Unravelling the mystery of the M31 bar
نویسندگان
چکیده
The inclination of M31 is too close to edge-on for a bar component to be easily recognised and is not sufficiently edge-on for a boxy/peanut bulge to protrude clearly out of the equatorial plane. Nevertheless, a sufficient number of clues allow us to argue that this galaxy is barred. We use fully self-consistent N -body simulations of barred galaxies and compare them with both photometric and kinematic observational data for M31. In particular, we rely on the near infrared photometry presented in a companion paper. We compare isodensity contours to isophotal contours and the light profile along cuts parallel to the galaxy major axis and offset towards the North, or the South, to mass profiles along similar cuts on the model. All these comparisons, as well as position velocity diagrams for the gaseous component, give us strong arguments that M31 is barred. We compare four fiducial N -body models to the data and thus set constraints on the parameters of the M31 bar, as its strength, length and orientation. Our ‘best’ models, although not meant to be exact models of M31, reproduce in a very satisfactory way the main relevant observations. We present arguments that M31 has both a classical and a boxy/peanut bulge. Its pseudo-ring-like structure at roughly 50 is near the outer Lindblad resonance of the bar and could thus be an outer ring, as often observed in barred galaxies. The shape of the isophotes also argues that the vertically thin part of the M31 bar extends considerably further out than its boxy bulge, i.e. that the boxy bulge is only part of the bar, thus confirming predictions from orbital structure studies and from previous N -body simulations. It seems very likely that the backbone of M31’s boxy bulge is families of periodic orbits, members of the x1-tree and bifurcating from the x1 family at its higher order vertical resonances, such as the x1v3 or x1v4 families.
منابع مشابه
Unravelling the Pathogenesis of Severe COVID-19 Pneumonia: Are There Possible Insights From High Altitude?
متن کامل
Unravelling the Mystery of Regional Unemploy- Ment in Finland*
BÖCKERMAN P. (2003) Unravelling the mystery of regional unemployment in Finland, Reg. Studies 37, 331–340. The study explores the determination of regional unemployment in Finland. The evaluation of regional labour markets is based on unique, linked panel data that is created by matching the conventional economic fundamentals with the measures based on gross flows of jobs and workers. The strik...
متن کاملOrigin of rotational kinematics in the globular cluster system of M31: a new clue to the bulge formation
We propose that the rotational kinematics of the globular cluster system (GCS) in M31 can result from a past major merger event that could have formed its bulge component. We numerically investigate kinematical properties of globular clusters (GCs) in remnants of galaxy mergers between two discs with GCs in both their disc and halo components. We find that the GCS formed during major merging ca...
متن کاملFace-on Barred Spiral Structure of Molecular Clouds in M31's Bulge
By image processing and color excess analyses of B, V, R, and I-band CCD images of the central region of M31 taken with the Kiso 105-cm Schmidt telescope, we found a bar of 200 pc length. We also found a more extended " face-on " spiral feature of dark clouds, which appear to be connected to this bar and is probably an out-of-plane structure. The 12 CO(J = 1 − 0)-line emission was detected from...
متن کاملSpitzer/mips Infrared Imaging of M31: Further Evidence for a Spiral/ring Composite Structure
New images of M31 at 24, 70, and 160 μm taken with the Multiband Imaging Photometer for Spitzer (MIPS) reveal the morphology of the dust in this galaxy. This morphology is well represented by a composite of two logarithmic spiral arms and a circular ring (radius ∼ 10 kpc) of star formation offset from the nucleus. The two spiral arms appear to start at the ends of a bar in the nuclear region an...
متن کامل