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September 2012 - present
July 2009 - August 2012
Publications
Publications (62)
The origin of supermassive black holes (SMBHs) that inhabit the centers of massive galaxies is largely unconstrained. Remnants from supermassive stars (SMSs) with masses around 10,000 solar masses provide the ideal seed candidates, known as direct collapse black holes. However, their very existence and formation environment in the early Universe ar...
The origin of supermassive black holes (SMBHs) that inhabit the centers of massive galaxies is largely unconstrained. Remnants from supermassive stars (SMSs) with masses around 10,000 solar masses provide the ideal seed candidates, known as direct collapse black holes. However, their very existence and formation environment in the early Universe ar...
We produce synthetic spectra and observations for metal-free stellar populations and high mass X-ray binaries in the Renaissance Simulations at a redshift of 15. We extend our methodology from the first paper in the series by modelling the production and extinction of emission lines throughout a dusty and metal-enriched interstellar and circum-gala...
We produce synthetic spectra and observations for metal-free stellar populations and high mass X-ray binaries in the Renaissance Simulations at a redshift of 15. We extend our methodology from the first paper in the series by modelling the production and extinction of emission lines throughout a dusty and metal-enriched interstellar and circum-gala...
Previously we identified a new class of early galaxy that we estimate contributes up to 30% of the ionizing photons responsible for reionization. These are low mass halos in the range $M_{\rm halo} =10^{6.5}-10^{8} M_{\odot}$ that have been chemically enriched by supernova ejecta from prior Pop III star formation. Despite their low star formation r...
Previously we identified a new class of early galaxy that we estimate contributes up to 30\% of the ionizing photons responsible for reionization. These are low mass halos in the range $M_h =10^{6.5}-10^{8} M_{\odot}$ that have been chemically enriched by supernova ejecta from prior Pop III star formation. Despite their low star formation rates, th...
(submitted to MNRAS January 10, 2017) We present synthetic observations for the first generations of galaxies in the Universe and make predictions for future deep field observations for redshifts greater than 6. Due to the strong impact of nebular emission lines and the relatively compact scale of HII regions, high resolution cosmological simulatio...
Due to their long mean free paths, X-rays are expected to have many significant impacts globally on the properties of the intergalactic medium (IGM) by their heating and ionizing processes on large scales. At high redshifts, X-rays from Population (Pop) III binaries might have important effects on cosmic reionization and the Lyman alpha forest. As...
Due to their long mean free paths, X-rays are expected to have many significant impacts globally on the properties of the intergalactic medium (IGM) by their heating and ionizing processes on large scales. At high redshifts, X-rays from Population (Pop) III binaries might have important effects on cosmic reionization and the Lyman alpha forest. As...
Cosmic reionization is thought to be primarily fueled by the first generations of galaxies. We examine their stellar and gaseous properties, focusing on the star formation rates and the escape of ionizing photons, as a function of halo mass, redshift, and environment using the full suite of the {\it Renaissance Simulations} with an eye to provide b...
Cosmic reionization is thought to be primarily fueled by the first generations of galaxies. We examine their stellar and gaseous properties, focusing on the star formation rates and the escape of ionizing photons, as a function of halo mass, redshift, and environment using the full suite of the {\it Renaissance Simulations} with an eye to provide b...
We present results on the formation of Pop III stars at redshift 7.6 from the Renaissance Simulations, a suite of extremely high-resolution and physics-rich radiation transport hydrodynamics cosmological adaptive-mesh refinement simulations of high redshift galaxy formation performed on the Blue Waters supercomputer. In a survey volume of about 220...
We present results on the formation of Pop III stars at redshift 7.6 from the Renaissance Simulations, a suite of extremely high-resolution and physics-rich radiation transport hydrodynamics cosmological adaptive-mesh refinement simulations of high redshift galaxy formation performed on the Blue Waters supercomputer. In a survey volume of about 220...
Additional physics beyond standard hydrodynamics is needed to fully model the
intracluster medium (ICM); however, as we move to more sophisticated models, it
is important to consider the role of magnetic fields and the way the fluid
approximation breaks down. This paper represents a first step towards
developing a self-consistent model of the ICM b...
In this paper, we present the first results from the Renaissance Simulations, a suite of extremely high-resolution and physics-rich AMR calculations of high-redshift galaxy formation performed on the Blue Waters supercomputer. These simulations contain hundreds of well-resolved galaxies at z ∼ 25-8, and make several novel, testable predictions. Mos...
