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Published May 1, 2018 | Published + Accepted Version
Journal Article Open

The Stellar Populations of Two Ultra-diffuse Galaxies from Optical and Near-infrared Photometry

Abstract

We present observational constraints on the stellar populations of two ultra-diffuse galaxies (UDGs) using optical through near-infrared (NIR) spectral energy distribution (SED) fitting. Our analysis is enabled by new Spitzer-IRAC 3.6 and 4.5 μm imaging, archival optical imaging, and the prospectorfully Bayesian SED fitting framework. Our sample contains one field UDG (DGSAT I), one Virgo cluster UDG (VCC 1287), and one Virgo cluster dwarf elliptical for comparison (VCC 1122). We find that the optical–NIR colors of the three galaxies are significantly different from each other. We infer that VCC 1287 has an old (≳7.7 Gyr) and surprisingly metal-poor ([Z/Z⊙] ≾ −1.0) stellar population, even after marginalizing over uncertainties on diffuse interstellar dust. In contrast, the field UDG DGSAT I shows evidence of being younger than the Virgo UDG, with an extended star formation history and an age posterior extending down to ~3 Gyr. The stellar metallicity of DGSAT I is sub-solar but higher than that of the Virgo UDG, with [Z/Z⊙] = -0.63^(+0.35)_(-0.62); in the case of exactly zero diffuse interstellar dust, DGSAT I may even have solar metallicity. With VCC 1287 and several Coma UDGs, a general picture is emerging where cluster UDGs may be "failed" galaxies, but the field UDG DGSAT I seems more consistent with a stellar feedback-induced expansion scenario. In the future, our approach can be applied to a large and diverse sample of UDGs down to faint surface brightness limits, with the goal of constraining their stellar ages, stellar metallicities, and circumstellar and diffuse interstellar dust content.

Additional Information

© 2018 The American Astronomical Society. Received 2017 November 7; revised 2018 February 12; accepted 2018 March 4; published 2018 April 30. We greatly thank Laura Ferrarese for providing us with Elixir-LSB CFHT imaging of VCC 1287. We thank James Ingalls for his help with "de-striping" our IRAC images, and Sean Carey and Tom Jarrett for advice on systematic uncertainties in IRAC imaging. We thank Fangzhou Jiang, Avishai Dekel, Andi Burkert, and Soeren Larsen for useful discussions; Johnny Greco and Chris Conselice for helpful comments on the paper; and the anonymous referee for invaluable suggestions. V.P. acknowledges useful conversations with Arianna di Cintio, Meng Gu, Timothy Carleton, and Tsang Keung Chan at the 2017 Santa Cruz Galaxy Formation Workshop, and separately Rachel Somerville, Joel Primack, Sandy Faber, and David Koo. A.J.R. was supported by National Science Foundation grant AST-1616710 and as a Research Corporation for Science Advancement Cottrell Scholar. J.P.B. was supported by NSF AST-1616598. This research was supported in part by the National Science Foundation under grant NSF PHY11-25915. This work is based in part on observations made with and archival data obtained with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. This research made use of Astropy (particularly photutils), a community-developed core Python package for Astronomy (Astropy Collaboration et al. 2013).

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Published - Pandya_2018_ApJ_858_29.pdf

Accepted Version - 1711.05272.pdf

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August 19, 2023
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October 18, 2023