J/ApJ/911/55 FUSE survey of H2 in the Galactic disk (Shull+, 2021)
A Far Ultraviolet Spectroscopic Explorer survey of interstellar molecular
hydrogen in the Galactic disk.
Shull J.M., Danforth C.W., Anderson K.L.
<Astrophys. J., 911, 55 (2021)>
=2021ApJ...911...55S 2021ApJ...911...55S
ADC_Keywords: Stars, OB; Ultraviolet; Surveys; Milky Way; Extinction;
Molecular data; Interstellar medium; H I data
Keywords: Diffuse interstellar clouds ; Milky Way disk ;
Interstellar molecules ; Ultraviolet astronomy ;
Ultraviolet extinction
Abstract:
We report results from a Far Ultraviolet Spectrographic Explorer
(FUSE) survey of interstellar molecular hydrogen (H2) in the
Galactic disk toward 139 O-type and early B-type stars at Galactic
latitudes |b|≤10°, with updated photometric and parallax
distances. H2 absorption is measured using the far-UV Lyman and
Werner bands, including strong R(0), R(1), and P(1) lines from
rotational levels J=0 and J=1 and excited states up to J=5 (sometimes
J=6 and 7). For each sight line, we report column densities NH2,
NHI, N(J), and NH=NHI+2NH2 and the molecular fraction
fH2=2NH2/NH. Our survey extends the 1977 Copernicus H2 survey
up to NH∼5x1021cm-2. The lowest rotational states have
excitation temperatures and rms dispersions <T01≥88±20K and
<T02≥77±18K, suggesting that J=0, 1, 2 are coupled to the gas
kinetic temperature. Populations of higher-J states exhibit mean
excitation temperatures <T24≥237±91K and <T35≥304±108K,
produced primarily by UV radiative pumping. Correlations of fH2 with
E(B-V) and NH show a transition to fH2≥0.1 at NH≳1021cm-2
and E(B-V)≳0.2, interpreted with an analytic model of H2
formation-dissociation equilibrium and attenuation of the far-UV
radiation field by self-shielding and dust opacity. Results of this
disk survey are compared to previous FUSE studies of H2 in
translucent clouds, at high Galactic latitudes, and in the Magellanic
Clouds. Using updated distances to the target stars, we find average
sight-line values <fH2≥0.20 and <NH/E(B-V)≥6.07x1021cm-2/mag.
Description:
The 139 targets in this survey were drawn primarily from FUSE programs
designed to study OB stars and interstellar gas in the Milky Way.
These stars have updated spectral types and both photometric and
Gaia-DR2 parallax distances determined by
Shull & Danforth (2019ApJ...882..180S 2019ApJ...882..180S) using new information from the
Galactic O-star Spectroscopic Survey (GOSS; Maiz Apellaniz+ 2004, V/116).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 110 139 Stellar parameters and distances
table2.dat 85 139 HI column density measurements
table3.dat 149 169 Column densities and Doppler parameters
table4.dat 74 139 Column densities and rotational temperatures
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See also:
III/274 : Galactic O-Star Spectroscopic Survey (GOSSS) (Sota+, 2014)
V/116 : Galactic O star catalog (Maiz-apellaniz+, 2004)
J/ApJS/93/211 : IUE survey of H I Lyα absorption. I. (Diplas+ 1994)
J/ApJS/163/282 : Molecular hydrogen column densities (Wakker+, 2006)
J/ApJS/176/59 : FUSE survey of OVI in the disk of the Milky Way (Bowen+, 2008)
J/ApJ/711/1236 : Equivalent width of H2 from FUSE (Jensen+, 2010)
