The remnants of galaxy formation from a panoramic survey of the region around M31 (2009)
McConnachie, Alan W., Irwin, Michael J., Ibata, Rodrigo A., Dubinski, John, Widrow, Lawrence M., Martin, Nicolas F., ...
In hierarchical cosmological models, galaxies grow in mass through the continual accretion of smaller ones. The tidal disruption of these systems is expected to result in loosely bound stars...
Martin, Nicolas F., McConnachie, Alan W., Irwin, Mike, Widrow, Lawrence M., Ferguson, Annette M. N., Ibata, Rodrigo A., ...
We present the discovery of two new dwarf galaxies, Andromeda XXI and Andromeda XXII, located in the surroundings of the Andromeda and Triangulum galaxies (M31 and M33). These discoveries stem from...
Powell, Leila C., Kay, Scott T., Babul, Arif
In this paper, we undertake a study to determine what insight can be reliably gleaned from the comparison of the X-ray and the weak lensing mass maps of galaxy clusters. We do this by investigating...
Maximum spin of black holes driving jets (2009)
Benson, Andrew J., Babul, Arif
Unbound outflows in the form of highly collimated jets and broad winds appear to be a ubiquitous feature of accreting black hole systems. The most powerful jets are thought to derive a significant...
Maximum Spin of Black Holes Driving Jets (2009)
Benson, Andrew J., Babul, Arif
Unbounded outflows in the form of highly collimated jets and broad winds appear to be a ubiquitous feature of accreting black hole systems. The most powerful jets are thought to derive a significant...
Galaxy-Induced Transformation of Dark Matter Halos (2009)
Abadi, Mario G., Navarro, Julio F., Fardal, Mark, Babul, Arif, Steinmetz, Matthias
We use N-body/gasdynamical LambdaCDM cosmological simulations to examine the effect of the assembly of a central galaxy on the shape and mass profile of its dark halo. Two series of simulations are...
The X-ray Cluster Normalization of the Matter Power Spectrum (2008)
Henry, J. Patrick, Evrard, August E., Hoekstra, Henk, Babul, Arif, Mahdavi, Andishieh
The number density of galaxy clusters provides tight statistical constraints on the matter fluctuation power spectrum normalization, traditionally phrased in terms of sigma_8, the root mean square...
The Role of the Radial Orbit Instability in Dark Matter Halo Formation and Structure (2008)
Bellovary, Jillian M., Dalcanton, Julianne J., Babul, Arif, Quinn, Thomas R., Maas, Ryan W., Austin, Crystal G., ...
For a decade, N-body simulations have revealed a nearly universal dark matter density profile, which appears to be robust to changes in the overall density of the universe and the underlying power...
The impact of mergers on relaxed X-ray clusters - III. Effects on compact cool cores (2008)
Poole, Gregory B., Babul, Arif, McCarthy, Ian G., Sanderson, A. J. R., Fardal, Mark A.
(Abridged) We use the simulations presented in Poole et al. 2006 to examine the effects of mergers on compact cool cores in X-ray clusters. We propose a scheme for classifying the morphology of...
that engendered a revolution in physics, and laid the foundations (2008)
Throughout the year, the worldwide physics community organized events to mark the pioneering contributions of Einstein, by highlighting the vitality of physics, and bringing the excitement of...
Was the Andromeda Stream Produced by a Disk Galaxy? (2008)
Fardal, Mark A., Babul, Arif, Guhathakurta, Puragra, Gilbert, Karoline M., Dodge, Cara
The halo region of M31 exhibits a startling level of stellar inhomogeneities, the most prominent of which is the "giant southern stream". Our previous analysis indicates that this stream, as well as...
The impact of mergers on relaxed x-ray clusters III: effects on compact cool cores (2008)
Poole, Gregory B., Babul, Arif, McCarthy, Ian G., Sanderson, Adam J. R., Fardal, Mark A.
We use the simulations presented in Poole et al. to examine the effects of mergers on the properties of cool cores in X-ray clusters. Motivated by recent Chandra and XMM–Newton observations, we...
The impact of mergers on relaxed x-ray clusters III: effects on compact cool cores (2008)
Poole, Gregory B., Babul, Arif, McCarthy, Ian G., Sanderson, Adam J. R., Fardal, Mark A.
We use the simulations presented in Poole et al. to examine the effects of mergers on the properties of cool cores in X-ray clusters. Motivated by recent Chandra and XMM–Newton observations, we...
