Hobby-Eberly Telescope Observations Of The Dark Halo In NGC 821

dc.contributor.utaustinauthorForestell, Amy D.en_US
dc.contributor.utaustinauthorGebhardt, Karlen_US
dc.creatorForestell, Amy D.en_US
dc.creatorGebhardt, Karlen_US
dc.date.accessioned2016-04-28T19:37:27Z
dc.date.available2016-04-28T19:37:27Z
dc.date.issued2010-06en
dc.description.abstractWe present stellar line-of-sight velocity distributions (LOSVDs) of elliptical galaxy NGC 821 obtained to approximately 100 '' (over two effective radii) with long-slit spectroscopy from the Hobby-Eberly Telescope. Our measured stellar LOSVDs are larger than the planetary nebulae measurements at similar radii. We fit axisymmetric orbit-superposition models with a range of dark halo density profiles, including two-dimensional kinematics at smaller radii from SAURON data. Within our assumptions, the best-fitted model gives a total enclosed mass of 2.0 x 10(11) M(circle dot) within 100 '', with an accuracy of 2%; this mass is equally divided between halo and stars. At 1 R(e), the best-fitted dark matter halo accounts for 13% of the total mass in the galaxy. This dark halo is inconsistent with previous claims of little to no dark matter halo in this galaxy from planetary nebula measurements. We find that a power-law dark halo with a slope 0.1 is the best-fitted model; both the no dark halo and Navarro-Frenk-White models are worse fits at a greater than 99% confidence level. NGC 821 does not appear to have the expected dark halo density profile. The internal moments of the stellar velocity distribution show that the model with no dark halo is radially anisotropic at small radii and tangentially isotropic at large radii, while the best-fitted halo models are slightly radially anisotropic at all radii. We test the potential effects of model smoothing and find that there are no effects on our results within the errors. Finally, we run models using the planetary nebula kinematics and assuming our best-fitted halos and find that the planetary nebulae require radial orbits throughout the galaxy.en_US
dc.description.departmentAstronomyen_US
dc.description.sponsorshipTexas Advanced Research Program 003658-0243-2001en_US
dc.description.sponsorshipNSF-CAREER AST03-49095en_US
dc.description.sponsorshipPennsylvania State Universityen_US
dc.description.sponsorshipStanford Universityen_US
dc.description.sponsorshipLudwig-Maximilians-Universitat Munchenen_US
dc.description.sponsorshipGeorg-August-Universitat Gottingenen_US
dc.description.sponsorshipUniversity of Texas at Austinen_US
dc.identifierdoi:10.15781/T26N74
dc.identifier.Filename2010_06_ngc821.pdfen_US
dc.identifier.citationForestell, Amy D., and Karl Gebhardt. "Hobby-Eberly Telescope Observations of the Dark Halo in NGC 821." The Astrophysical Journal, Vol. 716, no. 1 (Jun., 2010): 370.en_US
dc.identifier.doi10.1088/0004-637x/716/1/370en_US
dc.identifier.issn0004-637Xen_US
dc.identifier.urihttp://hdl.handle.net/2152/34941
dc.language.isoEnglishen_US
dc.relation.ispartofen_US
dc.relation.ispartofserialAstrophysical Journalen_US
dc.rightsAdministrative deposit of works to Texas ScholarWorks: This works author(s) is or was a University faculty member, student or staff member; this article is already available through open access or the publisher allows a PDF version of the article to be freely posted online. The library makes the deposit as a matter of fair use (for scholarly, educational, and research purposes), and to preserve the work and further secure public access to the works of the University.en_US
dc.rights.restrictionOpenen_US
dc.subjectdark matteren_US
dc.subjectgalaxies: elliptical and lenticular, cden_US
dc.subjectgalaxies: halosen_US
dc.subjectgalaxies: individual (ngc 821)en_US
dc.subjectgalaxies: kinematics and dynamicsen_US
dc.subjectearly-type galaxiesen_US
dc.subjecthubble-space-telescopeen_US
dc.subjectblack-hole massen_US
dc.subjectaxisymmetrical dynamical modelsen_US
dc.subjectto-light ratioen_US
dc.subjectelliptic galaxiesen_US
dc.subjectsauron projecten_US
dc.subjectlenticular galaxiesen_US
dc.subjectstellar populationsen_US
dc.subjectplanetary-nebulaeen_US
dc.subjectastronomy & astrophysicsen_US
dc.titleHobby-Eberly Telescope Observations Of The Dark Halo In NGC 821en_US
dc.typeArticleen_US
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