In this paper, we present the first results from the Renaissance Simulations,
a suite of extremely high-resolution and physics-rich AMR calculations of high
redshift galaxy formation performed on the Blue Waters supercomputer. These
simulations contain hundreds of well-resolved galaxies at $z \sim 25-8$, and
make several novel, testable predictions...
Galaxy clusters are unique laboratories to investigate turbulent fluid
motions and large scale magnetic fields. Synchrotron radio halos at the center
of merging galaxy clusters provide the most spectacular and direct evidence of
the presence of relativistic particles and magnetic fields associated with the
intracluster medium. The study of polarize...
The first galaxies in the Universe are the building blocks of all observed
galaxies. We present scaling relations for galaxies forming at redshifts $z \ge
15$ when reionization is just beginning. We utilize the ``Rarepeak'
cosmological radiation hydrodynamics simulation that captures the complete star
formation history in over 3,300 galaxies, start...
Due to their long mean free path, X-rays are expected to have an important impact on cosmic reionization by heating and ionizing the intergalactic medium (IGM) on large scales, especially after simulations have suggested that Population III (Pop III) stars may form in pairs at redshifts as high as 20-30. We use the Pop III distribution and evolutio...
We present our prediction for the local 21 cm differential brightness temperature ($\delta T_{b}$) from a set of strongly clustered sources of Population III (Pop III) and II (Pop II) objects in the early Universe, by a numerical simulation of their formation and radiative feedback. These objects are located inside a highly biased environment, whic...
We present our prediction for the local 21 cm differential brightness
temperature ($\delta T_{b}$) from a set of strongly clustered sources of
Population III (Pop III) and II (Pop II) objects in the early Universe, by a
numerical simulation of their formation and radiative feedback. These objects
are located inside a highly biased environment, whic...
This paper describes the open-source code Enzo, which uses block-structured
adaptive mesh refinement to provide high spatial and temporal resolution for
modeling astrophysical fluid flows. The code is Cartesian, can be run in 1, 2,
and 3 dimensions, and supports a wide variety of physics including
hydrodynamics, ideal and non-ideal magnetohydrodyna...
Cosmological MHD simulations of galaxy cluster formation show a significant amplification of seed magnetic fields. We developed a novel method to decompose cluster magnetized turbulence into modes and showed that the fraction of the fast mode is fairly large, around one-fourth in terms of energy. This is larger than that was estimated before, which...
Recent simulations of Population III star formation have suggested that some fraction form in binary systems, in addition to having a characteristic mass of tens of solar masses. The deaths of metal-free stars result in the initial chemical enrichment of the universe and the production of the first stellar-mass black holes. Here we present a cosmol...
Synchrotron radio halos at the center of merging galaxy clusters provide the
most spectacular and direct evidence of the presence of relativistic particles
and magnetic fields associated with the intracluster medium. The study of
polarized emission from radio halos has been shown to be extremely important to
constrain the properties of intracluster...
Cosmological MHD simulations of galaxy cluster formation show a significant
amplification of seed magnetic fields. We developed a novel method to decompose
cluster magnetized turbulence into modes and showed that the fraction of the
fast mode is fairly large, around 1/4 in terms of energy. This is larger than
that was estimated before, which implie...
Non-thermal radio emission from cosmic ray electrons in the vicinity of
merging galaxy clusters is an important tracer of cluster merger
activity, and is the result of complex physical processes that involve
magnetic fields, particle acceleration, gas dynamics, and radiation. In
particular, radio relics are thought to be the result of
shock-acceler...
Non-thermal radio emission from cosmic ray electrons in the vicinity of
merging galaxy clusters is an important tracer of cluster merger activity, and
is the result of complex physical processes that involve magnetic fields,
particle acceleration, gas dynamics, and radiation. In particular, objects
known as radio relics are thought to be the result...
The existence of supermassive black holes as early as z ~ 7 is one of the great, unsolved problems in cosmological structure formation. One leading theory argues that they are born during catastrophic baryon collapse in z ~?15 protogalaxies that form in strong Lyman-Werner UV backgrounds. Atomic line cooling in such galaxies fragments baryons into...
