ELBA 2002
"EARLY COSMIC STRUCTURES AND THE END OF THE DARK AGES"
Marciana Marina (Elba Island),
June 4-7, 2002
ABSTRACTS
Tom Abel
PSU
Direct numerical simulation have led to a detailed
understanding of the formation of the first stars in currently viable
models of structure formation. I will discuss some particular findings
related to the turbulence, angular momentum transport, and lack of
fragmentation in these simulated star forming regions.
Rennan Barkana
Tel Aviv University
We present physical processes which are essential for correctly
interpreting observations of reionization, and which are not accounted
for in current numerical simulations. We show that recent observations
do NOT necessarily imply that reionization has already been observed, or
that it occurred at a redshift just above six. One important ingredient
is the effect of gas minihalos which effectively screen ionizing
sources and delay the lifting of Gunn-Peterson absorption. To study such
screening, and other feedback processes, it is essential to understand
nonlinear halo bias in general, and we present a new theoretical method
for doing this.
Andrew Benson
California Institute of Technology
Reionization is an example of a "global feedback" - wherein the heating
of the IGM by the entire galaxy population can inhibit the formation of
galaxies at low redshift. I will present a model of this feedback
mechanism and discuss observational constraints on this and other
aspects of reionization.
Simone Bianchi
Istituto di Radioastronomia - CNR
As a result of radiation pressure from UV and optical starlight, dust
grains can escape the halo of a galaxy and be injected into the IGM.
Recent simulations predict high escape velocities, for which the
sputtering efficiency is high. Thus, dust could have a relevant role in
polluting the IGM with metals. I will present the first results of a
numerical code to study dust sputtering, with the aim of predicting both
the amount of metals and the their distribution in the IGM.
Volker Bromm
Harvard University
I review the recent theoretical progress in our understanding of
primordial star formation, and discuss the cosmological consequences
of an early generation of massive stars.
Marialuce Bruscoli
Dipartimento di Astronomia - Univ. di Firenze
I will briefly discuss some points related to the the build-up of
synthetic
spectra from cosmological simulations in which IGM metal enrichment from
galactic winds is followed in a self-consistent manner including
feedback processes (cfr. S. Marri talk).
The effect of the instrumental noise on
the spectra is considered.
The main aim is to derive an extended set of synthetic
data through which numerical simulations can be directly compared with
observed QSO absorption spectra of the Lya forest.
Benedetta Ciardi
Max Planck Inst. - Garching
In this talk I will present the latest results on IGM reionization,
based on a combination of high resolution numerical simulations
(accounting for the galaxy formation process) and the radiative transfer
code CRASH (to properly follow the propagation of ionizing photons into
the IGM). Problems and promises related to this kind of approach will be
reviewed.
Stephanie Courty
L.U.T.H. / Obs. Paris-Meudon
We are interested in galaxy formation problem and cosmological bias with
numerical simulations. We use an eulerian hydrodynamical code including
radiative cooling, star formation and thermal non-equipartition
processes between the species electrons, neutrals and ions (that means
we consider each species with its own temperature). We will show, in
hierarchical cold dark matter-type models, how these thermodynamic
processes modify the mass function of galaxy-like objects at very high
redshifts, compared to a classical simulation with equipartition
processes forced. Moreover the differences between the two simulations
modify the non-linearity and stochasticity coefficients of the
cosmological bias relation between the distribution of galaxies and the
distribution of matter.
Antoinette Cowie
Institute for Astronomy - University of Hawaii
.................
Lennox Cowie
Institute for Astronomy - University of Hawaii
.................
Paolo De Bernardis
Dipartimento di Fisica, Università di Roma La Sapienza
CMB anisotropy experiments have recently sub-horizon structures on the
last scattering surface at redshift 1000. We review the new techniques
used, the results and the consequences for cosmology. We also shortly
describe the forthcoming experiments with emphasis on the search for
polarization of the CMB.
