Main-sequence star populations in the virgo overdensity region

H. Jerjen, G. S. Da Costa, B. Willman, P. Tisserand, N. Arimoto, S. Okamoto, M. Mateo, I. Saviane, S. Walsh, M. Geha, A. Jordán, Edward W Olszewski, M. Walker, M. Zoccali, P. Kroupa

Research output: Contribution to journalArticle

9 Citations (Scopus)

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 ≈ 24 mag. Using theoretical isochrone fitting, we derive an age of 9.1+1.0-1.1Gyr, a median abundance of [Fe/H] = -0.70+0.15-0.20dex, 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 (Λ ≈ 265°, B ≈ 13°) are located at a mean distance of 23.3 ± 1.6 kpc and have an age of ∼8.2 Gyr, and an abundance of [Fe/H] -0.67+0.16-0.12= 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 also agree with the peak in the metallicity distribution of 2-3 Gyr old M giants, [Fe/H] ≈-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 & 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 ∼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.

Original languageEnglish (US)
Article number14
JournalAstrophysical Journal
Volume769
Issue number1
DOIs
StatePublished - May 20 2013

Fingerprint

main sequence stars
stars
color-magnitude diagram
debris
metallicity
diagram
giant stars
cams
M stars
galactic halos
dwarf galaxies
bifurcation
photometry
halos

Keywords

  • galaxies: individual (Sagittarius)
  • galaxies: stellar content
  • Galaxy: abundances
  • Galaxy: halo Galaxy: structure

ASJC Scopus subject areas

  • Space and Planetary Science
  • Astronomy and Astrophysics

Cite this

Jerjen, H., Da Costa, G. S., Willman, B., Tisserand, P., Arimoto, N., Okamoto, S., ... Kroupa, P. (2013). Main-sequence star populations in the virgo overdensity region. Astrophysical Journal, 769(1), [14]. https://doi.org/10.1088/0004-637X/769/1/14

Main-sequence star populations in the virgo overdensity region. / Jerjen, H.; Da Costa, G. S.; Willman, B.; Tisserand, P.; Arimoto, N.; Okamoto, S.; Mateo, M.; Saviane, I.; Walsh, S.; Geha, M.; Jordán, A.; Olszewski, Edward W; Walker, M.; Zoccali, M.; Kroupa, P.

In: Astrophysical Journal, Vol. 769, No. 1, 14, 20.05.2013.

Research output: Contribution to journalArticle

Jerjen, H, Da Costa, GS, Willman, B, Tisserand, P, Arimoto, N, Okamoto, S, Mateo, M, Saviane, I, Walsh, S, Geha, M, Jordán, A, Olszewski, EW, Walker, M, Zoccali, M & Kroupa, P 2013, 'Main-sequence star populations in the virgo overdensity region', Astrophysical Journal, vol. 769, no. 1, 14. https://doi.org/10.1088/0004-637X/769/1/14
Jerjen H, Da Costa GS, Willman B, Tisserand P, Arimoto N, Okamoto S et al. Main-sequence star populations in the virgo overdensity region. Astrophysical Journal. 2013 May 20;769(1). 14. https://doi.org/10.1088/0004-637X/769/1/14
Jerjen, H. ; Da Costa, G. S. ; Willman, B. ; Tisserand, P. ; Arimoto, N. ; Okamoto, S. ; Mateo, M. ; Saviane, I. ; Walsh, S. ; Geha, M. ; Jordán, A. ; Olszewski, Edward W ; Walker, M. ; Zoccali, M. ; Kroupa, P. / Main-sequence star populations in the virgo overdensity region. In: Astrophysical Journal. 2013 ; Vol. 769, No. 1.
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AU - Da Costa, G. S.

AU - Willman, B.

AU - Tisserand, P.

AU - Arimoto, N.

AU - Okamoto, S.

AU - Mateo, M.

AU - Saviane, I.

AU - Walsh, S.

AU - Geha, M.

AU - Jordán, A.

AU - Olszewski, Edward W

AU - Walker, M.

AU - Zoccali, M.

AU - Kroupa, P.

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N2 - 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 ≈ 24 mag. Using theoretical isochrone fitting, we derive an age of 9.1+1.0-1.1Gyr, a median abundance of [Fe/H] = -0.70+0.15-0.20dex, 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 (Λ⊙ ≈ 265°, B⊙ ≈ 13°) are located at a mean distance of 23.3 ± 1.6 kpc and have an age of ∼8.2 Gyr, and an abundance of [Fe/H] -0.67+0.16-0.12= 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 also agree with the peak in the metallicity distribution of 2-3 Gyr old M giants, [Fe/H] ≈-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 & 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 ∼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.

AB - 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 ≈ 24 mag. Using theoretical isochrone fitting, we derive an age of 9.1+1.0-1.1Gyr, a median abundance of [Fe/H] = -0.70+0.15-0.20dex, 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 (Λ⊙ ≈ 265°, B⊙ ≈ 13°) are located at a mean distance of 23.3 ± 1.6 kpc and have an age of ∼8.2 Gyr, and an abundance of [Fe/H] -0.67+0.16-0.12= 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 also agree with the peak in the metallicity distribution of 2-3 Gyr old M giants, [Fe/H] ≈-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 & 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 ∼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.

KW - galaxies: individual (Sagittarius)

KW - galaxies: stellar content

KW - Galaxy: abundances

KW - Galaxy: halo Galaxy: structure

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