Publications


Weak lensing in the Horizon-AGN simulation lightcone. Small scale baryonic effects

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C Gouin, R Gavazzi, C Pichon, Y Dubois, C Laigle, NE Chisari, S Codis, JULIEN Devriendt, S Peirani

Context. Accurate model predictions including the physics of baryons are required to make the most of the upcoming large cosmological surveys devoted to gravitational lensing. The advent of hydrodynamical cosmological simulations enables such predictions on sufficiently sizeable volumes. Aims. Lensing quantities (deflection, shear, convergence) and their statistics (convergence power spectrum, shear correlation functions, galaxy-galaxy lensing) are computed in the past lightcone built in the Horizon-AGN hydrodynamical cosmological simulation, which implements our best knowledge on baryonic physics at the galaxy scale in order to mimic galaxy populations over cosmic time. Methods. Lensing quantities are generated over a one square degree field of view by performing multiple-lens plane ray-tracing through the lightcone, taking full advantage of the 1 kpc resolution and splitting the line of sight over 500 planes all the way to redshift z~7. Two methods are explored (standard projection of particles with adaptive smoothing, and integration of the acceleration field) to assert a good implementation. The focus is on small scales where baryons matter most. Results. Standard cosmic shear statistics are impacted at the 10% level by the baryonic component for angular scales below a few arcmin. The galaxy-galaxy lensing signal, or galaxy-shear correlation function, is consistent with measurements for the redshift z~0.5 massive galaxy population. At higher redshift z>1, the impact of magnification bias on this correlation is relevant for separations greater than 1 Mpc. Conclusions. This work is pivotal for all current and upcoming weak lensing surveys and represents a first step towards building a full end-to-end generation of lensed mock images from large cosmological hydrodynamical simulations.


Star formation feedback and metal-enrichment history of the intergalactic medium

Astrophysical Journal 731 (2011)

R Cen, NE Chisari

Using the state-of-the-art cosmological hydrodynamic simulations of the standard cold dark matter model with star formation feedback strength normalized to match the observed star formation history of the universe at z= 0-6, we compute the metal-enrichment history of the intergalactic medium (IGM). Overall we show that galactic superwind (GSW) feedback from star formation can transport metals to the IGM and that the properties of simulated metal absorbers match current observations. The distance of influence of GSW from galaxies is typically limited to about ≤0.5Mpc and within regions of overdensity δ ≥ 10. Most C IV and O VI absorbers are located within shocked regions of elevated temperature (T ≥ 2 × 104K), overdensity (δ ≥ 10), and metallicity ([Z/ Z] = [ - 2.5, - 0.5]), enclosed by double shocks propagating outward. O VI absorbers have typically higher metallicity, lower density, and higher temperature than C IV absorbers. For O VI absorbers, collisional ionization dominates over the entire redshift range z= 0-6, whereas for C IV absorbers the transition occurs at moderate redshift z 3 from collisionally dominated to photoionization dominated. We find that the observed column density distributions for C IV and O VI in the range log N cm 2=12-15 are reasonably reproduced by the simulations. The evolution of mass densities contained in C IV and O VI lines, ΩC IV and ΩO VI, is also in good agreement with observations, which shows a near constancy at low redshifts and an exponential drop beyond redshift z= 3-4. For both C IV and O VI, most absorbers are transient and the amount of metals probed by C IV and O VI lines of column log N cm2=12-15 is only 2% of total metal density at any epoch. While gravitational shocks from large-scale structure formation dominate the energy budget (80%-90%) for turning about 50% of the IGM to the warm-hot intergalactic medium (WHIM) by z = 0, GSW feedback shocks are energetically dominant over gravitational shocks at z≥1-2. Most of the so-called missing metals at z= 2-3 are hidden in a warm-hot (T = 104.5-107K) gaseous phase, heated up by GSW feedback shocks. Their mass distribution is broadly peaked at δ=1-10 in the IGM, outside virialized halos. Approximately 37%, 46%, 10%, and 7% of the total metals at z = 0 are in stars, WHIM, X-ray gas, and cold gas, respectively; the distributions stand at 23%, 57%, 2%, and 18% and 14%, 51%, 4%, and 31% at z = 2 and z = 4, respectively. © 2011. The American Astronomical Society. All rights reserved.