Ger De Bruyn
Kapteyn Institute
We will describe the feasibility of using LOFAR, a new radio telescope
to be built on the principle of phased arrays, to image, at a few arcmin
resolution, HI signals from the epoch of reionization. The frequency
range where to search is now expected to lie in the range from 130 - 180
MHz, with signal levels of a few tens of mK. LOFAR, its deliverables and
the project timeline will be briefly described. The main technical
challenge is how to deal with the ionospheric phase distortions and how
to get to the extremely high dynamic range required. Among astronomical
challenges are the discrete and diffuse foreground contaminants. Their
properties, however, seem well behaved in the spectral domain and some
results will be shown which give confidence that they can be removed .
Topics under study are the optimization of the LOFAR design to the
expected power spectra of instrumental, foreground and cosmic noise
Mark Dickinson
Space Telescope Science Institute
description........
Simon Glover
American Museum of Natural History - NY
The first stars in the Universe are expected to form in small
protogalaxies, cooled by molecular hydrogen. Ultraviolet radiation
produced by these stars can destroy molecular hydrogen in newly forming
protogalaxies and delay further star formation until larger objects
collapse. However, if a sufficiently strong X-ray background is present,
this negative feedback effect can be reduced or overcome. In this talk, I
discuss the contributions to this background from the various sources of
X-rays associated with star formation, and present the results of recent
simulations examining their effectiveness at overcoming negative
feedback.
Nick Gnedin
University of Colorado
I will briefly discuss approaches to numerical modeling of reionization,
their advantages and problems, and show some examples of what can be
achieved today.
Francesco Haardt
Univ. Insubria - Como
I present improved synthesis models of the energy spectrum and its
evolution with redshift of the UV/X-ray cosmic radiation background with
the radiative transfer code CUBA, updating and extending our previous
results (Haardt & Madau 1996). Two main new components are included: (i)
the ionizing flux from Lyman-break galaxies at z>3; and (ii) the X-ray
radiation from a numerous population of dusty AGNs with strong intrinsic
absorption, as invoked in popular models for the X-ray background. We
also adopt up-to-date determinations of the quasar luminosity function
and spectra, cosmic star formation history, and distribution of
intervening absorbers. We discuss the ionization and thermal history of
the IGM and provide simple analytical fits to the predicted HeII Lya
line opacity, HI and HeII photoionization and photoheating rates, and
the Compton heating rate of electrons by hard X-ray background photons,
for use e.g. in cosmological hydrodynamics simulations of the Lya
forest.
Martin Haehnelt
Inst. of Astronomy, Cambridge - UK
description........
Alexander Heger
The University of Chicago
While at present the number of stars formed strongly decreases as a
function of their mass, recent theoretical investigations suggest that
the first generation of stars that formed on the primordial composition,
as produced by the Big Bang, might have been dominated by massive or
very massive stars of more than 100 solar masses. In contrast to stars
that form at present, the first generation of very massive stars may
reach the late evolutionary stages without major mass loss: After
central helium depletion, these stars encounter the electron-positron
pair creation instability which leads to explosive burning of oxygen
and, later, silicon. We find explosion with up to 100 times that of
typical core collapse supernovae and more than 50 solar masses of Ni56
are expelled which radioactively decays into iron. For more massive
stars photo-disintegration lead to collapse into a black hole instead of
disruption. These explosions might be visible with upcoming far infrared
space telescopes up to redshifts of 20 or more, where the first of these
stars are expected to have formed. We also present the nucleosynthesis
yields and signature form these stars.
Hiroyuki Hirashita
Osservatorio Astrofisico di Arcetri - Firenze
Stars are formed in molecular gas. In particular, dust plays an
important role in the formation of molecular hydrogen. How much dust is
produced in the first evolution of galaxies? To what extent the star
formation rate is enhanced by the dust production? To answer these
questions, we model the star formation history of galaxies formed in the
redshift range of 5.
A. Hujeirat
Max Planck Institut fuer Astronomie
The evolution of supermassive black holes of several billion
solar masses is one of the greatest mystery in modern cosmology.
Various scenarios relying on galaxy-mergers, super-Eddington accretion
and collapse of primordial massive stars have been proposed to solve
the rapid mass-growth of these objects.
In this talk I will critically discuss and address the difficulties
underlying these scenarios, and argue that very massive BHs in an
accelerating universe are likely to be of primordial origin that
survived the Hawking-radiation.
