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.
Past X-ray observations of the nearby luminous quasar PDS 456 (at z = 0.184) have revealed a wide-angle accretion disk wind with an outflow velocity of ∼−0.25c, as observed through observations of ...its blueshifted iron K-shell absorption line profile. Here we present three new XMM-Newton observations of PDS 456: one in 2018 September where the quasar was bright and featureless and two in 2019 September, 22 days apart, occurring when the quasar was five times fainter and where strong blueshifted lines from the wind were present. During the second 2019 September observation, three broad ( = 3000 km s−1) absorption lines were resolved in the high-resolution Reflection Grating Spectrometer spectrum that are identified with blueshifted O viii Ly , Ne ix He , and Ne x Ly . The outflow velocity of this soft X-ray absorber was found to be v/c = −0.258 0.003, fully consistent with an iron K absorber with v/c = −0.261 0.007. The ionization parameter and column density of the soft X-ray component (log = 3.4, NH = 2 × 1021 cm−2) outflow was lower by about 2 orders of magnitude when compared to the high-ionization wind at iron K (log = 5, NH = 7 × 1023 cm−2). Substantial variability was seen in the soft X-ray absorber between the 2019 observations, declining from NH = 1023 to 1021 cm−2 over 20 days, while the iron K component was remarkably stable. We conclude that the soft X-ray wind may originate from an inhomogeneous wind streamline passing across the line of sight that, due to its lower ionization, is located further from the black hole, on parsec scales, than the innermost disk wind.
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.
Black hole feedback in the luminous quasar PDS 456 Nardini, E.; Reeves, J. N.; Gofford, J. ...
Science (American Association for the Advancement of Science),
02/2015, Letnik:
347, Številka:
6224
Journal Article
Recenzirano
Odprti dostop
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.
Past X-ray observations of the nearby luminous quasar PDS 456 (at z = 0.184) have revealed a wide angle accretion disk wind, with an outflow velocity of ∼−0.25c. Here, we unveil a new, relativistic ...component of the wind through hard X-ray observations with NuSTAR and XMM-Newton, obtained in 2017 March when the quasar was in a low-flux state. This very fast wind component, with an outflow velocity of −0.46 0.02c, is detected in the iron K band, in addition to the −0.25c wind zone. The relativistic component may arise from the innermost disk wind, launched from close to the black hole at a radius of ∼10 gravitational radii. The opacity of the fast wind also increases during a possible obscuration event lasting for 50 ks. We suggest that the very fast wind may only be apparent during the lowest X-ray flux states of PDS 456, becoming overly ionized as the luminosity increases. Overall, the total wind power may even approach the Eddington value.
We present a detailed analysis of a recent, 2013 Suzaku campaign on the nearby (z = 0.184) luminous (L
bol ∼ 1047 erg s−1) quasar PDS 456. This consisted of three observations, covering a total ...duration of ∼1 Ms and a net exposure of 455 ks. During these observations, the X-ray flux was unusually low, suppressed by a factor of >10 in the soft X-ray band when compared to previous observations. We investigated the broad-band continuum by constructing a spectral energy distribution (SED), making use of the optical/UV photometry and hard X-ray spectra from the later simultaneous XMM–Newton and NuSTAR campaign in 2014. The high-energy part of this low-flux SED cannot be accounted for by physically self-consistent accretion disc and corona models without attenuation by absorbing gas, which partially covers a substantial fraction of the line of sight towards the X-ray continuum. At least two layers of absorbing gas are required, of column density log (N
H,low/cm−2) = 22.3 ± 0.1 and log (N
H,high/cm−2) = 23.2 ± 0.1, with average line-of-sight covering factors of ∼80 per cent (with typical ∼5 per cent variations) and 60 per cent (±10–15 per cent), respectively. During these observations PDS 456 displays significant short-term X-ray spectral variability, on time-scales of ∼100 ks, which can be accounted for by variable covering of the absorbing gas along the line of sight. The partial covering absorber prefers an outflow velocity of
$v_{\rm pc} = 0.25^{+0.01}_{-0.05}\,c$
at the >99.9 per cent confidence level over the case where v
pc = 0. This is consistent with the velocity of the highly ionized outflow responsible for the blueshifted iron K absorption profile. We therefore suggest that the partial covering clouds could be the denser, or clumpy part of an inhomogeneous accretion disc wind. Finally estimates are placed upon the size-scale of the X-ray emission region from the source variability. The radial extent of the X-ray emitter is found to be of the order ∼15–20R
g, although the hard X-ray (>2 keV) emission may originate from a more compact or patchy corona of hot electrons, which is typically ∼6–8R
g in size.
