Villaume, Alexa and Romanowsky, Aaron J. and Brodie, Jean and van Dokkum, Pieter and Conroy, Charlie and Forbes, Duncan A. and Danieli, Shany and Martin, Christopher and Matuszewski, Matt (2022) Spatially Resolved Stellar Spectroscopy of the Ultra-diffuse Galaxy Dragonfly 44. III. Evidence for an Unexpected Star Formation History under Conventional Galaxy Evolution Processes. Astrophysical Journal, 924 (1). Art. No. 32. ISSN 0004-637X. doi:10.3847/1538-4357/ac341e. https://resolver.caltech.edu/CaltechAUTHORS:20220114-265463000
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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.
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| Alternate Title: | Spatially Resolved Stellar Spectroscopy of the Ultra-diffuse Galaxy Dragonfly 44. III. Evidence for an Unexpected Star-Formation History | ||||||||||||||||||
| 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). | ||||||||||||||||||
| Group: | Astronomy Department, Space Astrophysics Laboratory | ||||||||||||||||||
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| Subject Keywords: | Coma Cluster; Chemical abundances; Galaxy evolution; Galaxy quenching; Galaxy stellar content | ||||||||||||||||||
| Issue or Number: | 1 | ||||||||||||||||||
| Classification Code: | Unified Astronomy Thesaurus concepts: Coma Cluster (270); Chemical abundances (224); Galaxy evolution (594); Galaxy quenching (2040); Galaxy stellar content (621) | ||||||||||||||||||
| DOI: | 10.3847/1538-4357/ac341e | ||||||||||||||||||
| Record Number: | CaltechAUTHORS:20220114-265463000 | ||||||||||||||||||
| Persistent URL: | https://resolver.caltech.edu/CaltechAUTHORS:20220114-265463000 | ||||||||||||||||||
| Official Citation: | Alexa Villaume et al 2022 ApJ 924 32 | ||||||||||||||||||
| Usage Policy: | No commercial reproduction, distribution, display or performance rights in this work are provided. | ||||||||||||||||||
| ID Code: | 112928 | ||||||||||||||||||
| Collection: | CaltechAUTHORS | ||||||||||||||||||
| Deposited By: | George Porter | ||||||||||||||||||
| Deposited On: | 18 Jan 2022 16:33 | ||||||||||||||||||
| Last Modified: | 18 Jan 2022 16:33 |
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