The relation between AGN hard X-ray emission and mid-infrared continuum from ISO spectra: Scatter and unification aspects ,

We use mid-infrared spectral decomposition to separate the 6  μ m mid-infrared AGN continuum from the host emission in the ISO low resolution spectra of 71 active galaxies and compare the results to observed and intrinsic 2-10 keV hard X-ray fluxes from the literature. We find a correlation between mid-infrared luminosity and absorption corrected hard X-ray luminosity, but the scatter is about an order of magnitude, significantly larger than previously found with smaller statistics. Main contributors to this scatter are likely variations in the geometry of absorbing dust, and AGN variability in combination with non-simultaneous observations. There is no significant difference between type 1 and type 2 objects in the average ratio of mid-infrared and hard X-ray emission, a result which is not consistent with the most simple version of a unified scheme in which an optically and geometrically thick torus dominates the mid-infrared AGN continuum. Most probably, significant non-torus contributions to the AGN mid-IR continuum are masking the expected difference between the two types of AGN.

[1]  Yasushi Fukazawa,et al.  Excess hard X-ray emission from the obscured low luminosity AGN in the nearby galaxy M 51 (NGC 5194) , 2001 .

[2]  J. Bock,et al.  High-Resolution Mid-Infrared Imaging of the Nucleus of NGC 1068 , 1998, astro-ph/9807035.

[3]  G. Palumbo,et al.  BATSE Observations of the Piccinotti Sample of Active Galactic Nuclei , 1999 .

[4]  David H. Lumb,et al.  Simultaneous XMM-Newton and BeppoSAX observation of the Seyfert I galaxy IC 4329A , 2001 .

[5]  M. Gerin,et al.  ISOCAM-CVF 5-12 Micron Spectroscopy of Ultraluminous Infrared Galaxies , 2001, astro-ph/0101187.

[6]  J. Graham,et al.  Near-infrared continuum and 3.3 micrometer(s) polycyclic aromatic hydrocarbon imaging of the starburst ring in the type 1 Seyfert galaxy NGC 7469 , 1994 .

[7]  G. Matt,et al.  Compton reflection and iron fluorescence in BeppoSAX observations of Seyfert type 1 galaxies , 2002, astro-ph/0205045.

[8]  P. Gondoin,et al.  XMM-Newton observation of the Seyfert 1 galaxy Fairall 9 , 2001 .

[9]  Z. Ivezic,et al.  Dust Emission from Active Galactic Nuclei , 2002 .

[10]  W. Brandt,et al.  ASCA Observations of Two Ultraluminous IRAS Galaxies: IRAS 15307+3252 and IRAS 20460+1925 , 1997 .

[11]  G. Palumbo,et al.  High-Energy Spectra of Active Galactic Nuclei. II. Absorption in Seyfert Galaxies , 1997 .

[12]  A. Sternberg,et al.  ISO spectroscopy of star formation and active nuclei in the luminous infrared galaxy NGC 6240 , 2003, astro-ph/0307552.

[13]  M. Sauvage,et al.  Dust in an Extremely Metal-Poor Galaxy: Mid-infrared Observations ofSBS 0335–052 , 1998, astro-ph/9811126.

[14]  R. Della Ceca,et al.  A Three-dimensional Diagnostic Diagram for Seyfert 2 Galaxies: Probing X-Ray Absorption and Compton Thickness , 1998, astro-ph/9811074.

[15]  XMM-Newton observations of the Seyfert 1 galaxy ESO 141-G55 , 2003 .

[16]  G. Palumbo,et al.  Unveiling the AGN powering the "Composite" Seyfert/Star-forming galaxy NGC 7679: BeppoSAX and ASCA results , 2001, astro-ph/0106444.

[17]  C. Reynolds,et al.  An X-ray spectral study of 24 type 1 active galactic nuclei , 1997 .

[18]  R. Maiolino,et al.  An X-ray and near-IR spectroscopic analysis of the ULIRG IRAS 05189-2524 , 2000, astro-ph/0012506.

[19]  K. Nandra,et al.  GINGA observations of the X-ray spectra of Seyfert galaxies. , 1994 .

[20]  George H. Rieke,et al.  Low-luminosity and obscured seyfert nuclei in nearby galaxies , 1995 .

[21]  W. Brandt,et al.  Probing the Complex and Variable X-Ray Absorption of Markarian 6 with XMM-Newton , 2003, astro-ph/0304032.

[22]  A. Franceschini,et al.  Origin of the X-ray background and AGN unification: new perspectives , 2002, astro-ph/0205529.

[23]  L. Spinoglio,et al.  Multiwavelength energy distributions and bolometric luminosities of the 12 micron galaxy sample , 1995, astro-ph/9506139.

