Point/Counterpoint: Blanks Fired

The following post is part of a series meant to conduct and spark a friendly philosophical discussion of broadly visible themes. It is not our intent to single out any one group or person, and by no means should the points expressed herein be regarded as any kind of attack on either the reenacting community or academia. [excerpt

Point/Counterpoint: Insidious Cycle

Heather: In our last post, Bryan and I explored the unique challenges that the reenacting hobby poses to the interpretation and public understanding of the American Civil War. In it, we touched on just a few of the many motivations that inspire individuals to reenact. As we continue our Point/Counterpoint series below, we look to explore the relationship of the reenacting hobby with a particularly complex and problematic ideology–the Lost Cause. [excerpt

Cooling and Clusters: When Is Heating Needed?

There are (at least) two unsolved problems concerning the current state of the thermal gas in clusters of galaxies. The first is identifying the source of the heating which offsets cooling in the centers of clusters with short cooling times (the ``cooling flow'' problem). The second is understanding the mechanism which boosts the entropy in cluster and group gas. Since both of these problems involve an unknown source of heating it is tempting to identify them with the same process, particular since AGN heating is observed to be operating at some level in a sample of well-observed ``cooling flow'' clusters. Here we show, using numerical simulations of cluster formation, that much of the gas ending up in clusters cools at high redshift and so the heating is also needed at high-redshift, well before the cluster forms. This indicates that the same process operating to solve the cooling flow problem may not also resolve the cluster entropy problem.Comment: 10 pages, 5 figures, published in Philosophical Transactions A (Royal Society

Point/Counterpoint: Anchoring Historical Memory

Wednesday, November 19, 2014 saw citizens and students of Gettysburg crowd into the Majestic Theater for the fifty-third annual Robert Fortenbaugh Memorial Lecture. The audience listened attentively as Dr. Nina Silber, a renowned historian of the American Civil War, explored the nuanced application of the memory of Abraham Lincoln during the 1930s and ‘40s, especially as associated with the figure of Franklin Delano Roosevelt. [excerpt

Confusion of Diffuse Objects in the X-ray Sky

Most of the baryons in the present-day universe are thought to reside in intergalactic space at temperatures of 10^5-10^7 K. X-ray emission from these baryons contributes a modest (~10%) fraction of the ~ 1 keV background whose prominence within the large-scale cosmic web depends on the amount of non-gravitational energy injected into intergalactic space by supernovae and AGNs. Here we show that the virialized regions of groups and clusters cover over a third of the sky, creating a source-confusion problem that may hinder X-ray searches for individual intercluster filaments and contaminate observations of distant groups.Comment: accepted to ApJ Letters, 7 pages, 3 figure