10,635 research outputs found
Driving the Gaseous Evolution of Massive Galaxies in the Early Universe
Studies of the molecular interstellar medium that fuels star formation and
supermassive black hole growth in galaxies at cosmological distances have
undergone tremendous progress over the past few years. Based on the detection
of molecular gas in >120 galaxies at z=1 to 6.4, we have obtained detailed
insight on how the amount and physical properties of this material in a galaxy
are connected to its current star formation rate over a range of galaxy
populations. Studies of the gas dynamics and morphology at high spatial
resolution allow us to distinguish between gas-rich mergers in different stages
along the "merger sequence" and disk galaxies. Observations of the most massive
gas-rich starburst galaxies out to z>5 provide insight into the role of cosmic
environment for the early growth of present-day massive spheroidal galaxies.
Large-area submillimeter surveys have revealed a rare population of extremely
far-infrared-luminous gas-rich high-redshift objects, which is dominated by
strongly lensed, massive starburst galaxies. These discoveries have greatly
improved our understanding of the role of molecular gas in the evolution of
massive galaxies through cosmic time.Comment: 8 pages, 6 figures, invited talk paper, to appear in ASP Conference
Series, "Galaxy Mergers in an Evolving Universe", 23-28 October 2011,
Hualien, Taiwa
Constraints on the Star-Forming Interstellar Medium in Galaxies Back to the First Billion Years of Cosmic Time
Constraints on the molecular gas content of galaxies at high redshift are
crucial to further our understanding of star formation and galaxy evolution
through cosmic times, as molecular gas is the fuel for star formation. Since
its initial detection at large cosmic distances almost two decades ago, studies
of molecular gas in the early universe have come a long way. We have detected
CO emission from >100 galaxies, covering a range of galaxy populations at z>1,
reaching out to z>6, down to sub-kpc scale resolution, and spanning ~2 orders
of magnitude in gas mass (aided by gravitational lensing). Recently, it has
even become possible to directly identify distant galaxies through their
molecular emission lines without prior knowledge of their redshifts. The new
generation of powerful long wavelength interferometers such as the Expanded
Very Large Array (EVLA) and Atacama Large (sub)Millimeter Array (ALMA) thus
hold the promise to liberate studies of molecular gas in high redshift galaxies
from their heavy pre-selection. This will enable more systematic studies of the
molecular gas content in star-forming galaxies back to the earliest cosmic
times.Comment: 12 pages, 6 figures, invited talk paper, to appear in ASP Conference
Series, "Galaxy Evolution: Infrared to Millimeter Wavelength Perspective",
25-29 October 2010, Guilin, Chin
Molecular Gas in Lensed z >2 Quasar Host Galaxies and the Star Formation Law for Galaxies with Luminous Active Galactic Nuclei
We report the detection of luminous CO(J = 2→1), CO(J = 3→2), and CO(J = 4→3) emission in the strongly lensed high-redshift quasars B1938+666 (z = 2.059), HE 0230-2130 (z = 2.166), HE 1104-1805 (z = 2.322), and B1359+154 (z = 3.240), using the Combined Array for Research in Millimeter-wave Astronomy. B1938+666 was identified in a "blind" CO redshift search, demonstrating the feasibility of such investigations with millimeter interferometers. These galaxies are lensing-amplified by factors of μ_L ≃ 11-170, and thus allow us to probe the molecular gas in intrinsically fainter galaxies than currently possible without the aid of gravitational lensing. We report lensing-corrected intrinsic CO line luminosities of L'_(CO) = 0.65-21×10^9 K km s^(-1) pc^2, translating to H_2 masses of M(H_2) = 0.52-17 × 10^9 (α_(CO)/0.8) M_☉. To investigate whether or not the active galactic nucleus (AGN) in luminous quasars substantially contributes to L FIR, we study the L'_(CO)-L_(FIR) relation for quasars relative to galaxies without a luminous AGN as a function of redshift. We find no substantial differences between submillimeter galaxies and high-z quasars, but marginal evidence for an excess in L_(FIR) in nearby low-L FIR AGN galaxies. This may suggest that an AGN contribution to L_(FIR) is significant in systems with relatively low gas and dust content, but only minor in the most far-infrared-luminous galaxies (in which L_(FIR) is dominated by star formation)
Astrometric Resolution of Severely Degenerate Binary Microlensing Events
We investigate whether the "close/wide" class of degeneracies in
caustic-crossing binary microlensing events can be broken astrometrically.
