J/ApJ/919/27 NIR H2 line em. from 5 photodissociation regions (Kaplan+, 2021)
A near-infrared survey of UV-excited molecular Hydrogen in photodissociation
regions.
Kaplan K.F., Dinerstein H.L., Kim H., Jaffe D.T.
<Astrophys. J., 919, 27 (2021)>
=2021ApJ...919...27K 2021ApJ...919...27K
ADC_Keywords: Molecular clouds; H II regions; Interstellar medium;
Spectra, infrared; Molecular data
Keywords: Photodissociation regions ; Interstellar molecules ;
Interstellar line emission ; Near infrared astronomy ;
Molecular spectroscopy
Abstract:
We present a comparative study of the near-infrared (NIR) H2 line
emission from five regions near hot young stars: Sharpless 140,
NGC2023, IC63, the Horsehead Nebula, and the Orion Bar. This emission
originates in photodissociation or photon-dominated regions (PDRs),
interfaces between photoionized and molecular gas near hot (O) stars
or reflection nebulae illuminated by somewhat cooler (B) stars. In
these environments, the dominant excitation mechanism for NIR emission
lines originating from excited rotational-vibrational (rovibrational)
levels of the ground electronic state is radiative or UV excitation
(fluorescence), wherein absorption of far-UV photons pumps H2
molecules into excited electronic states from which they decay into
the upper levels of the NIR lines. Our sources span a range of UV
radiation fields (G0=102-105) and gas densities
(nH=104-106cm-3), enabling examination of how these properties
affect the emergent spectrum. We obtained high-resolution (R∼45000)
spectra spanning 1.45-2.45µm on the 2.7m Harlan J. Smith Telescope
at McDonald Observatory with the Immersion Grating INfrared
Spectrometer (IGRINS), detecting up to over 170 transitions per source
from excited vibrational states (v=1-14). The populations of
individual rovibrational levels derived from these data clearly
confirm UV excitation. Among the five PDRs in our survey, the Orion
Bar shows the greatest deviation of the populations and spectrum from
pure UV excitation, while Sharpless 140 shows the least deviation.
However, we find that all five PDRs exhibit at least some modification
of the level populations relative to their values under pure UV
excitation, a result we attribute to collisional effects.
Description:
We selected Sharpless 140, NGC 2023, IC 63, and the Horsehead Nebula
photon-dominated regions (PDRs) for this survey based on their
observability in the northern sky, previous detections of UV-excited
H2. We also include our data and results for the Orion Bar from
K17 (Kaplan+ 2017, J/ApJ/838/152).
Table 1 summarizes the observations and physical properties of the
PDRs in this survey.
All targets were observed with the Immersion GRating INfrared
Spectrometer (IGRINS; R∼45000) on the 2.7m Harlan J. Smith telescope
at McDonald Observatory. Observation dates span 2014-Oct-24 to
2015-Nov-03.
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 184 5 Photon-dominated region (PDR) properties and
observations
table2.dat 96 194 H2 line fluxes for our photon-dominated regions
(normalized to the 4-2 O(3) line)
table3.dat 38 194 Physical Constants for H2 Lines
table4.dat 151 194 H2 rovibrational level column densities for
our PDRs and comparison to pure UV-excited
Cloudy model
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See also:
II/36 : UBV and uvby-beta obs. of Orion OB1 Association (Warren+ 1977)
I/345 : Gaia DR2 (Gaia Collaboration, 2018)
J/ApJ/786/29 : Catalog of distances to molecular clouds (Schlafly+, 2014)
J/ApJ/838/152 : Deep NIR spectrum of the Orion Bar PDR (Kaplan+, 2017)
J/A+A/630/A58 : Full infrared spectrum of molecular hydrogen (Roueff+, 2019)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 16 A16 --- Name PDR name
18- 34 A17 --- Type PDR type
36- 38 I3 pc Dist [188/764] Distance
40- 41 I2 pc e_Dist [9/50] Dist uncertainty
43 A1 --- r_Dist Reference on Dist (1)
45- 56 A12 --- IStar Illuminating star
58- 65 A8 --- SpT Spectral type
67 A1 --- r_SpT Reference on SpT (1)
