arXiv subjects

Susanna Bisogni

Publications and source records attributed to Susanna Bisogni.

22 records · Page 2Linked to original sources

arXiv2017

A Hubble diagram for quasars

The cosmological model is at present not tested between the redshift of the farthest observed supernovae (z ~ 1.4) and that of the Cosmic Microwave Background (z ~ 1,100). Here we introduce a new method to measure the cosmological parameters: we show that quasars can be used as "standard candles" by employing the non-linear relation between their intrinsic UV and X-ray emission as an absolute distance indicator. We built a sample of ~ 1,900 quasars with available UV and X-ray observations, and produced a Hubble Diagram up to z ~ 5. The analysis of the quasar Hubble Diagram, when used in combination with supernovae, provides robust constraints on the matter and energy content in the cosmos. The application of this method to forthcoming, larger quasar samples, will also provide tight constraints on the dark energy equation of state and its possible evolution with time.

astro-ph.GA↗

arXiv2017

EW[OIII] as an orientation indicator for quasars: implications for the torus

We present an analysis of the average spectral properties of 12,000 SDSS quasars as a function of accretion disc inclination, as measured from the equivalent width of the [O III] 5007Å line. The use of this indicator on a large sample of quasars from the SDSS DR7 has proven the presence of orientation effects on the features of UV/optical spectra, confirming the presence of outflows in the NLR gas and that the geometry of the BLR is disc-like. Relying on the goodness of this indicator, we are now using it to investigate other bands/components of AGN. Specifically, the study of the UV/optical/IR SED of the same sample provides information on the obscuring "torus". The SED shows a decrease of the IR fraction moving from face-on to edge-on sources, in agreement with models where the torus is co-axial with the accretion disc. Moreover, the fact we are able to observe the broad emission lines also in sources in an edge-on position, suggests that the torus is rather clumpy than smooth as in the Unified Model. The behaviour of the SED as a function of EW[OIII] is in agreement with the predictions of the clumpy torus models as well.

astro-ph.GA↗

arXiv2017

Simultaneous detection and analysis of optical and ultraviolet broad emission lines in quasars at z~2.2

We studied the spectra of six $z \sim 2.2$ quasars obtained with the X-shooter spectrograph at the Very Large Telescope. The redshift of these sources and X-shooter's spectral coverage allow us to cover the rest spectral range $\sim1200 - 7000$Å for the simultaneous detection of optical and ultraviolet lines emitted by the Broad Line Region. Simultaneous measurements, avoiding issues related to quasars variability, help us understanding the connection between different Broad Line Region line profiles generally used as virial estimators of Black Holes masses in quasars. The goal of this work is comparing the emission lines from the same object to check on the reliability of H$α$, MgII and CIV with respect to H$β$. H$α$ and MgII linewidths correlate well with H$β$, while CIV shows a poorer correlation, due to the presence of strong blueshifts and asymmetries in the profile. We compare our sample with the only other two whose spectra were taken with the same instrument and for all examined lines our results are in agreement with the ones obtained with X-shooter at $z \sim 1.5 - 1.7$. We finally evaluate CIII] as a possible substitute of CIV in the same spectral range and find that its behaviour is more coherent with those of the other lines: we believe that, when a high quality spectrum such as the ones we present is available and a proper modelization with the FeII and FeIII emissions is performed, the use of this line is more appropriate than that of CIV if not corrected for the contamination by non-virialized components.

astro-ph.GA↗

arXiv2016

Orientation effects on spectral emission features of quasars

We present an analysis of the orientation effects in SDSS quasar composite spectra. In a previous work we have shown that the equivalent width EW of the [OIII] λ5008Å line is a reliable indicator of the inclination of the accretion disk. Here, we have selected a sample of ~15,000 quasars from the SDSS 7th Data Release and divided it in sub-samples with different values of EW([OIII]). We find inclination effects both on broad and narrow quasars emission lines, among which an increasing broadening from low to high EW for the broad lines and a decreasing importance of the blue component for the narrow lines. These effects are naturally explained with a variation of source inclination from nearly face-on to edge-on, confirming the goodness of EW([OIII]) as an orientation indicator. Moreover, we suggest that orientation effects could explain, at least partially, the origin of the anticorrelation between [OIII] and FeII intensities, i.e. the well known Eigenvector 1.

astro-ph.GA↗