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Register a new userThe Masses of Supernova Remnant Progenitors in M83
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Added by
Benjamin F. Williams
Publication date
2019
fields
Physics
and research's language is
English
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We determine the ages of the young, resolved stellar populations at the locations of 237 optically-identified supernova remnants in M83. These age distributions put constraints on the progenitor masses of the supernovae that produced 199 of the remnants. The other 38 show no evidence for having a young progenitor and are therefore good Type Ia SNR candidates. Starting from Hubble Space Telescope broadband imaging, we measured resolved stellar photometry of seven archival WFC3/UVIS fields in F336W, F438W, and F814W. We generate color-magnitude diagrams of the stars within 50 pc of each SNR and fit them with stellar evolution models to obtain the population ages. From these ages we infer the progenitor mass that corresponds to the lifetime of the most prominent age that is $<$50 Myr. In this sample, there are 47 SNRs with best-fit progenitor masses $>$15 M$_{odot}$, and 5 of these are $>$15 M$_{odot}$ at 84% confidence. This is the largest collection of high-mass progenitors to date, including our highest-mass progenitor inference found so far, with a constraint of $<$8 Myr. Overall, the distribution of progenitor masses has a power-law index of $-3.0^{+0.2}_{-0.7}$, steeper than Salpeter initial mass function ($-2.35$). It remains unclear whether the reason for the low number of high-mass progenitors is due to the difficulty of finding and measuring such objects or because only a fraction of very massive stars produce supernovae.
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We constrained the progenitor masses for 169 supernova remnants, 8 historically observed supernovae, and the black hole formation candidate in NGC 6946, finding that they are consistent with originating from a standard initial mass function. Additionally, there were 16 remnants that showed no sign of nearby star formation consistent with a core-collapse supernova, making them good Type Ia candidates. Using $Hubble$ $Space$ $Telescope$ broadband imaging, we measured stellar photometry of ACS/WFC fields in F435W, F555W, F606W, and F814W filters as well as WFC3/UVIS fields in F438W, F606W, and F814W. We then fitted this photometry with stellar evolutionary models to determine the ages of the young populations present at the positions of the SNRs and SNe. We then infer a progenitor mass probability distribution from the fitted age distribution. For 37 SNRs we tested how different filter combinations affected the inferred masses. We find that filters sensitive to H$alpha$, [N II], and [S II] gas emission can bias mass estimates for remnants that rely on our technique. Using a KS-test analysis on our most reliable measurements, we find the progenitor mass distribution is well-matched by a power-law index of $-2.6^{+0.5}_{-0.6}$, which is consistent with a standard initial mass function.
We report the results from a spectrophotometric study sampling the roughly 300 candidate supernova remnants (SNRs) in M83 identified through optical imaging with Magellan/IMACS and HST/WFC3. Of the 118 candidates identified based on a high [S II] $lambdalambda$ 6716,6731 to H$alpha$ emission ratio, 117 show spectroscopic signatures of shock-heated gas, confirming them as SNRs---the largest uniform set of SNR spectra for any galaxy. Spectra of 22 objects with a high [O III] 5007 $lambda$ to H$alpha$ emission ratio, selected in an attempt to identify young ejecta-dominated SNRs like Cas A, reveal only one (previously reported) object with the broad (over 1000 km/s) emission lines characteristic of ejecta-dominated SNRs, beyond the known SN1957D remnant. The other 20 [O III]-selected candidates include planetary nebulae, compact H II regions, and one background QSO. Although our spectroscopic sample includes 22 SNRs smaller than 11 pc, none of the other objects shows broad emission lines; instead their spectra stem from relatively slow (< 200 km/s) radiative shocks propagating into the metal-rich interstellar medium of M83. With six SNe in the past century, one might expect more of M83s small-diameter SNRs to show evidence of ejecta; this appears not to be the case. We attribute their absence to several factors, including that SNRs expanding into a dense medium evolve quickly to the ISM-dominated phase, and that SNRs expanding into regions already evacuated by earlier SNe are probably very faint.
