Open AccessA multiwavelength investigation of the temperature of the cold neutral medium
Author(s) -
Roy Nirupam,
Chengalur Jayaram N.,
Srianand Raghunathan
Publication year - 2006
Publication title -
monthly notices of the royal astronomical society: letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.067
H-Index - 122
eISSN - 1745-3933
pISSN - 1745-3925
DOI - 10.1111/j.1745-3933.2005.00114.x
Subject(s) - physics , astrophysics , stars , mean kinetic temperature , ionization , kinetic energy , line of sight , ultraviolet , ion , optics , quantum mechanics
We present measurements of the H i spin temperatures ( T s ) of the cold neutral medium (CNM) towards radio sources that are closely aligned with stars for which published H 2 ortho–para temperatures ( T 01 ) are available from ultraviolet (UV) observations. Our sample consists of 18 radio sources close to 16 nearby stars. The transverse separation of the lines of sight of the corresponding UV and radio observations varies from 0.1 to 12.0 pc at the distance of the star. The UV measurements do not have velocity information, so we use the velocities of low ionization species (e.g. Na i /K i /C i ) observed towards these same stars to make a plausible identification of the CNM corresponding to the H 2 absorption. We then find that T 01 and T s match within observational uncertainties for lines of sight with H 2 column density above 10 15.8 cm −2 , but deviate from each other below this threshold. This is consistent with the expectation that in the CNM T s tracks the kinetic temperature due to collisions and that T 01 is driven towards the kinetic temperature by proton exchange reactions.