scholarly journals Quasars as standard candles

2020 ◽  
Vol 642 ◽  
pp. A150 ◽  
Author(s):  
E. Lusso ◽  
G. Risaliti ◽  
E. Nardini ◽  
G. Bargiacchi ◽  
M. Benetti ◽  
...  
Keyword(s):  
Cold Dark Matter ◽  
High Redshift ◽  
Full Description ◽  
X Rays ◽  
Hubble Diagram ◽  
X Ray ◽  
Flux Limit ◽  
Cold Dark Matter Model ◽  
Systematic Effects ◽  
The Stability

We present a new catalogue of ∼2400 optically selected quasars with spectroscopic redshifts and X-ray observations from either Chandra or XMM–Newton. The sample can be used to investigate the non-linear relation between the ultraviolet (UV) and X-ray luminosity of quasars as well as to build a Hubble diagram up to a redshift of z ∼ 7.5. We selected sources that are neither reddened by dust in the optical and UV nor obscured by gas in the X-rays, and whose X-ray fluxes are free from flux-limit-related biases. After checking for any possible systematics, we confirm, in agreement with our previous works, that the X-ray to UV relation provides distance estimates matching those from supernovae up to z ∼ 1.5, and its slope shows no redshift evolution up to z ∼ 5. We provide a full description of the methodology for testing cosmological models, further supporting a trend whereby the Hubble diagram of quasars is well reproduced by the standard flat cold dark matter model up to z ∼ 1.5–2, but strong deviations emerge at higher redshifts. Since we have minimised all non-negligible systematic effects and proven the stability of the LX − LUV relation at high redshifts, we conclude that an evolution of the expansion rate of the Universe should be considered as a possible explanation for the observed deviation, rather than some systematic (redshift-dependent) effect associated with high-redshift quasars.

scholarly journals The X-ray Spectra of High Redshift Quasars

1989 ◽  
Vol 134 ◽  
pp. 161-166
Author(s):  
Claude R. Canizares ◽  
Julia L. White
Keyword(s):  
High Redshift ◽  
Radio Spectrum ◽  
Clear Correlation ◽  
X Rays ◽  
Spectral Parameters ◽  
X Ray ◽  
Systematic Uncertainties ◽  
Two Component ◽  
X Ray Background ◽  
Single Power

We present mean spectral parameters for various ensembles of quasars observed with the Einstein Observatory Imaging Proportional Counter (IPC). Our sample contains 71 optically or radio selected quasars with 0.1 < z < 3.5, Galactic NH < 1021 cm−2, total counts of 30 −500, and IPC gain < 19. Quasars are grouped into ensembles according to radio properties (Flat Radio Spectrum [FRS], Steep Radio Spectrum [SRS] or Radio Quiet [RQ]), and either redshift or X-ray luminosity, lx. We find a clear correlation between radio properties and α. FRS quasars have α∼0.4, SRS quasars have α∼0.7 and RQ quasars have α ∼1–1.4. There is no evidence for a dependence of α on z nor, for the FRS and SRS ensembles, on lx over nearly three decades. FRS quasars with 2.0 < z < 3.5 have just as flat mean spectra as those with low z, implying that a single power law, which is flatter than the canonical one with α ∼ 0.65, continues into the 1–10 keV band (in which the observed softer X-rays were emitted). Unfortunately, the results for high redshift and high lx RQ quasars are ambiguous because of systematic uncertainties in the ensemble means. Thus we cannot test the two-component spectral hypothesis of Wilkes and Elvis for these objects. SRS X-ray spectra could be steeper than FRS spectra because of the mixing of two components, although a single intrinsically steeper spectrum is easier to reconcile with the absence of z dependence. The uncertainty in a for RQ quasars with high z leaves open the important question of their contribution to the cosmic X-ray background.

scholarly journals The Djorgovski–Gurzadyan dark energy integral equation and the Hubble diagram

2020 ◽  
Vol 642 ◽  
pp. L9
Author(s):  
H.G. Khachatryan ◽  
A. Stepanian
Keyword(s):  
Integral Equation ◽  
Dark Energy ◽  
Cold Dark Matter ◽  
Gamma Ray ◽  
Hubble Diagram ◽  
Dark Energy Density ◽  
Cold Dark Matter Model ◽  
Matter Model ◽  
Burst Data ◽  
Dark Matter Model

We consider the observational aspects of the value of dark energy density from quantum vacuum fluctuations based initially on the Gurzadyan–Xue model. We reduce the Djorgovski–Gurzadyan integral equation to a differential equation for the co-moving horizon and then, by means of the obtained explicit form for the luminosity distance, we construct the Hubble diagram for two classes of observational samples. For supernova and gamma-ray burst data we show that this approach provides viable predictions for distances up to z ≃ 9, quantitatively at least as good as those provided by the Λ cold dark matter model. The Hubble parameter dependence H(z) of the two models also reveals mutual crossing at z = 0.4018, the interpretation of which is less evident.

