J/ApJ/832/118 Emission-line spectroscopy in NGC 891 (Boettcher+, 2016)
Testing a dynamical equilibrium model of the extraplanar diffuse ionized gas in
NGC 891.
Boettcher E., Zweibel E.G., Gallagher III J.S., Benjamin R.A.
<Astrophys. J., 832, 118-118 (2016)>
=2016ApJ...832..118B 2016ApJ...832..118B (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies, nearby ; Spectroscopy ; Interstellar medium
Keywords: cosmic rays; galaxies: individual: NGC 891;
galaxies: ISM; ISM: kinematics and dynamics; ISM: magnetic fields
Abstract:
The observed scale heights of extraplanar diffuse ionized gas (eDIG)
layers exceed their thermal scale heights by a factor of a few in the
Milky Way and other nearby edge-on disk galaxies. Here, we test a
dynamical equilibrium model of the eDIG layer in NGC 891, where we ask
whether the thermal, turbulent, magnetic field, and cosmic-ray
pressure gradients are sufficient to support the layer. In optical
emission-line spectroscopy from the SparsePak integral field unit on
the WIYN 3.5m telescope, the Hα emission in position-velocity
space suggests that the eDIG is found in a ring between galactocentric
radii of Rmin≤R≤8kpc, where Rmin≥2kpc. We find that the thermal
(σth=11km/s) and turbulent (σturb=25km/s) velocity
dispersions are insufficient to satisfy the hydrostatic equilibrium
equation given an exponential electron scale height of hz=1.0kpc.
Using a literature analysis of radio continuum observations from the
CHANG-ES survey, we demonstrate that the magnetic field and cosmic-ray
pressure gradients are sufficient to stably support the gas at R≥8kpc
if the cosmic rays are sufficiently coupled to the system
(γcr=1.45). Thus, a stable dynamical equilibrium model is
viable only if the eDIG is found in a thin ring around R=8kpc, and
nonequilibrium models such as a galactic fountain flow are of interest
for further study.
Description:
Optical emission-line spectroscopy of the extraplanar diffuse ionized
gas (eDIG) layer in NGC 891 was obtained on the WIYN5 3.5m telescope
at KPNO on 2014 November 15-17 (wavelength coverage from ∼6380 to
6805Å; spectral resolution R=7770).
Objects:
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RA (ICRS) DE Designation(s)
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02 22 32.91 +42 20 53.9 NGC 891 = MCG+07-05-046
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table3.dat 68 328 Emission line spectroscopy
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See also:
II/249 : WHAM Northern Sky Survey, V-1.1 (Haffner+, 2003)
III/211 : Keck/HIRES Sky Line Atlas (Osterbrock+ 1997)
J/AJ/150/81 : CHANG-ES. IV. VLA D-configuration observations (Wiegert+, 2015)
J/A+A/575/A17 : NGC 891 Herschel PACS and SPIRE spectroscopy (Hughes+, 2015)
J/A+A/565/A4 : NGC 891 70-500um images (Hughes+, 2014)
J/MNRAS/396/1231 : Astrophotometric catalogue of NGC 891 (Rejkuba+, 2009)
J/other/RMxAA/45.261 : Diffuse ionized gas database DIGEDA
(Flores-Fajardo+ 2009)
J/ApJ/383/487 : Planetary nebulae as standard candles. VII. (Ciardullo+, 1991)
Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 5 F5.1 arcsec MajAxis [-64/183] Fiber offset along major axis (1)
7- 11 F5.1 arcsec MinAxis [-96/96] Fiber offset along minor axis (1)
13- 18 F6.1 10-20W/m2 IHa [0/1987] Hα intensity;
1e-17erg/s/cm2 (2)
20- 22 F3.1 10-20W/m2 e_IHa [0/6] Uncertainty in IHa
24- 27 F4.1 km/s sigmaHa [0/81] Hα line width (2)
29- 32 F4.1 km/s e_sigmaHa [0/22] Uncertainty in sigmaHa
34- 37 F4.1 km/s sigmaN2 [0/78] The [N II] 6583A line width (2)
39- 42 F4.1 km/s e_sigmaN2 [0/17] Uncertainty in sigmaN2
44- 47 F4.1 km/s sigmaS2a [0/87] The [S II] 6716A line width (2)
49- 52 F4.1 km/s e_sigmaS2a [0/26] Uncertainty in sigmaS2a
54- 57 F4.1 km/s sigmaS2b [0/84] The [S II] 6731A line width (2)
59- 62 F4.1 km/s e_sigmaS2b [0/20] Uncertainty in sigmaS2b
64- 68 F5.1 km/s Vel [0/640] Hα velocity centroid
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Note (1): Fiber offsets along the major and minor axes are measured with
respect to the galactic center at RA,DEC=02:22:33.4,+42:20:57.
Note (2): Fibers without eDIG detections have null values, and emission lines
with less than 4σ detections have null line widths.
All line widths are standard deviations; the line widths are
corrected for the instrumental resolution.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 21-Feb-2017