Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userSize and properties of the narrow-line region in Seyfert-1 galaxies from spatially-resolved optical spectroscopy
307
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Spatially resolved emission-line spectroscopy is a powerful tool to determine the physical conditions in the narrow-line region (NLR) of active galactic nuclei (AGNs). We recently used optical long-slit spectroscopy to study the NLRs of a sample of six Seyfert-2 galaxies. We have shown that such an approach, in comparison to the commonly used [OIII] narrow-band imaging alone, allows us to probe the size of the NLR in terms of AGN photoionisation. Moreover, several physical parameters of the NLR can be directly accessed. We here apply the same methods to study the NLR of six Seyfert-1 galaxies and compare our results to those of Seyfert-2 galaxies. We employ diagnostically valuable emission-line ratios to determine the physical properties of the NLR, including the core values and radial dependencies of density, ionisation parameter, and reddening. Tracking the radial change of emission-line ratios in diagnostic diagrams allows us to measure the transition between AGN-like and HII-like line excitation, and thus we are able to measure the size of the NLR. In the diagnostic diagrams, we find a transition between line ratios falling in the AGN regime and those typical for HII regions in two Seyfert-1 galaxies, thus determining the size of the NLR. The central electron temperature and ionisation parameter are in general higher in type-1 Seyferts than in type 2s. In almost all cases, both electron density and ionisation parameter decrease with radius. In general, the decrease is faster in Seyfert-1 galaxies than in type 2s. In several objects, the gaseous velocity distribution is characteristic for rotational motion in an (inclined) emission-line disk in the centre. We give estimates of the black hole masses. We discuss our findings in detail for each object.
rate research
Read More
While [OIII] narrow-band imaging is commonly used to measure the size of the narrow-line regions (NLRs) in active galactic nuclei (AGNs), it can be contaminated by emission from surrounding starbursts. Recently, we have shown that long-slit spectroscopy provides a valuable alternative approach to probe the size in terms of AGN photoionisation. Moreover, several parameters of the NLR can be directly accessed. We here apply the same methods developed and described for the Seyfert-2 galaxy NGC1386 to study the NLR of five other Seyfert-2 galaxies by using high-sensitivity spatially-resolved optical spectroscopy obtained at the VLT and the NTT. We probe the AGN-photoionisation of the NLR and thus, its ``real size using diagnostic line-ratio diagrams.We derive physical properties of the NLR such as reddening, ionisation parameter, electron density, and velocity as a function of distance from the nucleus. For NGC5643, the diagnostic diagrams unveil a similar transition between line ratios falling in the AGN regime and those typical for HII regions as found for NGC1386, thus determining the size of the NLR. For the other four objects, all measured line ratios fall in the AGN regime. In almost all cases, both electron density and ionisation parameter decrease with radius. Deviations from this general behaviour (such as a secondary peak) seen in both the ionisation parameter and electron density can be interpreted as signs of shocks from the interaction of a radio jet and the NLR gas. In several objects, the gaseous velocity distribution is characteristic for rotational motion in an (inclined) emission-line disk in the centre. We compare our results to those of NGC1386 and show that the latter can be considered as prototypical also for this larger sample. We discuss our findings in detail for each object.
We present optical integral field spectroscopy for five $z<0.062$ narrow-line Seyfert 1 galaxies (NLS1s) host galaxies, probing their host galaxies at $gtrsim 2-3$ kpc scales. Emission lines in the nuclear AGN spectra and the large-scale host galaxy are analyzed separately, based on an AGN-host decomposition technique. The host galaxy gas kinematics indicates large-scale gas rotation in all five sources. At the probed scales of $gtrsim 2-3$ kpc, the host galaxy gas is found to be predominantly ionized by star formation without any evidence of a strong AGN contribution. None of the five objects shows specific star formation rates exceeding the main sequence of low-redshift star forming galaxies. The specific star formation rates for MCG-05-01-013 and WPVS 007 are roughly consistent with the main sequence, while ESO 399-IG20, MS 22549-3712, and TON S180 show lower specific star formation rates, intermediate to the main sequence and red quiescent galaxies. The host galaxy metallicities, derived for the two sources with sufficient data quality (ESO 399-IG20 and MCG-05-01-013), indicate central oxygen abundances just below the low-redshift mass-metallicity relation. Based on this initial case study, we outline a comparison of AGN and host galaxy parameters as a starting point for future extended NLS1 studies with similar methods.
This work studies the optical emission line properties and physical conditions of the narrow line region (NLR) of seven narrow-line Seyfert 1 galaxies (NLS1). Our results show that the flux carried out by the narrow component of H-beta is, on average, 50% of the total line flux. As a result, the [OIII] 5007/H-beta ratio emitted in the NLR varies from 1 to 5, instead of the universally adopted value of 10. This has strong implications for the required spectral energy distribution that ionizes the NLR gas. Photoionization models that consider a NLR composed of a combination of matter-bounded and ionization-bounded clouds are successful at explaining the low [OIII] 5007/H-beta ratio and the weakness of low-ionization lines of NLS1s. Variation of the relative proportion of these two type of clouds nicely reproduce the dispersion of narrow line ratios found among the NLS1 sample. Assuming similar physical model parameters of both NLS1s and the normal Seyfert 1 galaxy NGC 5548, we show that the observed differences of emission line ratios between these two groups can be explained in terms of the shape of the input ionizing continuum. Narrow emission line ratios of NLS1s are better reproduced by a steep power-law continuum in the EUV -- soft X-ray region, with spectral index alpha ~ -2. Flatter spectral indices (alpha ~ -1.5) match the observed line ratios of NGC 5548 but are unable to provide a good match to the NLS1 ratios. This result is consistent with ROSAT observations of NLS1s, which show that these objects are characterized by steeper power-law indices than those of Sy1 galaxies with strong broad optical lines.
We study the narrow-line region (NLR) of six Seyfert-1 and six Seyfert-2 galaxies by means of spatially resolved optical spectroscopy and photoionization modelling. From spatially resolved spectral diagnostics, we find a transition between the AGN-excited NLR and the surrounding star-forming regions, allowing us to determine the NLR size independent of stellar contamination. CLOUDY photoionization models show that the observed transition represents a true difference in ionization source and cannot be explained by variations of physical parameters. The electron density and ionization parameter decrease with radius indicating that the NLR is photoionized by the central source only. The velocity field suggests a disky NLR gas distribution.
We present results from the analysis of the optical spectra of 47 radio-selected narrow-line Seyfert 1 galaxies (NLS1s). These objects are a subset of the First Bright Quasar Survey (FBQS) and were initially detected at 20 cm (flux density limit ~1 mJy) in the VLA FIRST Survey. We run Spearman rank correlation tests on several sets of parameters and conclude that, except for their radio properties, radio-selected NLS1 galaxies do not exhibit significant differences from traditional NLS1 galaxies. Our results are also in agreement with previous studies suggesting that NLS1 galaxies have small black hole masses that are accreting very close to the Eddington rate. We have found 16 new radio-loud NLS1 galaxies, which increases the number of known radio-loud NLS1 galaxies by a factor of ~5.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
