794 research outputs found
QSO 0130-4021: A third QSO showing a low Deuterium to Hydrogen Abundance Ratio
We have discovered a third quasar absorption system which is consistent with
a low deuterium to hydrogen abundance ratio, D/H = 3.4 times 10^-5. The z ~ 2.8
partial Lyman limit system towards QSO 0130-4021 provides the strongest
evidence to date against large D/H ratios because the H I absorption, which
consists of a single high column density component with unsaturated high order
Lyman series lines, is readily modeled -- a task which is more complex in other
D/H systems. We have obtained twenty-two hours of spectra from the HIRES
spectrograph on the W.M. Keck telescope, which allow a detailed description of
the Hydrogen. We see excess absorption on the blue wing of the H I Lyman alpha
line, near the expected position of Deuterium. However, we find that Deuterium
cannot explain all of the excess absorption, and hence there must be
contamination by additional absorption, probably H I. This extra H I can
account for most or all of the absorption at the D position, and hence D/H = 0
is allowed. We find an upper limit of D/H < 6.7 times 10^-5 in this system,
consistent with the value of D/H ~ 3.4 times 10^-5 deduced towards QSO
1009+2956 and QSO 1937-1009 by Burles and Tytler (1998a, 1998b). This
absorption system shows only weak metal line absorption, and we estimate [Si/H]
< -2.6 -- indicating that the D/H ratio of the system is likely primordial. All
four of the known high redshift absorption line systems simple enough to
provide useful limits on D are consistent with D/H = 3.4 +/- 0.25 times 10^-5.
Conversely, this QSO provides the third case which is inconsistent with much
larger values.Comment: 18 pages, 5 figures, submitted to Ap
Archeops: an instrument for present and future cosmology
Archeops is a balloon-borne instrument dedicated to measure the cosmic
microwave background (CMB) temperature anisotropies. It has, in the millimetre
domain (from 143 to 545 GHz), a high angular resolution (about 10 arcminutes)
in order to constrain high l multipoles, as well as a large sky coverage
fraction (30%) in order to minimize the cosmic variance. It has linked, before
WMAP, Cobe large angular scales to the first acoustic peak region. From its
results, inflation motivated cosmologies are reinforced with a flat Universe
(Omega_tot=1 within 3%). The dark energy density and the baryonic density are
in very good agreement with other independent estimations based on supernovae
measurements and big bang nucleosynthesis. Important results on galactic dust
emission polarization and their implications for Planck are also addressed.Comment: 4 pages, 2 figures, to appear in Proceedings of the Multiwavelength
Cosmology Conference, June 2003, Mykonos Island, Greec
The Keck+Magellan Survey for Lyman Limit Absorption I: The Frequency Distribution of Super Lyman Limit Systems
We present the results of a survey for super Lyman limit systems (SLLS;
defined to be absorbers with 19.0 <= log(NHI) <= 20.3 cm^-2) from a large
sample of high resolution spectra acquired using the Keck and Magellan
telescopes. Specifically, we present 47 new SLLS from 113 QSO sightlines. We
focus on the neutral hydrogen frequency distribution f(N,X) of the SLLS and its
moments, and compare these results with the Lyman-alpha forest and the damped
Lyman alpha systems (DLA; absorbers with log(NHI) >= 20.3 cm^-2). We find that
that f(N,X) of the SLLS can be reasonably described with a power-law of index
alpha = -1.43^{+0.15}_{-0.16} or alpha = -1.19^{+0.20}_{-0.21} depending on
whether we set the lower N(HI) bound for the analysis at 10^{19.0} cm^-2 or
10^{19.3}$ cm^-2, respectively. The results indicate a flattening in the slope
of f(N,X) between the SLLS and DLA. We find little evidence for redshift
evolution in the shape of f(N,X) for the SLLS over the redshift range of the
sample 1.68 < z < 4.47 and only tentative evidence for evolution in the zeroth
moment of f(N,X), the line density l_lls(X). We introduce the observable
distribution function O(N,X) and its moment, which elucidates comparisons of HI
absorbers from the Lyman-alpha through to the DLA. We find that a simple three
parameter function can fit O(N,X) over the range 17.0 <= log(NHI) <=22.0. We
use these results to predict that f(N,X) must show two additional inflections
below the SLLS regime to match the observed f(N,X) distribution of the
Lyman-alpha forest. Finally, we demonstrate that SLLS contribute a minor
fraction (~15%) of the universe's hydrogen atoms and, therefore, an even small
fraction of the mass in predominantly neutral gas.Comment: 15 pages, 10 figures, accepted to the Astrophysical Journal. Revision
