Dark Energy 2: DE and Large Scale Structure GUASA 2015 Octavio Valenzuela IA-UNAM Cosmic Large Scale Structure Ecuaciones que describen la evolución del Universo Ec. de Friedmann Ec. De aceleración de la expansión Parámetro de Hubble Tasa de expansión del Universo d =a(t)x, a(t): factor de escala x: coordenada comovil Historia de la Energía Oscura Dic. 1997: Contradicciones en nuestro entendimiento del Universo! Edad del Universo < a la de cúmulos globulares - Poca estructura a pequeña escala - Densidad promedio - Paradigma teórico motivado por simplicidad: Universo plano, compuesto de materia (normal + oscura fría), distribución de perturbaciones iniciales independiente de la escala. El modelo tenía que cambiar o extenderse! una de las hipótesis al menos-“plano,” “fría,” “invariante de escala,” o quizás “de materia.” Ecuaciones de campo de Einstein aplicadas al Universo como un todo: cambia con el tiempo, hay evolución: Dinámica Debemos estudiar la historia de expansión para acotar la geometría si conocemos el contenido: Materia? ⇔ Geometría Expressing Distances in an Expanding Universe The geometry and expansion rate of the Universe effects angular sizes and distances measured. Integrate over components of RW metric. DH = c/Ho ! Hubble Distance (distance light travels in Hubble time, tH = 1/Ho) DC= ! Radial Co-moving Distance DM = DC (flat) ! Transverse Co-moving Distance, differs for curved space (see Hogg 2000) DA = L(proper length)/θ(angular size) = DM/(1+z) ! Angular Distance DL = sqrt (L/4π*flux) = DM(1+z) = DA(1+z)2 ! Luminosity Distance If Λ = 0 and flat geometry, then DL = 2c/Ho [z/(G+1)] {1+[z/(G+1)]} where G = (1 + z)1/2 See Ned Wright’s Javascript Cosmology Calculator for DL for different cosmologies: http://www.astro.ucla.edu/~wright/CosmoCalc.html E(z)=\sqrt{\Omega_m(1+z)^3+\Omega_k(1+z)^2+\Omega_\Lambda} Angular diameter distance vs z (plotting DA/DH where DA=L/θ) Luminosity distance vs z (plotting DL/DH) DH=c/Ho= 3000h-1Mpc At high z, angular diameter distance is such that 1 arcsec is about 5 kpc. flat, Λ=0 – solid open, Λ=0 – dotted flat, non-zero Λ - dashed (from Hogg 2000 astro-ph 9905116) Now we need a standard candle or ruler Type Ia Supernovae Brightness Brightness tells us distance away DL (lookback time t) Redshift tells us the expansion factor a Time after explosion If we know the light curve slope we can estimate the maximum brightness sqrt(L/(4Pi Brightness)) 14 Four months in the life of a SN Ia On the Rise: Age: -6 days Maximum Powered by radioactivity Vejecta=10-20,000 km/s +26 days +47 days +102 days Elements produced= Fe,Co,Ni,Si,Ca Color Images of SNe Ia Fainter High Redshift SN and Expansion History: Acceleration Just recently 1.0 Found: Hubble, Followed: Hubble Dark Matter Dominated Found: Ground, Followed: Hubble Dark Energy Dominated Relative Brightness (Δm) Constant acceleration 0.5 Acceleration/ Deceleration 0.0 Freely expanding -0.5 Constant deceleration Brighter -1.0 0.0 present 0.5 1.0 Redshift z 1.5 2.0 past The Accelerating Universe By 1998 two teams measured ~100 SNe Ia Surprise! The Universe is accelerating, propelled by dark energy. High-z SCP ¿Cuál puede ser la razón de la aceleración? Algo cuya contribución a la densidad de energía no se diluya: Llamemoslo Energía Oscura ¿Qué tan importante es el nuevo factor? tamaño aceleración desaceleración > Big Bang < tiempo Información independiente de Curvatura? Ec. de Friedmann Parametro de densidad Ω que tanto se aleja de modelo plano: Conociendo Ω, restringimos la geometría: La materia (ordinaria + oscura) contribuyen con Ω ≈ 0.3, curvature negativa. Suma de ángulos en triángulos < 180o. Radiación de fondo proporciona una regla estándar (Velocidad del sonido en el plasma primordial) 400,000 año después del Big Bang 400,000 años luz. Horizonte acústico depende cosmología, bariones, fotones ΩTot = [θpeak(deg)]-1/2. Observación: θpeak = 1o. flat El universo es plano: positively curved negatively curved ΩTot = 1 . [Miller et al.; de Bernardis et al; WMAP] Concordance: ΩΜ = 0.3, ΩΛ = 0.7 . ¿What is the DE Nature? • Cosmological Constant? • Other? • How can we test it? • Stay tuned Modelo de deSitter: Inflación cósmica ρ=Λ= cte, plano ● Ec de Friedman: 3H2= Λ, H=cte ● edad=2/(3H) ● Horizont dH = 3c*edad = 2/H, constante!! Aceleración restringe la relación entre presión y densidad del Universo es decir la ecuación de estado w= / w < -1/3 para que haya aceleración ¿Is w, constant? We must accurately measure the expansion history? PPProbing DE via cosmology • We “see” dark energy through its effects on the expansion of the universe: • Three (3) main approaches – Standard candles • measure dL (integral of H-1) – Standard rulers • measure dA (integral of H-1) and H(z) – Growth of fluctuations. • Crucial for testing extra ! components vs modified gravity. Standard Ruler • Suppose we had an object whose length we know as a function of cosmic epoch. • By measuring the angle (⍬) subtended by this ruler (✗) as a function of redshift we map out the angular diameter distance dA • By measuring the redshift interval (△z) associated with this distance we map out the Hubble parameter H(z) Ideal Properties of Standard Ruler To get competitive constraints on Dark Energy, we need to see changes in H(z) at ~1 % level, this would give us statistical errors in DE equation of State to ~10% We need to be able to calibrate the ruler accurately over most of the age of the Universe. We need to be able to measure the ruler over much of the volume of the Universe We need to be able to make independent accurate measurements of the ruler Where do we find such a ruler? Individual Cosmological objects will probably never be uniform enough. Use Statistics of large scale structure of matter and radiation. (aka. if we stick with early times and large scale, perturbative treatment of the Universe will still be valid, and the calculations will be under control.) Preferred length scales arise from Physics of early Universe and imprinted on the distribution of matter and radiation Sunyaev & Zel’dovich (1970); Peebles & Yu (1970); Doroshkevitch, Sunyaev & Zel’dovich (1978) Cooray, Hu, Huterer & Joffre (2001); Eisenstein (2003); Seo & Eisenstein (2003); Blake & Glazebrook (2003); Hu & Haiman (2003) Slide from Shirley Ho Non-Linear Linear Cartoon Picture • At early times the universe was hot, dense and ionized. Photons and matter were tightly coupled by Thomson scattering. – Short m.f.p. allows fluid approximation. • Initial fluctuations in density and gravitational potential drive acoustic waves in the fluid: compressions and rarefactions. • These show up as temperature fluctuations in the CMB [harmonic wave] The 2-point correlation function • The two-point correlation function ξ (r ): One way to describe the tendency of galaxies to cluster together • If we make a random choice of two small volumes V1 and V2, and the average spatial density of galaxies is n per cubic megaparsec, then the chance of finding a galaxy in V1 is just nV1. • If galaxies tend to clump together, then the probability that we then also have a galaxy in V2 will be greater when the separation r12 between the two regions is small. • We write the joint probability of finding a galaxy in both volumes as if ξ (r ) > 0 at small r , then galaxies are clustered, whereas if ξ (r ) < 0, they tend to avoid each other. Sparke & Gallagher 2007 • We generally compute ξ (r ) by estimating the distances of galaxies from their redshifts, making a correction for the distortion introduced by peculiar velocities. • Observationally it has been found that on scales r<=10h−1 Mpc, the 2-point correlation function takes roughly the form ξ (r ) ≈ (r/r0)−γ , γ > 0 • r0 is the