scholarly journals Starburst and post-starburst high-redshift protogalaxies

2019 ◽  
Vol 626 ◽  
pp. A85 ◽  
Author(s):  
Ellis R. Owen ◽  
Kinwah Wu ◽  
Xiangyu Jin ◽  
Pooja Surajbali ◽  
Noriko Kataoka
Keyword(s):  
Star Formation ◽  
High Redshift ◽  
High Energy ◽  
Starburst Galaxies ◽  
X Rays ◽  
X Ray ◽  
Inverse Compton Scattering ◽  
High Energy Cosmic Rays ◽  
Radiation Fields ◽  
Inverse Compton

Quenching of star-formation has been identified in many starburst and post-starburst galaxies, indicating burst-like star-formation histories (SFH) in the primordial Universe. Galaxies undergoing violent episodes of star-formation are expected to be rich in high energy cosmic rays (CRs). We have investigated the role of these CRs in such environments, particularly how they could contribute to this burst-like SFH via quenching and feedback. These high energy particles interact with the baryon and radiation fields of their host via hadronic processes to produce secondary leptons. The secondary particles then also interact with ambient radiation fields to generate X-rays through inverse-Compton scattering. In addition, they can thermalise directly with the semi-ionised medium via Coulomb processes. Heating at a rate of ∼10−25 erg cm−3 s−1can be attained by Coulomb processes in a star-forming galaxy with one core-collapse SN event per decade, and this is sufficient to cause quenching of star-formation. At high-redshift, a substantial amount of CR secondary electron energy can be diverted into inverse-Compton X-ray emission. This yields an X-ray luminosity of above 1041 erg s−1by redshiftz = 7 which drives a further heating effect, operating over larger scales. This would be able to halt inflowing cold gas filaments, strangulating subsequent star-formation. We selected a sample of 16 starburst and post-starburst galaxies at 7 ≲ z ≲ 9 and determine the star-formation rates they could have sustained. We applied a model with CR injection, propagation and heating to calculate energy deposition rates in these 16 sources. Our calculations show that CR feedback cannot be neglected as it has the strength to suppress star-formation in these systems. We also show that their currently observed quiescence is consistent with the suffocation of cold inflows, probably by a combination of X-ray and CR heating.

The influence of X-rays on the stability of selected properties of polyethylene

2018 ◽  
Vol 23 (1) ◽  
pp. 3-11
Author(s):  
Anna Wiśniewska ◽  
Gabriela Chwalik ◽  
Sylwia Łagan
Keyword(s):  
Free Energy ◽  
Surface Free Energy ◽  
Living Organism ◽  
Degradation Process ◽  
Material Surface ◽  
Control Group ◽  
X Rays ◽  
X Ray ◽  
The Stability

The evaluation of a degradation process of polyethylene (PE) in in vitro conditions under the influence of X-rays (X) and an in-cubation in two solutions simulating the environment of a living organism (SBF – simulated body fluid) was carried out. A dose corresponding to 10 standard X-ray pictures of the skeletal system as well as Ringer's and saline solutions at 40°C were used in the study. The paper presents the results of the influence of the 12-month studies on the selected surface properties of the material: surface wettability and abrasiveness. The value of surface free energy (SFE) was determined on the basis of the wetting angle measurements. The conductivity of the incubation fluids was also analyzed. The obtained results indicate that the adopted dose of X-ray radiation has no significant effect on the wettability of the surface of polyethylene. The nature of the surface layer of polyethylene did not change as a result of the 12-month incubation and remained hydrophilic. For the samples incubated in both immersion fluids, a decrease in surface free energy (SFE) was observed. For both the irradiated material and the control group, no significant changes in the mass of the samples and the conductivity of the incubation fluids were found, which indicates the stability of polyethylene. However, the abrasion value increased by approximately 26%. With the passage of the incubation time, a decrease in the value of this parameter was observed for the polyethylene subjected to radiation. No significant changes were found for the control group.

scholarly journals Inverse-Compton scattering in the resolved jet of the high-redshift quasar PKS J1421−0643

2020 ◽  
Vol 497 (1) ◽  
pp. 988-1000 ◽  
Author(s):  
D M Worrall ◽  
M Birkinshaw ◽  
H L Marshall ◽  
D A Schwartz ◽  
A Siemiginowska ◽  
...  
Keyword(s):  
Gamma Ray ◽  
High Redshift ◽  
Lorentz Factor ◽  
High Energy ◽  
Radio Spectrum ◽  
X Rays ◽  
X Ray ◽  
Inverse Compton Scattering ◽  
Inverse Compton ◽  
Jet Power