69- 73 I5 K Teff [23700/39000] Effective temperature
75 A1 --- r_Teff Reference on Teff (1)
77- 81 E5.2 --- G0 [100/30000] UV intensity, G0 (2)
83 A1 --- r_G0 Reference on G0 (1)
85- 89 E5.2 cm-3 nH [10000/1e+06] Gas density, nH
91 A1 --- r_nH Reference on nH (1)
93- 98 E6.2 cm3 G0/nH [0.005/0.09] G0 to nH ratio
100-101 I2 h RAh Hour of right ascension (J2000)
103-104 I2 min RAm Minute of right ascension (J2000)
106-110 F5.2 s RAs Second of right ascension (J2000)
112 A1 --- DE- Sign of declination (J2000)
113-114 I2 deg DEd Degree of declination (J2000)
116-117 I2 arcmin DEm Arcminute of declination (J2000)
119-122 F4.1 arcsec DEs Arcsecond of declination (J2000)
124-134 A11 "Y/M/D" Date Date of observation (UT)
136-138 I3 min Exp [30/100] Exposure time
140-142 I3 deg PA [15/135] Position angle
144-151 A8 --- StdStar Standard star
153-156 F4.2 mag Ak [0.3/0.72] K-band dust extinction (3)
158-161 F4.2 --- O/P [1.3/3] ortho-to-para ratio (4)
163-166 F4.2 --- e_O/P [0.1/0.4] O/P uncertainty
168-171 F4.2 --- 1-0S/2-1S [2.4/5.4] Flux ratio of the H2 1-0S(1)
to 2-1S(1) lines in each PDR (5)
173-176 F4.2 --- e_1-0S/2-1S [0.3/0.7] 1-0S/2-1S uncertainty
178-184 A7 --- AName Abbreviated name used in other tables;
column added by CDS
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Note (1): Reference as follows:
a = Hirota et al. (2008PASJ...60..961H 2008PASJ...60..961H)
b = Gaia Collaboration et al. (2018, I/345)
c = Perryman et al. (1997, I/239)
d = Caballero (2008MNRAS.383..750C 2008MNRAS.383..750C)
e = Schlafly et al. (2014, J/ApJ/786/29)
f = Timmermann et al. (1996A&A...315L.281T 1996A&A...315L.281T)
g = Compiegne et al. (2008A&A...491..797C 2008A&A...491..797C)
h = Shenavrin et al. (2011, J/AZh/88/34)
i = Warren & Hesser (1977, II/36)
j = Ferland et al. (2012ApJ...757...79F 2012ApJ...757...79F)
k = Sigut & Jones (2007ApJ...668..481S 2007ApJ...668..481S)
l = Panagia (1973AJ.....78..929P 1973AJ.....78..929P)
m = Sheffer et al. (2011ApJ...741...45S 2011ApJ...741...45S)
n = Andrews et al. (2018A&A...619A.170A 2018A&A...619A.170A)
o = Habart et al. (2005A&A...437..177H 2005A&A...437..177H)
p = Marconi et al. (1998A&A...330..696M 1998A&A...330..696M)
q = Goicoechea et al. (2016Natur.537..207G 2016Natur.537..207G)
Note (2): G0 is a dimensionless measure of the UV intensity normalized to
the interstellar radiation field of Habing (1968BAN....19..421H 1968BAN....19..421H).
Note (3): The best-fit K-band dust extinction in magnitudes (AK), used to
extinction correct H2 line fluxes for each PDR, as described in Section 3.1.
Note (4): The best-fit ortho-to-para ratio (O/P) observed for the
rovibrationally excited H2, as described in Sections 3.3 & 4.5.
Note (5): Flux ratio of the H2 1-0 S(1) to 2-1 S(1) lines in each PDR, as
described in Section 4.2. The individual line fluxes are reported in
Table 2.
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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- 11 A11 --- ID H2 line rovibrational identifier
13- 20 F8.6 um lambda [1.45/2.5] H2 line vacuum wavelength
22- 23 I2 --- vu [1/14] Transition upper vibrational state
25- 26 I2 --- Ju [0/19] Transition upper rotational state
28- 33 F6.3 --- Fs140 [0.013/4.4]? Line flux for S 140 (1)
35- 40 F6.3 --- e_Fs140 [0.003/0.5]? One-sigma uncertainty in Fs140
42- 47 F6.3 --- Fngc2023 [0.01/8]? Line flux for NGC 2023 (1)
49- 54 F6.3 --- e_Fngc2023 [0.001/0.9]? One-sigma uncertainty in Fngc2023
56- 61 F6.3 --- Fic63 [0.02/5.3]? Line flux for IC 63 (1)
63- 68 F6.3 --- e_Fic63 [0.004/0.7]? One-sigma uncertainty in Fic63
70- 75 F6.3 --- Fhorse [0.08/5.3]? Line flux for the Horsehead
Nebula (1)
77- 82 F6.3 --- e_Fhorse [0.01/0.5]? One-sigma uncertainty in Fhorse
84- 89 F6.3 --- Foribar [0.02/23.4]? Line flux for the Orion Bar (1)
91- 96 F6.3 --- e_Foribar [0.003/2.1]? One-sigma uncertainty in Foribar
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Note (1): Undetected lines are left blank.
