Thermal unfolding of holo and apo pseudoazurin

The role of the copper ion in the thermal unfolding of pseudoazurin has been investigated by differential scanning calorimetry, optical density and fluorescence. In the presence of copper the denaturation of pseudoazurin (holo form) is irreversible and scan rate dependent. The melting temperature ranges between 60.0 and 67.3◦C, depending on the scan rate and the technique used. The DSC data analysis indicates that the denaturation pathway of the holo pseudoazurin is described by the classical Lumry-Eyring model, N ⇔ U ⇒ F. The simulation of the experimental DSC profiles according to this model has allowed the calculation of the thermodynamic and kinetic parameters related to the two steps. The destabilization of the copper active site and of the hydrophobic core precedes the global denaturation of the protein. The removal of the copper ion (apo from) significantly reduces the stability of the protein: the denaturation occurs at 41.8◦C. Moreover, the thermal unfolding of apo pseudoazurin is compatible with a two-state reversible process, N ⇔ U

Blue outliers among intermediate redshift quasars

[Oiii]{\lambda}{\lambda}4959,5007 "blue outliers" -- that are suggestive of outflows in the narrow line region of quasars -- appear to be much more common at intermediate z (high luminosity) than at low z. About 40% of quasars in a Hamburg ESO intermediate-z sample of 52 sources qualify as blue outliers (i.e., quasars with [OIII] {\lambda}{\lambda}4959,5007 lines showing large systematic blueshifts with respect to rest frame). We discuss major findings on what has become an intriguing field in active galactic nuclei research and stress the relevance of blue outliers to feedback and host galaxy evolution.Comment: Accepted for publication in Astrophysics and Space Science, Special Issue on Line Shifts in Astrophysics and Laboratory Plasm

BeppoSAX observations of the Seyfert 1 Galaxy NGC 3516

We present the results of two observations of the bright Seyfert 1 galaxy NGC 3516, obtained with BeppoSAX in 1996 November and 1997 March. Useful signal is detected between 0.2 and 60 keV, allowing for the first time the simultaneous observation of all main spectral features. The source was brighter by a factor 2 at the second epoch of observation. Both spectra present a strong Fe Kalpha line, and a reflection hump at high energy. An absorption edge at 0.8 keV is visible in the later spectrum, but not in the earlier one, indicating that this feature is strongly variable.Comment: to appear in : The Active X-ray Sky: Results from BeppoSAX and Rossi-XTE, Nuclear Physics B Proceedings Supplements, L. Scarsi, H. Bradt, P. Giommi and F. Fiore (eds.), Elsevier Science B.V. 4 pages LateX and 6 ps figures, using espcrc2 and epsfi

The Case for Optically-Thick High Velocity Broad Line Region Gas in Active Galactic Nuclei

A combined analysis of the profiles of the main broad quasar emission lines in both Hubble Space Telescope and optical spectra shows that while the profiles of the strong UV lines are quite similar, there is frequently a strong increase in the Ly-alpha/H-alpha ratio in the high-velocity gas. We show that the suggestion that the high velocity gas is optically-thin presents many problems. We show that the relative strengths of the high velocity wings arise naturally in an optically-thick BLR component. An optically-thick model successfully explains the equivalent widths of the lines, the Ly-alpha/H-alpha ratios and flatter Balmer decrements in the line wings, the strengths of CIII] and the lambda 1400 blend, and the strong variability of high-velocity, high-ionization lines (especially HeII and HeI).Comment: 34 pages in AASTeX, including 10 pages of figures. Submitted to Astrophysical Journa

Quasars: from the Physics of Line Formation to Cosmology

Quasars accreting matter at very high rates (known as extreme Population A [xA] or super-Eddington accreting massive black holes) provide a new class of distance indicators covering cosmic epochs from the present-day Universe up to less than 1 Gyr from the Big Bang. The very high accretion rate makes it possible that massive black holes hosted in xA quasars radiate at a stable, extreme luminosity-to-mass ratio. This in turns translates into stable physical and dynamical conditions of the mildly ionized gas in the quasar low-ionization line emitting region. In this contribution, we analyze the main optical and UV spectral properties of extreme Population A quasars that make them easily identifiable in large spectroscopic surveys at low-z (z < 1) and intermediate-z (2 < z < 2.6), and the physical conditions that are derived for the formation of their emission lines. Ultimately, the analysis supports the possibility of identifying a virial broadening estimator from low-ionization line widths, and the conceptual validity of the redshift-independent luminosity estimates based on virial broadening for a known luminosity-to-mass ratio.Comment: 13 pages, 5 figures. Invited lecture at SPIG 2018, Belgrade. To appear in Ato

1H0419-577: a two-state Seyfert Galaxy?

