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Register a new userPolarization of broad line emission from AGNs with determined virial factors
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We calculated the polarization degree of hydrogen Balmer broad emission lines from a number of active galactic nuclei (AGNs) with determined virial factors. The objects were selected from the sample presented by Decarli et al.(2008). In our calculations, we used the model of the flattened disc-like structure of the broad-line emission region (BLR). In this model, the expression for the virial factor makes it possible to determine the inclination angle for the flattened BLR, which in turn yields the polarization degree of the broad emission lines. As a result, we obtained the direct relation between the polarization degree and the virial factor. We also compared the determined values of the polarization degree with those obtained in polarimetric observations.
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Apart from viewing-dependent obscuration, intrinsic broad-line emission from active galactic nuclei (AGNs) follows an evolutionary sequence: Type $1 to 1.2/1.5 to 1.8/1.9 to 2$ as the accretion rate onto the central black hole is decreasing. This spectral evolution is controlled, at least in part, by the parameter $L_{rm bol}/M^{2/3}$, where $L_{rm bol}$ is the AGN bolometric luminosity and $M$ is the black hole mass. Both this dependence and the double-peaked profiles that emerge along the sequence arise naturally in the disk-wind scenario for the AGN broad-line region.
Based on the gravitational redshift, one prediction of Einsteins general relativity theory, of broad optical emission lines in active galactic nuclei (AGNs), a new method is proposed to estimate the virial factors $f$ in measuring black hole masses $M_{rm{RM}}$ by the reverberation mapping of AGNs. The factors $f$ can be measured on the basis of two physical quantities, i.e. the gravitational redshifts $z_{rm{g}}$ and full widths at half maxima $v_{rm{FWHM}}$ of broad lines. In the past it has been difficult to determine the factors $f$ for individual AGNs. We apply this new method to several reverberation mapped Seyfert 1 galaxies. There is a correlation between $f$ and broad-line region (BLR) radius $r_{rm{BLR}}$, $f=5.4 r_{rm{BLR}}^{0.3}$, for the gravitationally redshifted broad lines He II, He I, H$beta$ and H$alpha$ in narrow-line Seyfert 1 galaxy (NLS1) Mrk 110. This correlation results from the radiation pressure influence of the accretion disc on the BLR clouds. The radiation pressure influence seems to be more important than usually thought in AGNs. Mrk 110 has $f approx$ 8--16, distinctly larger than the mean $langle frangle approx 1$, usually used to estimate $M_{rm{RM}}$ in the case of $v_{rm{FWHM}}$. NGC 4593 and NLS1 Mrk 486 has $fapprox 3$ and $fapprox 9$, respectively. Higher $f$ values of several tens are derived for three other NLS1s. There is a correlation between $f$ and accretion rate $mathscr{dot M}_{f=1}$, $f=6.8mathscr{dot M}^{0.4}_{f=1}$ for five objects, where $mathscr{dot M}_{f=1}=dot M_{bullet}/L_{rm{Edd}}c^{-2}$ as $f=1$ is assumed to estimate $M_{rm{RM}}$ used in the Eddington luminosity $L_{rm{Edd}}$, $dot M_{bullet}$ is the mass accretion rate, and $c$ is the speed of light. These larger $f$ values will produce higher $M_{rm{RM}}$ values and lower Eddington ratios.
