Improved Dark Energy Constraints From ~ 100 New CfA Supernova Type Ia Light Curves Page: 3 of 102
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curve shape and color to obtain the absolute intrinsic SN Ia magnitude. The main source
of uncertainty here is how to treat host-galaxy reddening and disentangle this from intrinsic
SN Ia color variation. A third source could also be that there are different populations of
SN Ia that are equivalent in light-curve shape and color but actually have slightly different
intrinsic luminosities.
The CfA3 sample is useful in identifying and reducing systematic errors on the photo-
metric front because it provides a large, homogeneously-reduced and nearly homogeneously-
observed nearby sample. The CfA3 sample can be used on its own as the nearby component
and thus reduce the effects of systematic offsets with other samples. Also, the same pho-
tometric reduction pipeline that was used for the ESSENCE survey (Miknaitis et al. 2007)
was used for the CfA3 sample, reducing one source of systematic uncertainty between nearby
and faraway SN Ia. Regarding light-curve fitting and distance estimation methods, the CfA3
sample can be added to existing training sets to improve their accuracy and precision, espe-
cially since the inclusion of the slightly less-common slow and fast decliners was emphasized.
For the first time we are in a position to examine different fitting methods on a large sam-
ple that was not used to train them. With the larger sample, light curve fitters can be
trained better and a proper prediction error can be calculated by excluding individual ob-
jects (or groups of objects) from the training sample one at a time. Mandel et al. (2009)
have developed the machinery for this in the near infrared and will be including the optical
bands shortly. Additionally, many of the CfA3 objects were also observed spectroscopi-
cally (Matheson et al. 2008; Blondin et al. 2009) and photometrically in the near infrared
(Wood-Vasey 2008; Friedman et al. 2009). The combination of the optical and near-infrared
photometry should help disentangle host reddening from intrinsic SN Ia color and reduce
this source of systematic error. Finally, the larger sample assists the search for different SN
Ia populations, perhaps by host-galaxy morphology (see @4.2) or by host-galaxy color (Kelly
et al. 2009).
Due to the light-curve-shape/luminosity relationship (broader brighter, narrower fainter),
the natural scatter in intrinsic SN Ia luminosity is reduced by a factor of three. This makes SN
Ia into standardizable candles and the most useful distance indicators at cosmological scales
(e.g., Phillips 1993; Hamuy et al. 1996a; Riess, Press, & Kirshner 1996; Perlmutter et al.
1997; Jha et al. 1999; Goldhaber et al. 2001; Guy et al. 2005; Jha, Riess, & Kirshner 2007;
Guy et al. 2007; Conley et al. 2008). They have been the key element in the discovery
that the universe is accelerating and dominated by dark energy (e.g., Riess et al. 1998;
Perlmutter et al. 1999; Knop et al. 2003; Tonry et al. 2003; Barris et al. 2004; Astier et al.
2006; Riess et al. 2007; Wood-Vasey et al. 2007; Davis et al. 2007; Kowalski et al. 2008). Ob-
servational efforts have moved beyond merely establishing the existence of dark energy and
are focused on determining its simplest properties. This is most often done in terms of the
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Hicken, Malcolm; U., /Harvard-Smithsonian Ctr. Astrophys. /Harvard; Wood-Vasey, W.Michael; U., /Pittsburgh; Blondin, Stephane; Observ., /European Southern et al. Improved Dark Energy Constraints From ~ 100 New CfA Supernova Type Ia Light Curves, article, April 6, 2012; United States. (https://digital.library.unt.edu/ark:/67531/metadc836308/m1/3/: accessed July 16, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.