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October 27-28 2009
Probes to the Early Universe
Cosmological Constraints from the SDSS maxBCG Cluster Catalog
Last modified:
10/13/09
I will discuss observational and instrumentation efforts to use Gamma-ray
Bursts (GRBs) as tracers of cosmic star formation and as probes to the high
redshift (z>6) Universe. At X- and Gamma-ray energies, the uniquely
piercing GRB itself sheds light on the rate and nature of GRB production
directly, provided the detection process is sufficiently well understood. I
will discuss modelling efforts using Swift and other satellite data to
constrain the GRB rate density and luminosity function. On the experimental
front, I am leading the effort to build a simultaneous 6-color imaging
camera called RATIR (http://ratir.org) -- the Reionization and Transients
InfraRed camera -- which will be mounted on an existing 1.5m telescope in
Baja, CA for 2 years starting in 2010. RATIR will point to GRB satellite
locations within minutes and identify z>6 GRBs for larger aperture followup
via the attenuation of the GRB light (in the r,i,Z,Y,J, and H bands) by the
IGM.
Brian Metzger
Princeton
Short-Duration Gamma-ray Burst Central Engines
One of the most important discoveries made with Swift is that long and
short-duration gamma-ray bursts (GRBs) originate from distinct stellar
progenitors. While long GRBs track ongoing star formation and result from
the deaths of massive stars, short GRBs have been localized to both early
and late-type galaxies, suggesting a more evolved progenitor population.
Although the origin of short GRBs remains a mystery, the most popular and
well-studied model is accretion following the merger of neutron star
binaries. This model is qualitatively consistent with both the
demographics of short GRBs and the lack of a bright associated supernova
in some cases. Despite these successes, this picture has grown complex
with the discovery that short GRBs are often followed by a "tail" of
emission (usually soft X-rays) lasting 100 seconds after the burst. Such
energetic, late-time emission from the central engine is difficult to
explain in standard merger pictures. One proposed explanation is
late-time "fall-back" onto the black hole of material that was ejected
during the merger into highly-eccentric, marginally-bound orbits. As this
matter decompresses from nuclear densities, however, it undergoes
rapid-neutron capture (r-process) nucleosynthesis, which can release
energy comparable to the orbital binding energy. This implies that the
r-process (normally thought unimportant dynamically in astrophysical
contexts) has important implications for the quantity and time-dependence
of fall-back and, ultimately, the source of flaring and identity of the
central engine.
Eran Ofek
Cal Tech
On the Nature of Long-Duration Radio Transients
Recently, a new class of 5-GHz radio transients with durations
of order hours to days, lacking any visible-light counterparts,
have been detected. I will present new observations and
searches for such transients, and discuss their nature.
Vasiliki Pavlidou
Cal Tech
Deciphering
the Gamma-ray Background: Starforming Galaxies, AGN and
the search for Dark Matter in the GeV Band
The recently launched Fermi Gamma-ray Space Telescope promises a
decade of excitement and discovery in the GeV Band. While Fermi
represents a dramatic improvement in instrumental capabilities for
point source observations in GeV gammas compared to its predecessors,
much of GeV science will still be encoded in the unresolved, diffuse
background, due to restrictions in point source sensitivity and
angular resolution inherent in GeV energies. I will discuss the two
guaranteed astrophysical contributions to the isotropic diffuse gamma-
ray background (starforming galaxies and gamma-ray--loud AGN), and our
efforts to use diffuse GeV observations to understand the high-energy
properties of these familiar populations. Finally, I will describe
some promising techniques for disentangling unresolved diffuse
emission from different source classes and circumventing the
difficulties presented by astrophysical backgrounds to hopefully
uncover a dark matter annihilation signal which may be hiding among
the diffuse GeV photons.
