J/ApJS/238/14 21-SPONGE HI Absorption Line Survey. I. (Murray+, 2018)
The 21-SPONGE HI Absorption Line Survey.
I. The temperature of Galactic HI.
Murray C.E., Stanimirovic S., Goss W.M., Heiles C., Dickey J.M., Babler B.,
Kim C.-G.
<Astrophys. J. Suppl. Ser., 238, 14-14 (2018)>
=2018ApJS..238...14M 2018ApJS..238...14M (SIMBAD/NED BibCode)
ADC_Keywords: Radio lines; H I data; Interstellar medium; Surveys;
Active gal. nuclei
Keywords: ISM: clouds; ISM: structure; radio lines: ISM
Abstract:
We present 21cm Spectral Line Observations of Neutral Gas with the VLA
(21-SPONGE), a Karl G. Jansky Very Large Array (VLA) large project
(∼600hr) for measuring the physical properties of Galactic neutral
hydrogen (HI). 21-SPONGE is distinguished among previous Galactic HI
studies as a result of (1) its exceptional optical depth sensitivity
(στ<10-3 per 0.42km/s channel over 57 lines of sight),
(2) matching 21cm emission spectra with the highest possible angular
resolution (∼4') from the Arecibo Observatory, and (3) detailed
comparisons with numerical simulations for assessing observational
biases. We autonomously decompose 21cm spectra and derive the physical
properties (i.e., spin temperature, Ts, and column density) of the
cold neutral medium (CNM; Ts<250K), thermally unstable medium (UNM;
250K<Ts<1000K), and warm neutral medium (WNM; Ts>1000K)
simultaneously. Of the total HI mass observed, 50% is detected in both
absorption and emission. The CNM makes up the majority of the
absorbing gas (56%±10%) and 28% of the total HI mass including gas
detected only in emission. We find that 20% of the total HI mass is
thermally unstable (41%±10% of HI detected in absorption), with no
significant variation with Galactic latitude. Finally, although the
WNM makes up 52% of the total HI mass, we detect little evidence for
WNM absorption with 1000K<Ts<4000K. Following spectral modeling, we
detect a stacked residual absorption feature corresponding to WNM with
Ts∼104K. We conclude that excitation in excess of collisions
likely produces significantly higher WNM Ts than predicted by
steady-state models.
Description:
The observing strategy for the 21cm Spectral Line Observations of
Neutral Gas with the VLA (21-SPONGE) HI absorption is described in
Murray+ 2015ApJ...804...89M 2015ApJ...804...89M
Our targets are bright (S1.4GHz>3Jy), radio continuum sources from
the NRAO/VLA Sky Survey (NVSS; Condon+ 1998, VIII/65).
For all VLA observations (10C-196, 12A-256, 13A-205), we used three
separate 500kHz bands with 1.95kHz channel spacing centered on the HI
line (1.42040575GHz) and ±1.5MHz, respectively.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 97 62 VLA observation information
table2.dat 75 57 Column densities
table5.dat 106 284 Fitted parameters
--------------------------------------------------------------------------------
See also:
VIII/54 : Atlas of Galactic Neutral Hydrogen (Hartmann+, 1997)
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/145/329 : Millennium Arecibo 21-cm Survey (Heiles+, 2003)
J/ApJ/793/132 : Perseus cloud sources Gaussian param. (Stanimirovic+, 2014)
J/A+A/585/A41 : EBHIS spectra and HI column density maps (Winkel+, 2016)
J/ApJS/234/2 : The GALFA-HI survey data release 2 (Peek+, 2018)
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 9 A9 --- Name Name of the radio source
11- 13 A3 --- Rej Reason for the 5 rejected source (1)
15- 16 I2 h RAh Hour of right ascension (J2000)
18- 19 I2 min RAm Minute of right ascension (J2000)
21- 24 F4.1 s RAs Second of right ascension (J2000)
26 A1 --- DE- Sign of declination (J2000)
27- 28 I2 deg DEd Degree of declination (J2000)
30- 31 I2 arcmin DEm Arcminute of declination (J2000)
33- 36 F4.1 arcsec DEs Arcsecond of declination (J2000)
38- 44 F7.3 deg GLON [7/353] Galactic longitude
46- 52 F7.3 deg GLAT [-62/81.1] Galactic latitude
54- 58 F5.2 --- S1.4GHz [2.8/55] NVSS flux density at 1.4GHz
60- 63 F4.1 arcsec Beam1 [0.1/20.3]? Synthesized beam
64 A1 --- --- [x]
65- 68 F4.1 arcsec Beam2 [0/13.7]? Synthesized beam
70- 72 F3.1 10-3 errTau [0.4/6.9]? rms uncertainty in optical depth (2)
74- 78 F5.3 --- TauPk [0.003/3.6]? Peak optical depth, τpeak
80- 84 F5.3 --- e_TauPk [0.001/0.01]? TauPk uncertainty
86- 91 F6.3 km/s Taudv [0.001/17.8]? Integrated optical depth (3)
93- 97 F5.3 km/s e_Taudv [0.002/0.03]? dv uncertainty
--------------------------------------------------------------------------------
Note (1): Sources rejected following preliminary observations as follows:
res = overly resolved
sat = saturated
Note (2): rms uncertainty in optical depth, στ, measured in
offline channels (0.42km/s channel spacing).
