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EOR as sequestration: Geoscience perspective
CO2 Enhanced Oil Recovery (EOR) has a development and operational history several decades longer than geologic sequestration of CO2 designed to benefit the atmosphere and provides much of the experience on which confidence in the newer technology is based. With modest increases in surveillance and accounting, future CO2 EOR using anthropogenic CO2 (CO2-A) captured to decrease atmospheric emissions can be used as part of a sequestration program.Bureau of Economic Geolog
From Galaxy-Galaxy Lensing to Cosmological Parameters
Galaxy-galaxy lensing measures the mean excess surface density DS(r) around a
sample of lensing galaxies. We develop a method for combining DS(r) with the
galaxy correlation function xi_gg(r) to constrain Omega_m and sigma_8, going
beyond the linear bias model to reach the level of accuracy demanded by current
and future measurements. We adopt the halo occupation distribution (HOD)
framework, and we test its applicability to this problem by examining the
effects of replacing satellite galaxies in the halos of an SPH simulation with
randomly selected dark matter particles from the same halos. The difference
between dark matter and satellite galaxy radial profiles has a ~10% effect on
DS(r) at r<1 Mpc/h. However, if radial profiles are matched, the remaining
impact of individual subhalos around satellite galaxies and environmental
dependence of the HOD at fixed halo mass is <5% in DS(r) for 0.1<r<15 Mpc/h. We
develop an analytic approximation for DS(r) that incorporates halo exclusion
and scale-dependent halo bias, and we demonstrate its accuracy with tests
against a suite of populated N-body simulations. We use the analytic model to
investigate the dependence of DS(r) and the galaxy-matter correlation function
xi_gm(r) on Omega_m and sigma_8, once HOD parameters for a given cosmological
model are pinned down by matching xi_gg(r). The linear bias prediction is
accurate for r>2 Mpc/h, but it fails at the 30-50% level on smaller scales. The
scaling of DS(r) ~ Omega_m^a(r) sigma_8^b(r) approaches the linear bias
expectation a=b=1 at r>10 Mpc/h, but a(r) and b(r) vary from 0.8 to 1.6 at
smaller r. We calculate a fiducial DS(r) and scaling indices a(r) and b(r) for
two SDSS galaxy samples; galaxy-galaxy lensing measurements for these samples
can be combined with our predictions to constrain Omega_m and sigma_8.Comment: 18 pages, 10 figures, accepted for publication in The Astrophysical
Journa
Cosmic Voids and Galaxy Bias in the Halo Occupation Framework
(Abridged) We investigate the power of void statistics to constrain galaxy
bias and the amplitude of dark matter fluctuations. We use the halo occupation
distribution (HOD) framework to describe the relation between galaxies and dark
matter. After choosing HOD parameters that reproduce the mean space density
n_gal and projected correlation function w_p measured for galaxy samples with
M_r<-19 and M_r<-21 from the Sloan Digital Sky Survey (SDSS), we predict the
void probability function (VPF) and underdensity probability function (UPF) of
these samples by populating the halos of a large, high-resolution N-body
simulation. If we make the conventional assumption that the HOD is independent
of large scale environment at fixed halo mass, then models constrained to match
n_gal and w_p predict nearly identical void statistics, independent of the
scatter between halo mass and central galaxy luminosity or uncertainties in HOD
parameters. Models with sigma_8=0.7 and sigma_8=0.9 also predict very similar
void statistics. However, the VPF and UPF are sensitive to environmental
variations of the HOD in a regime where these variations have little impact on
w_p. For example, doubling the minimum host halo mass in regions with large
scale (5 Mpc/h) density contrast delta<-0.65 has a readily detectable impact on
void probabilities of M_r<-19 galaxies, and a similar change for delta<-0.2
alters the void probabilities of M_r<-21 galaxies at a detectable level. The
VPF and UPF provide complementary information about the onset and magnitude of
density- dependence in the HOD. By detecting or ruling out HOD changes in low
density regions, void statistics can reduce systematic uncertainties in the
cosmological constraints derived from HOD modeling, and, more importantly,
reveal connections between halo formation history and galaxy properties.Comment: emulateapj, 16 pages, 13 figure
Redshift space 21 cm power spectra from reionization
We construct a simple but self-consistent analytic ionization model for rapid
exploration of 21cm power spectrum observables in redshift space. It is fully
described by the average ionization fraction and HII patch size
and has the flexibility to accommodate various reionization scenarios. The
model associates ionization regions with dark matter halos of the number
density required to recover and treats redshift space distortions
self-consistently with the virial velocity of such halos. Based on this model,
we study the line-of-sight structures in the brightness fluctuations since they
are the most immune to foreground contamination. We explore the degeneracy
between the HII patch size and nonlinear redshift space distortion in the one
dimensional power spectrum. We also discuss the limitations experimental
frequency and angular resolutions place on their distinguishability. Angular
resolution dilutes even the radial signal and will be a serious limitation for
resolving small bubbles before the end of reionization. Nonlinear redshift
space distortions suggest that a resolution of order 1 -- 10\arcsec and a
frequency resolution of 10kHz will ultimately be desirable to extract the full
information in the radial field at . First generation instruments
such as LOFAR and MWA can potentially measure radial HII patches of a few
comoving Mpc and larger at the end of reionization and are unlikely to be
affected by nonlinear redshift space distortions.Comment: 13 pages, 10 figures. Revised version. Includes minor changes. Adds
appendix on accomodating a distribution of radii for the HII regions.