Unveiling the nature of IGR J16283-4838

ASTRONOMY & ASTROPHYSICS 526 (2011) ARTN A15

LJ Pellizza, S Chaty, NE Chisari


Vortex dipolar structures in a rigid model of the larynx at flow onset

EXPERIMENTS IN FLUIDS 50 (2011) 397-406

NE Chisari, G Artana, D Sciamarella


Host galaxies of long gamma-ray bursts in the Millennium Simulation

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 408 (2010) 647-656

NE Chisari, PB Tissera, LJ Pellizza


Experimental and numerical study of patterns in laryngeal flow

Journal of Physics: Conference Series 166 (2009)

NE Chisari, G Artana, D Sciamarella

Unsteady airflow is investigated in a channel with a geometry approximating that of the human larynx. The laryngeal flow is simulated by solving the Navier-Stokes equations for an incompressible two-dimensional viscous fluid, and visualized using the Schlieren technique in an experimental setup consisting of a rigid replica of the larynx, with and without ventricular bands. This study shows the spontaneous formation of vortex couples in several regions of the laryngeal profile, and at different stages of the evolution of the starting glottal jet. © 2009 IOP Publishing Ltd.


Bayesian galaxy shape measurement for weak lensing surveys - I. Methodology and a fast-fitting algorithm

Monthly Notices of the Royal Astronomical Society 382 (2007) 315-324

L Miller, TD Kitching, C Heymans, AF Heavens, L Van Waerbeke

The principles of measuring the shapes of galaxies by a model-fitting approach are discussed in the context of shape measurement for surveys of weak gravitational lensing. It is argued that such an approach should be optimal, allowing measurement with maximal signal-to-noise ratio, coupled with estimation of measurement errors. The distinction between likelihood-based and Bayesian methods is discussed. Systematic biases in the Bayesian method may be evaluated as part of the fitting process, and overall such an approach should yield unbiased shear estimation without requiring external calibration from simulations. The principal disadvantage of model fitting for large surveys is the computational time required, but here an algorithm is presented that enables large surveys to be analysed in feasible computation times. The method and algorithm is tested on simulated galaxies from the Shear TEsting Programme (STEP). © 2007 The Authors.


Photometry and spectroscopy of GRB 030329 and its associated supernova 2003dh: The first two months

Astrophysical Journal 599 (2003) 394-407

T Matheson, PM Garnavich, KZ Stanek, D Bersier, ST Holland, K Krisciunas, N Caldwell, P Berlind, JS Bloom, M Bolte, AZ Bonanos, MJI Brown, WR Brown, ML Calkins, P Challis, R Chornock, L Echevarria, DJ Eisenstein, ME Everett, AV Filippenko, K Flint, RJ Foley, DL Freedman, M Hamuy, P Harding, NP Hathi, M Hicken, C Hoopes, C Impey, BT Jannuzi, RA Jansen, S Jha, J Kaluzny, S Kannappan, RP Kirshner, DW Latham, JC Lee, DC Leonard, W Li, KL Luhman, P Martini, H Mathis, J Maza, ST Megeath, LR Miller, D Minniti, EW Olszewski, M Papenkova, MM Phillips, B Pindor, DD Sasselov, R Schild, H Schweiker, T Spahr, J Thomas-Osip, I Thompson, D Weisz, R Windhorst, D Zaritsky

We present extensive optical and infrared photometry of the afterglow of gamma-ray burst (GRB) 030329 and its associated supernova (SN) 2003dh over the first two months after detection (2003 March 30-May 29 UT). Optical spectroscopy from a variety of telescopes is shown and, when combined with the photometry, allows an unambiguous separation between the afterglow and SN contributions. The optical afterglow of the GRB is initially a power-law continuum but shows significant color variations during the first week that are unrelated to the presence of an SN. The early afterglow light curve also shows deviations from the typical power-law decay. An SN spectrum is first detectable ∼7 days after the burst and dominates the light after ∼11 days. The spectral evolution and the light curve are shown to closely resemble those of SN 1998bw, a peculiar Type Ic SN associated with GRB 980425, and the time of the SN explosion is close to the observed time of the GRB. It is now clear that at least some GRBs arise from core-collapse SNe.


Erratum: Discovery of radio-loud broad absorption line Quasars using ultraviolet excess and deep radio selection (The Astrophysical Journal (1998) 505 (L7))

Astrophysical Journal 571 (2002)

MS Brotherton, W Van Breugel, RJ Smith, BJ Boyle, T Shanks, SM Croom, L Miller, RH Becker


A search for star formation around the Galactic halo B-type star PHL 346

Astronomy and Astrophysics 306 (1996) 119-124

NC Hambly, KD Wood, EP Keenan, D Kilkenny, PL Dufton, L Miller, G Gilmore, MJ Irwin, EJ Totten

A search is presented for stars that may have formed coevally with the apparently young halo star PHL 346. Candidates were selected for spectroscopy from UBR Schmidt Telescope plates in U.K. Schmidt Telescope survey field 603 scanned with the COSMOS facility at the Royal Observatory, Edinburgh. Spectroscopic observations at ∼ 3.5 Å resolution were made of 72 field stars using the 1.9m telescope at the South African Astronomical Observatory; 16 A- and B-type stars were found, one of which had the appropriate spectral type and radial velocity to be associated with PHL 346. Further photometry and spectroscopy confirmed this identification. The remaining low gravity early-type stars have a mean LSR radial velocity of -75 km s-1, consistent with a non-rotating halo Population.


