Type Iax supernovae as a source of iron-rich silicate dust

TL;DR

This work demonstrates that the low-luminosity Type Iax subclass of thermonuclear SNe can efficiently form iron-rich silicate dust in their chemically mixed, relatively dense ejecta, unlike standard Type Ia explosions. Using a non-equilibrium chemical kinetic approach (NECSA) with an expanded Fe–Mg silicate network, the authors predict dust masses of roughly $M_{ m dust} \sim (3.7\times 10^{-6} - 6.7\times 10^{-5})\,M_\odot$ at ~4000 days, dominated by FeSiO$_3$, Fe$_2$SiO$_4$, and MgFeSiO$_4$, yielding dust-to-gas ratios of $(4-8)\times 10^{-5}$. The study finds that Type Iax dust production is 1–2 orders of magnitude more efficient than Type Ia ejecta (which yield $M_{ m dust} \lesssim 3\times 10^{-6}\,M_\odot$ and $D/M \lesssim 2.4\times 10^{-6}$), due to higher densities and abundant unburned C/O that seed precursor molecules like CO and SiO. These results position Type Iax SNe as plausible iron-rich dust sources in galaxies and motivate late-time infrared observations to test dust formation in their ejecta, while highlighting sensitivity to ejecta mass, $^{56}$Ni content, and physical conditions.

Abstract

We model the formation of dust in the ejecta of Type Iax supernovae (SNe), which is a low-luminosity subclass of Type Ia SNe. A non-equilibrium chemical kinetic approach is adopted to trace the synthesis of molecules, molecular clusters, and dust grains in the ejecta of thermonuclear SNe. We find that Type Iax SNe provide conditions conducive to the formation of several O-rich dust species in the ejecta. Particularly, iron-rich silicates of chemical type FeSiO3, Fe2SiO4, and MgFeSiO4 are found to form in abundance, suggesting that the ejecta of low-luminosity thermonuclear SNe can be a site where a large fraction of iron is locked up in dust, unlike other stellar sources. The final mass of dust formed in the ejecta ranges between 10^{-5} and 10^{-4} Msun, where most of the dust forms between 1000 and 2000 days post-explosion. Apart from Fe-rich silicates, Mg-silicates, and silicon carbide are also formed in the ejecta of Type Iax SNe. When compared to the dust budget of typical Type Ia SNe, we find that the expected dust-to-ejecta mass ratio is one or two orders of magnitude larger in Type Iax SNe. We conclude that the ejecta of typical Type Ia SNe form a negligible amount of dust, in agreement with observation, while the low-luminosity subclass Type Iax SNe are potential producers of iron-rich silicates.

Figures (10)

• Figure 1: Left: Abundance profile of deflagration models (Type Iax) in enclosed mass coordinateFink_2014. Right:Abundance profile of delayed detonation models (Type Ia) in enclosed mass coordinate Seithenzahl_2013. Both models use a similar 1.4 M$_{\odot}$ initial mass of WD. Type Iax ejecta is increasing in mass for higher configuration models due to more powerful deflagration waves. Type Ia ejecta as initial deflagration ignition sites are increasing the ejecta is giving elements other than $^{56}$Ni up to more inner regions.
• Figure 2: The Temperature profiles at 100 days used in this study. Type Ia temperature profile is taken from Nozawa_2011 and the hotter profile of Type Iax is taken from jack_2011. The enclosed mass is normalized to the ejecta mass of the SN Ia ($M_{ejecta}$ = 1.38 $M_{\odot}$) used in Nozawa_2011.
• Figure 3: Top: Density profile of Fink_2014 deflagration models of Type Iax in enclosed mass coordinate at 100 days. Bottom: Density profile of Seithenzahl_2013 DDT models of Type Ia in enclosed mass coordinate at 100 days.
• Figure 4: Comparison of molecules produced in Type Iax and Type Ia SN ejecta.
• Figure 5: Dust mass evolution in Type Iax SN ejecta for different deflagration models. Each panel shows the time evolution of individual dust species produced in dashed colored lines with the total dust mass in a solid black line. The bottom-right panel compares total dust masses across all models.