One of the mysterious components of galaxies is dust. Dust not only plays an important role in the physics and chemistry of the interstellar medium, but also shapes our views of galaxies by absorbing and scattering UV and optical light and re-emitting it in longer IR wavelengths. Despite its importance, we know very little about dust at high redshifts. In this talk, which is built on an extensive dataset from Keck/MOSFIRE near-IR spectrograph (the MOSDEF survey), I will highlight our new results on the properties of dust in emission (mid-IR PAH emission) and absorption (dust attenuation curve) for galaxies at redshift of z~2, the peak epoch of cosmic star formation activity.
THURSDAY, MAY 21
The Discovery of the Long-Period, Eccentric Planet Kepler-88 d and System Characterization with Radial Velocities and Photodynamical Analysis
GUEST SPEAKER: LAUREN WEISS, PARRENT POSTDOCTORAL FELLOW, INSTITUTE FOR ASTRONOMY, UNIVERSITY OF HAWAI`I, MĀNOA
We present the discovery of Kepler-88 d (Pd=1403+/-14 days, Msinid = 965±44M⊕ = 3.04±0.13MJ, e_d=0.41+/- 0.03 ) based on six years of radial velocity (RV) follow-up from the W. M. Keck Observatory High Resolution Echelle Spectrometer spectrograph. Kepler-88 has two previously identified planets. Kepler-88 b (KOI-142.01) transits in the NASA Kepler photometry and has very large transit timing variations (TTVs). Nesvorný et al. performed a dynamical analysis of the TTVs to uniquely identify the orbital period and mass of the perturbing planet (Kepler-88 c), which was later was confirmed with RVs from the Observatoire de Haute-Provence (OHP). To fully explore the architecture of this system, we performed photodynamical modeling on the Kepler photometry combined with the RVs from Keck and OHP and stellar parameters from spectroscopy and Gaia. Planet d is not detectable in the photometry, and long-baseline RVs are needed to ascertain its presence. A photodynamical model simultaneously optimized to fit the RVs and Kepler photometry yields the most precise planet masses and orbital properties yet for b and c: Pb=10.91647±0.00014days, Mb =9.5 +/- 1.2 Me, and Pc=22.2649±0.0007days, Mc=214.0+/- 5.3 Me. The photodynamical solution also finds that planets b and c have low eccentricities and low mutual inclination, are apsidally anti-aligned, and have conjunctions on the same hemisphere of the star. Continued RV follow-up of systems with small planets will improve our understanding of the link between inner planetary system architectures and giant planets.
WEDNESDAY, MAY 13
A Population of G-objects in the Central Region of the Galactic Center
GUEST SPEAKER: RANDY CAMPBELL, W. M. KECK OBSERVATORY MANAGER OF OBSERVING SUPPORT
In recent years, two unusual objects have been found orbiting closely around the supermassive black hole at the center of our Galaxy: so-called G2 and G1. No broad consensus has yet been reached concerning their nature: they show characteristics of dusty clouds with ionized gas features, but when monitored over time they display the dynamical properties of stellar-mass objects. Presented in this talk are the observations of four additional G-objects identified through a closer examination of the past 13 years of Keck Galactic center data. The data are were acquired with the instrument OSIRIS, an integral field spectrometer that benefits from the high spatial resolution of the laser guide star adaptive optics on Keck I. I will discuss the data analysis that identified the new members of these peculiar class of objects that all lie within 0.04 pc of the supermassive black hole, and that is, so far, unique to this environment.
WEDNESDAY, APRIL 29
Gimme Enough Variables and I Can Fit Anything!
Modeling Colliding Wind Spectra of Massive Star Binaries
GUEST SPEAKER: GRANT HILL, W. M. KECK OBSERVATORY MANAGER OF OPERATIONS AND INFRASTRUCTURE
Like our Sun’s solar wind, massive stars also have winds but millions of times more powerful. When you get two of these in a binary, the winds crash into each other and produce all kinds of excitement including visible effects in spectra of these stars. I’ll describe how the modeling code I’ve written permits one to learn more about these wind collisions and the stars that create them.
FRIDAY, APRIL 24
Cosmic-ray Elimination: A Convolutional Neural Network Approach
GUEST SPEAKER: TERRY COX, W. M. KECK OBSERVATORY/CARROLL COLLEGE DATA SCIENCE FELLOW
The reduction of cosmic rays has been an ongoing problem within the astronomy community, given cosmic rays are present in every instruments’ image readouts. With many different algorithms, such as median filtering, interpopulation methods, and the widely used method Laplacian edge detection, none are currently accurate and fast enough. In this talk, I will explain an alternative method using Convolutional Neural Networks to ultimately speed up and improve the quality of visible wavelength spectroscopy.
FRIDAY, APRIL 17
Just How Big is an 800 Pound Gorilla? Unveiling the Nature of Damped Lyman Alpha Systems
GUEST SPEAKER: JOHN O’MEARA, CHIEF SCIENTIST, W. M. KECK OBSERVATORY
Although quasar absorption lines systems have been part of the astronomy tool belt for nearly 50 years, some basics are still unknown, such as the mass and size of the absorbers. In this talk, I will focus on the class of absorbers most directly linked to galaxies: the Damped Lyman Alpha (DLA) systems. I will give a brief introduction to the DLA as a population and highlight some of my recent work to go back to the basics for the DLA and absorption line systems as a whole.
THURSDAY, APRIL 9
Molecular Gas Heating and Modified Dust Properties in Active Galaxies:
Growing Black Holes or Tidal Shocks?
GUEST SPEAKER: REBECCA MINSLEY, BATES COLLEGE
We investigate if and how growing super-massive black holes (SMBH) known as Active Galactic Nuclei (AGN) and gravitational interactions affect the warm molecular gas and dust of galaxies. Our analysis focuses on the morphologies and warm ISM properties of 630 galaxies at z < 0.1. We use grizy images from the Pan-STARRS survey to classify the galaxies into mergers, early mergers, and non-mergers. We use MIR spectroscopic measurements of emission from rotational H2 transitions, dust and PAH features, and silicate emission or absorption lines at 9.7 μm to study how gravitational interactions impact the warm ISM in AGN and non-AGN hosts.
We find that in AGN-hosts, the ISM is warmer, the ratios of H2 to PAHs are larger, the PAH emission line ratios and silicate strengths have a wider range of values than in non-AGN hosts. We find some statistical differences between the H2 emission of mergers and non-mergers, but those differences are less statistically significant than those between AGN and non-AGN hosts.
Our results do not establish a relation between the rate of BH growth and the warm ISM but point to highly statistically significant differences between AGN hosts and non-AGN hosts, differences that are not present with the same statistical significance between mergers and non-mergers. We speculate that the combination of triggering mechanisms, AGN orientations, and evolutionary stages that allow AGN to be classified as such in the MIR indicate that those AGN are energetically coupled on kpc scales to their host galaxies’s warm ISM. Future optical and IR, spatially resolved spectroscopic studies are best suited to characterize this connection.