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J/ApJ/653/127       9.7um silicate features in AGNs            (Shi+, 2006)

9.7µm silicate features in active galactic nuclei: new insights into unification models. Shi Y., Rieke G.H., Hines D.C., Gorjian V., Werner M.W., Cleary K., Low F.J., Smith P.S., Bouwman J. <Astrophys. J., 653, 127-136 (2006)> =2006ApJ...653..127S
ADC_Keywords: Active gal. nuclei ; Abundances Keywords: galaxies: active - galaxies: nuclei Abstract: We describe observations of 9.7um silicate features in 97 AGNs, exhibiting a wide range of AGN types and of X-ray extinction toward the central nuclei. We find that the strength of the silicate feature correlates with the HI column density estimated from fitting the X-ray data, such that low HI columns correspond to silicate emission, while high columns correspond to silicate absorption. The behavior is generally consistent with unification models in which the large diversity in AGN properties is caused by viewing-angle-dependent obscuration of the nucleus. Radio-loud AGNs and radio-quiet quasars follow roughly the correlation between HI columns and the strength of the silicate feature defined by Seyfert galaxies. The agreement among AGN types suggests a high-level unification with similar characteristics for the structure of the obscuring material. We demonstrate the implications for unification models qualitatively with a conceptual disk model. The model includes an inner accretion disk (<0.1pc in radius), a middle disk (0.110pc in radius) with a dense diffuse component and with embedded denser clouds, and an outer clumpy disk (10-300pc in radius). Description: Our sample (see table 1) includes a variety of types of AGNs: radio-loud quasars, FR II radio galaxies, Seyfert 1 and Seyfert 2 galaxies, broad absorption-line quasars (BALQs), low-ionization nuclear emission-line region (LINER) galaxies, and non-BAL radio-quiet quasars, including optically selected Palomar-Green (PG) quasars and IR quasars selected by the Two Micron All Sky Survey (2MASS), File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table1.dat 83 97 Source Characteristics refs.dat 42 25 References
Byte-by-byte Description of file: table1.dat
Bytes Format Units Label Explanations
1- 23 A23 --- Name Source name 25- 29 F5.3 --- z Redshift 31- 35 A5 --- Type AGN type (1) 37- 41 F5.2 --- Str Silicate feature strength (2) 43- 46 F4.2 --- E_Str ? Upper uncertainty limit in Str 48- 51 F4.2 --- e_Str ? Lower uncertainty limit in Str 53 I1 --- r_Str Reference on Str, in refs.dat file 55 A1 --- l_NH Limit flag on NH 57- 64 F8.3 10+22/cm2 NH ? Intrinsic H I column density 66- 72 F7.3 10+22/cm2 E_NH ? Upper uncertainty limit in NH 74- 80 F7.3 10+22/cm2 e_NH ? Lower uncertainty limit in NH 82- 83 I2 --- r_NH ? Reference on NH, in refs.dat file
Note (1): AGN type as follows: PG = PG quasar RLQ = radio-loud quasar Sy1 = Seyfert 1 galaxies Sy2 = Seyfert 2 galaxies BALQ = broad absorption-line quasar FRII = FR II radio galaxies LINER = low-ionization nuclear emission-line region 2MQ = 2MASS quasar Note (2): The strength of the 9.7um silicate feature is defined as (Ff-Fc)/Fc , where Ff and Fc and are the observed flux density and underlying continuum flux density, respectively, at the peak (for emission) or the minimum (for absorption) of the silicate feature. The feature strength in this definition is a direct measure of the optical depth for the silicate absorption.
Byte-by-byte Description of file: refs.dat
Bytes Format Units Label Explanations
1- 2 I2 --- Ref Reference number 4- 22 A19 --- BibCode BibCode 24- 42 A19 --- Aut Author's name
History: From electronic version of the journal
(End) Greg Schwarz [AAS], Patricia Vannier [CDS] 31-Jul-2008
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