Imperial College London

DrDanielMortlock

Faculty of Natural SciencesDepartment of Physics

Senior Lecturer
 
 
 
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Contact

 

+44 (0)20 7594 7878d.mortlock Website

 
 
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Location

 

1018ABlackett LaboratorySouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

89 results found

Ahlgren B, Larrson J, Valan V, Mortlock D, Ryde F, Asaf Pet al., Investigating subphotospheric dissipation in gamma-ray bursts using joint Fermi-Swift observations, Astronomy and Astrophysics, ISSN: 0004-6361

The jet photosphere has been proposed as the origin for the gamma-ray burst (GRB) prompt emis-sion. In many such models, characteristic features in the spectra appear below the energy range of theFermiGBM detectors, so joint fits with X-ray data are important in order to assess the photosphericscenario. Here we consider a particular photospheric model which assumes localized subphotosphericdissipation by internal shocks in a non-magnetized outflow. We investigate it using Bayesian inferenceand a sample of 8 GRBs with known redshifts which are observed simultaneously withFermiGBM andSwiftXRT. This provides us with an energy range of 0.3 keV to 40 MeV and much tighter parameterconstraints. We analyze 32 spectra and find that 16 are well described by the model. We also findthat the estimates of the bulk Lorentz factor, Γ, and the fireball luminosity,L0,52, decrease while thefraction of dissipated energy,εd, increase in the joint fits compared to GBM only fits. These changesare caused by a small excess of counts in the XRT data, relative to the model predictions from fits toGBM only data. The fact that our limited implementation of the physical scenario yields 50% acceptedspectra is promising, and we discuss possible model revisions in the light of the new data. Specifically,we argue that the inclusion of significant magnetization, as well as removing the assumption of internalshocks, will provide better fits at low energies.

Journal article

O'Riordan CM, Warren SJ, Mortlock DJ, 2019, Galaxy mass profiles from strong lensing I: the circular power-law model, Publisher: arXiv

In this series of papers we develop a formalism for constraining mass profiles in strong gravitational lenses with extended images, using fluxes in addition to positional information. We start in this paper with a circular power-law profile and show that the slope γ is uniquely determined by only two observables: the flux ratio f1/f2 and the image position ratio θ1/θ2 of the two images. We derive an analytic expression relating these two observables to the slope, a result which does not depend on the Einstein angle or the structure or brightness of the source. We then find an expression for the uncertainty on the slope σγ that depends only on the position ratio θ1/θ2 and the total S/N in the images. For example, in a system with position ratio θ1/θ2=0.5, S/N =100 and γ=2 we find that γ is constrained to a precision of ±0.03. We then test these results against a series of mock observations. We invert the images and fit an 11 parameter model, including ellipticity and position angle for both lens and source and measure the uncertainty on γ. We find agreement with the theoretical estimate for all mock observations. In future papers we will examine the radial range of the galaxy over which the constraint on the slope applies, and extend the analysis to elliptical lenses.

Working paper

Widmark A, Mortlock DJ, Peiris HV, 2019, A Bayesian model for inferring properties of the local white dwarf population in astrometric and photometric surveys, Monthly Notices of the Royal Astronomical Society, Vol: 485, Pages: 179-188, ISSN: 0035-8711

The Gaia mission is providing precise astrometry for an unprecedented number of white dwarfs (WDs), encoding information on stellar evolution, Type Ia supernovae progenitor scenarios, and the star formation and dynamical history of the Milky Way. With such a large data set, it is possible to infer properties of the WD population using only astrometric and photometric informations. We demonstrate a framework to accomplish this using a mock data set with Sloan Digital Sky Survey ugriz photometry and Gaia astrometric information. Our technique utilizes a Bayesian hierarchical model for inferring properties of a WD population while also taking into account all observational errors of individual objects, as well as selection and incompleteness effects. We demonstrate that photometry alone can constrain the WD population’s distributions of temperature, surface gravity, and atmospheric composition, and that astrometric information significantly improves determination of the WD surface gravity distribution. We also discuss the possibility of identifying unresolved binary WDs using only photometric and astrometric informations.

Journal article

Capel F, Mortlock DJ, 2019, Impact of using the ultrahigh-energy cosmic ray arrival energies to constrain source associations, Monthly Notices of the Royal Astronomical Society, Vol: 484, Pages: 2324-2340, ISSN: 0035-8711

We present a Bayesian hierarchical model which enables a joint fit of the ultrahigh-energy cosmic ray (UHECR) energy spectrum and arrival directions within the context of a physical model for the UHECR phenomenology. In this way, possible associations with astrophysical source populations can be assessed in a physically and statistically principled manner. The importance of including the UHECR energy data and detection effects is demonstrated through simulation studies, showing that the effective GZK horizon is significantly extended for typical reconstruction uncertainties. We also verify the ability of the model to fit and recover physical parameters from crpropa 3 simulations. Finally, the model is used to assess the fraction of the publicly available data set of 231 UHECRs detected by the Pierre Auger Observatory which are associated with the Fermi-LAT 2FHL catalogue, a set of starburst galaxies, and Swift-BAT hard X-ray sources. We find association fractions of 9.5+2.4−5.9⁠, 22.7+6.6−12.4⁠, and 22.8+6.6−8.0 per cent for the 2FHL, starburst galaxies, and Swift-BAT catalogues respectively.