Accepted for publication in Ap
Redshift-Space Distortions with the Halo Occupation Distribution I: Numerical Simulations
We show how redshift-space distortions of the galaxy correlation function or
power spectrum can constrain the matter density parameter Omega_m and the
linear matter fluctuation amplitude sigma_8. We improve on previous treatments
by adopting a fully non-linear description of galaxy clustering and bias, which
allows us to break parameter degeneracies by combining large-scale and small-
scale distortions. We consider different combinations of Omega_m and sigma_8
and find parameters of the galaxy halo occupation distribution (HOD) that yield
nearly identical galaxy correlation functions in real space. We use these HOD
parameters to populate the dark matter halos of large N-body simulations, from
which we measure redshift-space distortions on small and large scales. We
include a velocity bias parameter alpha_v that allows the velocity dispersions
of satellite galaxies in halos to be systematically higher or lower than those
of dark matter. Large-scale distortions are determined by the parameter
combination beta = Omega_m^{0.6}/b_g, where b_g is the galaxy bias, in
agreement with linear theory. However, linear theory does not accurately
describe the distortions themselves on scales accessible to our simulations. We
provide fitting formulas to estimate beta from the redshift-space correlation
function or power spectrum, and we show that these formulas are significantly
more accurate than those in the existing literature. On small scales, the
``finger-of-god'' distortions at projected separations ~0.1 Mpc/h depend on
Omega_m*alpha_v^2 but are independent of sigma_8, while at intermediate
separations they depend on sigma_8 as well. One can thus use redshift-space
distortions over a wide range of scales to separately determine Omega_m,
sigma_8, and alpha_v. (Abridged)Comment: 25 pages, submitted to Monthly Notice
The Extended Baryon Oscillation Spectroscopic Survey: Variability Selection and Quasar Luminosity Function
The SDSS-IV/eBOSS has an extensive quasar program that combines several
selection methods. Among these, the photometric variability technique provides
highly uniform samples, unaffected by the redshift bias of traditional
optical-color selections, when quasars cross the stellar locus
or when host galaxy light affects quasar colors at . Here, we present
the variability selection of quasars in eBOSS, focusing on a specific program
that led to a sample of 13,876 quasars to over a 94.5
deg region in Stripe 82, an areal density 1.5 times higher than over the
rest of the eBOSS footprint. We use these variability-selected data to provide
a new measurement of the quasar luminosity function (QLF) in the redshift range
. Our sample is denser, reaches deeper than those used in previous
studies of the QLF, and is among the largest ones. At the faint end, our QLF
extends to at low redshift and to
at . We fit the QLF using two independent double-power-law models with
ten free parameters each. The first model is a pure luminosity-function
evolution (PLE) with bright-end and faint-end slopes allowed to be different on
either side of . The other is a simple PLE at , combined with a
model that comprises both luminosity and density evolution (LEDE) at .
Both models are constrained to be continuous at . They present a
flattening of the bright-end slope at large redshift. The LEDE model indicates
a reduction of the break density with increasing redshift, but the evolution of
the break magnitude depends on the parameterization. The models are in
excellent accord, predicting quasar counts that agree within 0.3\% (resp.,
1.1\%) to (resp., ). The models are also in good agreement over
the entire redshift range with models from previous studies.Comment: 15 pages, 12 figures, accepted for publication in A&
Halo Occupation Distribution Modeling of Green Valley Galaxies
We present a clustering analysis of near ultraviolet (NUV) - optical color
selected luminosity bin samples of green valley galaxies. These galaxy samples
are constructed by matching the Sloan Digital Sky Survey Data Release 7 with
the latest Galaxy Evolution Explorer source catalog which provides NUV
photometry. We present cross-correlation function measurements and determine
the halo occupation distribution of these transitional galaxies using a new
multiple tracer analysis technique.
We extend the halo-occupation formalism to model the cross-correlation
function between a galaxy sample of interest and multiple tracer populations
simultaneously. This method can be applied to commonly used luminosity
threshold samples as well as to color and luminosity bin selected galaxy
samples, and improves the accuracy of clustering analyses for sparse galaxy
populations.
We confirm the previously observed trend that red galaxies reside in more
massive halos and are more likely to be satellite galaxies than average
galaxies of similar luminosity. While the change in central galaxy host mass as
a function of color is only weakly constrained, the satellite fraction and
characteristic halo masses of green satellite galaxies are found to be
intermediate between those of blue and red satellite galaxies.Comment: matches MNRAS accepted version; minor revisions, results unchange
Differential effects of inhibitory G protein isoforms on G protein-gated inwardly rectifying K+ currents in adult murine atria.
G protein-gated inwardly rectifying K+ (GIRK) channels are the major inwardly rectifying K+ currents in cardiac atrial myocytes and an important determinant of atrial electrophysiology. Inhibitory G protein α-subunits can both mediate activation via acetylcholine but can also suppress basal currents in the absence of agonist. We studied this phenomenon using whole cell patch clamping in murine atria from mice with global genetic deletion of Gαi2, combined deletion of Gαi1/Gαi3, and littermate controls. We found that mice with deletion of Gαi2 had increased basal and agonist-activated currents, particularly in the right atria while in contrast those with Gαi1/Gαi3 deletion had reduced currents. Mice with global genetic deletion of Gαi2 had decreased action potential duration. Tissue preparations of the left atria studied with a multielectrode array from Gαi2 knockout mice showed a shorter effective refractory period, with no change in conduction velocity, than littermate controls. Transcriptional studies revealed increased expression of GIRK channel subunit genes in Gαi2 knockout mice. Thus different G protein isoforms have differential effects on GIRK channel behavior and paradoxically Gαi2 act to increase basal and agonist-activated GIRK currents. Deletion of Gαi2 is potentially proarrhythmic in the atria.We thank the British Heart Foundation (RG/15/15/31742) and the Intramural
Research Program of the NIH (project Z01ES101643) for funding this research. D.M. was
supported by a grant from la Fédération Française de Cardiologie
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