Relevant Literature¶
This page outlines notes on a subset of relevant literature to our project.
Definitions of Spectrocopic Classification Schemes¶
- Wang 2009
Branch 2006¶
Note
TLDR: SNe Ia are subclassed into shallow silicon, core-normal, broad line, and cool groups based on relative the strength of Si II features at 5750 and 6100 Angstroms.
This paper identifies classifications of SNe Ia using the width of the 5750 and 6100 features (usually attributed to Si ii at 5972 and 6355). To simplify the process of feature comparison, spectra are first tilted by multiplying the flux by \(\lambda^\alpha\) where \(\alpha\) is chosen such that the peak flux near 4600 and 6300 A are equal. The Equivalent widths are then plotted for the feature at 5750 A vs the feature at 6100 A. After applying a nearest neighbor algorithm, four groups emerged: shallow silicon, core-normal, broad line, and cool (which includes SN 1991bg).
Broad-line SNe Ia have absorption features at 6100 A absorptions that are broader and deeper than core-normal SNe Ia. However, SNe in this category do not appear to follow a simple one-dimensional sequence based on their distance from the core-normal population.
The shallow silicon group are not (necessarily) very different from the core normal group. Other than a narrower Si feature, they look remarkably similar. The primary reason for the spectroscopic differences seems to be the lower temperature, as indicated by low temperature ion signatures (e.g. Ti). Otherwise, they have the same ions evident in their spectra, just at very different optical depths. This aligns with their lower temperatures since “as noted by Hatano+ (2002) and Ho Flich+ (2002), there is a temperature threshold below which, owing to abrupt changes in key ionization ratios, line optical depths change abruptly (Hatano+ 1999).”
The core-normal subgroup have a very high degree of similarity, suggesting a standard, common physical mechanism involving no large inhomogeneities near the characteristic photosphere velocity of 12,000 km/s.
Papers investigating Host Galaxy Correlations¶
- Gallagher 2008
- Kelly 2010 (?)
- Sullivan 2010 (?)
- Lampeitl 2010
- Gupta 2011
- Rigault et al. 2013
- Jones 2015
- Moreno-Raya 2016
- Uddin 2017
- Kim 2018
- Rigault 2018
- Jones 2018
- Rose 2019
Papers Investigating Redshift Evolution¶
Hook 2005¶
- Sample Size: 14 SNe
- Survey: Supernova Cosmology Project
- Dates:
- Sampling: Peak only
- Redshift: 0.17 < z < 0.83
Conclusions:
No evidence was found for evolution in SNe Ia properties with redshift. Plotting the high-redshift sample against well-observed local SNe showed a clear indication that the overall trends spectroscopic evolution are the same at low and high z. Furthermore, measurements of the Ca ejecta velocity in the high-redshift spectra were also consistent with those measured from low-redshift, Branch-normal SNe Ia.
Bronder 2008¶
- Sample Size:
- Survey:
- Dates:
- Sampling:
- Redshift:
Conclusions:
No evidence was found of SNe Ia evolution with redshift. Measured pseudo-equivalent widths (PEW) for a group of high and low redshift SNe and plotted feature strength with respect to redshift for MgII, SiII, and CaII, as well as CaII ejection velocity. This paper uses 3 guidelines for calculating PEW. First, the measurements for the PEW bounds must fall within the ranges defined in Table 3. Second, the boundaries should be chosen to maximize the PEW area. Third, the measurements should be taken in the rest frame. The core normal SNe showed no consistent trend. They did observe a correlation between the strength of the SiII feature and the peak magnitude. However, this trend did not significantly improve standardization over stretch parameter corrections.
Papers Investigating Inherent Spectroscopic Diversity¶
Blondin 2012¶
- Sample Size: 2603 spectra of 462 SNe Ia
- Survey: Center for Astrophysics (CfA) Supernova Program
- Dates: October 1993 through August 2008.
- Sampling: 313 SNe have two or more spectra, and of these each SN has an average of 8 observed spectra.
- Redshift: z < 0.1 with a median \(z ~ 0.023\). One high redshift target (SN 1996ab) at \(z ~ 0.123\).
Conclusions:
Using the classification schemes of Branch 2006 Wang 2009 there was found to be a continuum of spectroscopic properties (i.e., no strict boundaries) between the different subclasses that was unlikely to be explained by a single parameter.
In Branch 2009 it was proposed that SNe Ia from the Core Normal subclass 1) have a significantly smaller scatter in intrinsic peak brightness, and 2) decline photometrically at the same rate as the Shallow Silicon (SS) subclass. The first claim is rejected and the second is shown not to be universally true. It was also found that SS, CN, and Broad Line (BL) SNe form a sequence of increasingly steep width-luminosity relations. The same is true for the 91T, Normal, High-velocity sequence used in the Wang 2009 classification scheme
Using early-time spectra to probe the outermost ejecta, Silicon is shown to absorb at velocities that are larger than expected for a pure deflagration model.
In Mazzali 1998 the correlation of Δm15(B) and the FWHM of the iron emission feature at ∼4700 Å was interpreted as a correlation between luminosity and explosion kinetic energy. This paper finds that the correlation is largely driven by SN 1991bg-like SNe and that by excluding low luminosity SNe (Δm15(B) < 1.6 mag), there is no correlation between both quantities (r=−0.17)