Note (3): Integrated optical depth, int(τ)dv, computed for channels
above 3στ(v) (see Section 2.3).
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 9 A9 --- Name Name of the radio source
11- 15 F5.2 10+20cm-2 NHIthin [0.71/38.53] Optically thin HI column
density; see Equation 7
17- 20 F4.2 10+20cm-2 e_NHIthin [0.02/2.81] NHIthin uncertainty
22- 26 F5.2 10+20cm-2 NHIiso [0.7/54.1] Isothermal HI column density;
see Equation 8
28- 31 F4.2 10+20cm-2 e_NHIiso [0.03/4] NHIiso uncertainty
33- 37 F5.2 10+20cm-2 NHItot [0.71/53.13] Total HI column density (4)
39- 43 F5.2 10+20cm-2 e_NHItot [0/18.06] NHItot uncertainty
45- 49 F5.2 10+20cm-2 NHICNM [0/24.46] Sum of N(HI)abs in the CNM
(Ts≤250K) (5)
51- 55 F5.2 10+20cm-2 NHIUNM [0/26.6] Sum of N(HI)abs in the UNM
(250<Ts≥1000K) (5)
57- 60 F4.2 --- fCNM [0/0.7]?=0 Cold Neutral Medium (CNM)
fraction per LOS
(fCNM=N(HI)CNM/N(HI)total)
62- 65 F4.2 --- e_fCNM [0.02/0.5] fCNM uncertainty
67- 70 F4.2 --- fUNM [0/0.77]?=0 Thermally unstable medium (UNM)
fraction per LOS
(fUNM=N(HI)UNM/N(HI)total)
72- 75 F4.2 --- e_fUNM [0.04/1] fUNM uncertainty
--------------------------------------------------------------------------------
Note (4): Total HI column density following the autonomous computation of Ts
and N(HI)abs for individual spectral components (Equation (9));
see section 5.
Note (5): If no CNM/UNM components were detected within uncertainties,
equal to 0.0.
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table5.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 9 A9 --- Name Name of the radio source
11- 15 F5.3 --- tau0 [0.001/2.8]? Amplitude (1)
17- 25 F9.3 --- e_tau0 [0.001/20000]? tau0 uncertainty
27- 30 F4.1 km/s Delnu0 [0.1/37.4]? Mean velocity (1)
32- 38 F7.1 km/s e_Delnu0 [0.1/10000]? Delnu0 uncertainty
40- 44 F5.1 km/s nu0 [-69/46.1]? FWHM (1)
46- 50 F5.1 km/s e_nu0 [0.1/900]? nu0 uncertainty
52- 55 F4.1 K TBn [0.1/87.5]? Fit parameter, TB,n (2)
57- 60 F4.1 K e_TBn [0/16.7]? TBn uncertainty
62- 65 F4.1 km/s Delnu0n [0.6/33.7]? Fit parameter,
Δν0,n (2)
67- 69 F3.1 km/s e_Delnu0n [0.1/0.4]? Delnu0n uncertainty
71- 75 F5.1 km/s nu0n [-65.4/42.1]? Fit parameter, ν0,n (2)
77- 79 F3.1 km/s e_nu0n [0.1/0.3]? nu0n uncertainty
81- 84 I4 K Ts [10/2613]? Average spin temperature (3)
86- 88 I3 K e_Ts [0/403]? Ts uncertainty
90- 94 F5.2 10+20cm-2 NHI [0/25.55]? Column density computed
from fitted parameters (Equation (6))
96- 99 F4.2 10+20cm-2 e_NHI [0/9.16]? NHI uncertainty
101- 102 I2 --- O [1/13]? Order of components along the
line of sight (LOS) (4)
104- 106 F3.1 --- f [0/1]? Fraction of the warm neutral medium
(WNM) (5)
--------------------------------------------------------------------------------
Note (1): Gaussian parameters fit to HI absorption (Equation (1));
see Section 3.1.
Note (2): Gaussian parameters fit to HI emission (Equations (2));
see Section 3.1.
Note (3): Average spin temperature from all permutations of components
with overlap along the LOS (Equations (3), (4)); see Section 3.1.
Note (4): Order of components along the LOS corresponding to the smallest
model residuals. Components whose position along the LOS is extremely
uncertain or unaffected by order permutations are assumed to lie
behind all others (i.e., O=N, for N total components).
Note (5): Fraction of WNM (emission-detected only) components that lie in
front of all absorption-detected components, allowed to be 1.0 or 0.0
for all emission-detected components. Fit parameters for components
with Ts≤3K are omitted, as these are either spurious Autonomous
Gaussian Decomposition algorithm (AGD; Lindner+ 2015AJ....149..138L 2015AJ....149..138L)
detections or were not recovered in the fit to TB,exp(v) due to
strong line blending.
--------------------------------------------------------------------------------
History:
From electronic version of the journal
References:
Murray et al. 21-SPONGE HI absorption survey. 2015ApJ...804...89M 2015ApJ...804...89M
Murray et al. Paper I. 2018ApJS..238...14M 2018ApJS..238...14M This cat.
(End) Emmanuelle Perret [CDS] 25-May-2022