Papers by Daniel Mortlock
We present the statistical properties of the first version of the Cold Core Catalogue of Planck O... more We present the statistical properties of the first version of the Cold Core Catalogue of Planck Objects (C3PO), in terms of their spatial distribution, temperature, distance, mass, and morphology. We also describe the statistics of the Early Cold Core Catalogue (ECC) that is a subset of the complete catalogue, and that contains only the 915 most reliable detections. ECC is delivered as a part of the Early Release Compact Source Catalogue (ERCSC). We have used the CoCoCoDeT algorithm to extract about 10 thousand cold sources. The method uses the IRAS 100µm data as a warm template that is extrapolated to the Planck bands and subtracted from the signal, leading to a detection of the cold residual emission. We have used cross-correlation with ancillary data to increase the reliability of our sample, and to derive other key properties such as distance and mass. Temperature and dust emission spectral index values are derived using the fluxes in the IRAS 100 µm band and the three highest frequency Planck bands. The range of temperatures explored by the catalogue spans from 7 K to 17 K, and peaks around 13 K. Data are not consistent with a constant value of the associated spectral index β over the all temperature range. β ranges from 1.4 to 2.8 with a mean value around 2.1, and several possible scenarios are possible, including β(T ) and the effect of multiple temperature components folded into the measurements. For one third of the objects the distances are obtained using various methods such as the extinction signature, or the association with known molecular complexes or Infra-Red Dark Clouds. Most of the detections are within 2 kpc in the Solar neighbourhood, but a few are at distances greater than 4 kpc. The cores are distributed over the whole range of longitude and latitude, from the deep Galactic plane, despite the confusion, to high latitudes (> 30 • ). The associated mass estimates derived from dust emission range from 1 to 10 5 solar masses. Using their physical properties such as temperature, mass, luminosity, density and size, these cold sources are shown to be cold clumps, defined as the intermediate cold substructures between clouds and cores. These cold clumps are not isolated but mostly organized in filaments associated with molecular clouds. The Cold Core Catalogue of Planck Objects (C3PO) is the first unbiased all-sky catalogue of cold compact objects and contains 10783 objects. It gives an unprecedented statistical view to the properties of these potential pre-stellar clumps and offers a unique possibility for their classification in terms of their intrinsic properties and environment.
IAUC 8218 available at Central Bureau for Astronomical Telegrams.
The first large release of data from the UKIDSS ESO public survey took place in July 2006. The si... more The first large release of data from the UKIDSS ESO public survey took place in July 2006. The size of the data set is about 7% of the size of the final survey data set. Early science results are presented here, ranging from the nearest coolest brown dwarfs, to the most luminous, rarest, galaxies at 5 < z < 6.
Monthly Notices of the Royal Astronomical Society, 2014
We present optical and near-infrared imaging of the field of the z = 7.0842 quasar ULAS J112001.4... more We present optical and near-infrared imaging of the field of the z = 7.0842 quasar ULAS J112001.48+064124.3 taken with the Hubble Space Telescope. We use these data to search for galaxies that may be physically associated with the quasar, using the Lyman break technique, and find three such objects, although the detection of one in Spitzer Space Telescope imaging strongly suggests it lies at z ∼ 2. This is consistent with the field luminosity function and indicates that there is no excess of > L * galaxies within 1 Mpc of the quasar. A detection of the quasar shortward of the Lyα line is consistent with the previously observed evolution of the intergalactic medium at z > 5.5.
