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Extragalactic
Astrophysics &
Observational Cosmology Group
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| Oliver
Hahn |
Contact
Information:
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ETH
Hönggerberg Campus
Institut für Astronomie, HIT J12.3
CH-8093 Zürich
Switzerland |
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Curriculum
Vitae
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| Education |
| 2005- |
PhD
student at the Institute of Astronomy, ETH Zurich |
2005
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Diploma
degree in
Physics,
Eberhard-Karls-Universität
Tübingen, Germany.
Thesis:
"Über den Kollaps selbstgravitierender Systeme in
sphärischer Symmetrie" ("On the collapse of self-gravitating
systems in spherical symmetry") [PDF]
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| Awards |
| 2008 |
ETH Extragalactic
Astrophysics Excellence Award
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2001-2
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DAAD fellow, University of Toronto,
Canada. |
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| Employment |
2005 -
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Doktorand,
Institute of Astronomy, ETH Zurich
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2003-4
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Eberhard-Karls-Universität
Tübingen, Germany
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Research
Interests
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| Overview |
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I am currently doing my PhD with Marcella Carollo.
My main research interests include
- Large-Scale Structure
- Galaxy Formation in a Cosmological
Context
- Cosmological (Hydrodynamical)
Simulations of
Structure Formation
- Weak Lensing
- Nature of dark
matter and dark
energy
You
find some more
details about topics I am currently working on and things I have been
doing in the following brief summary.
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| Dark
Matter Haloes and Large-Scale Structure |
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In
collaboration with C.
Porciani
(formerly at ETH,
now at Uni Bonn),
in the first part of my PhD, I used numerical simulations to
investigate several key aspects of cosmic structure formation in a Lambda-CDM
universe.
I have run and analysed high-resolution dark matter simulations
performed with GADGET2 to investigate the build up of angular momentum
in proto-galaxies, and the alignment of haloes with the large
scale-structure as a function of their formation process over
cosmic
time. We ran all of our simulations on the Gonzales
Beowulf cluster of the ETH Physics Department.
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Haloes in
clusters (red) and filaments (blue) as detected by
our dynamical classification algorithm. Haloes in sheets and voids are
not shown in this picture.(astro-ph/0610280)
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Inspired
by
the Zel'dovich approximation, we developed a novel
classification scheme for dark-matter haloes based on a local stability
criterion for the orbits of test particles. A series expansion of the
equation of 'motion' for a test particle in the frozen matter
distribution gives a zero order acceleration term and a first order
deformation term that is determined by the tidal field of the potential
(i.e. the Hessian of the potential). We then classify the
contraction/expansion behaviour of this first order term by the number
of its negative/positive eigenvalues. Given the three eigenvalues, this
criterion gives rise to four categories: cluster, filament, sheet and
void environments (astro-ph/0610280).
In addition,
this method naturally provides for local measures of the geometry of
large cosmic structures. The direction of a filament, e.g., is readily
recovered from the eigenvectors of the filtered tidal field tensor. It
is thus straight-forward to analyse alignments of halo spins and shapes
with the surrounding large-scale structure. We find that such
alignments are present with high significance (arXiv:0704.2595).
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Eigenvectors of the filtered Tidal
Field that point in the
direction of the large-scale fiilaments. They can be used to probe
alignments of spins and shapes of haloes with the large-scale structure (arXiv:0704.2595).
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Hydrodynamical
Simulations of Galaxy Formation in Cosmic Context
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In
collaboration with R. Teyssier
and U.
Seljak, we are now running cosmological hydrodynamical
simulations at the Swiss National Center for Supercomputing, CSCS, where we have been granted an
allocation of 540'000 CPUh over 6 months (PI: Carollo). We aim to
address a
fundamental open issue in cosmic
structure formation: What is the influence of cosmic large-scales
on the small scales on which galaxies form and evolve by mergers and
accretion? Answering this question is imperative both (i) to elucidate
the interplay between galaxy and cosmic structure formation processes
and (ii) to understand and remove systematic contaminations in weak gravitational
lensing measurements (as e.g. proposed ESA cosmic vision project EUCLID).
A huge dynamic range is required to tackle this problem, cosmic
filaments stretch over scales of tens of Mpc while galactic disks are
not much larger than a few tens of kpc. We achive the necessary
resolution by making use of the adaptive
mesh refinement technique.
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Projected gas density maps at redshift
z=1.1 from a cosmological simulation run with the RAMSES adaptive mesh
refinement code at CSCS. Each mesh cell can be individually refined
based on a density criterion allowing for a huge dynamic range. The
simulation includes gas cooling, recipes for star formation, supernova
feedback and metal enrichment. The effective maximum resolution is 0.38
kpc/h (physical coordinates). The panels show progressive zooms into
the simulation volume. The simulation is used to study the formation
and evolution of galaxies in the context of the cosmic web. |
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Structure
Formation from Non-Gaussian Initial Conditions
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In
collaboration with C.
