X-ray properties of z ≳ 6.5 quasars Pons, E; McMahon, R G; Banerji, M ...
Monthly notices of the Royal Astronomical Society,
01/2020, Letnik:
491, Številka:
3
Journal Article
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ABSTRACT
We present XMM–Newton X-ray observations and analysis of three Dark Energy Survey z > 6.5 quasars (VDES J0020−3653 at z = 6.824, VDES J0244−5008 at z = 6.724, and VDES J0224−4711 at z = ...6.526) and six other quasars with 6.438 < z < 6.747 from the XMM–Newton public archive. Two of the nine quasars are detected at a high (>4σ) significance level: VDES J0224−4711(z = 6.53) at 9σ and PSO J159−02 (z = 6.38) at 8σ. They have a photon index of $\Gamma =1.82^{+0.29}_{-0.27}$ and $1.94^{+0.31}_{-0.29}$, respectively, which is consistent with the mean value of ∼1.9 found for quasars at all redshifts. The rest-frame 2–10 keV luminosity of VDES J0224−4711 is $L_{2\!-\!10\, \mathrm{keV}} = (2.92\pm 0.43)\times 10^{45}\,\mathrm{erg\,s^{-1}}$, which makes this quasar one of the most X-ray luminous quasars at z > 5.5 and the most X-ray luminous quasar at z > 6.5, with a luminosity 6 times and 2.5 times larger than ULAS J1120+0641 (z = 7.08) and ULAS J1342+0928 (z = 7.54), respectively. The X-ray-to-optical power-law slopes of the nine quasars are consistent with the previously observed anticorrelation of αox with UV luminosity $L_{2500\, \mathrm{\mathring{\rm A} }}$. We find no evidence for evolution of αox with redshift when the anticorrelation with UV luminosity is taken into account. Similar to previous studies at z ∼ 6, we have found remarkably consistent X-ray spectral properties between low-redshift quasars (z ∼ 1) and high-redshift quasars. Our results add further evidence to the picture that the observable properties of high-luminosity quasars over the UV-to-X-ray spectral region have not evolved significantly from z ∼ 7 to the present day and that quasars comparable to local versions existed 800 Myr after the big bang.
ABSTRACT
We present new X-ray observations of luminous heavily dust-reddened quasars (HRQs) selected from infrared (IR) sky surveys. HRQs appear to be a dominant population at high redshifts and the ...highest luminosities, and may be associated with a transitional ‘blowout’ phase of black hole and galaxy co-evolution models. Despite this, their high-energy properties have been poorly known. We use the overall sample of 10 objects with XMM–Newton coverage to study the high-energy properties of HRQs at $\langle$Lbol$\rangle$ =1047.5 erg s−1 and $\langle$z$\rangle$ =2.5. For seven sources with strong X-ray detections, we perform spectral analyses. These find a median X-ray luminosity of $\left\langle L_{\rm 2\!-\!10\, keV} \right\rangle = 10^{45.1}$ erg s−1, comparable to the most powerful X-ray quasars known. The gas column densities are NH = (1–8) × 1022 cm−2, in agreement with the amount of dust extinction observed. The dust-to-gas ratios are sub-Galactic, but are higher than found in local AGN. The intrinsic X-ray luminosities of HRQs are weak compared to the mid-IR ($L_{\rm 6\, \mu m}$) and bolometric luminosities (Lbol), in agreement with findings for other luminous quasar samples. For instance, the X-ray to bolometric corrections range from κbol ≈ 50 to 3000. The moderate absorption levels and accretion rates close to the Eddington limit ($\langle$λEdd$\rangle$ =1.06) are in agreement with a quasar blowout phase. Indeed, we find that the HRQs lie in the forbidden region of the NH–λEdd plane, and therefore that radiation pressure feedback on the dusty interstellar medium may be driving a phase of blowout that has been ongoing for a few 105 yr. The wider properties, including O iii narrow-line region kinematics, broadly agree with this interpretation.
Pheochromocytoma: A review Tsirlin, A; Oo, Y; Sharma, R ...
Maturitas,
03/2014, Letnik:
77, Številka:
3
Journal Article
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Abstract Pheochromocytomas are catecholamine producing neuroendocrine tumors that can be adrenal or extra-adrenal in origin. The classic symptoms of pheochromocytoma are headache, palpitation, ...anxiety and diaphoresis and the tumor can occur at any age with equal gender distribution. In patients with an established mutation or hereditary syndrome the condition may manifest at a younger age than in those with sporadic disease. Pheochromocytoma can be associated with certain genetic syndromes such as multiple endocrine neoplasia type 2 (MEN 2), neurofibromatosis (NF) and von Hippel–Lindau (VHL) syndrome. Pheochromocytoma is diagnosed with biochemical confirmation of hormonal excess followed by anatomical localization (CT or MRI). The mainstay of definitive therapy is surgical resection. In this review, we discuss in detail about the symptomatology, diagnosis, genetic aspects and management of pheochromocytoma.