Ilian Iliev
Osservatorio Astrofisico di Arcetri
In the standard Cold Dark Matter (CDM) theory of structure formation,
virialized minihalos (with Tvir<104 K)
form in abundance at high
redshift (z>6), during the cosmic "dark ages". The hydrogen in these
minihalos, the first nonlinear baryonic structures to form in the
universe, is mostly neutral and sufficiently hot and dense to emit
strongly at the 21-cm line. I will present results for the emission from
individual minihalos and the radiation background contributed by their
combined effect. Minihalos create a "21-cm forest" of emission lines.
The angular fluctuations in this 21-cm background should be detectable
with the planned LOFAR and SKA radio arrays, thus providing a direct
probe of structure formation during the "dark ages. Such a detection
will serve to confirm the basic CDM paradigm while also constraining the
shape of the power-spectrum of primordial density fluctuations, the
onset and duration of the reionization epoch, and the conditions which
led to the first stars and quasars.
Toshihiro Kawaguchi
Department of Astronomy, Univ. of Kyoto - Japan
We examined the effects of electron scattering (opacity and
Comptonization) on the emergent spectrum from super-Eddington accretion
flows (the so called slim disks). Then, the model is applied to
Narrow-Line Seyfert 1 galaxys (NLS1s) to estimate their accretion rates.
We found that a NLS1, PG 1448+273, has an extremely large accretion rate
in the unit of Eddington luminosity (LEdd):
1000 LEdd / c2. This
implys that the object is really young: its age inferred from the
black-hole mass divided by the accretion rate is
about 106 years.
Chiaki Kobayashi
Max-Planck-Institute for Astrophysics, Garching
I simulate the chemodynamical evolution of a hundred elliptical galaxies
using the GRAPE-SPH code. By reproducing the detailed observations, I
discuss the origin of elliptical galaxies: Elliptical galaxies form
through the successive merging of galaxies with various masses, which
looks like a major merger on one extreme end, and a monolithic collapse
of slow-rotating gas cloud in the other extreme end. The global
properties of elliptical galaxies are mainly determined from the galaxy
masses, while the metallicity gradients are much affected by the merging
events. Therefore, the merging histories can in principle be inferred
from the observed metallicity gradients of the present-day galaxies. The
observed variation in the metallicity gradients cannot be explained by
either the monolithic collapse only or the major merger only. It is well
reproduced in the present model where both formation processes arise
based on the CDM scenario.
Sangeeta Malhotra
Space Telescope Science
The earliest stellar populations are expected to be much hotter than
their modern counterparts, both because of high temperatures in zero
metallicity stars and because zero-metallicity gas is expected to
produce high mass stars preferentially. These conditions, combined with
low dust content, make primitive galaxies ideal factories for Lyman
alpha photons. Our Large Area Lyman Alpha survey has found a population
of Lyman-alpha emitters at z=4.5 and 5.7 whose median equivalent width
(EW) exceeds the 240 Angstrom maximum expected under "normal" stellar
population models. To reproduce the high EWs seen in the sample, we need
to postulate a stellar initial mass function with an extreme slope of =
0.5 (instead of 2.35), zero-metallicity stars, or narrow-line active
galactic nuclei (AGNs). Chandra observations scheduled this spring will
provide a strong test of the AGN hypothesis, but we already know that
not all the high-EW sources can be AGNs without violating X-ray source
counts or requiring a very steep redshift evolution. It thus seems
probable that we are detecting a galaxy population whose Lyman alpha
emission is dominated by hot stellar populations exhibiting some of the
expected physics of Population III. Only 7-15% of galaxies need to show
Ly-alpha emission to explain the observed number counts. This raises the
possibility either that star formation in high-redshift galaxies is
episodic or that the Ly galaxies we are seeing are the youngest 7-15%
and that Ly is strongly quenched by dust at about 107 yr
of age.
Simone Marri
Osservatorio Astrofisico di Arcetri
I present a new implementation of the Smoothed Particle Hydrodynamics
technique (SPH) for astrophysical multiphase gas.
In addition, a
description of a novel numerical implementation of star formation and a
new scheme for feedback and metal enrichment is given, that allows to
simulate the effect of energy injection due to stellar activities and
the pollution of primordial gas in the Intergalactic Medium (IGM).
