Friday, January 11, 2013
Astronomy Tea Talk
Sodium Absorption as a Tracer of Dust Extinction, and much more, using SDSS
Dovi Poznanski, Tel Aviv University
Dust extinction is the leading systematic uncertainty in most cosmological and astrophysical measurements. By both absorbing and reddening radiation, it impedes distance and color measurements, as well as biasing any method that relies on statistics of samples. In a recent publication, we took about a million spectra from the Sloan Digital Sky Survey (SDSS), to derive the relation between extinction and sodium absorption. Every object in SDSS is observed through the gas and dust in the Milky Way, but a single spectrum does not offer the signal to noise to recover this imprint. We stacked every tens of thousands of spectra with a similar expected extinction (as derived from the maps of Schlegel et al. 1998). Our approach allowed us to see beyond the ample noise and original signal from every source, recovering just the imprint of the Galaxy's ISM with very high signal-to-noise. We showed that there is indeed a strong correlation between the sodium lines and extinction, and that high resolution spectra have the potential to leverage this correlation well. In this talk I will describe this result, as well as our ongoing effort to improve the method and extend its reach, so as to ultimately derive a high-resolution and high-signal-to-noise spectrum of the ISM as a function of direction over most of the northern sky. This will enable us to measure the multitude of correlations in the ISM between metal absorptions, hydrogen, dust, and the elusive carriers of the diffuse interstellar bands.