# Is there Evidence for a Hubble bubble? The Nature of SN Ia Colors and Dust in External Galaxies

Abstract : We examine recent evidence from the luminosity-redshift relation of Type Ia Supernovae for the $\sim 3 \sigma$ detection of a Hubble bubble'' -- a departure of the local value of the Hubble constant from its globally averaged value \citep{Jha:07}. By comparing the MLCS2k2 fits used in that study to the results from other light-curve fitters applied to the same data, we demonstrate that this is related to the interpretation of SN color excesses (after correction for a light-curve shape-color relation) and the presence of a color gradient across the local sample. If the slope of the linear relation ($\beta$) between SN color excess and luminosity is fit empirically, then the bubble disappears. If, on the other hand, the color excess arises purely from Milky-Way like dust, then SN data clearly favors a Hubble bubble. We demonstrate that SN data give $\beta \simeq 2$, instead of the $\beta \simeq 4$ one would expect from purely Milky-Way-like dust. This suggests that either SN intrinsic colors are more complicated than can be described with a single light-curve shape parameter, or that dust around SN is unusual. Disentangling these possibilities is both a challenge and an opportunity for large-survey SN Ia cosmology.
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http://hal.in2p3.fr/in2p3-00148817
Contributor : Dominique Girod <>
Submitted on : Wednesday, May 23, 2007 - 12:52:02 PM
Last modification on : Saturday, April 11, 2020 - 1:53:32 AM

### Citation

A. Conley, R. G. Carlberg, J. Guy, D. A. Howell, S. Jha, et al.. Is there Evidence for a Hubble bubble? The Nature of SN Ia Colors and Dust in External Galaxies. The Astrophysical Journal, American Astronomical Society, 2007, 664, pp.L13-L16. ⟨10.1086/520625⟩. ⟨in2p3-00148817⟩

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