Two Talks! Speakers: Joel Leja (Harvard) And Andrew Vanderburg (Harvard)

Monday October 31, 2016 12:05 pm

The Next Step in SED Fitting: Accurate Physical Properties from Broadband Photometry for 129 Nearby Galaxies
Speaker: Joel Leja, Harvard

We present a new model framework for fitting the broadband photometry of galaxies, based on the Flexible Stellar Populations Synthesis (FSPS) code. Our default model, Prospector-Gold, includes dust attenuation and re-radiation, a flexible attenuation curve, nebular emission, stellar metallicity, and a 6-component non-parametric star formation history. The parameter space is sampled via MCMC techniques within the Prospector inference framework to account for the considerable degeneracies inherent in fitting broadband photometry. A common concern with modeling stellar populations is that different models predict significant differences in parameters of interest, such as star formation rates, stellar masses, and dust attenuation, while fitting the observed photometry equally well. We address this issue by modeling a sample of 129 local galaxies with UV to far-IR photometry and high quality aperture-matched spectra. We test the accuracy of the model fit, which is fit only to the broadband photometry, by comparing the predicted strength of key diagnostic spectral features, such as L(Hα) and the 4000 Angstrom break, to the measured values from the spectra. Our model predicts the Hα luminosities with a scatter of ∼0.16 dex and an offset of 0.08 dex across a wide range of morphological types and stellar masses. This agreement is remarkable, as the Hα luminosity is dependent on accurate star formation rates, dust attenuation, and stellar metallicities. This small scatter implies that galaxy star formation rates do not strongly vary over 100 Myr timescales. The model also accurately predicts the dust-sensitive Balmer decrements, spectroscopic stellar metallicities, and the stellar absorption features Dn4000 and Hδ, which are sensitive to the age of the stellar population. To our knowledge these are the first models that provide star formation rates from broadband photometry with uncertainties <50%.


The Past, Present, and Future of Planetary Systems
Speaker: Andrew Vanderburg, Harvard

We are using the Kepler space telescope in its new K2 mission to study the past, present, and future of planetary systems — that is, the history of how planets might form and migrate, their present-day characteristics, and the ultimate fate of planetary systems. I will discuss what we have learned, in particular from the discovery of a hot Jupiter with close planetary companions, planets orbiting nearby bright stars, and a disintegrating minor planet transiting a white dwarf.