Color Profiles of Spiral Galaxies: Clues on Outer-Disk Formation Scenarios

Abstract

We have explored radial color and stellar surface mass density profiles for a sample of 85 latetype spiral galaxies with deep (down to ∼27 mag arcsec −2 ) SDSS g ′ and r ′ band surface brightness profiles. About 90% of the light profiles have been classified as broken exponentials, exhibiting either truncations (Type II galaxies) or antitruncations (Type III galaxies). The color profiles of Type II galaxies show a "U shape" with a minimum of (g ′ −r ′ ) = 0.47 ± 0.02 mag at the break radius. Around the break radius, Type III galaxies have a plateau region with a color of (g ′ − r ′ ) = 0.57 ± 0.02. Using the color to calculate the stellar surface mass density profiles reveals a surprising result. The breaks, well established in the light profiles of the truncated galaxies, are almost gone, and the mass profiles now resemble those of the pure exponential (Type I) galaxies. This result suggests that the origin of the break in Type II galaxies is more likely due to a radial change in stellar population than being associated with an actual drop in the distribution of mass. Type III galaxies, however, seem to preserve their shape in the stellar mass density profiles. We find that the stellar surface mass density at the break for truncated galaxies is 13.6 ± 1.6 M ⊙ pc −2 and for the antitruncated ones is 9.9 ± 1.3 M ⊙ pc −2 for the antitruncated ones. We estimate that the fraction of stellar mass outside the break radius is ∼15% for truncated galaxies and ∼9% for antitruncated galaxies.

Multi-wavelength characterization of the outskirts of spiral galaxies

“…) Discussion The inner-outer scale-length ratio of NGC0450, which is galaxy with truncated (TYPE II) surface brightness profile, depends on the observing wavelength. There is a dramatic decrease towards redder wavelength which supports the idea suggested in Bakos et al (2008) that in the outer regions of truncated galaxies the change on the slope of the surface brightness is in reality caused by a change in the stellar population: having a very few young stars, the outer disk is dominated by the old stellar disk.…”

“…These stars are very often located beyond the break radius of Type II galaxies. In order to investigate how the star formation progresses in the different parts of the disks, Bakos et al (2008) studied the color and stellar mass ditribution of a large sample of disk galaxies, where they found have that truncated galaxies have an older stelar population in the outskirts, meanwhile it is not accompanied with a significant drop in the stellar mass. An observable consequence of this is the wavelength dependence of the inner-outer scale-length ratio, which whould decrease towards redder wavelength as we approach to tackle the old stellar disk.…”

“…Based on the study of optical color profiles, Bakos et al (2008) suggested that truncated (TYPE II) galaxies have a generally older stellar population in their outer regions: one observable consequence of this would be a strong dependence of the structural parameters of the outer disk on the observing wavelength. To corroborate this result, we obtained surface brightness profiles using data from GALEX(UV), SDSS(optical), UKIDSS(NIR) and SPITZER-IRAC(IR).…”

Integral field spectroscopy of a sample of nearby galaxies

“…The overall result is a change in the slope of the surface brightness profile and colours of these galaxies (e.g. Bakos et al 2008). However, gas clumps, like H ii regions, may also be affected (e.g.…”

Extragalactic archeology with the GHOSTS Survey

“…They can be observed even at redshifts of z ≈ 1 (Pérez 2004;Trujillo & Pohlen 2005). Truncated disks have a color minimum at the break radius, while antitruncated, that is, disks whose scale length is greater beyond the break, and unbroken disks only show a flattening of their color profile at large radii, both in the local Universe and at higher redshifts (z ≈ 1) (Bakos et al 2008;Azzollini et al 2008a,b).…”