Dynamics in the satellite system of Triangulum: is And XXII a dwarf satellite of M33?

S. C. Chapman, L. Widrow, M. L. M. Collins, J. Dubinski, R. A. Ibata, M. Rich, A. M. N. Ferguson, M. J. Irwin, G. F. Lewis, N. Martin, A. McConnachie, J. Peñarrubia, N. Tanvir

Research output: Contribution to journalArticlepeer-review

Abstract / Description of output

We present results from a spectroscopic survey of the dwarf spheroidalgalaxy And XXII and the two extended clusters EC1 and EC2. These threeobjects are candidate satellites of the Triangulum galaxy, M33, whichitself is likely a satellite of M31. We use the DEep ImagingMulti-Object Spectrograph (DEIMOS) mounted on the Keck II telescope toderive radial velocities for candidate member stars of these objects andthereby identify the stars that are most likely actual members. 11probable stellar members are found for And XXII. We obtain an upperlimit of σv <6.0 km s-1 for the velocitydispersion of And XXII, [Fe/H] ˜ -1.6 for its metallicity and 255pc for the Plummer radius of its projected density profile. We constructa colour-magnitude diagram for And XXII and identify both the red giantbranch and the horizontal branch. The position of the latter is used toderive a heliocentric distance to And XXII of 853 ± 26 kpc. Thecombination of the radial velocity, distance and angular position of AndXXII indicate that it is a strong candidate as the first known satelliteof M33 and one of the very few examples of a galactic satellite of asatellite. N-body simulations imply that this conclusion is unchangedeven if M31 and M33 had a strong encounter in the past few Gyr. We testthe hypothesis that the extended clusters highlight tidally strippedgalaxies by searching for an excess cloud of halo-like stars in theirvicinity. We find such a cloud for the case of EC1 but not for EC2. Thethree objects imply a dynamical mass for M33 that is consistent withprevious estimates.
Original languageEnglish
Pages (from-to)37-49
JournalMonthly Notices of the Royal Astronomical Society
Publication statusPublished - 1 Mar 2013

Keywords / Materials (for Non-textual outputs)

  • instrumentation: spectrographs
  • galaxies: dwarf
  • galaxies: individual: M31
  • galaxies: individual: M33


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