The Astrophysical Journal, 2014
ABSTRACT We present the analysis of optical and near-infrared spectra of the only four z&gt;6... more ABSTRACT We present the analysis of optical and near-infrared spectra of the only four z&gt;6.5 quasars known to date, discovered in the UKIDSS-LAS and VISTA-VIKING surveys. Our data-set consists of VLT/X-Shooter and Magellan/FIRE observations of the z&gt;6.5 quasars, and includes new deep VLT/X-Shooter observations of the highest redshift quasar known to date (z=7.1). These are the best optical/NIR spectroscopic data that are likely to be obtained for the z&gt;6.5 sample using current 6-10 m facilities. We estimate the black hole mass, the Eddington ratio, and the SiIV/CIV, CIII]/CIV, and FeII/MgII emission-line flux ratios. We perform spectral modeling using a procedure that allows us to derive a probability distribution for the continuum components and to obtain the quasar properties weighted upon the underlying distribution of continuum models. The z&gt;6.5 quasars show the same emission properties as their counterparts at lower redshifts. The z&gt;6.5 quasars host black holes with masses of ~10^9 M_sun that are accreting close to the Eddington luminosity (&lt;log(L_Bol/L_Edd)&gt;= -0.4+/-0.2), in agreement with what has been observed for a sample of 4.0&lt;z&lt;6.5 quasars. By comparing the SiIV/CIV and CIII]/CIV flux ratios with the results obtained from luminosity-matched samples at z~6 and 2&lt;z&lt;4.5, we find no evidence of evolution of the line ratios with cosmic time. We compare the measured FeII/MgII flux ratios with those obtained for a sample of 4.0&lt;z&lt;6.4 sources. The two samples are analyzed using a consistent procedure. The FeII/MgII flux ratio does not show any evolution in the 4.0&lt;z&lt;7.1 redshift range. Under the assumption that the FeII/MgII traces the Fe/Mg abundance ratio, this implies the presence of major episodes of chemical enrichment in the quasar hosts in the first ~0.8 Gyr after the Big Bang.
EPJ Web of Conferences, 2011
This paper discusses benchmark brown dwarfs in various environments, and focuses on those in wide... more This paper discusses benchmark brown dwarfs in various environments, and focuses on those in wide binary systems. We present a summary of the recently discovered T dwarf population from the UKIDSS Large Area Survey, and describe the constraints that it places on our knowledge of the sub-stellar initial mass function. We also present some exciting results from our ongoing search
The Astrophysical Journal, 2003
We present the results of a novel new search of the first data-release from the Sloan Digital Sky... more We present the results of a novel new search of the first data-release from the Sloan Digital Sky Survey (SDSS-DR1) for the spectra of supernovae. The use of large spectroscopic galaxy surveys offers the prospect of obtaining improved estimates of the local supernova rate, with the added benefit of a very different selection function to that of conventional photometric surveys. In this Letter we present an overview of our search methodology and the details of 19 Type Ia supernovae found in SDSS-DR1. The supernovae sample is used to make a preliminary estimate, Γ Ia = 0.4 ± 0.2h 2 SNu, of the cosmological SNe rate.
Publications of the Astronomical Society of Australia, 2001
The 2 degree Field (2dF) galaxy redshift survey will involve obtaining spectra of approximately 2... more The 2 degree Field (2dF) galaxy redshift survey will involve obtaining spectra of approximately 2.5 × 105 objects which have previously been identified as galaxy candidates on morphological grounds. Included in these spectra should be about ten gravitationally-lensed quasars, all with low-redshift galaxies as deflectors (as the more common lenses with high-redshift deflectors will be rejected from the survey as
Physical Review Letters, 2012
Fluctuations in the cosmic microwave background (CMB) contain information which has been pivotal ... more Fluctuations in the cosmic microwave background (CMB) contain information which has been pivotal in establishing the current cosmological model. These data can also be used to test well-motivated additions to this model, such as cosmic textures. Textures are a type of topological defect that can be produced during a cosmological phase transition in the early Universe, and which leave characteristic hot and cold spots in the CMB. We apply bayesian methods to carry out a rigorous test of the texture hypothesis, using full-sky data from the Wilkinson Microwave Anisotropy Probe. We conclude that current data do not warrant augmenting the standard cosmological model with textures. We rule out at 95% confidence models that predict more than 6 detectable cosmic textures on the full sky.