Journal article

Ball WT, Rozanov EV, Alsing J, Marsh DR, Tummon F, Mortlock DJ, Kinnison D, Haigh JDet al., 2019, The upper stratospheric solar cycle ozone response, Geophysical Research Letters, Vol: 46, Pages: 1831-1841, ISSN: 0094-8276

The solar cycle (SC) stratospheric ozone response is thought to influence surface weather and climate. To understand the chain of processes and ensure climate models adequately represent them, it is important to detect and quantify an accurate SC ozone response from observations. Chemistry climate models (CCMs) and observations display a range of upper stratosphere (1–10 hPa) zonally averaged spatial responses; this and the recommended data set for comparison remains disputed. Recent data-merging advancements have led to more robust observational data. Using these data, we show that the observed SC signal exhibits an upper stratosphere U-shaped spatial structure with lobes emanating from the tropics (5–10 hPa) to high altitudes at midlatitudes (1–3 hPa). We confirm this using two independent chemistry climate models in specified dynamics mode and an idealized timeslice experiment. We recommend the BASIC v2 ozone composite to best represent historical upper stratospheric solar variability, and that those based on SBUV alone should not be used.

Journal article

Feeney SM, Peiris HV, Williamson AR, Nissanke SM, Mortlock DJ, Alsing J, Scolnic Det al., 2019, Prospects for resolving the Hubble constant tension with standard sirens, Physical Review Letters, Vol: 122, ISSN: 0031-9007

The Hubble constant ($H_0$) estimated from the local Cepheid-supernova (SN)distance ladder is in 3-$\sigma$ tension with the value extrapolated fromcosmic microwave background (CMB) data assuming the standard cosmologicalmodel. Whether this tension represents new physics or systematic effects is thesubject of intense debate. Here, we investigate how new, independent $H_0$estimates can arbitrate this tension, assessing whether the measurements areconsistent with being derived from the same model using the posteriorpredictive distribution (PPD). We show that, with existing data, the inversedistance ladder formed from BOSS baryon acoustic oscillation measurements andthe Pantheon SN sample yields an $H_0$ posterior near-identical to the PlanckCMB measurement. The observed local distance ladder value is a very unlikelydraw from the resulting PPD. Turning to the future, we find that a sample of$\sim50$ binary neutron star "standard sirens" (detectable within the nextdecade) will be able to adjudicate between the local and CMB estimates.

Journal article

Argyle JJ, Mendez-Abreu J, Wild V, Mortlock DJet al., 2018, Bayesian bulge-disc decomposition of galaxy images, Monthly Notices of the Royal Astronomical Society, Vol: 479, Pages: 3076-3093, ISSN: 0035-8711

We introduce phi, a fully Bayesian Markov chain Monte Carlo algorithm designed for the structural decomposition of galaxy images. phi uses a triple layer approach to effectively and efficiently explore the complex parameter space. Combining this with the use of priors to prevent non-physical models, phi offers a number of significant advantages for estimating surface brightness profile parameters over traditional optimization algorithms. We apply phi to a sample of synthetic galaxies with Sloan Digital Sky Survey (SDSS)-like image properties to investigate the effect of galaxy properties on our ability to recover unbiased and well-constrained structural parameters. In two-component bulge+disc galaxies, we find that the bulge structural parameters are recovered less well than those of the disc, particularly when the bulge contributes a lower fraction to the luminosity, or is barely resolved with respect to the pixel scale or point spread function (PSF). There are few systematic biases, apart from for bulge+disc galaxies with large bulge Sérsic parameter, n. On application to SDSS images, we find good agreement with other codes, when run on the same images with the same masks, weights, and PSF. Again, we find that bulge parameters are the most difficult to constrain robustly. Finally, we explore the use of a Bayesian information criterion method for deciding whether a galaxy has one or two components.

Journal article

Feeney SM, Mortlock DJ, Dalmasso N, 2018, Clarifying the Hubble constant tension with a Bayesian hierarchical model of the local distance ladder, Monthly Notices of the Royal Astronomical Society, Vol: 476, Pages: 3861-3882, ISSN: 0035-8711

Estimates of the Hubble constant, H0, from the local distance ladder and from the cosmic microwave background (CMB) are discrepant at the ∼3-σ level, indicating a potential issue with the standard ΛCDM cosmology. A probabilistic (i.e., Bayesian) interpretation of this tension requires a model comparison calculation, which in turn depends strongly on the tails of the H₀ likelihoods. Evaluating the tails of the local H₀ likelihood requires the use of non-Gaussian distributions to faithfully represent anchor likelihoods and outliers, and simultaneous fitting of the complete distance ladder dataset to ensure correct uncertainty propagation. We have hence developed a Bayesian hierarchical model of the full distance ladder that does not rely on Gaussian distributions and allows outliers to be modelled without arbitrary data cuts. Marginalizing over the full ∼3000-parameter joint posterior distribution we find H0 = (72.72 ± 1.67) km s¯¹ Mpc¯¹ when applied to the outlier-cleaned Riess et al. (2016) data, and (73.15 ± 1.78) km s¯¹ Mpc¯¹ with SN outliers reintroduced (the pre-cut Cepheid dataset is not available). Using our precise evaluation of the tails of the H0 likelihood, we apply Bayesian model comparison to assess the evidence for deviation from ΛCDM given the distance-ladder and CMB data. The odds against ΛCDM are at worst ∼10:1 when considering the Planck Collaboration (2016b) data, regardless of outlier treatment, considerably less dramatic than naïvely implied by the 2.8-σ discrepancy. These odds become ∼60:1 when an approximation to the more-discrepant Planck Collaboration (2016c) likelihood is included.

