Supernovae and their host galaxies – VI. Normal Type Ia and 91bg-like supernovae in ellipticals

Abstract

We present an analysis of the galactocentric distributions of the "normal" and peculiar "91bglike" subclasses of 109 supernovae (SNe) Ia, and study the global parameters of their elliptical hosts. The galactocentric distributions of the SN subclasses are consistent with each other, and with the radial light distribution of host stellar populations, when excluding bias against central SNe. Among the global parameters, only the distributions of u−r colours and ages are inconsistent significantly between the ellipticals of different SN Ia subclasses: the normal SN hosts are on average bluer/younger than those of 91bg-like SNe. In the colour-mass diagram, the tail of colour distribution of normal SN hosts stretches into the Green Valley -transitional state of galaxy evolution, while the same tail of 91bg-like SN hosts barely reaches that region. Therefore, the bluer/younger ellipticals might have more residual star formation that gives rise to younger "prompt" progenitors, resulting in normal SNe Ia with shorter delay times. The redder and older ellipticals that already exhausted their gas for star formation may produce significantly less normal SNe with shorter delay times, outnumbered by "delayed" 91bg-like events. The host ages (lower age limit of the delay times) of 91bg-like SNe does not extend down to the stellar ages that produce significant u-band fluxes -the 91bg-like events have no prompt progenitors. Our results favor SN Ia progenitor models such as He-ignited violent mergers that have the potential to explain the observed SN/host properties.

Characterizing the Host Galaxies and Delay Times of Ca-rich Gap Transients versus 91bg-like SNe and Normal Type Ia SNe

“…Almost none of the Type II SNe hosts are quiescent and a minority of SNe Ia hosts are quiescent, in agreement with Irani et al (2022). The hosts of 91bg-like SNe being more massive and less star-forming compared to hosts of SNe Ia also agrees well with the literature (Barkhudaryan et al 2019;Panther et al 2019;Burgaz et al 2025;Dimitriadis et al 2025;Senzel et al 2025).…”

“…Compared to previous samples of Ca-rich transients, our sample includes only those that are faint/fast and do not include hydrogen. Our results for the delay times of the other three classes of SNe (Section 4) agree with previous work, where 91bg-like SNe, a subset of SNe Ia, have been found to have longer delay times than normal SNe Ia (Barkhudaryan et al 2019;Panther et al 2019) and Type II SNe having short delay times (e.g., Zapartas et al 2017). This paper is the first to calculate DTDs for Ca-rich gap transients, and future work should attempt to connect the DTDs of Ca-rich gap transients to their potential formation histories, as has been done with SNe Ia delay times to distinguish between the single degenerate and double degenerate formation scenario (Maoz et al 2012).…”

Characterizing the Host Galaxies and Delay Times of Ca-rich Gap Transients versus 91bg-like SNe and Normal Type Ia SNe

“…Almost none of the Type II SNe hosts are quiescent and a minority of SNe Ia hosts are quiescent, in agreement with Irani et al (2022). The hosts of 91bg-like SNe being more massive and less star-forming compared to hosts of SNe Ia also agrees well with the literature (Barkhudaryan et al 2019;Panther et al 2019;Burgaz et al 2025;Dimitriadis et al 2025;Senzel et al 2025).…”

“…Compared to previous samples of Ca-rich transients, our sample includes only those that are faint/fast and do not include hydrogen. Our results for the delay times of the other three classes of SNe (Section 4) agree with previous work, where 91bg-like SNe, a subset of SNe Ia, have been found to have longer delay times than normal SNe Ia (Barkhudaryan et al 2019;Panther et al 2019) and Type II SNe having short delay times (e.g., Zapartas et al 2017). This paper is the first to calculate DTDs for Ca-rich gap transients, and future work should attempt to connect the DTDs of Ca-rich gap transients to their potential formation histories, as has been done with SNe Ia delay times to distinguish between the single degenerate and double degenerate formation scenario (Maoz et al 2012).…”

Supernovae and their host galaxies -- VII. The diversity of Type Ia supernova progenitors

“…However, the results concerning to the hosts morphologies of this peculiar subgroup are not comparable with those of our case, because their subgroup include nearly equal numbers of 02cx-and 06gz-like SNe whose hosts morphologies have different distributions (e.g. Valenti et al 2009;Taubenberger et al 2011; Barkhudaryan et al 2019), thus mixing the morphological types. spirals (Fig.…”

“…(vi) As in our previous study (Barkhudaryan et al 2019), for the progenitors of 91bg-like events we favour the DD channel, in particular the progenitor models such as He-ignited violent mergers (CO WD primary with He WD companion, e.g. Pakmor et al 2013;Crocker et al 2017).…”

Multiphase Gas in Elliptical Galaxies: The Role of Type Ia Supernovae

“…For a stellar population of age ∼10 Gyr, the SN Ia energy injection rate is given by of energy and that the SN Ia goes off at a rate 300(Myr) −1 (M * /10 10 M e ), consistent with the delay-time distribution of the SN Ia in Maoz & Graur (2017; see also Scannapieco & Bildsten 2005;Barkhudaryan 2019). We show  e SN (  E SN per unit volume) in the lower panel of Figure 1.…”