Porciani and
A.
Pillepich,
I have contributed my experience with high-resolution numerical
simulations to study the
influence of
primordial non-Gaussian fluctuations on cosmic structure
formation. Such primordial non-Gaussianity is predicted by several
models of cosmological
inflation. Finding the signature it leaves in the evolved Universe
will allow to check these inflation models against observations. (arXiv:0811.4176)
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| Environment
in COSMOS |
Another
project I have been working on during my PhD has been the determination
of the environmental
density of
galaxies in the COSMOS
field by employing directly the output of photometric redshift
estimators (see ZEBRA)
to reconstruct the cosmic density field. My
observational colleagues at ETH are using these densities to study
aspects of galaxy evolution as a function of environment. I will be a
co-author of several upcoming papers on this topic.
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Publications
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>Link
to all ADS published papers<
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Refereed
Publications
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O. Hahn, C.
Porciani, A. Dekel and C.M. Carollo
Tidal Effects and the Environment Dependence of Halo
Assembly
MNRAS in press
(2009),
arXiv:0803.4211
(preprint), or hi-res preprint here
(PDF, 2 MB).
J. M. Colberg, F.
Pearce, C. Foster, E. Platen, R. Brunino, M. Neyrinck, S. Basilakos, A.
Fairall,
H. A. Feldman, S. Gottloeber, O. Hahn, F. Hoyle, V. Mueller, L. Nelson,
M. Plionis, C. Porciani,
S. Shandarin, M. S. Vogeley, R. van de Weygaert
The
Aspen-Amsterdam Void Finder Comparison Project
MNRAS
387(2). pp. 933 (2008) (HTML)
arXiv:0803.0918
(preprint).
O. Hahn, C.M.
Carollo, C. Porciani and A. Dekel
The Evolution of
Dark Matter Halo Properties
in Clusters, Filaments, Sheets and Voids
MNRAS
381(1), pp.41 (2007) (HTML),
arXiv:0704.2595
(preprint), or hi-res preprint here
(PDF, 18 MB).
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| Submitted
Papers |
A. Pillepich, C.
Porciani, O. Hahn
Universal mass
function and scale-dependent bias from N-body
simulations with non-Gaussian initial conditions
MNRAS submitted
(2008),
arXiv:0811.4176
(preprint)
J. Lee, O. Hahn, C.
Porciani
The Anisotropic
Two-Point Correlation Functions of the Nonlinear
Traceless Tidal Field in the Principal-Axis Frame
ApJ submitted
(2009),
arXiv:0906.5163
(preprint)
J. Lee, O. Hahn, C.
Porciani
Lagrangian
Statistics of Dark Halos in a LCDM Cosmology
ApJ submitted
(2009),
arXiv:0906.5166
(preprint)
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| Conference
Proceeedings |
O. Hahn, C.
Porciani, C.M. Carollo and A. Dekel
Halo Formation
and Evolution in the Cosmic Web
43eme Rencontres de
Moriond, Cosmology, La Thuile, Italy, 2008,
get
preprint here (PDF, 150 kB).
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| Conferences, Workshops, Schools |
Seminar Talks
UC Berkeley, USA,
2008
KIPAC Stanford, USA, 2008
UC Santa Cruz, USA, 2008
CfA Harvard, USA, 2008
Frontiers in Computational
Astrophysics: The
Origin of Stars, Planets and Galaxies
Conference, Ascona, Switzerland,
2008, contributed poster
Intrinsic Alignments and Cosmic Shear
Workshop, UCL London, UK, 2008,
invited talk [slides]
43eme Rencontres de Moriond, Cosmology
Conference, La Thuile, Italy,
2008, contributed talk [slides]
Helmholtz Summerschool in Supercomputational
Cosmology
School, AIP Potsdam, Germany, 2006
Evolution of galaxies and their large-scale
environment
School, Bad Honnef, Germany, 2006
Galaxies and Structures through Cosmic Times
Conference, Venice, Italy, 2006,
contributed poster
Structure and Dynamics of Compact Objects
School, AEI Potsdam, Germany, 2004
Computational Fluid Dynamics
Workshop, HLRS Stuttgart,
Germany, 2004
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Student Supervision
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I have supervised the following student
projects:
P.Steger
(2008) -
the radial alignment of galaxies around simulated clusters in SPH
simulations.
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| My Collaborators |
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| Useful
Resources |
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| Links |
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last changes -
Jun 19, 2009
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About
us