Journal article

Burgess JM, Yu HF, Greiner J, Mortlock DJet al., 2018, Awakening the BALROG: bayesian location reconstruction of GRBs, Monthly Notices of the Royal Astronomical Society, Vol: 476, Pages: 1427-1444, ISSN: 0035-8711

The accurate spatial location of gamma-ray bursts (GRBs) is crucial for both accurately characterizing their spectra and follow-up observations by other instruments. The Fermi Gamma-ray Burst Monitor (GBM) has the largest field of view for detecting GRBs as it views the entire unocculted sky, but as a non-imaging instrument it relies on the relative count rates observed in each of its 14 detectors to localize transients. Improving its ability to accurately locate GRBs and other transients is vital to the paradigm of multimessenger astronomy, including the electromagnetic follow-up of gravitational wave signals. Here we present the BAyesian Location Reconstruction Of GRBs (balrog) method for localizing and characterizing GBM transients. Our approach eliminates the systematics of previous approaches by simultaneously fitting for the location and spectrum of a source. It also correctly incorporates the uncertainties in the location of a transient into the spectral parameters and produces reliable positional uncertainties for both well-localized sources and those for which the GBM data cannot effectively constrain the position. While computationally expensive, balrog can be implemented to enable quick follow-up of all GBM transient signals. Also, we identify possible response problems that require attention and caution when using standard, public GBM detector response matrices. Finally, we examine the effects of including the uncertainty in location on the spectral parameters of GRB 080916C. We find that spectral parameters change and no extra components are required when these effects are included in contrast to when we use a fixed location. This finding has the potential to alter both the GRB spectral catalogues and the reported spectral composition of some well-known GRBs.

Journal article

Ball WT, Alsing J, Mortlock DJ, Staehelin J, Haigh JD, Peter T, Tummon F, Stubi R, Stenke A, Anderson J, Bourassa A, Davis SM, Degenstein D, Frith S, Froidevaux L, Roth C, Sofieva V, Wang R, Wild J, Yu P, Ziemke JR, Rozanov EVet al., 2018, Evidence for a continuous decline in lower stratospheric ozone offsetting ozone layer recovery, Atmospheric Chemistry and Physics, Vol: 18, Pages: 1379-1394, ISSN: 1680-7316

Ozone forms in the Earth's atmosphere from the photodissociation of molecular oxygen, primarily in the tropical stratosphere. It is then transported to the extratropics by the Brewer–Dobson circulation (BDC), forming a protective "ozone layer" around the globe. Human emissions of halogen-containing ozone-depleting substances (hODSs) led to a decline in stratospheric ozone until they were banned by the Montreal Protocol, and since 1998 ozone in the upper stratosphere is rising again, likely the recovery from halogen-induced losses. Total column measurements of ozone between the Earth's surface and the top of the atmosphere indicate that the ozone layer has stopped declining across the globe, but no clear increase has been observed at latitudes between 60° S and 60° N outside the polar regions (60–90°). Here we report evidence from multiple satellite measurements that ozone in the lower stratosphere between 60° S and 60° N has indeed continued to decline since 1998. We find that, even though upper stratospheric ozone is recovering, the continuing downward trend in the lower stratosphere prevails, resulting in a downward trend in stratospheric column ozone between 60° S and 60° N. We find that total column ozone between 60° S and 60° N appears not to have decreased only because of increases in tropospheric column ozone that compensate for the stratospheric decreases. The reasons for the continued reduction of lower stratospheric ozone are not clear; models do not reproduce these trends, and thus the causes now urgently need to be established.

Journal article

Ball WT, Alsing J, Mortlock DJ, Rozanov EV, Tummon F, Haigh JDet al., 2017, Reconciling differences in stratospheric ozone composites, Atmospheric Chemistry and Physics, Vol: 17, Pages: 12269-12302, ISSN: 1680-7316

Observations of stratospheric ozone from multipleinstruments now span three decades; combining these intocomposite datasets allows long-term ozone trends to be estimated.Recently, several ozone composites have been published,but trends disagree by latitude and altitude, even betweencomposites built upon the same instrument data. Weconfirm that the main causes of differences in decadal trendestimates lie in (i) steps in the composite time series when theinstrument source data changes and (ii) artificial sub-decadaltrends in the underlying instrument data. These artefacts introducefeatures that can alias with regressors in multiple linearregression (MLR) analysis; both can lead to inaccuratetrend estimates. Here, we aim to remove these artefacts usingBayesian methods to infer the underlying ozone time seriesfrom a set of composites by building a joint-likelihoodfunction using a Gaussian-mixture density to model outliersintroduced by data artefacts, together with a data-driven prioron ozone variability that incorporates knowledge of problemsduring instrument operation. We apply this Bayesianself-calibration approach to stratospheric ozone in 10◦ bandsfrom 60◦ S to 60◦ N and from 46 to 1 hPa (∼ 21–48 km) for1985–2012. There are two main outcomes: (i) we independentlyidentify and confirm many of the data problems previouslyidentified, but which remain unaccounted for in existingcomposites; (ii) we construct an ozone composite, withuncertainties, that is free from most of these problems – wecall this the BAyeSian Integrated and Consolidated (BASIC)composite. To analyse the new BASIC composite, we usedynamical linear modelling (DLM), which provides a morerobust estimate of long-term changes through Bayesian inferencethan MLR. BASIC and DLM, together, provide astep forward in improving estimates of decadal trends. Ourresults indicate a significant recovery of ozone since 1998 inthe upper stratosphere, of both northern and southern midlatitudes,in all f