Physical Review D, 2013
ABSTRACT A number of theoretically well-motivated additions to the standard cosmological model pr... more ABSTRACT A number of theoretically well-motivated additions to the standard cosmological model predict weak signatures in the form of spatially localized sources embedded in the cosmic microwave background (CMB) fluctuations. We present a hierarchical Bayesian statistical formalism and a complete data analysis pipeline for testing such scenarios. We derive an accurate approximation to the full posterior probability distribution over the parameters defining any theory that predicts sources embedded in the CMB, and perform an extensive set of tests in order to establish its validity. The approximation is implemented using a modular algorithm, designed to avoid a posteriori selection effects, which combines a candidate-detection stage with a full Bayesian model-selection and parameter-estimation analysis. We apply this pipeline to theories that predict cosmic textures and bubble collisions, extending previous analyses by using: (1) adaptive-resolution techniques, allowing us to probe features of arbitrary size, and (2) optimal filters, which provide the best possible sensitivity for detecting candidate signatures. We conclude that the WMAP 7-year data do not favor the addition of either cosmic textures or bubble collisions to the standard cosmological model, and place robust constraints on the predicted number of such sources. The expected numbers of bubble collisions and cosmic textures on the CMB sky within our detection thresholds are constrained to be fewer than 4.0 and 5.2 at 95% confidence, respectively.
Physical Review D, 2004
Gravitational lensing introduces the possibility of multiple (macroscopic) paths from an astrophy... more Gravitational lensing introduces the possibility of multiple (macroscopic) paths from an astrophysical neutrino source to a detector. Such a multiplicity of paths can allow for quantum mechanical interference to take place that is qualitatively different to neutrino oscillations in flat space. After an illustrative example clarifying some under-appreciated subtleties of the phase calculation, we derive the form of the quantum mechanical phase for a neutrino mass eigenstate propagating non-radially through a Schwarzschild metric. We subsequently determine the form of the interference pattern seen at a detector. We show that the neutrino signal from a supernova could exhibit the interference effects we discuss were it lensed by an object in a suitable mass range. We finally conclude, however, that -given current neutrino detector technology -the probability of such lensing occurring for a (neutrino-detectable) supernova is tiny in the immediate future.
Physical Review D, 2011
The eternal inflation scenario predicts that our observable universe resides inside a single bubb... more The eternal inflation scenario predicts that our observable universe resides inside a single bubble embedded in a vast inflating multiverse. We present the first observational tests of eternal inflation, performing a search for cosmological signatures of collisions with other bubble universes in cosmic microwave background data from the WMAP satellite. We conclude that the WMAP 7-year data do not warrant augmenting ΛCDM with bubble collisions, constraining the average number of detectable bubble collisions on the full skyNs < 1.6 at 68% CL. Data from the Planck satellite can be used to more definitively test the bubble collision hypothesis.
Physical Review D, 2000
We discuss all-sky convolution of the instrument beam with the sky signal in polarimetry experime... more We discuss all-sky convolution of the instrument beam with the sky signal in polarimetry experiments, such as the Planck mission which will map the temperature anisotropy and polarization of the cosmic microwave background (CMB). To account properly for stray light (from e.g. the galaxy, sun, and planets) in the far side-lobes of such an experiment, it is necessary to perform the beam convolution over the full sky. We discuss this process in multipole space for an arbitrary beam response, fully including the effects of beam asymmetry and cross-polarization. The form of the convolution in multipole space is such that the Wandelt-Górski fast technique for all-sky convolution of scalar signals (e.g. temperature) can be applied with little modification. We further show that for the special case of a pure co-polarized, axisymmetric beam the effect of the convolution can be described by spin-weighted window functions. In the limits of a small angle beam and large Legendre multipoles, the spin-weight 2 window function for the linear polarization reduces to the usual scalar window function used in previous analyses of beam effects in CMB polarimetry experiments. While we focus on the example of polarimetry experiments in the context of CMB studies, we emphasise that the formalism we develop is applicable to anisotropic filtering of arbitrary tensor fields on the sphere. 98.70.Vc,
