Searching for Dwarf Satellites around Milky Way – Analog Galaxies with the SAGA survey
Ben Weiner, Steward Observatory
Dwarf satellites of massive galaxies are a probe of many issues in galaxy evolution and cosmology, including the nature of low-mass galaxies, star formation at early times, accretion into halos, and the abundance of low-mass dark matter halos. Much attention has been devoted to the number and nature of Milky Way and M31 dwarf satellites, especially the “missing satellites problem.” However, we know very little about dwarf satellites outside the Local Group below the mass of the LMC, and we don’t know if the MW and M31 satellite systems are typical. The SAGA (Satellites Around Galactic Analogs) survey collaboration aims to address this with both observational and theoretical studies of satellite abundances and properties around Milky Way analog central galaxies. I will present results from our MMT/Hectospec wide field spectroscopic surveys for satellites. We have surveyed the fields of several nearby galaxies that are similar to the Milky Way to detect and spectroscopically confirm dwarf satellites. We find a range of numbers of satellites, suggesting that there is a significant variance in halo histories. We also find that not all dwarf systems resemble the Milky Way and M31 systems. I will discuss these results and some of the implications on the life cycle of satellites that we can infer from satellite abundances and properties, including their images and spectra.
BOSS DR12 survey: Clustering of galaxies and Dark Matter Haloes
Sergio Rodriguez, UAM, Madrid and Cal. Berkeley
BOSS SDSS-III is the largest redshift survey for the large scale structure and a powerful sample for the study of the low redshift Baryonic Acoustic Oscillations. We combine the features of the survey, such as, geometry, angular incompleteness and stellar mass incompleteness, with the BigMultiDark cosmological simulation to do a study of the distribution of galaxies in the dark matter halos. Using this large N-Body simulation and the halo abundance matching technique, we found a remarkably good agreement with the 2-point and 3-point statistics of the data.
New Tools for Galactic Archaeology from the Milky Way
Gail Zasowski, John Hopkins University
One of the critical components for understanding galaxy evolution is understanding the Milky Way Galaxy itself — its detailed structure and chemodynamical properties, as well as fundamental stellar physics, which we can only study in great detail locally. This field is currently undergoing a dramatic expansion towards the kinds of large-scale statistical analyses long used by the extragalactic and other communities, thanks in part to an enormous influx of data from space- and ground-based surveys. I will describe the Milky Way and Local Group in the context of general galaxy evolution and highlight some recent developments in Galactic astrophysics that take advantage of these big data sets and analysis techniques. In particular, I will focus on two diverse approaches: one to characterize the distribution and dynamics of the carbon-rich, dusty diffuse ISM, and one to map the resolved bulk stellar properties of the inner disk and bulge. The rapid progress in these areas promises to continue, with the arrival of data sets from missions like SDSS, Gaia, LSST, and WFIRST.
The Chemical History and Evolution of Titan’s Atmosphere as Revealed by ALMA
Saturn’s largest moon, Titan, possesses a substantial atmosphere containing significant minorities of nitrile and hydrocarbon species, predominantly due to the photodissociation of the major gases, N2 and CH4. Titan’s methane cycle, liquid lakes, and complex organic chemistry make it an intriguing target through its similarities to Earth and the allure of its astrobiological potential. Though the existence of heavy nitrile species – such as CH3C3N, HC5N, and C3H7CN – has been inferred through Cassini Ion and Neutral Mass Spectrometer (INMS) data, confirmation of these species has yet to be made spectroscopically. Other hydrocarbon species, such as C3H4 and C3H8 have been detected using Voyager’s Infrared Spectrometer (IRIS; Maguire et al., 1981) and later mapped by the Composite Infrared Spectrometer (CIRS; Nixon et al., 2013) onboard Cassini, but abundance constraints for these species in the mesosphere is poor. To fully understand the production of these species and their spatial distribution in Titan’s atmosphere, vertical abundance profiles must be produced to use with current photochemical models. Utilizing early science calibration images of Titan obtained with the Atacama Large Millimeter/Submillimeter Array (ALMA), Cordiner et al. (2014; 2015) determined the vertical distribution of various nitriles and hydrocarbons in Titan’s atmosphere, including at least one previously undetected molecule – C2H5CN. For my dissertation project, I will calibrate and model sub-millimeter emissions from molecules in Titan’s atmosphere, and quantify variations in the spatial distribution of various species throughout its seasonal cycle by utilizing high resolution ALMA data. The main goals of this project are as follows:
1. To search for previously undetected molecules in Titan’s atmosphere through analysis of the existing public ALMA data, and/or through ALMA proposals of my own;
2. Constrain abundance profiles of detected molecular species, and provide upper abundance limits for those we cannot detect;
3. Map the spatial distribution of detected species in order to improve our understanding of Titan’s atmospheric transport and circulation;
4. Determine how these spatial distributions change over Titan’s seasonal cycle by utilizing multiple years of public ALMA data.
The majority of this work will employ the Non-linear Optimal Estimator for MultivariatE Spectral analySIS (NEMESIS) software package, developed by Oxford University (Irwin et al., 2008), to retrieve abundance and temperature information through radiative transfer models. These results will allow us to investigate the chemical evolution and history of Titan’s rich, pre-biotic atmosphere by providing valuable abundance measurements and constraints to molecular photochemical and dynamical models. We will compare our results with measurements made by the Cassini spacecraft, thereby enhancing the scientific return from both orbiter and ALMA datasets. The increased inventory of complex, organic molecules observable with ALMA’s sub-mm frequency range and high spatial resolution may also yield detections of species fundamental to the formation of living organisms, such as amino acids. Thus, by informing photochemical and dynamical models and increasing our known inventory of complex molecular species, we will also assess Titan’s potential habitability.
Giant Planet Shielding of the Inner Solar System Revisited: Blending Celestial Mechanics with Advanced Computation
Dr. William Newman, UCLA
The Earth has sustained during the last billion years as many as five catastrophic collisions with asteroids and comets which led to widespread species extinctions. Our own atmosphere was literally blown away 4.5 billion years ago by a collision with a Mars-sized impactor. However, collisions with comets originating in the outer solar system accreted much of the present-day atmosphere. Relatively advanced life on our planet is the beneficiary of a number of impact events during Earth’s history which built our atmosphere without destroying a large fraction of terrestrial life. Using very high precision Monte Carlo integration methods to explore the orbital evolution over hundreds of millions of years followed by the application of celestial mechanical techniques, the presentation will explain directly how Earth was shielded by the combined influence of Jupiter and Saturn, assuring that only 1 in 100,000 potential collisions with the Earth will materialize.