J/ApJ/734/65 : CI radial velocities with HST/STIS (Jenkins+, 2011)
J/A+A/613/A9 : Extinction towards Galactic O stars (Maiz Apellaniz+, 2018)
J/ApJ/872/55 : OI, GeII, KrI & H abundances from HST UV sp. (Jenkins, 2019)
J/ApJ/906/73 : Extinction & emission PostPlanck Era (Hensley+, 2021)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- Seq [1/139] Internal target number
5- 17 A13 --- Name Target identifier
19- 24 F6.2 deg GLON [2.26/355.36] Galactic longitude
26- 31 F6.2 deg GLAT [-23.23/13.5] Galactic latitude
33- 37 F5.2 mag Bmag [5.3/10.61] Apparent B band magnitude
39- 43 F5.2 mag Vmag [5/10.7] Apparent V band magnitude
45- 48 F4.2 mag E(B-V) [0.02/1.1] The(B-V) color excess
50- 66 A17 --- SpType Spectral type
68- 71 F4.2 kpc Dphot [0.2/9.9] Photometric distance (1)
73 A1 --- f_Dphot [b] Flag on Dphot (2)
75 A1 --- l_DGaia Limit flag on DGaia
76- 80 F5.2 kpc DGaia [0.28/14]? Parallax distance (3)
82- 85 F4.2 kpc e_DGaia [0.27/7.7]? Lower limit on DGaia
87- 91 F5.2 kpc E_DGaia [0.29/20.1]? Upper limit on DGaia
93- 94 A2 --- f_DGaia Flag on DGaia (4)
96-103 A8 --- FUSE FUSE program identifier
105-110 F6.3 ks Texp [0.059/31.6] FUSE spectroscopic exposure time
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Note (1): Based on GOSS photometry, extinctions, and spectral types and a new
set of absolute magnitudes (see Shull & Danforth 2019ApJ...882..180S 2019ApJ...882..180S).
Note (2): Flag as follows:
b = No GOSS data therefore photometric distance based on photometry and
spectral type in the literature.
Note (3): Based on parallaxes and errors from the Gaia-DR2 archive, after
adding a constant parallax offset of 0.03mas.
Note (4): Flag as follows:
u = uncertain flag.
dp = data problem.
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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- 3 I3 --- Seq [1/139] Internal target number
4- 18 A15 --- Name Target identifier
20- 23 F4.2 mag E(B-V) [0.02/1.1] The(B-V) color excess (1)
25- 29 F5.2 [cm-2] logNHI-A [20.5/21.7] Adopted log HI column density (2)
31- 35 F5.2 [cm-2] logNHI-S [20.9/21.5]? log HI column density from
Shull & Van Steenberg 1985ApJ...294..599S 1985ApJ...294..599S
37- 40 F4.2 [cm-2] e_logNHI-S [0.05/0.15]? Uncertainty in logNHI-S
42- 46 F5.2 [cm-2] logNHI-D [20.56/21.65]? log HI column density from
Diplas & Savage, 1994, J/ApJS/93/211
48- 51 F4.2 [cm-2] e_logNHI-D [0.06/0.23]? Uncertainty in logNHI-D
53- 57 F5.2 [cm-2] logNHI-J [20.55/21.5]? log HI column density
from Jenkins 2019, J/ApJ/872/55
59- 62 F4.2 [cm-2] E_logNHI-J [0.03/0.1]? Upper uncertainty in logNHI-J
64- 67 F4.2 [cm-2] e_logNHI-J [0.02/0.13]? Lower uncertainty in logNHI-J
69- 73 F5.2 [cm-2] logNHI-O [20.8/21.6]? Other log HI column density
75- 78 F4.2 [cm-2] e_logNHI-O [0.05/0.3]? Uncertainty in logNHI-O
80- 85 A6 --- r_logNHI-O Reference for logNHI-O (3)
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Note (1): Updated values of color excess (Shull & Danforth 2019ApJ...882..180S 2019ApJ...882..180S)
were derived using digital photometry, visual extinction, and new
spectral types from the Galactic O-star Spectroscopic Survey
(Maiz Apellaniz+ 2004, V/116 ; Sota+ 2011 and 2014, III/274).
