X-ray ionization of the intergalactic medium by quasars

We investigate the impact of quasars on the ionization of the surrounding intergalactic medium (IGM) with the radiative transfer code \texttt{CRASH4}, now accounting for X-rays and secondary electrons. After comparing with analytic solutions, we post-process a cosmic volume ($\approx 1.5\times 10^4$ Mpc$^3 h^{-3}$) containing a ULAS J1120+0641-like quasar (QSO) hosted by a $5 \times 10^{11} {\rm M}_\odot h^{-1}$ dark matter (DM) halo. We find that: (i) the average HII region ($R\sim3.2$~pMpc in a lifetime $t_f = 10^7$~yrs) is mainly set by UV flux, in agreement with semi-analytic scaling relations; (ii) a largely neutral ($x_{\textrm{HII}} < 0.001$), warm ($T\sim 10^3$~K) tail extends up to few Mpc beyond the ionization front, as a result of the X-ray flux; (iii) LyC-opaque inhomogeneities induce a line of sight (LOS) scatter in $R$ as high as few physical Mpc, consistent with the DLA scenario proposed to explain the anomalous size of the ULAS J1120+0641 ionized region. On the other hand, with an ionization rate $\dot{N}_{\gamma,0} \sim 10^{57}$~s$^{-1}$, the assumed DLA clustering and gas opacity, only one LOS shows an HII region compatible with the observed one. We deduce that either the ionization rate of the QSO is at least one order of magnitude lower or the ULAS J1120+0641 bright phase is shorter than $10^7$~yrs.Comment: Accepted for publication in MNRAS Main Journal, Accepted 2018 May 2

Kepler's First Rocky Planet: Kepler-10b

NASA's Kepler Mission uses transit photometry to determine the frequency of Earth-size planets in or near the habitable zone of Sun-like stars. The mission reached a milestone toward meeting that goal: the discovery of its first rocky planet, Kepler-10b. Two distinct sets of transit events were detected: (1) a 152 ± 4 ppm dimming lasting 1.811 ± 0.024 hr with ephemeris T [BJD] = 2454964.57375^(+0.00060)_(–0.00082) + N * 0.837495^(+0.000004)_(–0.000005) days and (2) a 376 ± 9 ppm dimming lasting 6.86 ± 0.07 hr with ephemeris T [BJD] = 2454971.6761^(+0.0020)_(–0.0023) + N * 45.29485^(+0.00065) _(–0.00076) days. Statistical tests on the photometric and pixel flux time series established the viability of the planet candidates triggering ground-based follow-up observations. Forty precision Doppler measurements were used to confirm that the short-period transit event is due to a planetary companion. The parent star is bright enough for asteroseismic analysis. Photometry was collected at 1 minute cadence for >4 months from which we detected 19 distinct pulsation frequencies. Modeling the frequencies resulted in precise knowledge of the fundamental stellar properties. Kepler-10 is a relatively old (11.9 ± 4.5 Gyr) but otherwise Sun-like main-sequence star with T_(eff) = 5627 ± 44 K, M_⋆ = 0.895 ± 0.060 M_⊙ , and R_⋆ = 1.056 ± 0.021 R_⊙. Physical models simultaneously fit to the transit light curves and the precision Doppler measurements yielded tight constraints on the properties of Kepler-10b that speak to its rocky composition: M_P = 4.56^9+1.17)_(–1.29) M_⊕, R_P = 1.416^(+0.033)_(–0.036) R_⊕, and ρ_P = 8.8^(+2.1)_(–2.9) g cm^(–3). Kepler-10b is the smallest transiting exoplanet discovered to date

The Herschel view of GAS in Protoplanetary Systems (GASPS): First comparisons with a large grid of models

The Herschel GASPS key program is a survey of the gas phase of protoplanetary discs, targeting 240 objects which cover a large range of ages, spectral types, and disc properties. To interpret this large quantity of data and initiate self-consistent analyses of the gas and dust properties of protoplanetary discs, we have combined the capabilities of the radiative transfer code MCFOST with the gas thermal balance and chemistry code ProDiMo to compute a grid of ≈300  000 disc models (DENT). We present a comparison of the first Herschel/GASPS line and continuum data with the predictions from the DENT grid of models. Our objective is to test some of the main trends already identified in the DENT grid, as well as to define better empirical diagnostics to estimate the total gas mass of protoplanetary discs. Photospheric UV radiation appears to be the dominant gas-heating mechanism for Herbig stars, whereas UV excess and/or X-rays emission dominates for T Tauri stars. The DENT grid reveals the complexity in the analysis of far-IR lines and the difficulty to invert these observations into physical quantities. The combination of Herschel line observations with continuum data and/or with rotational lines in the (sub-)millimetre regime, in particular CO lines, is required for a detailed characterisation of the physical and chemical properties of circumstellar discs