Abstract
New populations of hyper-luminous, dust-obscured quasars have been recently discovered around the peak epoch of galaxy formation (z ∼ 2–3), in addition to similar sources found at lower ...redshifts. Such dusty quasars are often interpreted as sources ‘in transition’, from dust-enshrouded starbursts to unobscured luminous quasars, along the evolutionary sequence. Here we consider the role of the active galactic nucleus (AGN) radiative feedback, driven by radiation pressure on dust, in high-luminosity, dust-obscured sources. We analyse how the radiation pressure-driven dusty shell models, with different shell mass configurations, may be applied to the different populations of dusty quasars reported in recent observations. We find that expanding shells, sweeping up matter from the surrounding environment, may account for prolonged obscuration in dusty quasars, e.g. for a central luminosity of L ∼ 1047 erg s−1, a typical obscured phase (with extinction in the range AV ∼ 1–10 mag) may last a few ∼106 yr. On the other hand, fixed-mass shells, coupled with high dust-to-gas ratios, may explain the extreme outflows recently discovered in red quasars at high redshifts. We discuss how the interaction between AGN radiative feedback and the ambient medium at different temporal stages in the evolutionary sequence may contribute to shape the observational appearance of dusty quasar populations.
We present ALMA observations of cold dust and molecular gas in four high-luminosity, heavily reddened (AV ~ 2.5-6 mag) type 1 quasars at z ~ 2.5 with virial ..., to test whether dusty, massive ...quasars represent the evolutionary link between submillimetre-bright galaxies and unobscured quasars. All four quasars are detected in both the dust continuum and in the super( 12)CO(3-2) line. The mean dust mass is ... assuming a typical high-redshift quasar spectral energy distribution (T = 41 K, beta = 1.95 or T = 47 K, beta = 1.6). The implied star formation rates are very high -- ... in all cases. Gas masses estimated from the CO line luminosities cover ... and the gas depletion time-scales are very short -- ~5-20 Myr. A range of gas-to-dust ratios is observed in the sample. We resolve the molecular gas in one quasar -- ULASJ2315+0143 (z = 2.561) -- which shows a strong velocity gradient over ~20 kpc. The velocity field is consistent with a rotationally supported gas disc but other scenarios, e.g. mergers, cannot be ruled out at the current resolution of these data. In another quasar -- ULASJ1234+0907 (z = 2.503) -- we detected molecular line emission from two millimetre-bright galaxies within 200 kpc of the quasar, suggesting that this quasar resides in a significant overdensity. The high detection rate of both cold dust and molecular gas in these sources, suggests that reddened quasars could correspond to an early phase in massive galaxy formation associated with large gas reservoirs and significant star formation. (ProQuest: ... denotes formulae/symbols omitted.)
Abstract
We present the discovery of a new $z$ ∼ 6.8 quasar discovered with the near-(IR) VISTA Hemisphere Survey (VHS) which has been spectroscopically confirmed by the ESO New Technology Telescope ...(NTT) and the Magellan telescope. This quasar has been selected by spectral energy distribution (SED) classification using near-IR data from VISTA, optical data from Pan-STARRS, and mid-IR data from WISE. The SED classification algorithm is used to statistically rank two classes; foreground Galactic low-mass stars and high-redshift quasars, prior to spectroscopic observation. Forced photometry on Pan-STARRS pixels for VHS J0411–0907 allows to improve the SED-classification-reduced-χ2 and photometric redshift. VHS J0411–0907 ($z$ = 6.82, yAB = 20.1 mag, JAB = 20.0 mag) has the brightest J-band continuum magnitude of the nine known quasars at $z$ > 6.7 and is currently the highest redshift quasar detected in the Pan-STARRS survey. This quasar has one of the lowest black hole mass (MBH = (6.13 ± 0.51) × 108 M⊙) and the highest Eddington ratio (2.37 ± 0.22) of the known quasars at $z$ > 6.5. The high Eddington ratio indicates that some very high-$z$ quasars are undergoing super Eddington accretion. We also present coefficients of the best polynomials fits for colours versus spectral type on the Pan-STARRS, VISTA, and WISE system for MLT dwarfs and present a forecast for the expected numbers of quasars at $z$ > 6.5.
We present an X-ray point-source catalogue from the XMM-Large Scale Structure (XMMLSS) survey region, one of the XMM-Spitzer Extragalactic Representative Volume Survey (XMM-SERVS) fields. We target ...the XMM-LSS region with 1.3 Ms of new XMM-Newton AO-15 observations, transforming the archival X-ray coverage in this region into a 5.3 deg2 contiguous field with uniform X-ray coverage totaling 2.7 Ms of flare-filtered exposure, with a 46 ks median PN exposure time. We provide an X-ray catalogue of 5242 sources detected in the soft (0.5-2 keV), hard (2-10 keV), and/or full (0.5-10 keV) bands with a 1 per cent expected spurious fraction determined from simulations. A total of 2381 new X-ray sources are detected compared to previous source catalogues in the same area. Our survey has flux limits of 1.7 × 10-15, 1.3 × 10-14, and 6.5 × 10-15 erg cm-2 s-1 over 90 per cent of its area in the soft, hard, and full bands, respectively, which is comparable to those of the XMM-COSMOS survey. We identify multiwavelength counterpart candidates for 99.9 per cent of the X-ray sources, of which 93 per cent are considered as reliable based on their matching likelihood ratios. The reliabilities of these high-likelihood-ratio counterparts are further confirmed to be ≈97 per cent reliable based on deep Chandra coverage over ≈5 per cent of the XMM-LSS region. Results of multiwavelength identifications are also included in the source catalogue, along with basic optical-to-infrared photometry and spectroscopic redshifts from publicly available surveys. We compute photometric redshifts for X-ray sources in 4.5 deg2 of our field where forced-aperture multiband photometry is available; > 70 per cent of the X-ray sources in this subfield have either spectroscopic or high-quality photometric redshifts.
