Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 2000
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000aas...197.2804c&link_type=abstract
American Astronomical Society, 197th AAS Meeting, #28.04; Bulletin of the American Astronomical Society, Vol. 32, p.1444
Astronomy and Astrophysics
Astronomy
Scientific paper
We investigate the interaction of Local Group dwarf galaxies M32 & NGC 205 with their parent galaxy M31. A 2ox5o mosaic of KPNO Burrell Schmidt 20482 CCD images is used to obtain surface photometry of M31 and its satellites in the B and I bands. The M31 background is modeled and removed using standard ellipse fitting techniques. The satellites are measured down to a limiting isophote of 27 mag arcsec-2 in the B band and 25 mag arcsec-2 in the I band. These limiting isophotes correspond to semi-major axis lengths of 420'' (1.6 kpc) and 720'' (2.7 kpc) for M32 and NGC 205, respectively. We confirm earlier hints of excess light in the outskirts of M32: clear evidence is seen for a sharp (upward) break in the radial surface brightness profile at r=2.5' relative to the r eff=30'' (0.11 kpc) de Vaucouleurs profile which fits the inner portion of M32. A more subtle, previously undetected (downward) break is also detected at r=1'. Tests show that the excess: (1) is insensitive to details of background subtraction; and (2) has the same B-I color as M32's interior and significantly different from the colors of typical M31 residual spiral arm/dust lane features. The breaks in M32's profile are accompanied by sharp changes in ellipticity. NGC 205 displays severe isophote twisting (Δ θ pa ~30o) between r=2.5'--12'. This is accompanied by a subtle downward break in the brightness profile at r=2.5', relative to the extrapolation of the r scale=150''--170'' (0.56--0.63 kpc) exponential laws that fit the inner parts of NGC 205 (75''--300''). The isophotal distortion and profiles features of M32 and NGC 205 are the same across B, R and I. To better constrain the nature of the interaction, surface brightness measurements are being complemented by N-body simulations and Keck/ESI spectroscopic measurements of the mean velocity and dispersion of ~50 red giant branch stars in the vicinity of the profile break in M32 (1.5'
Choi Philip I.
Guhathakurta Puraga
Johnston Kathryn V.
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