اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدExtended emission-line regions in low-redshift quasars: Dependence on nuclear spectral properties
125
0
0.0
(
0
)
تأليف
B. Husemann
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
We searched for the presence of extended emission-line regions (EELRs) around low-redshift QSOs. We observed a sample of 20 mainly radio-quiet low-redshift quasars (z<0.3) by means of integral field spectroscopy. After decomposing the extended and nuclear emission components, we constructed [OIII] 5007 narrow-band images of the EELR to measure the total flux. From the same data we obtained high S/N (>50) nuclear spectra to measure properties such as [OIII]/Hbeta flux ratios, FeII equivalent widths and Hbeta line widths. A significant fraction of the quasars (8/20) show a luminous EELR, with detected linear sizes of several kpc. Whether or not a QSO has a luminous EELR is strongly related with nuclear properties, in the sense that an EELR was detected in objects with low FeII equivalent width and large Hbeta FWHM. The EELRs were detected preferentially in QSOs with larger black hole masses. There is no discernible relation, however, between EELR detection and QSO luminosity and Eddington ratio.
قيم البحث
اقرأ أيضاً
We present the results of spectroscopic and imaging observations of the FRII radio galaxies PKS2250-41 and PKS1932-46. Both sources display very extensive emission line regions, and appear to be undergoing interactions with companion bodies. In addit
ion to disturbed gas kinematics associated with interactions with the radio source, the more distant emitting material displays simple, narrow emission line profiles, often at significant velocity offsets from the system rest-frame, and may be associated with tidal debris.
We analyze X-ray spectra of 43 Palomar-Green quasars observed with {it XMM-Newton} in order to investigate their mean Fe K line profile and its dependence on physical properties. The continuum spectra of 39 objects are well reproduced by a model cons
isting of a power law and a blackbody modified by Galactic absorption. The spectra of the remaining four objects require an additional power-law component absorbed with a column density of $sim 10^{23} {rm cm}^{-2}$. We fit the entire sample simultaneously to derive average Fe line parameters by assuming a common Fe line shape. The Fe line is relatively narrow ($sigma=0.36$ keV), with a center energy of 6.48 keV and a mean equivalent width (EW) of 248 eV. By combining black hole masses estimated from the virial method and bolometric luminosities derived from full spectral energy distributions, we examine the dependence of the Fe K line profile on Eddington ratio. As the Eddington ratio increases, the line becomes systematically stronger (EW = 130 to 280 eV), broader ($sigma=0.1$ to 0.7 keV), and peaks at higher energies (6.4 to 6.8 keV). This result suggests that the accretion rate onto the black hole directly influences the geometrical structure and ionization state of the accretion disk.
We give an overview of our recent integral-field-unit spectroscopy of luminous extended emission-line regions (EELRs) around low-redshift quasars, including new observations of 5 fields. Previous work has shown that the most luminous EELRs are found
almost exclusively around steep-spectrum radio-loud quasars, with apparently disordered global velocity fields, and little, if any, morphological correlation with either the host-galaxy or the radio structure. Our new observations confirm and expand these results. The EELRs often show some clouds with velocities exceeding 500 km/s, ranging up to 1100 km/s, but the velocity dispersions, with few exceptions, are in the 30-100 km/s range. Emission-line ratios show that the EELRs are clearly photoionized by the quasars. Masses of the EELRs range up to >10^10 Msun. Essentially all of the EELRs show relatively low metallicities, and they are associated with quasars that, in contrast to most, show similarly low metallicities in their broad-line regions. The two objects in our sample that do not have classical double-lobed radio morphologies (3C48, with a compact-steep-spectrum source; Mrk1014, radio-quiet, but with a weak compact-steep-spectrum source) are the only ones that appear to have recent star formation. While some of the less-luminous EELRs may have other origins, the most likely explanation for the ones in our sample is that they are examples of gas swept out of the host galaxy by a large-solid-angle blast wave accompanying the production of the radio jets. The triggering of the quasar activity is almost certainly the result of the merger of a gas-rich galaxy with a massive, gas-poor galaxy hosting the supermassive black hole.
We present a correlation between the presence of luminous extended emission-line regions (EELRs) and the metallicity of the broad-line regions (BLRs) of low-redshift quasars. The result is based on ground-based [O III] 5007 narrow-band imaging and Hu
bble Space Telescope UV spectra of 12 quasars at 0.20 < z < 0.45. Quasars showing luminous EELRs have low-metallicity BLRs (Z < 0.6 Z_Solar), while the remaining quasars show typical metal-rich gas (Z > Z_Solar). Previous studies have shown that EELRs themselves also have low metallicities (Z < 0.5 Z_Solar). The correlation between the occurrence of EELRs and the metallicity of the BLRs, strengthened by the sub-Solar metallicity in both regions, indicates a common external origin for the gas, almost certainly from the merger of a gas-rich galaxy. Our results provide the first direct observational evidence that the gas from a merger can indeed be driven down to the immediate vicinity (< 1 pc) of the central black hole.
We present the spectra of 14 quasars with a wide coverage of rest wavelengths from 1000 to 7300 A. The redshift ranges from z = 0.061 to 0.555 and the luminosity from M_{B} = -22.69 to -26.32. We describe the procedure of generating the template spec
trum of Fe II line emission from the spectrum of a narrow-line Seyfert 1 galaxy I Zw 1 that covers two wavelength regions of 2200-3500 A and 4200-5600 A. Our template Fe II spectrum is semi-empirical in the sense that the synthetic spectrum calculated with the CLOUDY photoionization code is used to separate the Fe II emission from the Mg II line. The procedure of measuring the strengths of Fe II emission lines is twofold; (1) subtracting the continuum components by fitting models of the power-law and Balmer continua in the continuum windows which are relatively free from line emissions, and (2) fitting models of the Fe II emission based on the Fe II template to the continuum-subtracted spectra. From 14 quasars, we obtained the Fe II fluxes in five wavelength bands, the total flux of Balmer continuum, and the fluxes of Mg II, Halpha, and other emission lines, together with the full width at half maxima (FWHMs) of these lines. Regression analysis was performed by assuming a linear relation between any two of these quantities. Eight correlations were found with a confidence level higher than 99%. The fact that six of these eight are related to FWHM or M_{BH} may imply that M_{BH} is a fundamental quantity that controls Gamma or the spectral energy distribution (SED) of the incident continuum, which in turn controls the Fe II emission. Furthermore, it is worthy of noting that Fe II(O1)/Fe II(U1) is found to tightly correlate with Fe II(O1)/Mg II, but not with Fe II(U1)/Mg II.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
