CosmoPhys

This paper [arxiv: 1902.03261] is a current status review on improving systematics¹ in SNe Ia distance measurements by combining optical with near-infrared (NIR) photometry. Though initially being done at low redshifts (z <= 0.04), there are plans to extend this work to higher redshifts². The paper is authored by some of the more noted researchers in this area, e.g., Arturo Avelino and Robert Kirshner³. My goal here is a top-level summary, so that if you don't read the paper you'll hopefully get the gist of it, while also including helpful supplemental info. In a few cases, I added some font bolding for emphasis.

“This is significant for supernova cosmology because, along with photometric-calibration uncertainties, uncertain dust [extinction](https://en.wikipedia.org/wiki/Extinction_(astronomy) estimates and the intrinsic variability of SN Ia colors present challenging and important systematic problems for dark energy measurements. (pg2)”

“Recent work has demonstrated that SN Ia in the NIR are more nearly standard candles, even before correction for light curve (LC) shape or host galaxy dust reddening... Overall, a substantial body of evidence indicates that rest-frame LCs of SN Ia in NIR are both better standard candles than at optical wavelengths and less sensitive to the confounding effects of dust. When NIR data are combined with UBV RI photometry, this yields accurate and precise distance estimates. (pg2)”

This study analyzed 89 SNe Ia having both optical and NIR data avaiable. “While the current sample of optical SN Ia LCs exceeds 1000, and will be increased by orders of magnitude by ongoing and future surveys including the Dark Energy Survey, the Zwicky Transient Facility, and the Large Synoptic Survey Telescope, the number of normal SN Ia with published NIR LCs is still less than 250.” (abstract)

This growing NIR work is useful not only to help to standardize SNe Ia distance measurements, but also for Hubble constant estimates, “and eventually, cosmological parameter estimates, when the nearby and high-z samples² are combined as in the HST RAISIN⁴ program.” (pg3)

“We implement two different methods to derive the distance modulus for each supernova from the NIR LCs. We call them the template method and the Gaussian-process method (GP). The GP method requires data near the NIR maximum for all NIR bands being used, while the template method works for arbitrarily sampled data, even if the LC is sparse near maximum. For this reason, we have more objects in the template method Hubble diagrams...At the ∼2.5-3.1σ level, that NIR SN Ia LCs at NIR maximum, without LC shape or dust corrections, are already better standard candles than optical-only SN Ia LCs ... that apply such corrections. (pg12)” ... “For all NIR band subsets, the GP (NIR max) method produces the smallest scatter. (pg19)”

These NIR studies “could help to limit systematic galaxy distance errors that arise from the degeneracy between the intrinsic supernova colors and reddening of light by dust, that affects optical-only SN Ia cosmology...Studies combining NIR and optical SN Ia photometry have already shown that the addition of NIR data is an extremely promising way to break the degeneracy between intrinsic color and dust reddening, allowing distance estimates to become increasingly insensitive to the assumptions behind individual LC fitting models. (pg25)

“Upcoming missions that could exploit nearby NIR data as a low-z anchor include the Large Synoptic Survey Telescope, the NASA Wide-Field Infrared Survey Telescope, the European Space Agency’s EUCLID mission, as well as the NASA James Webb Space Telescope. (pg28)”

Another paper that might be of interest: Carnegie Supernova Project-II: The Near-infrared Spectroscopy Program ___

¹ “Systematic errors introduced by photometry, light curve fitters, and by dust extinction pose the limit of precision for today's large optical samples. Theory predicts and empirical evidence demonstrates that SN Ia are more nearly standard candles in infrared bands than in optical bands. Dust absorption is 3 times smaller in the near IR.” [Kirshner source]

² “This investigation is for a low-z sample, but we are working to extend this technique to cosmologically-interesting distances with the Hubble Space Telescope. (pg 1)”

³ Both Adam Riess and Brian Schmidt were Kirshner's PhD students. [source]

⁴ RAISIN: Tracers of cosmic expansion with SN IA in the IR (aside: what a convoluted acronym!)

Tags: #astrophysics #cosmology