (5 × 10−8 erg cm−2 s−1 sr−1).4 Summary and ConclusionsWe obtained the CO SLED (from Jup = 1 to 12) of six nearby Seyfert galaxies using SPIRE/FTS spectroscopic observations. The average CO SLED was fitted using simple radiativetransfer models (RADEX) as well as more elaborate PDR and XDR models.From the RADEX modeling we derived a kinetic temperature of 500+500−250 K and H2density of 103.7±1.0 cm−3. However, we note that an homogeneous model with a single tem-perature and gas density may not be a realistic representation of the molecular gas conditionsin a Seyfert galaxy.PDR models can explain the observed CO SLED up to Jup ∼ 8. Higher J CO linesare underpredicted by these models and another component (PDR or XDR) is needed toreproduce the SLED. We also show that XDR models can fit the CO SLED, however themeasured LCO/LX ratios disagree with those expected for these models. Nevertheless, there4LX is the 1–100 keV X-ray luminosity.6 Mid-J CO Emission in Nearby Seyfert Galaxiesare XDR models compatible with the observed LCO/LX ratios, although they do not fit wellthe CO SLED. In summary, an individual PDR or XDR model cannot explain the observedCO emission in these local Seyfert galaxies and, at least, two components (two PDRs orPDR+XDR) are needed.Future high sensitivity and high angular resolution observations with ALMA of themid-J CO lines will help to disentangle the AGN and star-formation CO emission, as wellas, to determine the excitation mechanism and heating source of the warm molecular gas.AcknowledgmentsThis work has been funded by the Agenzia Spaziale Italiana (ASI) under contract I/005/11/0. SPIREhas been developed by a consortium of institutes led by Cardiff Univ. (UK) and including: Univ.Lethbridge (Canada); NAOC (China); CEA, LAM (France); IFSI, Univ. Padua (Italy); IAC (Spain);Stockholm Observatory (Sweden); Imperial College London, RAL, UCL-MSSL, UKATC, Univ. Sussex(UK); and Caltech, JPL, NHSC, Univ. Colorado (USA). This development has been supported bynational funding agencies: CSA (Canada); NAOC (China); CEA, CNES, CNRS (France); ASI (Italy);MCINN (Spain); SNSB (Sweden); STFC, UKSA (UK); and NASA (USA). This research has madeuse of the NASA/IPAC Extragalactic Database (NED) which is operated by the Jet PropulsionLaboratory, California Institute of Technology, under contract with the National Aeronautics andSpace Administration.References[1] Flower, D. R. & Pineau Des Forêts, G. 2010, MNRAS, 406, 1745[2] Griffin, M. J., Abergel, A., Abreu, A., et al. 2010, A&A, 518, L3[3] Kamenetzky, J., Glenn, J., Rangwala, N., et al. 2012, ApJ, 753, 70[4] Kaufman, M. J., Wolfire, M. G., Hollenbach, D. J., & Luhman, M. L. 1999, ApJ, 527, 795[5] Meijerink, R., Spaans, M., & Israel, F. P. 2006, ApJ, 650, L103[6] Naylor, D. A., Baluteau, J.-P., Barlow, M. J., et al. 2010, in SPIE Conference Series, Vol. 7731[7] Pereira-Santaella, M., Spinoglio, L., Busquet, G., et al. 2013, ApJ submitted[8] Pilbratt, G. L., Riedinger, J. R., Passvogel, T., et al. 2010, A&A, 518, L1[9] Rangwala, N., Maloney, P. R., Glenn, J., et al. 2011, ApJ, 743, 94[10] Rush, B., Malkan, M. A., & Spinoglio, L. 1993, ApJS, 89, 1[11] Spinoglio, L., Pereira-Santaella, M., Busquet, G., et al. 2012, ApJ, 758, 108[12] Swinyard, B. M., Ade, P., Baluteau, J.-P., et al. 2010, A&A, 518, L4[13] van der Tak, F. F. S., Black, J. H., Schöier, F. L., Jansen, D. J., & van Dishoeck, E. F. 2007,A&A, 468, 627[14] Wolfire, M. G., Hollenbach, D., & McKee, C. F. 2010, ApJ, 716, 1191

Mid-J CO Emission in Nearby Seyfert Galaxies

We study for the first time the complete sub-millimeter spectra (450 GHz to
1550 GHz) of a sample of nearby active galaxies observed with the SPIRE Fourier
Transform Spectrometer (SPIRE/FTS) onboard Herschel. The CO ladder (from Jup =
4 to 12) is the most prominent spectral feature in this range. These CO lines
probe warm molecular gas that can be heated by ultraviolet photons, shocks, or
X-rays originated in the active galactic nucleus or in young star-forming
regions. In these proceedings we investigate the physical origin of the CO
