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Post Info TOPIC: North Polar Spur
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RE: North Polar Spur
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Title: On the distance to the North Polar Spur and the local CO-H2 factor
Author: R. Lallement, S. Snowden, K.D. Kuntz, T.M. Dame, D. Koutroumpa, I. Grenier, J.M. Casandjian

Most models identify the X-ray bright North Polar Spur (NPS) with a hot interstellar (IS) bubble in the Sco-Cen star-forming region at 130 pc. An opposite view considers the NPS as a distant structure associated with Galactic nuclear outflows. Constraints on the NPS distance can be obtained by comparing the foreground IS gas column inferred from X-ray absorption to the distribution of gas and dust along the line of sight. Absorbing columns towards shadowing molecular clouds simultaneously constrain the CO-H2 conversion factor. We derived the columns of X-ray absorbing matter NH(abs) from spectral fitting of dedicated XMM-Newton observations towards the NPS southern terminus (l=29°, b=+5 to +11°).

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Title: Suzaku Observations of the North Polar Spur: Evidence for Nitrogen Enhancement
Authors: Eric D. Miller, Hiroshi Tsunemi, Mark W. Bautz, Dan McCammon, Ryuichi Fujimoto, John P. Hughes, Satoru Katsuda, Motohide Kokubun, Kazuhisa Mitsuda, F. Scott Porter, Yoh Takei, Yohko Tsuboi, Noriko Y. Yamasaki

We present observations of the North Polar Spur (NPS) using the X-ray Imaging Spectrometer (XIS) aboard the Suzaku X-ray satellite. The NPS is a large region of enhanced soft X-ray and radio emission projected above the plane of the Galaxy, likely produced by a series of supernovae and stellar winds from the nearby Sco-Cen OB association. The exceptional sensitivity and spectral resolution of the XIS below 1 keV allow unprecedented probing of low-energy spectral lines, including CVI (0.37 keV) and NVII (0.50 keV), and we have detected highly-ionised nitrogen toward the NPS for the first time. For this single pointing toward the brightest 3/4 keV emission (l = 26.8 deg, b = +22.0 deg), the best-fit NPS emission model implies a hot (kT ~ 0.3 keV), collisional ionisation equilibrium (CIE) plasma with depleted C, O, Ne, Mg, and Fe abundances of less than 0.5 solar, but an enhanced N abundance, with N/O = 4.0 +0.4,-0.5 times solar. The temperature and total thermal energy of the gas suggest heating by one or more supernovae, while the enhanced nitrogen abundance is best explained by enrichment from stellar material that has been processed by the CNO cycle. Due to the time required to develop AGB stars, we conclude that this N/O enhancement cannot be caused by the Sco-Cen OB association, but may result from a previous enrichment episode in the solar neighbourhood.

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