correlation length • When r < r0, the probability of finding one galaxy within radius r of another is significantly larger than for a strictly random distribution. • Since ξ (r ) represents the deviation from an average density, it must at some point become negative as r increases. Sparke & Gallagher 2007 The two-point correlation function ξ (r ) for galaxies in the 2dF survey. • Ellis et al. 2002, MNRAS The correlation length r0 ≈ 5h−1 Mpc – 6h−1 Mpc for the ellipticals, which are more strongly clustered, – smaller for the star-forming galaxies • The slope γ ≈ 1.7 • For r 0>~50h−1 Mpc, which is roughly the size of the largest wall or void features, ξ (r ) oscillates around zero: the galaxy distribution is fairly uniform on larger scales. The correlation function is not very useful for describing the one-dimensional filaments or two-dimensional walls. If our volume V1 lies in one of these, the probability of finding a galaxy in V2 is high only when it also lies within the structure. Since ξ (r ) is an average over all possible placements of V2, it will not rise far above zero once the separation r Exceeds the thickness of the wall or filament (use of three-point and four-point correlation functions?) We do not yet have a good statistical method to describe the strength and prevalence of walls and filaments. Power spectrum • The Fourier transform of ξ (r) is the power spectrum P(k) so that small k corresponds to a large spatial scale. • Since ξ (r ) is dimensionless, P(k) has the dimensions of a volume. • The function sin(kr)/kr is positive for |kr| < π, and it oscillates with decreasing amplitude as kr becomes large • so, very roughly, P(k) will have its maximum when k−1 is close to the radius where ξ (r ) drops to zero. What are we waiting for? • Find a tracer of the mass density field and compute its 2-point function. • Locate the features in the above corresponding to the sound horizon, s. • Measure the !" and !z subtended by the sound horizon, s, at a variety of redshifts, z. • Compare to the value at z~103 to get dA and H(z) Is this our Universe? Do you believe it? Conclusions • Baryonic Acoustic Oscillations provide an accurate standard ruler • How good is that? • More information? Redshift Space distortion? • What is Dark energy? We´ve got some tools, more yet to come. Thursday and Friday. Conclusions • Crisis in Cosmology at late 90´s triggered a detailed study of cosmic expansion history • Unexpected: SNIa —> Universe is not slowing down instead is accelerating, but only since recently • The agent may contribute with a constant in Energy density and dominates the Energy inventory. • We don´t know the physics behind El crecimiento de la estructura cósmica depende de la naturaleza de la energía oscura efecto de la expansión del universo ¿Qué Hacer? " " " Medir con gran precisión: La historia de expansión del Universo, se acelera siempre igual o cambia esta aceleración? (BAO) El crecimiento de la estructura: como se agregan a la estructura las galaxias (Redshift space distortion) Conclusiones • La naturaleza de la Energía Oscura es un reto • Las mediciones recientes sugieren que es consistente con una constante pero grandes inconsistencias sugieren más elementos • La opción de una nueva teoría de gravedad suena atractiva pero es mucho más compleja de lo que se esperaba, no existe una opción completa, aunque es un reto muy grande • Un nuevo campo podría representar a esta energía oscura, pero puede afectar fuertemente el crecimiento de estructura. • El la siguiente década los nuevos catastros de galaxias definirán fuertes restricciones a las explicaciones • Universo Ec de Friedmann, de Sitter • Historia en 1997 • SNIa calibradores, aceleración, • Energía Oscura: Como se estudia? Expansión, crecimiento de estructura • Naturaleza: Campo/partícula, Gravedad, Cte: Vacío • Futuros Sondeos