ABSTRACT Despite the fact that kpc-scale inverse-Compton (iC) scattering of cosmic microwave background (CMB) photons into the X-ray band is mandated, proof of detection in resolved quasar jets is often insecure. High redshift provides favourable conditions due to the increased energy density of the CMB, and it allows constraints to be placed on the radio synchrotron-emitting electron component at high energies that are otherwise inaccessible. We present new X-ray, optical, and radio results from Chandra, HST, and the VLA for the core and resolved jet in the z = 3.69 quasar PKS J1421−0643. The X-ray jet extends for about 4.5 arcsec (32 kpc projected length). The jet’s radio spectrum is abnormally steep and consistent with electrons being accelerated to a maximum Lorentz factor of about 5000. Results argue in favour of the detection of iC X-rays for modest magnetic field strength of a few nT, Doppler factor of about 4, and viewing angle of about 15°, and predict the jet to be largely invisible in most other spectral bands including the far- and mid-infrared and high-energy gamma-ray. The jet power is estimated to be about 3 × 1046 erg s−1 which is of order a tenth of the quasar bolometric power, for an electron–positron jet. The jet radiative power is only about 0.07 per cent of the jet power, with a smaller radiated power ratio if the jet contains heavy particles, so most of the jet power is available for heating the intergalactic medium.

scholarly journals Cosmological test using the Hubble diagram of high-z quasars

2019 ◽  
Vol 489 (1) ◽  
pp. 517-523 ◽  
Author(s):  
Fulvio Melia
Keyword(s):  
Bayesian Information Criterion ◽  
Cold Dark Matter ◽  
Information Criterion ◽  
Hubble Diagram ◽  
High Quality ◽  
Diverse Range ◽  
Comparative Tests ◽  
X Ray ◽  
The Standard Model ◽  
Free Parameters

ABSTRACT It has been known for over three decades that the monochromatic X-ray and UV luminosities in quasars are correlated, though non-linearly. This offers the possibility of using high-z quasars as standard candles for cosmological testing. In this paper, we use a recently assembled, high-quality catalogue of 1598 quasars extending all the way to redshift ∼6, to compare the predictions of the Rh = ct and Lambda cold dark matter (ΛCDM) cosmologies. In so doing, we affirm that the parameters characterizing the correlation depend only weakly on the chosen cosmology, and that both models account very well for the data. Unlike ΛCDM, however, the Rh = ct model has no free parameters for this work, so the Bayesian Information Criterion favours it over ΛCDM with a relative likelihood of $\sim 88{{\ \rm per\ cent}}$ versus $\sim 10{{\ \rm per\ cent}}$. This result is consistent with the outcome of other comparative tests, many of which have shown that Rh = ct is favoured over the standard model based on a diverse range of observations.

An Examination of the Overall Stability of an XRF Spectrometer with Special Reference to Fourier Analysis of Temporal Variation

1984 ◽  
Vol 28 ◽  
pp. 103-106
Author(s):  
T. K. Smith
Keyword(s):  
X Rays ◽  
Short Term ◽  
X Ray ◽  
External Perturbations ◽  
Overall Stability ◽  
Design And Manufacturing ◽  
Temperature And Pressure ◽  
Manufacturing Techniques ◽  
The Stability ◽  
Source Of Error

In any analytical method, one of the first considerations in obtaining precise and accurate results is the stability of the instrument. Progressive refinement in design and manufacturing techniques over many years has led to short-term stability of X-ray generation, transmission and detection in XRF spectrometers of a magnitude such that, in favourable cases, the random process of emission (and to some extent, absorption) is the major source of error; superimposed on this, however, are other variations, some of them periodic.Many processes modify the intensity of X-rays recorded by a spectrometer's sealer and timer: besides those produced by the instrument itself there are potential external perturbations perhaps reverting to electricity generating stations or even further. More important effects may be caused by local features such as ambient temperature and pressure, and in the case of improper setting of machine conditions or of existence of a fault, enhancement may be observed.

scholarly journals The SIX survey: evolution and properties of AGN in the local universe

2013 ◽  
Vol 9 (S304) ◽  
pp. 139-139
Author(s):  
Eugenio Bottacini
Keyword(s):  
Ad Hoc ◽  
High Redshift ◽  
Local Universe ◽  
X Ray ◽  
Systematic Effects ◽  
Coded Mask ◽  
X Ray Background ◽  
Cross Calibration ◽  
End Stage ◽  
Calibration Techniques