Radio observations of galaxy clusters show that there are $\mu$G magnetic
fields permeating the intra-cluster medium (ICM), but it is hard to accurately
constrain the strength and structure of the magnetic fields without the help of
advanced computer simulations. We present qualitative comparisons of synthetic
VLA observations of simulated galaxy c...
We examine the effects of self-gravity and magnetic fields on supersonic
turbulence in isothermal molecular clouds with high resolution simulations and
adaptive mesh refinement. These simulations use large root grids (512^3) to
capture turbulence and four levels of refinement to capture high density, for
an effective resolution of 8,196^3. Three Ma...
Theory and simulations suggest that magnetic fields from radio jets and lobes powered by their central super massive black holes can be an important source of magnetic fields in the galaxy clusters. This is Paper II in a series of studies where we present self-consistent high-resolution adaptive mesh refinement cosmological magnetohydrodynamic simu...
Theory and simulations suggest that magnetic fields from radio jets and lobes
powered by their central super massive black holes can be an important source
of magnetic fields in the galaxy clusters. This is paper II in a series of
studies where we present self-consistent high-resolution adaptive mesh
refinement cosmological magnetohydrodynamic (MHD...
We employ simulations of supersonic super-Alfvenic turbulence decay as a
benchmark test problem to assess and compare the performance of nine
astrophysical MHD methods actively used to model star formation. The set of
nine codes includes: ENZO, FLASH, KT-MHD, LL-MHD, PLUTO, PPML, RAMSES, STAGGER,
and ZEUS. We present a comprehensive set of statisti...
In this work, we present the mass and magnetic distributions found in a recent adaptive mesh refinement magnetohydrodynamic simulation of supersonic, super-Alfvénic, self-gravitating turbulence. Power-law tails are found in both mass density and magnetic field probability density functions, with P(ρ) ρ–1.6 and P(B) B –2.7. A power-law relationship...
Radio observations suggested micro Gauss magnetic fields permeating the Intra Cluster Medium (ICM) in the galaxy clusters. Theory and simulations suggest that magnetic fields from Active Galactic Nucleus (AGNs) powered by their central super massive black holes can be an important source of these magnetic fields in the ICM. We present cosmological...
We present a series of cosmological magnetohydrodynamic simulations that simultaneously follow the formation of a galaxy cluster and evolution of magnetic fields ejected by an active galactic nucleus (AGN). Specifically, we investigate the influence of both the epoch of the AGN (z ~ 3-0.5) and the AGN energy (~3 × 1057- 2 × 1060 erg) on the final m...
We present a series of cosmological magnetohydrodynamic (MHD) simulations that simultaneously follow the formation of a galaxy cluster and evolution of magnetic fields ejected by an Active Galactic Nucleus (AGN). Specifically, we investigate the influence of both the epoch of AGN (z $\sim$ 3-0.5) and the AGN energy ($\sim$ 3 $\times$ 10$^{57}$ - 2...
In this work, we present the mass and magnetic distributions found in a recent Adaptive Mesh Refinement (AMR) MHD simulation of supersonic, \sa, self gravitating turbulence. Powerlaw tails are found in both volume density and magnetic field probability density functions, with $P(\rho) \propto \rho^{-1.67}$ and $P(B)\propto B^{-2.74}$. A power law i...
In this work, we present EnzoMHD, the extension of the cosmological code Enzo to include the effects of magnetic fields through the ideal magnetohydrodynamics approximation. We use a higher order Godunov method for the computation of interface fluxes. We use two constrained transport methods to compute the electric field from those interface fluxes...
We present self-consistent cosmological magnetohydrodynamic (MHD) simulations that simultaneously follow the formation of a galaxy cluster and the magnetic field ejection by an active galactic nucleus (AGN). We find that the magnetic fields ejected by the AGNs, though initially distributed in relatively small volumes, can be transported throughout...
It is believed that AGN feedback from the SMBH at the central elliptical galaxy in galaxy clusters is a major source to heat the Intra-Cluster Medium (ICM) to avoid the catastrophic collapse of the cluster core. The morphologies of the jet/lobes of the radio galaxies and the sizes of the large X-ray cavities indicate that the energy of magnetic fie...
We present self-consistent cosmological magnetohydrodynamic (MHD) simulations that simultaneously follow the formation of a galaxy cluster and the magnetic field ejection by an active galactic nuclei (AGN). We find that the magnetic fields ejected by the AGN, though initially distributed in relatively small volumes, can be transported throughout th...