A 325 square degree survey of B-type stars at high galactic latitudes

Astrophysical Journal 447 (1995) 783-788

JE Little, PL Dufton, FP Keenan, NC Hambly, ES Conlon, PJF Brown, L Miller

Final results from model atmosphere analyses of all blue stars in a ∼325 square degree region of the Galactic halo are presented. A kinematic analysis reveals the presence of one star which cannot have been ejected from the disk according to contemporary theories. Ten other objects have, however, evolutionary times consistent with classification as disk runaway stars. Our results therefore imply the existence of some 200 stars in the Galaxy unexplainable in terms of disk ejection models, and set a lower limit of 10,000 runaway halo B-type stars.


A new candidate brown dwarf from an infrared survey

Monthly Notices of the Royal Astronomical Society 270 (1994) L47-L51

HRA Jones, L Miller, K Glazebrook

© Royal Astronomical Society. We report the discovery at infrared wavelengths of a very cool field brown dwarf candidate. It has infrared colours J-H = 0.90±0.19 and H-K = 0.83±0.18, compared with the previously known coolest dwarf GD165B which has J-H=1M± 0.05 and H - K = 0.64 ± 0.05. Both are much redder than the expected colours J-H=0J0 and H-K = 0.27 for stars of intermediate age with masses of 0.08 M⊙. Based on the colours and spectra of a probable companion star and by comparison with evolutionary models, we infer that the new brown dwarf candidate is of intermediate age with a mass of 0.071-0.079 M⊙, a temperature of 1825 ± 300 K and a bolometric magnitude of 14.56 ± 0.35. Classification as a star or a brown dwarf depends on the adopted age and the evolutionary model used. The discovery of this object within an infrared field survey places the first lower limit on the space density for objects fainter than Mbol = 14, and suggests that the luminosity function does not fall dramatically into the brown dwarf regime.


Model atmosphere and kinematical analyses of early-type, high Galactic latitude stellar candidates from the UKST UBVRI survey

Astrophysical Journal 417 (1993) 706-712

NC Hambly, ES Conlon, PL Dufton, FP Keenan, JE Little, L Miller

From the UKST UBVRI survey, six high Galactic latitude stars have been previously identified which may be young hydrogen-burning objects. Using high-dispersion optical spectra, model atmosphere analyses are presented for these targets. Two have normal or nearly normal Population I chemical compositions, one appears to be subluminous while the remaining three are possibly normal late B-type stars. A kinematic analysis indicates that one star having normal parameters is an excellent candidate for formation in the halo, having an evolutionary age an order of magnitude less than the time required for it to attain its current position following ejection from the Galactic disk. A preliminary analysis implies that there may currently be a few thousand normal B-type stars in the Galactic halo with z-distances from the plane of the Galaxy in the range 3 < z < 22 kpc.


The high surface density of bright ultraviolet-excess quasars

Monthly Notices of the Royal Astronomical Society 256 (1992) 65P-68P

P Goldschmidt, L Miller, F La Franca, S Cristiani

© Royal Astronomical Society. We have measured the surface density of bright {B ≤ 16.5) UVX quasars in the recently completed Edinburgh quasar survey, and have found a higher density, by a factor of 3.4, than has previously been measured. The surface density of quasars brighter than B = 16.50 is 0.024 deg-2 in this survey, and the gradient of the differential log (number)-magnitude relation for quasars brighter than B = 17.7 has decreased from 0.98 to 0.78. Future work is expected to show that new models of the optical luminosity function for luminous quasars will need a smaller amount of cosmological evolution, more comparable to that seen at radio wavelengths.


The Edinburgh infrared survey

Advances in Space Research 11 (1991) 337-340

K Glazebrook, JA Peacock, L Miller, CA Collins

We have completed a large-area infrared survey to K = 17.5 covering 0.2□° of sky using the infrared camera (IRCAM) on the U.K. Infrared telescope. The aim of this is to study galaxy evolution at moderate redshifts (z < 0.5) and too look for any new populations that may appear in the infrared. For example, dust free protogalaxies at high redshift would have the Lyman break shifted into the optical producing objects with very red R - K colours and such objects are ideal for an infrared survey. © 1991.


