Spatially Resolved Stellar Spectroscopy of the Ultra-diffuse Galaxy Dragonfly 44. III. Evidence for an Unexpected Star Formation History under Conventional Galaxy Evolution Processes
Abstract
We use the Keck Cosmic Web Imager integral field unit spectrograph to (1) measure the global stellar population parameters for the ultra-diffuse galaxy (UDG) Dragonfly 44 (DF44) to much higher precision than previously possible for any UDG and (2) for the first time measure spatially resolved stellar population parameters of a UDG. We find that DF44 falls below the mass–metallicity relation established by canonical dwarf galaxies both in and beyond the Local Group. We measure a flat radial age gradient (m_(logage) = +0.01_(-0.08)^(+0.08) log Gyr kpc⁻¹) and a flat to positive metallicity gradient (m_[Fe/H] = +0.09_(-0.12)^(+0.11) dex kpc⁻¹), which are inconsistent with the gradients measured in similarly pressure-supported dwarf galaxies. We also measure a negative [Mg/Fe] gradient (m_[Mg/Fe] = -0.20_(-0.18)^(+0.18)) dex kpc⁻¹ such that the central 1.5 kpc of DF44 has stellar population parameters comparable to metal-poor globular clusters. Overall, DF44 does not have internal properties similar to other dwarf galaxies and is inconsistent with it having been puffed up through a prolonged, bursty star formation history, as suggested by some simulations. Rather, the evidence indicates that DF44 experienced an intense epoch of "inside-out" star formation and then quenched early and catastrophically, such that star formation was cut off more quickly than in canonical dwarf galaxies.
Additional Information
© 2022. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Received 2021 January 5; revised 2021 September 23; accepted 2021 October 26; published 2022 January 10. We would like to thank the anonymous referee for their constructive comments, J. Gannon for some discussion about GC candidate selection, M. Gu for help with various technical odds and ends, S. Laine for discussions about SFHs, R. Schiavon for helping with EZ_Ages, and J. Taylor for very helpful discussion about the dynamics of satellites in clusters. This research was supported in part by the National Science Foundation under grant No. NSF PHY-1748958 through the Kavli Institute for Theoretical Physics workshop Globular Clusters at the Nexus of Star and Galaxy Formation for enabling useful discussions relevant to this paper. A.V. would like to acknowledge the NSF Graduate Fellowship, the UC Santa Cruz Chancellor's Dissertation Year Fellowship, and the Waterloo Centre Astrophysics Postdoctoral Fellowship for their support. A.J.R. was supported by National Science Foundation grant AST-1616710, and as a Research Corporation for Science Advancement Cottrell Scholar. S.D. is supported by NASA through Hubble Fellowship grant #HST-HF2-51454.001-A awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Incorporated, under NASA contract NAS5-26555. Software: IPython (Pérez & Granger 2007), SciPy (Virtanen et al. 2020), NumPy (Van Der Walt et al. 2011), matplotlib (Hunter 2007), Astropy (Astropy Collaboration et al. 2018), PyMC3 (Salvatier & Wiecki 2016), SPI (Villaume et al. 2017) alf (Conroy et al. 2018), EZ_Ages (Schiavon 2007; Graves & Schiavon 2008).Attached Files
Published - Villaume_2022_ApJ_924_32.pdf
Accepted Version - 2101.02220.pdf
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Additional details
- Alternative title
- Spatially Resolved Stellar Spectroscopy of the Ultra-diffuse Galaxy Dragonfly 44. III. Evidence for an Unexpected Star-Formation History
- Eprint ID
- 112928
- Resolver ID
- CaltechAUTHORS:20220114-265463000
- NSF
- PHY-1748958
- NSF Graduate Research Fellowship
- University of California, Santa Cruz
- Waterloo Centre Astrophysics Postdoctoral Fellowship
- NSF
- AST-1616710
- Cottrell Scholar of Research Corporation
- NASA Hubble Fellowship
- HST-HF2-51454.001-A
- NASA
- NAS5-26555
- Created
-
2022-01-18Created from EPrint's datestamp field
- Updated
-
2022-01-18Created from EPrint's last_modified field
- Caltech groups
- Astronomy Department, Space Astrophysics Laboratory