Infrared photometric study of SDSS selected narrow line Seyfert 1 galaxies

The infrared photometric study of SDSS selected Narrow Line Seyfert 1 Galaxies (NLS1s) is presented in this paper. We have made cross-identifications for such NLS1s with 2MASS and WISE observations. Finally 992 NLS1s have 2MASS and WISE counterparts. Comparisons of NLS1s with the Broad Line Seyfert 1 (BLS1s) and Seyfert 2 galaxies are made. It is shown that from 1 µm to 5 µm NLS1s are redder than BLS1s and Seyfert 2 galaxies possibly due to the richer dust environment in NLS1 nuclei or to the orientation effect while in the longer wavelengths those three kinds of sources have quite similar behavior indicative of radiation mainly from the similar warm starburst-related dust and the related AGN dust.In addition, relations between infrared colors and related (to H_β) strengths of some important lines are also investigated. The results show that the related strengths of [FeII] 4570 Å are positively correlated with infrared colors in the 1–5 µm region, but negatively correlated with infrared colors in the 12–22 µm region; the related strength of [OIII] 5007 Å are negatively correlated with infrared colors in the 1–5 µm region, but positively correlated with infrared colors in the 12–22 µm region; the related strength of [NII]6583 Å are also negatively correlated with infrared colors in the 1–5 µm region, but positively correlated with infrared colors in the 12–22 µm region. Therefore it is indicated that the behavior of [FeII] 4570 Å is just opposed to that for [OIII] 5007 Å and [NII] 6583 Å This result may be caused by different origins of such lines.     

Near-infrared spectra of Seyfert galaxies and line production mechanisms

New observations are reported of J -band spectra (1.04–1.4 μm) of three Seyfert 2 galaxies, Mkn 34, Mkn 78 and NGC 5929. In each case the spectral range includes the near-infrared lines of [Fe  ii ], [P  ii ], He  i and Paβ. Each Seyfert galaxy has a known radio jet, and we investigate the infrared line ratios of the nuclear and extended regions of each galaxy compared to the radio structure. In Mkn 34 there is a clear indication of an extranuclear region, probably coincident with a shock induced by the radio jet, in which [Fe  ii ] is considerably enhanced, although the nuclear emission is almost certainly the result of photoionization by the continuum of the active nucleus. Similar effects in extranuclear regions are seen in the other objects, in the case of Mkn 78 confirming recent studies by Ramos Almeida et al. A possible detection of extranuclear [P  ii ] emission suggests, if real, that photoionization by the active nucleus is the dominant line excitation mechanism over the whole source, including the regions coincident with the radio jet.     

Soft X-ray spectroscopy of Compton-thick Seyfert 2 galaxies with BeppoSAX

We present an X-ray spectroscopic study of the bright Compton-thick Seyfert 2 galaxies NGC 1068 and the Circinus Galaxy, performed with BeppoSAX . Matt et al. interpreted the spectrum above 4 keV as the superposition of Compton reflection and warm plasma scattering of the nuclear radiation. When this continuum is extrapolated downwards to 0.1 keV, further components arise. The NGC 1068 spectrum is rich in emission lines, mainly owing to K _α transitions of He-like elements from oxygen to iron, plus a K _α fluorescent line from neutral iron. If the ionized lines originate in the warm scatterer, its thermal and ionization structure must be complex. From the continuum and line properties, we estimate a column density, N _warm, of the warm scatterer less than a few×10²¹ cm⁻². In the Circinus Galaxy, the absence of highly ionized iron is consistent with a scattering medium with U _X≲5 and N _warm∼ a few×10²² cm⁻². In both cases the neutral iron line is most naturally explained as fluorescence in the medium responsible for the Compton reflection continuum. In NGC 1068 an optically thin plasma emission with kT ≃500 eV and strongly sub-solar metallicity is required, while such a component is only marginal in the Circinus Galaxy. We tentatively identify this component as emission of diffuse hot gas in the nuclear starbursts. Possible causes for the metal depletion are discussed.     

