Publications by Philip James Marshall


A blind detection of a large, complex, Sunyaev-Zel'dovich structure

Monthly Notices of the Royal Astronomical Society 423 (2012) 1463-1473

TW Shimwell, RW Barker, P Biddulph, D Bly, RC Boysen, AR Brown, ML Brown, C Clementson, M Crofts, TL Culverhouse, J Czeres, RJ Dace, ML Davies, R D'Alessandro, P Doherty, K Duggan, JA Ely, M Felvus, F Feroz, W Flynn, TMO Franzen, J Geisbüsch, R Génova-Santos, KJB Grainge, WF Grainger, D Hammett, MP Hobson, CM Holler, N Hurley-Walker, R Jilley, T Kaneko, R Kneissl, K Lancaster, AN Lasenby, PJ Marshall, F Newton, O Norris, I Northrop, DM Odell, M Olamaie, YC Perrott, JC Pober, GG Pooley, MW Pospieszalski, V Quy, C Rodríguez-Gonzálvez, RDE Saunders, AMM Scaife, MP Schammel, J Schofield, PF Scott, C Shaw, H Smith, DJ Titterington, M Velić, EM Waldram, S West, BA Wood, G Yassin, JTL Zwart

We present an interesting Sunyaev-Zel'dovich (SZ) detection in the first of the Arcminute Microkelvin Imager (AMI) 'blind', degree-square fields to have been observed down to our target sensitivity of. In follow-up deep pointed observations the SZ effect is detected with a maximum peak decrement greater than eight times the thermal noise. No corresponding emission is visible in the ROSAT all-sky X-ray survey and no cluster is evident in the Palomar all-sky optical survey. Compared with existing SZ images of distant clusters, the extent is large (≈10arcmin) and complex; our analysis favours a model containing two clusters rather than a single cluster. Our Bayesian analysis is currently limited to modelling each cluster with an ellipsoidal or spherical β model, which does not do justice to this decrement. Fitting an ellipsoid to the deeper candidate we find the following. (a) Assuming that the Evrard et al. approximation to Press & Schechter correctly gives the number density of clusters as a function of mass and redshift, then, in the search area, the formal Bayesian probability ratio of the AMI detection of this cluster is 7.9 × 10 4 :1; alternatively assuming Jenkins et al. as the true prior, the formal Bayesian probability ratio of detection is 2.1 × 10 5 :1. (b) The cluster mass is (c) Abandoning a physical model with number density prior and instead simply modelling the SZ decrement using a phenomenological β model of temperature decrement as a function of angular distance, we find a central SZ temperature decrement of K - this allows for cosmic microwave background primary anisotropies, receiver noise and radio sources. We are unsure if the cluster system we observe is a merging system or two separate clusters. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS.


Luminous satellites. II. Spatial distribution, luminosity function, and cosmic evolution

Astrophysical Journal 752 (2012)

AM Nierenberg, MW Auger, T Treu, PJ Marshall, CD Fassnacht, MT Busha

We infer the normalization and the radial and angular distributions of the number density of satellites of massive galaxies (log10[M* h/M] > 10.5) between redshifts 0.1 and 0.8 as a function of host stellar mass, redshift, morphology, and satellite luminosity. Exploiting the depth and resolution of the COSMOS Hubble Space Telescope images, we detect satellites up to 8mag fainter than the host galaxies and as close as 0.3 (1.4) arcsec (kpc). Describing the number density profile of satellite galaxies to be a projected power law such that , we find γp = -1.1 ± 0.3. We find no dependency of γp on host stellar mass, redshift, morphology, or satellite luminosity. Satellites of early-type hosts have angular distributions that are more flattened than the host light profile and are aligned with its major axis. No significant average alignment is detected for satellites of late-type hosts. The number of satellites within a fixed magnitude contrast from a host galaxy is dependent on its stellar mass, with more massive galaxies hosting significantly more satellites. Furthermore, high-mass late-type hosts have significantly fewer satellites than early-type galaxies of the same stellar mass, possibly indicating that they reside in more massive halos. No significant evolution in the number of satellites per host is detected. The cumulative luminosity function of satellites is qualitatively in good agreement with that predicted using SubHalo Abundance Matching techniques. However, there are significant residual discrepancies in the absolute normalization, suggesting that properties other than the host galaxy luminosity or stellar mass determine the number of satellites. © 2012. The American Astronomical Society. All rights reserved..


