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Title:
The Elongated Structure of the Hercules Dwarf Spheroidal Galaxy from Deep Large Binocular Telescope Imaging
Authors:
Coleman, Matthew G.; de Jong, Jelte T. A.; Martin, Nicolas F.; Rix, Hans-Walter; Sand, David J.; Bell, Eric F.; Pogge, Richard W.; Thompson, David J.; Hippelein, H.; Giallongo, E.; Ragazzoni, R.; DiPaola, Andrea; Farinato, Jacopo; Smareglia, Riccardo; Testa, Vincenzo; Bechtold, Jill; Hill, John M.; Garnavich, Peter M.; Green, Richard F.
Affiliation:
AA(Max-Planck-Institut für Astronomie, Königstuhl 17, D-69117 Heidelberg, Germany.), AB(Max-Planck-Institut für Astronomie, Königstuhl 17, D-69117 Heidelberg, Germany.), AC(Max-Planck-Institut für Astronomie, Königstuhl 17, D-69117 Heidelberg, Germany.), AD(Max-Planck-Institut für Astronomie, Königstuhl 17, D-69117 Heidelberg, Germany.), AE(Steward Observatory, University of Arizona, Tucson, AZ 85721.; Chandra Fellow.), AF(Max-Planck-Institut für Astronomie, Königstuhl 17, D-69117 Heidelberg, Germany.), AG(Department of Astronomy, Ohio State University, 140 West 18th Avenue, Columbus, OH 43210-1173.), AH(Large Binocular Telescope Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721-0065.), AI(Max-Planck-Institut für Astronomie, Königstuhl 17, D-69117 Heidelberg, Germany.), AJ(INAF, Osservatorio Astronomico di Roma, via Frascati 33, I-00040 Monteporzio, Italy.), AK(INAF, Osservatorio Astronomico di Roma, via Frascati 33, I-00040 Monteporzio, Italy.), AL(INAF, Osservatorio Astronomico di Roma, via Frascati 33, I-00040 Monteporzio, Italy.), AM(INAF, Osservatorio Astronomico di Padova, vicolo dell'Osservatorio, 5, 35122 Padova, Italy.), AN(INAF, Osservatorio Astronomico di Trieste, via G. B. Tiepolo, 11, 34131 Trieste, Italy.), AO(INAF, Osservatorio Astronomico di Roma, via Frascati 33, I-00040 Monteporzio, Italy.), AP(Steward Observatory, University of Arizona, Tucson, AZ 85721.), AQ(Large Binocular Telescope Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721-0065.), AR(Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge MA 02138.), AS(Large Binocular Telescope Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721-0065.)
Publication:
The Astrophysical Journal, Volume 668, Issue 1, pp. L43-L46. (ApJL Homepage)
Publication Date:
10/2007
Origin:
UCP
ApJ Keywords:
galaxies: individual (Hercules dwarf spheroidal galaxy), Galaxies: Kinematics and Dynamics
DOI:
10.1086/522672
Bibliographic Code:
2007ApJ...668L..43C

Abstract

We present a deep, wide-field photometric survey of the newly discovered Hercules dwarf spheroidal galaxy (dSph), based on data from the Large Binocular Telescope. Images in B, V, and r were obtained with the Large Binocular Camera covering a 23'×23' field of view to a magnitude of ~25.5 (5 σ). This permitted the construction of color-magnitude diagrams that reach approximately 1.5 mag below the Hercules main-sequence turnoff. Three-filter photometry allowed us to preferentially select probable Hercules member stars and to examine the structure of this system at a previously unattained level. We find that the Hercules dwarf is highly elongated (3:1), considerably more so than any other dSph satellite of the Milky Way, except the disrupting Sagittarius dwarf. Although we cannot rule out that the unusual structure is intrinsic to Hercules as an equilibrium system, our results suggest tidal disruption as a likely cause of this highly elliptical structure. Given the relatively large galactocentric distance of this system (132+/-12 kpc), signs of tidal disruption would require the Hercules dwarf to be on a highly eccentric orbit around the Milky Way.

Based on data acquired using the Large Binocular Telescope (LBT). The LBT is an international collaboration among institutions in the US, Italy, and Germany. LBT Corporation partners are the University of Arizona, on behalf of the Arizona university system; Istituto Nazionale di Astrofisica, Italy; LBT Beteiligungsgesellschaft, Germany, representing the Max Planck Society, the Astrophysical Institute Potsdam, and Heidelberg University; Ohio State University; and the Research Corporation, on behalf of the University of Notre Dame, the University of Minnesota, and the University of Virginia.


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