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Low metallicities and old ages for three ultra-diffuse galaxies in the Coma cluster

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Date
21/05/2018
Author
Gu, Meng
Conroy, Charlie
Law, David
van Dokkum, Pieter
Yan, Renbin
Wake, David
Bundy, Kevin
Merritt, Allison
Abraham, Roberto
Zhang, Jielai
Bershady, Matthew
Bizyaev, Dmitry
Brinkmann, Jonathan
Drory, Niv
Grabowski, Kathleen
Masters, Karen
Pan, Kaike
Parejko, John
Weijmans, Anne-Marie
Zhang, Kai
Keywords
Galaxies: clusters: individual (Coma)
Galaxies: evolution
Galaxies: stellar content
QB Astronomy
QC Physics
DAS
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Abstract
A large population of ultra-diffuse galaxies (UDGs) was recently discovered in the Coma cluster. Here we present optical spectra of three such UDGs, DF 7, DF 44, and DF 17, which have central surface brightnesses of μ g ≈ 24.4–25.1 mag arcsec−2. The spectra were acquired as part of an ancillary program within the SDSS-IV MaNGA Survey. We stacked 19 fibers in the central regions from larger integral field units (IFUs) per source. With over 13.5 hr of on-source integration, we achieved a mean signal-to-noise ratio in the optical of 9.5 Å−1, 7.9 Å−1, and 5.0 Å−1, respectively, for DF 7, DF 44, and DF 17. Stellar population models applied to these spectra enable measurements of recession velocities, ages, and metallicities. The recession velocities of DF 7, DF 44, and DF 17 are ${6599}_{-25}^{+40}$ km s−1, ${6402}_{-39}^{+41}$ km s−1, and ${8315}_{-43}^{+43}$ km s−1, spectroscopically confirming that all of them reside in the Coma cluster. The stellar populations of these three galaxies are old and metal-poor, with ages of ${7.9}_{-2.5}^{+3.6}$ Gyr, ${8.9}_{-3.3}^{+4.3}$ Gyr, and ${9.1}_{-5.5}^{+3.9}$ Gyr, and iron abundances of [Fe/H] $-{1.0}_{-0.4}^{+0.3}$, $-{1.3}_{-0.4}^{+0.4}$, and $-{0.8}_{-0.5}^{+0.5}$, respectively. Their stellar masses are (3–6) × 108M⊙. The UDGs in our sample are as old or older than galaxies at similar stellar mass or velocity dispersion (only DF 44 has an independently measured dispersion). They all follow the well-established stellar mass–stellar metallicity relation, while DF 44 lies below the velocity dispersion-metallicity relation. These results, combined with the fact that UDGs are unusually large for their stellar masses, suggest that stellar mass plays a more important role in setting stellar population properties for these galaxies than either size or surface brightness.
Citation
Gu , M , Conroy , C , Law , D , van Dokkum , P , Yan , R , Wake , D , Bundy , K , Merritt , A , Abraham , R , Zhang , J , Bershady , M , Bizyaev , D , Brinkmann , J , Drory , N , Grabowski , K , Masters , K , Pan , K , Parejko , J , Weijmans , A-M & Zhang , K 2018 , ' Low metallicities and old ages for three ultra-diffuse galaxies in the Coma cluster ' , Astrophysical Journal , vol. 859 , 37 . https://doi.org/10.3847/1538-4357/aabbae
Publication
Astrophysical Journal
Status
Peer reviewed
DOI
https://doi.org/10.3847/1538-4357/aabbae
ISSN
0004-637X
Type
Journal article
Rights
© 2018. The American Astronomical Society. All rights reserved. This work is made available online in accordance with the publisher’s policies. This is the final published version of the work, which was originally published at: https://doi.org/10.3847/1538-4357/aabbae
Description
A.W. acknowledges support of a Leverhulme Trust Early Career Fellowship.
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  • University of St Andrews Research
URL
http://adsabs.harvard.edu/abs/2017arXiv170907003G
URI
http://hdl.handle.net/10023/13771

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