Primordial magnetic fields: Fluctuating . . . HI signal: CDM - PowerPoint PPT Presentation

Post-recombination . . . The . . . Primordial magnetic . . . Ionization History Global HI signal Primordial magnetic fields: Fluctuating . . . HI signal: ΛCDM Fluctuating . . . Cosmological implications Detectability of the signal Magnetic fields and . . . Thermal evolution: . . . Ionization evolution based on Sethi and Subramanian, JCAP, 2009 Formation of . . . Sethi, Haiman, and Pandey, ApJ, 2010 Formation of first SMBHs Pandey and Sethi, ApJ, 2011 Weak Gravitational . . . Pandey and Sethi, ApJ, 2012 Power Spectrum . . . Cosmological weak . . . March 12, 2013 Cosmological weak . . . Constraints on . . . Conclusions Title Page ◭◭ ◮◮ ◭ ◮ Page 1 of 29 Go Back

Primordial magnetic . . . Ionization History 1. Primordial magnetic fields: Motivation Global HI signal Fluctuating . . . • Scalar and tensor perturbation were generated at the HI signal: ΛCDM time of inflation. Is it not conceivable that a process Fluctuating . . . existed then (breaking of conformal invariance?) that Detectability of the signal led to the generation of magnetic fields? (Turner and Magnetic fields and . . . Widrow 1988, Ratra 1992) Thermal evolution: . . . • Magnetic field coherent at scales � 10 kpc exist in Ionization evolution galaxies and clusters of galaxies. Can they be Formation of . . . explained using amplification of a small seed ∼ 10 − 20 G using dynamo mechanism? Formation of first SMBHs < magnetic field Weak Gravitational . . . Not clear. Evidence of µG magnetic field at z ≃ 2 Power Spectrum . . . and synchrotron emission at super-cluster scales Cosmological weak . . . favour primordial field hypothesis. Cosmological weak . . . • Magnetic fields of strength ≃ 10 − 9 G interesting from Constraints on . . . the point of view of observed fields in galaxies, Conclusions clusters of galaxies and cosmology. Title Page ◭◭ ◮◮ ◭ ◮

Primordial magnetic . . . Ionization History 2. Direct probe of magnetic field at large scales Global HI signal Fluctuating . . . • Detection of synchrotron radiation from structures larger HI signal: ΛCDM than clusters (e.g Kim et al. 1989). Difficult as the gas Fluctuating . . . density falls and diffuse low-surface brightness emission is Detectability of the signal difficult to image with radio interferometers. Magnetic fields and . . . • Correlation of Faraday rotation of high Thermal evolution: . . . redshift radio sources : Such correlation can reveal Ionization evolution the presence of magnetic field coherent on very large Formation of . . . scales ( > 100 Mpc) (e.g. Kollat 1998, Sethi 2003). Not Formation of first SMBHs possible so far owing to lack of homogeneous samples of Faraday rotation measurement. Upcoming interferometers Weak Gravitational . . . such as LOFAR will create such a sample with 10 5 Power Spectrum . . . sources. This is one of the primary goals of SKA, which Cosmological weak . . . will be able to reliably observe 10 7 Faraday rotations. Cosmological weak . . . Constraints on . . . Conclusions Title Page ◭◭ ◮◮ ◭ ◮

Primordial magnetic . . . Ionization History 3. Tangled Magnetic fields Global HI signal Fluctuating . . . • Statistically homogeneous and isotropic tangled HI signal: ΛCDM magnetic fields: Fluctuating . . . � ˜ B i ( q ) ˜ B ∗ j ( k ) � = δ 3 � δ ij − k i k j /k 2 � D ( q − k ) M ( k ) (1) Detectability of the signal Magnetic fields and . . . • The magnetic fields are further assumed to be Thermal evolution: . . . Gaussian and therefore their statistical properties are Ionization evolution completely described by power spectrum: M ( k ) with Formation of . . . M ( k ) = Ak n (2) Formation of first SMBHs Weak Gravitational . . . with the spectral index of power spectrum n > ∼ − 3. Power Spectrum . . . • Time evolution : In an expanding universe: Cosmological weak . . . Ba 2 = const, flux-frozen: Bρ − 2 / 3 = const Cosmological weak . . . • Normalization : Normalized to the present, B 0 refers Constraints on . . . to RMS using the cut-off scale k c = 1 Mpc − 1 . Conclusions Title Page ◭◭ ◮◮ ◭ ◮