Nomads of the Galaxy

Monthly Notices of the Royal Astronomical Society 423 (2012) 1856-1865

LE Strigari, M Barnabè, PJ Marshall, RD Blandford

We estimate that there may be up to ∼10 5 compact objects in the mass range 10 -8-10 -2M ⊙ per-main-sequence star that are unbound to a host star in the Galaxy. We refer to these objects as nomads; in the literature a subset of these are sometimes called free-floating or rogue planets. Our estimate for the number of Galactic nomads is consistent with a smooth extrapolation of the mass function of unbound objects above the Jupiter-mass scale, the stellar mass density limit and the metallicity of the interstellar medium. We analyse the prospects for detecting nomads via Galactic microlensing. The Wide-Field Infrared Survey Telescope will measure the number of nomads per-main-sequence star greater than the mass of Jupiter to ∼13per cent, and the corresponding number greater than the mass of Mars to ∼25per cent. All-sky surveys such as Gaia and Large Synoptic Survey Telescope can identify nomads greater than about the mass of Jupiter. We suggest a dedicated drift scanning telescope that covers approximately 100deg 2 in the Southern hemisphere could identify nomads via microlensing of bright stars with characteristic time-scales of tens to hundreds of seconds. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS.


The SWELLS survey - IV. Precision measurements of the stellar and dark matter distributions in a spiral lens galaxy

Monthly Notices of the Royal Astronomical Society 423 (2012) 1073-1088

M Barnabè, AA Dutton, PJ Marshall, MW Auger, BJ Brewer, T Treu, AS Bolton, DC Koo, LVE Koopmans

We construct a fully self-consistent mass model for the lens galaxy SDSSJ2141 at redshift 0.14, and use it to improve on previous studies by modelling its gravitational lensing effect, gas rotation curve and stellar kinematics simultaneously. We adopt a very flexible axisymmetric mass model constituted by a generalized Navarro-Frenk-White (NFW) dark matter halo and a stellar mass distribution obtained by deprojecting the multi-Gaussian expansion fit to the high-resolution K'-band laser guide star adaptive optics imaging data of the galaxy, with the (spatially constant) mass-to-light ratio as a free parameter. We model the stellar kinematics by solving the anisotropic Jeans equations. We find that the inner logarithmic slope of the dark halo is weakly constrained, i.e., and consistent with an unmodified NFW profile; we can conclude, however, that steep profiles (γ≥ 1.5) are disfavoured (<14 per cent posterior probability). We marginalize over this parameter to infer the galaxy to have (i) a dark matter fraction within 2.2 disc radii of, independent of the galaxy stellar population, implying a maximal disc for SDSSJ2141; (ii) an apparently uncontracted dark matter halo, with concentration and virial velocity, consistent with Λ cold dark matter (ΛCDM) predictions; (iii) a slightly oblate halo, consistent with predictions from baryon-affected models. Comparing the tightly constrained gravitational stellar mass inferred from the combined analysis with that inferred from stellar population modelling of the galaxies' colours, and accounting for an expected cold gas fraction of 20 ± 10 per cent, we determine a preference for a Chabrier IMF over Salpeter IMF by a Bayes factor of 5.7 (corresponding to substantial evidence). We infer a value for the orbital anisotropy parameter in the meridional plane, in agreement with most studies of local disc galaxies, and ruling out at 99 per cent confidence level that the dynamics of this system can be described by a two-integral distribution function. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS.


