Journal Article

Antitruncated stellar light profiles in the outer regions of STAGES spiral galaxies: bulge or disc related?

David T. Maltby, Carlos Hoyos, Meghan E. Gray, Alfonso Aragón-Salamanca and Christian Wolf

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 420, issue 3, pages 2475-2479
Published in print March 2012 | ISSN: 0035-8711
Published online February 2012 | e-ISSN: 1365-2966 | DOI:
Antitruncated stellar light profiles in the outer regions of STAGES spiral galaxies: bulge or disc related?

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We present a comparison of azimuthally averaged radial surface brightness μ(r) profiles and analytical bulge–disc 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 μ(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 > 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 > rbrk for a large sample of 78 (barred/unbarred, Sa-Sd) spiral galaxies with outer disc antitruncations (). In the majority of cases (∼85 per cent), evidence indicates that excess light at r > rbrk is related to an outer shallow disc (Type III-d). Here, the contribution of bulge light at r > rbrk is either negligible (∼70 per cent) or too little to explain the antitruncation (∼15 per cent). However in the latter cases, bulge light can affect the measured disc properties (e.g. μbrk, outer scalelength). In the remaining cases (∼15 per cent), light at r > rbrk is dominated by the bulge (Type III-s). Here, for most cases the bulge profile dominates at all radii and only occasionally ( galaxies, ∼5 per cent) extends beyond that of a dominant disc and explains the excess light at r > 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.

Keywords: galaxies: spiral; galaxies: structure

Journal Article.  3237 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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