Journal article

Bosman SEI, Becker GD, Haehnelt MG, Hewett PC, McMahon RG, Mortlock DJ, Simpson C, Venemans BPet al., 2017, A deep search for metals near redshift 7: the line of sight towards ULAS J1120+0641, Monthly Notices of the Royal Astronomical Society, Vol: 470, Pages: 1919-1934, ISSN: 0035-8711

We present a search for metal absorption line systems at the highest redshifts to date using a deep (30 h) Very Large Telescope/X-Shooter spectrum of the z = 7.084 quasi-stellar object (QSO) ULAS J1120+0641. We detect seven intervening systems at z > 5.5, with the highest redshift system being a C iv absorber at z = 6.51. We find tentative evidence that the mass density of C iv remains flat or declines with redshift at z < 6, while the number density of C ii systems remains relatively flat over 5 < z < 7. These trends are broadly consistent with models of chemical enrichment by star formation-driven winds that include a softening of the ultraviolet background towards higher redshifts. We find a larger number of weak (Wrest < 0.3 Å) Mg ii systems over 5.9 < z < 7.0 than predicted by a power-law fit to the number density of stronger systems. This is consistent with trends in the number density of weak Mg ii systems at z ≲ 2.5, and suggests that the mechanisms that create these absorbers are already in place at z ∼ 7. Finally, we investigate the associated narrow Si iv, C iv and N v absorbers located near the QSO redshift, and find that at least one component shows evidence of partial covering of the continuum source.

Journal article

Barnett R, Warren SJ, Becker GD, Mortlock DJ, Hewett PC, McMahon RG, Simpson C, Venemans BPet al., 2017, Observations of the Lyman series forest towards the redshift 7.1 quasar ULAS J1120+0641, ASTRONOMY & ASTROPHYSICS, Vol: 601, ISSN: 1432-0746

We present a 30 h integration Very Large Telescope X-shooter spectrum of the Lyman series forest towards the z = 7.084 quasar ULAS J1120+0641. The only detected transmission at S/N > 5 is confined to seven narrow spikes in the Lyα forest, over the redshift range 5.858 <z < 6.122, just longward of the wavelength of the onset of the Lyβ forest. There is also a possible detection of one further unresolved spike in the Lyβ forest at z = 6.854, with S/N = 4.5. We also present revised Hubble Space Telescope F814W photometry of the source. The summed flux from the transmission spikes is in agreement with the F814W photometry, so all the transmission in the Lyman series forest may have been detected. There is a Gunn-Peterson (GP) trough in the Lyα forest from z = 6.122 all the way to the quasar near zone at z = 7.04. The trough, of comoving length 240 h-1 Mpc, is over twice as long as the next longest known GP trough. We combine the spectroscopic and photometric results to constrain the evolution of the Lyα effective optical depth (τGPeff) with redshift, extending a similar analysis by Simpson et al. We find τGPeff ∝ (1 + z)ξ where ξ = 11.2+ 0.4-0.6, for z > 5.5. The data nevertheless provide only a weak limit on the volume-weighted intergalactic medium (IGM) hydrogen neutral fraction at z ~ 6.5, xH i > 10-4, similar to limits at redshift z ~ 6 from less distant quasars. The new observations cannot extend measurements of the neutral fraction of the IGM to higher values because absorption in the Lyα forest is already saturated near z ~ 6. For higher neutral fractions, other methods such as measuring the red damping wing of the IGM will be required.

Journal article

Venemans BP, Walter F, Decarli R, Bañados E, Hodge J, Hewett P, McMahon RG, Mortlock DJ, Simpson Cet al., 2017, The compact, ∼1 kpc host galaxy of a quasar at a redshift of 7.1, The Astrophysical Journal: an international review of astronomy and astronomical physics, Vol: 837, Pages: 146-146, ISSN: 0004-637X

We present Atacama Large Millimeter/submillimeter Array (ALMA) observations of the [C ii] fine-structure line and the underlying far-infrared (FIR) dust continuum emission in J1120+0641, the most distant quasar currently known ($z=7.1$). We also present observations targeting the CO(2–1), CO(7–6), and [C i] 369 μm lines in the same source obtained at the Very Large Array and Plateau de Bure Interferometer. We find a [C ii] line flux of ${F}_{[{\rm{C}}{\rm{II}}]}=1.11\pm 0.10$ Jy $\mathrm{km}\,{{\rm{s}}}^{-1}$ and a continuum flux density of ${S}_{227\mathrm{GHz}}=0.53\pm 0.04$ mJy beam−1, consistent with previous unresolved measurements. No other source is detected in continuum or [C ii] emission in the field covered by ALMA (~ 25''). At the resolution of our ALMA observations (0farcs23, or 1.2 kpc, a factor of ~70 smaller beam area compared to previous measurements), we find that the majority of the emission is very compact: a high fraction (~80%) of the total line and continuum flux is associated with a region 1–1.5 kpc in diameter. The remaining ~20% of the emission is distributed over a larger area with radius lesssim4 kpc. The [C ii] emission does not exhibit ordered motion on kiloparsec scales: applying the virial theorem yields an upper limit on the dynamical mass of the host galaxy of $(4.3\pm 0.9)\times {10}^{10}$ ${M}_{\odot }$, only ~20 × higher than the central black hole (BH). The other targeted lines (CO(2–1), CO(7–6), and [C i]) are not detected, but the limits of the line ratios with respect to the [C ii] emission imply that the heating in the quasar host is dominated by star formation, and not by the accreting BH. The star formation rate (SFR) implied by the FIR continuum is 105–340 ${M}_{\odot }\,{\mathrm{yr}}^{-1}$, with a resulting SFR surface density of ~100–350 ${M}_{\odot }\,{\mathrm{yr}}^{-1}$ kpc−2, well below the value for Eddington-accretion-limited star formation.