Antonella Maselli
Dipartimento di Astronomia - Univ. di Firenze
I will briefly describe the implementation of the code CRASH
(Cosmological
Radiative transfer scheeme for Hydrodynamic), and show some preliminary
results of its application to test cases.
Silvia Masi
Dipartimento di Fisica, Università di Roma La Sapienza
OLIMPO is a 2.6 meter on-axis millimeter-wave Cassegrain telescope,
mounted on an attitude controlled stratospheric balloon payload. The
system contains 4 arrays of bolometers in the wavelength bands centered
at 150, 220, 350, 600 GHz. The instrument is diffraction limited at 150
GHz (3.5 arcminutes FWHM). It is currently planned to have a test flight
from Trapani in 2004. Science targets are a survey of SZ clusters, the
measurement of CMB anisotropy power spectrum at high multipoles, and the
measurement of the FIR Background from early Galaxies.
Alessandro Melchiorri
University of Oxford - UK
description...............
Siang Peng Oh
Caltech
I discuss the impact of X-rays produced by QSOs and various star
formation processes at high redshift. Because of their high energies and
large mean free path, hard photons at high redshift introduce novel
features into standard reionization scenarious. I discuss the impact of
X-rays on the topology of reionization, reheating, and H2 production.
Kazu Omukai
National Astronomical Observatory, Japan
We investigate the formation of first stars by accretion.
The mass accretion rate (Mdot) onto the first stars is higher
(say,10-(2-3) Msun/yr)
than that in the Pop I case, owing to higher
temperature of the protostellar clouds. This high accretion rate causes
some peculiar evolutionary features of the first stars. For example, the
H burning is delayed until the protostar reaches several tens of Msun.
The final mass of formed star is determined when the accretion stops. We
found that this value depends on the value of Mdot. In this
contribution, I also mention effects of small amount of metals on star
formation.
Michael Rauch
Carnegie Observatories - USA
Observing the Impact of Galaxies on the Intergalactic Medium Stellar
winds and supernova explosions in young galaxies are thought to deposit
energy, momentum, and metals in the proto- and intergalactic medium
(IGM). We discuss observational searches for the signatures of these
processes in the IGM at redshift three and beyond. Among other things we
describe how observations of QSO absorption systems towards
gravitationally lensed QSOs and galaxies can be used to statistically
probe density fluctuations and turbulence in the IGM and in the metal
enriched gas surrounding high redshift galaxies. We show how these
measurements may allow us to constrain the rate with which energy is
injected into intergalactic space, and the timescales of stellar
feedback. Aside from these global constraints we ll briefly discuss new
evidence for the presence of individual galactic winds at high redshift.
James Rhoads
Space Telescope Science
James E. Rhoads & Sangeeta Malhotra Searches for low luminosity Lyman
alpha sources allow a robust test of the reionization redshift: A
neutral intergalactic medium acts as a scattering "fog" for Lyman alpha
photons, which will effectively hide Lyman alpha emitters. Thus, counts
of Lyman alpha emitters will show a sharp decrease at redshifts prior to
reionization. This test is independent of Gunn-Peterson trough searches
in quasar spectra. Moreover, the Lyman alpha line test is sensitive to
higher neutral fractions than the Gunn-Peterson test. By applying both
tests, we can therefore probe the evolution of the neutral fraction with
redshift. We will discuss the observational status of this test, which
has been applied to samples of 18 sources at z=5.7 (Rhoads & Malhotra
2001) and 1 source at z=6.56 (Hu et al 2002). We also consider possible
"loopholes" in this test. These involve removing opacity either through
local ionization or velocity structure in the intergalactic medium.
While such effects may allow the detection of a few Lyman alpha sources
before reionization, it remains likely that statistical samples of Lyman
alpha sources will show a significant decrement associated with
reionization. We close with a discussion of future observational
prospects.
Phillip Richter
Osservatorio Astrofisico di Arcetri
......................