AbstractCurrent most sensitive surveys at soft X-ray (~ 0.5–10 keV) energies by Chandra and XMM-Newton preferably sample AGN at high-redshift (z > 0.5). At low-redshift (z < 0.5), where AGN are supposed to be in their evolution end-stage, these sources are very sparsely sampled. The low-redshift universe is best fathomed at hard X–ray energies (> 15 keV) by the INTEGRAL and the Swift missions with their coded-mask telescopes IBIS/ISGRI and BAT respectively. These instruments have two major advantages: 1) they have a huge field of view, hence allowing to sample a large number of AGN at low-redshift; 2) they operate at energies above 15 keV, hence allowing detecting photons with enough power to efficiently pierce even through the Compton-thick torus of AGN. Estimates based on observations with PDS on board the BeppoSAX satellite predict that Compton-thick AGN should dominate over unabsorbed AGN in the local universe playing an important role in reproducing the shape and intensity of the cosmic X-ray background (CXB). However coded-mask detectors suffer from heavy systematic effects preventing them from reaching their theoretical limiting sensitivity. We overcome this limit with a new and alternative approach, which has been designed ad hoc to improve the sensitivity of hard X–ray surveys by using IBIS/ISGRI and BAT. Both telescopes are so close in design that their observations can be combined to obtain a more sensitive survey. The observations are combined with resampling, merging, and cross-calibration techniques. We are able to sample limiting fluxes of the order of ~3.3 times 10−12 erg cm−2 s−1 in the 18–55 keV energy range. This is called the SIX survey, that stands for Swift-INTEGRAL X-ray survey. The SIX survey extends over a wide sky area of 6200 deg2 and it is used to obtain a persistent sample of faint AGN. The source number density (log N - log S) is a factor of 3 better than current parent surveys of BAT and IBIS/ISGRI alone. I will present a study of the evolution of AGN in the local universe discussing the X-ray luminosity function. The properties of the AGN circum-nuclear environment will be discussed checking the consistency with the AGN unification scheme. Also I will compare the results from the SIX survey to the results predicted for the NuSTAR survey. Finally preliminary results of the all-sky SIX survey are presented.

scholarly journals X-ray emission of z > 2.5 active galactic nuclei can be obscured by their host galaxies

2019 ◽  
Vol 623 ◽  
pp. A172 ◽  
Author(s):  
C. Circosta ◽  
C. Vignali ◽  
R. Gilli ◽  
A. Feltre ◽  
F. Vito ◽  
...  
Keyword(s):  
Active Galactic Nuclei ◽  
High Redshift ◽  
Galactic Nuclei ◽  
Far Infrared ◽  
Host Galaxy ◽  
Spectral Energy ◽  
X Rays ◽  
Host Galaxies ◽  
X Ray ◽  
Stellar Masses

We present a multiwavelength study of seven active galactic nuclei (AGN) at spectroscopic redshift >2.5 in the 7 Ms Chandra Deep Field South that were selected for their good far-infrared (FIR) and submillimeter (submm) detections. Our aim is to investigate the possibility that the obscuration observed in the X-rays can be produced by the interstellar medium (ISM) of the host galaxy. Based on the 7 Ms Chandra spectra, we measured obscuring column densities NH,  X in excess of 7 × 1022 cm−2 and intrinsic X-ray luminosities LX >  1044 erg s−1 for our targets, as well as equivalent widths for the Fe Kα emission line EWrest ≳ 0.5−1 keV. We built the UV-to-FIR spectral energy distributions (SEDs) by using broadband photometry from the CANDELS and Herschel catalogs. By means of an SED decomposition technique, we derived stellar masses (M* ∼ 1011 M⊙), IR luminosities (LIR >  1012 L⊙), star formation rates (SFR ∼ 190−1680 M⊙ yr−1) and AGN bolometric luminosities (Lbol ∼ 1046 erg s−1) for our sample. We used an empirically calibrated relation between gas masses and FIR/submm luminosities and derived Mgas ∼ 0.8−5.4 × 1010 M⊙. High-resolution (0.3−0.7″) ALMA data (when available, CANDELS data otherwise) were used to estimate the galaxy size and hence the volume enclosing most of the ISM under simple geometrical assumptions. These measurements were then combined to derive the column density associated with the ISM of the host, which is on the order of NH,  ISM ∼ 1023−24 cm−2. The comparison between the ISM column densities and those measured from the X-ray spectral analysis shows that they are similar. This suggests that at least at high redshift, significant absorption on kiloparsec scales by the dense ISM in the host likely adds to or substitutes that produced by circumnuclear gas on parsec scales (i.e., the torus of unified models). The lack of unobscured AGN among our ISM-rich targets supports this scenario.

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