THE ENIGMATIC PAIR OF DWARF GALAXIES LEO IV AND LEO V: COINCIDENCE OR COMMON ORIGIN?

被引:45
作者
de Jong, Jelte T. A. [1 ]
Martin, Nicolas F. [1 ]
Rix, Hans-Walter [1 ]
Smith, Kester W. [1 ]
Jin, Shoko [2 ]
Maccio, Andrea V. [1 ]
机构
[1] Max Planck Inst Astron, D-69117 Heidelberg, Germany
[2] Heidelberg Univ, Zentrum Astron, Astron Rechen Inst, D-69120 Heidelberg, Germany
关键词
galaxies: individual (Leo IV dSph; Leo V dSph); Local Group; COLOR-MAGNITUDE DIAGRAM; DIGITAL SKY SURVEY; STRUCTURAL-PROPERTIES; SPHEROIDAL GALAXY; DARK-MATTER; SATELLITES; VIEW; POPULATION; DISCOVERY; RAY;
D O I
10.1088/0004-637X/710/2/1664
中图分类号
P1 [天文学];
学科分类号
0704 ;
摘要
We have obtained deep photometry in two 1 degrees x 1 degrees fields covering the close pair of dwarf spheroidal galaxies Leo IV and Leo V and part of the area in between. From the distribution of likely red giant branch (RGB) and horizontal-branch (HB) stars in the data set, we find that both Leo IV and Leo V are significantly larger than indicated by previous measurements based on shallower data. With a half-light radius of r(h) = 4.'6 +/- 0.'8 (206 +/- 36 pc) and r(h) = 2.'6 +/- 0.'6 (133 +/- 31 pc), respectively, both systems are now well within the physical size bracket of typical dwarf spheroidal Milky Way satellites. Both are also found to be significantly elongated with an ellipticity of epsilon similar or equal to 0.5, a characteristic shared by many of the fainter (M-V > -8) Milky Way dwarf spheroidals. The large spatial extent of our survey allows us to search for extra-tidal features in the area between the two dwarf galaxies with unprecedented sensitivity. The spatial distribution of candidate RGB and HB stars in this region is found to be non-uniform at the similar to 3 sigma level. Interestingly, this substructure is aligned along the direction connecting the two systems, indicative of a possible "bridge" of extra-tidal material. Fitting the stellar distribution with a linear Gaussian model yields a significance of 4 sigma for this overdensity, a most likely FWHM of similar to 16 arcmin, and a central surface brightness of similar or equal to 32 mag arcsec(-2). We investigate different scenarios to explain the close proximity of Leo IV and Leo V, and the possible tidal bridge between them. Orbit calculations demonstrate that the two systems cannot share the exact same orbit, while a compromise orbit does not approach the Galactic center more than similar to 160 kpc, rendering it unlikely that they are remnants of a single disrupted progenitor. A comparison with cosmological simulations shows that a chance collision between unrelated subhalos is negligibly small. Given their relative distance and velocity, Leo IV and Leo V could be a bound " tumbling pair," if their combined mass exceeds (8 +/- 4) x 10(9) M-circle dot. The scenario of an internally interacting pair that fell into the Milky Way together appears to be the most viable explanation for this close celestial companionship.
引用
收藏
页码:1664 / 1671
页数:8
相关论文
共 31 条
[1]   THE SEVENTH DATA RELEASE OF THE SLOAN DIGITAL SKY SURVEY [J].
Abazajian, Kevork N. ;
Adelman-McCarthy, Jennifer K. ;
Agueros, Marcel A. ;
Allam, Sahar S. ;
Prieto, Carlos Allende ;
An, Deokkeun ;
Anderson, Kurt S. J. ;
Anderson, Scott F. ;
Annis, James ;
Bahcall, Neta A. ;
Bailer-Jones, C. A. L. ;
Barentine, J. C. ;
Bassett, Bruce A. ;
Becker, Andrew C. ;
Beers, Timothy C. ;
Bell, Eric F. ;
Belokurov, Vasily ;
Berlind, Andreas A. ;
Berman, Eileen F. ;
Bernardi, Mariangela ;
Bickerton, Steven J. ;
Bizyaev, Dmitry ;
Blakeslee, John P. ;
Blanton, Michael R. ;
Bochanski, John J. ;
Boroski, William N. ;
Brewington, Howard J. ;
Brinchmann, Jarle ;
Brinkmann, J. ;
Brunner, Robert J. ;
Budavari, Tamas ;
Carey, Larry N. ;
Carliles, Samuel ;
Carr, Michael A. ;
Castander, Francisco J. ;
Cinabro, David ;
Connolly, A. J. ;
Csabai, Istvan ;
Cunha, Carlos E. ;
Czarapata, Paul C. ;
Davenport, James R. A. ;
de Haas, Ernst ;
Dilday, Ben ;
Doi, Mamoru ;
Eisenstein, Daniel J. ;
Evans, Michael L. ;
Evans, N. W. ;
Fan, Xiaohui ;
Friedman, Scott D. ;
Frieman, Joshua A. .
ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES, 2009, 182 (02) :543-558
[2]   LEO V: A COMPANION OF A COMPANION OF THE MILKY WAY GALAXY? [J].
Belokurov, V. ;
Walker, M. G. ;
Evans, N. W. ;
Faria, D. C. ;
Gilmore, G. ;
Irwin, M. J. ;
Koposov, S. ;
Mateo, M. ;
Olszewski, E. ;
Zucker, D. B. .
ASTROPHYSICAL JOURNAL LETTERS, 2008, 686 (02) :L83-L86
[3]   Cats and dogs, hair and a hero: A quintet of new Milky Way companions [J].
Belokurov, V. ;
Zucker, D. B. ;
Evans, N. W. ;
Kleyna, J. T. ;
Koposov, S. ;
Hodgkin, S. T. ;
Irwin, M. J. ;
Gilmore, G. ;
Wilkinson, M. I. ;
Fellhauer, M. ;
Bramich, D. M. ;
Hewett, P. C. ;
Vidrih, S. ;
De Jong, J. T. A. ;
Smith, J. A. ;
Rix, H. -W. ;
Bell, E. F. ;
Wyse, R. F. G. ;
Newberg, H. J. ;
Mayeur, P. A. ;
Yanny, B. ;
Rockosi, C. M. ;
Gnedin, O. Y. ;
Schneider, D. P. ;
Beers, T. C. ;
Barentine, J. C. ;
Brewington, H. ;
Brinkmann, J. ;
Harvanek, M. ;
Kleinman, S. J. ;
Krzesinski, J. ;
Long, D. ;
Nitta, A. ;
Snedden, S. A. .
ASTROPHYSICAL JOURNAL, 2007, 654 (02) :897-906
[4]   The discovery of Segue 2: a prototype of the population of satellites of satellites [J].
Belokurov, V. ;
Walker, M. G. ;
Evans, N. W. ;
Gilmore, G. ;
Irwin, M. J. ;
Mateo, M. ;
Mayer, L. ;
Olszewski, E. ;
Bechtold, J. ;
Pickering, T. .
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 2009, 397 (04) :1748-1755
[5]   SExtractor: Software for source extraction [J].
Bertin, E ;
Arnouts, S .
ASTRONOMY & ASTROPHYSICS SUPPLEMENT SERIES, 1996, 117 (02) :393-404
[6]  
Bertin E., 2006, ASP C SER, P112
[7]   A wide-field view of Leo II: A structural analysis using the sloan digital sky survey [J].
Coleman, Matthew G. ;
Jordi, Katrin ;
Rix, Hans-Walter ;
Grebel, Eva K. ;
Koch, Andreas .
ASTRONOMICAL JOURNAL, 2007, 134 (05) :1938-1951
[8]   The elongated structure of the Hercules dwarf spheroidal galaxy from deep Large Binocular Telescope imaging [J].
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. .
ASTROPHYSICAL JOURNAL, 2007, 668 (01) :L43-L46
[9]   SMALL DWARF GALAXIES WITHIN LARGER DWARFS: WHY SOME ARE LUMINOUS WHILE MOST GO DARK [J].
D'Onghia, Elena ;
Lake, George .
ASTROPHYSICAL JOURNAL LETTERS, 2008, 686 (02) :L61-L65
[10]   ABELL-548 - AN X-RAY AND OPTICAL ANALYSIS OF SUBSTRUCTURE [J].
DAVIS, DS ;
BIRD, CM ;
MUSHOTZKY, RF ;
ODEWAHN, SC .
ASTROPHYSICAL JOURNAL, 1995, 440 (01) :48-59