Kevin Schawinski
Yale
The Co-Evolution of Black Holes and their Host Galaxies
In order to understand the co-evolution of galaxies and the supermassive black
holes at their centers, we need to know which galaxies are more likely to host
active black holes and how they differ systematically from their normal
counterparts, if they do at all. I present some recent results based on data
from the Sloan Digital Sky Survey and the Galaxy Zoo project on the properties
of AGN host galaxies in the local Universe. I show that early- and late-type
galaxies with active black holes form a very different sub-set of their parent
population and that in turn, the role of the AGN phase in the evolution of the
host is very different. While we have a relatively good understanding of the
role of the AGN phase in early-type galaxies, the triggering and role
of AGN in late-type galaxies is less clear.
Ezequiel Treister
Hawaii
The Co-Evolution of Black Holes and their Host Galaxies
We constrain the number density and evolution of Compton-thick (CT)
Active Galactic Nuclei (AGN). In the local Universe we use the wide
area surveys from the Swift and INTEGRAL satellites, while for high
redshifts we explore candidate selections based on a combination of
X-ray and mid-IR parameters.
To find CT AGN at high redshifts we study the properties of a sample
of 211 objects in the Extended Chandra Deep Field-South selected based
on their very high mid-IR to optical flux ratios. We present
significant evidence supporting the CT AGN nature of a large fraction
of these sources, including a strong stacked X-ray signal. By
performing spectral fitting to the rest-frame UV/optical light
(dominated by the host galaxy) we found evidence for a significant
young stellar population, indicating that these sources are
experiencing considerable star-formation. Using this sample we
measured the space density of CT AGN at z~2, finding a strong
evolution in the number of high-luminosity sources from z=1.5 to 2.5.
Such strong evolution was not predicted by any existing AGN luminosity
function, but can be accurately explained by a simple prescription in
which every new quasar is generated by a major merger of two gas-rich
massive galaxies, which is originally heavily obscured and after ~100
Myrs removes most of the surrounding gas and dust to reveal an
unobscured quasar.
Bret Lehmer
Johns Hopkins
New Results from the Chandra Deep Protocluster Survey
It is now widely accepted that the growth of galaxies and their
central supermasive black holes (SMBHs) are linked. Observations and CDM
theories of large scale structures indicate that galaxy growth is
accelerated in high-density environments, and the highest density
structures underwent their most vigorous star formation at z > 2--3. To
study the corresponding growth of SMBHs in such high-density environments,
we have conducted a deep ~400 ks Chandra survey covering the SSA22
protocluster at z=3.09: the Chandra Deep Protocluster Survey. The
protocluster itself contains a factor of ~6 overdensity in galaxies (i.e.,
LBGs and LAEs) and is predicted to collapse into a z=0 cluster resembling
a rich local cluster (e.g., Coma). I will report on the current status of
the Chandra Deep Protocluster Survey and will highlight two recent
investigations that make use of the new Chandra data. These
investigations include (1) a study of how the growth of galaxies and SMBHs
depends on environment in the z=3 Universe, and (2) a comprehensive
explorationof the role that AGN and star-formation activity play in the
production of enigmatic extended (>30 kpc) Lyman-alpha emitting blobs
(LABs) that are found in excess in the protocluster.
Eduardo Rozo
Chicago
The maxBCG cluster catalog is a volume limited cluster catalog of
optically selected clusters drawn from the SDSS photometric data. We
present the constraints that the observed cluster abundance function
places on cosmological parameters, and demonstrate that these results
are in excellent agreement and competitive with X-ray cluster
abundance measurements. As in X-ray studies, our errors are dominated
by systematic uncertainties, and we will discuss ongoing efforts to
mitigate these. The lessons learned here should prove to be an
invaluable stepping stone for upcoming photometric surveys such as the
Dark Energy Survey (DES).
Matt McQuinn
Berkeley
A New Constraint on the Intergalactic HeII Fraction at z~3
I will discuss three different ways to detect and study the
reionization of helium in the intergalactic medium. First, I will
show that temperature inhomogeneities imprinted by this process may be
detectable in measurements of the HI Lyman-alpha forest. Second, I
will argue that one can still infer HeII fractions of the order of
unity from the HeII Lyman-alpha forest even though this absorption
saturates for HeII fractions of 10^-3. Third, I will propose a new
and more direct probe of helium reionization -- 8.7 GHz hyperfine
absorption from intergalactic ^3HeII.
