Session J4: Astronomy, Astrophysics and Space Science II

What does the distribution of satellites around galaxies 8-11 billion years ago tell us about their dark matter halos?

We present the statistical study of the dependence of the satellite galaxies distribution on the stellar mass and star-formation activities of their massive central galaxies at $1 < z < 3$, using the deep near-IR from FourStar Galaxy Evolution Survey (ZFOURGE) and the Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey (CANDELS) to select a sample of galaxies at $z<3$ to low masses ($10^{9} M_{\odot}$). The satellites distribution is derived by measuring the projected radial number density of galaxies around centrals and random positions to account for the contamination from foreground and background galaxies. For the massive centrals ($\log(M/M_{\odot}) >10.78$), there are more satellites around quiescent centrals compared with those around star-forming centrals with a significant of $2.7\sigma$ even after accounting for differences in the stellar mass of quiescent and star-forming centrals. To understand this observation, we use a semi-analytic model. At fix halo mass of central galaxies, we find that the difference between the number density of satellites around quiescent and star-forming galaxies is not significant. The excess of satellites around quiescence is due to more massive halos of the quiescent compared with those of star-forming central at fixed stellar mass.   

Pseudo-bolometric calibration of IIP Supernovae using Unfiltered Photometry

Type IIP supernovae are the most frequent Core Collapse supernovae. These events seem to occur from progenitors of mass $M \sim 8-20 M_{\odot}$ that are able to retain their hydrogen envelop throughout their life. Their luminosity rises rapidly to peak soon after the shock breaks out, with the most contribution coming from UV photons (up to 80\%). The post-peak phase is followed by a characterstic photospheric plateau/recombination phase that normally lasts for $\sim 100$ days. This phase is contributed by the optical photons in the most part. Because of such homologously expanding ejecta in a long duration photospheric phase, IIPs have been used as accurate cosmological distance probes using the Expanding Photospheric Method ($EPM$). Bolometric properties of such events is not only crucial for the EPM analysis, but also to extract explosion kinematics. We present an emperical calibration of pseudo-bolometric light curve for some well observed IIPs using open CCD ($clear$) and broadband data. We show that a direct comaparison of $clear$ flux with integrated $BVRI$ flux yields $ \sim 13\%$ residual, while a color dependent calibration yields better than $2\%$ residual. From this calibration, we derive the pseudo-bolometric lightcurve for events that lack filtered photometry.   

Swift Ultraviolet Observations of Supernovae

The Swift satellite's Ultra-Violet Optical Telescope has observed over 300 supernovae during its first nine years in operation. This represents an order of magnitude increase in the number of ultraviolet observations and has enhanced many active lines of inquiry. These include shock breakouts, bolometric light curves, progenitor constraints, and evolution with redshift. Ultraviolet observations are also very sensitive to many of the effects leading to possible systematic errors in using type Ia supernovae as cosmological distance indicators. I will describe the whole Swift supernova sample and highlight some of the most interesting objects observed by Swift.   

Bolometric Spectra and Lightcurves of Type Ia Supernovae

The use of Type Ia supernova as distance indicators in the optical revolutionized cosmology by revealing the accelerating universe and are widely viewed as a valuable tool in efforts to distinguish between differing cosmological models. I will discuss our work observing nearby ($z < 0.015$) SNe Ia in the ultraviolet, optical and near-infrared and our method of combining these observations into bolometric spectra and lightcurves to gain a full-spectrum view of rest-frame SNe Ia evolution. I will highlight the importance of this data set with regard to our basic understanding of the underlying physics of SNe Ia and also its utility in analyzing SNe found at higher redshifts by large surveys like Dark Energy Survey and LSST.   