Primordial magnetic . . . Ionization History 4. Early structure formation with tangled magnetic Global HI signal fields Fluctuating . . . HI signal: ΛCDM • Magnetic fields generate density perturbations in the Fluctuating . . . post-recombination era (Wasserman 1978). Detectability of the signal • For nearly scale-invariant power spectrum of magnetic Magnetic fields and . . . fields, the matter power spectrum P ( k ) ∝ k . At scales Thermal evolution: . . . ∼ 1 Mpc − 1 this could dominate corresponding to k < Ionization evolution over the inflation-era produced density perturbations. Formation of . . . • Important scales : Comoving Formation of first SMBHs � 10 − 9 G � Weak Gravitational . . . k max ≃ 235 Mpc − 1 B 0 Power Spectrum . . . � 10 − 9 G � Cosmological weak . . . k J ≃ 15 Mpc − 1 (3) B 0 Cosmological weak . . . Constraints on . . . k J is independent of time. Conclusions • Magnetic fields can aid early structure formation. Title Page How early and at what scales? ◭◭ ◮◮ ◭ ◮

Primordial magnetic . . . Ionization History 5. Matter power spectrum Global HI signal Fluctuating . . . HI signal: ΛCDM Fluctuating . . . Detectability of the signal Magnetic fields and . . . Thermal evolution: . . . Ionization evolution Formation of . . . Formation of first SMBHs Weak Gravitational . . . Power Spectrum . . . Cosmological weak . . . Cosmological weak . . . Constraints on . . . Conclusions Title Page (Gopal and Sethi 2003) ◭◭ ◮◮ ◭ ◮

Primordial magnetic . . . Ionization History 6. Post-recombination effects of magnetic fields Global HI signal Fluctuating . . . • Early structure formation : The redshift of collapse HI signal: ΛCDM depends strongly on the spectral index of magnetic Fluctuating . . . field power spectrum. All models other than nearly Detectability of the signal scales invariant n ≃ − 3 are ruled out by these Magnetic fields and . . . considerations. The collapse redshift is not sensitive to the value of the magnetic field. Thermal evolution: . . . Ionization evolution • Dissipation of magnetic fields : Tangled magnetic Formation of . . . fields can dissipate by ambi-polar diffusion and Formation of first SMBHs decaying turbulence in the post-recombination era. Weak Gravitational . . . This can lead to an altered ionization and thermal Power Spectrum . . . history (Sethi and Subramanian 2005). Cosmological weak . . . • Molecular Hydrogen formation : Can be significantly Cosmological weak . . . altered in the IGM and in the collapsing haloes Constraints on . . . (Sethi, Nath, and Subramanian 2008, Schicheler et al. Conclusions 2009, Sethi, Haiman, Pandey 2010) Title Page ◭◭ ◮◮ ◭ ◮

Primordial magnetic . . . Ionization History 7. The post-Recombination Era Global HI signal Fluctuating . . . HI signal: ΛCDM Fluctuating . . . Detectability of the signal Magnetic fields and . . . Thermal evolution: . . . Ionization evolution Formation of . . . Formation of first SMBHs Weak Gravitational . . . Power Spectrum . . . Cosmological weak . . . Cosmological weak . . . Constraints on . . . Conclusions Title Page ◭◭ ◮◮ ◭ ◮

Primordial magnetic . . . Ionization History 8. Primordial magnetic fields and reionization: Global HI signal semi-analytic models Fluctuating . . . HI signal: ΛCDM • Press-Schechter formalism to determine the mass Fluctuating . . . function. Most haloes are close to 1– σ in this case as Detectability of the signal opposed to the usual case. Magnetic fields and . . . • Choose halo UV luminosity, clumping factor, to solve Thermal evolution: . . . for the radius of evolving Stromgren sphere around Ionization evolution each source. Formation of . . . • Compute the evolution of ionized fraction. Formation of first SMBHs Weak Gravitational . . . • Normalize to WMAP results. Power Spectrum . . . • magnetic field v/s the usual case : f eff f esc ≃ 0 . 01 Cosmological weak . . . in the usual case. It could be two orders of magnitude Cosmological weak . . . smaller for B 0 ≃ 3 × 10 − 9 G. Constraints on . . . Conclusions Title Page ◭◭ ◮◮ ◭ ◮

Primordial magnetic . . . Ionization History 9. Ionization History Global HI signal Fluctuating . . . HI signal: ΛCDM Fluctuating . . . Detectability of the signal Magnetic fields and . . . Thermal evolution: . . . Ionization evolution Formation of . . . Formation of first SMBHs Weak Gravitational . . . Power Spectrum . . . Cosmological weak . . . Cosmological weak . . . Constraints on . . . Conclusions Title Page ◭◭ ◮◮ ◭ ◮

Primordial magnetic . . . Ionization History 10. Global HI signal Global HI signal Fluctuating . . . HI signal: ΛCDM Fluctuating . . . Detectability of the signal Magnetic fields and . . . Thermal evolution: . . . Ionization evolution Formation of . . . Formation of first SMBHs Weak Gravitational . . . Power Spectrum . . . Cosmological weak . . . Cosmological weak . . . Constraints on . . . Conclusions Title Page ◭◭ ◮◮ ◭ ◮