Wednesday, May 29, 2013

Barger, K.A.; Haffner, L.M.; Bland-Hawthorn, J.; Warm Ionized Gas Revealed in the Magellanic Bridge Tidal Remnant: Constraining the Baryon Content and the Escaping Ionizing Photons around Dwarf Galaxies

Warm Ionized Gas Revealed in the Magellanic Bridge Tidal Remnant: Constraining the Baryon Content and the Escaping Ionizing Photons around Dwarf Galaxies
This paper deals with the "bridge" (a remnant of tidal interaction) between the Large Magellanic Cloud (LMC) and the Small Magellanic Cloud (SMC). The bridge in this case is a region of ionized gas that stretches between the two clouds. In the paper they present the results of an Hα survey which they did using the Wisconsin Hα Mapper (WHAM) observatory. Some of the interesting results that they got were that the ionization fraction was higher in the bridge than in the SMC tail (36 − 52% compared to 5 − 24%).

They also found that the amount of ionizing radiation from the Milky Way and from extragalactic sources is insufficient to ionize the bridge. Thus they conclude that there needs to be a small amount of ionizing radiation that leaks out of the SMC and the LMC (about 4-5%). This has implications about how dwarf galaxies affect their surroundings and how much they affect their surroundings.
Figure 1 from Barger et al. The contours show column density of H I.
The contours are at 10, 20, 35, and 50 x 1019 cm−2.
I thought that this was a good paper that included a good discussion about how they made their observations and how they had to work with their data in order to subtract off atmospheric and other interference. This is relevant to me because in my simulations I am trying to reproduce some of these features observed here so I need to know what people are observing, how they are observing it and what is possible to observe so that I can fit that with my models.

Tuesday, May 14, 2013

McClure-Griffiths, N. M.; et al.;Atomic Hydrogen in a Galactic Center Outflow

Atomic Hydrogen in a Galactic Center Outflow
[arXiv:1304.7538v1, pdf, First author, second, third, fourth]
This is part of the results from a survey where the authors found several cool, T < 4000 K, H I clouds in a definite pattern around the Galactic Center. The distribution and kinematics of the cloud implied that they were created from a starburst located at the center of the galaxy that has been affecting the galaxy for the past ∼ 2 × 106 years.

They did this by calculating the local standard of rest (LSR) velocities for the cloud centers and then using a simulation that calculated the effect on clouds with a random distribution of velocities and comparing to their observations they determined that the observed clouds did not have kinematics similar to galactic rotation but have a distribution that implies ballistic motion away from the galactic center (see figure below).

They also give a bound on the velocity of the stellar winds that can create this type of distribution  "The [Kolmogorov-Smirnov] test implies that wind velocities greater than 270 km s−1 and less than 150 km s−1 are not consistent with the observed cloud velocities."

They conclude that these clouds are the remnants of a superbubble which was created by a starburst at the center of the Milky Way. They also mention survivability and life spans of the clouds. They provide some bounds to the life spans. They also rely heavily on the simulations of Jackie Cooper to reach some conclusions about the environment of the wind and clouds.