ISO-SWS Spectroscopy of NGC 1068

We present Infrared Space Observatory-Short Wave Spectrometer (ISO-SWS) spectroscopy of NGC 1068 for the complete wavelength range 2.4-45 μm at resolving power ~1500. Selected subranges have been observed at higher sensitivity and full resolving power ~2000. We detect a total of 36 emission lines and derive upper limits for 13 additional transitions. Most of the observed transitions are fine-structure and recombination lines originating in the narrow-line region (NLR) and the inner part of the extended emission-line region. We compare the line profiles of optical lines and reddening-insensitive infrared lines to constrain the dynamical structure and extinction properties of the NLR. The most likely explanation of the considerable differences found is a combination of two effects: (1) The spatial structure of the NGC 1068 NLR is a combination of a highly ionized outflow cone and lower excitation extended emission. (2) Parts of the NLR, mainly in the receding part at velocities above systemic, are subject to extinction that is significantly suppressing optical emission from these clouds. Line asymmetries and net blueshifts remain, however, even for infrared fine-structure lines suffering very little obscuration. This may be either due to an intrinsic asymmetry of the NLR, as perhaps also suggested by the asymmetric radio continuum emission or due to a very high column density obscuring component which is hiding part of the NLR even from infrared view. We present detections and limits for 11 rotational and rovibrational emission lines of molecular hydrogen (H2). They arise in a dense molecular medium at temperatures of a few hundred kelvins that is most likely closely related to the warm and dense components seen in the near-infrared H2 rovibrational transitions, and in millimeter-wave tracers (CO, HCN) of molecular gas. Any emission of the putative parsec-scale molecular torus is likely overwhelmed by this larger scale emission. In companion papers we use the SWS data to derive the spectral energy distribution emitted by the active nucleus of NGC 1068, to put limits on infrared emission from the obscured broad-line region, and discuss the continuum and its features in conjunction with SWS spectra of other galaxies.

[1]  A. Sternberg,et al.  Infrared Spectroscopy of NGC 1068: Probing the Obscured Ionizing AGN Continuum , 2000, astro-ph/0002107.

[2]  A. Sternberg,et al.  A Search for Broad Infrared Recombination Lines in NGC 1068 , 1999, astro-ph/9910101.

[3]  Rodger I. Thompson,et al.  NICMOS observations of two classic AGNS , 1999 .

[4]  A. Sternberg,et al.  Infrared Spectroscopy of NGC 4151: Infrared Space Observatory Observations and Narrow Emission Line Region Line Profiles , 1999 .

[5]  A. Sternberg,et al.  Infrared Spectroscopy of NGC 4151: Probing the Obscured Ionizing Active Galactic Nucleus Continuum , 1998, astro-ph/9809094.

[6]  A. Sternberg,et al.  The Ratio of Ortho- to Para-H2 in Photodissociation Regions , 1998, astro-ph/9812049.

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

[8]  R. Davies,et al.  Star formation in the circumnuclear environment of NGC 1068 , 1998, astro-ph/9806345.

[9]  R. Terlevich,et al.  HI Observations of NGC 1068 , 1997 .

[10]  Pierre Ferruit,et al.  Bi-Dimensional Spectrography at HST-Like Spatial Resolution: [OIII] Kinematics and Ionization in the NLR of NGC 1068 , 1997 .

[11]  D. Kunze,et al.  What Powers Ultraluminous IRAS Galaxies? , 1997, astro-ph/9711255.

[12]  Andreas Quirrenbach,et al.  The Nuclear Stellar Core, the Hot Dust Source, and the Location of the Nucleus of NGC 1068 , 1997 .

[13]  E. Valentijn,et al.  New Wavelength Determinations of Mid-Infrared Fine-structure Lines by Infrared Space Observatory Short Wavelength Spectrometer , 1997 .

[14]  A. Sternberg,et al.  ISO-SWS Observations of NGC 1068 , 1997 .

[15]  I. Glass.  Variability in the Nucleus of NGC 1068 , 1997 .

[16]  F. Macchetto,et al.  Jet-Driven Motions in the Narrow-Line Region of NGC 1068 , 1997, astro-ph/9801253.

[17]  Margarita Karovska,et al.  Astronomical Data Analysis Software and Systems VI , 1997 .

[18]  A. Tielens,et al.  X-Ray--irradiated Molecular Gas. I. Physical Processes and General Results , 1996 .

[19]  L. Blitz,et al.  High-Resolution Berkeley-Illinois-Maryland Association Observations of CO, HCN, and 13CO in NGC 1068 , 1995 .

[20]  J. Hough,et al.  Spatially resolved spectropolarimetry of the galaxy NGC 1068 , 1995 .