Image stacking through a geometrical phase retrieval algorithm for JWST

The James Webb Space Telescope is an 18-segment cryogenic telescope scheduled to be launched in 2018. Since it has a deployable primary mirror, part of its commissioning process requires aligning and phasing the mirror segments. The current proposed method, image stacking, is a long, complicated process that could take more than a week. Phase retrieval would be capable of handling the task, but it cannot handle large errors without a good starting estimate for the phase. We have adapted a geometrical phase retrieval (GPR) algorithm for use along with the traditional phase retrieval to phase the primary mirror. This talk will focus on the operation of the GPR algorithm, as well as a demonstration of its effectiveness.   

Interactive Cosmological Modeling with Easy Java Simulations: Constraints from a New Growth of Structure Module of CosmoEJS

Several cosmological observations suggest the universe's expansion is accelerating. Some possible explanations include a cosmological constant, or other form of repulsive dark energy, i.e. negative pressure and negative equation of state, a modification to general relativity at cosmological scales of distances, or an apparent effect of inhomogeneities in the universe. CosmoEJS is an interactive simulation package that allows educators and researchers to investigate cosmological models by simultaneously fitting several observations numerically. Previously, this package only used expansion history data sets, like supernovae, gamma ray bursts, baryon acoustic oscillations, the Hubble parameter, and the cosmic microwave background radiation; but data sets which measure the growth of galaxy structure formation, or clustering, have been shown to be more constraining for particular sets of models. We present a new module that enables constraints from growth data sets for various cosmological models. When combined with expansion history observations, these constraints from the growth of structure can drastically reduce the number of competitive cosmological models. CosmoEJS is available from Compadre Open Source Physics website, i.e. http://www.compadre.org/osp/items/detail.cfm?ID=12406.   

Fractal Analysis in a One-dimensional Universe

While the universe we observe today exhibits local, filament-like, structures with galaxy clusters and large voids between them, the primordial universe is believed to have been nearly homogeneous with slight variations in matter density. To understand how the observed hierarchical structure was formed, researchers have developed a one-dimensional analogue of the universe that can simulate the evolution of a large number of matter particles. Investigations to date demonstrate that this model reveals structure formation that shares essential features with the three-dimensional observations. In the present work, we have expanded on this concept to include two species of matter, specifically dark matter and luminous matter. In our simulation, luminous matter is treated in a way that loses energy in interaction. The results of the simulations clearly show the formation of a Cantor set like multifractal pattern over time. In contrast with most earlier studies, mass-oriented methods for computing multifractal dimensions were applied to analyze the bottom-up structure formation.   

Characterization of Gravitational Waves from Primordial Relativistic Turbulenc

This work is a follow-up to the paper, ``Numerical Relativity as a Tool for Studying the Early Universe.'' In this article, we present the first results of direct numerical simulations of primordial plasma turbulence as it applies to the generation of gravitational waves. We calculate the normalized energy density, strain and degree of polarization of gravitational waves produced by a simulated turbulent plasma similar to what was believed to have existed at the electroweak scale, 246 GeV. The initial random magnetic field amplitude was allowed to vary between otherwise identical data runs. We find that in the absence of an initial magnetic field, no gravitational waves are produced but as the amplitude increases, gravitational waves with normalized energy densities as high as 10$^{-47}$ may be produced. We also observed a significant degree of polarization in gravitational waves produced by the turbulent plasma field in agreement with Kahniahvili's results. The spectrum of gravitational waves produced appeared to mirror the spectrum of density and temperature fluctuations as expected. These and future results can be used to determine the conditions of the early universe, specifically the magnitude of primordial magnetic fields, from future gravitational wave observations.   

Probing the First Billion Years of Universe

Most of the major events in the history of the universe occurred during the first billion years. However, this era also remains one of the least explored epoch. Specifically, our knowledge about when and how did the first stars and first galaxies form and how did the entire universe transition from a neutral to an ionized phase, called the epoch of reionization, remains limited. To probe this epoch of reionization, we have recently obtained extremely deep spectroscopic observations of galaxies within the first 800 Myrs after the Bigbang. Our results suggest that universe is significantly neutral by redshift of about 8 (nearly 650 Myrs after the Bigbang) and this transition occurs over a very short time interval of about 300 Myrs.