Super-Chandrasekhar SNe Ia Strong Prefer Metal Poor Environments
Rubab Khan, K. Z. Stanek, R. Stoll, J. L. Prieto
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.
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. 2.— A
Palomar Schmidt telescope image of the SN 2006gz host galaxy IC 1277
taken through the POSS-I blue filter. The location of the SN is marked
with a circle.
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.
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.
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.