Dominik showed that these degeneracies are particularly severe because they
arise from a degeneracy in the lens equation itself rather than a mere
"accidental" mimicking of one light curve by another. A massive observing
campaign of five microlensing collaborations was unable to break this
degeneracy photometrically in the case of the binary lensing event MACHO
98-SMC-1. We show that this degeneracy indeed causes the image centroids of the
wide and close solutions to follow an extremely similar pattern of motion
during the time when the source is in or near the caustic. Nevertheless, the
two image centroids are displaced from one another and this displacement is
detectable by observing the event at late times. Photometric degeneracies
therefore can be resolved astrometrically, even for these most severe cases.Comment: 11 pages, including 4 figures. Submitted to Ap
On the Nature and Location of the Microlenses
This paper uses the caustic crossing events in the microlens data sets to
explore the nature and location of the lenses. We conclude that the large
majority of lenses, whether they are luminous or dark, are likely to be
binaries. Further, we demonstrate that blending is an important feature of all
the data sets. An additional interpretation suggested by the data, that the
caustic crossing events along the directions to the Magellanic Clouds are due
to lenses located in the Clouds, implies that most of the LMC/SMC events to
date are due to lenses in the Magellanic Clouds. All of these conclusions can
be tested. If they are correct, a large fraction of lenses along the direction
to the LMC may be ordinary stellar binary systems, just as are the majority of
the lenses along the direction to the Bulge. Thus, a better understanding of
the larger-than-anticipated value derived for the Bulge optical depth may allow
us to better interpret the large value derived for the optical depth to the
LMC. Indeed, binarity and blending in the data sets may illuminate connections
among several other puzzles: the dearth of binary-source light curves, the
dearth of non-caustic-crossing perturbed binary-lens events, and the dearth of
obviously blended point-lens events.Comment: 15 pages, 2 figures. Submitted to the Astrophysical Journal Letters,
4 January 199
Large-Scale Suppression from Stochastic Inflation
We show non-perturbatively that the power spectrum of a self-interacting
scalar field in de Sitter space-time is strongly suppressed on large scales.
The cut-off scale depends on the strength of the self-coupling, the number of
e-folds of quasi-de Sitter evolution, and its expansion rate. As a consequence,
the two-point correlation function of field fluctuations is free from infra-red
divergencies.Comment: 4 pages, 1 figure; v2 minor changes to match published PRL versio
Magnetic fields in primordial accretion disks
Magnetic fields are considered as a vital ingredient of contemporary star
formation, and may have been important during the formation of the first stars
in the presence of an efficient amplification mechanism. Initial seed fields
are provided via plasma fluctuations, and are subsequently amplified by the
small-scale dynamo, leading to a strong tangled magnetic field. Here we explore
how the magnetic field provided by the small-scale dynamo is further amplified
via the dynamo in a protostellar disk and assess its
implications. For this purpose, we consider two characteristic cases, a typical
Pop.~III star with ~M and an accretion rate of
~M~yr, and a supermassive star with ~M
and an accretion rate of ~M~yr. For the ~M
Pop.~III star, we find that coherent magnetic fields can be produced on scales
of at least ~AU, which are sufficient to drive a jet with a luminosity of
~L and a mass outflow rate of ~M~yr. For
the supermassive star, the dynamical timescales in its environment are even
shorter, implying smaller orbital timescales and an efficient magnetization out
to at least ~AU. The jet luminosity corresponds to
~L, and a mass outflow rate of
~M~yr. We expect that the feedback from the
supermassive star can have a relevant impact on its host galaxy.Comment: Accepted for publication in Astronomy & Astrophysics, comments are
still welcom
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