We use the H3O+ molecule to investigate the impact of starburst and AGN activity on the chemistry of the molecular interstellar medium. Using the JCMT, we have observed the 3+_2 - 2-_2 364 GHz line of p-H3O+ towards the centers of seven active galaxies. We have detected p-H3O+ towards IC342, NGC253, NGC1068, NGC4418, and NGC6240. Upper limits were obtained for IRAS15250 and Arp299. We find large H3O+ abundances (N(H3O+)/N(H2)>10^{-8}) in all detected galaxies apart from in IC342 where it is about one order of magnitude lower. We note, however, that uncertainties in N(H3O+) may be significant due to lack of definite information on source size and excitation. We furthermore compare the derived N(H3O+) with N(HCO+) and find that the H3O+ to HCO+ column density ratio is large in NGC1068 (24), moderate in NGC4418 and NGC253 (4-5), slightly less than unity in NGC6240 (0.7) and lowest in IC342 (0.2-0.6). We compare our results with models of X-ray and photon dominated regions (XDRs and PDRs). For IC342 we find that a starburst PDR chemistry can explain the observed H3O+ abundance. For the other galaxies, the large H3O+ columns are generally consistent with XDR models. In particular for NGC1068 the elevated N(H3O+)/N(HCO+) ratio suggests a low column density XDR. For NGC4418 however, large HC3N abundances are inconsistent with the XDR interpretation. An alternative possibility is that H3O+ forms through H2O evaporating off dust grains and reacting with HCO+ in warm, dense gas. This scenario could also potentially fit the results for NGC253. Further studies of the excitation and distribution of H3O+ - as well as Herschel observations of water abundances - will help to further constrain the models.
Using a new color-color diagnostic diagram in the mid infrared built from WISE data, the MIRDD, we compare narrow emission-line galaxies (NELGs) that exhibit different activity types (star-forming galaxies, SFGs, and AGNs, i.e.,LINERs, Sy2s and TOs), with broad-line AGNs (QSOs and Sy1s) and BL Lac objects at low redshift ($z le 0.25$). We show that the BL Lac objects occupy in the MIRDD the same region as the LINERs, whereas the QSOs and Sy1s occupy an intermediate region, between the LINERs and the Sy2s.In the MIRDD these galaxies trace a sequence that can be reproduced by a power law, $F_ u = u^{alpha}$, where the spectral index, $alpha$, varies from 0 to $-2$, which is similar to what is observed in the optical-ultraviolet part of the spectra of AGNs with different luminosities. For the NELGs, we perform a stellar population synthesis analysis, demonstrating that the ${rm W}2-{rm W}3$ color is tightly correlated with the level of star formation in their host galaxies. A comparison of their MIR colors with the colors yielded by energy distributions (SEDs) of galaxies with different activity types, shows that the SED of the LINERs is similar to the SEDs of the QSOs and Sy1s, consistent with AGN galaxies with mild star formation, whereas the SEDs of the Sy2s and TOs are consistent with AGN galaxies with strong star formation components. For the BL Lac objects, we can only fit a SED that has no star formation component, consistent with AGNs in elliptical-type galaxies. From their similarities in MIR colors and SEDs, we infer that, in the nearby universe, the level of star formation activity most probably increases in the host galaxies of emission-line galaxies with different activity types along the sequence BL Lac$rightarrow$LINER$rightarrow$QSO/Sy1$rightarrow$Sy2$rightarrow$TO$rightarrow$SFG.
The flux ratios of high-ionization lines are commonly assumed to indicate the metallicity of the broad emission line region in luminous quasars. When accounting for the variation in their kinematic profiles, we show that the NV/CIV, (SiIV+OIV])/CIV and NV/Lya line ratios do not vary as a function of the quasar continuum luminosity, black hole mass, or accretion rate. Using photoionization models from CLOUDY , we further show that the observed changes in these line ratios can be explained by emission from gas with solar abundances, if the physical conditions of the emitting gas are allowed to vary over a broad range of densities and ionizing fluxes. The diversity of broad line emission in quasar spectra can be explained by a model with emission from two kinematically distinct regions, where the line ratios suggest that these regions have either very different metallicity or density. Both simplicity and current galaxy evolution models suggest that near-solar abundances, with parts of the spectrum forming in high-density clouds, are more likely. Within this paradigm, objects with stronger outflow signatures show stronger emission from gas which is denser and located closer to the ionizing source, at radii consistent with simulations of line-driven disc-winds. Studies using broad-line ratios to infer chemical enrichment histories should consider changes in density and ionizing flux before estimating metallicities.
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