Evidence for dark matter contraction and a Salpeter IMF in a massive early-type galaxy

ArXiv e-prints (2011)

A Sonnenfeld, T Treu, R Gavazzi, PJ Marshall, MW Auger, SH Suyu, LVE Koopmans, AS Bolton


A weak-lensing and near-infrared study of A3192: Disassembling a richness class 3 abell cluster

Astrophysical Journal Letters 748 (2012)

V Hamilton-Morris, GP Smith, AC Edge, E Egami, CP Haines, PJ Marshall, AJR Sanderson, TA Targett

We present a joint gravitational lensing and near-infrared study of the galaxy cluster Abell 3192 (A3192) that has been associated both with galaxies at z = 0.168 and with the X-ray luminous cluster RXCJ0358.8-2955 (RXCJ0358) at z = 0.425. Weak-lensing analysis of our Hubble Space Telescope snapshot observation with the Advanced Camera for Surveys detects two mass over-densities separated by 2 arcmin, one adjacent to the optical position of A3192 (4.4σ significance) and the other adjacent to the X-ray position of RXCJ0358 (6.2σ significance). These mass peaks coincide with peaks in the K-band luminosity density of galaxies with near-infrared colors consistent with the red sequence at z = 0.168 and z = 0.425, respectively. Moreover, the Bayesian evidence of parameterized mass models that include two cluster/group-scale halos centered on the respective mass peaks exceeds that of single-halo models by a factor of ≥10. The total projected mass of each galaxy system within 250 kpc of the respective peaks is M WL(z = 0.168) ≃ 3 × 10 13 M and M WL(z = 0.425) ≃ 1.2 × 10 14 M, both with total mass-to-light ratios of M WL/L K ≃ 20 M/L. The original Abell cluster therefore comprises two independent galaxy systems - a foreground group at z = 0.168 and RXCJ0358 at z = 0.425. Our results demonstrate the power of combining X-ray, near-infrared, and weak-lensing observations to select massive clusters, place those clusters and interloper galaxy systems along the line of sight, and measure their masses. This combination will be invaluable to robust interpretation of future high-redshift cluster surveys, including eROSITA. © 2012. The American Astronomical Society. All rights reserved..


Resource Letter GL-1: Gravitational Lensing

American Journal of Physics 80 (2012) 753-763

T Treu, PJ Marshall, D Clowe

This Resource Letter provides a guide to a selection of the literature on gravitational lensing and its applications. Journal articles, books, popular articles, and websites are cited for the following topics: foundations of gravitational lensing, foundations of cosmology, history of gravitational lensing, strong lensing, weak lensing, and microlensing. © 2012 American Association of Physics Teachers.


The SWELLS survey - III. Disfavouring 'heavy' initial mass functions for spiral lens galaxies

Monthly Notices of the Royal Astronomical Society 422 (2012) 3574-3590

BJ Brewer, AA Dutton, T Treu, MW Auger, PJ Marshall, M Barnabè, AS Bolton, DC Koo, LVE Koopmans

We present gravitational lens models for 20 strong gravitational lens systems observed as part of the Sloan WFC Edge-on Late-type Lens Survey (SWELLS) project. 15 of the lenses are taken from Paper I, while five are newly discovered systems. The systems are galaxy-galaxy lenses where the foreground deflector has an inclined disc, with a wide range of morphological types, from late-type spiral to lenticular. For each system, we compare the total mass inside the critical curve inferred from gravitational lens modelling to the stellar mass inferred from stellar population synthesis (SPS) models, computing the stellar mass fraction f*≡M SPS/M lens. We find that, for the lower mass SWELLS systems, adoption of a Salpeter stellar initial mass function (IMF) leads to estimates of f* that exceed 1. This is unphysical and provides strong evidence against the Salpeter IMF being valid for these systems. Taking the lower mass end of the SWELLS sample (σ SIE < 230kms -1), we find that the IMF is lighter (in terms of stellar mass-to-light ratio) than Salpeter with 98 percent probability, and consistent with the Chabrier IMF and IMFs between the two. This result is consistent with previous studies of spiral galaxies based on independent techniques. In combination with recent studies of massive early-type galaxies that have favoured a heavier Salpeter-like IMF, this result strengthens the evidence against a universal stellar IMF. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS.


