THE SHAPE OF LITTLE THINGS DWARF GALAXIES DDO 46 AND DDO 168: UNDERSTANDING THE STELLAR AND GAS KINEMATICS
Determining the shape of dwarf irregular (dIrr) galaxies is controversial because if one assumes that these objects are disks and if these disks are randomly distributed over the sky, then their projected minor-to-major axis ratios should follow a particular statistical distribution, which is not ob...
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IOP Publishing
2015
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| Online Access: | http://hdl.handle.net/1721.1/98304 https://orcid.org/0000-0003-1327-1398 |
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| author | Johnson, Megan C. Hunter, Deidre Wood, Sarah Oh, Se-Heon Zhang, Hong-Xin Herrmann, Kimberly A. Levine, Stephen E. |
| author2 | Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences |
| author_facet | Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences Johnson, Megan C. Hunter, Deidre Wood, Sarah Oh, Se-Heon Zhang, Hong-Xin Herrmann, Kimberly A. Levine, Stephen E. |
| author_sort | Johnson, Megan C. |
| collection | MIT |
| description | Determining the shape of dwarf irregular (dIrr) galaxies is controversial because if one assumes that these objects are disks and if these disks are randomly distributed over the sky, then their projected minor-to-major axis ratios should follow a particular statistical distribution, which is not observed. Thus, different studies have led to different conclusions. Some believe that the observed distributions can be explained by assuming the dIrrs are thick disks while others have concluded that dIrrs are triaxial. Fortunately, the central stellar velocity dispersion, σ[subscript z,0], combined with maximum rotation speed, V[subscript max], provides a kinematic measure, V[subscript max]/σ[subscript z,0], which gives the three-dimensional shape of a system. In this work, we present the stellar and gas kinematics of DDO 46 and DDO 168 from the Local Irregulars That Trace Luminosity Extremes; The H i Nearby Galaxy Survey (LITTLE THINGS) and determine their respective V[subscript max]/σ[subscript z,0] values. We used the Kitt Peak National Observatory's Mayall 4 m telescope with the Echelle spectrograph as a long-slit spectrograph, which provided a two-dimensional, 3'-long slit. We acquired spectra of DDO 168 along four position angles (PAs) by placing the slit over the morphological major and minor axes and two intermediate PAs. However, due to poor weather conditions during our observing run for DDO 46, we were able to extract only one useful data point from the morphological major axis. We determined a central stellar velocity dispersion perpendicular to the disk, σ[subscript z,0], of 13.5 ± 8 km s[superscript −1] for DDO 46 and ‹σ[subscript z,0› of 10.7 ± 2.9 km s[superscript −1] for DDO 168. We then derived the maximum rotation speed in both galaxies using the LITTLE THINGS H i data. We separated bulk motions from non-circular motions using a double Gaussian decomposition technique and applied a tilted-ring model to the bulk velocity field. We corrected the observed H i rotation speeds for asymmetric drift and found a maximum velocity, V[subscript max], of 77.4 ± 3.7 and 67.4 ± 4.0 for DDO 46 and DDO 168, respectively. Thus, we derived a kinematic measure, V[subscript max]/σ[subscript z,0], of 5.7 ± 0.6 for DDO 46 and 6.3 ± 0.3 for DDO 168. Comparing these values to ones determined for spiral galaxies, we find that DDO 46 and DDO 168 have V[subscript max]/σ[subscript z,0] values indicative of thin disks, which is in contrast to minor-to-major axis ratio studies. |
| first_indexed | 2024-09-23T17:05:16Z |
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| id | mit-1721.1/98304 |
| institution | Massachusetts Institute of Technology |
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| publishDate | 2015 |
| publisher | IOP Publishing |
