10 research outputs found
The Structure and Metallicity Gradient in the Extreme Outer Disk of NGC 7793
Studies of outer regions of spirals disks are fundamental to our
understanding of both the process of galaxy assembly and the subsequent secular
evolution of galaxies. In an earlier series of papers we explored the extent
and abundance gradient in the outer disk of NGC 300 and found an extended
purely exponential disk with a metallicity gradient which flattens off in the
outermost regions. We now continue the study of outskirts of pure disk spirals
with another Sculptor Group spiral, NGC 7793. Using Gemini Multi Object
Spectrograph camera at Gemini South, we trace the disk of NGC 7793 with star
counts out to ~9 scale lengths, corresponding to 11.5 kpc at our calibrated
distance of 3.61+/-0.53 Mpc. The outer disk of NGC 7793 shows no evidence of a
break in its light profile down to an effective surface brightness of ~30
mag/arcsec^2 (~3 mag/arcsec^2 deeper than what has been achieved with surface
photometry) and exhibits a non-negative abundance gradient within the radial
extent of our data.Comment: 11 pages, 9 figures, ApJ accepte
Outer-Disk Populations in NGC 7793: Evidence for Stellar Radial Migration
We analyzed the radial surface brightness profile of the spiral galaxy NGC
7793 using HST/ACS images from the GHOSTS survey and a new HST/WFC3 image
across the disk break. We used the photometry of resolved stars to select
distinct populations covering a wide range of stellar ages. We found breaks in
the radial profiles of all stellar populations at 280" (~5.1 kpc). Beyond this
disk break, the profiles become steeper for younger populations. This same
trend is seen in numerical simulations where the outer disk is formed almost
entirely by radial migration. We also found that the older stars of NGC 7793
extend significantly farther than the underlying HI disk. They are thus
unlikely to have formed entirely at their current radii, unless the gas disk
was substantially larger in the past. These observations thus provide evidence
for substantial stellar radial migration in late-type disks.Comment: 8 pages, 6 figure. Accepted for publication in Ap