Monthly Notices of the Royal Astronomical Society: Letters, 2011
Monthly Notices of the Royal Astronomical Society, 2012
High redshift quasars (HZQs) with redshifts of z 6 are so rare that any photometrically-selected ... more High redshift quasars (HZQs) with redshifts of z 6 are so rare that any photometrically-selected sample of sources with HZQ-like colours is likely to be dominated by Galactic stars and brown dwarfs scattered from the stellar locus. It is impractical to reobserve all such candidates, so an alternative approach was developed in which Bayesian model comparison techniques are used to calculate the probability that a candidate is a HZQ, P q , by combining models of the quasar and star populations with the photometric measurements of the object. This method was motivated specifically by the large number of HZQ candidates identified by cross-matching the UKIRT Infrared Deep Sky Survey (UKIDSS) Large Area Survey (LAS) to the Sloan Digital Sky Survey (SDSS): in the ∼ 1900 deg 2 covered by the LAS in the UKIDSS Seventh Data Release (DR7) there are ∼ 10 3 real astronomical point-sources with the measured colours of the target quasars, of which only ∼ 10 are expected to be HZQs. Applying Bayesian model comparison to the sample reveals that most sources with HZQ-like colours have P q 0.1 and can be confidently rejected without the need for any further observations. In the case of the UKIDSS DR7 LAS, there were just 88 candidates with P q 0.1; these object were prioritized for reobservation by ranking according to P q (and their likely redshift, which was also inferred from the photometric data). Most candidates were rejected after one or two (moderate depth) photometric measurements by recalculating P q using the new data. That left seven confirmed HZQs, three of which were previously identified in the SDSS and four of which were new UKIDSS discoveries. The high efficiency of this Bayesian selection method suggests that it could usefully be extended to other HZQ surveys (e.g. searches by the Panoramic Survey Telescope And Rapid Response System, Pan-STARRS, or the Visible and Infrared Survey Telescope for Astronomy, VISTA) as well as to other searches for rare objects.
Monthly Notices of the Royal Astronomical Society, 2008
We report the discovery of three very late T dwarfs in the UKIRT Infrared Deep Sky Survey (UKIDSS... more We report the discovery of three very late T dwarfs in the UKIRT Infrared Deep Sky Survey (UKIDSS) Third Data Release: ULAS J101721.40+011817.9 (ULAS1017), ULAS J123828.51+095351.3 (ULAS1238) and ULAS J133553.45+113005.2 (ULAS1335). We detail optical and near-infrared photometry for all three sources, and mid-infrared photometry for ULAS1335. We use near-infrared spectra of each source to assign spectral types T8p (ULAS1017), T8.5 (ULAS1238) and T9 (ULAS1335) to these objects. ULAS1017 is classed as a peculiar T8 (T8p) due to appearing as a T8 dwarf in the J-band, whilst exhibiting H and K-band flux ratios consistent with a T6 classification. Through comparison to BT-Settl model spectra we estimate that ULAS1017 has 750K < ∼ T eff < ∼ 850K, and 5.0 < ∼ log g(cms −2 ) < ∼ 5.5, assuming solar metallicity. This estimate for gravity is degenerate with varying metallicity. We estimate that ULAS1017 has an age of 1.6-15 Gyr, a mass of 33-70 M J and lies at a distance of 31-54 pc. We do not estimate atmospheric parameters for ULAS1238 due to a lack of K-band photometry. We extend the unified scheme of to the type T9 and suggest the inclusion of the W J index to replace the now saturated J-band indices. We propose ULAS1335 as the T9 spectral type standard. ULAS1335 is the same spectral type as ULAS J003402.77-005206.7 and CFBDS J005910.90-011401.3. We argue that given the similarity of the currently known >T8 dwarfs to the rest of the T dwarf sequence, the suggestion of the Y0 spectral class for these objects is premature. Comparison of model spectra with that of ULAS1335 suggest a temperature below 600K, possibly combined with low-gravity and/or high-metallicity. We find ULAS1335 to be extremely red in near to mid-infrared colours, with H − [4.49] = 4.34 ± 0.04 . This is the reddest near to mid-infrared colour yet observed for a T dwarf. The near to mid-infrared spectral energy distribution of ULAS1335 further supports T eff < 600K, and we estimate T eff ∼ 550 − 600K for ULAS1335. We estimate that ULAS1335 has an age of 0.6-5.3 Gyr, a mass of 15-31 M J and lies at a distance of 8-12 pc.