Note (2): The adopted source for NHI was selected in priority order of:
J19 (Jenkins, J/ApJ/872/55 ; 57 stars),
DS94 (Diplas & Savage 1994, J/ApJS/93/211 ; 51 stars),
FM90 (Fitzpatrick & Massa 1990ApJS...72..163F 1990ApJS...72..163F ; 2 stars), and three
other sources (3 stars). For 26 stars that lack fits to Lyα
profiles, we estimated NHI by scaling with color excess E(B-V);
see Section 2.1.
Note (3): Reference as follows:
Scaled = scaled estimate from NHI from E(B-V).
FM90 = Fitzpatrick & Massa (1990ApJS...72..163F 1990ApJS...72..163F);
Rat02 = Rachford et al. (2002ApJ...577..221R 2002ApJ...577..221R);
Han92 = Hanson et al. (1992ApJ...392..571H 1992ApJ...392..571H);
Sno96 = Snow et al. (1996ApJ...465..245S 1996ApJ...465..245S).
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- Seq [1/139] Internal target number
5- 18 A14 --- Target Target identifier
20 A1 --- f_Target [bc] Flag on Target (1)
22- 26 F5.2 [cm-2] logN0 [16.8/21.1]? log J=0 rotational state
column density (2)
28- 31 F4.2 [cm-2] E_logN0 [0.05/0.15]? Upper uncertainty in logN0
33- 36 F4.2 [cm-2] e_logN0 [0.05/0.15]? Lower uncertainty in logN0
38- 42 F5.2 [cm-2] logN1 [17.3/20.8]? log J=1 rotational state
column density (2)
44- 47 F4.2 [cm-2] E_logN1 [0.05/0.15]? Upper uncertainty in logN1
49- 52 F4.2 [cm-2] e_logN1 [0.05/0.15]? Lower uncertainty in logN1
54- 58 F5.2 [cm-2] logN2 [14.36/19.64]? log J=2 rotational state
column density (2)
60- 63 F4.2 [cm-2] E_logN2 [0.03/1.5]? Upper uncertainty in logN2
65- 68 F4.2 [cm-2] e_logN2 [0.04/0.5]? Lower uncertainty in logN2
70- 74 F5.2 [cm-2] logN3 [14.93/18.24]? log J=3 rotational state
column density (2)
76- 79 F4.2 [cm-2] E_logN3 [0.04/1.9]? Upper uncertainty in logN3
81- 84 F4.2 [cm-2] e_logN3 [0.04/0.8]? Lower uncertainty in logN3
86- 90 F5.2 [cm-2] logN4 [13.95/16.93] log J=4 rotational state
column density (2)
92- 95 F4.2 [cm-2] E_logN4 [0.02/1.9]? Upper uncertainty in logN4
97-100 F4.2 [cm-2] e_logN4 [0.02/0.7]? Lower uncertainty in logN4
102 A1 --- l_logN5 Limit flag on logN5
104-108 F5.2 [cm-2] logN5 [13.88/16.68]? log J=5 rotational state
column density (2)
110-113 F4.2 [cm-2] E_logN5 [0.03/1.4]? Upper uncertainty in logN5
115-118 F4.2 [cm-2] e_logN5 [0.02/0.3]? Lower uncertainty in logN5
120 A1 --- l_logN6 Limit flag on logN6
122-126 F5.2 [cm-2] logN6 [13.53/15.71]? log J=6 rotational state
column density (2)
128-131 F4.2 [cm-2] E_logN6 [0.04/0.2]? Upper uncertainty in logN6
133-136 F4.2 [cm-2] e_logN6 [0.04/0.2]? Lower uncertainty in logN6
138-141 F4.1 km/s b [2.8/20]? Doppler parameter
143-145 F3.1 km/s E_b [0.3/4.4]? Upper uncertainty in b
147-149 F3.1 km/s e_b [0.4/3.7]? Lower uncertainty in b
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Note (1): Flag as follows:
b = In 15 sight lines, multiple velocity components were observable and
measured in high-J states. We report individual column densities,
denoted as "blue and red" components, and sum them to find total
column densities.
