Monday 11/12/12

Title: Present-day Galactic Evolution: Low-metallicity, Warm, Ionized Gas Inflow Associated with High-Velocity Cloud Complex A
Authors: Barger, Kathleen A.; Haffner, Lawrence M.; Wakker, Bart P.; Hill, Alex S.; Madsen, Greg J.; Duncan, Allison K.
Publication: eprint arXiv:1211.1973
Publication Date: 11/2012
Origin: ARXIV
Keywords: Astrophysics – Galaxy Astrophysics
Comment: Accepted to Astrophysical Journal
Bibliographic Code: 2012arXiv1211.1973B

Abstract

The high-velocity cloud (HVC) Complex A is a probe of the physical conditions in the Galactic halo. The kinematics, morphology, distance, and metallicity of Complex A indicate that it represents new material that is accreting onto the Galaxy. We present Wisconsin H-alpha Mapper (WHAM) kinematically resolved observations of Complex A over the velocity range of -250 to -50 km/s in the local standard of rest reference frame. These observations include the first full H-alpha intensity map of Complex A across (l, b) = (124, 18) to (171, 53) and deep targeted observations in H-alpha, [S II]6716, [N II]6584, and [O I]6300 towards regions with high H I column densities, background quasars, and stars. The H-alpha data imply that the masses of neutral and ionized material in the cloud are similar, both being greater than a million solar masses. We find that the Bland-Hawthorn & Maloney (1999, 2001) model for the intensity of the ionizing radiation near the Milky Way is consistent with the known distance of the high-latitude part of Complex A and an assumed cloud geometry that puts the lower-latitude parts of the cloud at a distance of 7 to 8 kpc. This compatibility implies a 5% ionizing photon escape fraction from the Galactic disk. We also provide the nitrogen and sulfur upper abundance solutions for a series of temperatures, metallicities, and cloud configurations for purely photoionized gas; these solutions are consistent with the sub-solar abundances found by previous studies, especially for temperatures above 10,000 K or for gas with a high fraction of singly-ionized nitrogen and sulfur.

Title: Modes of star formation from Herschel
Authors: Testi, Leonardo; Bressert, Eli; Longmore, S.
Publication: eprint arXiv:1211.2170
Publication Date: 11/2012
Origin: ARXIV
Keywords: Astrophysics – Galaxy Astrophysics
Comment: To appear in the IAUS292 proceedings
Bibliographic Code: 2012arXiv1211.2170T

Abstract

We summarize some of the results obtained from Herschel surveys of the nearby star forming regions and the Galactic plane. We show that in the nearby star forming regions the starless core spatial surface density distribution is very similar to that of the young stellar objects. This, taken together with the similarity between the core mass function and the initial mass function for stars and the relationship between the amount of dense gas and star formation rate, suggest that the cloud fragmentation process defines the global outcome of star formation. This "simple" view of star formation may not hold on all scales. In particular dynamical interactions are expected to become important at the conditions required to form young massive clusters. We describe the successes of a simple criterion to identify young massive cluster precursors in our Galaxy based on (sub-)millimetre wide area surveys. We further show that in the location of our Galaxy where the best candidate for a precursor of a young massive cluster is found, the "simple" scaling relationship between dense gas and star formation rate appear to break down. We suggest that in regions where the conditions approach those of the central molecular zone of our Galaxy it may be necessary to revise the scaling laws for star formation.

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