How much does dust affect light from high redshift quasars?

[oldman]

As I understand it, the conclusion that our spatially flat universe is expanding at an accelerating rate is supported by observations of 'standard candles' (type S1a supernovae) which appear less bright than expected when their z exceeds about 0.3 --- . Robert Kirschner has discussed these observations in his popular book The Extravagent Universe. He dismissed the possibility that the supernovae were instead dimmed appreciably by intergalactic dust.

In his Fig. 10.7, for example, the dimming seems to be quite a small effect. Smoothed out, it seems to be about 0.3 magnitudes as z approaches 1, which is comparable with the observational scatter for individual quasars. These are not easy observations. They have considerable cosmological implications.

In a http://arxiv.org/PS_cache/arxiv/pdf/0902/0902.4240v1.pdf" just out Menard, Scranton, Fukugita and Richards report an analysis of SDSS data which suggest that dust may indeed affect the dimming of distant supernovae. They comment that: "The magnitude of this effect and its impact on dark energy constraints must be investigated and quantified." and later add that: "This will affect the brightness estimates of Type Ia supernovae at high redshift, which require high precision in order to maximize their constraints on cosmological parameters."

The dimming they talk of is about .03 magnitudes up to z = .5 and possibly .05 to .09 at z = 1, if I read correctly.

I'd appreciate an assessment of their results in relation to those of say, Perlmutter and Kirschner to date by folk more competent than I to judge their significance.

 

[Chronos]

A valid point, but does not have a great deal of observational support from deep sky surveys. We know that dust is a very relevant issue with regard to the galactic plane. Problem is, there is not enough difference between on plane and off plane observations to contradict the Perlmutter studies.

 

[Chalnoth]

As I understand it, the conclusion that our spatially flat universe is expanding at an accelerating rate is supported by observations of 'standard candles' (type S1a supernovae) which appear less bright than expected when their z exceeds about 0.3 --- . Robert Kirschner has discussed these observations in his popular book The Extravagent Universe. He dismissed the possibility that the supernovae were instead dimmed appreciably by intergalactic dust.

Well, what really puts the idea that dust extinction can explain the appearance of acceleration to rest is the observation that when you look very far back, the universe is in a decelerating phase, which means that the supernovae are brighter than they should otherwise appear:
Adam Riess's website description
Arxiv preprint of the most recent work
Basically, if the appearance of accelerated expansion were explained by dust, we should see what looks like accelerated expansion all the way back, as the supernova light has to go through more and more dust. On the other hand, a Lambda-CDM cosmology predicts a late-phase accelerated expansion, but deceleration early on.

In a http://arxiv.org/PS_cache/arxiv/pdf/0902/0902.4240v1.pdf" just out Menard, Scranton, Fukugita and Richards report an analysis of SDSS data which suggest that dust may indeed affect the dimming of distant supernovae. They comment that: "The magnitude of this effect and its impact on dark energy constraints must be investigated and quantified." and later add that: "This will affect the brightness estimates of Type Ia supernovae at high redshift, which require high precision in order to maximize their constraints on cosmological parameters."

Well, bear in mind that supernova teams already do perform dust corrections: the spectra of supernovae is affected by the dust in a way that depends upon the frequency of the light, so it can be corrected for (at least partially). And yes, it is a good idea to quantify the effect. It's just that dust extinction can't account for our measurements of accelerated expansion.

 

[oldman]

Thanks, both Chronos and Chalnoth, for putting this paper in the correct perspective for me. And thanks for the links also, Chalnoth.