Constraining the dark energy equation of state with double-source plane strong lenses

Monthly Notices of the Royal Astronomical Society (2012)

TE Collett, MW Auger, V Belokurov, PJ Marshall, AC Hall


Bayesian analysis of weak gravitational lensing and Sunyaev-Zel'dovich data for six galaxy clusters

Monthly Notices of the Royal Astronomical Society 419 (2012) 2921-2942

N Hurley-Walker, S Bridle, ES Cypriano, ML Davies, T Erben, F Feroz, TMO Franzen, K Grainge, MP Hobson, A Lasenby, PJ Marshall, M Olamaie, G Pooley, C Rodríguez-Gonzálvez, RDE Saunders, AMM Scaife, MP Schammel, PF Scott, T Shimwell, D Titterington, E Waldram, JTL Zwart

We present an analysis of observations made with the Arcminute Microkelvin Imager (AMI) and the Canada-France-Hawaii Telescope (CFHT) of six galaxy clusters in a redshift range of 0.16-0.41. The cluster gas is modelled using the Sunyaev-Zel'dovich (SZ) data provided by AMI, while the total mass is modelled using the lensing data from the CFHT. In this paper, we (i) find very good agreement between SZ measurements (assuming large-scale virialization and a gas-fraction prior) and lensing measurements of the total cluster masses out to r 200; (ii) perform the first multiple-component weak-lensing analysis of A115; (iii) confirm the unusual separation between the gas and mass components in A1914 and (iv) jointly analyse the SZ and lensing data for the relaxed cluster A611, confirming our use of a simulation-derived mass-temperature relation for parametrizing measurements of the SZ effect. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.


The SWELLS survey - IV. Precision measurements of the stellar and dark matter distributions in a spiral lens galaxy

Monthly Notices of the Royal Astronomical Society (2012)

M Barnabè, AA Dutton, PJ Marshall, MW Auger, BJ Brewer, T Treu, AS Bolton, DC Koo, LVE Koopmans


Luminous Satellites of Early-type Galaxies. I. Spatial Distribution

\apj 731 (2011) 44-44

AM Nierenberg, MW Auger, T Treu, PJ Marshall, CD Fassnacht


The Mass Distribution and Assembly of the Milky Way from the Properties of the Magellanic Clouds

\apj 743 (2011) 40-40

MT Busha, PJ Marshall, RH Wechsler, A Klypin, J Primack


The SWELLS survey - II. Breaking the disc-halo degeneracy in the spiral galaxy gravitational lens SDSS J2141-0001

\mnras 417 (2011) 1621-1642-1621-1642

AA Dutton, BJ Brewer, PJ Marshall, MW Auger, T Treu, DC Koo, AS Bolton, BP Holden, LVE Koopmans


The SWELLS survey - I. A large spectroscopically selected sample of edge-on late-type lens galaxies

Monthly Notices of the Royal Astronomical Society 417 (2011) 1601-1620

T Treu, AA Dutton, MW Auger, PJ Marshall, AS Bolton, BJ Brewer, DC Koo, LVE Koopmans

