J/ApJS/145/329 Millennium Arecibo 21-cm Survey (Heiles+, 2003)
The Millennium Arecibo 21 centimeter Absorption-Line Survey.
I. Techniques and gaussian fits.
Heiles C., Troland T.H.
<Astrophys. J. Suppl. Ser. 145, 329 (2003)>
=2003ApJS..145..329H 2003ApJS..145..329H
ADC_Keywords: Radio lines ; Interstellar medium ; H I data
Keywords: ISM: atoms - ISM: structure - radio lines: ISM
Abstract:
We review the theory of measuring spectral lines in emission/
absorption observations and apply it to a new survey of the 21-cm line
against 79 continuum sources. We develop an observing technique and
least-squares procedure to determine the opacity profile, the expected
emission profile, and their uncertainty profiles. We discuss the
radiative transfer for the two-component interstellar HI gas and use
Gaussian components, separate ones for the warm and cold neutral media
(WNM and CNM), as a practical implementation of a simple but
physically correct model that successfully treats both simple and
complicated profiles.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
sources.dat 40 79 Sources parameters
table1.dat 121 161792 Derived spectra for all sources
table2.dat 114 374 Table of Gaussian Fit Parameters
--------------------------------------------------------------------------------
Byte-by-byte Description of file: sources.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 9 A9 --- Name Source name
14- 21 F8.4 deg RAdeg Right Ascension in decimal hours (B1950)
23- 30 F8.4 deg DEdeg Declination in decimal degrees (B1950)
34- 40 F7.3 K Ta Source antenna temperature
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 9 A9 --- Name Source name
11- 23 E13.6 km/s ChVel Channel velocity
25- 37 E13.6 K EProf Expected profile (antenna temperature at
source position) (1)
39- 51 E13.6 K/arcmin dTa/da Derivative of Ta with respect to right
ascension in Kelvins per great-circle
arcminute
53- 65 E13.6 K/arcmin dTa/dd Derivative of Ta with respect to
declination in Kelvins per arcminute
67- 79 E13.6 K/arcmin2 d2Ta/da2 ?=-9999. Second derivative of Ta with
respect to right ascension in Kelvins per
arcminute2 (2)
81- 93 E13.6 K/arcmin2 d2Ta/dadd ?=-9999. Second derivative of Ta with
respect to right ascension and declination
in Kelvins per arcminute2 (2)
95-107 E13.6 K/arcmin2 d2Ta/dd2 ?=-9999. Second derivative of Ta with
respect to declination in Kelvins per
arcminute2 (2)
109-121 E13.6 --- OProf The opacity profile (exp-tau)
--------------------------------------------------------------------------------
Note (1): This is Stokes I, which is TWICE the conventionally defined
brightness temperature.
Note (2): -9999 = Observed with the Z4 pattern.
All others observed with the Z16 pattern
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 6 F6.2 K Tpeak Component intrinsic peak brightness
temperature (1)
8- 13 F6.2 K e_Tpeak ? Error in Tpeak
15- 21 F7.3 --- tau ? Component central opacity (2)
23- 29 F7.3 --- e_tau ? Error in tau
31- 35 F5.1 km/s VLSR Central Local Standard of Rest velocity
37- 39 F3.1 km/s e_VLSR Error in VLSR
41- 46 F6.2 km/s DelV Gaussian Full-Width of Half-Maximum
48- 52 F5.2 km/s e_DelV Error in DelV
54- 60 F7.2 K Tspin ? Spin temperature (3)
62- 67 F6.2 K e_Tspin ? Error in Tspin
69- 74 I6 K Tkmax Component kinetic temperature (4)
76- 80 F5.2 10+20cm-2 NHI The H I column density (5)
82 I1 --- CNM ? Cold neutral medium (CNM) component
order (6)
84- 87 F4.2 --- Frac ? Warm neutral medium (WNM) component
weighted fraction average (6)
89- 92 F4.2 --- e_Frac ? Error in Frac
94- 98 F5.1 deg GLON Galactic longitude
100-104 F5.1 deg GLAT Galactic latitude
106-114 A9 --- Name Source name (7)
--------------------------------------------------------------------------------
Note (1): For WNM components it is equal to the unabsorbed central height
of the emission Gaussian T0,k (see equation 20) and its error is
derived as discussed in Section 3.5. For CNM components, Tpeak is equal
to the spin temperature times (1-e-τ0,n_^) (see equations 18 and
19) and its error is not quoted.
Note (2): For CNM components, it is τ0,n from equation 18, derived
directly from the least squares fit to the opacity profile. For WNM
components it is the upper limit to peak opacity τ0,k, estimated
by eye (Section 3.6), and has a very large error.
Note (3): For CNM components it is derived from the fit to the expected
profile; its error is derived as discussed in Section 3.5. For a few
CNM components, Tspin had to be forcibly set to zero to attain
convergence of the fit to the expected profile. For WNM components
Tspin is a lower limit (Section 3.6), and has a very large error; this
is TSMIN in the two-panel plots.
Note (4): If there was no nonthermal broadening; Tkmax=21.86DelV2.
Note (5): For the few CNM components with Tspin=0, we assign NHI=0.
Note (6): Fraction of the WNM that lies in front of the CNM so that a
fraction (1-frac) of the WNM emission is absorbed by the CNM gas.
Note (7): The ordering is by source name as follows: 3C, 4C, CTA, DW, NRAO,
P, T. CNM components have no error for Tpeak; WNM components have no
error for tau.
--------------------------------------------------------------------------------
History:
From electronic version of the journal
References:
Heiles & Troland, Paper II 2003ApJ...586.1067H 2003ApJ...586.1067H
Heiles & Troland, Paper III 2004ApJS..151..271H 2004ApJS..151..271H, Cat. J/ApJS/151/271
(End) Greg Schwarz [AAS], Patricia Bauer [CDS] 13-May-2003