Open AccessThe lifetime of grand design
Author(s) -
Merrifield M. R.,
Rand R. J.,
Meidt S. E.
Publication year - 2006
Publication title -
monthly notices of the royal astronomical society: letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.067
H-Index - 122
eISSN - 1745-3933
pISSN - 1745-3925
DOI - 10.1111/j.1745-3933.2005.00122.x
Subject(s) - spiral (railway) , physics , spiral galaxy , radius , galaxy , rotation (mathematics) , astrophysics , metric (unit) , grand design spiral galaxy , lenticular galaxy , geometry , elliptical galaxy , computer science , mathematics , mathematical analysis , operations management , computer security , economics
The lifetime of the structure in grand design spiral galaxies is observationally ill‐determined, but is essentially set by how accurately the rotation of the pattern can be characterized by a single angular pattern speed. This paper derives a generalized version of the Tremaine–Weinberg method for observationally determining pattern speeds, in which the pattern speed is allowed to vary arbitrarily with radius. The departures of the derived pattern speed from a constant then provide a simple metric of the lifetime of the spiral structure. Application of this method to CO observations of NGC 1068 reveals that the pattern speed of the spiral structure in this galaxy varies rapidly with radius, and that the lifetime of the spiral structure is correspondingly very short. If this result turns out to be common in grand‐design spiral galaxies, then these features will have to be viewed as highly transient phenomena.