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View Full Version : dust assumptions affect Delay Time Distributions in type 1a's



trinitree88
2011-Nov-01, 12:46 PM
Assuming is necessary, but always has caveats. DTD's from different surveys need to have the same ones http://arxiv.org/PS_cache/arxiv/pdf/1110/1110.6442v1.pdf

Jerry
2011-Nov-02, 02:56 PM
In light of the large systematic differences due to dust, it is vitally important to use caution when comparing rate results from studies that use different dust assumptions. In particular, systematic offsets from dust assumptions could affect the shape of the derived SN Ia delay time distribution. The DTD shape is obtained not from the SN rate itself, but from the change in the rate with redshift. To measure the change, one typically must compare surveys covering different redshift ranges.

Comparing low- and high-redshift measurements that correct their rates using different extinction distributions will inducea systematic error on the slope of the SN rate and thereby the DTD shape.

To avoid such a systematic bias, studies of the DTD should strive to use consistent extinction corrections between low
and high redshift. To aid this, we have provided our rates calculated under a variety of extinction assumptions. Consistency will go a long way towards reducing potential errors in the DTD, even if the extinction distribution remains
poorly known. However, in the long run one would like a better understanding of SN extinction distributions at both low
and high redshift, particularly to avoid uncertainties due to a changing extinction distribution with redshift.

Dust extinction is one of those nagging, degenerate parameters that (in most studies) is a function of the initial assumptions. In cosmological studies, some authors have chosen to ignore dust extinction completely and it has bitten them in the butt. I like the author's assertion that local methods should be used until better discriminators are analytically derived. Assuming dust evolution without any justification other than the theory you are trying to establish demands it just doesn't cut it.