The nature of the ghost cavity in the NGC 741 group (2007)
Jetha, Nazirah N., Hardcastle, Martin J., Babul, Arif, O'Sullivan, Ewan, Ponman, Trevor J., Raychaudhury, Somak, ...
We discuss the effects of energy injection into the intra-group medium of the group of galaxies associated with NGC 741. The X-ray emission reveals a large bubble, which in the absence of a currently...
Pre-Heated Isentropic Gas in Groups of Galaxies (2007)
Mike Balogh, Arif Babul, David R. Patton
We confirm that the standard assumption of isothermal, shock--heated gas in cluster potentials is unable to reproduce the observed X-ray luminosity--temperature relation of groups of galaxies. As an...
Powell, Leila C., Kay, Scott T., Babul, Arif, Mahdavi, Andisheh
Various differences in galaxy cluster properties derived from X-ray and weak lensing observations have been highlighted in the literature. One such difference is the observation of mass...
Towards a Holistic View of the Heating and Cooling of the Intracluster Medium (2007)
McCarthy, Ian G., Babul, Arif, Bower, Richard G., Balogh, Michael L.
(Abridged) X-ray clusters are conventionally divided into two classes: "cool core" (CC) clusters and "non-cool core" (NCC) clusters. Yet relatively little attention has been given to the origins of...
The Sunyaev-Zeldovich Background (2007)
Holder, Gilbert, McCarthy, Ian G., Babul, Arif
The cosmic background due to the Sunyaev-Zeldovich (SZ) effect is expected to be the largest signal at mm and cm wavelengths at a resolution of a few arcminutes. We investigate some simple statistics...
Poole, Gregory B., Babul, Arif, McCarthy, Ian G., Fardal, Mark A., Bildfell, C. J., Quinn, Thomas, ...
We use the suite of simulations presented in Poole et al (2006) to examine global X-ray and Sunyaev-Zel'dovich (SZ) observables for systems of merging relaxed X-ray clusters. In all of the scaling...
Modelling Shock Heating in Cluster Mergers: I. Moving Beyond the Spherical Accretion Model (2007)
McCarthy, Ian G., Bower, Richard G., Balogh, Michael L., Voit, G. Mark, Pearce, Frazer R., Theuns, Tom, ...
(Abridged) The thermal history of the intracluster medium (ICM) is complex. Heat input from cluster mergers, AGN, and galaxy winds offsets and may even halt the cooling of the ICM. Consequently, the...
Poole, Gregory B., Babul, Arif, McCarthy, Ian G., Fardal, Mark A., Bildfell, C. J., Quinn, Thomas R., ...
We use the suite of simulations presented by Poole et al. to examine global X-ray and Sunyaev-Zel'dovich (SZ) observables for systems of merging relaxed X-ray clusters. The time evolution of our...
Poole, Gregory B., Babul, Arif, McCarthy, Ian G., Fardal, Mark A., Bildfell, C. J., Quinn, Thomas, ...
We use the suite of simulations presented by Poole et al. to examine global X-ray and Sunyaev-Zel'dovich (SZ) observables for systems of merging relaxed X-ray clusters. The time evolution of our...
Poole, Gregory B., Babul, Arif, McCarthy, Ian G., Fardal, Mark A., Bildfell, C. J., Quinn, Thomas, ...
We use the suite of simulations presented by Poole et al. to examine global X-ray and Sunyaev-Zel'dovich (SZ) observables for systems of merging relaxed X-ray clusters. The time evolution of our...
Modelling the jet power in elliptical galaxies: support for rapidly spinning black holes (2006)
Nemmen, Rodrigo S., Bower, Richard G., Babul, Arif, Storchi-Bergmann, Thaisa
Recently, Allen et al. measured a tight correlation between the Bondi accretion rates and jet powers of the nuclei of nearby X-ray luminous elliptical galaxies. We employ two models of jet powering...
Models for jet power in elliptical galaxies: A case for rapidly spinning black holes (2006)
Nemmen, Rodrigo S., Bower, Richard G., Babul, Arif, Storchi-Bergmann, Thaisa
The power of jets from black holes are expected to depend on both the spin of the black hole and the structure of the accretion disk in the region of the last stable orbit. We investigate these...