Characterizing the Host Galaxies and Delay Times of Ca-rich Gap Transients versus 91bg-like SNe and Normal Type Ia SNe

“…Almost none of the Type II SNe hosts are quiescent and a minority of SNe Ia hosts are quiescent, in agreement with Irani et al (2022). The hosts of 91bg-like SNe being more massive and less star-forming compared to hosts of SNe Ia also agrees well with the literature (Barkhudaryan et al 2019;Panther et al 2019;Burgaz et al 2025;Dimitriadis et al 2025;Senzel et al 2025).…”

“…Compared to previous samples of Ca-rich transients, our sample includes only those that are faint/fast and do not include hydrogen. Our results for the delay times of the other three classes of SNe (Section 4) agree with previous work, where 91bg-like SNe, a subset of SNe Ia, have been found to have longer delay times than normal SNe Ia (Barkhudaryan et al 2019;Panther et al 2019) and Type II SNe having short delay times (e.g., Zapartas et al 2017). This paper is the first to calculate DTDs for Ca-rich gap transients, and future work should attempt to connect the DTDs of Ca-rich gap transients to their potential formation histories, as has been done with SNe Ia delay times to distinguish between the single degenerate and double degenerate formation scenario (Maoz et al 2012).…”

Supernovae and their host galaxies -- VII. The diversity of Type Ia supernova progenitors

“…However, the results concerning to the hosts morphologies of this peculiar subgroup are not comparable with those of our case, because their subgroup include nearly equal numbers of 02cx-and 06gz-like SNe whose hosts morphologies have different distributions (e.g. Valenti et al 2009;Taubenberger et al 2011; Barkhudaryan et al 2019), thus mixing the morphological types. spirals (Fig.…”

“…(vi) As in our previous study (Barkhudaryan et al 2019), for the progenitors of 91bg-like events we favour the DD channel, in particular the progenitor models such as He-ignited violent mergers (CO WD primary with He WD companion, e.g. Pakmor et al 2013;Crocker et al 2017).…”

Multiphase Gas in Elliptical Galaxies: The Role of Type Ia Supernovae

“…For a stellar population of age ∼10 Gyr, the SN Ia energy injection rate is given by of energy and that the SN Ia goes off at a rate 300(Myr) −1 (M * /10 10 M e ), consistent with the delay-time distribution of the SN Ia in Maoz & Graur (2017; see also Scannapieco & Bildsten 2005;Barkhudaryan 2019). We show  e SN (  E SN per unit volume) in the lower panel of Figure 1.…”

Characterizing the Host Galaxies and Delay Times of Ca-rich Gap Transients versus 91bg-like SNe and Normal Type Ia SNe

“…Almost none of the Type II SNe hosts are quiescent and a minority of SNe Ia hosts are quiescent, in agreement with Irani et al (2022). The hosts of 91bg-like SNe being more massive and less star-forming compared to hosts of SNe Ia also agrees well with the literature (Barkhudaryan et al 2019;Panther et al 2019;Burgaz et al 2025;Dimitriadis et al 2025;Senzel et al 2025).…”

“…Compared to previous samples of Ca-rich transients, our sample includes only those that are faint/fast and do not include hydrogen. Our results for the delay times of the other three classes of SNe (Section 4) agree with previous work, where 91bg-like SNe, a subset of SNe Ia, have been found to have longer delay times than normal SNe Ia (Barkhudaryan et al 2019;Panther et al 2019) and Type II SNe having short delay times (e.g., Zapartas et al 2017). This paper is the first to calculate DTDs for Ca-rich gap transients, and future work should attempt to connect the DTDs of Ca-rich gap transients to their potential formation histories, as has been done with SNe Ia delay times to distinguish between the single degenerate and double degenerate formation scenario (Maoz et al 2012).…”

Supernovae and their host galaxies -- VII. The diversity of Type Ia supernova progenitors

“…However, the results concerning to the hosts morphologies of this peculiar subgroup are not comparable with those of our case, because their subgroup include nearly equal numbers of 02cx-and 06gz-like SNe whose hosts morphologies have different distributions (e.g. Valenti et al 2009;Taubenberger et al 2011; Barkhudaryan et al 2019), thus mixing the morphological types. spirals (Fig.…”

“…(vi) As in our previous study (Barkhudaryan et al 2019), for the progenitors of 91bg-like events we favour the DD channel, in particular the progenitor models such as He-ignited violent mergers (CO WD primary with He WD companion, e.g. Pakmor et al 2013;Crocker et al 2017).…”

Multiphase Gas in Elliptical Galaxies: The Role of Type Ia Supernovae

“…For a stellar population of age ∼10 Gyr, the SN Ia energy injection rate is given by of energy and that the SN Ia goes off at a rate 300(Myr) −1 (M * /10 10 M e ), consistent with the delay-time distribution of the SN Ia in Maoz & Graur (2017; see also Scannapieco & Bildsten 2005;Barkhudaryan 2019). We show  e SN (  E SN per unit volume) in the lower panel of Figure 1.…”