Journal article

Ade PAR, Aghanim N, Arnaud M, Aumont J, Baccigalupi C, Banday AJ, Barreiro RB, Bartolo N, Battaner E, Benabed K, Benoit-Levy A, Bernard J-P, Bersanelli M, Bielewicz P, Bonaldi A, Bonavera L, Bond JR, Borrill J, Bouchet FR, Boulanger F, Burigana C, Butler RC, Calabrese E, Catalano A, Chiang HC, Christensen PR, Clements DL, Colombo LPL, Couchot F, Coulais A, Crill BP, Curto A, Cuttaia F, Danese L, Davies RD, Davis RJ, de Bernardis P, de Rosa A, de Zotti G, Delabrouille J, Dickinson C, Diego JM, Dole H, Dore O, Douspis M, Ducout A, Dupac X, Elsner F, Ensslin TA, Eriksen HK, Falgarone E, Finelli F, Flores-Cacho I, Frailis M, Fraisse AA, Franceschi E, Galeotta S, Galli S, Ganga K, Giard M, Giraud-Heraud Y, Gjerlow E, Gonzalez-Nuevo J, Gorski KM, Gregorio A, Gruppuso A, Gudmundsson JE, Hansen FK, Harrison DL, Helou G, Hernandez-Monteagudo C, Herranz D, Hildebrandt SR, Hivon E, Hobson M, Hornstrup A, Hovest W, Huffenberger KM, Hurier G, Jaffe AH, Jaffe TR, Keihanen E, Keskitalo R, Kisner TS, Kneissl R, Knoche J, Kunz M, Kurki-Suonio H, Lagache G, Lamarre J-M, Lasenby A, Lattanzi M, Lawrence CR, Leonardi R, Levrier F, Liguori M, Lilje PB, Linden-Vornle M, Lopez-Caniego M, Lubin PM, Macias-Perez JF, Maffei B, Maggio G, Maino D, Mandolesi N, Mangilli A, Maris M, Martin PG, Martinez-Gonzalez E, Masi S, Matarrese S, Melchiorri A, Mennella A, Migliaccio M, Mitra S, Miville-Deschenes M-A, Moneti A, Montier L, Morgante G, Mortlock D, Munshi D, Murphy JA, Nati F, Natoli P, Nesvadba NPH, Noviello F, Novikov D, Novikov I, Oxborrow CA, Pagano L, Pajot F, Paoletti D, Partridge B, Pasian F, Pearson TJ, Perdereau O, Perotto L, Pettorino V, Piacentini F, Piat M, Plaszczynski S, Pointecouteau E, Polenta G, Pratt GW, Prunet S, Puget J-L, Rachen JP, Reinecke M, Remazeilles M, Renault C, Renzi A, Ristorcelli I, Rocha G, Rosset C, Rossetti M, Roudier G, Rubino-Martin JA, Rusholme B, Sandri M, Santos D, Savelainen M, Savini G, Scott D, Spencer LD, Stolyarov V, Stompor R, Sudiwala R, Sunyaev Ret al., 2016, Planck intermediate results XXXIX. The Planck list of high-redshift source candidates, Publisher: EDP SCIENCES S A

Working paper

Leistedt B, Mortlock DJ, Peiris HV, 2016, Hierarchical Bayesian inference of galaxy redshift distributions from photometric surveys, Monthly Notices of the Royal Astronomical Society, Vol: 460, Pages: 4258-4267, ISSN: 1365-2966

Accurately characterizing the redshift distributions of galaxies is essential for analysing deep photometric surveys and testing cosmological models. We present a technique to simultaneously infer redshift distributions and individual redshifts from photometric galaxy catalogues. Our model constructs a piecewise constant representation (effectively a histogram) of the distribution of galaxy types and redshifts, the parameters of which are efficiently inferred from noisy photometric flux measurements. This approach can be seen as a generalization of template-fitting photometric redshift methods and relies on a library of spectral templates to relate the photometric fluxes of individual galaxies to their redshifts. We illustrate this technique on simulated galaxy survey data, and demonstrate that it delivers correct posterior distributions on the underlying type and redshift distributions, as well as on the individual types and redshifts of galaxies. We show that even with uninformative priors, large photometric errors and parameter degeneracies, the redshift and type distributions can be recovered robustly thanks to the hierarchical nature of the model, which is not possible with common photometric redshift estimation techniques. As a result, redshift uncertainties can be fully propagated in cosmological analyses for the first time, fulfilling an essential requirement for the current and future generations of surveys.

Journal article

Khanin A, Mortlock DJ, 2016, A Bayesian analysis of the 69 highest energy cosmic rays detected by the Pierre Auger Observatory, Monthly Notices of the Royal Astronomical Society, Vol: 460, Pages: 2765-2778, ISSN: 0035-8711

The origins of ultrahigh energy cosmic rays (UHECRs) remain an open question. Several attempts have been made to cross-correlate the arrival directions of the UHECRs with catalogues of potential sources, but no definite conclusion has been reached. We report a Bayesiananalysis of the 69 events, from the Pierre Auger Observatory (PAO), that aims to determine the fraction of the UHECRs that originate from known AGNs in the Veron-Cety & Verson (VCV) catalogue, as well as AGNs detected with the Swift Burst Alert Telescope (Swift-BAT),galaxies from the 2MASS Redshift Survey (2MRS), and an additional volume-limited sample of 17 nearby AGNs. The study makes use of a multilevel Bayesian model of UHECR injection, propagation and detection. We find that for reasonable ranges of prior parameters theBayes factors disfavour a purely isotropic model. For fiducial values of the model parameters, we report 68 per cent credible intervals for the fraction of source originating UHECRs of 0.09+0.05 −0.04, 0.25+0.09 −0.08, 0.24+0.12 −0.10, and 0.08+0.04 −0.03 for the VCV, Swift-BAT and 2MRS catalogues, and the sample of 17 AGNs, respectively.