Massimo Ricotti
University of Colorado - USA
I present recent theoretical results on the formation and the evolution
of the first galaxies. The theory of galaxy formation predicts that the
creation process is hierarchical: small objects form first, and large
galaxies form later from mergers of smaller subunits. The first galaxies
are believed to have formed 100 million years after the Big Bang, at
redshift z ~ 30. In these primordial galaxies, the first stars emitted
light into a previously dark universe. The radiation emitted at this
time influenced the subsequent evolution of the universe in a
still-unknown way. This process of self-regulation, in which the
radiation emitted by galaxies influenced the surrounding intergalactic
medium and the future formation of other galaxies, is termed "radiative
feedback from galaxy formation". We find that the first luminous objects
("small-halos") are characterized by a bursting star formation that is
self-regulated by a feedback process acting on cosmological scale. The
global star formation history is regulated by the fraction,
fesc, of
ionizing photons that escape from each source. The main feedback
processes that regulate "small-halo" objects formation are
H2 formation
in front of H~II regions and inside relic H~II regions. The H~II regions
remain confined, producing a cyclic destruction/reformation
of H2 in
the dense regions that are the birthplaces of galaxies.
If fesc <0.01,
positive feedback dominates, and "small-halo" objects constitute the
bulk of the mass in stars and metals until redshift z ~ 10.
In contrast to massive objects, which reionize voids first, "small-halos"
partially ionize only the dense filaments, while leaving the voids
neutral.
Emanuele Ripamonti
Pennsylvania State University
The collapse leading to the formation of the very first stars is thought
to be driven by the cooling due to molecular hydrogen emission. We have
investigated such emission during proto-stellar collapse by means of a
numerical code, obtaining the evolution of the H2 line and continuum
luminosities prior to the onset of nuclear reactions. We then combine
these informations with the Press-Schechter formalism and with hypotesis
on the number evolution of protostellar objects inside a star forming
mini-halo in order to get estimates about the detectability of high
redshift H2 emission.
Sean Ryan
The Open University - UK
Element abundances and the first stars Element abundances measured in
extremely metal-deficient stars in the Galactic halo provide a highly
detailed diagnostic of the chemical composition of the Galaxy around the
time of the first episodes of star formation in the Galaxy. They enable
us to trace the first period of Galactic chemical enrichment, and
provide constraints on nucleosynthesis and stellar evolution in
low-metallicity environments. In some cases, the elements in these stars
may exhibit the composition resulting from Pop III enrichment of the
pre-Galactic medium. In this talk, I will present recent evidence for
the role of low- and zero-metallicity progenitors.
Ruben Salvaterra
SISSA - Trieste
I will discuss the contribution of the first population of luminous
objects (Pop III stars) to the NIR background using a model which
includes realistic IMFs and the up-to-date stellar spectra of
ZAMS metal-free stars. By comparing the results with all the
available
NIR observations and recent QSO absorption line results we are able
to
constrain the star formation efficiency and the impact on IGM metal
enrichment of PopIII stars.
Michael Santos
Theoretical Astrophysics, Caltech
authors: M. Santos, R.S. Ellis, J.P.Kneib, K. Kuijken.
The lowest mass scale for galaxy formation at high redshift is unknown,
but it is important because it sets the abundance and clustering
properties of the first proto-galaxies. Since these proto-galaxies may
reionize the universe and enrich it with metals, probing their
properties is important for studies of the IGM as well as for
understanding the role proto-galaxies play as building blocks for larger
structure. We are surveying the high-redshift universe, 4.4 < z < 6.8,
for Lyman-alpha emitting sources, using the LRIS spectrograph on Keck
and, when it becomes available, VIMOS on the VLT. Our survey targets
intrinsically faint systems, whose abundance depends on the lowest mass
halo that can form stars. To meet this goal, we take advantage of strong
lensing by low-redshift clusters of galaxies with well constrained mass
models. We typically achieve a magnification boost of greater than a
factor of 10 over our survey area. Lensing decreases the effective area
of our survey to less than 1 sq arcmin, but with a corresponding gain in
sensitivity. Thus we have unmatched ability to probe the faint end of
the Lyman-alpha luminosity function at redshifts around 5. By combining
our results with wider, shallower Lyman-alpha surveys, we constrain
models for star formation in low-mass halos just after the epoch of
reionization.