includes updated reference
The Deuterium to Hydrogen Abundance Ratio Towards a Fourth QSO: HS0105+1619
We report the measurement of the primordial D/H abundance ratio towards QSO
\object. The column density of the hydrogen in the Lyman limit
system is high, \lnhi \cmm, allowing for the deuterium to
be seen in 5 Lyman series transitions. The measured value of the D/H ratio
towards QSO \object is found to be D/H. The
metallicity of the system showing D/H is found to be solar,
indicating that the measured D/H is the primordial D/H within the measurement
errors. The gas which shows D/H is neutral, unlike previous D/H systems which
were more highly ionized. Thus, the determination of the D/H ratio becomes more
secure since we are measuring it in different astrophysical environments, but
the error is larger because we now see more dispersion between measurements.
Combined with prior measurements of D/H, the best D/H ratio is now D/H, which is 10% lower than the previous value. The new
values for the baryon to photon ratio, and baryonic matter density derived from
D/H are and \ob
respectively.Comment: Minor text and reference changes. To appear in the May 10, 2001 issue
of the Astrophysical Journa
Constraining The Universal Lepton Asymmetry
The relic cosmic background neutrinos accompanying the cosmic microwave
background (CMB) photons may hide a universal lepton asymmetry orders of
magnitude larger than the universal baryon asymmetry. At present, the only
direct way to probe such an asymmetry is through its effect on the abundances
of the light elements produced during primordial nucleosynthesis. The relic
light element abundances also depend on the baryon asymmetry, parameterized by
the baryon density parameter (eta_B = n_B/n_gamma = 10^(-10)*eta_10), and on
the early-universe expansion rate, parameterized by the expansion rate factor
(S = H'/H) or, equivalently by the effective number of neutrinos (N_nu = 3 +
43(S^2 - 1)/7). We use data from the CMB (and Large Scale Structure: LSS) along
with the observationally-inferred relic abundances of deuterium and helium-4 to
provide new bounds on the universal lepton asymmetry, finding for eta_L, the
analog of eta_B, 0.072 +/- 0.053 if it is assumed that N_nu = 3 and, 0.115 +/-
0.095 along with N_nu = 3.3^{+0.7}_{-0.6}, if N_nu is free to vary
New HST spectra indicate the QSO PG1718+4807 will not give the primordial deuterium abundance
The z ~ 0.701 absorption system towards the QSO PG1718+4807 is the only
example of a QSO absorption system which might have a deuterium/hydrogen ratio
approximately ten times the value found towards other QSOs. We have obtained
new STIS spectra from the Hubble Space Telescope of the Lyman alpha and Lyman
limit regions of the system. These spectra give the redshift and velocity
dispersion of the neutral hydrogen which produces most of the observed
absorption. The Lyman alpha line is too narrow to account for all of the
observed absorption. It was previously known that extra absorption is needed on
the blue side of the main H I near to the expected position of deuterium. The
current data suggests with a 98% confidence level that the extra absorption is
not deuterium. Some uncertainty persists because we have a low signal to noise
ratio and the extra absorption - be it deuterium or hydrogen - is heavily
blended with the Lyman alpha absorption from the main hydrogen component.Comment: 18 pages, 7 figures, Submitted to Ap
Early-universe constraints on a time-varying fine structure constant
Higher-dimensional theories have the remarkable feature of predicting a time
(and hence redshift) dependence of the `fundamental' four dimensional constants
on cosmological timescales. In this paper we update the bounds on a possible
variation of the fine structure constant alpha at the time of BBN (z =10^10)
and CMB (z=10^3). Using the recently-released high-resolution CMB anisotropy
data and the latest estimates of primordial abundances of 4He and D, we do not
find evidence for a varying alpha at more than one-sigma level at either epoch.Comment: 5 pages, 1 figure, minor misprints corrected, references added. The
analysis has been updated using new BOOMERanG and DASI data on CMB anisotrop
Precision Primordial He Measurement with CMB Experiments
Big bang nucleosynthesis (BBN) and the cosmic microwave background (CMB) are
two major pillars of cosmology. Standard BBN accurately predicts the primordial
light element abundances (He, D, He and Li), depending on one
parameter, the baryon density. Light element observations are used as a
baryometers. The CMB anisotropies also contain information about the content of
the universe which allows an important consistency check on the Big Bang model.
