科研之友
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摘要
We present a comparison of azimuthally averaged radial surface brightness mu(r) profiles and analytical bulgedisc decompositions (de Vaucouleurs, r1/4 bulge plus exponential disc) for spiral galaxies using Hubble Space Telescope/Advanced Camera for Surveys V-band imaging from the Space Telescope A901/2 Galaxy Evolution Survey (STAGES). In the established classification scheme, antitruncated mu(r) profiles (Type III) have a broken exponential disc with a shallower region beyond the break radius rbrk. The excess light at large radii (r %26gt; rbrk) can either be caused by an outer exponential disc (Type III-d) or an extended spheroidal component (Type III-s). Using our comparisons, we determine the contribution of bulge light at r %26gt; rbrk for a large sample of 78 (barred/unbarred, Sa-Sd) spiral galaxies with outer disc antitruncations. In the majority of cases (similar to 85 per cent), evidence indicates that excess light at r %26gt; rbrk is related to an outer shallow disc (Type III-d). Here, the contribution of bulge light at r %26gt; rbrk is either negligible (similar to 70 per cent) or too little to explain the antitruncation (similar to 15 per cent). However in the latter cases, bulge light can affect the measured disc properties (e.g. mu brk, outer scalelength). In the remaining cases (similar to 15 per cent), light at r %26gt; rbrk is dominated by the bulge (Type III-s). Here, for most cases the bulge profile dominates at all radii and only occasionally ( galaxies, similar to 5 per cent) extends beyond that of a dominant disc and explains the excess light at r %26gt; rbrk. We thus conclude that in the vast majority of cases antitruncated outer discs cannot be explained by bulge light and thus remain a pure disc phenomenon.
- 出版日期2012-3
