J/ApJ/793/132 Perseus cloud sources Gaussian parameters (Stanimirovic+, 2014)
Cold and warm atomic gas around the Perseus molecular cloud.
I. Basic properties.
Stanimirovic S.Z., Murray C.E., Lee M.-Y., Heiles C., Miller J.
<Astrophys. J., 793, 132 (2014)>
=2014ApJ...793..132S 2014ApJ...793..132S (SIMBAD/NED BibCode)
ADC_Keywords: Milky Way ; Molecular clouds ; Interstellar medium ;
Radio sources ; Spectroscopy ; Line Profiles ; H I data
Keywords: ISM: clouds - ISM: structure - radio lines: ISM
Abstract:
Using the Arecibo Observatory, we have obtained neutral hydrogen (HI)
absorption and emission spectral pairs in the direction of 26
background radio continuum sources in the vicinity of the Perseus
molecular cloud. Strong absorption lines were detected in all cases,
allowing us to estimate spin temperature (Ts) and optical depth for
107 individual Gaussian components along these lines of sight. Basic
properties of individual H I clouds (spin temperature, optical depth,
and the column density of the cold and warm neutral medium (CNM and
WNM), respectively) in and around Perseus are very similar to those
found for random interstellar lines of sight sampled by the Millennium
H I survey. This suggests that the neutral gas found in and around
molecular clouds is not atypical. However, lines of sight in the
vicinity of Perseus have, on average, a higher total H I column
density and the CNM fraction, suggesting an enhanced amount of cold
H I relative to an average interstellar field. Our estimated optical
depth and spin temperature are in stark contrast with the recent
attempt at using Planck data to estimate properties of the optically
thick H I. Only ∼15% of lines of sight in our study have a column
density weighted average spin temperature lower than 50 K, in
comparison with ≳85% of Planck's sky coverage. The observed CNM
fraction is inversely proportional to the optical depth weighted
average spin temperature, in excellent agreement with the recent
numerical simulations by Kim et al. (2014ApJ...786...64K 2014ApJ...786...64K). While the
CNM fraction is, on average, higher around Perseus relative to a
random interstellar field, it is generally low, between 10%-50%. This
suggests that extended WNM envelopes around molecular clouds and/or
significant mixing of CNM and WNM throughout molecular clouds are
present and should be considered in the models of molecule and star
formation. Our detailed comparison of H I absorption with CO emission
spectra shows that only 3 of the 26 directions are clear candidates
for probing the CO-dark gas as they have N(H I)>1021/cm2 yet no
detectable CO emission.
Description:
We selected 27 radio continuum sources from the NVSS survey (Condon et al.
1998AJ....115.1693C 1998AJ....115.1693C, Cat. VIII/65), located over an area of roughly
500 deg2 centered on Perseus with flux densities at 1.4 GHz greater
than 0.8 Jy. The observations were conducted with the Arecibo
telescope. Using the L-wide receiver, we simultaneously recorded
spectra centered at 1420 MHz and the two OH main lines (1665 and 1667 MHz),
achieving a velocity resolution of 0.16 km/s. We sampled
simultaneously two linearly polarized channels performing both auto-
and cross-correlations with the Arecibo's three-level "interim"
digital correlator. The Arecibo telescope has an angular resolution of
3.5' at these frequencies. As shown by Heiles & Troland (2003,
J/ApJS/145/329) in their Millennium H I survey, Arecibo can accurately
measure H I absorption lines for strong sources (flux density larger
than ∼1 Jy).
Objects:
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RA (ICRS) DE Designation(s)
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03 35.0 +31 13 Perseus molecular cloud = NAME PMC
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 45 27 Source List
table2.dat 81 182 Gaussian Parameters Associated with All CNM and
WNM Components for Each Source from Erratum,
2015, ApJ, 799, 239
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See also:
VIII/65 : 1.4GHz NRAO VLA Sky Survey (NVSS) (Condon+ 1998)
J/ApJS/145/329 : Millennium Arecibo 21-cm Survey (Heiles+, 2003)
J/ApJ/638/293 : 1.1mm sources in the Perseus Molecular Cloud (Enoch+, 2006)
J/ApJ/646/1009 : Structures of dust in Perseus molecular cloud (Kirk+, 2006)
J/ApJ/668/1042 : Dense cores in Perseus molecular cloud (Kirk+, 2007)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 9 A9 --- ID Source identifier
11- 12 I2 h RAh Hour of Right Ascension (J2000)
14- 15 I2 min RAm Minute of Right Ascension (J2000)
17- 21 F5.2 s RAs Second of Right Ascension (J2000)
23- 24 I2 deg DEd Degree of Declination (J2000)
26- 27 I2 arcmin DEm Arcminute of Declination (J2000)
29- 33 F5.2 arcsec DEs Arcsecond Declination (J2000)
35- 37 F3.1 Jy Tsrc NVSS flux density at 1.4GHz
39- 43 F5.3 K Tsky Sky temperature
45 A1 --- Note [a] Note on 4C+32.14 (1)
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Note (1): a = One source that we exclude from analysis is 4C+32.14 which has a
highly saturated absorption profile and therefore all fitted parameters are
highly uncertain for this source.
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 9 A9 --- ID Source identifier
11- 15 F5.2 K TB Brightness temperature (1)
17- 20 F4.2 K e_TB ? Uncertainty in TB
22- 27 F6.2 km/s VLSR Central velocity of fitted Gaussian
function (2)
29- 32 F4.2 km/s e_VLSR ? Uncertainty in VLSR
34- 38 F5.2 km/s DelV FWHM of fitted Gaussian function (2)
40- 43 F4.2 km/s e_DelV ? Uncertainty in DelV
45- 49 F5.3 --- tau Peak optical depth (3)
51- 55 F5.3 --- e_tau ? Uncertainty in tau
57- 60 I4 K Ts Spin temperature (4)
62- 64 I3 K e_Ts ? Uncertainty in Ts
66- 71 I6 K Tkmax Maximum kinetic temperature (5)
73- 77 F5.2 10+20/cm2 NHI H I column density (6)
79- 81 F3.1 --- ForO [0/8] WNM or CNM code (7)
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Note (1): For emission components: equal to fitted peak brightness temperature
of each Gaussian function, with errors from the fit. For absorption
components: equal to Ts*(1-e-tau), quoted without error.
Note (2): To both emission and absorption spectra, with errors from the fits.
Note (3): For absorption components: equal to the fitted peak optical depth of
each Gaussian function, with error from the fit. For emission
components: equal to the 1σ noise level in absorption at the
central velocity of the emission component, quoted without error.
Note (4): For absorption components: equal to the result from the total fit to
the emission profile, with errors estimated from varying the possible
order of CNM components along the line of sight (see Section 3). For
emission components: equal to TB/tau, quoted without error.
Note (5): Equal to 21.86*DelV2 (Heiles & Troland 2003ApJ...586.1067H 2003ApJ...586.1067H),
quoted without error.
Note (6): For absorption components: equal to 1.064467*0.0183*Ts*tau*DelV.
For emission components: equal to 1.064467*0.0183*TB*DelV.
Note (7): WNM or CNM code as follows:
F = fraction of each WNM component lying in front of CNM clouds (for
emission components only, equal to 0.0, 0.5 or 1.0);
O = order of CNM clouds along the line of sight (for absorption components
only, equal to integer values).
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History:
From electronic version of the journal
References:
Lee et al., Paper II, 2015ApJ...809...56L 2015ApJ...809...56L
(End) Prepared by [AAS], Tiphaine Pouvreau [CDS] 20-Apr-2017