Beecroft Institute for Particle Astrophysics and Cosmology

Abstract:

Aims: The true nature of primordial magnetic fields (PMFs) and their role in the formation of galaxies still remains elusive. To shed light on these unknowns, we investigate their impact by varying two sets of properties: (i) accounting for the effect of PMFs on the initial matter power spectrum, and (ii) accounting for their magneto-hydrodynamical effects on the formation of galaxies. By comparing both we can determine the dominant agent in shaping galaxy evolution.

Methods: We use the magneto-hydrodynamics code RAMSES, to generate multiple new zoom-in simulations for eight different host halos of dwarf galaxies across a wide luminosity range of 103 − 106 L⊙. These halos are selected from a ΛCDM cosmological box, tracking their evolution down to redshift z = 0. We explore a variety of primordial magnetic field (comoving) strengths Bλ ranging from 0.05 to 0.50 nG.

Results: We find magnetic fields in the interstellar medium not only modify star formation in dwarf spheroidal galaxies but also completely prevent the formation of stars in less compact ultra-faints with halo mass and stellar mass below ∼ 2.5 · 109 and 3 · 106 M⊙, respectively. At high redshifts, the impact of PMFs on host halos of dwarf galaxies through the modification of the matter power spectrum is more dominant than the influence of magneto-hydrodynamics in shaping their gaseous structure. Through the amplification of small perturbations ranging in mass from 107 to 109 M⊙ in the ΛCDM+PMFs matter power spectrum, primordial fields expedite the formation of the first dark matter halos, leading to an earlier onset and a higher star formation rate at redshifts z > 12. We investigate the evolution of various energy components and demonstrate that magnetic fields with an initial strength of Bλ ≥ 0.05 nG exhibit a strong growth of magnetic energy, accompanied by a saturation phase, that starts quickly after the growth phase. These trends persist consistently, regardless of the initial conditions, whether it is the classical ΛCDM or modified by PMFs. Lastly, we investigate the impact of PMFs on the present-time observable properties of dwarf galaxies, namely, the half light radius, V-band luminosity, mean metallicity and velocity dispersion profile. We find that PMFs with moderate strengths of Bλ ≤ 0.10 nG show great agreement with the scaling relations of the observed Local group dwarfs. However, stronger fields lead to large sizes and high velocity dispersion.

Abstract:

We study how bar strength and bar kinematics affect star formation in different regions of the bar by creating radial profiles of EW[Hα] and Dn4000 using data from Sloan Digital Sky Survey-IV Mapping Nearby Galaxies at Apache Point Observatory (MaNGA). Bars in galaxies are classified as strong or weak using Galaxy Zoo DESI, and they are classified as fast and slow bars using the Tremaine–Weinberg method on stellar kinematic data from the MaNGA survey. In agreement with previous studies, we find that strong bars in star-forming (SF) galaxies have enhanced star formation in their center and beyond the bar-end region, while star formation is suppressed in the arms of the bar. This is not found for weakly barred galaxies, which have very similar radial profiles to unbarred galaxies. In addition, we find that slow bars in SF galaxies have significantly higher star formation along the bar than fast bars. However, the global star formation rate is not significantly different between galaxies with fast and slow bars. This suggests that the kinematics of the bar do not affect star formation globally, but changes where star formation occurs in the galaxy. Thus, we find that a bar will influence its host the most if it is both strong and slow.

Abstract:

We investigate the three-dimensional clustering of sources emitting electromagnetic pulses traveling through cold electron plasma, whose radial distance is inferred from their dispersion measure. As a distance indicator, dispersion measure is systematically affected by inhomogeneities in the electron density along the line of sight and special and general relativistic effects, similar to the case of redshift surveys. We present analytic expressions for the correlation function of fast radio bursts (FRBs) and for the galaxy-FRB cross-correlation function, in the presence of these dispersion measure-space distortions. We find that the even multipoles of these correlations are primarily dominated by nonlocal contributions (e.g., the electron density fluctuations integrated along the line of sight), while the dipole also receives a significant contribution from the Doppler effect, one of the major relativistic effects. A large number of FRBs, O(105-106), expected to be observed in the Square Kilometre Array, would be enough to measure the even multipoles at very high significance, S/N≈100, and perhaps to make a first detection of the dipole (S/N≈10) in the FRB correlation function and FRB-galaxy cross correlation function. This measurement could open a new window to study and test cosmological models.

Abstract:

Context. The Euclid space satellite mission will measure the large-scale clustering of galaxies at an unprecedented precision, providing a unique probe of modifications to the ?CDM model. Aims. We investigated the approximations needed to efficiently predict the large-scale clustering of matter and dark matter halos in the context of modified gravity and exotic dark energy scenarios. We examined the normal branch of the Dvali-Gabadadze-Porrati model, the Hu-Sawicki f(R) model, a slowly evolving dark energy model, an interacting dark energy model, and massive neutrinos. For each, we tested approximations for the perturbative kernel calculations, including the omission of screening terms and the use of perturbative kernels based on the Einstein-de Sitter universe; we explored different infrared-resummation schemes, tracer bias models and a linear treatment of massive neutrinos; we investigated various approaches for dealing with redshift-space distortions and modelling the mildly nonlinear scales, namely the Taruya-Nishimishi-Saito prescription and the effective field theory of large-scale structure. This work provides a first validation of the various codes being considered by Euclid for the spectroscopic clustering probe in beyond-?CDM scenarios. Methods. We calculated and compared the χ2 statistic to assess the different modelling choices. This was done by fitting the spectroscopic clustering predictions to measurements from numerical simulations and perturbation theory-based mock data. We compared the behaviour of this statistic in the beyond-?CDM cases, as a function of the maximum scale included in the fit, to the baseline ?CDM case. Results. We find that the Einstein-de Sitter approximation without screening is surprisingly accurate for the modified gravity cases when comparing to the halo clustering monopole and quadrupole obtained from simulations and mock data. Further, we find the same goodness-of-fit for both cases - the one including and the one omitting non-standard physics in the predictions. Our results suggest that the inclusion of multiple redshift bins, higher-order multipoles, higher-order clustering statistics (such as the bispectrum), and photometric probes such as weak lensing, will be essential to extract information on massive neutrinos, modified gravity and dark energy. Additionally, we show that the three codes used in our analysis, namely, PBJ, Pybird and MG-Copter, exhibit sub-percent agreement for k ≤ 0.5 h Mpc-1 across all the models. This consistency underscores their value as reliable tools.