In this work, we present MHDEnzo, the extension of the cosmological code Enzo to include the effects magnetic fields through the ideal MHD approximation. We use a higher order Godunov Riemann solver for the computation of interface fluxes. We use two constrained transport methods to compute the electric field from those interface fluxes, which simu...
Observations have revealed that the intra-cluster medium (ICM) of galaxy clusters could be significantly magnetized. Observations further revealed that magnetic fields in the ICM appear to have a power-law spectrum. It is often suggested that such magentic fields could be generated via a turbulent dynamo. Here, we study a different scenario where s...
The origin of magnetic fields in galaxy clusters is one of the most fascinating but challenging problems in astrophysics. In this dissertation, the possibility of an Active Galactic Nucleus (AGN) origin of cluster magnetic fields is studied through state of the art simulations of magnetic field evolution in large scale structure formation using a n...
Recent observations have revealed that the intra-cluster medium (ICM) of galaxy clusters could be significantly magnetized. Observations further revealed that magnetic fields in the ICM have large amount of fluxes, yet appearing to have a power-law spectrum. It is often suggested that such magentic fields could be generated via a turbulent dynamo....
We report the results of the first self-consistent three-dimensional adaptive mesh refinement magnetohydrodynamical simulations of Population III star formation including the Biermann battery effect. We find that the Population III stellar cores formed including this effect are both qualitatively and quantitatively similar to those from hydrodynami...
We present cosmological magnetohydrodynamic simulations of the formation of a galaxy cluster with magnetic energy feedback from an active galactic nuclei (AGN). We demonstrate that X-ray cavities can be produced by the magnetically dominated jet-lobe system that is supported by a central axial current. The cavities are magnetically dominated and th...
Magnetic fields play an important role in almost all astrophysical phenomena, including star formation. Due to the difficulty of analytic modeling and observations, magnetic fields are still poorly studied, and numerical simulation has become a major tool. We have implemented a cosmological magnetohydrodynamics package for Enzo, an AMR
hydrodynami...
We present the formulation of magnetically dominated relativistic MHD flows as a model for extra-galactic jets produced by accretion onto supermassive black holes. Three-dimensional relativistic MHD simulations will be presented on how the energy outflow partitions among different physical components and on how the collimation occurs. We will also...
An important global property of a bit string is the number of ones in it. It has been found that the parity (odd or even) of this number can be found by a sequence of deterministic, translational invariant cellular automata with parallel update in succession for a total of O(N^2) time. In this paper, we discover a way to check if this number is div...
Cellular Automaton (CA) is a simple local interaction model for studying the evolution and self-organization of various physical and biological systems. We find that if a system evolves according to some special sets of CA rules, its state will become highly uniform, with non-trivial patterns that keep the requested original property, such as parit...
The parity of a bit string of length N is a global quantity that can be efficiently computed using a global counter in O(N) time. But is it possible to find the parity using cellular automata with a set of local rule tables without using any global counter? Here, we report a way to solve this problem using a number of r=1 binary, uniform, parallel,...
Given a continuous function $f(x)$, suppose that the sign of $f$ only has finitely many discontinuous points in the interval $[0,1]$. We show how to use a sequence of one dimensional deterministic binary cellular automata to determine the sign of $f(\rho)$ where $\rho$ is the (number) density of 1s in an arbitrarily given bit string of finite lengt...
Tolls are collected on many highways as a means of traffic control and revenue generation. However, the presence of tollbooths on highway surely slows down traffic flow. Here, we investigate how the presence of tollbooths affect the average car speed using a simple-minded single lane deterministic discrete traffic model. More importantly, the model...
X-ray and radio observations of galaxy clusters have revealed a wealth of structure in the intra-cluster medium (ICM) associated with extragalactic radio sources. Structures in the form of large scale cavities and weak shocks provide a reliable gauge of the mechanical output of extragalactic radio jets launched by AGNs. By analyzing the properties...
We will report our research on magnetic fields and MHD turbulence in galaxy clusters using Cosmological Adaptive Mesh Refinement(AMR) MHD simulations of cluster formation with seed magnetic fields from Active Galactic Nuclei(AGNs). In our simulations, magnetic fields with energy between ˜ 10^58 to 10^60 erg are put into the center of forming cluste...
