THE LOCAL LEO COLD CLOUD AND NEW LIMITS ON A LOCAL HOT BUBBLE
- Department of Astronomy, Columbia University, Pupin Physics Laboratories, 550 West 120th Street, New York, NY 10027 (United States)
- Department of Astronomy, University of California, Berkeley, Berkeley, CA 94720 (United States)
- Center for Interdisciplinary Exploration and Research in Astrophysics, Department of Physics and Astronomy, Northwestern University, Evanston, IL 60208 (United States)
We present a multi-wavelength study of the local Leo cold cloud (LLCC), a very nearby, very cold cloud in the interstellar medium (ISM). Through stellar absorption studies we find that the LLCC is between 11.3 pc and 24.3 pc away, making it the closest known cold neutral medium cloud and well within the boundaries of the local cavity. Observations of the cloud in the 21 cm H I line reveal that the LLCC is very cold, with temperatures ranging from 15 K to 30 K, and is best fit with a model composed of two colliding components. The cloud has associated 100 {mu}m thermal dust emission, pointing to a somewhat low dust-to-gas ratio of 48 x10{sup -22} MJy sr{sup -1} cm{sup 2}. We find that the LLCC is too far away to be generated by the collision among the nearby complex of local interstellar clouds but that the small relative velocities indicate that the LLCC is somehow related to these clouds. We use the LLCC to conduct a shadowing experiment in 1/4 keV X-rays, allowing us to differentiate between different possible origins for the observed soft X-ray background (SXRB). We find that a local hot bubble model alone cannot account for the low-latitude SXRB, but that isotropic emission from solar wind charge exchange (SWCX) does reproduce our data. In a combined local hot bubble and SWCX scenario, we rule out emission from a local hot bubble with an 1/4 keV emissivity greater than 1.1 Snowdens pc{sup -1} at 3{sigma}, four times lower than previous estimates. This result dramatically changes our perspective on our local ISM.
- OSTI ID:
- 21578376
- Journal Information:
- Astrophysical Journal, Vol. 735, Issue 2; Other Information: DOI: 10.1088/0004-637X/735/2/129; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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