2006/09/21 by David M. Meyer, J. T. Lauroesch, Carl Heiles +3 · 52 citations
Physics and Astronomy · #Absorption (acoustics) #Astronomy #Astrophysical Phenomena and Observations #Astrophysics #Astrophysics and Star Formation Studies #Bubble #Cloud computing #Galaxy #Interstellar medium #Line (geometry) #Line-of-sight #Local Bubble #Meteorology #Optics #Physics #Spectroscopy #Stars #Stellar, planetary, and galactic studies #Turbulence #astro-ph
paper · pdf · doi:10.1086/508658
published in The Astrophysical Journal 650(1), L67-L70 (IOP Publishing) · 11 pages, 3 figures, accepted for publication in ApJ Letters
arxiv created 2006/09/21 · openalex publication_date 2006/09/21 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
The high-latitude Galactic H I cloud toward the extragalactic radio source 3C 225 is characterized by very narrow 21 cm emission and absorption indicative of a very low H I spin temperature of about 20 K. Through high-resolution optical spectroscopy, we report the detection of strong, very narrow Na I absorption corresponding to this cloud toward a number of nearby stars. Assuming that the turbulent H I and Na I motions are similar, we derive a cloud temperature of 20 K (in complete agreement with the 21 cm results) and a line-of-sight turbulent velocity of 0.37 ± 0.08 km s -1 from a comparison of the H I and Na I absorption line widths. We also place a firm upper limit of 45 pc on the distance of the cloud, which situates it well inside the Local Bubble in this direction and makes it the nearest known cold diffuse cloud discovered to date.