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 11 A11 --- ID H2 line rovibrational identifier
13- 20 F8.6 um lambda [1.45/2.5] H2 line vacuum wavelength (1)
22- 23 I2 --- vu [1/14] Transition upper vibrational state
25- 26 I2 --- Ju [0/19] Transition upper rotational state
28- 32 I5 K Eu/k [6148/51782] Energy of the upper state (1)
34- 38 F5.2 [s-1] logAul [-8/-5.5] Log rovibrational radiative transition
probability (1)
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Note (1): Values are from Roueff et al. (2019, J/A+A/630/A58).
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 11 A11 --- ID H2 line rovibrational identifier
13- 20 F8.6 um lambda [1.45/2.5] H2 line vacuum wavelength
22- 23 I2 --- vu [1/14] Transition upper vibrational
state
25- 26 I2 --- Ju [0/19] Transition upper rotational
state
28- 33 F6.3 [-] lnRs140 [-5.5/2.52]? Natural log of S 140 ratio
(1)
35- 39 F5.3 [-] E_lnRs140 [0.03/0.2]? Upper uncertainty in
lnRs140
41- 45 F5.3 [-] e_lnRs140 [0.03/0.3]? Lower uncertainty in
lnRs140
47- 51 F5.2 --- (Nu/Nm)s140 [0.2/11.26]? S 140 ratio (2)
53- 58 F6.3 [-] lnRngc2023 [-7/3.2]? Natural log of NGC 2023 ratio
(1)
60- 64 F5.3 [-] E_lnRngc2023 [0.049/0.2]? Upper uncertainty in
lnRngc2023
66- 70 F5.3 [-] e_lnRngc2023 [0.05/0.3]? Lower uncertainty in
lnRngc2023
72- 76 F5.2 --- (Nu/Nm)ngc2023 [0.2/23]? NGC 2024 Nu/Nm ratio (2)
78- 83 F6.3 [-] lnRic63 [-5.1/2.8]? Natural log IC 63 ratio (1)
85- 89 F5.3 [-] E_lnRic63 [0.05/0.3]? Upper uncertainty in lnRic63
91- 95 F5.3 [-] e_lnRic63 [0.05/0.3]? Lower uncertainty in lnRic63
97- 101 F5.2 --- (Nu/Nm)ic63 [0.2/11.2]? IC 63 Nu/Nm ratio (2)
103- 108 F6.3 [-] lnRhorse [-3.2/2.8]? Natural log of Horsehead
Nebula ratio (1)
110- 114 F5.3 [-] E_lnRhorse [0.02/0.2]? Upper uncertainty in
lnRhorse
116- 120 F5.3 [-] e_lnRhorse [0.02/0.2]? Lower uncertainty in
lnRhorse
122- 126 F5.2 --- (Nu/Nm)horse [0.36/7.1]? Horsehead Nebula ratio (2)
128- 133 F6.3 [-] lnRoribar [-5.4/4.2]? Natural log of Orion Bar
ratio (1)
135- 139 F5.3 [-] E_lnRoribar [0.04/0.2]? Upper uncertainty in
lnRoribar
141- 145 F5.3 [-] e_lnRoribar [0.04/0.2]? Lower uncertainty in
lnRoribar
147- 151 F5.2 --- (Nu/Nm)oribar [0.3/16.5]? Orion Bar Nu/Nm ratio (2)
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Note (1): Natural log of the ratio (Nu/gu)/(Nr/gr) which is the column
density (Nu) for the H2 transition divided by the level's
quantum degeneracy (gu) and normalized to (Nr/gr) which is the
column density derived from 4-2 O(3) divided by that transition's
quantum degeneracy (gr). Undetected lines are left blank.
Note (2): Column density (Nu) from the H2 transition divided by the column
density (Nm) from a pure UV-excited Cloudy model. Undetected
lines are left blank.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 18-Jan-2023