We present a study of the relation between X-rays and ultraviolet emission in quasars for a sample of broad-line, radio-quiet objects obtained from the cross-match of the Sloan Digital Sky Survey ...DR14 with the latest
Chandra
Source Catalog 2.0 (2332 quasars) and the
Chandra
COSMOS Legacy survey (273 quasars). The non-linear relation between the ultraviolet (at 2500 Å,
L
UV
) and the X-ray (at 2 keV,
L
X
) emission in quasars has been proved to be characterised by a smaller intrinsic dispersion than the observed one, as long as a homogeneous selection, aimed at preventing the inclusion of contaminants in the sample, is fulfilled. By leveraging on the low background of
Chandra
, we performed a complete spectral analysis of all the data available for the SDSS-CSC2.0 quasar sample (i.e. 3430 X-ray observations), with the main goal of reducing the uncertainties on the source properties (e.g. flux, spectral slope). We analysed whether any evolution of the
L
X
−
L
UV
relation exists by dividing the sample in narrow redshift intervals across the redshift range spanned by our sample,
z
≃ 0.5−4. We find that the slope of the relation does not evolve with redshift and it is consistent with the literature value of 0.6 over the explored redshift range, implying that the mechanism underlying the coupling of the accretion disc and hot corona is the same at the different cosmic epochs. We also find that the dispersion decreases when examining the highest redshifts, where only pointed observations are available. These results further confirm that quasars are ‘standardisable candles’, that is we can reliably measure cosmological distances at high redshifts where very few cosmological probes are available.
We present an X-ray spectral analysis of a large sample of 25 'bare' active galactic nuclei (AGN), sources with little or no complicating intrinsic absorption, observed with Suzaku. Our work focuses ...on studying the potential contribution from relativistic disc reflection and examining the implications of this interpretation for the intrinsic spectral complexities frequently displayed by AGN in the X-ray bandpass. During the analysis, we take the unique approach of attempting to simultaneously undertake a systematic analysis of the whole sample, as well as a detailed treatment of each individual source, and find that disc reflection has the required flexibility to successfully reproduce the broad-band spectrum observed for all of the sources considered. Where possible, we use the reflected emission to place constraints on the black hole spin for this sample of sources. Our analysis suggests a general preference for rapidly rotating black holes, which if taken at face value is most consistent with the scenario in which supermassive black hole growth is dominated by prolonged, ordered accretion. However, there may be observational biases towards AGN with high spin in the compiled sample, limiting our ability to draw strong conclusions for the general population at this stage. Finally, contrary to popular belief, our analysis also implies that the dichotomy between radio-loud/radio-quiet AGN is not solely related to black hole spin.
Abstract
We present a detailed spectral and imaging analysis of the central 15″ radius (∼7.5 kpc) region of the merger galaxy NGC 6240 that makes use of all the available Chandra-ACIS data (0.3–3 keV ...effective exposure of ∼190 ks). This region shows extended X-ray structures with lower-energy counterparts imaged in CO, O
iii
, and H
α
line emission. We find both photoionized phases of possible nuclear excitation and thermal shock-excited emission in the different large-scale components: the northwest “loop” detected in H
α
, the region surrounding the two nuclei, the large outflow region to the northeast detected in O
iii
, and the southern X-ray extensions. The latter could be the ionization cone of the northern nucleus, with the N counterpart being obscured by the galaxy disk. The radial distribution of the X-ray surface brightness suggests a confined hot interstellar medium at
r
< 2.5 kpc, with a free-flowing wind at larger radii; if the confinement is magnetic, we estimate
B
-field values of ∼100
μ
G, similar to those measured in the halo of M82. The thermal gas of the extended halo at
kT
∼ 1 keV absorbs soft X-rays from the active galactic nucleus, but not the extreme ultraviolet radiation leading to a rapid increase in
F
O
III
/
F
X
beyond ∼3 kpc. The
α
-element to Fe abundance ratios of the thermal components in the different regions of the extended X-ray emission are generally compatible with Type II supernova yields, confirming the importance of active star formation in NGC 6240.
We present the results of a 5–8 μm spectral analysis performed on the largest sample of local ultraluminous infrared galaxies (ULIRGs) selected so far, consisting of 164 objects up to a redshift of ...∼0.35. The unprecedented sensitivity of the Infrared Spectrograph onboard Spitzer allowed us to develop an effective diagnostic method to quantify the active galactic nucleus (AGN) and starburst (SB) contribution to this class of objects. The large AGN over SB brightness ratio at 5–8 μm and the sharp difference between the spectral properties of AGN and SB galaxies in this wavelength range make it possible to detect even faint or obscured nuclear activity, and disentangle its emission from that of star formation. By defining a simple model we are also able to estimate the intrinsic bolometric corrections for both the AGN and SB components, and obtain the relative AGN/SB contribution to the total luminosity of each source. Our main results are the following. The AGN detection rate among local ULIRGs amounts up to 70 per cent, with 113/164 convincing detections within our sample, while the global AGN/SB power balance is ∼1/3. A general agreement is found with optical classification; however, among the objects with no spectral signatures of nuclear activity, our IR diagnostics find a subclass of elusive, highly obscured AGN. We analyse the correlation between nuclear activity and IR luminosity, recovering the well-known trend of growing AGN significance as a function of the overall energy output of the system: the sources exclusively powered by star formation are mainly found at LIR < 1012.3 L⊙, while the average AGN contribution rises from ∼10 to ∼60 per cent across the ULIRG luminosity range. From a morphological point of view, we confirm that the AGN content is larger in compact systems, but the link between activity and evolutionary stage is rather loose. By analysing a control sample of IR-luminous galaxies around z∼ 1, we find evidence for only minor changes with redshift of the large-scale spectral properties of the AGN and SB components. This underlines the potential of our method as a straightforward and quantitative AGN/SB diagnostic tool for ULIRG-like systems at high redshift as well, and hints to possible photometric variants for fainter sources.
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