EVN observations of low-luminosity flat-spectrum AGNs

We present and discuss the results of VLBI (EVN) observations of three low-luminosity (P(5 GHz)<10^25 W/Hz) Broad Emission Line AGNs carefully selected from a sample of flat spectrum radio sources (CLASS). Based on the total and the extended radio power at 5 GHz and at 1.4 GHz respectively, these objects should be technically classified as radio-quiet AGN and thus the origin of their radio emission is not clearly understood. The VLBI observations presented in this paper have revealed compact radio cores which imply a lower limit on the brightness temperature of about 3X10^8 K. This result rules out a thermal origin for the radio emission and strongly suggests an emission mechanism similar to that observed in more powerful radio-loud AGNs. Since, by definition, the three objects show a flat (or inverted) radio spectrum between 1.4 GHz and 8.4 GHz, the observed radio emission could be relativistically beamed. Multi-epoch VLBI observations can confirm this possibility in two years time.Comment: Accepted for publication in MNRA

The CLASS blazar survey: testing the blazar sequence

We discuss the properties of the sources in the CLASS Blazar survey which aims at the selection of low radio power (P(5GHz)<10^25 W Hz^-1) blazars. We use VLA data from available catalogues and from our own observations to constrain the radio core-dominance of the sample which, together with the flat radio spectral index, is a signature of the blazar activity. X-ray data from the ROSAT All Sky Survey were also collected in order to constrain the radio-to-X-ray luminosity ratio (alpha_RX) of the sources. The data analysis shows that more than 30% of sources at low radio power (P(5 GHz)<10^25 W Hz^-1) have an alpha_RX steeper than that expected in the framework of the ``blazar sequence'' recently put forward to unify the high and low power blazars. The possibility that this result is influenced by contaminating sources in the current sample is discussed. The conclusion is that, even if a number of non-blazars (typically CSO/GPS sources) are expected in the survey, it is unlikely that this constitutes the sole reason for the observed deviation. In particular, we show 2 examples for which the blazar nature is confirmed from VLBI data and for which the steep alpha_RX (suggesting a synchrotron peak frequency below 10^15.5 Hz) and the low radio power (0.6-2x10^24 W Hz^-1) put these sources outside the ``blazar sequence''. The results presented here show the importance of a correct and unbiased sampling of the low-power regime of the blazar population.Comment: 20 pages, accepted for publication in MNRA

The space density of z>4 blazars

High redshift blazars are an important class of Active Galactic Nuclei (AGN) that can provide an independent estimate of the supermassive black-hole mass function in high redshift radio-loud AGN without the bias due to absorption along the line-of-sight. Using the Cosmic Lens All Sky Survey (CLASS) we built a complete radio flux-limited sample of high redshift (z>4) blazars suitable for statistical studies. By combining dedicated optical observations and the SDSS spectroscopic database, we obtained a sample of 26 blazar candidates with a spectroscopic redshift above 4. On the basis of their radio spectrum we distinguish between blazars and QSO with a Gigahertz Peaked Spectrum (GPS) like spectrum. Out of the 18 confirmed blazars 14 constitute a completely identified, flux-limited sample down to a magnitude of 21 (AB). Using this complete sample we derive a space density of blazars with 4<z<5.5 of rho=0.13 (+0.05,-0.03) Gpc^-3. This is the first actual estimate of the blazar space density in this range of redshift. This value is in good agreement with the extrapolation of the luminosity function and cosmological evolution based on a sample of flat-spectrum radio quasars selected at lower redshifts and it is consistent with a cosmological evolution peaking at z$\sim$2 similar to radio-quiet QSO. We do not confirm, instead, the presence of a peak at z~4 in the space density evolution, recently suggested using an X-ray selected sample of blazars. It is possible that this extreme peak of the evolution is present only among the most luminous blazars.Comment: 14 pages, accepted for publication on MNRAS (https://doi.org/10.1093/mnras/sty3526

SDSSJ143244.91+301435.3: a link between radio-loud narrow-line Seyfert 1 galaxies and compact steep-spectrum radio sources?

We present SDSSJ143244.91+301435.3, a new case of radio-loud narrow line Seyfert 1 (RL NLS1) with a relatively high radio power (P1.4GHz=2.1x10^25 W Hz^-1) and large radioloudness parameter (R1.4=600+/-100). The radio source is compact with a linear size below ~1.4 kpc but, contrary to most of the RL NLS1 discovered so far with such a high R1.4, its radio spectrum is very steep (alpha=0.93) and not supporting a 'blazar-like' nature. Both the small mass of the central super-massive black-hole and the high accretion rate relative to the Eddington limit estimated for this object (3.2x10^7 Msun and 0.27, respectively, with a formal error of ~0.4 dex on both quantities) are typical of the class of NLS1. Through a modeling of the spectral energy distribution of the source we have found that the galaxy hosting SDSSJ143244.91+301435.3 is undergoing a quite intense star-formation (SFR=50 Msun y^-1) which, however, is expected to contribute only marginally (~1 per cent) to the observed radio emission. The radio properties of SDSSJ143244.91+301435.3 are remarkably similar to those of compact steep spectrum (CSS) radio sources, a class of AGN mostly composed by young radio galaxies. This may suggest a direct link between these two classes of AGN, with the CSS sources possibly representing the misaligned version (the so-called parent population) of RL NLS1 showing blazar characteristics.Comment: 14 pages, 7 figures, 4 tables, accepted for publication in MNRA