Journal article

Arnaud M, Ashdown M, Atrio-Barandela F, Aumont J, Baccigalupi C, Banday AJ, Barreiro RB, Battaner E, Benabed K, Benoit-Levy A, Bernard J-P, Bersanelli M, Bielewicz P, Bobin J, Bond JR, Borrill J, Bouchet FR, Brogan CL, Burigana C, Cardoso J-F, Catalano A, Chamballu A, Chiang HC, Christensen PR, Colombi S, Colombo LPL, Crill BP, Curto A, Cuttaia F, Davies RD, Davis RJ, de Bernardis P, de Rosa A, de Zotti G, Delabrouille J, Desert F-X, Dickinson C, Diego JM, Donzelli S, Dore O, Dupac X, Ensslin TA, Eriksen HK, Finelli F, Forni O, Frailis M, Fraisse AA, Franceschi E, Galeotta S, Ganga K, Giard M, Giraud-Heraud Y, Gonzalez-Nuevo J, Gorski KM, Gregorio A, Gruppuso A, Hansen FK, Harrison DL, Hernandez-Monteagudo C, Herranz D, Hildebrandt SR, Hobson M, Holmes WA, Huffenberger KM, Jaffe AH, Jaffe TR, Keihaenen E, Keskitalo R, Kisner TS, Kneissl R, Knoche J, Kunz M, Kurki-Suonio H, Lahteenmaki A, Lamarre J-M, Lasenby A, Lawrence CR, Leonardi R, Liguori M, Lilje PB, Linden-Vornle M, Lopez-Caniego M, Lubin PM, Maino D, Maris M, Marshall DJ, Martin PG, Martinez-Gonzalez E, Masi S, Matarrese S, Mazzotta P, Melchiorri A, Mendes L, Mennella A, Migliaccio M, Miville-Deschenes M-A, Moneti A, Montier L, Morgante G, Mortlock D, Munshi D, Murphy JA, Naselsky P, Nati F, Noviello E, Novikov D, Novikov I, Oppermann N, Oxborrow CA, Pagano L, Pajot F, Paladini R, Pasian F, Peel M, Perdereau O, Perrotta F, Piacentini F, Piat M, Pietrobon D, Plaszczynski S, Pointecouteau E, Polenta G, Popa L, Pratt GW, Puget J-L, Rachen JP, Reach WT, Reich W, Reinecke M, Remazeilles M, Renault C, Rho J, Ricciardi S, Riller T, Ristorcelli I, Rocha G, Rosset C, Roudier G, Rusholme B, Sandri M, Savini G, Scott D, Stolyarov V, Sutton D, Suur-Uski A-S, Sygnet J-F, Tauber JA, Terenzi L, Toffolatti L, Tomasi M, Tristram M, Tucci M, Umana G, Valenziano L, Valiviita J, Van Tent B, Vielva P, Villa F, Wade LA, Yvon D, Zacchei A, Zonca Aet al., 2016, Planck intermediate results XXXI. Microwave survey of Galactic supernova remnants, Astronomy & Astrophysics, Vol: 586, ISSN: 1432-0746

The all-sky Planck survey in 9 frequency bands was used to search for emission from all 274 known Galactic supernova remnants. Of these, 16 were detected in at least two Planck frequencies. The radio-through-microwave spectral energy distributions were compiled to determine the mechanism for microwave emission. In only one case, IC 443, is there high-frequency emission clearly from dust associated with the supernova remnant. In all cases, the low-frequency emission is from synchrotron radiation. As predicted for a population of relativistic particles with energy distribution that extends continuously to high energies, a single power law is evident for many sources, including the Crab and PKS 1209-51/52. A decrease in flux density relative to the extrapolation of radio emission is evident in several sources. Their spectral energy distributions can be approximated as broken power laws, Sν ∝ ν−α, with the spectral index, α, increasing by 0.5–1 above a break frequency in the range 10–60 GHz. The break could be due to synchrotron losses.

Journal article

Mortlock D, 2016, Quasars as Probes of Cosmological Reionization, Understanding the Epoch of Cosmic Reionization, Publisher: Springer International Publishing, Pages: 187-226, ISBN: 9783319219561

Book chapter

Mortlock DJ, Bayesian model comparison in cosmology, Statistical Challenges in 21st Century Cosmology

The standard Bayesian model formalism comparison cannot be applied to mostcosmological models as they lack well-motivated parameter priors. However, ifthe data-set being used is separable then it is possible to use some of thedata to obtain the necessary parameter distributions, the rest of the databeing retained for model comparison. While such methods are not fullyprescriptive, they provide a route to applying Bayesian model comparison incosmological situations where it could not otherwise be used.

