Archive for January 14, 2020

Luminosity Evolution in Type 1a Supernovae?

Posted in The Universe and Stuff with tags , , , , on January 14, 2020 by telescoper

Figure 1 of Kang et al.

During this afternoon’s very exciting Meeting of the Faculty of Science and Engineering at Maynooth University I suddenly remembered a paper I became aware of over Christmas but then forgot about. There’s an article here describing the paper that makes some pretty strong claims, which was what alerted me to it. The actual paper, by Kang et al., which has apparently been refereed and accepted for publication by the Astrophysical Journal, can be found on the arXiv here. The abstract reads:

The most direct and strongest evidence for the presence of dark energy is provided by the measurement of galaxy distances using type Ia supernovae (SNe Ia). This result is based on the assumption that the corrected brightness of SN Ia through the empirical standardization would not evolve with look-back time. Recent studies have shown, however, that the standardized brightness of SN Ia is correlated with host morphology, host mass, and local star formation rate, suggesting a possible correlation with stellar population property. In order to understand the origin of these correlations, we have continued our spectroscopic observations to cover most of the reported nearby early-type host galaxies. From high-quality (signal-to-noise ratio ~175) spectra, we obtained the most direct and reliable estimates of population age and metallicity for these host galaxies. We find a significant correlation between SN luminosity (after the standardization) and stellar population age at a 99.5% confidence level. As such, this is the most direct and stringent test ever made for the luminosity evolution of SN Ia. Based on this result, we further show that the previously reported correlations with host morphology, host mass, and local star formation rate are most likely originated from the difference in population age. This indicates that the light-curve fitters used by the SNe Ia community are not quite capable of correcting for the population age effect, which would inevitably cause a serious systematic bias with look-back time. Notably, taken at face values, a significant fraction of the Hubble residual used in the discovery of the dark energy appears to be affected by the luminosity evolution. We argue, therefore, that this systematic bias must be considered in detail in SN cosmology before proceeding to the details of the dark energy.

Of course evidence for significant luminosity evolution of Type Ia supernovae would throw a big spanner in the works involved in using these objects to probe cosmology (specifically dark energy), but having skimmed the paper I’m a bit skeptical about the results, largely because they seem to use only a very small number of supernovae to reach their conclusions and I’m not convinced about selection effects. I have an open mind, though, so I’d be very interested to hear through the comments box the views of any experts in this field.

Maynooth University Library Cat Update

Posted in Maynooth with tags , on January 14, 2020 by telescoper

It’s high time for the first update about the famous Maynooth University Library Cat for 2020. I gave him some breakfast on the way in to work yesterday morning, before Storm Brendan arrived. He scoffed it rapidly, even though I strongly suspect I wasn’t the first person to give him food!

I was a bit worried about said feline before the Christmas break because he had a problem with one of his front legs which gave him a limp. I couldn’t see any cuts or anything but it was clearly causing him some bother. Fortunately he seemed to shake it off and there’s no sign of the limp any more.  You can often tell if a cat is poorly because that’s the one situation when they lose their appetite, and there’s no sign of that! Indeed he was quite skittish yesterday when I said hello.

Although the rain hadn’t arrived with Storm Brendan when I fed him yesterday it was already quite windy.  There’s something about windy weather that makes cats freak out a bit. I don’t know what it is. Perhaps the it’s noise? Cats have very sensitive hearing and maybe the sound of the wind causes a kind of sensory overload? My old cat Columbo used to run around like a mad thing when it was windy outside. It’s not that he was unhappy about it – it just got him very excited.

Anyway, today it’s raining quite heavily so I expect Maynooth University Library Cat is tucked up in his little box or somewhere else that’s cosy.