Title: MAIN-SEQUENCE STAR POPULATIONS IN THE VIRGO OVERDENSITY REGION

Abstract

We present deep color-magnitude diagrams (CMDs) for two Subaru Suprime-Cam fields in the Virgo Stellar Stream (VSS)/Virgo Overdensity (VOD) and compare them to a field centered on the highest concentration of Sagittarius (Sgr) Tidal Stream stars in the leading arm, Branch A of the bifurcation. A prominent population of main-sequence stars is detected in all three fields and can be traced as faint as g Almost-Equal-To 24 mag. Using theoretical isochrone fitting, we derive an age of 9.1{sup +1.0}{sub -1.1} Gyr, a median abundance of [Fe/H] = -0.70{sup +0.15}{sub -0.20} dex, and a heliocentric distance of 30.9 {+-} 3.0 kpc for the main sequence of the Sgr Stream Branch A. The dominant main-sequence populations in the two VSS/VOD fields ({Lambda}{sub Sun} Almost-Equal-To 265 Degree-Sign , B{sub Sun} Almost-Equal-To 13 Degree-Sign ) are located at a mean distance of 23.3 {+-} 1.6 kpc and have an age of {approx}8.2 Gyr, and an abundance of [Fe/H] = -0.67{sup +0.16}{sub -0.12} dex, similar to the Sgr Stream stars. These statistically robust parameters, derived from the photometry of 260 main-sequence stars, are also in good agreement with the age of the main population in the Sgr dwarf galaxy (8.0 {+-} 1.5 Gyr). They alsomore » agree with the peak in the metallicity distribution of 2-3 Gyr old M giants, [Fe/H] Almost-Equal-To -0.6 dex, in the Sgr north leading arm. We then compare the results from the VSS/VOD fields with the Sgr Tidal Stream model by Law and Majewski based on a triaxial Galactic halo shape that is empirically calibrated with Sloan Digital Sky Survey Sgr A-branch and Two Micron All Sky Survey M-giant stars. We find that the most prominent feature in the CMDs, the main-sequence population at 23 kpc, is not explained by the model. Instead the model predicts in these directions a low-density filamentary structure of Sgr debris stars at {approx}9 kpc and a slightly higher concentration of Sgr stars spread over a heliocentric distance range of 42-53 kpc. At best there is only marginal evidence for the presence of these populations in our data. Our findings then suggest that while there are probably some Sgr debris stars present, the dominant stellar population in the VOD originates from a different halo structure that has an almost identical age and metallicity as some sections of the Sgr tidal stream.« less

Authors:

Jerjen, H.; Da Costa, G. S.; Tisserand, P. ^[1]; Willman, B. ^[2]; Arimoto, N. ^[3]; Okamoto, S. ^[4]; Mateo, M. ^[5]; Saviane, I. ^[6]; Walsh, S. ^[7]; Geha, M. ^[8]; Jordan, A.; Zoccali, M. ^[9]; Olszewski, E. ^[10]; Walker, M. ^[11]; Kroupa, P. ^[12]

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+ Show Author Affiliations

1. Research School of Astronomy and Astrophysics, Australian National University, Mt Stromlo Observatory, via Cotter Road, Weston, ACT 2611 (Australia)
2. Haverford College, Department of Astronomy, 370 Lancaster Avenue, Haverford, PA 19041 (United States)
3. National Astronomical Observatory of Japan, Subaru Telescope, 650 North A'ohoku Place, Hilo, HI 96720 (United States)
4. Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing 100871 (China)
5. Department of Astronomy, University of Michigan, Ann Arbor, MI (United States)
6. European Southern Observatory, Casilla 19001, Santiago 19 (Chile)
7. Australian Astronomical Observatory, PO Box 915, North Ryde, NSW 1670 (Australia)
8. Astronomy Department, Yale University, New Haven, CT 06520 (United States)
9. Departamento de Astronomia y Astrofisica, Pontificia Universidad Catolica de Chile, 7820436 Macul, Santiago (Chile)
10. Steward Observatory, University of Arizona, Tucson, AZ (United States)
11. Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)
12. Argelander Institute for Astronomy, University of Bonn, Auf dem Huegel 71, D-53121 Bonn (Germany)

Publication Date:

Mon May 20 00:00:00 EDT 2013

OSTI Identifier:

22126664

Resource Type:

Journal Article

Journal Name:

Astrophysical Journal

Additional Journal Information:

Journal Volume: 769; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0004-637X

Country of Publication:

United States

Language:

English

Subject:

79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ABUNDANCE; BIFURCATION; COLOR; CONCENTRATION RATIO; DENSITY; DISTANCE; DISTRIBUTION; GALAXIES; GIANT STARS; MAIN SEQUENCE STARS; PEAKS; PHOTOMETRY; STREAMS