12 research outputs found
Constraints on the Abundance of Highly Ionized Proto-Cluster Regions from the Absence of Large Voids in the Lyman Alpha Forest
Energetic feedback processes during the formation of galaxy clusters may have
heated and ionized a large fraction of the intergalactic gas in proto-cluster
regions. When such a highly ionized hot ``super-bubble'' falls along the
sightline to a background quasar, it would be seen as a large void, with little
or no absorption, in the Lyman alpha forest. We examine the spectra of 137
quasars in the Sloan Digital Sky Survey, to search for such voids, and find no
clear evidence of their existence. The size distribution of voids in the range
5-70 Angstrom (corresponding to physical sizes of approximately 3-35 comoving
Mpc/h) is consistent with the standard model for the Lyman alpha forest without
additional hot bubbles. We adapt a physical model for HII bubble growth during
cosmological reionization (Furlanetto, Zaldarriaga and Hernquist 2004), to
describe the expected size-distribution of hot super-bubbles at redshift around
z = 3. This model incorporates the conjoining of bubbles around individual
neighboring galaxies. Using the non-detection of voids, we find that models in
which the volume filling factor of hot bubbles exceeds approximately 20 percent
at z=3 can be ruled out, primarily because they overproduce the number of large
(40-50 Angstrom) voids. We conclude that any pre-heating mechanism that
explains galaxy cluster observations must avoid heating the low-density gas in
the proto-cluster regions, either by operating relatively recently (z<3) or by
depositing entropy in the high-density regions.Comment: submitted to ApJ, 9 emulateapj pages with 3 figure
Cosmology with Standard Sirens: the Importance of the Shape of the Lensing Magnification Distribution
The gravitational waves (GWs) emitted by inspiraling binary black holes,
expected to be detected by the Laser Interferometer Space Antenna (LISA), could
be used to determine the luminosity distance to these sources with the
unprecedented precision of <~ 1%. We study cosmological parameter constraints
from such standard sirens, in the presence of gravitational lensing by
large-scale structure. Lensing introduces magnification with a probability
distribution function (PDF) whose shape is highly skewed and depends on
cosmological parameters. We use Monte-Carlo simulations to generate mock
samples of standard sirens, including a small intrinsic scatter, as well as the
additional, larger scatter from lensing, in their inferred distances. We derive
constraints on cosmological parameters, by simultaneously fitting the mean and
the distribution of the residuals on the distance vs redshift (d_L - z) Hubble
diagram. We find that for standard sirens at redshift z ~ 1, the sensitivity to
a single cosmological parameter, such as the matter density Omega_m, or the
dark energy equation of state w, is ~ 50%-80% tighter when the skewed lensing
PDF is used, compared to the sensitivity derived from a Gaussian PDF with the
same variance. When these two parameters are constrained simultaneously, the
skewness yields a further enhanced improvement (by ~ 120%), owing to the
correlation between the parameters. The sensitivity to the amplitude of the
matter power spectrum, sigma_8 from the cosmological dependence of the PDF
alone, however, is ~ 20% worse than that from the Gaussian PDF. At higher
redshifts, the PDF resembles a Gaussian more closely, and the effects of the
skewness become less prominent. These results highlight the importance of
obtaining an accurate and reliable PDF of the lensing convergence, in order to
realize the full potential of standard sirens as cosmological probes.Comment: 16 pages, 9 tables, 12 figures, submitted to MNRA
Constraining Intra-cluster Gas Models with AMiBA13
Clusters of galaxies have been used extensively to determine cosmological
parameters. A major difficulty in making best use of Sunyaev-Zel'dovich (SZ)
and X-ray observations of clusters for cosmology is that using X-ray
observations it is difficult to measure the temperature distribution and
therefore determine the density distribution in individual clusters of galaxies
out to the virial radius. Observations with the new generation of SZ
instruments are a promising alternative approach. We use clusters of galaxies
drawn from high-resolution adaptive mesh refinement (AMR) cosmological
simulations to study how well we should be able to constrain the large-scale
distribution of the intra-cluster gas (ICG) in individual massive relaxed
clusters using AMiBA in its configuration with 13 1.2-m diameter dishes
(AMiBA13) along with X-ray observations. We show that non-isothermal beta
models provide a good description of the ICG in our simulated relaxed clusters.
We use simulated X-ray observations to estimate the quality of constraints on
the distribution of gas density, and simulated SZ visibilities (AMiBA13
observations) for constraints on the large-scale temperature distribution of
the ICG. We find that AMiBA13 visibilities should constrain the scale radius of
the temperature distribution to about 50% accuracy. We conclude that the
upgraded AMiBA, AMiBA13, should be a powerful instrument to constrain the
large-scale distribution of the ICG.Comment: Accepted for publication in The Astrophysical Journal, 12 pages, 9
figure
Improved Models for Cosmic Infrared Background Anisotropies: New Constraints on the IR Galaxy Population
The power spectrum of cosmic infrared background (CIB) anisotropies is
sensitive to the connection between star formation and dark matter halos over
the entire cosmic star formation history. Here we develop a model that
associates star-forming galaxies with dark matter halos and their subhalos. The
model is based on a parameterized relation between the dust-processed infrared
luminosity and (sub)halo mass. By adjusting 3 free parameters, we attempt to
simultaneously fit the 4 frequency bands of the Planck measurement of the CIB
anisotropy power spectrum. To fit the data, we find that the star-formation
efficiency must peak on a halo mass scale of ~ 5x10^12 solar mass and the
infrared luminosity per unit mass must increase rapidly with redshift. By
comparing our predictions with a well-calibrated phenomenological model for
shot noise, and with a direct observation of source counts, we show that the
mean duty cycle of the underlying infrared sources must be near unity,
indicating that the CIB is dominated by long-lived quiescent star formation,
rather than intermittent short "star bursts". Despite the improved flexibility
of our model, the best simultaneous fit to all four Planck channels remains
relatively poor. We discuss possible further extensions to alleviate the
remaining tension with the data. Our model presents a theoretical framework for
a future joint analysis of both background anisotropy and source count
measurements.Comment: 14 pages, 2 tables, 7 figures, submitted to MNRA