Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userAn additional source of gas ionization in the extended narrow line region of NGC1068
66
0
0.0
(
0
)
Authors
L.S. Nazarova
Ask ChatGPT about the research
No Arabic abstract
The results of calculations of gas emission spectra with both central and extended sources of ionization have been compared to the ratio of line intensities observed in the extended narrow line region of NGC1068. The origin of an extended structure of anomalous strength in the $[OIII] lambda 5007$ and $[NeV] lambda 3425$ lines found by Evans & Dopita (1986) and Bergeron et al. (1989) could be due to an additional stellar source of gas ionization located at a distance 1-2 kpc from the nucleus.
rate research
Read More
We have obtained HST FOC f/48 long-slit spectroscopy of the inner 4 of the Narrow Line Region of NGC 1068 between 3500-5400A with a spectral resolution of 1.78A/pixel. At a spatial scale of 0.0287 per pixel these data provide an order of magnitude improvement in resolution over previous ground based spectra and allow us to trace the interaction between the radio jet and the gas in the NLR. Our results show that, within +/-0.5 of the radio-jet the emission lines are kinematically disturbed and split into two components whose velocity separation is 1500 km/sec. The filaments associated with the radio lobe also show a redshifted kinematic disturbance of the order of 300 km/sec which probably is a consequence of the expansion of the radio plasma. Furthermore, the material enveloping the radio-jet is in a much higher ionization state than that of the surrounding NLR gas. The highest excitation is coincident with the jet axis where emission in the coronal line of [FeVII] 3769A is detected and the HeII 4686A is strong but where [OII] 3727A is depressed. This large localized increase in ionization on the jet axis is accompanied by the presence of an excess continuum. Because the electron density is substantially larger in the jet compared to the surrounding NLR, these results can only be explained if there is a more intense ionizing continuum associated with the jet. This can be accomplished in a variety of ways which include an intrinsically anisotropic nuclear radiation field, a reduced gas covering factor or the presence of a local ionization source. The morphology, kinematics and, possibly, the ionization structure of the NLR in the vicinity of the jet of NGC 1068 are a direct consequence of the interaction with the radio outflow.
We present deep long slit spectra of Mkn79 in position angles PA=12$^{o}$ and PA=50$^{o}$ obtained with the WHT. These data prove the existence of an extended narrow line region in PA=12$^{o}$, which coincides with the triplet radio structure (Ulvestad & Wilson 1984) and the observed outflow of material from the nucleus at PA=10$^{o}$ (Whittle et al. 1988). The ratios of the high to low ionization lines indicate a higher level of gas excitation in PA=12$^{o}$ compared to PA=50$^{o}$. The [NII]$lambda$6583/H$alpha$ and [SII]$lambda$6717,31/H$alpha$ versus [OIII]$lambda$5007/H$beta$ line ratios are consistent with excitation by an AGN continuum rather than a HII region.
We present our recent results about the extended narrow-line region (ENLR) of two nearby Seyfert 2 galaxies (IC 5063 and NGC 7212) obtained by modelling the observed line profiles and spectra with composite models (photoionization+shocks) in the different regions surrounding the AGN. Then, we compare the Seyfert 2 ENLRs with the very extended one recently discovered in the narrow-line Seyfert 1 (NLS1) galaxy Mrk 783. We have found several evidences of interaction between the ISM of the galaxies and their radio jets, such as a) the contribution of shocks in ionizing the high velocity gas, b) the complex kinematics showed by the profile of the emission lines, c) the high fragmentation of matter, etc. The results suggest that the ENLR of IC 5063 have a hollow bi-conical shape, with one edge aligned to the galaxy disk, which may cause some kind of dependence on velocity of the ionization parameter. Regarding the Mrk 783 properties, it is found that the extension of the optical emission is almost twice the size of the radio one and it seems due to the AGN activity, although there is contamination by star formation around 12 arcsec from the nucleus. Diagnostic diagrams excluded the contribution of star formation in IC 5063 and NGC 7212, while the shock contribution was used to explain the spectra emitted by their high velocity gas.
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 investigate the narrow-line region (NLR) of two radio-quiet QSOs, PG1012+008 and PG1307+085, using high signal-to-noise spatially resolved long-slit spectra obtained with FORS1 at the Very Large Telescope. Although the emission is dominated by the point-spread function of the nuclear source, we are able to detect extended NLR emission out to several kpc scales in both QSOs by subtracting the scaled central spectrum from outer spectra. In contrast to the nuclear spectrum, which shows a prominent blue wing and a broad line profile of the [O III] line, the extended emission reveals no clear signs of large scale outflows. Exploiting the wide wavelength range, we determine the radial change of the gas properties in the NLR, i.e., gas temperature, density, and ionization parameter, and compare them with those of Seyfert galaxies and type-II QSOs. The QSOs have higher nuclear temperature and lower electron density than Seyferts, but show no significant difference compared to type-II QSOs, while the ionization parameter decreases with radial distance, similar to the case of Seyfert galaxies. For PG1012+008, we determine the stellar velocity dispersion of the host galaxy. Combined with the black hole mass, we find that the luminous radio-quiet QSO follows the local M_BH-sigma* relation of active galactic nuclei.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
