The unusual vertical mass distribution of NGC 4013 seen though the Spitzer Survey of Stellar Structure in Galaxies (S4G).

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Aceptado para ser publicado en ApJL. ArXiv:1107.0529

NGC 4013 is a nearby Sb edge-on galaxy known for its “prodigious” HI warp and its “giant” tidal stream. Previous work on this unusual object shows that it cannot be fitted satisfactorily by a canonical thin+thick disk structure. We have produced a new decomposition of NGC 4013, considering three stellar flattened components (thin+thick disk plus an extra and more extended component) and one gaseous disk. All four components are considered to be gravitationally coupled and isothermal. To do so, we have used the 3.6µm images from the Spitzer Survey of Stellar Structure in Galaxies (S4G).

We find evidence for NGC 4013 indeed having a thin and a thick disk and an extra flattened component. This smooth and extended component (scaleheight zEC~3 kpc) could be interpreted as a thick disk or as a squashed ellipsoidal halo and contains ~20% of the total mass of all three stellar components. We argue it is unlikely to berelated to the ongoing merger or due to the off-plane stars from a warp in the other two disk components. Instead, we favor a scenario in whichthe thick disk and the extended component were formed in a two-stageprocess, in which an initially thick disk has been dynamically heated bya merger soon enough in the galaxy history to have a new thick diskformed within it.

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