J/ApJ/832/118ivo://CDS.VizieR/J/ApJ/832/118doi:10.26093/cds/vizier.18320118CDSBoettcher E.Zweibel E.G.Gallagher III J.S.Benjamin R.A.2017-12-15T10:55:38Z2017-03-29T14:06:44ZCDS support team

CDS, Observatoire de Strasbourg, 11 rue de l'Universite, F-67000 Strasbourg, France

cds-question@unistra.frgalaxiesspectroscopyinterstellar-mediumThe 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 H{alpha} emission in position-velocity space suggests that the eDIG is found in a ring between galactocentric radii of R_min_<=R<=8kpc, where R_min_>=2kpc. We find that the thermal ({sigma}_th_=11km/s) and turbulent ({sigma}_turb_=25km/s) velocity dispersions are insufficient to satisfy the hydrostatic equilibrium equation given an exponential electron scale height of h_z_=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 ({gamma}_cr_=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.2016ApJ...832..118Bhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/ApJ/832/118CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toII/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 DIGEDAJ/ApJ/383/487 : Planetary nebulae as standard candles. VII. (Ciardullo+, 1991)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/ApJ/832/118https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/ApJ/832/118http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/ApJ/832/118https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/ApJ/832/118https://vizier.iucaa.in/viz-bin/votable?-source=J/ApJ/832/118http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/ApJ/832/118GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/ApJ/832/118/table3 (Emission line spectroscopy)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/ApJ/832/118/table3?https://vizier.iucaa.in/viz-bin/conesearch/J/ApJ/832/118/table3?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/ApJ/832/118/table3?GETtext/xml+votable180.050000true35.62872542.35527970.0055555555555555566/2409https://cdsarc.cds.unistra.fr/viz-bin/moc/J/ApJ/832/118?format=asciiOpticaldefaultJ/ApJ/832/118/table3Emission line spectroscopyrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintMajAxis[-64/183] Fiber offset along major axis (1)arcsecpos;arith.difffloatMinAxis[-96/96] Fiber offset along minor axis (1)arcsecpos;arith.difffloatIHa[0/1987] H{alpha} intensity; 1e-17erg/s/cm^2^ (2)1e-20W.m**-2spect.line.intensityfloate_IHa[0/6] Uncertainty in IHa1e-20W.m**-2stat.errorfloatsigmaHa[0/81] H{alpha} line width (2)km/sspect.line.widthfloate_sigmaHa[0/22] Uncertainty in sigmaHakm/sstat.errorfloatsigmaN2[0/78] The [N II] 6583A line width (2)km/sspect.line.widthfloate_sigmaN2[0/17] Uncertainty in sigmaN2km/sstat.errorfloatsigmaS2a[0/87] The [S II] 6716A line width (2)km/sspect.line.widthfloate_sigmaS2a[0/26] Uncertainty in sigmaS2akm/sstat.errorfloatsigmaS2b[0/84] The [S II] 6731A line width (2)km/sspect.line.widthfloate_sigmaS2b[0/20] Uncertainty in sigmaS2bkm/sstat.errorfloatVel[0/640] H{alpha} velocity centroidkm/sspect.dopplerVelocfloat_RASimbad column added by the CDSdegpos.eq.ra;meta.main_DESimbad column added by the CDSdegpos.eq.dec;meta.main