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Deep Subaru Hyper Suprime-Cam Observations of Milky Way Satellites Columba I and Triangulum II

Carlin, Jeffrey L. and Sand, David J. and Muñoz, Ricardo R. and Spekkens, Kristine and Willman, Beth and Crnojević, Denija and Forbes, Duncan A. and Hargis, Jonathan and Kirby, Evan and Peter, Annika H. G. and Romanowsky, Aaron J. and Strader, Jay (2017) Deep Subaru Hyper Suprime-Cam Observations of Milky Way Satellites Columba I and Triangulum II. Astronomical Journal, 154 (6). Art. No. 267. ISSN 1538-3881.

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We present deep, wide-field Subaru Hyper Suprime-Cam photometry of two recently discovered satellites of the Milky Way (MW): Columba I (Col I) and Triangulum II (Tri II). The color–magnitude diagrams of both objects point to exclusively old and metal-poor stellar populations. We re-derive structural parameters and luminosities of these satellites, and find M_(V,Col I) = -4.2 ± 0.2 for Col I and M_(V,Tri II) = -1.2 ± 0.4 for Tri II, with corresponding half-light radii of r_(h,Col I) = 117 ± 17 pc and r_(h,Tri II) = 21 ± 4 pc. The properties of both systems are consistent with observed scaling relations for MW dwarf galaxies. Based on archival data, we derive upper limits on the neutral gas content of these dwarfs, and find that they lack H I, as do the majority of observed satellites within the MW virial radius. Neither satellite shows evidence of tidal stripping in the form of extensions or distortions in matched-filter stellar density maps or surface-density profiles. However, the smaller Tri II system is relatively metal-rich for its luminosity (compared to other MW satellites), possibly because it has been tidally stripped. Through a suite of orbit simulations, we show that Tri II is approaching pericenter of its eccentric orbit, a stage at which tidal debris is unlikely to be seen. In addition, we find that Tri II may be on its first infall into the MW, which helps explain its unique properties among MW dwarfs. Further evidence that Tri II is likely an ultra-faint dwarf comes from its stellar mass function, which is similar to those of other MW dwarfs.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Carlin, Jeffrey L.0000-0002-3936-9628
Sand, David J.0000-0003-4102-380X
Spekkens, Kristine0000-0002-0956-7949
Willman, Beth0000-0003-2892-9906
Crnojević, Denija0000-0002-1763-4128
Kirby, Evan0000-0001-6196-5162
Peter, Annika H. G.0000-0002-8040-6785
Romanowsky, Aaron J.0000-0003-2473-0369
Strader, Jay0000-0002-1468-9668
Additional Information:© 2017 The American Astronomical Society. Received 2017 July 4; revised 2017 October 5; accepted 2017 October 17; published 2017 December 1. Based in part on data collected at the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan. We thank the referee for a careful reading of the manuscript, and comments that helped us improve the paper. We thank Fumiaki Nakata and Rita Morris for assistance at the Subaru Telescope. J.L.C. and B.W. are partially supported by NSF Faculty Early Career Development (CAREER) award AST-1151462. D.J.S. acknowledges support from NSF grant AST-1412504. J.S. acknowledges support from NSF grant AST-1514763 and a Packard Fellowship. A.J.R. was supported by NSF grant AST-1616710 and as a Research Corporation for Science Advancement Cottrell Scholar. We thank Edouard Bernard for kindly sharing the PS1 globular cluster fiducials, and Keith Bechtol and David Nidever for helpful discussions. The authors wish to recognize and acknowledge the very 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 research has made use of NASA's Astrophysics Data System, and Astropy, a community-developed core Python package for Astronomy (Astropy Collaboration et al. 2013). This work has made use of the IAC-STAR Synthetic CMD computation code. IAC-STAR is supported and maintained by the computer division of the Instituto de Astrofísica de Canarias. Some of the data presented in this paper were obtained from the Mikulski Archive for Space Telescopes (MAST). STScI is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. Support for MAST for non-HST data is provided by the NASA Office of Space Science via grant NNX09AF08G and by other grants and contracts. The Pan-STARRS1 Surveys have been made possible through contributions of the Institute for Astronomy, the University of Hawaii, the Pan-STARRS Project Office, the Max Planck Society and its participating institutes, the Max Planck Institute for Astronomy, Heidelberg and the Max Planck Institute for Extraterrestrial Physics, Garching, The Johns Hopkins University, Durham University, the University of Edinburgh, Queen's University Belfast, the Harvard-Smithsonian Center for Astrophysics, the Las Cumbres Observatory Global Telescope Network Incorporated, the National Central University of Taiwan, the Space Telescope Science Institute, the National Aeronautics and Space Administration under grant No. NNX08AR22G issued through the Planetary Science Division of the NASA Science Mission Directorate, the National Science Foundation under grant AST-1238877, the University of Maryland, Eotvos Lorand University (ELTE), and the Los Alamos National Laboratory. Facility: Subaru (Hyper Suprime-Cam) - . Software: Astropy (Astropy Collaboration et al. 2013), IDL astronomy users library (Landsman 1993), iPython (Perez & Granger 2007), Matplotlib (Hunter 2007), NumPy (van der Walt et al. 2011), Topcat (Taylor 2005).
Funding AgencyGrant Number
David and Lucile Packard FoundationUNSPECIFIED
Research CorporationUNSPECIFIED
Subject Keywords:galaxies: dwarf – galaxies: individual (Columba I, Triangulum II) – galaxies: photometry – Galaxy: halo – Local Group
Issue or Number:6
Record Number:CaltechAUTHORS:20171130-095952338
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Official Citation:Jeffrey L. Carlin et al 2017 AJ 154 267
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:83592
Deposited By: Tony Diaz
Deposited On:30 Nov 2017 18:15
Last Modified:03 Oct 2019 19:08

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