Skip to main content

Research Repository

Advanced Search

Structural Parameters and Possible Association of the Ultra-faint Dwarfs Pegasus III and Pisces II from Deep Hubble Space Telescope Photometry

Richstein, Hannah; Patel, Ekta; Kallivayalil, Nitya; Simon, Joshua D.; Zivick, Paul; Tollerud, Erik; Fritz, Tobias; Warfield, Jack T.; Besla, Gurtina; van der Marel, Roeland P.; Wetzel, Andrew; Choi, Yumi; Deason, Alis; Geha, Marla; Guhathakurta, Puragra; Jeon, Myoungwon; Kirby, Evan N.; Libralato, Mattia; Sacchi, Elena; Sohn, Sangmo Tony

Structural Parameters and Possible Association of the Ultra-faint Dwarfs Pegasus III and Pisces II from Deep Hubble Space Telescope Photometry Thumbnail


Authors

Hannah Richstein

Ekta Patel

Nitya Kallivayalil

Joshua D. Simon

Paul Zivick

Erik Tollerud

Tobias Fritz

Jack T. Warfield

Gurtina Besla

Roeland P. van der Marel

Andrew Wetzel

Yumi Choi

Marla Geha

Puragra Guhathakurta

Myoungwon Jeon

Evan N. Kirby

Mattia Libralato

Elena Sacchi

Sangmo Tony Sohn



Abstract

We present deep Hubble Space Telescope (HST) photometry of the ultra-faint dwarf (UFD) galaxies Pegasus III (Peg III) and Pisces II (Psc II), two of the most distant satellites in the halo of the Milky Way (MW). We measure the structure of both galaxies, derive mass-to-light ratios with newly determined absolute magnitudes, and compare our findings to expectations from UFD-mass simulations. For Peg III, we find an elliptical half-light radius of = ¢ - + ah 1.88 0.33 0.42 ( - + 118 30 31 pc) and = - - M + V 4.17 ; 0.22 0.19 for Psc II, we measure = ¢ - + ah 1.31 0.09 0.10 (69 ± 8 pc) and = - - M + V 4.28 0.16 0.19. We do not find any morphological features that indicate a significant interaction between the two has occurred, despite their close separation of only ∼40 kpc. Using proper motions (PMs) from Gaia early Data Release 3, we investigate the possibility of any past association by integrating orbits for the two UFDs in an MW-only and a combined MW and Large Magellanic Cloud (LMC) potential. We find that including the gravitational influence of the LMC is crucial, even for these outer-halo satellites, and that a possible orbital history exists where Peg III and Psc II experienced a close (∼10–20 kpc) passage about each other just over ∼1 Gyr ago, followed by a collective passage around the LMC (∼30–60 kpc) just under ∼1 Gyr ago. Considering the large uncertainties on the PMs and the restrictive priors imposed to derive them, improved PM measurements for Peg III and Psc II will be necessary to clarify their relationship. This would add to the rare findings of confirmed pairs of satellites within the Local Group.

Citation

Richstein, H., Patel, E., Kallivayalil, N., Simon, J. D., Zivick, P., Tollerud, E., …Sohn, S. T. (2022). Structural Parameters and Possible Association of the Ultra-faint Dwarfs Pegasus III and Pisces II from Deep Hubble Space Telescope Photometry. Astrophysical Journal, 933(2), Article 217. https://doi.org/10.3847/1538-4357/ac7226

Journal Article Type Article
Acceptance Date May 19, 2022
Online Publication Date Jul 15, 2022
Publication Date 2022-07
Deposit Date Jul 27, 2022
Publicly Available Date Mar 28, 2024
Journal Astrophysical Journal
Print ISSN 0004-637X
Electronic ISSN 1538-4357
Publisher American Astronomical Society
Peer Reviewed Peer Reviewed
Volume 933
Issue 2
Article Number 217
DOI https://doi.org/10.3847/1538-4357/ac7226

Files

Published Journal Article (3.9 Mb)
PDF

Publisher Licence URL
http://creativecommons.org/licenses/by/4.0/

Copyright Statement
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.





You might also like



Downloadable Citations