emission using the averaged CO spectral line energy distribution (SLED) of six
Seyfert galaxies. We use a radiative transfer model assuming an isothermal
homogeneous medium to estimate the molecular gas conditions. We also compare
this CO SLED with the predictions of photon and X-ray dominated region (PDR and
XDR) models

Oxford University Research Archive (ORA)

Mid-J CO emission in nearby Seyfert galaxies

Pereira-Santaella, Miguel

Oxford University Research Archive

TORUS2012workshopTORUS 2012workshopScientific MotivationThe nature and origin of the dusty material at the heart of active galaxies - whether it is inflowing, outflowing, its relation to star formation, etc. - has profound implications for our understanding of the evolution and lifecycle of AGN.A sound understanding of local AGN will also allow us to model them with confidence and apply our models to forthcoming observations of objects in the distant Universe. The last few years have seen numerous developments in the field: exquisitely sensitive Spitzer spectra have revealed the infrared properties of large numbers of AGN; mid-infrared interferometry is an increasingly mature technique; and models of increasing sophistication have been developed to explore the observations, to name just a few examples. By gathering the specialists in these and related areas, we can ensure that knowledge is shared, ideas debated, and that we come to the best possible understanding of the dusty structures in AGN.The University of Texas at San Antonio,December 5-7, 2012ii© 2012 The University of Texas at San Antonio LibrariesTorus Workshop 2012 Conference Proceedings published by The University of Texas at San Antonio Libraries. Content usage rights are specified by the Creative Commons Attribution-NonCommercial-NoDerivs (CC-BY-NC-ND) license.iiiCo-chair: Rachel MasonCo-chair: Almudena Alonso HerreroMoshe ElitzurSarah GallagherPoshak GandhiSebastian HonigMasa ImanishiNancy LevensonRodrigo NemmenChris PackhamCristina Ramos AlmeidaRalf SiebenmorgenChair: Chris PackhamSunil FernandesEnrique LopezLaura McMasterMarilyn MooreEric SchlegelLaura VegaTORUS Workshop 2012 Committee MembersSCIENTIFIC ORGANIZING COMMITTEE LOCAL ORGANIZING COMMITTEEContributing EditorsRachel Mason, Almudena Alonso-Herrero & Chris PackhamDevelopersHeather Williams and Joel JuarezivAlmudena Alonso-Herrero, IFCA, SpainItziar Aretxaga. INAOE, MexicoAndrés Asensio Ramos, IAC, SpainDaniel Asmus, MPIfR, GermanyJim Braatz, NRAO, USALeonard Burtscher, MPIA, GermanyMoshe Elitzur, University of Kentucky, USAPilar Esquej, CAB, SpainAnna Feltre, ESO, GermanySunil Fernandes, UTSA, USASarah Gallagher, UWO, CanadaPoshak Gandhi, JAXA, JapanAndy Goulding, CfA, USAAllison Hill, UWO, CanadaLuis Ho, Carnegie Observatories, USASebastian Hönig, UCSB, USAKohei Ichikawa, University of Kyoto, JapanMasa Imanishi, NAOJ, JapanToshihiro Kawaguchi, University of Tsukuba, JapanMakoto Kishimoto, MPIfR, GermanyJulian Krolik, Johns Hopkins University, USAStefanie LaMassa, Yale University, USA Andy Lawrence, ROE, UKNancy Levenson, Gemini ObservatoryEnrique López, University of Florida, USANoel López, Leiden Observatory, USAMariela Martínez, INAOE, MexicoRachel Mason, Gemini ObservatoryLaura McMaster, UTSA, USAMatt Merlo, Florida Institute of Technology, USAMarilyn Moore, UTSA, USARodrigo Nemmen, NASA Goddard, USARobert Nikutta, Universidad Andrés Bello, ChileNagisa Oi, JAXA, JapanChris Packham, UTSA, USAFrancesca Panessa, IAPS, INAF, ItalyMiguel Pereira-Santaella, IFSI, INAF, ItalyEric Perlman, Florida Institute of Technology, USACristina Ramos Almeida, IAC, SpainJosé Miguel Rodríguez Espinosa, IAC, SpainMarc Schartmann, MPE, GermanyEric Schlegel, UTSA, USAMarko Stalevski, Astronomical Observatory Belgrade, SerbiaYoshiki Toba, JAXA, JapanKonrad Tristram, MPIfR, GermanyYoshihiro Ueda, University of Kyoto, JapanLaura Vega, UTSA, USAMartin Ward, University of Durham, UKTORUS Workshop 2012 ParticipantsABSTRACTWe study for the first time the complete sub-millimeter spectra (450 GHz to 1550 GHz) of a sample of nearby active galaxies observed with the SPIRE Fourier Transform Spectrometer (SPIRE/FTS) onboard Herschela . The CO ladder (from Jup = 4 to 12) is the most prominent spectral feature in this range. These CO lines probe warm molecular gas that can be heated by ultraviolet photons, shocks, or X-rays originated in the active galactic nucleus or in young star-forming regions. In these proceedings we investigate the physical origin of the CO emission using the averaged CO spectral line energy distribution (SLED) of six Seyfert galaxies. We use a radiative transfer model assuming an isothermal homogeneous medium to estimate the molecular gas conditions. We also compare this CO SLED with the predictions of photon and X-ray dominated region (PDR and XDR) models.Article 2.4Mid-J CO Emission in Nearby Seyfert Galaxies25Miguel Pereira-Santaella, Luigi Spinoglio, Gemma Busquet, Jason Glenn, Kate Isaak, Julia Kamenetzky, Naseem Rangwala, Maximilien R. P. Schirm, Maarten Baes, Michael J. Barlow, Alessandro Boselli, Asantha Cooray, and Diane CormieraHerschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.Miguel Pereira-Santaella1, Luigi Spinoglio1, Gemma Busquet1, Jason Glenn2, Kate Isaak3, Julia Kamenetzky2, Naseem Rangwala2, Maximilien R. P. Schirm4, Maarten Baes5, Michael J. Barlow6, Alessandro Boselli7, Asantha Cooray8, and Diane Cormier91 Istituto di Astrofisica e Planetologia Spaziali, INAF, Via Fosso del Cavaliere 100, I-00133 Roma, Italy. e-mail: miguel.pereira@ifsi-roma.inaf.it2 Center for Astrophysics and Space Astronomy, 389-UCB, University of Colorado, Boulder, CO 80303, USA3 ESA Astrophysics Missions Division, ESTEC, PO Box 299, 2200 AG Noordwijk, The Netherlands4 Dept. of Physics & Astronomy, McMaster University, Hamilton, Ontario, L8S 4M1, Canada5 Sterrenkundig Observatorium, Universiteit Gent, Krijgslaan 281 S9, B-9000 Gent, Belgium6 Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT,UK7 Laboratoire d’Astrophysique de Marseille - LAM, Universitè d’Aix-Marseille & CNRS, UMR7326, 38 rue F. Joliot-Curie, 13388, Marseille Cedex 13, France8 Center for Cosmology, Department of Physics and Astronomy, University of California, Irvine, CA 92697, USA9 Laboratoire AIM, CEA/DSM-CNRS-Universitè Paris Diderot, Irfu/Service d’Astrophysique, CEA Saclay, F-91191, Gif-sur-Yvette, France261 IntroductionTo date, the sub-millimeter (sub-mm) spectrum of galaxies has not been fully explored, in part due to the low transparency of the atmosphere in this range. The SPIRE Fourier transform spectrometer (SPIRE/FTS) [2, 6, 12] onboard the Herschel Space Observatory [8] fills this gap, covering the spectral range between 450 and 1440 GHz (210 and  670 μm). In the SPIRE/FTS spectra the most obvious spectral feature is the mid-J CO ladder (Jup = 4 to 13). CO is one of the most abundant molecules in the interstellar medium; therefore it is considered a good tracer of the molecular gas phase. Specifically, the mid-J CO line emission originate from warm molecular gas (upper-level energies ranging from 55 to 500 K above the ground state) that can be excited by ultraviolet (UV) photons in photon dominated regions (PDRs; e.g., [14]), X-rays in X-ray dominated regions (XDRs; e.g., [5]) or by shocks (e.g., [1]). In these proceedings we analyze the average CO spectral line energy distribution (SLED) of local Seyfert galaxies, including both low- and mid-J CO transitions, in order to understand the physical conditions of the warm molecular gas and the dominant excitation mechanism in this class of galaxies.2 Sub-mm Spectra of Local Seyfert GalaxiesWe obtained sub-mm SPIRE/FTS spectra of eleven nearby (d = 12 − 16 Mpc) Seyfert galaxies selected from the 12 μm Galaxy Sample [10] through two guaranteed time projects: “Bright Seyfert Nuclei: FTS spectroscopy” (PI: L. Spinoglio) and “Physical Processes in the Interstellar Medium of Very Nearby Galaxies” (PI: C. D. Wilson). Our sample includes galaxies with different nuclear activity classes in similar proportions. Their infrared (IR) luminosities1 range from 1010 to 1012 L⊙ and their hard X-ray luminosities1 from 1040 to 1043 erg s−1 . The SPIRE/FTS beam size is 20–40′ ′  that corresponds to 1.4–32 