Exploiting flux ratio anomalies to probe warm dark matter in future large scale surveys. (arXiv:1912.02196v1 [astro-ph.CO])

<a href="http://arxiv.org/find/astro-ph/1/au:+Harvey_D/0/1/0/all/0/1">David Harvey</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Valkenburg_W/0/1/0/all/0/1">Wessel Valkenburg</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Tamone_A/0/1/0/all/0/1">Amelie Tamone</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Boyarsky_A/0/1/0/all/0/1">Alexey Boyarsky</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Courbin_F/0/1/0/all/0/1">Frederic Courbin</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Lovell_M/0/1/0/all/0/1">Mark Lovell</a>

Flux ratio anomalies in strong gravitationally lensed quasars constitute a

unique way to probe the abundance of non-luminous dark matter haloes, and hence

the nature of dark matter. In this paper we identify double imaged quasars as a

statistically efficient probe of dark matter, since they are 20 times more

abundant than quadruply imaged quasars. Using N-body simulations that include

realistic baryonic feedback, we measure the full distribution of flux ratios in

doubly imaged quasars for cold (CDM) and warm dark matter (WDM) cosmologies.

Through this method, we fold in two key systematics – quasar variability and

line-of-sight structures. We find that WDM cosmologies predict a ~6 per cent

difference in the cumulative distribution functions of flux ratios relative to

CDM, with CDM predicting many more small ratios. Finally, we estimate that ~600

doubly imaged quasars will need to be observed in order to be able to

unambiguously discern between CDM and the two WDM models studied here. Such

sample sizes will be easily within reach of future large scale surveys such as

Euclid. In preparation for this survey data we require discerning the scale of

the uncertainties in modelling lens galaxies and their substructure in

simulations, plus a strong understanding of the selection function of observed

lensed quasars.

Flux ratio anomalies in strong gravitationally lensed quasars constitute a

unique way to probe the abundance of non-luminous dark matter haloes, and hence

the nature of dark matter. In this paper we identify double imaged quasars as a

statistically efficient probe of dark matter, since they are 20 times more

abundant than quadruply imaged quasars. Using N-body simulations that include

realistic baryonic feedback, we measure the full distribution of flux ratios in

doubly imaged quasars for cold (CDM) and warm dark matter (WDM) cosmologies.

Through this method, we fold in two key systematics – quasar variability and

line-of-sight structures. We find that WDM cosmologies predict a ~6 per cent

difference in the cumulative distribution functions of flux ratios relative to

CDM, with CDM predicting many more small ratios. Finally, we estimate that ~600

doubly imaged quasars will need to be observed in order to be able to

unambiguously discern between CDM and the two WDM models studied here. Such

sample sizes will be easily within reach of future large scale surveys such as

Euclid. In preparation for this survey data we require discerning the scale of

the uncertainties in modelling lens galaxies and their substructure in

simulations, plus a strong understanding of the selection function of observed

lensed quasars.

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