[24]  Robert K. Pina,et al.  Resolved Mid-Infrared Emission in the Narrow-Line Region of NGC 4151 , 2002, astro-ph/0212307.

[25]  W. Marshall,et al.  The recent history of the X‐ray absorber in NGC 3516 , 2000 .

[26]  T. Heckman.  A Mid-Infrared Test of the ``Obscuring Torus'' Model for Seyfert Nuclei , 1995 .

[27]  A. Tielens,et al.  Ice features in the mid-IR spectra of galactic nuclei , 2002, astro-ph/0202163.

[28]  J. Turner.  X‐ray spectra of a large sample of quasars with ASCA , 2000, astro-ph/0003080.

[29]  M. Sauvage,et al.  Dust emission in early-type galaxies: The mid-infrared view , 2003, astro-ph/0312029.

[30]  Peter J. Serlemitsos,et al.  Complete x-ray sample of the high-latitude (Vertical BarbVertical Bar>20/sup 0/) sky from HEAO 1 A-2: Log N-log S and luminosity functions , 1982 .

[31]  R. Siebenmorgen,et al.  Subarcsecond mid-infrared imaging of warm dust in the narrow-line region of NGC 1068 , 1993 .

[32]  Space Telescope Science Institute,et al.  Chandra X-Ray Observations of NGC 4151 , 2001 .

[33]  R. Edelson,et al.  Multiwavelength Monitoring of the Narrow-Line Seyfert 1 Galaxy Arakelian 564. I. ASCA Observations and the Variability of the X-Ray Spectral Components , 2001, astro-ph/0105283.

[34]  T. Boller,et al.  Mrk 1014: an AGN-dominated ultraluminous infrared galaxy , 2002 .

[35]  Robert Antonucci,et al.  Unified models for active galactic nuclei and quasars , 1993 .

[36]  J. Huchra,et al.  The Spatial Distribution of Active Galactic Nuclei: I. The Density of Seyfert Galaxies , 1992 .

[37]  G. Palumbo,et al.  A Multiwavelength Catalog of Seyfert 2 Galaxies Observed in the 2--10 keV Energy Band , 1996 .

[38]  R. Siebenmorgen,et al.  Mid-infrared spectral evidence for a luminous dust enshrouded source in Arp 220 , 2003, astro-ph/0310721.

[39]  Julian H. Krolik,et al.  Infrared spectra of obscuring dust tori around active galactic nuclei. I - Calculational method and basic trends , 1992 .

[40]  Alfred Krabbe,et al.  Infrared Imaging and Spectroscopy of NGC 7469 , 1995 .

[41]  K. Makishima,et al.  Detection of Excess Hard X-Ray Emission from the Optical Jet Galaxy NGC 1097 , 1996 .

[42]  A. Sternberg,et al.  Near-Infrared Spectral Imaging of NGC 1808: Probing the Starburst , 1994 .

[43]  P. Gondoin,et al.  ${XMM{-}Newton}$ observations of the Seyfert 1 galaxy NGC 3227 , 2004 .

[44]  K. Nandra,et al.  X-Ray Observations of Optically Selected, Radio-quiet Quasars. I. The ASCA Results , 1999, astro-ph/9910218.

[45]  C. Beichman,et al.  Infrared emission of normal galaxies from 2.5 to 12 micron: Infrared Space Observatory spectra, near-infrared continuum, and mid-infrared emission features , 2003, astro-ph/0301481.

[46]  P. Gondoin,et al.  XMM-Newton observations of the Seyfert 1 galaxy Mrk 335 , 2002 .

[47]  XMM-Newton observations of ULIRGs: A Compton-thick AGN in IRAS 19254–7245 , 2002, astro-ph/0211237.

[48]  R. Maiolino,et al.  N-Band Imaging of Seyfert Nuclei and the Mid-Infrared-X-Ray Correlation , 2000, astro-ph/0010119.

[49]  Columbia,et al.  Multi-wavelength study of the Seyfert 1 galaxy NGC 3783 with XMM-Newton , 2002, astro-ph/0206316.

[50]  W. Brandt,et al.  ASCA spectroscopy of IRAS 23060 + 0505: penetrating the torus of a type 2 quasar with X-rays , 1997 .

[51]  G. Rieke,et al.  New constraints on the unified model of Seyfert galaxies , 1995 .

[52]  M. Turner,et al.  Ginga observations of the X-ray spectra of quasars , 1997 .

[53]  Alberto Franceschini,et al.  Thick Tori around Active Galactic Nuclei: The Case for Extended Tori and Consequences for Their X-Ray and Infrared Emission , 1997 .

[54]  C. Simpson,et al.  The Nonstellar Infrared Continuum of Seyfert Galaxies , 2000, astro-ph/0012096.

[55]  M. Rowan-Robinson,et al.  Dusty discs in active galactic nuclei , 1995 .