Strong gravitational lensing and dynamical dark energy

We study the strong gravitational lensing properties of galaxy clusters obtained from N-body simulations with different kinds of dark energy (DE). We consider both dynamical DE, due to a scalar field self-interacting through Ratra—Peebles (RP) or supergravity (SUGRA) potentials, and DE with constant negative w=p/ρ=−1 (ΛCDM). We have 12 high-resolution lensing systems for each cosmological model with mass greater than 5.0 × 1014 h−1 M⊙. Using a ray shooting technique, we make a detailed analysis of the lensing properties of these clusters, paying particular attention to the number of arcs and their properties (magnification, length and width). We find that the number of giant arcs produced by galaxy clusters changes in a considerable way from ΛCDM models to dynamical dark energy models with an RP or SUGRA potential. These differences originate from the different epochs of cluster formation and from the non-linearity of the strong lensing effect. We suggest that strong lensing is one of the best tools to discriminate among different kinds of dark energ

Constraining warm dark matter using QSO gravitational lensing

Warm dark matter (WDM) has been invoked to resolve apparent conflicts of cold dark matter (CDM) models with observations on subgalactic scales. In this work, we provide a new and independent lower limit for the WDM particle mass (e.g. sterile neutrino) through the analysis of image fluxes in gravitationally lensed quasi-stellar objects (QSOs). Starting from a theoretical unperturbed cusp configuration, we analyse the effects of intergalactic haloes in modifying the fluxes of QSO multiple images, giving rise to the so-called anomalous flux ratio. We found that the global effect of such haloes strongly depends on their mass/abundance ratio and it is maximized for haloes in the mass range 106-108 M⊙. This result opens up a new possibility to constrain CDM predictions on small scales and test different warm candidates, since free streaming of WDM particles can considerably dampen the matter power spectrum in this mass range. As a consequence, while a (Λ)CDM model is able to produce flux anomalies at a level similar to those observed, a WDM model, with an insufficiently massive particle, fails to reproduce the observational evidences. Our analysis suggests a lower limit of a few keV (mν∼ 10) for the mass of WDM candidates in the form of a sterile neutrino. This result makes sterile neutrino WDM less attractive as an alternative to CDM, in good agreement with previous findings from Lyman α forest and cosmic microwave background analysi

The effect of low-mass substructures on the cusp lensing relation

It has been argued that the flux anomalies detected in gravitationally lensed quasi-stellar objects (QSOs) are evidence for substructures in the foreground lensing haloes. In this paper, we investigate this issue in greater detail, focusing on the cusp relation which corresponds to images of a source located to the cusp of the inner caustic curve. We use numerical simulations combined with a Monte Carlo approach to study the effects of the expected power-law distribution of substructures within Λ cold dark matter (ΛCDM) haloes on the multiple images. Generally, the high number of anomalous flux ratios in the cusp configurations is unlikely to be explained by ‘simple' perturbers (subhaloes) inside the lensing galaxy, modelled by either point masses or extended Navarro, Frenk & White subhaloes. We considered in our analysis a mass range of 105-107 M⊙ for the subhaloes. We also demonstrate that including the effects of the surrounding mass distribution, such as other galaxies close to the primary lens, does not change the results. We conclude that triple images of lensed QSOs do not show any direct evidence for dark dwarf galaxies such as CDM substructur

NIHAO XIX: How supernova feedback shapes the galaxy baryon cycle

We have used the NIHAO simulations to explore how supernovae (SNe) affect star formation in galaxies. We find that SN feedback operates on all scales from the interstellar medium (ISM) to several virial radii. SNe regulate star formation by preventing condensation of HI into H$_2$ and by moving cold neutral gas to the hot HII phase. The first effect explains why the cold neutral gas in dwarf galaxies forms stars inefficiently. The second maintains the hot ISM of massive galaxies (HII vents out at lower masses). At $v_{\rm vir}\simeq 67{\rm\,km\,s}^{-1}$, the outflow rate follows the relation: $\dot{M}_{\rm out}=23\,(v_{\rm vir}/67{\rm\,km\,s}^{-1})^{-4.6}\,{\rm SFR}$. $20\%$ to $70\%$ of the gas expelled from galaxies escapes from the halo (ejective feedback) but outflows are dominated by cold swept-up gas, most of which falls back onto the galaxy on a $\sim 1\,$Gyr timescale. This `fountain feedback' reduces the masses of galaxies by a factor of two to four, since gas spends half to three quarter of its time in the fountain. Less than $10\%$ of the ejected gas mixes with the hot circumgalactic medium and this gas is usually not reaccreted. On scales as large as $6r_{\rm vir}$, galactic winds divert the incoming gas from cosmic filaments and prevent if from accreting onto galaxies (pre-emptive feedback). This process is the main reason for the low baryon content of ultradwarves.Comment: Submitted for publication in MNRA