Using HST photometry, we age-date 59 supernova remnants (SNRs) in the spiral galaxy M31 and use these ages to estimate zero-age main sequence masses (MZAMS) for their progenitors. To accomplish this, we create color-magnitude diagrams (CMDs) and use CMD fitting to measure the recent star formation history (SFH) of the regions surrounding cataloged SNR sites. We identify any young coeval population that likely produced the progenitor star and assign an age and uncertainty to that population. Application of stellar evolution models allows us to infer the MZAMS from this age. Because our technique is not contingent on precise location of the progenitor star, it can be applied to the location of any known SNR. We identify significant young SF around 53 of the 59 SNRs and assign progenitor masses to these, representing a factor of 2 increase over currently measured progenitor masses. We consider the remaining 6 SNRs as either probable Type Ia candidates or the result of core-collapse progenitors that have escaped their birth sites. The distribution of recovered progenitor masses is bottom heavy, showing a paucity of the most massive stars. If we assume a single power law distribution, dN/dM proportional to M^alpha, we find a distribution that is steeper than a Salpeter IMF (alpha=-2.35). In particular, we find values of alpha outside the range -2.7 to -4.4 inconsistent with our measured distribution at 95% confidence. If instead we assume a distribution that follows a Salpeter IMF up to some maximum mass, we find that values of M_max greater than 26 Msun are inconsistent with the measured distribution at 95% confidence. In either scenario, the data suggest that some fraction of massive stars may not explode. The result is preliminary and requires more SNRs and further analysis. In addition, we use our distribution to estimate a minimum mass for core collapse between 7.0 and 7.8 Msun.
The centroid energy of the Fe K$alpha$ line has been used to identify the progenitors of supernova remnants (SNRs). These investigations generally considered the energy of the centroid derived from the spectrum of the entire remnant. Here we use {it XMM-Newton} data to investigate the Fe K$alpha$ centroid in 6 SNRs: 3C~397, N132D, W49B, DEM L71, 1E 0102.2-7219, and Kes 73. In Kes 73 and 1E 0102.2-7219, we fail to detect any Fe K$alpha$ emission. We report a tentative first detection of Fe K$alpha$ emission in SNR DEM L71, with a centroid energy consistent with its Type Ia designation. In the remaining remnants, the spatial and spectral sensitivity is sufficient to investigate spatial variations of the Fe K$alpha$ centroid. We find in N132D and W49B that the centroids in different regions are consistent with that derived from the overall spectrum, although not necessarily with the remnant type identified via other means. However, in SNR 3C~397, we find statistically significant variation in the centroid of up to 100 eV, aligning with the variation in the density structure around the remnant. These variations span the intermediate space between centroid energies signifying core-collapse and Type Ia remnants. Shifting the dividing line downwards by 50 eV can place all the centroids in the CC region, but contradicts the remnant type obtained via other means. Our results show that caution must be used when employing the Fe K$alpha$ centroid of the entire remnant as the sole diagnostic for typing a remnant.
Supernovae are the dominant source of chemical enrichment of galaxies, and they are an important source of energy to heat the interstellar medium and accelerate cosmic rays. Our knowledge of supernovae in the Milky Way is based mostly on the study of Galactic supernova remnants (SNRs), providing an (incomplete) record to supernova activity over the last ~100,000 yr. Here we report on an investigation of the spatial distribution of Galactic SNRs. Given the limited number of SNRs it is common to assume a functional form for the Galactocentric distribution of SNRs. However, several functional forms have been used in the past, without much justification for the radial distribution. For example, one often used functional form implies that no supernova activity is present in the Galactic Centre region. However, the presence of a magnetar and a SNR near the Galactic Centre suggest that a spatial distribution with zero SNRs at the Galactic Centre is not realistic. In light of these concerns we reevaluate the Galactic SNR distribution. We provide a brief outline of the main detection biases in finding SNRs and we investigate whether or not the use of the most common functional form is justified and how it compares to other models for the SNR distribution. We do this by analysing the longitudinal distribution of SNRs. We find that a simple exponential distribution is the most consistent and simplest model for describing the radial SNR distribution in the Galaxy and draw comparisons with the massive star formation and metallicity distributions.
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