ABSTRACT The observed relation between the soft X-ray and the optical-ultraviolet emission in active galactic nuclei (AGNs) is nonlinear and it is usually parametrized as a dependence between the ...logarithm of the monochromatic luminosity at 2500 and at 2 keV. Previous investigations have found that the dispersion of this relation is rather high (∼0.35-0.4 in log units), which may be caused by measurement uncertainties, variability, and intrinsic dispersion due to differences in the AGN physical properties (e.g., different accretion modes). We show that, once optically selected quasars with homogeneous SED and X-ray detection are selected, and dust reddened and/or gas obscured objects are not included, the measured dispersion drops to significantly lower values (i.e., ∼0.21-0.24 dex). We show that the residual dispersion is due to some extent to variability, and to remaining measurement uncertainties. Therefore, the real physical intrinsic dispersion should be dex. Such a tight relation, valid over four decades in luminosity, must be the manifestation of an intrinsic (and universal) physical relation between the disk, emitting the primary radiation, and the hot electron corona emitting X-rays.
A HUBBLE DIAGRAM FOR QUASARS Risaliti, G.; Lusso, E.
Astrophysical journal/The Astrophysical journal,
12/2015, Volume:
815, Issue:
1
Journal Article
Peer reviewed
Open access
ABSTRACT We present a new method to test the ΛCDM cosmological model and to estimate cosmological parameters based on the nonlinear relation between the ultraviolet and X-ray luminosities of quasars. ...We built a data set of 1138 quasars by merging several samples from the literature with X-ray measurements at 2 keV and SDSS photometry, which was used to estimate the extinction-corrected 2500 flux. We obtained three main results: (1) we checked the nonlinear relation between X-ray and UV luminosities in small redshift bins up to , confirming that the relation holds at all redshifts with the same slope; (2) we built a Hubble diagram for quasars up to , which is well matched to that of supernovae in the common z = 0-1.4 redshift interval and extends the test of the cosmological model up to ; and (3) we showed that this nonlinear relation is a powerful tool for estimating cosmological parameters. Using the present data and assuming a ΛCDM model, we obtain = 0.22 and = 0.92 ( = 0.28 0.04 and = 0.73 from a joint quasar-SNe fit). Much more precise measurements will be achieved with future surveys. A few thousand SDSS quasars already have serendipitous X-ray observations from Chandra or XMM-Newton, and at least 100,000 quasars with UV and X-ray data will be made available by the extended ROentgen Survey with an Imaging Telescope Array all-sky survey in a few years. The Euclid, Large Synoptic Survey Telescope, and Advanced Telescope for High ENergy Astrophysics surveys will further increase the sample size to at least several hundred thousand. Our simulations show that these samples will provide tight constraints on the cosmological parameters and will allow us to test for possible deviations from the standard model with higher precision than is possible today.
In the current framework, the standard parametrization of our Universe is the so-called Lambda cold dark matter (ΛCDM) model. Recently, a ∼4σ tension with the ΛCDM model was shown to exist via a ...model-independent parametrization of a Hubble diagram of type Ia supernovae (SNe Ia) from the JLA survey and quasars. Model-independent approaches and independent samples over a wide redshift range are key to testing this tension and any possible systematic errors. Here we present an analysis of a combined Hubble diagram of SNe Ia, quasars, and gamma-ray bursts (GRBs) to check the agreement of the quasar and GRB cosmological parameters at high redshifts (z > 2) and to test the concordance flat ΛCDM model with improved statistical accuracy. We build a Hubble diagram with SNe Ia, quasars, and GRBs, where quasars are standardised through the observed non-linear relation between their ultraviolet and X-ray emission and GRBs through the correlation between the spectral peak energy and the isotropic-equivalent radiated energy (the so-called Amati relation). We fit the data with cosmographic models consisting of a fourth-order logarithmic polynomial and a fifth-order linear polynomial, and compare the results with the expectations from a flat ΛCDM model. We confirm the tension between the best-fit cosmographic parameters and the ΛCDM model at ∼4σ with SNe Ia and quasars, at ∼2σ with SNe Ia and GRBs, and at > 4σ with the whole SNe Ia+quasars+GRB data set. The completely independent high-redshift Hubble diagrams of quasars and GRBs are fully consistent with each other, strongly suggesting that the deviation from the standard model is not due to unknown systematic effects but to new physics.
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ABSTRACT
We analyse some open debates in cosmology in light of the most updated quasar (QSO) sample, covering a wide redshift range up to $\mathit{ z}$ ∼ 7.5, combined with type Ia supernovae (SNe) ...and baryon acoustic oscillations (BAOs). Indeed, extending the cosmological analyses with high-redshift data is key to distinguishing between different cosmological models that are degenerate at low redshifts, and allowing better constraints on a possible dark energy (DE) evolution. Also, we discuss combinations of BAO, SNe, and QSO data to understand their compatibility and implications for extensions of the standard cosmological model. Specifically, we consider a flat and non-flat ΛCDM cosmology, a flat and non-flat DE model with a constant DE equation of state parameter (w), and four flat DE models with variable w, namely the Chevallier–Polarski–Linder and Jassal–Bagla–Padmanabhan models, and an ‘exponential’, and Barboza–Alcaniz parametrizations. We find that a joint analysis of QSO+SNe with BAO is only possible in the context of a flat Universe. Indeed BAO confirms the flatness condition assuming a curved geometry, whilst SNe + QSO show evidence of a closed space. We also find ΩM,0 = 0.3 in all data sets assuming a flat ΛCDM model. Yet, all the other models show a statistically significant deviation at 2-3 σ with the combined SNe + SO + BAO data set. In the models where DE density evolves with time, SNe + QSO + BAO data always prefer ΩM,0 > 0.3, w0 < −1 and wa > 0. This DE phantom behaviour is mainly driven by SNe + QSO, while BAO are closer to the flat ΛCDM model.
