Bibcode
DOI
Knapen, J. H.; Beckman, J. E.; Heller, C. H.; Shlosman, I.; de Jong, R. S.
Bibliographical reference
Astrophysical Journal v.454, p.623
Advertised on:
12
1995
Citations
238
Refereed citations
190
Description
We present new high-resolution observations of the central region in the
late-type spiral galaxy M100 (NGC 4321) supplemented by
three-dimensional numerical modeling of stellar and gas dynamics,
including star formation (SF). Near-infrared imaging has revealed a
small bulge of 4" effective diameter; a 60" radial length stellar bar of
moderate strength, previously inferred from optical and 21 cm
observations; and an ovally shaped, ringlike structure in the plane of
the disk between 10"-22" from the center, whose major axis makes a large
angle with the bar. The K isophotes become progressively elongated and
skewed to the position angle of the bar both outside and inside the
"ring," forming an inner barlike region. The galaxy exhibits a mild
circumnuclear starburst concentrated in the inner part of the K "ring."
This SF is prominent in Hα and the U, B, and V bands, forming an
incomplete ring. In addition, two strong local maxima of K emission have
been observed to lie remarkably symmetrically with respect to the
galactic nucleus and equidistant from it at 7".5, slightly leading the
stellar bar. CO molecular emission is peaked in the dust lanes seen in
the I - K color index image.
We interpret the twists in K isophotes and the swinging of spiral arms
through ˜360° inside the corotation radius as being indicative
of the presence of a double inner Lindblad resonance (ILR) and test this
hypothesis by modeling the gas flow in a self-consistent gas + stars
disk embedded in a halo, with an overall NGC 4321- like mass
distribution in the system. Both ILRs have been verified using nonlinear
orbit analysis by determining the spatial extent of the family of orbits
oriented along the minor axis of the bar.
We have reproduced the basic morphology of the region inside corotation,
including (1) the ˜60" bar; (2) the large-scale trailing shocks
representing the offset dust lanes in the bar; (3) two symmetric K peaks
corresponding to gas compression maxima which lie at the caustic formed
by the interaction of a pair of trailing and leading shocks in the
vicinity of the inner ILR, both peaks being sites of SF; and (4) two
additional zones of SF corresponding to gas compression maxima at the
bar's minor axis, where the large-scale shocks start to curl and which
are referred in the literature as "twin peaks." We argue further that
the twisting of K isophotes in the neighborhood of the resonance region
requires a population of red stars which are dynamically young and
follow gas rather than stellar orbits, i.e., red supergiants At the same
time, a substantial contribution from OB stars to the K light is
expected within the inner kiloparsec and especially in the symmetric K
peaks. We also conclude that NGC 4321 hosts a single stellar bar which
fuels the starburst activity within the circumnuclear "ring" by
channeling gas there at the median rate of ˜0.1-1 Msun
yr-1.