XXXVI Reunión Bienal de la Real Sociedad Española de Física

Weak-lensing magnification as a probe for the dark Universe

17 jul. 2017 15:45

30m

Aula Química Técnica (Facultad de Química (USC))

Oral parallel contribution Particle and Theoretical Physics Particle and Theoretical Physics I

Descripción

Introduction Cosmological measurements show that the expansion of the Universe is accelerating. Generically, the entity that causes this acceleration (whether it is a new form of matter or modified gravity) is called dark energy [1]. Nevertheless, the nature of dark energy constitutes one of the biggest puzzles in Physics. Shedding light on dark energy requires the construction of big experiments that survey large volumes of the Universe. One of those experiments is The Dark Energy Survey (DES) [2]. One of the observational probes that may unravel the nature of dark energy is the weak gravitational lensing [3]. Weak-lensing is produced by the gravitational bending of the trajectory of photons by gravitational fields leading to the deflection of the light rays. Thus, the light emitted by foreground distant galaxies is deflected by the matter located between them and the observer. For extended sources, in addition to the change in position, this leads to two observational effects: an isotropic size enlargement (magnification) and an elongation/shrink along one axis (shear). Since the surface brightness is preserved, the isotropic size enlargement due to magnification produces an increase on the observed flux of the background galaxies. This allows to see galaxies that would be beyond the detection threshold if gravitational lensing was not present. Thus, nearby the lenses the observed density of sources is increased. This effect is known as number-count magnification and allows to probe the convergence profile of the lens sample selected, that is a proxy for the matter profile [4]. Weak-lensing magnification by voids Extensive wide-field programs have allowed accurate measurement of weak lensing effects. Previous magnification measurements involve the use of very massive objects as lenses, such as luminous red galaxies (LRGs) and clusters [5], or high redshift objects as sources, such as Lymanbreak galaxies (LBGs) or quasars (QSOs) [6,7]. Lyman break galaxies and quasars have demonstrated to be a very effective population of background samples to do magnification studies due to its high lensing efficiency. However, deep surveys or large areas are needed to reach a significant amount of these objects. Thus, shallow or small area surveys require the selection of a more numerous population of source galaxies to allow the measurement of the magnification signal. A new technique has been developed at the Dark Energy Survey [8], where galaxies selected only by its photo-z, are used both as lenses and sources. This procedure simplifies the analysis as no additional processing is needed to construct the sample (contrary to the methodology present on the literature). This new methodology allows the detection of the magnification signal on small area surveys, such as the DES Science Verification data-set, but the power of this methodology also applies to large area surveys such as LSST or the final footprint of DES, with 5000 deg^2 . The huge decrease on the shot-noise due to the increase on the surface density of sources, allows the selection of more exotic lenses, such as voids. Voids are the emptiest regions of the cosmic web that conform the large-scale-structure of the Universe (LSS) [9]. Thus, their structure and evolution is dominated by dark energy. Previous works on simulations show that different void properties such as their ellipticity or its total matter radial distribution (void-profile) is strongly dependent on the modified gravity model used [10-17]. Due to the presence of dark matter, the total matter distribution is only accessible through gravitational lensing. Thus, the determination of the void-profile with weak-lensing magnification constitutes a new and independent probe for dark energy. References [1] S. Perlmutter et al., ApJ 517 (1999) 565. [2] The Dark Energy Survey Collaboration, ArXiv astro-ph/0510346 (2005). [3] D. H. Weinberg et al., Phys. Rep. 530.2 (2013) 87. [4] M. Bartelmann and P. Schneider, Phys. Rep. 340 (2001) 291. [5] A. H. Bauer et al., MNRAS 440 (2014) 3701. [6] Ryan Scranton et al., ApJ 633.2 (2005) 589. [7] C. B. Morrison et al., MNRAS 426 (2012). [8] M. Garcia-Fernandez et al., ArXiv 1611.10326 (2016). [9] A. Kovács and J. García-Bellido., MNRAS 462 (2016), [10] F. von Braun-Bates et al., JCAP 3 (2017) 012. [11] G. Lavaux and B. D. Wandelt., MNRAS 403 ( 2010) 1392. [12] G. Lavaux and B. D. Wandelt., ApJ 754.2 (2012) 109. [13] D. Spolyar, M. Sahlén, and J. Silk., Phys. Rev. Lett. 111.24 (2013) 241103. [14] E. V. Arbuzova, A. D. Dolgov, and L. Reverberi., Astroparticle Physics 54 (2014) 44. [15] Y.-C. Cai, N. Padilla, and B. Li. ArXiv 1410.8355 (2014). [16] P. Zivick et al., MNRAS 451 (Aug. 2015) 4215. [17] A. Barreira et al., JCAP 8, (2015) 028.