Conference paper

Ade PAR, Aghanim N, Ahmed Z, Aikin RW, Alexander KD, Arnaud M, Aumont J, Baccigalupi C, Banday AJ, Barkats D, Barreiro RB, Bartlett JG, Bartolo N, Battaner E, Benabed K, Benoit A, Benoit-Levy A, Benton SJ, Bernard J-P, Bersanelli M, Bielewicz P, Bischoff CA, Bock JJ, Bonaldi A, Bonavera L, Bond JR, Borrill J, Bouchet FR, Boulanger F, Brevik JA, Bucher M, Buder I, Bullock E, Burigana C, Butler RC, Buza V, Calabrese E, Cardoso J-F, Catalano A, Challinor A, Chary R-R, Chiang HC, Christensen PR, Colombo LPL, Combet C, Connors J, Couchot F, Coulais A, Crill BP, Curto A, Cuttaia F, Danese L, Davies RD, Davis RJ, de Bernardis P, de Rosa A, de Zotti G, Delabrouille J, Delouis J-M, Desert F-X, Dickinson C, Diego JM, Dole H, Donzelli S, Dore O, Douspis M, Dowell CD, Duband L, Ducout A, Dunkley J, Dupac X, Dvorkin C, Efstathiou G, Elsner F, Ensslin TA, Eriksen HK, Falgarone E, Filippini JP, Finelli F, Fliescher S, Forni O, Frailis M, Fraisse AA, Franceschi E, Frejsel A, Galeotta S, Galli S, Ganga K, Ghosh T, Giard M, Gjerlow E, Golwala SR, Gonzalez-Nuevo J, Gorski KM, Gratton S, Gregorio A, Gruppuso A, Gudmundsson JE, Halpern M, Hansen FK, Hanson D, Harrison DL, Hasselfield M, Helou G, Henrot-Versille S, Herranz D, Hildebrandt SR, Hilton GC, Hivon E, Hobson M, Holmes WA, Hovest W, Hristov VV, Huffenberger KM, Hui H, Hurier G, Irwin KD, Jaffe AH, Jaffe TR, Jewell J, Jones WC, Juvela M, Karakci A, Karkare KS, Kaufman JP, Keating BG, Kefeli S, Keihanen E, Kernasovskiy SA, Keskitalo R, Kisner TS, Kneissl R, Knoche J, Knox L, Kovac JM, Krachmalnicoff N, Kunz M, Kuo CL, Kurki-Suonio H, Lagache G, Lahteenmaki A, Lamarre J-M, Lasenby A, Lattanzi M, Lawrence CR, Leitch EM, Leonardi R, Levrier F, Lewis A, Liguori M, Lilje PB, Linden-Vornle M, Lopez-Caniego M, Lubin PM, Lueker M, Macias-Perez JF, Maffei B, Maino D, Mandolesi N, Mangilli A, Maris M, Martin PG, Martinez-Gonzalez E, Masi S, Mason P, Matarrese S, Megerian KG, Meinhold PR, Melchiorri A, Mendes L, Mennella A, Migliaccio M, Mitet al., 2015, Joint Analysis of BICEP2/Keck Array and Planck Data, Physical Review Letters, Vol: 114, ISSN: 1079-7114

Journal article

Skrzypek N, Warren SJ, Faherty JK, Mortlock DJ, Burgasser AJ, Hewett PCet al., 2015, Photometric brown-dwarf classification I. A method to identify and accurately classify large samples of brown dwarfs without spectroscopy, Astronomy & Astrophysics, Vol: 574, ISSN: 1432-0746

Journal article

Barnett R, Warren SJ, Banerji M, McMahon RG, Hewett PC, Mortlock DJ, Simpson C, Venemans BP, Ota K, Shibuya Tet al., 2015, The spectral energy distribution of the redshift 7.1 quasar ULAS J1120+0641, Astronomy & Astrophysics, Vol: 575, ISSN: 1432-0746

Journal article

Ade PAR, Arnaud M, Ashdown M, Aumont J, Baccigalupi C, Banday AJ, Barreiro RB, Battaner E, Benabed K, Benoit-Levy A, Bernard J-P, Bersanelli M, Bielewicz P, Bond JR, Borrill J, Bouchet FR, Burigana C, Cardoso J-F, Catalano A, Challinor A, Chamballu A, Chiang HC, Christensen PR, Clements DL, Colombi S, Colombo LPL, Couchot F, Coulais A, Crill BP, Curto A, Cuttaia F, Danese L, Davies RD, Davis RJ, de Bernardis P, de Rosa A, de Zotti G, Delabrouille J, Desert F-X, Dickinson C, Diego JM, Dole H, Donzelli S, Dore O, Douspis M, Dupac X, Ensslin TA, Eriksen HK, Finelli F, Forni O, Frailis M, Fraisse AA, Franceschi E, Galeotta S, Ganga K, Giard M, Gonzalez-Nuevo J, Gorski KM, Gratton S, Gregorio A, Gruppuso A, Gudmundsson JE, Hansen FK, Hanson D, Harrison DL, Henrot-Versille S, Herranz D, Hildebrandt SR, Hivon E, Hobson M, Holmes WA, Hornstrup A, Hovest W, Huffenberger KM, Jaffe AH, Jaffe TR, Jones WC, Keihaenen E, Keskitalo R, Knoche J, Kunz M, Kurki-Suonio H, Lagache G, Lahteenmaki A, Lamarre J-M, Lasenby A, Lawrence CR, Leonardi R, Leon-Tavares J, Lesgourgues J, Liguori M, Lilje PB, Linden-Vornle M, Lopez-Caniego M, Lubin PM, Macias-Perez JF, Maino D, Mandolesi N, Maris M, Martin PG, Martinez-Gonzalez E, Masi S, Matarrese S, Mazzotta P, Meinhold PR, Melchiorri A, Mendes L, Mennella A, Migliaccio M, Mitra S, Miville-Deschenes M-A, Moneti A, Montier L, Morgante G, Mortlock D, Moss A, Munshi D, Murphy JA, Naselsky P, Nati F, Natoli P, Norgaard-Nielsen HU, Noviello F, Novikov D, Novikov I, Oxborrow CA, Pagano L, Pajot F, Paoletti D, Partridge B, Pasian F, Patanchon G, Pearson D, Pearson TJ, Perdereau O, Perrotta F, Piacentini F, Piat M, Pierpaoli E, Pietrobon D, Plaszczynski S, Pointecouteau E, Polenta G, Ponthieu N, Popa L, Pratt GW, Prunet S, Puget J-L, Rachen JP, Reinecke M, Remazeilles M, Renault C, Ricciardi S, Ristorcelli I, Rocha G, Roudier G, Rubino-Martin JA, Rusholme B, Sandri M, Scott D, Stolyarov V, Sudiwala R, Sutton D, Suur-Uski A-S, Sygnet J-F, Tauber JA, Tereet al., 2014, Planck 2013 results. XXXI. Consistency of the Planck data, Astronomy & Astrophysics, Vol: 571, ISSN: 1432-0746