Optical observations of supernova 1993 J from la Palma-I. Days 2 to 125

Monthly Notices of the Royal Astronomical Society 266 (1991) L27-L39

JR Lewis, NA Walton, WPS Meikle, R Martin, J Robert Cumming, RM Catchpole, M Arevalo, RW Argyle, CR Benn, PS Bunclark, HO Castaneda, M Centurion, RES Clegg, A Delgado, VS Dhillon, P Goudfrooij, EH Harlaftis, BJM Hassall, L Helmer, PW Hill, DHP Jones, DL King, C Lazaro, JR Lucey, EL Martin, L Miller, LV Morrison, AJ Penny, E Perez, M Read, PJ Rudd, RGM Rutten, RM Sharpies, SW Unger, J Vilchez

© 2019 Royal Astronomical Society. We present astrometric, photometric and spectroscopic observations of supernova 1993J in M81, obtained with the Isaac Newton Group telescopes and the Carlsberg Automatic Meridian Circle. The spectral data set includes the first spectrum ever taken of SN1993J. The early spectra also yield an estimate of the total visual extinction, Av. This is combined with the photometric data to produce a bolometric light curve. Implications of the latter and of the spectral development are also discussed. The spectral evolution includes an infrared excess, which appeared after day 50 and may be indicative of an IR echo. The unchanging nature of blueshifted oxygen lines in the spectra argues for asymmetry in the distribution of the line-emitting region.


The bimodal radio luminosity function of quasars

Monthly Notices of the Royal Astronomical Society 244 (1990) 207-213

L Miller, JA Peacock, ARG Mead


Spectrophotometry of FRII radiogalaxies in an unbiased, low-redshift sample

Monthly Notices of the Royal Astronomical Society 238 (1989) 777-790

R Saunders, JE Baldwin, S Rawlings, PJ Warner, L Miller

© 1989 Royal Astronomical Society. As the first part of a programme aimed at understanding the links between radio and optical-line emission from radiogalaxies, we present spectrophotometry of eight FRII radiogalaxies from the complete, 3CR-based sample of Laing, Riley & Longair. With our data, narrow-line luminosities integrated over suitably large apertures are now available for 16 of the 17 FRIIs in this sample that have z <02 and 03h<RA<19h. The relations between line ratios and luminosities of objects in this unbiased, low-redshift sample support the usually assumed model of photoionization by an active galactic nucleus which predicts a scaling between narrow-line and photo-ionizing luminosities; the excitation levels of the narrow lines reflect a range of effective ionization parameter of 10-1 ≤ Ue ≤ 10-5. There is also evidence of a continuous correlation between narrow-line and extended radio luminosities. We argue that proof of the existence of such a correlation - and an understanding of its causes - cannot be obtained with existing data; spectrophotometry of an unbiased sample of FRII radiogalaxies extending to higher radio luminosities is required.


An X-ray survey of a complete sample of 3CR radio galaxies

The Astrophysical Journal IOP Publishing 277 (1984) 115-115

G Fabbiano, G Trinchieri, M Elvis, L Miller, M Longair


Clusters, brightest cluster galaxies and galaxy alignments

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N Chisari

This thesis develops two main topics related to the study of the large-scale structure of the Universe. The first one is the intrinsic alignment of galaxies. These are correlations between the shapes and orientations of galaxies that arise mainly as a consequence of tidal forces across a large range of scales. I use the tidal alignment model to predict how the intrinsic alignment of Luminous Red Galaxies could in the future provide constraints on the Baryon Acoustic Oscillation scale, a standard ruler for measuring the expansion of the Universe. I also show that primordial signatures of inflation can translate into a non-Gaussian bias in the correlation of the intrinsic shapes of galaxies, which could be observed with future surveys. The second main topic discussed in this thesis is clusters of galaxies. I use data from the Sloan Digital Sky Survey and a public catalog of galaxy clusters to estimate the alignment of galaxies around groups and clusters of galaxies. The novelty of this work is mainly in the method for estimating the alignment signal. In photometric surveys, the redshift uncertainty is large compared to the size of a cluster, making the distinction between galaxies in the cluster and in the background very challenging. In the method developed here, each galaxy is assigned a posterior probability distribution function of its redshift to separate the alignment component from the gravitational lensing of galaxies in the background. Among the galaxies that make up a cluster, Brightest Cluster Galaxies stand out by their luminosity. I study the connection between these galaxies and other ellipticals to understand the physics of their formation. Finally, I re-develop the Adaptive Matched Filter method for finding clusters in spectroscopic and photometric surveys to include a new treatment of the distances to galaxies. Again, I model the distance to each galaxy using a redshift posterior and propose other modifications to the algorithm that will be of use to upcoming photometric surveys.

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