[21]  W. Sparks,et al.  HST Imaging Polarimetry of NGC 1068 , 1995 .

[22]  A. Sternberg,et al.  HCN and CO in the nucleus of NGC 1068 , 1994 .

[23]  William B. Sparks,et al.  HST/FOC imaging of the narrow-line region of NGC 1068 , 1994 .

[24]  A. Sternberg,et al.  NEAR-INFRARED SPECTROSCOPIC IMAGING OF THE CIRCUMNUCLEAR ENVIRONMENT OF NGC 1068 , 1994 .

[25]  R. Genzel,et al.  The Nature of the dense obscuring material in the nucleus of NGC 1068 , 1993 .

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

[27]  C. Beichman,et al.  High-resolution mid-infrared imaging and astrometry of the nucleus of the Seyfert galaxy NGC 1068 , 1993 .

[28]  M. Malkan,et al.  Infrared line diagnostics of active galactic nuclei , 1992 .

[29]  D. Axon,et al.  TAURUS observations of the [O III] cone in NGC 1068 , 1992 .

[30]  A. Kinney,et al.  HST imaging of the inner 3 arcseconds of NGC 1068 in the light of forbidden O III 5007 A , 1991 .

[31]  S. Veilleux.  A study of the structure and kinematics of the narrow-line region in Seyfert galaxies. I, Atlas of line profiles , 1991 .

[32]  B. Draine,et al.  On the H2 line emission from NGC 6240 and other starburst galaxies , 1990 .

[33]  G. Cecil,et al.  Imaging spectrophotometry of ionized gas in NGC 1068. I - Kinematics of the narrow-line region , 1990 .

[34]  A. Moorwood,et al.  Detection of forbidden Si VI 1. 962 microns and new observations of infrared H, forbidden Fe II, and H2 line emission in the Seyfert galaxy NGC 1068 , 1990 .

[35]  Julian H. Krolik,et al.  The physical state of the obscuring torus in Seyfert galaxies , 1989 .

[36]  C. Telesco,et al.  The infrared structure and the origin of the starburst disk in NGC 1068 , 1988 .

[37]  Martin J. Ward,et al.  The polarization of NGC 1068. , 1988 .

[38]  M. Robertis,et al.  Extinction, profile asymmetry, and tidal effects in Seyfert and starburst galaxies , 1988 .

[39]  R. Pogge.  Extended ionizing radiation cone from the nucleus of the Seyfert 2 galaxy NGC 1068 , 1988 .

[40]  I. Appenzeller,et al.  High-ionization line profiles of Seyfert galaxies , 1988 .

[41]  S. Myers,et al.  The Molecular Cloud Ring in NGC 1068 , 1987 .

[42]  M. Whittle.  The narrow line region of active galaxies. III: Profile comparisons , 1985 .

[43]  J. Miller,et al.  Spectropolarimetry and the nature of NGC 1068 , 1985 .

[44]  N. Carleton,et al.  Seyfert galaxy narrow-line regions. I - Observations of forbidden O III lambda 5007 , 1985 .

[45]  D. Osterbrock,et al.  An analysis of the narrow line profiles in Seyfert 2 galaxies , 1985 .

[46]  M. Whittle.  The narrow line region of active galaxies – I. Nuclear [O III] profiles , 1985 .

[47]  M. Ward,et al.  The Fe9+ region in active galactic nuclei , 1984 .

[48]  W. Sargent,et al.  Study of the close environment of the active nucleus in NGC 1068 by decomposition of forbidden O III and H-beta emission-line profiles , 1983 .

[49]  A. Wilson,et al.  Radio jets and high velocity gas in the Seyfert galaxy NGC 1068 , 1983 .

[50]  D. Pelat,et al.  High resolution line profiles in the Seyfert galaxy NGC 3783: The structure of the emitting regions , 1981 .

[51]  T. Heckman,et al.  Emission-line profiles and kinematics of the narrow-line region in Seyfert and radio galaxies , 1981 .

[52]  A. Koski.  Spectrophotometry of Seyfert 2 galaxies and narrow-line radio galaxies , 1978 .

[53]  Rodger I. Thompson,et al.  The 2 - 2.5 micron spectrum of NGC 1068: a detection of extragalactic molecular hydrogen. , 1978 .

[54]  G. Rieke,et al.  Infrared photometry and polarimetry of NGC 1068 , 1978 .

[55]  G. Rieke,et al.  The infrared spectrum of NGC 1068 , 1975 .

[56]  J. B. Oke,et al.  The emission-line spectrum of NGC 1068. , 1975 .

[57]  M. Walker.  Studies of Extragalactic Nebulae. V. Motions in the Seyfert Galaxy NGC 1068 , 1968 .