Velocity Distributions from Nonextensive Thermodynamics (2006)
Barnes, Eric I., Williams, Liliya L. R., Babul, Arif, Dalcanton, Julianne J.
There is no accepted mechanism that explains the equilibrium structures that form in collisionless cosmological N-body simulations. Recent work has identified nonextensive thermodynamics as an...
Density Profiles of Collisionless Equilibria. II. Anisotropic Spherical Systems (2006)
Barnes, Eric I., Williams, Liliya L. R., Babul, Arif, Dalcanton, Julianne J.
It has long been realized that dark matter halos formed in cosmological N-body simulations are characterized by density profiles rho(r) that, when suitably scaled, have similar shapes. Additionally,...
Poole, Gregory B., Fardal, Mark A., Babul, Arif, McCarthy, Ian G., Quinn, Thomas, Wadsley, James
We report on the analysis of a suite of SPH simulations (incorporating cooling and star formation) of mergers involving idealised X-ray clusters whose initial conditions resemble relaxed clusters...
On the formation of extended galactic disks by tidally disrupted dwarf galaxies (2006)
Penarrubia, Jorge, McConnachie, Alan, Babul, Arif
We explore the possibility that extended disks, such as that recently discovered in M31, are the result of a single dwarf (10^9--10^10 Msun) satellite merger. We carry out N-body simulations of dwarf...
Nusser, Adi, Silk, Joseph, Babul, Arif
(Abridged) Existing models invoking AGN activty to resolve the cooling flow conundrum in galaxy clusters focus exclusively on the role of the central galaxy. Such models require fine-tuning of highly...
Poole, Gregory B., Fardal, Mark A., Babul, Arif, McCarthy, Ian G., Quinn, Thomas R., Wadsley, James W.
We report on the analysis of a suite of smoothed particle hydrodynamics simulations (in-corporating cooling and star formation) of mergers involving idealized X-ray clusters whose initial conditions...
Poole, Gregory B., Fardal, Mark A., Babul, Arif, McCarthy, Ian G., Quinn, Thomas R., Wadsley, James W.
We report on the analysis of a suite of smoothed particle hydrodynamics simulations (in-corporating cooling and star formation) of mergers involving idealized X-ray clusters whose initial conditions...
Balogh, Michael L., Babul, Arif, Voit, G. Mark, McCarthy, Ian G., Jones, Laurence R., Lewis, Geraint F., ...
(Abridged) We revisit the scaling relationships between the dark matter mass and observed X-ray luminosity and temperature of galaxy clusters and groups in the local Universe. Specifically, we...
Density Profiles of Collisionless Equilibria. I. Spherical Isotropic Systems (2005)
Barnes, Eric I., Williams, Liliya L. R., Babul, Arif, Dalcanton, Julianne J.
We investigate the connection between collisionless equilibria and the phase-space relation between density $\rho$ and velocity dispersion $\sigma$ found in simulations of dark matter halo formation,...
Semi-analytical dark matter halos and the Jeans equation (2005)
Austin, Crystal G., Williams, Liliya L. R., Barnes, Eric I., Babul, Arif, Dalcanton, Julianne J.
Although N-body studies of dark matter halos show that the density profiles, rho(r), are not simple power-laws, the quantity rho/sigma^3, where sigma(r) is the velocity dispersion, is in fact a...
A Simple and Accurate Model for Intra-Cluster Gas (2005)
Ostriker, Jeremiah P., Bode, Paul, Babul, Arif
Starting with the well-known NFW dark matter halo distribution, we construct a simple polytropic model for the intracluster medium which is in good agreement with high resolution numerical...
The Effects of Radiative Cooling on the Entropy Distribution of Intracluster Gas (2005)
McCarthy, Ian G., Fardal, Mark A., Babul, Arif
High resolution X-ray observations indicate that the entropy profiles in the central regions of some massive cooling flow clusters are well approximated by powerlaws. McCarthy and coworkers recently...
The phase-space density distribution of dark matter halos (2004)
Williams, Liliya L. R., Austin, Crystal, Barnes, Eric, Babul, Arif, Dalcanton, Julianne
High resolution N-body simulations have all but converged on a common empirical form for the shape of the density profiles of halos, but the full understanding of the underlying physics of halo...
The Evolution of Substructure in Galaxy, Group and Cluster Haloes II: Global Properties (2004)
In a previous paper, we described a new method for including detailed information about substructure in semi-analytic models of dark matter halo formation based on merger trees. In this paper, we...