We present a mid-infrared investigation of the scaling relations between supermassive black hole masses (M
BH) and the structural parameters of the host spheroids in local galaxies. This work is ...based on 2D bulge-disc decompositions of Spitzer/IRAC 3.6 μm images of 57 galaxies with M
BH estimates. We first verify the accuracy of our decomposition by examining the Fundamental Plane (FP) of spheroids at 3.6 μm. Our estimates of effective radii (R
e) and average surface brightnesses, combined with velocity dispersions from the literature, define a FP relation consistent with previous determinations but doubling the observed range in R
e. None of our galaxies is an outlier of the FP, demonstrating the accuracy of our bulge-disc decomposition which also allows us to independently identify pseudo-bulges in our sample. We calibrate M/L at 3.6 μm by using the tight M
dyn-L
bul relation (∼0.1 dex intrinsic dispersion) and find that no colour corrections are required to estimate the stellar mass. The 3.6 μm luminosity is thus the best tracer of stellar mass yet studied. We then explore the connection between M
BH and bulge structural parameters (luminosity, mass, effective radius). We find tight correlations of M
BH with both 3.6 μm bulge luminosity and dynamical mass (M
BH/M
dyn∼ 1/1000), with intrinsic dispersions of ∼0.35 dex, similar to the M
BH-σ relation. Our results are consistent with previous determinations at shorter wavelengths. By using our calibrated M/L, we rescale M
BH-L
bul to obtain the M
BH-M
★ relation, which can be used as the local reference for high-z studies which probe the cosmic evolution of M
BH-galaxy relations and where the stellar mass is inferred directly from luminosity measurements. The analysis of pseudo-bulges shows that four out of nine lie on the scaling relations within the observed scatter, while those with small M
BH are significantly displaced. We explore the different origins for such behaviour while considering the possibility of nuclear morphological components not reproduced by our 2D decomposition.
Cosmography is a powerful tool for investigating the Universe kinematic and then for reconstructing the dynamics in a model-independent way. However, recent new measurements of supernovae Ia and ...quasars have populated the Hubble diagram up to high redshifts (
z
∼ 7.5) and the application of the traditional cosmographic approach has become less straightforward due to the large redshifts implied. Here we investigate this issue through an expansion of the luminosity distance–redshift relation in terms of orthogonal logarithmic polynomials. In particular, we point out the advantages of a new procedure called orthogonalization, and we show that such an expansion provides a very good fit in the whole
z
= 0 ÷ 7.5 range to both real and mock data obtained assuming various cosmological models. Moreover, although the cosmographic series is tested well beyond its convergence radius, the parameters obtained expanding the luminosity distance–redshift relation for the Lambda cold dark matter (ΛCDM) model are broadly consistent with the results from a fit of mock data obtained with the same cosmological model. This provides a method for testing the reliability of a cosmographic function to study cosmological models at high redshifts, and it demonstrates that the logarithmic polynomial series can be used to test the consistency of the ΛCDM model with the current Hubble diagram of quasars and supernovae Ia. We confirm a strong tension (at > 4
σ
) between the concordance cosmological model and the Hubble diagram at
z
> 1.5. This tension is dominated by the contribution of quasars at
z
> 2 and also starts to be present in the few supernovae Ia observed at
z
> 1.
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Context. X-ray reflection is a very powerful method to assess the spin of supermassive black holes (SMBHs) in active galactic nuclei (AGN), yet this technique is not universally accepted. Indeed, ...complex reprocessing (absorption, scattering) of the intrinsic spectra along the line of sight can mimic the relativistic effects on which the spin measure is based. Aims. In this work, we test the reliability of SMBH spin measurements that can currently be achieved through the simulations of high-quality XMM-Newton and NuSTAR spectra. Methods. Each member of our group simulated ten spectra with multiple components that are typically seen in AGN, such as warm and (partial-covering) neutral absorbers, relativistic and distant reflection, and thermal emission. The resulting spectra were blindly analysed by the other two members. Results. Out of the 60 fits, 42 turn out to be physically accurate when compared to the input model. The SMBH spin is retrieved with success in 31 cases, some of which (9) are even found among formally inaccurate fits (although with looser constraints). We show that, at the high signal-to-noise ratio assumed in our simulations, neither the complexity of the multi-layer, partial-covering absorber nor the input value of the spin are the major drivers of our results. The height of the X-ray source (in a lamp-post geometry) instead plays a crucial role in recovering the spin. In particular, a success rate of 16 out of 16 is found among the accurate fits for a dimensionless spin parameter larger than 0.8 and a lamp-post height lower than five gravitational radii.
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The evolution of galaxies is connected to the growth of supermassive black holes in their centers. During the quasar phase, a huge luminosity is released as matter falls onto the black hole, and ...radiation-driven winds can transfer most of this energy back to the host galaxy. Over five different epochs, we detected the signatures of a nearly spherical stream of highly ionized gas in the broadband x-ray spectra of the luminous quasar PDS 456. This persistent wind is expelled at relativistic speeds from the inner accretion disk, and its wide aperture suggests an effective coupling with the ambient gas. The outflow's kinetic power larger than 1046 ergs per second is enough to provide the feedback required by models of black hole and host galaxy coevolution.
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