We present an updated version of MegaZ-LRG (Collister et al. 2007) with photometric redshifts derived with the neural network method ANNz as well as five other publicly available photometric redshift ...codes (HyperZ, SDSS, Le PHARE, BPZ and ZEBRA) for ∼1.5 million luminous red galaxies (LRGs) in SDSS DR6. This allows us to identify how reliable codes are relative to each other if used as described in their public release. We compare and contrast the relative merits of each code as well as the different templates using ∼13 000 spectroscopic redshifts from the 2SLAQ sample, and note that this comparison is only valid for LRGs. We find that the performance of each code depends on the figure of merit used to assess it, and note that all codes suffer from a redshift-dependent bias. As expected, the availability of a complete training set means that the training method performs best in the intermediate redshift bins where there are plenty of training objects. Codes such as Le PHARE, which use new observed templates, perform best in the lower redshift bins. All codes produce reasonable photometric redshifts, the 1σ scatters ranging from 0.057 to 0.097 if averaged over the entire redshift range. We also perform tests to check whether a training set from a small region of the sky such as 2SLAQ produces biases if used to train over a larger area of the sky. We conclude that this is not likely to be a problem for future wide-field surveys. The complete photometric redshift catalogue including redshift estimates and errors on these from all the six methods as well as the configuration files used to run the various codes can be found at http://www.ast.cam.ac.uk/~mbanerji/Research/MegaZLRGDR6/megaz.html.
There is a high prevalence of type 2 diabetes mellitus and coronary artery disease among urban and migrant Asian Indians despite the absence of traditional risk factors. Evidence exists that Asian ...Indians are more hyperinsulinemic than Caucasians and that hyperinsulinemia may be important in the development of these diseases. To test whether insulin action was related to total or regional adiposity and to explore the potential role of plasma leptin and lipids, we measured insulin-mediated glucose disposal by the euglycemic insulin clamp, adipose distribution and muscle volume using computed axial tomography, and fasting serum leptin and lipid levels in 20 healthy Asian Indian male volunteers (age, 36 +/- 10 yr). A mean body mass index of 24.5 +/- 2.5 kg/m2 was associated with an unusually high percentage of body fat (33 +/- 7%). The majority of the fat was sc, and 16% was visceral (intraabdominal) adipose tissue. The majority (66%) of these nonobese men were insulin resistant. The mean fasting serum leptin level was 7.6 +/- 3.3 ng/mL. Insulin action was inversely correlated with visceral adipose tissue, not total or abdominal sc adipose tissue. In contrast, leptin levels correlated with sc and total (not visceral) adipose tissue. Serum triglyceride and high density lipoprotein cholesterol levels were inversely correlated with each other and were directly related to insulin resistance and visceral (not subcutaneous) fat. Increased visceral fat in Asian Indians is associated with increased generalized obesity, which is not apparent from their nonobese body mass index. Increased visceral fat is related to dyslipidemia and increased frequency of insulin resistance and may account for the increased prevalence of diabetes mellitus and cardiovascular disease in Asian Indians.
The time lag between optical and near-infrared continuum emission in active galactic nuclei (AGN) shows a tight correlation with luminosity and has been proposed as a standardizable candle for ...cosmology. In this paper, we explore the use of these AGN hot-dust time lags for cosmological model fitting under the constraints of the new VISTA Extragalactic Infrared Legacy Survey (VEILS). This new survey will target a 9 deg2 field observed in J and Ks band with a 14-d cadence and will run for 3 yr. The same area will be covered simultaneously in the optical griz bands by the Dark Energy Survey, providing complementary time-domain optical data. We perform realistic simulations of the survey setup, showing that we expect to recover dust time lags for about 450 objects out of a total of 1350 optical type 1 AGN, spanning a redshift range of 0.1 < z < 1.2. We use the lags recovered from our simulations to calculate precise distance moduli, establish a Hubble diagram, and fit cosmological models. Assuming realistic scatter in the distribution of the dust around the AGN as well as in the normalization of the lag-luminosity relation, we are able to constrain ... in ...CDM with similar accuracy as current supernova samples. We discuss the benefits of combining AGN and supernovae for cosmology and connect the present work to future attempts to reach out to redshifts of z > 4. (ProQuest: ... denotes formulae/symbols omitted.)
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