In a previous paper, we described a new method for including detailed information about substructure in semi-analytic models of halo formation based on merger trees. In this paper, we compare the...
Predicting Substructure in CDM Haloes (2004)
Observations of multiple-image gravitational lens systems suggest that the projected mass distributions of galaxy haloes may contain substantial inhomogeneities. The fraction of the halo mass in...
McCarthy, Ian G., Balogh, Michael L., Babul, Arif, Poole, Gregory B., Horner, Donald J.
(Abridged) Theoretical models that include only gravitationally-driven processes fail to match the observed mean X-ray properties of clusters. As a result, there has recently been increased interest...
McCarthy, Ian G., Balogh, Michael L., Babul, Arif, Poole, Gregory B., Horner, Donald J.
Nonradiative simulations that only include heating due to gravitational processes fail to match the observed mean X-ray properties of galaxy clusters. As a result, there has recently been increased...
McCarthy, Ian G., Balogh, Michael L., Babul, Arif, Poole, Gregory B., Horner, Donald J.
Nonradiative simulations that only include heating due to gravitational processes fail to match the observed mean X-ray properties of galaxy clusters. As a result, there has recently been increased...
Small-scale Substructure in Dark Matter Haloes: Where Does Galaxy Formation Come to an End? (2003)
Taylor, James E., Silk, Joseph, Babul, Arif
Models of structure formation based on cold dark matter predict that most of the small dark matter haloes that first formed at high redshift would have merged into larger systems by the present...
The Satellite-substructure Connection (2003)
Taylor, James E., Babul, Arif, Silk, Joseph
We describe our recent attempts to model substructure in dark matter halos down to very small masses, using a semi-analytic model of halo formation. The results suggest that numerical simulations of...
Investigating the Origins of Dark Matter Halo Density Profiles (2003)
Williams, Liliya L. R., Babul, Arif, Dalcanton, Julianne J.
Although high-resolution N-body simulations make robust empirical predictions for the density distribution within cold dark matter halos, these studies have yielded little physical insight into the...
On the Intracluster Medium in Cooling Flow & Non-Cooling Flow Clusters (2003)
Babul, Arif, McCarthy, Ian G., Poole, Greg B.
Recent X-ray observations have highlighted clusters that lack entropy cores. At first glance, these results appear to invalidate the preheated ICM models. We show that a self-consistent preheating...
The SZ Effect Signature of Excess Entropy in Distant, Massive Clusters (2003)
McCarthy, Ian G., Holder, Gilbert P., Babul, Arif, Balogh, Michael L.
Studies of cluster X-ray scaling relations have led to suggestions that non-gravitational processes, e.g., radiative cooling and/or "preheating", have significantly modified the entropy of the...
On the Relationship between Cooling Flows and Bubbles (2003)
McCarthy, Ian G., Babul, Arif, Katz, Neal, Balogh, Michael L.
A common feature of the X-ray bubbles observed in Chandra images of some "cooling flow" clusters is that they appear to be surrounded by bright, cool shells. Temperature maps of a few nearby luminous...
Cluster Sunyaev-Zeldovich Effect Scaling Relations (2003)
McCarthy, Ian G., Babul, Arif, Holder, Gilbert P., Balogh, Michael L.
X-ray observations of an "entropy floor" in nearby groups and clusters of galaxies offer evidence that important non-gravitational processes, such as radiative cooling and/or "preheating", have...
The Evolution of Substructure in Galaxy, Group and Cluster Haloes I: Basic Dynamics (2003)
The hierarchical mergers that form the haloes of dark matter surrounding galaxies, groups and clusters are not entirely efficient, leaving substantial amounts of dense substructure, in the form of...
Modelling the Formation of Individual Galaxies: A Morphology Problem for CDM? (2002)
We use a semi-analytic model of halo formation to study the dynamical history of giant field galaxies like the Milky Way. We find that in a concordance LCDM cosmology, most isolated disk galaxies...
New Tests of the Cluster Entropy Floor Hypothesis (2002)
McCarthy, Ian G., Babul, Arif, Balogh, Michael L., Holder, Gilbert P.
Recent efforts to account for the observed X-ray luminosity - temperature relation of galaxy clusters has led to suggestions that the ICM has an apparent ``entropy floor'' at or above the level of...
