AGN with strong forbidden high‐ionization lines selected from the Sloan Digital Sky Survey

Department of Physics, Durham University, South Road, Durham DH1 3LE
Monthly Notices of the Royal Astronomical Society (Impact Factor: 5.11). 07/2009; 397(1):172 - 189. DOI: 10.1111/j.1365-2966.2009.14961.x
Source: arXiv


We have defined a sample of 63 active galactic nuclei with strong forbidden high-ionization line (FHIL) emission. These lines,
with ionization potentials ≳100 eV, respond to a portion of the spectrum that is often difficult to observe directly, thereby
providing constraints on the extreme ultraviolet-soft X-ray continuum. The sources are selected from the Sloan Digital Sky
Survey (SDSS) on the basis of their [Fe x]λ6374 Å emission, yielding one of the largest and the most homogeneous samples of FHIL-emitting galaxies. We fit a sequence
of models to both FHILs ([Fe xi], [Fe x] and [Fe vii]) and lower ionization emission lines ([O iii], [O i], Hα, [N ii], [S ii]) in the SDSS spectra. These data are combined with X-ray measurements from the ROSAT satellite, which are available for half of the sample. The correlations between these parameters are discussed for both the
overall sample and subsets defined by spectroscopic classifications. The primary results are evidence that (1) the [Fe x] and [Fe xi] lines are photoionized and their strength is proportional to the continuum flux around 250 eV, (2) the FHIL-emitting clouds
form a stratified outflow in which the [Fe x] and [Fe xi] source regions extend sufficiently close to the broad-line region that they are partially obscured in Seyfert 2s, whereas
the [Fe vii] source region is more extended and is unaffected by obscuration, (3) narrow-lined Seyfert 1s (NLS1s) tend to have the strongest
[Fe x] flux (relative to lower ionization lines) and (4) the most extreme [Fe x] ratios (such as [Fe x]/[O iii] or [Fe x]/[Fe vii]) are found in the NLS1s with the narrowest broad lines and appear to be an optical-band indication of objects with strong
X-ray soft excesses.

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    • "This paper tests the validity and limitations of the unified scheme hypothesis for Seyfert galaxies. Here, we present results for a Seyfert galaxy sample defined by Gelbord et al. (2009, hereafter GMW09), using Very Large Array (VLA) survey images. This large sample contains a diverse types of Seyfert galaxies. "
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    ABSTRACT: We study the radio properties at 1.4 GHz of Seyfert galaxies with strong forbidden high-ionization lines (FHILs), selected from the Sloan Digital Sky Survey - a large-sized sample containing nearly equal proportion of diverse range of Seyfert galaxies showing similar redshift distributions compiled by Gelbord et al. (2009) using the Very Large Array survey images. The radio detection rate is low, 49%, which is lower than the detection rate of several other known Seyfert galaxy samples. These galaxies show low star formation rates and the radio emission is dominated by the active nucleus with $\le$10% contribution from thermal emission, and possibly, none show evidence for relativistic beaming. The radio detection rate, distributions of radio power, and correlations between radio power and line luminosities or X-ray luminosity for narrow-line Seyfert 1 (NLS1), Seyfert 1 and Seyfert 2 galaxies are consistent with the predictions of the unified scheme hypothesis. Using correlation between radio and [O\,III]\,$\lambda$ \,5007\,\AA\ luminosities, we show that $\sim$8% sample sources are radio-intermediate and the remaining are radio-quiet. There is possibly an ionization stratification associated with clouds on scales of 0.1-1.0 kpc, which have large optical depths at 1.4 GHz, and it seems these clouds are responsible for free-free absorption of radio emission from the core, hence, leading to low radio detection rate for these FHIL-emitting Seyfert galaxies.
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    ABSTRACT: The spectra of AGN, from the ultraviolet to the near infrared, exhibit emission lines covering a wide range of ionization states, from neutral species such as [O i] λ 6300, up to [Fe iv] λ 5303. Here we report on some recent studies of the properties of highly ionized lines (HILs), plus two case studies of individual objects. Future IFU observations at high spatial and good spectral resolution will probe the excitation and kinematics of the gas in the zone between the extended NLR and unresolved BLR. Multi-component SED fitting can be used to link the source of photoionization with the strengths and ratios of the HILs.
    Preview · Article · Jul 2009 · Proceedings of the International Astronomical Union
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    ABSTRACT: We present an analysis of Space Telescope Imaging Spectrograph (STIS)/Hubble Space Telescope optical spectra of a sample of 10 Seyfert galaxies aimed at studying the structure and physical properties of the coronal-line region (CLR). The high spatial resolution provided by STIS allowed us to resolve the CLR and obtain key information about the kinematics of the CL gas, measure directly its spatial scale, and study the mechanisms that drive the high-ionization lines. We find CLRs extending from just a few parsecs ( pc) up to 230 pc in radius, consistent with the bulk of the coronal lines (CLs) originating between the broad-line region and narrow-line region (NLR), and extending into the NLR in the case of [Fe vii] and [Ne v] lines. The CL profiles strongly vary with the distance to the nucleus. We observed line splitting in the core of some of the galaxies. Line peak shifts, both redshift and blueshift, typically reached 500 km s−1, and even higher velocities (1000 km s−1) in some of the galaxies. In general, CLs follow the same pattern of rotation curves as low-ionization lines like [O iii]. From a direct comparison between the radio and the CL emission we find that neither the strength nor the kinematics of the CLs scales in any obvious and strong way with the radio jets. Moreover, the similarity of the flux distributions and kinematics of the CLs and low-ionization lines, the low temperatures derived for the gas, and the success of photoionization models to reproduce, within a factor of a few, the observed line ratios, point towards photoionization as the main driving mechanism of CLs.
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