SPITZER-IRS HIGH-RESOLUTION SPECTROSCOPY OF THE 12 mum SEYFERT GALAXIES. II. RESULTS FOR THE COMPLETE DATA SET

Journal Article · Mon Feb 01 00:00:00 EST 2010 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/709/2/1257· OSTI ID:21392254

Tommasin, Silvia; Spinoglio, Luigi ^[1]; Malkan, Matthew A ^[2]; Fazio, Giovanni ^[3]

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1. Istituto di Fisica dello Spazio Interplanetario, INAF, Via Fosso del Cavaliere 100, I-00133 Roma (Italy)
2. Astronomy Division, University of California, Los Angeles, CA 90095-1547 (United States)
3. Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)

We present our Spitzer-Infrared Spectrometer (IRS) spectroscopic survey from 10 mum to 37 mum of the Seyfert galaxies of the 12 mum Galaxy Sample, collected in a high-resolution mode (R approx 600). The new spectra of 61 galaxies, together with the data we already published, give us a total of 91 12 mum Seyfert galaxies observed, out of 112. We discuss the mid-IR emission lines and features of the Seyfert galaxies, using an improved active galactic nucleus (AGN) classification scheme: instead of adopting the usual classes of Seyfert 1's and Seyfert 2's, we use the spectropolarimetric data from the literature to divide the objects into categories '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. The remaining category, AGN 2's, contains only Seyferts with no detectable broad lines in either direct or polarized spectroscopy. We present various mid-IR observables, such as ionization-sensitive and density-sensitive line ratios, the polycyclic aromatic hydrocarbon (PAH) 11.25 mum feature and the H{sub 2} S(1) rotational line equivalent widths (EWs), the (60-25 mum) spectral index, and the source extendedness at 19 mum, to characterize similarities and differences in the AGN populations, in terms of AGN dominance versus star formation dominance. We find that the mid-IR emission properties characterize all the AGN 1's objects as a single family, with strongly AGN-dominated spectra. In contrast, the AGN 2's can be divided into two groups, the first one with properties similar to the AGN 1's except without detected broad lines, and the second with properties 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 19 mum. For 59 galaxies with appropriate data, we can separate the 19 mum emission into AGN and starburst components using the measured mid-IR spectral features. We use these to quantify the brightness thresholds that an AGN must meet to satisfy our classifications: AGN 1's have an AGN contribution >=73% and AGN 2 >= 45% of their total emission at 19 mum. The detection of [Ne V] lines turns out to be an almost perfect signature of energy production by an AGN. Only four (approx7.5%) of 55 AGN 1's and two (10%) out of 20 AGN 2's do not have [Ne V] 14.3 mum down to a flux limit of approx4 x 10{sup -15} erg s{sup -1} cm{sup -2}. We present mean spectra of the various AGN categories. Passing from AGN-dominated to starburst-dominated objects, the continuum steepens, especially at wavelengths shorter than 20 mum, while the PAH feature increases in its EW and the high ionization lines decrease. We estimate H{sub 2} mass and excitation temperature through the measurement of the S(1) rotational line of this molecule. Finally, we derive the first local luminosity functions for the brightest mid-IR lines and the PAH feature at 11.25 mum. No statistical difference is apparent in the space densities for Seyfert 1's and 2's of a given line luminosity, or for the new classes of AGN 1's and 2's. We use the correlation between [Ne V] line and nonstellar IR continuum luminosity to derive the global output of accretion-powered galactic nuclei in the local universe.

• OSTI ID: 21392254
• Journal Information: Astrophysical Journal, Vol. 709, Issue 2; Other Information: DOI: 10.1088/0004-637X/709/2/1257; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
BRIGHTNESS
EMISSION
EXCITATION
GALAXY NUCLEI
HYDROGEN
INFRARED SPECTROMETERS
IONIZATION
LUMINOSITY
MASS
POLYCYCLIC AROMATIC HYDROCARBONS
SEYFERT GALAXIES
SPECTROSCOPY
STARS
UNIVERSE
AROMATICS
ELEMENTS
ENERGY-LEVEL TRANSITIONS
GALAXIES
HYDROCARBONS
MEASURING INSTRUMENTS
NONMETALS
OPTICAL PROPERTIES
ORGANIC COMPOUNDS
PHYSICAL PROPERTIES
SPECTROMETERS