Jesper Rasmussen
Carnegie Observatory
Witnessing the Formation of a Brightest Cluster Galaxy
The central dominant galaxies in galaxy clusters constitute the
most massive and luminous galaxies in the Universe. Despite this, the
formation of these brightest cluster galaxies (BCGs) and the impact of
this on the surrounding cluster environment remain poorly understood. I
will discuss recent multi-wavelength observations of the nearby cluster MZ
10451, in which both processes can be studied in unprecedented detail. The
core of this low-mass X-ray cluster harbors two optically bright
early-type galaxies in the process of merging. Using Chandra observations
of the cluster core, we can determine the nature of the merger and, for
the first time, obtain a detailed picture of how such mergers may have
affected the thermodynamics of baryons in cluster cores throughout cosmic
history. I will discuss the first results of this study, along with some
implications for our understanding of BCG formation.
Aurora Simionescu
Stanford
Metal Transport by Cold Fronts in M87
We used Suzaku's low background and good collecting area
to observe a prominent cold front in the outskirts of M87
in the nearby Virgo cluster. Observations of the center
of M87 with Chandra and XMM-Newton have already revealed
important information about the physical processes in
cool-core clusters, and this large-scale feature towards
the outskirts presents an optimal target to extend our
detailed knowledge of M87. We show accurate temperature
and metallicity profiles across this cold front and prove
that it is also associated with a discontinuity in the
chemical composition. The gas on the inner, bright region
of the front is more abundant in Fe than the gas outside
the front, while the Mg abundance remains similar between
the two regions, indicating a drastic change in the relative
contributions by type Ia vs. core-collapse supernovae. We
discuss the implications of variations in the Mg/Si/Fe
ratios in terms of currently available supernova yield models.
We also present preliminary hydrodynamic simulations of
gas sloshing in the M87 gravitational potential to deduce
details about the formation of the cold front and about the
role of the cold front in transporting and distributing
metals in the ICM.
Norbert Werner
Stanford
Small-Scale Turbulence in Giant Elliptical Galaxies
The dense cores of X-ray emitting gaseous halos of large elliptical
galaxies with temperatures below about 0.8 keV show two prominent Fe
XVII emission features, which provide a sensitive diagnostic tool to
measure the effects of resonant scattering. We present here
high-resolution spectra of five bright nearby elliptical galaxies,
obtained with the Reflection Grating Spectrometers (RGS) on the
XMM-Newton satellite. The spectra for the cores of four of the
galaxies show the Fe XVII line at 15.01 Angstrom being suppressed by
resonant scattering. The data for NGC 4636 in particular allow the
effects of resonant scattering to be studied in detail and to prove
that the 15.01 Angstrom line is suppressed only in the dense core and
not in the surrounding regions. Using deprojected density and
temperature profiles for this galaxy obtained with the Chandra
satellite, we model the radial intensity profiles of the strongest
resonance lines, accounting for the effects of resonant scattering,
for different values of the characteristic turbulent velocity.
Comparing the model to the data, we are able for the first time to
directly deduce upper limits on turbulent velocities. We find that the
isotropic turbulent velocities on spatial scales smaller than about 1
kpc are less than 100 km/s and the turbulent pressure support in the
galaxy core is smaller than 5% of the thermal pressure at the 90%
confidence level, and less than 20% at 95% confidence. Furthermore, I
will discuss the prospects of using observations of resonant
scattering and turbulent velocity broadening of emission lines with
Astro-H and IXO, which will produce a real breakthrough by extending
these measurements to higher mass systems and large radii.
Uri Keshet
Harvard
Cold Fronts and Spiral Flows in Galaxy Clusters
In recent years, spiral patterns were detected in several cool core
galaxy clusters (CCCs), through cold fronts and thermodynamic or
chemical inhomogeneities. I will show that cold fronts directly gauge
the local flow, revealing bulk tangential velocities that constitute a
considerable fraction of the sound speed. I will argue that spiral
flows are ubiquitous in CCCs, and point out some properties and
implications of such flows. For example, spiral inflows could provide
a natural, self regulating solution to the cooling problem in CCCs and
large galaxies.
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