We present new measurements of the evolution of the X-ray luminosity functions (XLFs) of unabsorbed and absorbed active galactic nuclei (AGNs) out to z ∼ 5. We construct samples containing 2957 ...sources detected at hard (2–7 keV) X-ray energies and 4351 sources detected at soft (0.5–2 keV) energies from a compilation of Chandra surveys supplemented by wide-area surveys from ASCA and ROSAT. We consider the hard and soft X-ray samples separately and find that the XLF based on either (initially neglecting absorption effects) is best described by a new flexible model parametrization where the break luminosity, normalization, and faint-end slope all evolve with redshift. We then incorporate absorption effects, separately modelling the evolution of the XLFs of unabsorbed (20 < log N
H < 22) and absorbed (22 < log N
H < 24) AGNs, seeking a model that can reconcile both the hard- and soft-band samples. We find that the absorbed AGN XLF has a lower break luminosity, a higher normalization, and a steeper faint-end slope than the unabsorbed AGN XLF out to z ∼ 2. Hence, absorbed AGNs dominate at low luminosities, with the absorbed fraction falling rapidly as luminosity increases. Both XLFs undergo strong luminosity evolution which shifts the transition in the absorbed fraction to higher luminosities at higher redshifts. The evolution in the shape of the total XLF is primarily driven by the changing mix of unabsorbed and absorbed populations.
We study the propagation of probe scalar fields in the background of 4D Einstein–Gauss–Bonnet black holes with anti-de Sitter (AdS) asymptotics and calculate the quasinormal modes. Mainly, we show ...that the quasinormal spectrum consists of two different branches, a branch perturbative in the Gauss–Bonnet coupling constant
α
and another branch, nonperturbative in
α
. The perturbative branch consists of complex quasinormal frequencies that approximate the quasinormal frequencies of the Schwarzschild AdS black hole in the limit of a null coupling constant. On the other hand, the nonperturbative branch consists of purely imaginary frequencies and is characterized by the growth of the imaginary part when
α
decreases, diverging in the limit of null coupling constant; therefore they do not exist for the Schwarzschild AdS black hole. Also, we find that the imaginary part of the quasinormal frequencies is always negative for both branches; therefore, the propagation of scalar fields is stable in this background.
The extragalactic background light (EBL) is of fundamental importance both for understanding the entire process of galaxy evolution and for γ-ray astronomy, but the overall spectrum of the EBL ...between 0.1 and 1000 μm has never been determined directly from galaxy spectral energy distribution (SED) observations over a wide redshift range. The evolving, overall spectrum of the EBL is derived here utilizing a novel method based on observations only. This is achieved from the observed evolution of the rest-frame K-band galaxy luminosity function up to redshift 4, combined with a determination of galaxy-SED-type fractions. These are based on fitting Spitzer Wide-Area Infrared Extragalactic Survey (SWIRE) templates to a multiwavelength sample of about 6000 galaxies in the redshift range from 0.2 to 1 from the All-wavelength Extended Groth Strip International Survey (AEGIS). The changing fractions of quiescent galaxies, star-forming galaxies, starburst galaxies and active galactic nucleus (AGN) galaxies in that redshift range are estimated, and two alternative extrapolations of SED types to higher redshifts are considered. This allows calculation of the evolution of the luminosity densities from the ultraviolet (UV) to the infrared (IR), the evolving star formation rate density of the Universe, the evolving contribution to the bolometric EBL from the different galaxy populations including AGN galaxies and the buildup of the EBL. Our EBL calculations are compared with those from a semi-analytic model, another observationally based model and observational data. The EBL uncertainties in our modelling based directly on the data are quantified, and their consequences for attenuation of very-high-energy γ-rays due to pair production on the EBL are discussed. It is concluded that the EBL is well constrained from the UV to the mid-IR, but independent efforts from IR and γ-ray astronomy are needed in order to reduce the uncertainties in the far-IR.
We study the propagation of scalar fields in the background of an asymptotically de Sitter black hole solution in
f
(
R
) gravity. The aim of this work is to analyze in modified theories of gravity ...the existence of an anomalous decay rate of the quasinormal modes (QNMs) of a massive scalar field which was recently reported in Schwarzschild black hole backgrounds, in which the longest-lived modes are the ones with higher angular number, for a scalar field mass smaller than a critical value, while that beyond this value the behavior is inverted. We study the QNMs for various overtone numbers and they depend on a parameter
β
which appears in the metric and characterizes the
f
(
R
) gravity. For small
β
, i.e. small deviations from the Schwarzschild–dS black hole the anomalous behavior in the QNMs is present for the photon sphere modes, and the critical value of the mass of the scalar field depends on the parameter
β
while for large
β
, i.e. large deviations, the anomalous behavior and the critical mass does not appear. Also, the critical mass of the scalar field increases when the overtone number increases until the
f
(
R
) gravity parameter
β
approaches the near extremal limit at which the critical mass of the scalar field does not depend anymore on the overtone number. The imaginary part of the quasinormal frequencies is always negative leading to a stable propagation of the scalar fields in this background.
Background
The general medical impacts of coronavirus (COVID‐19) are increasingly appreciated. However, its impact on neurocognitive, psychiatric health and quality of life (QoL) in survivors after ...the acute phase is poorly understood. We aimed to evaluate neurocognitive function, psychiatric symptoms and QoL in COVID‐19 survivors shortly after hospital discharge.
Methods
This was a cross‐sectional analysis of a prospective study of hospitalized COVID‐19 survivors followed up for 2 months after discharge. A battery of standardized instruments evaluating neurocognitive function, psychiatric morbidity and QoL (mental and physical components) was administered by telephone.
Results
Of the 229 screened patients, 179 were included in the final analysis. Amongst survivors, the prevalence of moderately impaired immediate verbal memory and learning was 38%, delayed verbal memory (11.8%), verbal fluency (34.6%) and working memory (executive function) (6.1%), respectively. Moreover, 58.7% of patients had neurocognitive impairment in at least one function. Rates of positive screening for anxiety, depression and post‐traumatic stress disorder were 29.6%, 26.8% and 25.1%, respectively. In addition, 39.1% of the patients had psychiatric morbidity. Low QoL for physical and mental components was detected in 44.1% and 39.1% of patients respectively. Delirium and psychiatric morbidity were associated with neurocognitive impairment, and female gender was related with psychiatric morbidity.
Conclusion
Hospitalized COVID‐19 survivors showed a considerable prevalence of neurocognitive impairment, psychiatric morbidity and poor QoL in the short term. It is uncertain if these impacts persist over the long term.
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