Obscuration in high redshift jetted QSO

Obscuration in high-redshift quasi-stellar objects (QSO) has a profound impact on our understanding of the evolution of supermassive black holes across the cosmic time. An accurate quantification of its relevance is therefore mandatory. We present a study aimed at evaluating the importance of obscuration in high redshift jetted QSO, i.e. those active nuclei characterized by the presence of powerful relativistic jets. We compare the observed number of radio detected QSO at different radio flux density limits with the value predicted by the beaming model on the basis of the number of oriented sources (blazars). Any significant deficit of radio-detected QSO compared to the predictions can be caused by the presence of obscuration along large angles from the jet direction. We apply this method to two sizable samples characterized by the same optical limit (mag=21) but significantly different radio density limits (30 mJy and 1 mJy respectively) and containing a total of 87 independent radio-loud 4<z<6.8 QSO, 31 of which classified as blazars. We find a general good agreement between the numbers predicted by the model and those actually observed, with only a marginal discrepancy at 0.5 mJy that could be caused by the lack of completeness of the sample. We conclude that we have no evidence of obscuration within angles 10-20deg from the relativistic jet direction. We also show how the ongoing deep wide-angle radio surveys will be instrumental to test the presence of obscuration at much larger angles, up to 30-35deg. We finally suggest that, depending on the actual fraction of obscured QSO, relativistic jets could be much more common at high redshifts compared to what is usually observed in the local UniverseComment: 14 pages, 5 figures. Accepted for publication on A&

Estimating Nosocomial Infection and its Outcomes in Hospital Patients in England with a Diagnosis of COVID-19 Using Machine Learning

BACKGROUND: COVID-19 nosocomial infections (NIs) may have played a significant role in the dynamics of the pandemic in England, but analysis of their impact at the national scale has been lacking. Our aim was to provide a comprehensive account of NIs, identify their characteristics and outcomes in patients with a diagnosis of COVID-19 and use machine learning modelling to refine these estimates. METHODS: From the Hospital Episodes Statistics database all adult hospital patients in England with a diagnosis of COVID-19 and discharged between March 1st 2020 and March 31st 2021 were identified. A cohort of suspected COVID-19 NIs was identified using four empirical methods linked to hospital coding. A random forest classifier was designed to model the relationship between acquiring NIs and the covariates: patient characteristics, comorbidities, frailty, trust capacity strain and severity of COVID-19 infections. FINDINGS: In total, 374,244 adult patients with COVID-19 were discharged during the study period. The four empirical methods identified 29,896 (8.0%) patients with NIs. The random forest classifier estimated a mean NI rate of 10.5%, with a peak close to 18% during the first wave, but much lower rates thereafter and around 7% in early spring 2021. NIs were highly correlated with longer lengths of stay, high trust capacity strain, greater age and a higher degree of patient frailty. NIs were also found to be associated with higher mortality rates and more severe COVID-19 sequelae, including pneumonia, kidney disease and sepsis. INTERPRETATION: Identification of the characteristics of patients who acquire NIs should help trusts to identify those most at risk. The evolution of the NI rate over time may reflect the impact of changes in hospital management practices and vaccination efforts. Variations in NI rates across trusts may partly reflect different data recording and coding practice

XMM-Newton spectroscopy of an X-ray selected sample of RL AGNs

This paper presents the X-ray spectroscopy of an X-ray selected sample of 25 radio-loud (RL) AGNs extracted from the XBSS sample. The main goal is to study the origin of the X-ray spectral differences usually observed between radio-loud and radio-quiet (RQ) AGNs. To this end, a comparison sample of 53 RQ AGNs has been also extracted from the same XBSS sample and studied together with the sample of RL AGNs. We have focused the analysis on the distribution of the X-ray spectral indices of the power-law component that models the large majority of the spectra in both samples. We find that the mean X-ray energy spectral index is very similar in the 2 samples and close to alpha_X~1. However, the intrinsic distribution of the spectral indices is significantly broader in the sample of RL AGNs. In order to investigate the origin of this difference, we have divided the RL AGNs into blazars and ``non-blazars'', on the basis of the available optical and radio information. We find strong evidence that the broad distribution observed in the RL AGN sample is mainly due to the presence of the blazars. Furthermore, within the blazar class we have found a link between the X-ray spectral index and the value of the radio-to-X-ray spectral index suggesting that the observed X-ray emission is directly connected to the emission of the relativistic jet. This trend is not observed among the ``non-blazars'' RL AGNs. This favours the hypothesis that, in these latter sources, the X-ray emission is not significantly influenced by the jet emission and it has probably an origin similar to the RQ AGNs. Overall, the results presented here indicate that the observed distribution of the X-ray spectral indices in a given sample of RL AGNs is strongly dependent on the amount of relativistic beaming present in the selected sources.Comment: 18 pages, 10 figures, accepted for publication in A&