The relative contribution of baryons and dark matter to the inner regions of spiral galaxies provides critical clues to their formation and evolution, but it is generally difficult to determine. For spiral galaxies that are strong gravitational lenses, however, the combination of lensing and kinematic observations can be used to break the disc-halo degeneracy. In turn, such data constrain fundamental parameters such as (i) the mass density profile slope and axial ratio of the dark matter halo, and by comparison with dark matter-only numerical simulations the modifications imposed by baryons; (ii) the mass in stars and therefore the overall star formation efficiency, and the amount of feedback; (iii) by comparison with stellar population synthesis models, the normalization of the stellar initial mass function. In this first paper of a series, we present a sample of 16 secure, one probable and six possible strong lensing spiral galaxies, for which multiband high-resolution images and rotation curves were obtained using the Hubble Space Telescope and KeckII telescope as part of the Sloan WFC Edge-on Late-type Lens Survey (SWELLS). The sample includes eight newly discovered secure systems. We characterize the sample of deflector galaxies in terms of their morphologies, structural parameters and stellar masses. We find that the SWELLS sample of secure lenses spans a broad range of morphologies (from lenticular to late-type spiral), spectral types (quantified by Hα emission) and bulge to total stellar mass ratio (0.22-0.85), while being limited to M* > 1010.5M⊙. The SWELLS sample is thus well suited for exploring the relationship between dark and luminous matter in a broad range of galaxies. We find that the deflector galaxies obey the same size-mass relation as that of a comparison sample of elongated non-lens galaxies selected from the Sloan Digital Sky Survey. We conclude that the SWELLS sample is consistent with being representative of the overall population of high-mass high-inclination discy galaxies. © 2011 The Authors. Monthly Notices of the Royal Astronomical Society © 2011 RAS.


Accurate Cosmography with LSST Time Delay Lenses

American Astronomical Society Meeting Abstracts #217 43 (2011) #252.22-#252.22

PJ Marshall, CP Sandford, CD Fassnacht, DR Meldgin, M Oguri, SH Suyu, MW Auger, LSSTSLS Collaboration


Strong Lenses with LSST: Simulated 10-year Movies of Multiply-Imaged Quasars

American Astronomical Society Meeting Abstracts #217 43 (2011) #252.21-#252.21

J Garrett Jernigan, PJ Marshall, M Oguri, R Gibson, J Pizagno, A Connolly, JR Peterson, Z Ahmad, J Bankert, D Bard, C Chang, E Grace, K Gilmore, M Hannel, L Jones, SM Kahn, S Krughoff, S Lorentz, S Marshall, S Nagarajan, AP Rasmussen, M Shmakova, N Sylvestre, N Todd, M Young, LSSTSLS Collaboration


Extragalactic Science with LSST

American Astronomical Society Meeting Abstracts #217 43 (2011) #122.04-#122.04

PJ Marshall


The SWELLS survey - I. A large spectroscopically selected sample of edge-on late-type lens galaxies

Monthly Notices of the Royal Astronomical Society (2011)

T Treu, AA Dutton, MW Auger, PJ Marshall, AS Bolton, BJ Brewer, DC Koo, LVE Koopmans


The mass distribution and assembly of the milky way from the properties of the magellanic clouds

Astrophysical Journal 743 (2011)

MT Busha, PJ Marshall, RH Wechsler, A Klypin, J Primack

We present a new measurement of the mass of the Milky Way (MW) based on observed properties of its largest satellite galaxies, the Magellanic Clouds (MCs), and an assumed prior of a ΛCDM universe. The large, high-resolution Bolshoi cosmological simulation of this universe provides a means to statistically sample the dynamical properties of bright satellite galaxies in a large population of dark matter halos. The observed properties of the MCs, including their circular velocity, distance from the center of the MW, and velocity within the MW halo, are used to evaluate the likelihood that a given halo would have each or all of these properties; the posterior probability distribution function (PDF) for any property of the MW system can thus be constructed. This method provides a constraint on the MW virial mass, 1.2 +0.7- 0.4 (stat.)+0.3- 0.3 (sys.) × 1012 M ⊙ (68% confidence), which is consistent with recent determinations that involve very different assumptions. In addition, we calculate the posterior PDF for the density profile of the MW and its satellite accretion history. Although typical satellites of 10 12 M ⊙ halos are accreted over a wide range of epochs over the last 10Gyr, we find a ∼72% probability that the MCs were accreted within the lastGyr, and a 50% probability that they were accreted together. © 2011. The American Astronomical Society. All rights reserved.

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