Engineering topics

Stirpe, G. M.

Publications and source records attributed to Stirpe, G. M..

4 records

DOE OSTI2023

High-redshift quasars along the main sequence

The 4D Eigenvector 1 empirical formalism (4DE1) and its main sequence (MS) for quasars has emerged as a powerful tool for organising the diversity among quasar populations, as several key observational measures and physical parameters are systematically changing along it. Trends revealed by 4DE1 are very well established to explain all the diverse characteristics seen in low-redshift quasar samples. Nevertheless, the situation is far less clear when dealing with high-luminosity and high-redshift sources. Here, we aim to evaluate the behaviour of our sample of 22 quasars at high redshift (2.2 ≤ z ≤ 3.7) and high luminosity (47.39 ≤ L bol ≤ 48.36) in the context of the 4DE1. Our approach involves studying quasar physics through a spectroscopic exploration of UV and optical emission line diagnostics. We used new observations from the ISAAC instrument at ESO-VLT and primarily from the SDSS to cover the optical and the UV rest-frames, respectively. The emission lines were characterised both via a quantitative parametrisation of the line profiles and a decomposition of the emission line profiles using multicomponent fitting routines. We provide spectrophotometric properties and line profile measurements for Hβ+[O III]λλ4959,5007, as well as Si IVλ1397+O IV]λ1402, C IVλ1549+He IIλ1640, and the 1900 Å blend (including Al IIIλ1860, Si III]λ1892, and C III]λ1909). For six out of the 22 objects, a significantly blueshifted component on the Hβ profile is present. In 14 out of 22 cases, an Hβ outflowing component associated with [O III] is detected. The majority of [O III]λλ4959,5007 emission line profiles show blueshifted velocities higher than 250 km s -1 . We find extremely broad [O III]λλ4959,5007 emission that is comparable to the width of Hβ broad profile in some highly accreting quasars. The [O III]λλ4959,5007 and C IVλ1549 blueshifts show very high amplitudes and a high degree of correlation. The line widths and shifts are correlated for both [O III]λλ4959,5007 and C IVλ1549, suggesting that emission from outflowing gas is providing a substantial broadening effect to both lines. Otherwise, the links between C IVλ1549 centroid velocity at half intensity (c(1/2)), Eddington ratio (L/L Edd ), and bolometric luminosity are found to be in agreement with previous studies of high-luminosity quasars. Our analysis suggests that the behaviour of quasars of very high luminosity all along the main sequence is strongly affected by powerful outflows involving a broad range of spatial scales. The main sequence correlations remain valid at high redshift and high luminosity even if a systematic increase in line width is observed. Scaling laws based on UV Al IIIλ1860 and Hβ emission lines are equally reliable estimators of M BH .

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS1995

A Snapshot of the Continuous Emission of the Active Galactic Nucleus in NGC 3783 from Gamma-Ray to Radio Wavelengths

To better understand the physical processes that produce the continuous emission in active galactic nuclei (AGN), a snapshot of the overall continuous energy distribution of NGC 3783, from gamma ray to radio wavelengths, has been obtained within the framework of the World Astronomy Days. The data collected in this campaign are from GRO, ROSAT, Voyager 2, IUE, HST, CTIO, SAAO, and the VLA. Great care has been taken in disentangling the genuine AGN continusous emission from other contributions; depending on the waveband, the latter might be (1) unrelated contaminating sources in cases where the instrument field of view is large (2) components within which the AGN is embedded, such as the stellar bulge population which accounts for a significant fraction of the optical continuum, and free-bound and FE2 blends wich contribute to the ultraviolet flux. After correction for these other contributins, the continuous emission of the isolated AGN appears to be rather flat (i.e., approximately equal energy per unit logarithmic frequency) from soft gamma ray to infrared wavelengths. At high energies (0.1 MeV to 0.1 keV), the AGN continuum can be fitted by a power law F nu approaches Nu(exp -a) with a spectral index of alpha approximately 1. At longer wavelengths, two excesses above this power law ('bumps') appear: in the ultraviolet, the classical big blue bump, which can be interpreted as thermal emission from the accretion disc surrounding a massive black hole, and in the infrared, a second bump which can be ascribed to thermal emission from dust in the vicinity of the AGN, heated by ultraviolet radiation from the central source. By fitting accretion-disk models to the observed AGN spectral energy distribution, we find values for the accretion disk innermost temperature, accretion rate, and black hole mass, with some differences that depend on whether or not we extrapolate the high energy power law up to infrared wavelengths. A fit to the IR bump above the extended alpha equals 1 power law suggests the presence of a dust component covering the region from a distance rho approximately equals 80 light days (hot grains at a temperature of approximately equals 1500 K) to rho approximately equals 60 light years (cool grains at T approximately equals 200 K). The total mass of dust is around 60 solar masses.

Alloin, D.↗

NASA NTRS1994

Steps toward determination of the size and structure of the broad-line region in active galactic nuclei. 6: Variability of NGC 3783 from ground-based data

The Seyfert 1 galaxy NGC 3783 was intensely monitored in several bands between 1991 December and 1992 August. This paper presents the results from the ground-based observations in the optical and near-IR bands, which complement the data set formed by the International Ultraviolet Explorer (IUE) spectra, discussed elsewhere. Spectroscopic and photometric data from several observatories were combined in order to obtain well-sampled light curves of the continuum and of H(beta). During the campaign the source underwent significant variability. The light curves of the optical continuum and of H(beta) display strong similarities to those obtained with the IUE. The near-IR flux did not vary significantly except for a slight increase at the end of the campaign. The cross-correlation analysis shows that the variations of the optical continuum have a lag of 1 day or less with respect to those of the UV continuum, with an uncertainty of is less than or equal to 4 days. The integrated flux of H(beta) varies with a delay of about 8 days. These results confirm that (1) the continuum variations occur simultaneously or with a very small lag across the entire UV-optical range, as in the Seyfert galaxy NGC 5548; and (2) the emission lines of NGC 3783 respond to ionizing continuum variations with less delay than those of NGC 5548. As observed in NGC 5548, the lag of H(beta) with respect to the continuum is greater than those of the high-ionization lines.

Stirpe, G. M.↗

NASA NTRS1994

The international AGN watch: A multiwavelength monitoring consortium

The International AGN Watch, an informal consortium of over 100 astronomers, was established to coordinate multiwavelength monitoring of a limited number of active galactic nuclei and thus obtain comprehensive continuum and emission-line variability data with unprecedented temporal and wavelength coverage. We summarize the principal scientific results from two completed space-based and ground-based campaigns on the Seyfert galaxies NGC 5548 and NGC 3783. We describe a project in progress and outline our future plans.

Alloin, D.↗