Monthly Notices of the Royal Astronomical Society, 2008
We present the discovery of fifteen new T2.5-T7.5 dwarfs (with estimated distances between ∼24-93... more We present the discovery of fifteen new T2.5-T7.5 dwarfs (with estimated distances between ∼24-93pc), identified in the first three main data releases of the UKIRT Infrared Deep Sky Survey. This brings the total number of T dwarfs discovered in the Large Area Survey (to date) to 28. These discoveries are confirmed by near infrared spectroscopy, from which we derive spectral types on the unified scheme of . Seven of the new T dwarfs have spectral types of T2.5-T4.5, five have spectral types of T5-T5.5, one is a T6.5p, and two are T7-7.5. We assess spectral morphology and colours to identify T dwarfs in our sample that may have non-typical physical properties (by comparison to solar neighbourhood populations), and find that one of these new T dwarfs may be metal poor, three may have low surface gravity, and one may have high surface gravity. The colours of the full sample of LAS T dwarfs show a possible trend to bluer Y − J with decreasing effective temperature, and some interesting colour changes in J − H and z − J (deserving further investigation) beyond T8. The LAS T dwarf sample from the first and second main data releases show good evidence for a consistent level of completion to J=19. By accounting for the main sources of incompleteness (selection, follow-up and spatial) as well as the effects of unresolved binarity and Malmquist bias, we estimate that there are 17±4 T4 dwarfs in the J 19 volume of the LAS second data release. Comparing this to theoretical predictions is most consistent with a sub-stellar mass function exponent α between -1.0 and 0. This is consistent with the latest 2MASS/SDSS constraint (which is based on lower number statistics), and is significantly lower than the α ∼ 1.0 suggested by L dwarf field populations, possibly a result of the lower mass range probed by the T dwarf class. . T dwarf photometry and colours. Unless otherwise indicated, near infrared photometry was measured on the MKO system. Uncertainties are indicated in brackets as integer multiples of the last decimal place. The last two T dwarfs are from , and here we present additional z-band measurements.
Monthly Notices of the Royal Astronomical Society, 2008
A directional spherical wavelet analysis is performed to examine the Gaussianity of the Wilkinson... more A directional spherical wavelet analysis is performed to examine the Gaussianity of the Wilkinson Microwave Anisotropy Probe (WMAP) 1-year data. Such an analysis is facilitated by the introduction of a fast directional continuous spherical wavelet transform. The directional nature of the analysis allows one to probe orientated structure in the data. Significant deviations from Gaussianity are detected in the skewness and kurtosis of spherical elliptical Mexican hat and real Morlet wavelet coefficients for both the WMAP and Tegmark et al. foreground-removed maps. The previous non-Gaussianity detection made by using the spherical symmetric Mexican hat wavelet is confirmed, although their detection at the 99.9% significance level is only made at the 95.3% significance level using our most conservative statistical test. Furthermore, deviations from Gaussianity in the skewness of spherical real Morlet wavelet coefficients on a wavelet scale of 550 ′ (corresponding to an effective global size on the sky of ∼ 26 • and an internal size of ∼ 3 • ) at an azimuthal orientation of 72 • , are made at the 98.3% significance level, using the same conservative method. The wavelet analysis inherently allows one to localise on the sky those regions that introduce skewness and those that introduce kurtosis. Preliminary noise analysis indicates that these detected deviation regions are not atypical and have average noise dispersion. Further analysis is required to ascertain whether these detected regions correspond to secondary or instrumental effects, or whether in fact the non-Gaussianity detected is due to intrinsic primordial fluctuations in the cosmic microwave background.
Monthly Notices of the Royal Astronomical Society, 2002
... The resulting b J values are given in column 5 of Table 1. Seven candidate quasars do not app... more ... The resulting b J values are given in column 5 of Table 1. Seven candidate quasars do not appear in the SSS scans and ... to establish TGS187Z041 as a strong lens candidate, particularly since ESO NTT V-band imaging obtained on 2002 February 2 using the SUSI instrument in ...
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Papers by Daniel Mortlock