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| spelling | mit-1721.1/983042022-09-29T23:34:23Z THE SHAPE OF LITTLE THINGS DWARF GALAXIES DDO 46 AND DDO 168: UNDERSTANDING THE STELLAR AND GAS KINEMATICS Johnson, Megan C. Hunter, Deidre Wood, Sarah Oh, Se-Heon Zhang, Hong-Xin Herrmann, Kimberly A. Levine, Stephen E. Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences Levine, Stephen E. Determining the shape of dwarf irregular (dIrr) galaxies is controversial because if one assumes that these objects are disks and if these disks are randomly distributed over the sky, then their projected minor-to-major axis ratios should follow a particular statistical distribution, which is not observed. Thus, different studies have led to different conclusions. Some believe that the observed distributions can be explained by assuming the dIrrs are thick disks while others have concluded that dIrrs are triaxial. Fortunately, the central stellar velocity dispersion, σ[subscript z,0], combined with maximum rotation speed, V[subscript max], provides a kinematic measure, V[subscript max]/σ[subscript z,0], which gives the three-dimensional shape of a system. In this work, we present the stellar and gas kinematics of DDO 46 and DDO 168 from the Local Irregulars That Trace Luminosity Extremes; The H i Nearby Galaxy Survey (LITTLE THINGS) and determine their respective V[subscript max]/σ[subscript z,0] values. We used the Kitt Peak National Observatory's Mayall 4 m telescope with the Echelle spectrograph as a long-slit spectrograph, which provided a two-dimensional, 3'-long slit. We acquired spectra of DDO 168 along four position angles (PAs) by placing the slit over the morphological major and minor axes and two intermediate PAs. However, due to poor weather conditions during our observing run for DDO 46, we were able to extract only one useful data point from the morphological major axis. We determined a central stellar velocity dispersion perpendicular to the disk, σ[subscript z,0], of 13.5 ± 8 km s[superscript −1] for DDO 46 and ‹σ[subscript z,0› of 10.7 ± 2.9 km s[superscript −1] for DDO 168. We then derived the maximum rotation speed in both galaxies using the LITTLE THINGS H i data. We separated bulk motions from non-circular motions using a double Gaussian decomposition technique and applied a tilted-ring model to the bulk velocity field. We corrected the observed H i rotation speeds for asymmetric drift and found a maximum velocity, V[subscript max], of 77.4 ± 3.7 and 67.4 ± 4.0 for DDO 46 and DDO 168, respectively. Thus, we derived a kinematic measure, V[subscript max]/σ[subscript z,0], of 5.7 ± 0.6 for DDO 46 and 6.3 ± 0.3 for DDO 168. Comparing these values to ones determined for spiral galaxies, we find that DDO 46 and DDO 168 have V[subscript max]/σ[subscript z,0] values indicative of thin disks, which is in contrast to minor-to-major axis ratio studies. 2015-09-01T19:24:51Z 2015-09-01T19:24:51Z 2015-05 2014-10 Article http://purl.org/eprint/type/JournalArticle 1538-3881 0004-6256 http://hdl.handle.net/1721.1/98304 Johnson, Megan C., Deidre Hunter, Sarah Wood, Se-Heon Oh, Hong-Xin Zhang, Kimberly A. Herrmann, and Stephen E. Levine. “THE SHAPE OF LITTLE THINGS DWARF GALAXIES DDO 46 AND DDO 168: UNDERSTANDING THE STELLAR AND GAS KINEMATICS.” The Astronomical Journal 149, no. 6 (May 21, 2015): 196. © 2015 The American Astronomical Society https://orcid.org/0000-0003-1327-1398 en_US http://dx.doi.org/10.1088/0004-6256/149/6/196 The Astronomical Journal Article is made available in accordance with the publisher's policy and may be subject to US copyright law. Please refer to the publisher's site for terms of use. application/pdf IOP Publishing IOP Publishing |
| spellingShingle | Johnson, Megan C. Hunter, Deidre Wood, Sarah Oh, Se-Heon Zhang, Hong-Xin Herrmann, Kimberly A. Levine, Stephen E. THE SHAPE OF LITTLE THINGS DWARF GALAXIES DDO 46 AND DDO 168: UNDERSTANDING THE STELLAR AND GAS KINEMATICS |
| title | THE SHAPE OF LITTLE THINGS DWARF GALAXIES DDO 46 AND DDO 168: UNDERSTANDING THE STELLAR AND GAS KINEMATICS |
| title_full | THE SHAPE OF LITTLE THINGS DWARF GALAXIES DDO 46 AND DDO 168: UNDERSTANDING THE STELLAR AND GAS KINEMATICS |
| title_fullStr | THE SHAPE OF LITTLE THINGS DWARF GALAXIES DDO 46 AND DDO 168: UNDERSTANDING THE STELLAR AND GAS KINEMATICS |
| title_full_unstemmed | THE SHAPE OF LITTLE THINGS DWARF GALAXIES DDO 46 AND DDO 168: UNDERSTANDING THE STELLAR AND GAS KINEMATICS |
| title_short | THE SHAPE OF LITTLE THINGS DWARF GALAXIES DDO 46 AND DDO 168: UNDERSTANDING THE STELLAR AND GAS KINEMATICS |
| title_sort | shape of little things dwarf galaxies ddo 46 and ddo 168 understanding the stellar and gas kinematics |
| url | http://hdl.handle.net/1721.1/98304 https://orcid.org/0000-0003-1327-1398 |
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