kpc at the distance of our galaxies. More details on the sample and data reduction are given in [7]. In the SPIRE/FTS spectra of these galaxies we detected transitions of several molecules. The brightest lines are those produced by CO, but lines from other molecules like H2O, OH+, and HF are often detected. In addition, atomic lines from neutral gas ([C I] at 492 and 809 GHz) and ionized gas ([N II] at 1461 GHz) are bright in these galaxies [7]. In these proceedings we focus on the mid-J CO emission.For six of these galaxies we detected more than three CO lines at >3σ level in their SPIRE/FTS spectra (see Fig. 1) that were used, together with ground observations of the low-J CO lines (Jup = 1 to 3), to 271The IR luminosity refers to the 8–1000 μm galaxy integrated luminosity while the hard X-ray luminosity is the 2–10 keV luminosity.construct the CO SLEDs for each galaxy. The CO SLEDs of five of them (UGC 05101, NGC 3227, NGC 4388, NGC 7130, and NGC 7582) are remarkably similar. Therefore we averaged them (normalized by their CO luminosity) to construct an average SLED which we used to study the typical conditions in the warm molecular gas in Seyfert galaxies. We note that the Seyfert type, the AGN luminosity, or the total IR luminosity (mainly related to their star-formation rate) do not seem to affect the CO SLED shape in our sample of galaxies.Figure 1: Observed SPIRE/FTS spectra of the Seyfert 1.5 NGC 3227. e dashed red lines mark the position of the detected lines. e error bars indicate the median 1σ uncertainty.3 CO Emission Modeling3.1 Radiative Transfer ModelWe used the non-LTE radiative transfer code RADEX, with the assumption that the mid-J CO emission originates from a homogeneous medium, to infer the physical conditions of the emitting regions. We produced a grid of models that was used to model the average CO SLED. The best fit RADEX model is shown in Fig. 2 (dotted red line). The derived kinetic temperature is 500+500−250 K and the H2 density 103.7±1.0 cm−3. As expected, these values agree with those obtained from the individual galaxies (see [7]). Moreover, these conditions are similar to those observed in the starburst M 82 [3]. Differently, in the ultra-luminous IR galaxy Arp 220 the gas temperature is higher (∼ 1300 K) [9], whereas in the Seyfert 2 NGC 1068 it is lower (∼ 90 K) [11]. This is consistent with the mid-J CO emission from our sub-sample of Seyfert galaxies being driven by star-formation activity rather than by the AGN.3.2 PDR ModelsIn star-forming regions where UV photons from young stars heat the ISM we expect PDR excitation of the molecular gas. Therefore we compared the average CO SLED with the PDR models of [14]. In Fig. 2 we plot the best-fit model (solid green line). The plotted model corresponds to nH2 = 104.25 cm−3 and far-UV flux 105.5 G0, where G0 = 1.6 × 10−3 erg cm−2 s−1.28500 600 700 800 900-20246CO 4-3CO 5-4CO 6-5CO 7-6CO 8-7[CI][CI]1000 1100 1200 1300 1400 15000246810CO 9-8CO 10-9CO 11-10H2O 220-211[NII]NGC3227νobs [GHz]Fν [Jy]Figure 2: Average CO SLED of our sample of nearby Seyfert galaxies (gray squares) normalized by the total CO luminosity. e dotted red line represents the best-"t RADEX model. e solid green line is the best-"t PDR model [14]. XDR models of [5] are plotted with purple, blue, and orange dashed lines (see Section 3.3).However, models with nH2 = 104.2 − 105.0 cm−3 and FFUV = 10 − 106.5 G02 also provide equally good fits. These PDR models provide a good fit to the emission of CO lines with Jup < 8, however emission from higher-J transitions is clearly underpredicted. Fig. 3 shows the LCO /LIR3 ratio as a function of the incident far-UV flux and gas density. In our galaxies this ratio is ∼ 10−4, however this is a lower limit because not all the IR luminosity have to be associated with the warm molecular gas emitting the mid-J CO lines. Consequently, from this figure we can constrain the far-UV radiation field to be between 10 and 104 G0.3.3 XDR ModelsWe also fitted our averaged CO SLED using the XDR models of [5]. These authors model three possible scenarios for XDR emission: high-density (nH2 ∼ 104 − 106.5 cm−3) compact molecular clouds close to the AGN (XDR A); “traditional” mid-range density (nH2 ∼ 103 − 104 cm−3) molecular c louds (XDR B) ; and d i ffuse molecular gas (nH2 ∼ 102 − 103 cm−3) where XDR B type clouds are usually embedded (XDR C). The best-fit models are plotted in Fig. 2 with dashed lines. The XDR models better reproduce the CO emission for Jup > 8 than do the PDR models. The best one is the XDR B, although it systematically underpredicts the CO luminosities for Jup > 8. Conversely, the XDR A model underpredict CO lines with Jup > 6, but agrees with the observed higher-J emission.292 4 6 8 10 12 14Jup0.0010.0100.100CO Norm. LuminosityRADEXPDRXDR AXDR BXDR C2FFUV = 106.5 G0 is the upper limit of the grid of PDR models, so higher FFUV could be compatible as well.3LCO is defined as the integrated luminosity of the CO lines from Jup = 4 to Jup = 12.4LX is the 1–100 keV X-ray luminosity.Figure 3: e black contours represent the logarithm of the LCO /LIR ratio as a function of the incident far-UV %ux and gas density. e models capable of "tting the observed CO SLED (up to Jup = 7) are marked with a shaded green area. We assumed LIR = 2 × LFUV [4]. The LCO /LX4 ratio, for these two XDR models is ∼ 10−4; therefore for our Seyfert galaxies the observed LCO implies X-ray luminosities 100 − 10 000 times higher than those observed. Other XDR models in these grids have higher LCO /LX ratios (up to ∼ 10−2) that would be compatible with the AGN luminosities although they produce worse fits to the CO SLED. On the other hand we can reject the extended diffuse XDR emission (C model) since the observed CO surface brightness in our galaxies ( > 10−6 erg cm−2 s−1 sr−1) is almost two order of magnitude higher than that of the best-fit model (5 × 10−8 erg cm−2 s−1 sr−1).4 Summary and ConclusionsWe obtained the CO SLED (from Jup = 1 to 12) of six nearby Seyfert galaxies using SPIRE/FTS spectroscopic observations. The average CO SLED was fitted using simple radiative transfer models (RADEX) as well as more elaborate PDR and XDR models. From the RADEX modeling we derived a kinetic temperature of 500+500−250K and H2 density of 103.7±1.0 cm−3. However, we note that an homogeneous model with a single temperature and gas density may not be a realistic representation of the molecular gas conditions in a Seyfert galaxy. PDR models can explain the observed CO SLED up to Jup ∼ 8. Higher J CO lines are underpredicted by these models and another component (PDR or XDR) is needed to reproduce the SLED. We also show that XDR models can fit the CO SLED, however the measured LCO /LX ratios disagree with those expected for these models. Nevertheless, there are XDR models compatible with the observed LCO /LX ratios, although they do not fit well the CO SLED. In summary, an individual PDR or XDR model cannot explain the observed CO emission in these local Seyfert galaxies and, at least, two components (two PDRs or PDR+XDR) are needed. Future high sensitivity and high angular resolution observations with ALMA of the mid-J CO lines will help to disentangle the AGN and 300 1 2 3 4 5 6log FUV [G0]123456log n [cm-3]-10-8-6-6-4-4-2 -2star-formation CO emission, as well as, to determine the excitation mechanism and heating source of the warm molecular gas.AcknowledgmentsThis work has been funded by the Agenzia Spaziale Italiana (ASI) under contract I/005/11/0. SPIRE has been developed by a consortium of institutes led by Cardiff Univ. (UK) and including: Univ. Lethbridge (Canada); NAOC (China); CEA, LAM (France); IFSI, Univ. Padua (Italy); IAC (Spain); Stockholm Observatory (Sweden); Imperial College London, RAL, UCL-MSSL, UKATC, Univ. Sussex (UK); and Caltech, JPL, NHSC, Univ. Colorado (USA). This development has been supported by national funding agencies: CSA (Canada); NAOC (China); CEA, CNES, CNRS (France); ASI (Italy); MCINN (Spain); SNSB (Sweden); STFC, UKSA (UK); and NASA (USA). 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Mid-J CO Emission in Nearby Seyfert Galaxies

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