Evan Scannapieco
Osservatorio Astrofisico di Arcetri
A wide range of arguments suggest that the intergalactic medium (IGM)
experienced a high-redshift period of intense heating and metal
enrichment by outflows from starbursting dwarf galaxies. We use a
three-dimensional linear peaks model as well as hydrodynamic simulations
to study the evolution of such outflows and their feedback on galaxy
formation. We find that enrichment from these sources is likely to have
been incomplete, with only 30% the IGM volume reaching metallicities
above 10-3 solar, and early, with the majority of metals ejected at
redshifts above 5. Thus dwarf-outflow models naturally reproduce the
nearly constant (2 < z <5, Z approximately 3. 5 x 10-4 solar)
metallicity of the low column density Ly-alpha forest derived by
Songaila (2001), an effect of the decreasing efficiency of metal loss
from larger galaxies. We also show that IGM enrichment is intimately
tied to the properties of later-forming galaxies. Outflows strip baryons
from pre-viralized overdense regions with total masses less than
1010
solar, reducing the number density of galaxies in this mass range and
the overall star formation rate, and helping to reconcile these
quantities with observations. The metallicity of the surviving <
1010
solar mass galaxies increases with size, but with a large scatter,
reproducing the metallicity-luminosity relation of dwarf galaxies.
Finally, galaxies greater than
1010
solar masses form with a roughly
constant initial metallicity of 10% solar, explaining the observed lack
of metal-poor disk stars in these objects.
Raffaella Schneider
Osservatorio Astrofisico di Arcetri
Recent studies suggest that the first stars
were likely to be very massive, with typical masses of order 100 solar
masses. This finding is supported by several observational evidences,
from surveys of metal-poor stars to abundance ratios in the intracluster
medium. We propose a scenario to explain the transition from a top-heavy
initial mass function (IMF) to a normal IMF such as the one observed in
the present universe. We discuss several hitherto unexplored
implications of a high-mass dominated star formation mode in the early
Universe. In particular, the amount of black holes remnants of the first
stars and the high-energy neutrinos released in the course of their
evolution are compared with present and forthcoming observations. The
anticipated sensitivities of different experiments might be able to shed
some light on the dark ages of the universe.
Paul Shapiro
Dept of Astronomy, University of Texas
Energy released by a small fraction of the baryons in the universe,
which condensed out while the IGM was cold, dark, and neutral, reheated
and reionized it by redshift 6, exposing other baryons already condensed
into dwarf-galaxy minihalos to the glare of ionizing radiation. We will
describe the first gas dynamical simulations of the photoevaporation of
cosmological minihalos overtaken by the ionization fronts which swept
through the IGM during the reionization epoch in the currently-favored
LambdaCDM universe.
These simulations demonstrate the phenomena of
I-front trapping, the transition from R-type to D-type I-front with
shock wave, supersonic evaporative wind, and their observable
consequences. Such hitherto neglected feedback effects were widespread
during the reionization epoch. N-body simulations and analytical
estimates of halo formation in the LambdaCDM model show that these
sub-kpc minihalos with virial temperatures below
104 K, which would
have been photoevaporated by the I-fronts which reionized the universe,
were so common during reionization as to dominate the absorption of
ionizing photons. This means that previous estimates of the number of
ionizing photons per H atom required to complete reionization which
neglected this effect are too low.
Slawomir Stachniewicz
Henry Niewodniczanskiz
Inst of Nuclear Physics in Krakow - Poland
We trace evolution of a low-mass spherically symmetric
density perturbations
in the Ω Λ
=0.65, Ω M =0.35, h=0.72 Universe
up to the redshift z=8. The calculations are performed
for various cloud masses and initial overdensities. We compare our
calculations with results that assume flat, Dark Matter dominated
Universe.
Matthias Steinmetz
Astrophysikalisches Institut Potsdam
I present results from a series of N-body/gasdynamical simulations
designed to study the origin of galaxy morphologies in a cold dark
matter-dominated universe. The simulations include star formation
and feedback and have numerical resolution sufficiently high to allow
for a direct investigation of the morphology and kinematics of simulated
galaxies. In agreement with the results of previous theoretical work,
the presence of the main morphological components of galaxies - disks,
spheroids, bars - is regulated by the mode of gas accretion and
intimately linked to discrete accretion events. Disks arise from the
smooth deposition of cooled gas at the center of dark halos, spheroids
result from the stirring of preexisting disks during mergers, and bars
are triggered by tides generated by satellites.
