Keck Integral-field Spectroscopy of M87 Reveals an Intrinsically Triaxial Galaxy and a Revised Black Hole Mass
The three-dimensional intrinsic shape of a galaxy and the mass of the central supermassive black hole provide key insight into the galaxy’s growth history over cosmic time. Standard assumptions of a spherical or axisymmetric shape can be simplistic and can bias the black hole mass inferred from the...
| Main Authors: | , , |
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| Format: | Article |
| Language: | English |
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IOP Publishing
2023-01-01
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| Series: | The Astrophysical Journal Letters |
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| Online Access: | https://doi.org/10.3847/2041-8213/acbbcf |
| _version_ | 1797697170471649280 |
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| author | Emily R. Liepold Chung-Pei Ma Jonelle L. Walsh |
| author_facet | Emily R. Liepold Chung-Pei Ma Jonelle L. Walsh |
| author_sort | Emily R. Liepold |
| collection | DOAJ |
| description | The three-dimensional intrinsic shape of a galaxy and the mass of the central supermassive black hole provide key insight into the galaxy’s growth history over cosmic time. Standard assumptions of a spherical or axisymmetric shape can be simplistic and can bias the black hole mass inferred from the motions of stars within a galaxy. Here, we present spatially resolved stellar kinematics of M87 over a two-dimensional 250″ × 300″ contiguous field covering a radial range of 50 pc–12 kpc from integral-field spectroscopic observations at the Keck II Telescope. From about 5 kpc and outward, we detect a prominent 25 km s ^−1 rotational pattern, in which the kinematic axis (connecting the maximal receding and approaching velocities) is 40° misaligned with the photometric major axis of M87. The rotational amplitude and misalignment angle both decrease in the inner 5 kpc. Such misaligned and twisted velocity fields are a hallmark of triaxiality, indicating that M87 is not an axisymmetrically shaped galaxy. Triaxial Schwarzschild orbit modeling with more than 4000 observational constraints enabled us to determine simultaneously the shape and mass parameters. The models incorporate a radially declining profile for the stellar mass-to-light ratio suggested by stellar population studies. We find that M87 is strongly triaxial, with ratios of p = 0.845 for the middle-to-long principal axes and q = 0.722 for the short-to-long principal axes, and determine the black hole mass to be $({5.37}_{-0.25}^{+0.37}\pm 0.22)\times {10}^{9}{M}_{\odot }$ , where the second error indicates the systematic uncertainty associated with the distance to M87. |
| first_indexed | 2024-03-12T03:36:26Z |
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| institution | Directory Open Access Journal |
| issn | 2041-8205 |
| language | English |
| last_indexed | 2024-03-12T03:36:26Z |
| publishDate | 2023-01-01 |
| publisher | IOP Publishing |
| record_format | Article |
| series | The Astrophysical Journal Letters |
| spelling | doaj.art-23744715c6bb4667b390ccd7ee2ae1232023-09-03T13:08:53ZengIOP PublishingThe Astrophysical Journal Letters2041-82052023-01-019452L3510.3847/2041-8213/acbbcfKeck Integral-field Spectroscopy of M87 Reveals an Intrinsically Triaxial Galaxy and a Revised Black Hole MassEmily R. Liepold0https://orcid.org/0000-0002-7703-7077Chung-Pei Ma1https://orcid.org/0000-0002-4430-102XJonelle L. Walsh2https://orcid.org/0000-0002-1881-5908Department of Physics, University of California , Berkeley, CA 94720, USADepartment of Physics, University of California , Berkeley, CA 94720, USA; Department of Astronomy, University of California , Berkeley, CA 94720, USAGeorge P. and Cynthia Woods Mitchell Institute for Fundamental Physics and Astronomy, and Department of Physics and Astronomy, Texas A&M University , College Station, TX 77843, USAThe three-dimensional intrinsic shape of a galaxy and the mass of the central supermassive black hole provide key insight into the galaxy’s growth history over cosmic time. Standard assumptions of a spherical or axisymmetric shape can be simplistic and can bias the black hole mass inferred from the motions of stars within a galaxy. Here, we present spatially resolved stellar kinematics of M87 over a two-dimensional 250″ × 300″ contiguous field covering a radial range of 50 pc–12 kpc from integral-field spectroscopic observations at the Keck II Telescope. From about 5 kpc and outward, we detect a prominent 25 km s ^−1 rotational pattern, in which the kinematic axis (connecting the maximal receding and approaching velocities) is 40° misaligned with the photometric major axis of M87. The rotational amplitude and misalignment angle both decrease in the inner 5 kpc. Such misaligned and twisted velocity fields are a hallmark of triaxiality, indicating that M87 is not an axisymmetrically shaped galaxy. Triaxial Schwarzschild orbit modeling with more than 4000 observational constraints enabled us to determine simultaneously the shape and mass parameters. The models incorporate a radially declining profile for the stellar mass-to-light ratio suggested by stellar population studies. We find that M87 is strongly triaxial, with ratios of p = 0.845 for the middle-to-long principal axes and q = 0.722 for the short-to-long principal axes, and determine the black hole mass to be $({5.37}_{-0.25}^{+0.37}\pm 0.22)\times {10}^{9}{M}_{\odot }$ , where the second error indicates the systematic uncertainty associated with the distance to M87.https://doi.org/10.3847/2041-8213/acbbcfGalaxy dynamicsGalaxy massesSupermassive black holesEarly-type galaxiesGalaxy dark matter halosGalaxy evolution |
| spellingShingle | Emily R. Liepold Chung-Pei Ma Jonelle L. Walsh Keck Integral-field Spectroscopy of M87 Reveals an Intrinsically Triaxial Galaxy and a Revised Black Hole Mass The Astrophysical Journal Letters Galaxy dynamics Galaxy masses Supermassive black holes Early-type galaxies Galaxy dark matter halos Galaxy evolution |
| title | Keck Integral-field Spectroscopy of M87 Reveals an Intrinsically Triaxial Galaxy and a Revised Black Hole Mass |
| title_full | Keck Integral-field Spectroscopy of M87 Reveals an Intrinsically Triaxial Galaxy and a Revised Black Hole Mass |
| title_fullStr | Keck Integral-field Spectroscopy of M87 Reveals an Intrinsically Triaxial Galaxy and a Revised Black Hole Mass |
| title_full_unstemmed | Keck Integral-field Spectroscopy of M87 Reveals an Intrinsically Triaxial Galaxy and a Revised Black Hole Mass |
| title_short | Keck Integral-field Spectroscopy of M87 Reveals an Intrinsically Triaxial Galaxy and a Revised Black Hole Mass |
| title_sort | keck integral field spectroscopy of m87 reveals an intrinsically triaxial galaxy and a revised black hole mass |
| topic | Galaxy dynamics Galaxy masses Supermassive black holes Early-type galaxies Galaxy dark matter halos Galaxy evolution |
| url | https://doi.org/10.3847/2041-8213/acbbcf |
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