View Full Version : Type II supernovae as Standard Candles awaits dedicated survey

2010-Aug-07, 02:51 PM
Poznanski, Nugent and Fillipenko point out the need for a dedicated survey of type 2's to calibrate their possible use as standard candles in cosmology.....SEE:http://arxiv.org/PS_cache/arxiv/pdf/1008/1008.0877v1.pdf

2010-Aug-07, 11:36 PM
I can't load it. What does it say?

2010-Aug-09, 05:02 AM
There is a problem using type IIp extracted from non-dedicate surveys to evaluate events in the Hubble flow (redshifted space) specifically:

Posnaski mention that the contrast between a SN and its host galaxy was a selection criterion for spectroscopic follow-up observations. This was obviously done to increase the eciency of their spectroscopic observing runsand the number of SNe Ia they find. Unlike a regular Malmquist bias that skews the distribution near thedetection limit of the survey, such a criterion selects intrinsically bright objects, independent redshift. This is evident from the very dierent luminosity functions oft he two samples. Figure 3 shows that nearly half of the SDSS-II SNe are brighter than their host galaxies up to a factor of a few, unlike the samples of P09 and N06 that are consistently fainter than their hosts.

In other words, the sampling process preferentially recovered the brightest events at all redshifts - a type II Malmquist bias leading to a degeneracy in the Hubble curve fit...i think.

2010-Aug-09, 12:10 PM
...i think.

Why then not just post the conclusions of the paper

We nd that when measuring expansion velocities for the SDSS-II sample of SNe II-P by using H , the SCM correlation gives a tight Hubble diagram, with a scatter
of ~11% in distance. This is comparable to the scatter obtained with previous samples of SNe II-P, despite a systematic o set among the SDSS-II objects, which is
probably due to a strong bias favoring intrinsically bright SNe.

Our analysis shows that H velocities correlate well with those derived from Fe II lines, with a scatter of about 300km/s, enabling the use of early-time spectra
and data having low S/N. The SCM parameters and the true tightness of the cor-relation remain to be tested with high-quality Hubble-flow data. We are currently compiling such a set of SNe II-P from the Palomar Transient Factory (Rau et al. 2009; Law et al. 2009; Poznanski et al. 2009b), where
cosmology with SNe II-P is one of the key projects and should lead to less biased samples.