J/ApJ/814/133 Herschel Galactic plane survey of [NII] (Goldsmith+, 2015)
Herschel Galactic plane survey of [NII] fine structure emission.
Goldsmith P.F., Yildiz U.A., Langer W.D., Pineda J.L.
<Astrophys. J., 814, 133 (2015)>
=2015ApJ...814..133G 2015ApJ...814..133G (SIMBAD/NED BibCode)
ADC_Keywords: Milky Way ; Interstellar medium ; Spectroscopy
Keywords: ISM: general; ISM: structure
Abstract:
We present the first large-scale high angular resolution survey of
ionized nitrogen in the Galactic Plane through emission of its two
fine structure transitions ([N II]) at 122 and 205 µm. The
observations were largely obtained with the PACS instrument onboard
the Herschel Space Observatory. The lines of sight were in the
Galactic plane, following those of the Herschel OTKP project GOT C+.
Both lines are reliably detected at the 10-8-10-7 W/m2/sr
level over the range -60°≤l≤60°. The rms of the intensity
among the 25 PACS spaxels of a given pointing is typically less than
one third of the mean intensity, showing that the emission is
extended. [N II] is produced in gas in which hydrogen is ionized, and
collisional excitation is by electrons. The ratio of the two fine
structure transitions provides a direct measurement of the electron
density, yielding n(e) largely in the range 10-50 cm-3 with an average
value of 29 cm-3 and N+ column densities 1016-1017 cm-2. [N II]
emission is highly correlated with that of [C II], and we calculate
that between 1/3 and 1/2 of the [C II] emission is associated with the
ionized gas. The relatively high electron densities indicate that the
source of the [N II] emission is not the warm ionized medium (WIM),
which has electron densities more than 100 times smaller. Possible origins
of the observed [N II] include the ionized surfaces of dense atomic
and molecular clouds, the extended low-density envelopes of H II
regions, and low-filling factor high-density fluctuations of the WIM.
Description:
Observations of both fine structure transitions of [N II], at 121.898 µm
(2459.371 GHz) and 205.178 µm (1461.134 GHz) (Brown et al.
1994ApJ...428L..37B 1994ApJ...428L..37B), were carried out with the PACS spectrometer
(Poglitsch et al. 2010A&A...518L...2P 2010A&A...518L...2P) on Herschel (Pilbratt et al.
2010A&A...518L...1P 2010A&A...518L...1P). At 10 selected positions, the lower frequency
transition was also observed with the high spectral resolution
Heterodyne Instrument for the Far-Infrared (HIFI; de Graauw et al.
2010A&A...518L...6D 2010A&A...518L...6D). Based on the expected relative intensities of
the [N II] and [C II] lines (Bennett et al. 1994ApJ...434..587B 1994ApJ...434..587B),
observations were largely restricted to the inner galaxy, with both
lines detected only in the range -60°=<l=<60°.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 91 70 Observed PACS Integrated Intensities for
[N II] 122 and 205 µm Transitions are
Tabulated Together with the Inferred Electron
Volume Densities and N+ Column Densities
table3.dat 91 79 PACS Results
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See also:
VI/139 : Herschel Observation Log (Herschel Science Centre, 2013)
J/ApJ/829/93 : CO, [CI] and [NII] lines from Herschel spectra
(Kamenetzky+, 2016)
Byte-by-byte Description of file: table2.dat table3.dat
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Bytes Format Units Label Explanations
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1- 10 A10 --- ID Line of sight (LOS) label (GLLL.l+B.b)
12- 19 F8.4 deg GLON Galactic longitude
21- 23 F3.1 deg GLAT Galactic latitude
25- 34 I10 --- OBSID Herschel OBSID
36 I1 --- R [0/3]? Detection status (1)
38 A1 --- l_NII122 [<] Limit flag on NII122
39- 43 F5.2 10-8W/m2/sr NII122 ? [N II] 122 µm intensity averaged over
the 25 PACS spaxels
45- 49 F5.3 10-8W/m2/sr e_NII122 ? Uncertainty in NII122
51- 55 F5.2 10-8 RMS ? RMS variation among the 25 spaxels at
122 µm wavelength
57 I1 --- R1 [0/3]? Detection status (1)
59 A1 --- l_NII205 [<] Limit flag on NII205
60- 64 F5.2 10-8W/m2/sr NII205 ? [N II] 205 µm intensity averaged over
the 25 PACS spaxels
66- 70 F5.3 10-8W/m2/sr e_NII205 ? Uncertainty in NII205
72- 76 F5.1 cm-3 n(e) ? Electron density
78- 81 F4.1 cm-3 e_n(e) ? Uncertainty in n(e)
83- 86 F4.1 10+16cm-2 N(N+) ? N+ column density
88- 91 F4.2 10+16cm-2 e_N(N+) ? Uncertainty in N(N+)
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Note (1): Detection status as follows:
0 = Not observed;
1 = Non-detection;
2 = Detection in individual spaxel or spaxels;
3 = Only the average of all spaxels provides a detection.
For the non-detections, we give the 3σ upper limits on the intensities.
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History:
From electronic version of the journal
(End) Prepared by Tiphaine Pouvreau [CDS] 17-Oct-2017