The preliminary results of the BeppoSAX observation of the radio-quiet AGN 1H0419-577 are presented. Despite its broad line optical spectrum, the intermediate X-ray spectrum (i.e. 2--10 keV) is flatter than typically observed in Seyfert 1s and no iron line is significantly detected. Even more intriguingly, a 1992 ROSAT pointed observation suggests a dramatic (~ 1) change in the spectral shape for E < 2 keV. Such behavior is briefly discussed in the framework of our current understanding of Comptonization scenarios in the nuclear regions of radio-quiet AGN.Comment: 4 pages, Latex, 4 Postscript figures, `espcrc2.sty included, to appear in the Proceedigns of the Workshop "The active X-ray sky: results from Beppo-SAX and RXTE

Black hole mass estimates in quasars - A comparative analysis of high- and low-ionization lines

The inter-line comparison between high- and low-ionization emission lines has yielded a wealth of information on the quasar broad line region (BLR) structure and dynamics, including perhaps the earliest unambiguous evidence in favor of a disk + wind structure in radio-quiet quasars. We carried out an analysis of the CIV 1549 and Hbeta line profiles of 28 Hamburg-ESO high luminosity quasars and of 48 low-z, low luminosity sources in order to test whether the high-ionization line CIV 1549 width could be correlated with Hbeta and be used as a virial broadening estimator. We analyze intermediate- to high-S/N, moderate resolution optical and NIR spectra covering the redshifted CIV and H$\beta$ over a broad range of luminosity log L ~ 44 - 48.5 [erg/s] and redshift (0 - 3), following an approach based on the quasar main sequence. The present analysis indicates that the line width of CIV 1549 is not immediately offering a virial broadening estimator equivalent to H$\beta$. At the same time a virialized part of the BLR appears to be preserved even at the highest luminosities. We suggest a correction to FWHM(CIV) for Eddington ratio (using the CIV blueshift as a proxy) and luminosity effects that can be applied over more than four dex in luminosity. Great care should be used in estimating high-L black hole masses from CIV 1549 line width. However, once corrected FWHM(CIV) values are used, a CIV-based scaling law can yield unbiased MBH values with respect to the ones based on H$\beta$ with sample standard deviation ~ 0.3 dex.Comment: 43 pages, 15 Figures, submitted to A&

High-redshift quasars along the Main Sequence

We aim to evaluate the behaviour of our 22 high-redshift (2.2 < z < 3.7) and high-luminosity (47.39 < Lbol < 48.36) quasars in the context of the 4-Dimensional Eigenvector 1. Our approach involves studying quasar physics through spectroscopic exploration of UV and optical emission line diagnostics. We are using new observations from ISAAC/VLT and mainly from the SDSS to cover the optical and the UV rest-frames, respectively. Emission lines are characterised both through a quantitative parametrisation of the line profiles, and by decomposing the emission line profiles using multicomponent fitting routines. We provide spectrophotometric properties and line profile measurements for Hb+[O iii], as well as for Si iv+O iv], C iv+He ii and the 1900 blend. Six out of the 22 objects present a significant blueshifted component on the Hb profile, and in 14/22 cases an Hb outflowing component associated to [O iii] is detected. The majority of [O iii] emission line profiles show blueshifted velocities larger than 250 km s^-1. [O iii] and C iv blueshifts show very high amplitudes and a high degree of correlation. Line width and shift are correlated for both [O iii] and C iv, suggesting that emission from outflowing gas is providing a substantial broadening to both lines. Otherwise, the links between C iv centroid velocity at half intensity (c(1/2)), Eddington ratio (L/LEdd), 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 iii and Hb emission lines are equally reliable estimators of MBH.Comment: Accepted for publication at A&