X-ray background and its correlation with the 21 cm signal

We use high resolution hydrodynamical simulations to study the contribution to the X-ray background from high-$z$ energetic sources, such as X-ray binaries, accreting nuclear black holes and shock heated interstellar medium. Adopting the model discussed in Eide et al. (2018), we find that these X-ray sources during the Epoch of Reionization (EoR) contribute less than a few percent of the unresolved X-ray background. The same sources contribute to less than $\sim$2\% of the measured angular power spectrum of the fluctuations of the X-ray background. The outputs of radiative transfer simulations modeling the EoR are used to evaluate the cross-correlations of X-ray background with the 21~cm signal from neutral hydrogen. Such correlation could be used to confirm the origin of the 21 cm signal, as well as give information on the properties of the X-ray sources during the EoR. We find that the correlations are positive during the early stages of reionization when most of the hydrogen is neutral, while they become negative when the intergalactic medium gets highly ionized, with the transition from positive to negative depending on both the X-ray model and the scale under consideration. With {\tt SKA} as the reference instrument for the 21~cm experiment, the predicted S/N for such correlations is $<1$ if the corresponding X-ray survey is only able to resolve and remove X-ray sources with observed flux $>10^{-15}\,\rm erg\, cm^{-2} \, s^{-1}$, while the cumulative S/N from $l=1000$ to $10^{4}$ at $x_{\rm HI}=0.5$ is $\sim 5$ if sources with observed flux $>10^{-17}\,\rm erg\, cm^{-2} \, s^{-1}$ are detected.Comment: 9 pages, 8 figure

On the Formation of Cathedral Chapters and Cathedral Culture : Lund, Denmark, and Scandinavia, c. 1060–1225

The cathedral was one of the most important institutions in medieval Europe. The local as well as ecclesiastical elite gathered around it and its bishop; the liturgy was celebrated day and night, year after year; the cathedral served as educational institution of the clergy. The cathedral chapter, i.e. the organized clergy that served at the cathedral, played a decisive part in all this.The overarching purpose of this doctoral thesis has been to re-interpret essential aspects of the formation and functions of cathedral chapters in Scandinavia in the period c. 1060–1225. This is achieved through a number of articles on the cathedral chapter at St Lawrence’s in Lund, and, to a lesser extent, other cathedral chapters in medieval Denmark and Scandinavia. After a general introduction on the subject, starting with clarifications of those concepts that have been essential to this study and my understanding and application of them, i.e. ‘formation’, ‘functions’, ‘cathedral chapter’, and ‘cathedral culture’, I recapitulate what has been achieved, misinterpreted, or even neglected by previous scholarship by focusing on the formation and functions of cathedral chapters in a Scandinavian setting. In this section, I also present my own hypotheses and methodological approaches and define the chronological and geographical delimitations of this work. Finally, I introduce the sources of this work by categorizing them. In the second major part of the introduction, I present the context, hypotheses, methods, and results of the articles; I also present and discuss whether there has been any subsequent research or similar approaches on the various topics dealt with.In my articles, I consider four general topics: first, the textual transmission of normative text of the cathedral chapter in Lund and especially the customary, the Consuetudines Lundenses from c. 1120 (Articles 1 and 4); second, the concepts of ‘law & learning’ are examined in the context of the cathedral chapter at St Lawrence’s in Lund in the first quarter of the twelfth century (Article 2). Third, by focusing on the cult of saints in Scandinavia c. 1000–c. 1200 in relation to the emerging capitular institutions, I both introduce a new concept, ‘cathedral culture’, and demonstrate the importance of the local cathedral clergy and chapter are in the introduction and maintenance of both foreign and local saints’ cults (Article 3). Finally, I examine the various legal developments within the process of appointing bishops that were practiced in Latin Christendom until the mid-1220s (Article 5), arriving at the conclusion that this process and the formation of cathedral chapters were reciprocal and resulted in a more legally regulated electoral procedure.The major results of this work are the following. First, by a redefinition of the concept of ‘cathedral chapter’, meaning that any clerical organization occupied with the liturgical service at the cathedral church of the diocese could be designated as such rather than define this institution from those legal or administrative functions that were added later, and by demonstrating that the liturgical function was the primary function of the capitular institution throughout the Middle Ages, I contribute to a new, more organic view of this ecclesiastical institution. Second, by using a more flexible terminology, I demonstrate that a focus on the process of formation rather than the search for a fixed date of foundation is rewarding when dealing with the capitular institutions in this period, which are characterized by institutional, legal, and ideological transition. Finally, I introduce a new conceptual framework, ‘cathedral culture’, which not only facilitates our understanding of the activities undertaken and performed by the chapters and their members in the cathedral and its surrounding milieu, i.e. as agents of ecclesiastical tradition, but also this concept helps us to see the emergence of a specific culture out of a monastic, contemplative culture and closely related to a nascent scholastic, erudite culture

Numerical study of jets produced by conical wire arrays on the Magpie pulsed power generator

The aim of this work is to model the jets produced by conical wire arrays on the MAGPIE generator, and to design and test new setups to strengthen the link between laboratory and astrophysical jets. We performed the modelling with direct three-dimensional magneto-hydro-dynamic numerical simulations using the code GORGON. We applied our code to the typical MAGPIE setup and we successfully reproduced the experiments. We found that a minimum resolution of approximately 100 is required to retrieve the unstable character of the jet. We investigated the effect of changing the number of wires and found that arrays with less wires produce more unstable jets, and that this effect has magnetic origin. Finally, we studied the behaviour of the conical array together with a conical shield on top of it to reduce the presence of unwanted low density plasma flows. The resulting jet is shorter and less dense.Comment: Accepted for publication in Astrophysics & Space Science. HEDLA 2010 conference procedings. Final pubblication will be available on Springe