In addition CMB observations now have sufficient accuracy to not only determine
the total baryon density, but also resolve its principal constituents, H and
He. We present a global analysis of all recent CMB data, with special
emphasis on the concordance with BBN theory and light element observations. We
find and
(fraction of baryon mass as He) using CMB data alone, in agreement with
He abundance observations. With this concordance established we show that
the inclusion of BBN theory priors significantly reduces the volume of
parameter space. In this case, we find
and . We also find that the inclusion of deuterium
abundance observations reduces the and ranges by a factor
of 2. Further light element observations and CMB anisotropy experiments
will refine this concordance and sharpen BBN and the CMB as tools for precision
cosmology.Comment: 7 pages, 3 color figures made minor changes to bring inline with
journal versio
Spontaneous baryogenesis in flat directions
We discuss a spontaneous baryogenesis mechanism in flat directions. After
identifying the Nambu-Goldstone mode which derivatively couples to the
associated (1) current and rotates due to the A-term, we show that
spontaneous baryogenesis can be naturally realized in the context of the flat
direction. As applications, we discuss two scenarios of baryogenesis in detail.
One is baryogenesis in a flat direction with a vanishing charge,
especially, with neither baryon nor lepton charge, which was recently proposed
by Chiba and the present authors. The other is a baryogenesis scenario
compatible with a large lepton asymmetry.Comment: 10 pages, no figure, the version accepted to Phys. Rev. D; a few
explanatory comments are adde
Gas Accretion via Lyman Limit Systems
In cosmological simulations, a large fraction of the partial Lyman limit
systems (pLLSs; 16<log N(HI)<17.2) and LLSs (17.2log N(HI)<19) probes
large-scale flows in and out of galaxies through their circumgalactic medium
(CGM). The overall low metallicity of the cold gaseous streams feeding galaxies
seen in these simulations is the key to differentiating them from metal rich
gas that is either outflowing or being recycled. In recent years, several
groups have empirically determined an entirely new wealth of information on the
pLLSs and LLSs over a wide range of redshifts. A major focus of the recent
research has been to empirically determine the metallicity distribution of the
gas probed by pLLSs and LLSs in sizable and representative samples at both low
(z2) redshifts. Here I discuss unambiguous evidence for
metal-poor gas at all z probed by the pLLSs and LLSs. At z<1, all the pLLSs and
LLSs so far studied are located in the CGM of galaxies with projected distances
<100-200 kpc. Regardless of the exact origin of the low-metallicity pLLSs/LLSs,
there is a significant mass of cool, dense, low-metallicity gas in the CGM that
may be available as fuel for continuing star formation in galaxies over cosmic
time. As such, the metal-poor pLLSs and LLSs are currently among the best
observational evidence of cold, metal-poor gas accretion onto galaxies.Comment: Invited review to appear in Gas Accretion onto Galaxies, Astrophysics
and Space Science Library, eds. A. J. Fox & R. Dav\'e, to be published by
Springe
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