J/A+A/651/A59 Dense warm ionized medium in the inner Galaxy (Langer+, 2021)
The dense warm ionized medium in the inner Galaxy.
Langer W.D., Pineda J.L., Goldsmith P.F., Chambers E.T., Riquelme D.,
Anderson L.D., Luisi M., Justen M, Buchbender C.
<Astron. Astrophys. 651, A59 (2021)>
=2021A&A...651A..59L 2021A&A...651A..59L (SIMBAD/NED BibCode)
ADC_Keywords: Interstellar medium ; Spectroscopy
Keywords: ISM: structure -ISM: abundances - HII regions
Abstract:
Ionized interstellar gas is an important component of the interstellar
medium and its lifecycle. The recent evidence for a widely distributed
highly ionized warm interstellar gas with a density intermediate
between the warm ionized medium (WIM) and compact HII regions suggests
that there is a major gap in our understanding of the interstellar
gas.
Our goal is to investigate the properties of the dense warm ionized
medium in the Milky Way using spectrally resolved SOFIA GREAT [NII]
205um fine-structure lines and Green Bank Telescope hydrogen radio
recombination lines (RRL) data, supplemented by spectrally unresolved
Herschel PACS [NII] 122um data, and spectrally resolved 12CO.
We observed eight lines of sight (LOS) in the 20°<l<30°region
in the Galactic plane. We spectrally unresolved Herschel PACS [NII]
122um data, and spectrally resolved 12CO. Methods. We observed eight
lines of sight (LOS) in the 20°<l<30°region in the Galactic
plane. We analyzed spectrally resolved lines of [NII] at 205um and RRL
observations, along with the spectrally unresolved Herschel PACS 122um
emission, using excitation and radiative transfer models to determine
the physical parameters of the dense warm ionized medium. We derived
the kinetic temperature, as well as the thermal and turbulent velocity
dispersions from the [NII] and RRL linewidths.
The regions with [NII] 205um emission are characterized by electron
densities, n(e)∼10-35cm-3, temperatures range from 3400 to 8500K,
and nitrogen column densities N(N+)∼7x1016 to 3x1017cm-2. The
ionized hydrogen column densities range from 6x1020 to
1.7x1021cm-2 and the fractional nitrogen ion abundance
x(N+)∼1.1x10-4 to 3.0x10-4, implying an enhanced nitrogen
abundance at a distance ∼4.3kpc from the Galactic Center. The [NII]
205um emission lines coincide with CO emission, although often with
an offset in velocity, which suggests that the dense warm ionized gas
is located in, or near, star-forming regions, which themselves are
associated with molecular gas.
These dense ionized regions are found to contribute ≳50% of the
observed [CII] intensity along these LOS. The kinetic temperatures we
derive are too low to explain the presence of N+ resulting from
electron collisional ionization and/or proton charge transfer of
atomic nitrogen. Rather, these regions most likely are ionized by
extreme ultraviolet (EUV) radiation from nearby star-forming regions
or as a result of EUV leakage through a clumpy and porous interstellar
medium.
Description:
These files contain spectra that were part of a program to study the
dense warm ionized medium in the inner Galaxy using spectrally
resolved observations of emission from ionized nitrogen, carbon, and
hydrogen. Eight lines of sight (LOS), previously observed in [CII]
with Herschel HIFI, were observed with upGREAT onboard SOFIA as part
of Guest Observer Cycle 7 (proposal ID 07_0009; PI Langer). The
observations were made on four flights from June 24 to 27, 2019, from
Christchurch, NZ, as part of SOFIA's southern deployment. Hα
Radio Recombination Lines (RRL) were also observed along all eight LOS
using the Versatile GBT Astronomical Spectrometer (VEGAS) on the Green
Bank Telescope (GBT) in X-band (8-10GHz). Several Hα
recombinations lines in X-band were combined for improved
signal-to-noise. The data reduction for [NII] and RRL are described in
detail in the paper. The [CII] HIFI observations are from the Herschel
data archives (Langer et al., 2010A&A...521L..17L 2010A&A...521L..17L, Pineda et al.,
2013A&A...554A.103P 2013A&A...554A.103P, Langer, 2014A&A...561A.122L 2014A&A...561A.122L). The [NII], RRL, and
[CII] spectra used for the analysis were displayed in Figure 2 of the
paper and their values are listed in the attached files.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 39 8 List of tables
g020p9+0.dat 46 2371 G020.9+0.0 velocities and main beam temperatures
g021p7+0.dat 46 1483 G021.7+0.0 velocities and main beam temperatures
g023p5+0.dat 46 1779 G023.5+0.0 velocities and main beam temperatures
g024p3+0.dat 46 2075 G024.3+0.0 velocities and main beam temperatures
g025p2+0.dat 46 2964 G025.2+0.0 velocities and main beam temperatures
g026p1+0.dat 46 1779 G026.1+0.0 velocities and main beam temperatures
g027p0+0.dat 46 2075 G027.0+0.0 velocities and main beam temperatures
g028p7+0.dat 46 1779 G028.7+0.0 velocities and main beam temperatures
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See also:
J/ApJ/814/133 : Herschel Galactic plane survey of [NII] (Goldsmith+, 2015)
Byte-by-byte Description of file: list.dat
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Bytes Format Units Label Explanations
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1- 10 A10 --- Name Eight lines of sight name (GLLL.ll+B.b)
12- 18 F7.4 deg GLON Galactic longitude
20- 26 F7.4 deg GLAT Galactic latitude
28- 39 A12 --- Table Name of the table with velocities and
main beam temperatures
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Byte-by-byte Description of file: g*.dat
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Bytes Format Units Label Explanations
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1- 7 F7.3 km/s V([NII]) ? [NII] LSR velocity (1)
9- 14 F6.3 K T([NII]) ? [NII] main beam antenna temperature (1)
16- 22 F7.3 km/s V(RRL) RRL LSR velocity (2)
24- 29 F6.3 mK T(RRL) RRL main beam antenna temperature (2)
31- 38 F8.4 km/s V([CII]) ? [CII] LSR velocity (3)
40- 46 F7.4 K T([CII]) ? [CII] main beam antenna temperature (3)
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Note (1): channel width [NII] 2.004km/s.
Note (2): channel width RRL 0.084km/s.
Note (3): channel width [CII] 0.789km/s.
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Acknowledgements:
William D. Langer, william.langer(at)jpl.caltech.edu
References:
Langer et al., 2016A&A...590A..43L 2016A&A...590A..43L,
[C II] and [N II] from dense ionized regions in the Galaxy.
Pineda et al., 2019ApJ...886....1P 2019ApJ...886....1P.
Electron densities and nitrogen abundances in ionized gas derived using
[N II] fine-structure and hydrogen recombination lines.
Anderson et al., 2021arXiv210310466A 2021arXiv210310466A,
The GBT Diffuse Ionized Gas Survey (GDIGS):
Survey Overview and First Data Release
(End) Patricia Vannier [CDS] 27-May-2021