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. =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 arcminute^2^ (2) 81- 93 E13.6 K/arcmin2 d2Ta/dadd ?=-9999. Second derivative of Ta with respect to right ascension and declination in Kelvins per arcminute^2^ (2) 95-107 E13.6 K/arcmin2 d2Ta/dd2 ?=-9999. Second derivative of Ta with respect to declination in Kelvins per arcminute^2^ (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 T_0,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^-{tau}_0,n_^) (see equations 18 and 19) and its error is not quoted. Note (2): For CNM components, it is {tau}_0,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 {tau}_0,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=21.86DelV^2^. 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 Heiles & Troland, Paper III 2004ApJS..151..271H, Cat. ================================================================================ (End) Greg Schwarz [AAS], Patricia Bauer [CDS] 13-May-2003