c = A few targets have no listed column densities N(2) or N(3). In several
cases this was a result of poor data quality, so that lines from
J≥2 could not be fitted accurately. In other cases, the accessible
(unblocked) lines from J=2 and J=3 were highly saturated, with
equivalent widths of 200-300mÅ and large effective Doppler parameters
(b≥10 km/s) likely produced by unresolved velocity components.
When equivalent widths of all the accessible lines lie on the "flat
portion" of the curve of growth, errors can exceed ±0.40 for
log N=16-17 and ±0.50 for logN=17-19.
Note (2): Derived from curve-of-growth fitting with Doppler parameter and
damping wings for lines from J=0 and J=1. No value is listed
when b was poorly determined. Error bars on low-J states (J=0,1 and
sometimes J=2,3) depend on data quality (see footnote in Table 3).
In damping-wing fits, errors on logN typically range from
±0.03 to ±0.10. Six targets had detectable column densities
in J=7:
#48 with logN(7)=15.54±0.15,
#52 with logN(7)=14.47±0.05,
#88 with logN(7)=14.14±0.06,
#116 with logN(7)=14.29±0.11,
#127 with logN(7)=14.25±0.05, and
#137 with logN(7)=15.43±0.15 (15.32 in blue component
and 14.80 in red component).
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- Seq [1/139] Internal target number
5- 18 A14 --- Target Target identifier
20- 24 F5.2 [cm-2] logNH2 [17.48/21.17] log H2 column density (1)
26- 28 I3 K T01 [40/159] Rotational excitation temperature
from N1/N0 ratio (2)
30- 32 I3 K T02 [44/331]? Rotational excitation temperature
from N2/N0 ratio (2)
34- 36 I3 K T24 [118/582]? Rotational excitation temperature
from N4/N2 ratio (2)
38- 41 I4 K T35 [171/1358]? Rotational excitation temperature
from N5/N3 ratio (2)
43- 47 F5.2 [cm-2] logNHI [20.55/21.65] log HI column density (1)
48 A1 --- f_logNHI [*] Flag on logNHI (3)
50- 54 F5.2 [cm-2] logNH [20.55/21.74] log H column density (1)
56- 59 F4.2 kpc Dphot [0.21/9.85] Photometric distance
61- 65 F5.3 cm-3 nH [0.02/3.9] Mean total hydrogen density
along sight line
67- 72 F6.4 --- fH2 [0.0017/0.747] Molecular fraction (4)
74 I1 --- Note [1/3] S/N ratio level (5)
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Note (1): Values of N(0) and N(1) come from fitting damping-wing Voigt profiles
of R(0), R(1), and P(1) lines. Their errors depend on data quality.
Neutral hydrogen column densities are taken from previous surveys by
Diplas & Savage (1994, J/ApJS/93/211), Jenkins (2019, J/ApJ/872/55),
Fitzpatrick & Massa (1990ApJS...72..163F 1990ApJS...72..163F), and several individual papers.
Details are discussed in Section 2.1 and Table 2
Note (2): As described in Sections 3.4 and 3.5.
Note (3): Flag as follows:
* = No Lyα fits. We use the relation,
NH=(5.8e21cm-2/mag)E(B-V)
from the Copernicus survey (Savage+ 1997ApJ...216..291S 1997ApJ...216..291S).
Note (4): Defined by fH2=2NH2/[NHI+2NH2].
Note (5): Note as follows:
1 = S/N≥15 with errors of ±0.03-0.05 on logN;
2 = 5≤S/N≤15 with errors of ±0.05-0.10;
3 = S/N≤5, with errors of ±0.10-0.20.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 11-Oct-2022