Rubab Khan: SCSNe

We discuss the emerging trend that super-Chandrasekhar Type Ia Supernovae (SCSNe) with progenitor mass estimates significantly exceeding 1.4 M_sun tend to explode in metal-poor environments. While Taubenberger et al. 2011 noted that some of the SCSNe host galaxies are relatively metal-poor, we focus quantitatively on their locations in the hosts to point out that in three out of four cases, the SCSNe explosions occurred in the outer edge of the disks of their hosts. It is therefore very likely that their progenitors had far lower metallicities than those implied by the metallicity of their hosts' central regions. In two cases (SN 2003fg and SN 2009dc) the explosion sites were outside 99% of the host's light, and in one case (SN 2006gz) the host's radial metallicity slope indicates that the explosion site is in a metal-poor region. The fourth case (SN 2007if) has the lowest spectroscopically measured SN Ia host metallicity (Childress et al. 2011. It may be possible to explain each of these unusually bright events through some progenitor scenario specific to that case, but a much simpler and straightforward conclusion would be to ascribe the controlling factor to the only physical aspect they have in common --- metal poor environments.

Fig. 1.— A HST WFPC2 view of the SN 2003fg explosion site in the F606W filter. The circle marks the location of the SN. The center of the presumed host (Howell et al. 2006) is inside the circle, although it could plausibly be a tidal feature of the large morphologically disturbed galaxyat the same redshift.

Fig. 3.— The radial oxygen abundance profile of the SN 2006gz host galaxy IC 1277 along a slit going through the SN and the center of the host (based on four off-center H II regions). The dashed line shows a linear fit to the metallicity measurementsand has a gradient of ∼ 0.03 dex kpc−1. Thesolid line marks the position of the SN and intersects the dashed line at 12+log(O/H)≃ 8.26.

Fig. 4.— A SDSS r′-band image of the SN 2009dc host galaxy UGC 10064. The other galaxy at the top right, UGC 10063, is at the same redshift, and the the two galaxies may be linked by atidal bridge (Taubenberger et al. 2011). The location of the SN is marked by a circle.

Table 1— Summary of the SCSNe events and their host properties. The SNe properties (coordinates, redshift, peak magnitude, light-curve decline rate, derived 56Ni mass and total progenitor mass) are from Howell et al. (2006), Hicken et al. (2007), Yamanaka et al. (2009), Scalzo et al. (2010), and Silverman et al. (2011). The host magnitudes are from the RC3 catalog (de Vaucouleurs et al. 1991) for SN 2006gz, Scalzo et al. (2010) for SN 2007if, and the SDSS DR6 catalog (Adelman-McCarthy et al. 2008) for SN 2009dc. As the SN 2003fg host properties, we present those of the morphologically disturbed large neighbouring galaxy at the same redshift as the presumed dwarf host, and the absolute magnitude was determined from its GALFIT profile. The exponential disk scale axis ratios are from our GALFIT results, while D1 (arcseconds) and D2 (kiloparsecs) are distances of the SNe explosion sites from the centers of their hosts. L(<r) is the approximate percentage of light located interior to the location of the SN in its host. No total progenitor mass estimate for SN 2003fg was made by Hicken et al. (2007). SN 2007if exploded at the center of its faint low metallicity dwarf host.