Narrow-line Seyfert 1 galaxies

This paper summarizes the soft X-ray properties of narrow-line Seyfert 1 galaxies (NLS1). NLS1 have generally steeper soft X-ray continuum slopes than Seyfert 1s with broader lines, and there exists an anticorrelation between 0.1–2.4 keV continuum slope and the FWHM of the Hβ line. Objects with steep 0.1–2.4 keV continuum slopes and Hβ FWHM > 3000 km s⁻¹ are clearly discriminated against by nature. When simple power-law models are fit to the data, photon indices reach values up to about 5, much higher than is usually seen in Seyfert 1s. Models with smaller mass black holes and/or higher Eddington fractions show some promise to explain the relation between the FWHM of the Hβ line and the X-ray continuum slope. We further report evidence for persistent gaint and rapid variability in the ultrasoft narrow-line Seyfert 1 galaxy IRAS 13224–3809. We have examined possible explanations for the gaint variability. Unusually strong relativistic effects provide a plausible explanation of the X-ray data. Relativistic boosting effects may be relevant to understanding the strong X-ray variability of some steep spectrum Seyferts more generally.     

Spectrophotometric investigation of two Seyfert galaxies

Erevan State University. Translated from Astrofizika, Vol. 36, No. 3, pp. 353–361, July–September, 1993.     

Long-term ultraviolet variability of Seyfert galaxies

Flux variability is one of the defining characteristics of Seyfert galaxies, a class of active galactic nuclei (AGN). Although these variations are observed over a wide range of wavelengths, results on their flux variability characteristics in the ultraviolet (UV) band are very limited. We present here the long-term UV flux variability characteristics of a sample of fourteen Seyfert galaxies using data from the International Ultraviolet Explorer acquired between 1978 and 1995. We found that all the sources showed flux variations with no statistically significant differences in the amplitude of UV flux variation between shorter and longer wavelengths. Also, the flux variations between different near-UV (NUV, \(1850{-}3300\) Å) and far-UV (FUV, \(1150{-}2000\) Å) passbands in the rest frames of the objects are correlated with no time lag. The data show indications of (i) a mild negative correlation of UV variability with bolometric luminosity and (ii) weak positive correlation between UV variability and black hole mass. At FUV, about 50% of the sources show a strong correlation between spectral indices and flux variations with a hardening when brightening behaviour, while for the remaining sources the correlation is moderate. In NUV, the sources do show a harder spectrum when brighter, but the correlation is either weak or moderate.     

Narrow-line Seyfert 1 galaxies and the evolution of galaxies and active galaxies

Narrow Line Seyfert 1 galaxies (NLS1s) are intriguing owing to their continuum as well as emission-line properties. The observed peculiar properties of the NLS1s are believed to be as a result of an accretion rate close to the Eddington limit. As a consequence of this, for a given luminosity, NLS1s have smaller black hole (BH) masses compared with normal Seyfert galaxies. Here we argue that NLS1s might be Seyfert galaxies in their early stage of evolution and as such may be low-redshift, low-luminosity analogues of high-redshift quasars. We propose that NLS1s may reside in rejuvenated, gas-rich galaxies. We also argue in favour of collisional ionization for production of Fe  ii in active galactic nuclei.     

Star formation in southern Seyfert galaxies

We have produced radio maps, using the Australia Telescope Compact Array, of the central regions of six southern type 2 Seyfert galaxies (NGC 1365, 4945, 6221, 6810, 7582 and Circinus) with circumnuclear star formation, to estimate the relative contribution of star formation activity compared to activity from the active galactic nucleus (AGN). The radio morphologies range from extended diffuse structures to compact nuclear emission, with no evidence, even in the relatively compact sources, for synchrotron self-absorption. In each case the radio to far-infrared (FIR) ratio has a value consistent with star formation, and in all but one case the radio to [Fe  II ] ratio is also consistent with star formation. We derive supernova rates and conclude that, despite the presence of a Seyfert nucleus in these galaxies, the radio, FIR and [Fe  II ] line emissions are dominated by processes associated with the circumnuclear star formation (i.e. supernova remnants and H  II regions) rather than with the AGN.     

Extended ionized emission from Seyfert galaxies

Preliminary results of a programme aimed at investigating the presence of Hii regions around Seyfert nuclei are presented. We have detected extended zones of ionized gas around some classical Seyfert galaxies. We think that the ionizing mechanism in these extended regions is UV radiation from young stars formed in a recent burst of star formation. In many instances the objects studied show morphological disturbances arising from the interaction with nearby companion galaxies.