Data consistency in the English Hospital Episodes Statistics database

BACKGROUND: To gain maximum insight from large administrative healthcare datasets it is important to understand their data quality. Although a gold standard against which to assess criterion validity rarely exists for such datasets, internal consistency can be evaluated. We aimed to identify inconsistencies in the recording of mandatory International Statistical Classification of Diseases and Related Health Problems, tenth revision (ICD-10) codes within the Hospital Episodes Statistics dataset in England. METHODS: Three exemplar medical conditions where recording is mandatory once diagnosed were chosen: autism, type II diabetes mellitus and Parkinson's disease dementia. We identified the first occurrence of the condition ICD-10 code for a patient during the period April 2013 to March 2021 and in subsequent hospital spells. We designed and trained random forest classifiers to identify variables strongly associated with recording inconsistencies. RESULTS: For autism, diabetes and Parkinson's disease dementia respectively, 43.7%, 8.6% and 31.2% of subsequent spells had inconsistencies. Coding inconsistencies were highly correlated with non-coding of an underlying condition, a change in hospital trust and greater time between the spell with the first coded diagnosis and the subsequent spell. For patients with diabetes or Parkinson's disease dementia, the code recording for spells without an overnight stay were found to have a higher rate of inconsistencies. CONCLUSIONS: Data inconsistencies are relatively common for the three conditions considered. Where these mandatory diagnoses are not recorded in administrative datasets, and where clinical decisions are made based on such data, there is potential for this to impact patient care

Elusive AGN in the XMM-Newton bright serendipitous survey

AIMS: We investigate here the nature of all the sources (35 in total) in the XBS survey (which is 86% optically identified) showing an optical spectrum dominated by the light from the host galaxy with no evidence (or little evidence) for the presence of an AGN. METHODS: We use the X-ray spectral analysis to assess the presence of an AGN in these sources and to characterize its properties. RESULTS: We detect AGN activity in 33 out of 35 sources. The remaining 2 sources are the ones with the lowest X-ray luminosity in the sample (L[2-10keV]<10^41 erg s^-1) and their X-ray emission could be produced within the host galaxy. We find that the ``recognition problem'' for AGN is very critical in the low-luminosity regime (at least 60% of the AGN with L[2-10keV]<10^43 erg s^-1 are elusive) becoming negligible for high X-ray luminosities (~1.5% of elusive AGN with L[2-10keV]>10^44 erg s^-1). This problem affects mostly absorbed AGN (~40% of type~2 AGN in the survey are elusive) but also a significant fraction of unabsorbed AGN (8%). CONCLUSIONS: We find that the simplest explanations of why these 33 (or most of them) AGNs are elusive are two: at low X-ray luminosities (<10^43 erg s^-1) the most important reason is the intrinsically low AGN/galaxy contrast (optical dilution) while at high luminosities (>10^44 erg s^-1) it is due to the optical absorption (in the Compton-thin regime, i.e. NH<10^24 cm^-2). Alternative hypotheses, like the presence of Compton-thick sources, BL Lac objects or ``non-standard'' AGN (e.g. with alpha_OX<1 or with weak/absorbed Narrow Line Region) are not supported by the data although we cannot exclude the presence in the sample of a few sources of these types.Comment: accepted for publication in A&A, 17 pages, 9 figure

Redshift Limits of BL Lacertae Objects from Optical Spectroscopy

Context: BL Lacertae objects have been the targets for numerous recent multiwavelength campaigns, continuum spectral variability studies, and theoretical spectral and variability modeling. A meaningful interpretation of the results of such studies requires a reliable knowledge of the objects' redshifts; however, the redshifts for many are still unknown or uncertain. Aims: Therefore, we hope to determine or constrain the redshifts of six BL Lac objects with unknown or poorly known redshifts. Methods: Observations were made of these objects with the MDM 2.4 m Hiltner telescope. Although no spectral features were detected, and thus no redshifts could be measured, lower redshift limits were assigned to the objects based on the expected equivalent widths of absorption features in their host galaxies. Redshifts were also estimated for some objects by assuming the host galaxies are standard candles and using host galaxy apparent magnitudes taken from the literature. Results: The commonly used redshift of $z=0.102$ for 1219+285 is almost certainly wrong, while the redshifts of the other objects studied remain undetermined.Comment: 4 pages, 2 figures. Accepted by A&A Research Note