The Cluster Gas Mass - Temperature Relation: Evidence for a High Level of Preheating (2002)
McCarthy, Ian G., Babul, Arif, Balogh, Michael L.
Recent X-ray observations have been used to demonstrate that the cluster gas mass-temperature relation is steeper than theoretical self-similar predictions drawn from numerical simulations that...
A Semi-analytic Model of Halo Dynamics (2002)
We have developed a new semi-analytic model for the formation and evolution of structure on galaxy, group and cluster scales. The model combines merger trees with a detailed, spatially resolved...
Physical implications of the x-ray properties of galaxy groups and clusters (2002)
Babul, Arif, Balogh, Michael L., Lewis, Geraint F., Poole, Gregory B.
Within the standard framework of structure formation, where clusters and groups of galaxies are built up from the merging of smaller systems, the physical properties of the intracluster medium, such...
Physical implications of the x-ray properties of galaxy groups and clusters (2002)
Babul, Arif, Balogh, Michael L., Lewis, Geraint F., Poole, Gregory B.
Within the standard framework of structure formation, where clusters and groups of galaxies are built up from the merging of smaller systems, the physical properties of the intracluster medium, such...
Physical Implications of the X-ray Properties of Galaxy Groups and Clusters (2001)
Babul, Arif, Balogh, Michael L., Lewis, Geraint F., Poole, Gregory B.
Within the standard framework of structure formation, where clusters and groups of galaxies are built up from the merging of smaller systems, the physical properties of the intracluster medium, such...
We have developed a simple yet surprisingly accurate analytic scheme for tracking the dynamical evolution of substructure within larger dark halos. The scheme incorporates the effects of dynamical...
Pre-Heated Isentropic Gas in Groups of Galaxies (1998)
Balogh, Mike L., Babul, Arif, Patton, David R.
We confirm that the standard assumption of isothermal, shock-heated gas in cluster potentials is unable to reproduce the observed X-ray luminosity- temperature relation of groups of galaxies. As an...
The Hubble Deep Field and the Disappearing Dwarf Galaxies (1998)
Ferguson, Henry C., Babul, Arif
Several independent lines of reasoning suggest that many of the very faint (B > 24) blue galaxies are low-mass objects that experienced a short epoch of star formation at redshifts 0.5 < z < 1 and...
Theory and Statistics of Weak Lensing from Large-Scale Mass Inhomogeneities (1997)
Kamionkowski, Marc, Babul, Arif, Cress, Catherine M., Refregier, Alexandre
Weak lensing by large-scale mass inhomogeneities in the Universe induces correlations in the observed ellipticities of distant sources. We first review the harmonic analysis and statistics required...
The Delayed Formation of Dwarf Galaxies (1997)
Kepner, Jeremy, Babul, Arif, Spergel, David
One of the largest uncertainties in understanding the effect of a background UV field on galaxy formation is the intensity and evolution of the radiation field with redshift. This work attempts to...
Statistics of Gravitational Microlensing Magnification. I. Two-Dimensional Lens Distribution (1996)
Kofman, Lev, Kaiser, Nick, Lee, Man Hoi, Babul, Arif
(Abridged) In this paper we refine the theory of microlensing for a planar distribution of point masses. We derive the macroimage magnification distribution P(A) at high magnification (A-1 >> tau^2)...
Lee, Man Hoi, Babul, Arif, Kofman, Lev, Kaiser, Nick
In Paper I we studied the theory of gravitational microlensing for a planar distribution of point masses. In this second paper, we extend the analysis to a three-dimensional lens distribution. First...
Faint Blue Galaxies and the Epoch of Dwarf-Galaxy Formation (1995)
Babul, Arif, Ferguson, Henry C.
Both theoretical and observational lines of reasoning suggest that the very faint (B > 24) galaxies seen in deep images of the sky are small low-mass galaxies that experienced starburst at 0.5
Miralda-Escude, Jordi, Babul, Arif
Long arcs in clusters of galaxies, produced by gravitational lensing, can be used to estimate the mass interior to the arcs and therefore, constrain the cluster mass distribution. The radial density...
Shear Fields and the Evolution of Galactic-Scale Density Peaks (1994)
Van De Weygaert, Rien, Babul, Arif
We present preliminary results of our investigation into the influence of shear fields on the evolution of galactic scale fluctuations in a primordial Gaussian random density field. Specifically, we...
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Thesis (Ph. D.)--Princeton University, 1989.