A DECam view of the diffuse dwarf galaxy Crater II: the colour–magnitude diagram

Journal Article · Thu Oct 10 00:00:00 EDT 2019 · Monthly Notices of the Royal Astronomical Society

DOI:https://doi.org/10.1093/mnras/stz2826· OSTI ID:1671830

Walker, A. R. ^[1]; Martínez-Vázquez, C. E.  ^[1]; Monelli, M.  ^[2]; Vivas, A. K.  ^[1]; Bono, G. ^[3]; Gallart, C. ^[2]; Cassisi, S. ^[4]; Andreuzzi, G. ^[5]; Bernard, E. J.  ^[6]; Dall’Ora, M. ^[7]; Fiorentino, G.  ^[8]; Nidever, D. L. ^[9]; Olsen, K. ^[10]; Pietrinferni, A. ^[11]; Stetson, P. B. ^[12]

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1. Cerro Tololo Inter-American Observatory, NSF’s National Optical-Infrared Astronomy Research Laboratory, Casilla 603, La Serena 1700000, Chile
2. Instituto de Astrofísica de Canarias, Calle Vía Láctea, E-38205 La Laguna, Tenerife, Spain, Departamento de Astrofísica, Universidad de La Laguna, E-38206 La Laguna, Tenerife, Spain
3. Departimento di Fisica, Universitá di Roma Tor Vergata, via della Ricerca Scientifica 1, I-00133 Rome, Italy
4. INAF–Osservatorio Astronomico d’Abruzzo, Via M. Maggini, I-64100 Teramo, Italy, INFN–Sezione di Pisa, Largo Pontocorvo 3, I-56127 Pisa, Italy
5. INAF–Fundación Galileo Galilei, Rambla José Ana Fernandez Pérez 7, E-38712 Breña Baja, Spain, INAF–Osservatorio Astronomico di Roma, via Frascati 33, I-0040 Monte Porzio Catone, Italy
6. Université Côte d’Azur, OCA, CNRS, Lagrange, F-06304 Nice, France
7. INAF–Osservatorio Astronomico di Capodimonte, salita Moiariello 16, I-80131 Napoli, Italy
8. INAF–Osservatorio Astronomico di Roma, via Frascati 33, I-0040 Monte Porzio Catone, Italy, INAF–Osservatorio Astronomico di Bologna, via Ranzani 1, I-40127 Bologna, Italy
9. NSF’s National Optical-Infrared Astronomy Research Laboratory, 950 North Cherry Avenue, Tucson, AZ 85719, USA, Department of Physics, Montana State University, PO Box 173840, Bozeman, MT 59717-3840, USA
10. NSF’s National Optical-Infrared Astronomy Research Laboratory, 950 North Cherry Avenue, Tucson, AZ 85719, USA
11. INAF–Osservatorio Astronomico d’Abruzzo, Via M. Maggini, I-64100 Teramo, Italy
12. Herzberg Astronomy and Astrophysics, National Research Council, 5071 West Saanich Road, Victoria, British Columbia V9E 2E7, Canada

ABSTRACT We present a deep Blanco/DECam colour–magnitude diagram (CMD) for the large but very diffuse Milky Way satellite dwarf galaxy Crater II. The CMD shows only old stars with a clearly bifurcated subgiant branch (SGB) that feeds a narrow red giant branch. The horizontal branch (HB) shows many RR Lyrae and red HB stars. Comparing the CMD with [Fe/H] = −2.0 and [α/Fe] = + 0.3 alpha-enhanced BaSTI isochrones indicates a mean age of 12.5 Gyr for the main event and a mean age of 10.5 Gyr for the brighter SGB. With such multiple star formation events Crater II shows similarity to more massive dwarfs that have intermediate age populations, however for Crater II there was early quenching of the star formation and no intermediate age or younger stars are present. The spatial distribution of Crater II stars overall is elliptical in the plane of the sky, the detailed distribution shows a lack of strong central concentration, and some inhomogeneities. The 10.5 Gyr subgiant and upper main-sequence stars show a slightly higher central concentration when compared to the 12.5 Gyr population. Matching to Gaia DR2 we find the proper motion of Crater II: μαcos δ = −0.14 ± 0.07, μδ = −0.10 ± 0.04 mas yr−1, approximately perpendicular to the semimajor axis of Crater II. Our results provide constraints on the star formation and chemical enrichment history of Crater II, but cannot definitively determine whether or not substantial mass has been lost over its lifetime.

• Sponsoring Organization: USDOE
• OSTI ID: 1671830
• Journal Information: Monthly Notices of the Royal Astronomical Society, Journal Name: Monthly Notices of the Royal Astronomical Society Vol. 490 Journal Issue: 3; ISSN 0035-8711
• Publisher: Oxford University Press
• Country of Publication: United Kingdom
• Language: English