Open AccessInside the whale: the structure and dynamics of the isolated Cetus dwarf spheroidal
Author(s) -
Lewis G. F.,
Ibata R. A.,
Chapman S. C.,
McConnachie A.,
Irwin M. J.,
Tolstoy E.,
Tanvir N. R.
Publication year - 2007
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1111/j.1365-2966.2007.11395.x
Subject(s) - physics , dwarf galaxy , dwarf spheroidal galaxy , astrophysics , local group , velocity dispersion , population , astronomy , galaxy , milky way , dwarf galaxy problem , irregular galaxy , interacting galaxy , demography , sociology
This paper presents a study of the Cetus dwarf, an isolated dwarf galaxy within the Local Group. A matched‐filter analysis of the INT/WFC imaging of this system reveals no evidence for significant tidal debris that could have been torn off the galaxy, bolstering the hypothesis that Cetus has never significantly interacted with either the Milky Way or M31. Additionally, Keck/Deimos spectroscopic observations identify this galaxy as a distinct kinematic population possessing a systematic velocity of −87 ± 2 km s −1 and with a velocity dispersion of 17 ± 2 km s −1 ; while tentative, these data also suggest that Cetus possesses a moderate rotational velocity of ∼8 km s −1 . The population is confirmed to be relatively metal‐poor, consistent with [Fe/H]∼−1.9 , and, assuming virial equilibrium, implies that the Cetus dwarf galaxy possesses a mass‐to‐light ratio of ∼70. It appears, therefore, that Cetus may represent a primordial dwarf galaxy, retaining the kinematic and structural properties lost by other members of the dwarf population of the Local Group in their interactions with the large galaxies. An analysis of Cetus' orbit through the Local Group indicates that it is at apocentre; taken in conjunction with the general dwarf population, this shows the mass of the Local Group to be ≳2 × 10 12 M ⊙ .