Astronomy Colloquium

In the last decade, there has been tremendous progress in understanding the overall evolution of the interstellar gas in galaxies and the processes leading to stars (and planetary system formation). From observations of nearby galaxies we gain insight into star formation processes, while from comprehensive surveys out to redshift ~ 6 (and some detections at z > 10), we now have a quantitative picture of the early cosmic evolution of interstellar gas. Despite the great observational progress, there is a diversity of understanding. I will highlight those issues where recognizing a few paradoxes can lead to surprising but fundamental understanding; e.g. the role of spiral structure, the trigger of star cluster formation, the lifetimes of molecular clouds and the role of atomic gas. And, lastly, we will have some open discussion of Pop III star formation at redshift 20 – 30. The talk will be interactive.

We used NASA's New Horizons spacecraft to measure the cosmic optical background (COB) intensity integrated over 0.4 ≲ λ ≲ 0.9 μm. The survey comprises 16 high Galactic-latitude fields.  Images were obtained with the LORRI camera when New Horizons was 57 AU distant from the Sun. As such, the sky intensity measurements were unaffected by zodiacal light, which strongly interferes with COB measurements attempted from the inner solar system. The survey yields a highly significant detection (6.8σ) of the COB at 11.2 ± 1.7 (nW m−2 sr−1. The estimated integrated intensity from background galaxies, 8.2 ± 1.2 nW m−2 sr−1, can account for the great majority of this signal. The rest of the COB signal is formally classified as anomalous intensity but is not significantly different from zero. The simplest interpretation is that the COB is completely due to galaxies.