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Register a new userA metallicity study of 1987A-like supernova host galaxies
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The origin of the blue supergiant (BSG) progenitor of Supernova (SN) 1987A has long been debated, along with the role that its sub-solar metallicity played. We now have a sample of 1987A-like SNe that arise from the core collapse (CC) of BSGs. The metallicity of the explosion sites of the known BSG SNe is investigated, as well as their association to star-forming regions. Both indirect and direct metallicity measurements of 13 BSG SN host galaxies are presented, and compared to those of other CC SN types. Indirect measurements are based on the known luminosity-metallicity relation and on published metallicity gradients of spiral galaxies. To provide direct estimates based on strong line diagnostics, we obtained spectra of each BSG SN host both at the SN explosion site and at the positions of other HII regions. Continuum-subtracted Ha images allowed us to quantify the association between BSG SNe and star-forming regions. BSG SNe explode either in low-luminosity galaxies or at large distances from the nuclei of luminous hosts. Therefore, their indirectly measured metallicities are typically lower than those of SNe IIP and Ibc. This is confirmed by the direct estimates, which show slightly sub-solar values (12+log(O/H)=8.3-8.4 dex), similar to that of the Large Magellanic Cloud (LMC), where SN 1987A exploded. However, two SNe (1998A and 2004em) were found at near solar metallicity. SNe IIb have a metallicity distribution similar to that of BSG SNe. Finally, the association to star-forming regions is similar among BSG SNe, SNe IIP and IIn. Our results suggest that LMC metal abundances play a role in the formation of some 1987A-like SNe. This would naturally fit in a single star scenario for the progenitors. However, the existence of two events at nearly solar metallicity suggests that also other channels, e.g. binarity, contribute to produce BSG SNe.
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We use a sample of 1338 spectroscopically confirmed and photometrically classified Type Ia Supernovae (SNe Ia), sourced from the CSP, CfA, SDSS-II, and SNLS supernova samples, to examine the relationships between SNe Ia and the galaxies that host them. Our results provide confirmation with improved statistical significance that SNe Ia, after standardization, are on average more luminous in massive hosts (significance $rm > 5 sigma$), and decline more rapidly in massive hosts (significance $rm > 9sigma$) and in hosts with low specific star formation rates (significance $rm > 8sigma$). We study the variation of these relationships with redshift and detect no evolution. We split SNe Ia into pairs of subsets that are based on the properties of the hosts, and fit cosmological models to each subset. Including both systematic and statistical uncertainties, we do not find any significant shift in the best-fit cosmological parameters between the subsets. Among different SN Ia subsets, we find that SNe Ia in hosts with high specific star formation rates have the least intrinsic scatter ($rm sigma_{int}=0.08pm0.01$) in luminosity after standardization.
High cadence ultraviolet, optical and near-infrared photometric and low-resolution spectroscopic observations of the peculiar Type II supernova (SN) 2018hna are presented. The early phase multiband light curves exhibit the adiabatic cooling envelope emission following the shock breakout up to ~14 days from the explosion. SN~2018hna has a rise time of $sim$,88 days in the V-band, similar to SN 1987A. A $rm^{56}Ni$ mass of ~0.087$pm$0.004 $rm M_{odot}$ is inferred for SN 2018hna from its bolometric light curve. Hydrodynamical modelling of the cooling phase suggests a progenitor with a radius ~50 $rm R_{odot}$, a mass of ~14-20 $rm M_{odot}$ and explosion energy of ~1.7-2.9$rm times$ $rm 10^{51} erg$. The smaller inferred radius of the progenitor than a standard red supergiant is indicative of a blue supergiant progenitor of SN 2018hna. A sub-solar metallicity (~0.3 $rm Z_{odot}$) is inferred for the host galaxy UGC 07534, concurrent with the low-metallicity environments of 1987A-like events.
We present the largest spectroscopic study of the host environments of Type Ibc supernovae (SN Ibc) discovered exclusively by untargeted SN searches. Past studies of SN Ibc host environments have been biased towards high-mass, high-metallicity galaxies by focusing on SNe discovered in galaxy-targeted SN searches. Our new observations more than double the total number of spectroscopic stellar population age and metallicity measurements published for untargeted SN Ibc host environments, and extend to a median redshift about twice as large as previous statistical studies (z = 0.04). For the 12 SNe Ib and 21 SNe Ic in our metallicity sample, we find median metallicities of log(O/H)+12 = 8.48 and 8.61, respectively, but determine that the discrepancy in the full distribution of metallicities is not statistically significant. This median difference would correspond to only a small difference in the mass loss via metal-line driven winds (<30%), suggesting this does not play the dominant role in distinguishing SN Ib and Ic progenitors. However, the median metallicity of the 7 broad-lined SN Ic (SN Ic-BL) in our sample is significantly lower, log(O/H)+12 = 8.34. The age of the young stellar population of SN Ic-BL host environments also seems to be lower than for SN Ib and Ic, but our age sample is small. A synthesis of SN Ibc host environment spectroscopy to date does not reveal a significant difference in SN Ib and Ic metallicities, but reinforces the significance of the lower metallicities for SN Ic-BL. This combined sample demonstrates that galaxy-targeted SN searches introduce a significant bias for studies seeking to infer the metallicity distribution of SN progenitors, and we identify and discuss other systematic effects that play smaller roles. We discuss the path forward for making progress on SN Ibc progenitor studies in the LSST era.
Supernova (SN) 1987A is the only young SN in which H_2 has been detected in the ejecta. The properties of the H_2 are important for understanding the explosion and the ejecta chemistry. Here, we present new VLT/SINFONI observations of H_2 in SN 1987A, focussing on the 2.12 mu m (1,0)S(1) line. We find that the 3D emissivity is dominated by a single clump in the southern ejecta, with weaker emission being present in the north along the plane of the circumstellar ring. The lowest observed velocities are in the range 400-800 km/s, in agreement with previous limits on inward mixing of H. The brightest regions of H_2 coincide with faint regions of Halpha, which can be explained by Halpha being powered by X-ray emission from the ring, while the H_2 is powered by 44Ti. A comparison with ALMA observations of other molecules and dust shows that the brightest regions of H_2, CO and SiO occupy different parts of the inner ejecta and that the brightest H_2 clump coincides with a region of very weak dust emission. The latter is consistent with theoretical predictions that the H_2 should form in the gas phase rather than on dust grains.
We measured high-quality surface brightness fluctuation (SBF) distances for a sample of 63 massive early-type galaxies using the WFC3/IR camera on the Hubble Space Telescope. The median uncertainty on the SBF distance measurements is 0.085 mag, or 3.9% in distance. Achieving this precision at distances of 50 to 100 Mpc required significant improvements to the SBF calibration and data analysis procedures for WFC3/IR data. Forty-two of the galaxies are from the MASSIVE Galaxy Survey, a complete sample of massive galaxies within ~100 Mpc; the SBF distances for these will be used to improve the estimates of the stellar and central supermassive black hole masses in these galaxies. Twenty-four of the galaxies are Type Ia supernova hosts, useful for calibrating SN Ia distances for early-type galaxies and exploring possible systematic trends in the peak luminosities. Our results demonstrate that the SBF method is a powerful and versatile technique for measuring distances to galaxies with evolved stellar populations out to 100 Mpc and constraining the local value of the Hubble constant.
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