Pizza Lunch: Charles Steinhardt: Is Hierarchical Merging Broken?
Aug 29 @ 12:30 pm – 1:30 pm
Pizza Lunch: Charles Steinhardt: Is Hierarchical Merging Broken? @ AY 119

Title: Is Hierarchical Merging Broken?

Charles Steinhardt (Caltech, DARK)

I will describe two sharp puzzles suggesting a possible mismatch
between the current hierarchical merging paradigm and observations of
evolving galaxies.  Current models predict that the z ~ 4-8 universe
should be a time in which the most massive galaxies are transitioning from
their initial halo assembly to the later baryonic evolution seen in
star-forming galaxies and quasars.  Instead, massive galaxies appear to
exist impossibly early, before their halos should even have been able to
assemble.  Further, small halos should have generally formed earlier than
larger halos, yet the observed hierarchy in galaxy formation is inverted,
with more massive galaxies completing their growth earlier.  After
describing these puzzles, we will consider hierarchical merging is truly
inconsistent with observation or whether other explanations might be more

Colloquium Thesis Proposal: Lauren Kahre
Sep 9 @ 3:15 pm – 4:15 pm
Colloquium Thesis Proposal: Lauren Kahre @ Biology Annex 102

Extinction mapping with LEGUS

Lauren Kahre

The study of star formation and galaxy evolution in nearby galaxies depends on obtaining accurate stellar photometry in those galaxies. However, dust in the galaxies hinders our ability to obtain accurate stellar photometry, particularly in star-forming galaxies that have the highest concentrations of dust. This proposal presents a thesis project to develop a method for generating extragalactic extinction maps using photometry of massive stars from the Hubble Space Telescope. This photometry spans nearly 50 galaxies observed by the Legacy Extragalactic Ultraviolet Survey (LEGUS). The derived extinction maps can be used to correct other stars and Halpha maps (from the Halpha LEGUS) for extinction, and will be used to constrain changes in the dust-to-gas ratio across the galaxy sample and in different star formation rate, metallicity and morphological environments. Previous studies have found links between galaxy metallicty and the dust-to-gas mass ratio. The relationship between these two quantities can be used to constrain chemical evolution models.

Selected galaxies will also be compared to IR-derived dust maps for comparison to recent M31 results from Dalcanton et al. (2015) which found a minimum factor of 2 inconsistency between their extinction-derived maps and emission-derived maps from Draine et al. (2014).

Pizza Lunch: Paul Hardersen
Sep 12 @ 12:30 pm – 1:30 pm
Pizza Lunch: Paul Hardersen @ AY 119

Title: Six orders of magnitude: Solar System studies of asteroids and the Sun

Paul Hardersen (U. of N. Dakota)

Pizza Lunch: Reta Beebe
Sep 19 @ 12:30 pm – 1:30 pm
Pizza Lunch: Reta Beebe @ AY 119

Title: JUNO

Reta Beebe

A .pdf of the talk can be found here.



Colloquium Thesis Proposal: Ethan Dederick
Sep 20 @ 3:00 pm – 4:00 pm
Colloquium Thesis Proposal: Ethan Dederick @ Science Hall 310

Utilizing Planetary Oscillations to Constrain the Interior Structure of the Jovian Planets

Ethan Dederick

Seismology has been the premier tool of study for understanding the
interior structure of the Earth, the Sun, and even other stars. Yet in this
thesis proposal, we wish to utilize these tools to understand the interior
structure of the Jovian planets, Saturn in particular. Recent observations
of spiral density structures in Saturn’s rings caused by its oscillations
have provided insight into which modes exist within Saturn and at what
frequencies. Utilizing these frequencies to compare to probable mode can-
didates calculated from Saturn models will also us to ascertain the interior
profiles of state variables such as density, sound speed, rotation, etc. Using
these profiles in a Saturn model, coupled with tweaking the interior struc-
ture of the model, i.e. the inclusion of stably stratified regions, should
allow us to explain which modes are responsible for the density structures
in the rings, as well as predict where to look to find more such structures.
In doing so, we will not only have a much greater understanding of Sat-
urn’s interior structure, but will have constructed a method that can also
be applied to Jupiter once observations of its mode frequencies become
available. In addition, we seek to explain if moist convection on Jupiter is
responsible for exciting its modes. We aim to do this by modeling Jupiter
as a 2D harmonic oscillator. By creating a resonance between moist con-
vective storms and Jovian modes, we hope to match the expected mode
energies and surface displacements of Jupiter’s oscillations.

Pizza Lunch: Keith Hawkins (Cambridge/Columbia)
Sep 26 @ 12:30 pm – 1:30 pm
Pizza Lunch: Keith Hawkins (Cambridge/Columbia) @ AY 119

Title: TBD

Keith Hawkins (Columbia/Cambridge)


Pizza Lunch: Laura Mayorga
Oct 10 @ 12:30 pm – 1:30 pm
Pizza Lunch: Laura Mayorga @ AY 119

Title: Proto-BD disks and the Kavli Summer Program in Astrophysics

Laura Mayorga


Pizza Lunch: Caitlin Doughty
Oct 17 @ 12:30 pm – 1:30 pm
Pizza Lunch: Caitlin Doughty @ AY 119

Title: Probing the z~6 UVB with Aligned Metal Absorbers

Caitlin Doughty


Pizza Lunch: Drew Chojnowski
Nov 14 @ 12:30 pm – 1:30 pm
Pizza Lunch: Drew Chojnowski @ AY 119

Title: H-band Spectral Variability of Classical Be Stars

Drew Chojnowski