J/ApJ/880/141 Arecibo 21cm obs. of sources in 5 GMC regions (Nguyen+, 2019)
Exploring the properties of warm and cold atomic hydrogen in the Taurus and
Gemini regions.
Nguyen H., Dawson J.R., Lee M.-Y., Murray C.E., Stanimirovic S., Heiles C.,
Miville-Deschenes M.-A., Petzler A.
<Astrophys. J., 880, 141 (2019)>
=2019ApJ...880..141N 2019ApJ...880..141N
ADC_Keywords: Radio sources; Molecular clouds; Radio lines
Keywords: ISM: clouds ; ISM: structure ; radio lines: ISM
Abstract:
We report Arecibo 21cm absorption-emission observations to
characterize the physical properties of neutral hydrogen (HI) in the
proximity of five giant molecular clouds (GMCs): Taurus, California,
Rosette, Mon OB1, and NGC 2264. Strong HI absorption was detected
toward all 79 background-continuum sources in the ∼60x20 square degree
region. Gaussian decompositions were performed to estimate
temperatures, optical depths, and column densities of the cold and
warm neutral medium (CNM and WNM). The properties of individual CNM
components are similar to those previously observed along random
Galactic sightlines and in the vicinity of molecular clouds,
suggesting a universality of cold HI properties. The CNM spin
temperature (Ts) histogram peaks at ∼50K. The turbulent Mach numbers
of CNM components vary widely, with a typical value of ∼4, indicating
that their motions are supersonic. About 60% of the total HI gas is
WNM, and nearly 40% of the WNM lies in thermally unstable regime
500-5000K. The observed CNM fraction is higher around GMCs than in
diffuse regions, and increases with increasing column density (NHI)
to a maximum of ∼75%. On average, the optically thin approximation
(NHI*) underestimates the total column density by ∼21%, but we
find large regional differences in the relationship between NHI and
the required correction factor, f=NHI/NHI*. We examine two
different methods (linear fit of f versus log10(NHI*) and
uniform Ts) to correct for opacity effects using emission data from
the GALFA-HI survey. We prefer the uniform Ts method because the
linear relationship does not produce convincing fits for all subregions.
Description:
We have conducted HI and OH absorption/emission measurements toward 79
extragalactic radio continuum sources in the vicinity of five giant
molecular clouds (Taurus, California, Rosette, Mon OB1, and NGC 2264)
using the Arecibo 305m radio telescope (project a2769, PI Stanimirovic).
The observations were conducted with Arecibo using the L-wide
receiver, which permits simultaneous recording of HI (centered at
1420.406MHz), and the two OH ground-state main lines at 1665.402 and
1667.359MHz, with a velocity resolution of 0.16km/s and an angular
resolution of 3.5' at these frequencies.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 77 79 79 sightlines
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See also:
VIII/65 : 1.4GHz NRAO VLA Sky Survey (NVSS) (Condon+ 1998)
VIII/76 : Leiden/Argentine/Bonn (LAB) Survey of Galactic HI (Kalberla+ 2005)
J/ApJS/97/1 : HST Quasar Absorption Line Key Project. X. (Lockman+ 1995)
J/A+A/376/861 : 1420MHz radio continuum survey of southern sky (Reich+, 2001)
J/ApJS/145/329 : Millennium Arecibo 21-cm Survey (Heiles+, 2003)
J/ApJ/793/132 : Perseus cloud sources Gaussian param. (Stanimirovic+, 2014)
J/A+A/580/A112 : THOR. The HI, OH, Recombination Line Survey (Bihr+, 2015)
J/A+A/594/A116 : HI4PI spectra and column density maps (HI4PI team+, 2016)
J/ApJS/234/2 : The GALFA-HI survey data release 2 (Peek+, 2018)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 14 A14 --- NVSS NVSS source identifier (JHHMMSS+DDMMSS)
16- 26 A11 --- Name Common source identifier
28- 28 A1 --- f_NVSS [*] *: indicates excluded from analysis
30- 31 I2 h RAh [3/7] Hour of Right Ascension (J2000)
33- 34 I2 min RAm Minute of Right Ascension (J2000)
36- 40 F5.2 s RAs Second of Right Ascension (J2000)
42 A1 --- DE- [+] Sign of Declination (J2000)
43- 44 I2 deg DEd [1/36] Degree of Declination (J2000)
46- 47 I2 arcmin DEm Arcminute of Declination (J2000)
49- 53 F5.2 arcsec DEs Arcsecond of Declination (J2000)
55- 60 F6.2 deg GLON [159.7/214.2] Galactic latitude
62- 67 F6.2 deg GLAT [-36.3/16.5] Galactic longitude
69- 72 F4.2 Jy S1.4 [0.57/8.6] NVSS 1.4GHz flux density (VIII/65)
74- 77 F4.2 K TSky [3.6/7.6] Sky brightness temperature
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 20-Jan-2021