Narrow absorption lines from intervening material in supernovae: III. Supernovae and their environments

TL;DR

This study analyzes how narrow interstellar absorption lines, notably Na I D, vary with SN subtype and host-galaxy properties using a large low-redshift SN sample (>10^4 spectra from ~1800 SNe). By measuring pseudo-equivalent widths and velocities of Nai D and other lines, and combining local/global host properties derived from photometry and SED fitting, the work reveals clear environment-driven differences: SNe Ia in passive hosts show weaker absorption, SNe II and SE-SNe inhabit more active, dusty regions, and Ia-SF and SE-SNe share strong local absorption despite differing progenitor channels. A key finding is the apparent similarity in Nai D EW distributions for Ia-SF and SE-SNe, which, together with multi-dimensional environmental tests, suggests that similar absorption signatures can arise from distinct progenitor pathways, including circumstellar material or interactions with patchy nearby ISM. Overall, the narrow-line diagnostics prove powerful for linking SN progenitors to their immediate environments and for constraining progenitor scenarios across diverse host galaxies.

Abstract

Narrow interstellar absorption features in supernova (SN) spectra serve as valuable diagnostics for probing dust extinction and the presence of circumstellar or interstellar material. In this third paper in a series, we investigate how the strength of narrow interstellar absorption lines in low-resolution spectra varies with SN type and host galaxy properties, both on local and global scales. Using a dataset of over 10000 spectra from $\sim1800$ low-redshift SNe, we find that Type Ia SNe (SNe Ia) in passive galaxies exhibit significantly weaker narrow absorption features compared to CC-SNe and SNe Ia in star-forming hosts (SNe Ia-SF), suggesting lower interstellar gas content in quiescent environments. Within the star-forming hosts, the Na I D equivalent-width distribution of SNe II is much lower than that of both SNe Ia-SF and stripped-envelope SNe (SE-SNe). This result is somewhat unexpected, since CC-SNe are generally associated with star-forming regions and occur deeper within galactic disks, where stronger line-of-sight extinction would be anticipated. This suggests that the observed behaviour cannot be explained solely by absorption from the integrated interstellar medium (ISM) along the line of sight. Instead, if part of the absorption arises from material near the explosion, the similarity between the Na I D EW distributions of SNe Ia-SF and SE-SNe implies that comparable absorption signatures can emerge from distinct progenitor pathways. Possible explanations include (a) circumstellar material (CSM) expelled by the progenitor system before explosion, or (b) interaction of SN radiation with nearby patchy ISM clouds. Our results highlight the diagnostic power of interstellar absorption features in revealing the diverse environments and progenitor pathways of SNe.

Figures (7)

• Figure 1: Galaxy type distribution of our sample split by the SN type. The SN type and the number of events are presented at the top of each panel.
• Figure 2: Cumulative distributions of the local M$_*^L$, sSFR$^L$, $t_{\mathrm{age}}^L$ and $sA_V^L$ ($A_V^L/M_*^L$) for different SN types. The number of events of each SN type and the results from the K-S test comparing two different populations are also shown in each panel.
• Figure 3: Cumulative distributions of the measured Nai D EW (left) and the EW normalised by the offset and M$_*^L$ (right) for each SN type. The number of events of each SN type and the results from the K-S test comparing two different populations are also shown in each panel.
• Figure 4: Cumulative distributions of the Nai D VEL divided into the SN type. The number of events of each SN type and the results from the K-S test comparing two different populations are also shown in each panel.
• Figure 5: Cumulative distributions of the local $A_V^L$ for different SN types. The number of events of each SN type and the results from the K-S test comparing two different populations are also shown in each panel.