A metallicity study of 1987A-like supernova host galaxies

Abstract

Context. The origin of the blue supergiant (BSG) progenitor of Supernova (SN) 1987A has long been debated, along with the role that its sub-solar metallicity played. We now have a sample of SN 1987A-like events that arise from the rare core collapse (CC) of massive (∼20 M ) and compact ( 100 R ) BSGs. Aims. The metallicity of the explosion sites of the known BSG SNe is investigated, as well as the association of BSG SNe to starforming regions. Methods. Both indirect and direct metallicity measurements of 13 BSG SN host galaxies are presented, and compared to those of other CC SN types. Indirect measurements are based on the known luminosity-metallicity relation and on published metallicity gradients of spiral galaxies. In order to provide direct metallicity measurements based on strong line diagnostics, we obtained spectra of each BSG SN host galaxy both at the exact SN explosion sites and at the positions of other H ii regions. We also observed these hosts with narrow Hα and broad R-band filters in order to produce continuum-subtracted Hα images. This allows us to measure the degree of association between BSG SNe and star-forming regions, and to compare it to that of other SN types. Results. BSG SNe are found to explode either in low-luminosity galaxies or at large distances from the nuclei of luminous hosts. Therefore, their indirectly measured metallicities are typically lower than those of SNe IIP and Ibc. This result is confirmed by the direct metallicity estimates, which show slightly sub-solar oxygen abundances (12 + log (O/H) ∼ 8.3-8.4 dex) for the local environments of BSG SNe, similar to that of the Large Magellanic Cloud (LMC), where SN 1987A exploded. However, we also note that two objects of our sample (SNe 1998A and 2004em) were found at near solar metallicity. SNe IIb have a metallicity distribution similar to that of our BSG SNe. Finally, we find that the degree of association to star-forming regions is similar among BSG SNe, SNe IIP and IIn. Conclusions. Our results suggest that LMC metal abundances play a role in the formation of some 1987A-like SNe. This would naturally fit in a single star scenario for the progenitors. However, the existence of two events at nearly solar metallicity suggests that also other channels, e.g. binarity, contribute to produce BSG SNe.

Metallicity from Type II supernovae from the (i)PTF

“…To estimate the Z at the location of our SNe within their hosts, we can correct the global Z of their hosts for the metallicity gradient that is known to characterize galaxies (e.g., Pilyugin et al 2004;Taddia et al 2013Taddia et al , 2015, where the nucleus is typically more metal-rich than the outer parts. We used the derived global Z as a proxy of the central Z, and then adopted an average Z gradient of −0.47 R −1 25 (see Pilyugin et al 2004).…”

Statistical Studies of Supernova Environments

“…We also include unpublished values from the CALIFA survey, which will be presented in Galbany et al Kuncarayakti et al (2013a,b), Inserra et al (2013), and Taddia et al (2013b) 3 . Our final sample is of 245 CC SN host H ii region oxygen abundances.…”

“…SNe IIn, observations suggest that mass-loss occurred close to the epoch of explosion, causing the large dispersion in properties observed in this class (see e.g. Kiewe et al 2012;Taddia et al 2013b). Deciphering which changes in progenitor properties link to changes in SN features is then a key question.…”

Metallicity measurements of gamma-ray burst and supernova explosion sites: lessons from H ii regions in M31

“…Among the major classes of CC SNe (II, Ib, and Ic), SNe Ib and Ic tend to occur in high-metallicity regions compared to SNe II (Anderson et al 2010), although the difference of the site metallicities of type Ib and Ic SNe is still a matter of debate (Modjaz et al 2011;Leloudas et al 2011;Sanders et al 2012b;Kuncarayakti et al 2013). It is also suggested that metallicity plays an important role in the occurrence of some subclasses of CC SNe (Modjaz et al 2011;Sanders et al 2012a;Taddia et al 2013;Lunnan et al 2014).…”

“…In the context of supernova remnant (SNR) searches, Matonick & Fesen (1997) have shown that the observed number density of SNR is higher in nearer galaxies, because it becomes easier to resolve a confused region in a galaxy when it is nearby. We can expect that our capability to investigate the explosion site of a transient event would depend on the distance to the event (e.g., Sanders et al 2012bSanders et al , 2013Taddia et al 2013), as in the cases of SNR searches.…”