A Comprehensive Spectral and Variability Study of Narrow‐Line Seyfert 1 Galaxies Observed by ASCA . II. Spectral Analysis and Correlations

Abstract

I present a comprehensive and uniform analysis of 25 ASCA observations from 23 narrow-line Seyfert 1 galaxies (NLS1s). The spectral analysis and correlations are presented in this paper ; the reduction and time series analysis are presented in the companion paper. A maximum likelihood analysis conÐrms that the hard X-ray photon index is signiÐcantly steeper at more than 90% conÐdence in this sample of NLS1s compared with a random sample of Seyfert galaxies with broad optical lines. Soft excess emission was detected in 17 of the 19 objects that had no signiÐcant absorption, a result that demonstrates that soft excesses appear considerably more frequently in NLS1s than in Seyfert 1 galaxies with broad optical lines. The strength of the soft excess, parameterized using a Ñux ratio obtained from the blackbody plus power-law model, has a wide range of values in these objects (a factor of 50). The photon index was found to be correlated with the Hb FWHM, despite the small range of the latter parameter ; however, neither parameter is correlated with the strength of the soft excess or ROSAT slope. Therefore, assuming that an excess of soft photons causes the steep photon index and narrow Hb FWHM, that excess may lie primarily in the unobservable EUV. The strength of the soft excess is correlated with the variability parameters, so that objects with strong soft excesses show higher amplitude variability ; this potentially important result is not easily explained. While a range of 2 orders of magnitude in luminosity is represented, the temperature of the soft excess is approximately consistent throughout the sample, in contrast with expectations of simple accretion disk models. The presence of ionized absorption was sought using a two-edge model. It was found that this component appears to be typically less common in NLS1s and some evidence was found that the typical ionization state is lower compared with broad-line Seyfert galaxies. This fact, plus evidence for a correlation between the presence of the warm absorber and signiÐcant optical polarization, may imply that the inner warm absorber is missing or is too highly ionized to be detected, and only the outer, dusty, less ionized warm absorber is present in many cases. The iron line equivalent width appears to be similar among narrow and broad-line Seyfert galaxies. This could mean that reprocessing occurs with similar geometry in both classes of objects ; however, the detection of ionized iron lines in a few objects, implying possibly altered Ñuorescence yields, and poor statistics, makes this conclusion tentative. Constraints on physical processes and models based on extreme values of orientation and accretion rate for NLS1s are examined in light of the observational results.

Iron Is Not Depleted in High-Ionization Nuclear Emission-Line Regions of Active Galactic Nuclei

“…Second, the inferred amount of extinction, 3 mag d A V d 10 mag, corresponds to (N H 0 ) $ (5-15) Â 10 21 cm À2 . This is far larger than the column density toward the nuclei of type 1 AGNs derived from X-ray spectral analysis (N H 0 ) d 10 21 cm À2 ; e.g., Reynolds 1997;Leighly 1999). These considerations suggest that it is hard to explain the observed data with the dusty models, even if a very large amount of dust selectively shielding only the HINERs is introduced.…”

Complex narrow-line Seyfert 1s: high spin or high inclination?

“…Any equatorial component to the velocity field will be suppressed in low inclination (simple) NLS1s, so their masses will be systematically biased towards higher values compared to high inclination (complex) NLS1s. Leighly (1999) gives the full width at half-maximum (FWHM) for the Hβ line widths in PG 1244+026 and 1H 0707−495 as 830 and 1050 km s −1 , respectively. These are corrected for Fe II and have the narrow Hβ component subtracted assuming that this is 0.1 times the [O III] line intensity (see also Leighly & Moore 2004).…”

The Black Hole Mass–stellar Velocity Dispersion Relation of Narrow-Line Seyfert 1 Galaxies

“…Sample selection NLS1s are generally defined with two criteria: (1) the fullwidth-at-half-maximum (FWHM) of broad component of the Balmer lines < 2000 km s −1 , and (2) the line flux ratio [O III]/Hβ < 3 (Osterbrock & Pogge 1985;Goodrich 1989). Additional characteristics of NLS1s include strong Fe II emission (Osterbrock & Pogge 1985), high Eddington ratio and soft X−ray emission (Leighly 1999;Grupe 2004;McHardy et al 2006). In this study, we selected a sample of NLS1s from SDSS DR7 (Abazajian et al 2009), based on the width of Balmer lines and the [O III]/Hβ flux ratios.…”