Still at odds with conventional galaxy evolution: the star formation history of ultradiffuse galaxy Dragonfly 44
Abstract
We study the star formation history (SFH) of the ultradiffuse galaxy (UDG) Dragonfly 44 (DF44) based on the simultaneous fit to near-ultraviolet to near-infrared photometry and high signal-to-noise optical spectroscopy. In fitting the observations, we adopt an advanced physical model with a flexible SFH and discuss the results in the context of the degeneracies between stellar population parameters. Through reconstructing the mass-assembly history with a prior for extended star formation (SF) (akin to methods in the literature), we find that DF44 formed 90 per cent of its stellar mass by z ∼ 0.9 (∼7.2 Gyr ago). In comparison, using a prior that prefers concentrated SF (as informed by previous studies of DF44's stellar populations) suggests that DF44 formed as early as z ∼ 8 (∼12.9 Gyr ago). Regardless of whether DF44 is old or very old, the SFHs imply early SF and rapid quenching. This result, together with DF44's large size and evidence that it is on its first infall into the Coma cluster, challenges UDG formation scenarios from simulations that treat all UDGs as contiguous with the canonical dwarf population. While our results cannot confirm any particular formation scenario, we can conclude from this that DF44 experienced a rare quenching event.
Additional Information
We thank Chris Lee for helpful discussions regarding the UV data of DF44. We would like to thank Meng Gu for providing the MaNGA spectrum of DF44, Josh Speagle for help with technical details in using DYNESTY, and Joel Leja for help with technical details related to the SFH priors and PROSPECTOR. We thank the anonymous referee's helpful report that improved the quality of this paper. This research is supported by the following grants: National Sciences and Engineering Research Council of Canada (NSERC) PGS award (KW), Discovery grants (MLB), Waterloo Centre Astrophysics Postdoctoral Fellowship (AV). DAF thanks the Australian Research Council (ARC) for financial assistance via DP220101863. AJR was supported as a Research Corporation for Science Advancement Cottrell Scholar. This work was partially supported by a National Aeronautics and Space Administration (NASA) Keck PI Data Award, administered by the NASA Exoplanet Science Institute. The data presented herein were obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W.M. Keck Foundation. We recognize and acknowledge the significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. This work made use of the following softwares: ASTROPY (The Astropy Collaboration et al. 2018, 2013), DYNESTY (Speagle 2020), FSPS (Conroy et al. 2009; Conroy & Gunn 2010), IPYTHON (Pérez & Granger 2007), MATPLOTLIB (Hunter 2007), NUMPY (van der Walt, Colbert & Varoquaux 2011), PYTHON-FSPS (Johnson et al. 2021a), PROSPECTOR (Leja et al. 2017; Johnson et al. 2019, 2021b), and SCIPY (Virtanen et al. 2020).Additional details
- Eprint ID
- 117167
- Resolver ID
- CaltechAUTHORS:20220928-285212100.11
- Natural Sciences and Engineering Research Council of Canada (NSERC)
- University of Waterloo
- DP220101863
- Australian Research Council
- Cottrell Scholar of Research Corporation
- NASA
- W. M. Keck Foundation
- Created
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2022-10-04Created from EPrint's datestamp field
- Updated
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2022-10-04Created from EPrint's last_modified field
- Caltech groups
- Infrared Processing and Analysis Center (IPAC)