54 research outputs found
Solving the system of atomic rate equations during recombination
Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2007.Includes bibliographical references (leaves 59-60).The recombination of hydrogen at z ~ 800 - 1800 induces distortions to the Cosmic Microwave Background (CMB) spectrum. We present a careful calculation and analysis of all of the main transitions occurring during this period in order to find the electron density throughout recombination and its dependence on each process. Our original motivation was to analyze the effects that Thomson scattering and resonance scattering will have on recombination. However, while working on the project, we found that first we had to thoroughly account for all of the atomic transitions. We present a new method for solving the system of equations throughout the period of recombination. This method allows us to show the effect of individual processes on the total ionization fraction.by Daniel Scolnic.S.B
Cosmicflows-4
With Cosmicflows-4, distances are compiled for 55,877 galaxies gathered into
38,065 groups. Eight methodologies are employed, with the largest numbers
coming from the correlations between the photometric and kinematic properties
of spiral galaxies (TF) and elliptical galaxies (FP). Supernovae that arise
from degenerate progenitors (SNIa) are an important overlapping component.
Smaller contributions come from distance estimates from the surface brightness
fluctuations of elliptical galaxies (SBF) and the luminosities and expansion
rates of core collapse supernovae (SNII). Cepheid Period-Luminosity Relation
(CPLR) and Tip of the Red Giant Branch (TRGB) observations founded on local
stellar parallax measurements along with the geometric maser distance to NGC
4258 provide the absolute scaling of distances. The assembly of galaxies into
groups is an important feature of the study in facilitating overlaps between
methodologies. Merging between multiple contributions within a methodology and
between methodologies is carried out with Bayesian Markov chain Monte Carlo
procedures. The final assembly of distances is compatible with a value of the
Hubble constant of km s Mpc with the small statistical
error km s Mpc but a large potential systematic error
~3 km s Mpc. Peculiar velocities can be inferred from the
measured distances. The interpretation of the field of peculiar velocities is
complex because of large errors on individual components and invites analyses
beyond the scope of this study.Comment: 38 pages, 24 figures. catalogs available at edd.ifa.hawaii.edu.
Accepted to Ap
Type Ia Supernova Distances at z > 1.5 from the Hubble Space Telescope Multi-Cycle Treasury Programs: The Early Expansion Rate
We present an analysis of 15 Type Ia supernovae (SNe Ia) at redshift z > 1 (9
at 1.5 < z < 2.3) recently discovered in the CANDELS and CLASH Multi-Cycle
Treasury programs using WFC3 on the Hubble Space Telescope. We combine these
SNe Ia with a new compilation of 1050 SNe Ia, jointly calibrated and corrected
for simulated survey biases to produce accurate distance measurements. We
present unbiased constraints on the expansion rate at six redshifts in the
range 0.07 < z < 1.5 based only on this combined SN Ia sample. The added
leverage of our new sample at z > 1.5 leads to a factor of ~3 improvement in
the determination of the expansion rate at z = 1.5, reducing its uncertainty to
~20%, a measurement of H(z=1.5)/H0=2.67 (+0.83,-0.52). We then demonstrate that
these six measurements alone provide a nearly identical characterization of
dark energy as the full SN sample, making them an efficient compression of the
SN Ia data. The new sample of SNe Ia at z > 1 usefully distinguishes between
alternative cosmological models and unmodeled evolution of the SN Ia distance
indicators, placing empirical limits on the latter. Finally, employing a
realistic simulation of a potential WFIRST SN survey observing strategy, we
forecast optimistic future constraints on the expansion rate from SNe Ia.Comment: 14 pages, 5 figures, 7 tables; submitted to Ap
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