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24 April 2024 |
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Calcium H & K and sodium D absorption induced by the interstellar and circumgalactic media of the Milky Way | | Maria Murga
; Guangtun Zhu
; Brice Ménard
; Ting-Wen Lan
; | | Date: |
9 Mar 2015 | | Abstract: | We map out calcium II & sodium I absorption (Fraunhofer H, K & D lines)
induced by both the interstellar medium and the circumgalactic medium of the
Milky Way. Our measurements cover more than $9000$ deg$^2$ and make use of
about $300,000$ extragalactic spectra from the Sloan Digital Sky Survey. We
present absorption maps for these two species and then compare their
distributions to those of neutral hydrogen and dust. We show that the abundance
of Na I with respect to neutral hydrogen stays roughly constant in different
environments, while that of Ca II decreases with hydrogen column density.
Studying how these tracers vary as a function of velocity, we show that, on
average, the N(Na I)/N(Ca II) ratio decreases at higher velocity with respect
to the local standard of rest, similar to the local Routly-Spitzer effect but
seen on Galactic scale. We show that it is likely caused by higher gas/dust
density at lower velocity. Finally, we show that Galactic Ca II and Na I
absorption needs to be taken into account for precision photometry and, more
importantly, for photometric redshift estimation with star forming galaxies.
Our maps of Ca II and Na I absorption are publicly available. | | Source: | arXiv, 1503.2697 | | Services: | Forum | Review | PDF | Favorites | |
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