Journal article

Ade PAR, Aghanim N, Armitage-Caplan C, Arnaud M, Ashdown M, Atrio-Barandela F, Aumont J, Baccigalupi C, Banday AJ, Barreiro RB, Battaner E, Benabed K, Benoit A, Benoit-Levy A, Bernard J-P, Bersanelli M, Bielewicz P, Bobin J, Bock JJ, Bond JR, Borrill J, Bouchet FR, Bridges M, Bucher M, Burigana C, Cardoso J-F, Catalano A, Challinor A, Chamballu A, Chiang HC, Chiang L-Y, Christensen PR, Church S, Clements DL, Colombi S, Colombo LPL, Couchot F, Coulais A, Crill P, Curto A, Cuttaia F, Danese L, Davies RD, de Bernardis P, de Rosa A, de Zotti G, Delabrouille J, Delouis J-M, Desert F-X, Diego JM, Dole H, Donzelli S, Dore O, Douspis M, Dupac X, Efstathiou G, Ensslin TA, Eriksen HK, Finelli F, Forni O, Frailis M, Franceschi E, Galeotta S, Gana K, Giard M, Girard D, Giraud-Heraud Y, Gonzalez-Nuevo J, Gorski KM, Gratton S, Gregorio A, Gruppuso A, Hansen FK, Hanson D, Harrison D, Henrot-Versille S, Hernandez-Monteagudo C, Herranz D, Hildebrandt SR, Hivon E, Hobson M, Holmes WA, Hornstrup A, Hovest W, Huffenberger KM, Jaffe AH, Jaffe TR, Jones WC, Juvela M, Keihanen E, Keskitalo R, Kisner TS, Kneissl R, Knoche J, Knox L, Kunz M, Kurki-Suonio H, Lagache G, Lamarre J-M, Lasenby A, Laureijs RJ, Lawrence CR, Leonardi R, Leroy C, Lesgourgues J, Liguori M, Lilje PB, Linden-Vornle M, Lopez-Caniego M, Lubin PM, Macias-Perez JF, Mandolesi N, Maris M, Marshall DJ, Martin PG, Martinez-Gonzalez E, Masi S, Massardi M, Matarrese S, Matthai F, Mazzotta P, McGehee P, Melchiorri A, Mendes L, Mennella A, Migliaccio M, Miniussi A, Mitra A, Miville-Deschenes M-A, Moneti A, Montier L, Morgante G, Mortlock D, Mottet S, Munshi D, Murphy JA, Naselsky P, Nati F, Natoli P, Netterfield CB, Norgaard-Nielsen HU, Noviello F, Novikov D, Novikov I, Osborne S, Oxborrow CA, Paci F, Pagano L, Pajot F, Paoletti D, Pasian F, Patanchon G, Perdereau O, Perotto L, Perrotta F, Piacentini F, Piat M, Pierpaoli E, Pietrobon D, Plaszczynski S, Pointecouteau E, Polenta G, Ponthieu N, Popa L, Poutanen T, Pratt GW, Prezeau Get al., 2014, Planck 2013 results. X. HFI energetic particle effects: characterization, removal, and simulation, Astronomy & Astrophysics, Vol: 571, ISSN: 1432-0746

Journal article

Khanin A, Mortlock DJ, 2014, A Bayesian self-clustering analysis of the highest energy cosmic rays detected by the Pierre Auger Observatory, MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Vol: 444, Pages: 1591-1599, ISSN: 0035-8711

Journal article

Simpson C, Mortlock D, Warren S, Cantalupo S, Hewett P, McLure R, McMahon R, Venemans Bet al., 2014, No excess of bright galaxies around the redshift 7.1 quasar ULAS J1120+0641, MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Vol: 442, Pages: 3454-3461, ISSN: 0035-8711

Journal article

Page MJ, Simpson C, Mortlock DJ, Warren SJ, Hewett PC, Venemans BP, McMahon RGet al., 2014, X-rays from the redshift 7.1 quasar ULAS J1120+0641, MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Vol: 440, Pages: L91-L95, ISSN: 0035-8711

Journal article

Leistedt B, Peiris HV, Mortlock DJ, Benoit-Levy A, Pontzen Aet al., 2013, Estimating the large-scale angular power spectrum in the presence of systematics: a case study of Sloan Digital Sky Survey quasars, MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Vol: 435, Pages: 1857-1873, ISSN: 0035-8711

Journal article

Mortlock D, 2013, Finding the most distant quasars using Bayesian selection methods, Statistical Science, Pages: 1-10

Journal article

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