This demonstrates that
morphology is a transient phenomenon within the lifetime of a galaxy and
that the Hubble sequence reflects the varied accretion histories of
galaxies in hierarchical formation scenarios.
In particular, it
demonstrates
directly that disk/bulge systems can be built and rebuilt by the
smooth accretion of gas onto the remnant of a major merger and that
the present-day remnants of late dissipative mergers between disks are
spheroidal stellar systems with structure resembling that of field
ellipticals. The perplexing variety of galaxy morphologies is thus
highly suggestive of - and may actually even demand - a universe where
structures have evolved hierarchically.
Daniel Stern
JPL - Caltech
I would like to present an oral contribution on
spectroscopically-confirmed galaxies at z>5. we have confirmed ~10
galaxies at z>5, selected using 4 techniques: (1) photometric selection
from deep, optical imaging, (2) narrow-band selection, (3) serendipitous
detection in deep spectroscopy, and (4) radio selection. These represent
most of the confirmed z>5 galaxies known currently. i will emphasize how
the samples compare and are related to one another. In particular, the
narrow-band selection (done as part of the Large-Area Lyman-Alpha, or
LALA, survey) finds a similar surface density of high-z galaxies as the
Lyman-break and Lyman-dropout techniques. Since only ~50% of the
Lyman-break galaxies show Lyman-alpha in emission, it implies the strong
Lyman-alpha emitters are an important, different population.
Tom Theuns
Institute of Astronomy - Cambridge, UK
I will discuss evidence for Helium II reionisation around redshift 3.3
from the thermal evolution of the IGM, and the evolution of the mean
absorption in the Lyman-alpha forest. I will discuss metal enrichment of
the IGM.
Eline Tolstoy
Kapteyn Institute - Groningen - NL
I will present some results of high resolution spectroscopy of
individual stars in a sample of nearby dwarf spheroidal galaxies.
These are the smallest galaxies we have ever detected - and thus
arguably the remanents of the formation of our Galaxy. These dSph
all contain ancient stellar populations, and their smallness and
perspective out of our Galaxy makes it relatively easy to age-date
the stars we observe. This allows us to accurately measure the
abundances of the stars formed the earliest times in these systems
(and thus perhaps in the Universe).
Masayuki Umemura
Center for Computational Physics, University of Tsukuba
The ultraviolet background radiation is thought to
significantly affect
the formation of protogalaxies through photoionization, photoheating,
and photodissociation of hydrogen molecules. We attempt to elucidate
quantitatively the effects of a ultraviolet background on the
protogalactic
collapse by solving radiative transfer for ionizing photons in the 1D as
well as
3D geometry, and some criteria are derived for the formation of
protogalactic objects in the ultraviolet background radiation.
Matteo Viel
IoA, Cambridge - UK
A variety of approximate schemes for modelling the low-density
Intergalactic Medium (IGM) in the high-redshift Universe is compared to
the results of a large high-resolution hydro-dynamical simulation. These
schemes use either an analytical description of the dark matter
distribution and the IGM or numerical simulations of the DM
distributions
combined with different approximate relations between dark matter field
and the
gas distribution.
Mario Vietri
Dipartimento di Fisica E.Amaldi, Università di Roma3
Gamma Ray Bursts are the birghtest sources of X rays in the Universe,
and dominate the counts at high flux elvels. This allows us the unique
opportunity of seeing the WIM in absorption against their continuum.
Also, they are remarkably constant in their total energy output, which
may lead to their use as standard candles out to very large redshifts.
Marta Volonteri
Università dell'Insubria - Milano
We present models for the evolution of SMBHs, from the seeds of BHs,
end-product of POPIII stars at redshift z~20, to nowadays observed
quiescent SMBHS. Along cosmic time, these pre-galactic BHs are
incorporated into larger and larger halos through mergers, sink to the
center of due to dynamical friction, accrete a fraction of the gas
gaining mass, form a binary system and eventually coalesce. The
evolution of SMBHs and AGNs should be therefore linked: the BH pair
timescale of coalescence is an important clue to the relation betweeen
QSOs activity and galaxy formation. We study the occurrence of SMBHs
binaries at different redshifts through Montecarlo realizations of halo
merging histories and semi-analytical techniques for the interactions
between the systems and their accretion histories.
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