Kyu-Hyun Chae, Harry Desmond, Federico Lelli, Stacy S. McGaugh, James M. Schombert

Theories of modified gravity generically violate the strong equivalence principle, so that the internal dynamics of a self-gravitating system in free fall depends on the strength of the external gravitational field (the external field effect). We fit rotation curves (RCs) from the SPARC database with a model inspired by Milgromian dynamics (MOND), which relates the outer shape of a RC to the external Newtonian field from the large-scale baryonic matter distribution through a dimensionless parameter $e_{\rm N}$. We obtain a $>4\sigma$ statistical detection of the external field effect (i.e. $e_{\rm N}>0$ on average), confirming previous results. We then locate the SPARC galaxies in the cosmic web of the nearby Universe and find a striking contrast in the fitted $e_{\rm N}$ {values} for galaxies in underdense versus overdense regions. Galaxies in an underdense region between 22 and 45 Mpc from the celestial axis in the northern sky have RC fits consistent with $e_{\rm N}\simeq0$, while those in overdense regions adjacent to the CfA2 great wall and the Perseus-Pisces supercluster return $e_{\rm N}$ that are a factor of two larger than the median for SPARC galaxies. We also calculate independent estimates of $e_{\rm N}$ from galaxy survey data and find that they agree with the $e_{\rm N}$ inferred from the RCs within the uncertainties, the chief uncertainty being the spatial distribution of baryons not contained in galaxies or clusters.

Eloy de Jong, Josu C. Aurrekoetxea, Eugene A. Lim

We study the formation of black holes from subhorizon and superhorizon perturbations in a matter dominated universe with 3+1D numerical relativity simulations. We find that there are two primary mechanisms of formation depending on the initial perturbation's mass and geometry -- via $\textit{direct collapse}$ of the initial overdensity and via $\textit{post-collapse accretion}$ of the ambient dark matter. In particular, for the latter case, the initial perturbation does not have to satisfy the hoop conjecture for a black hole to form. In both cases, the duration of the formation the process is around a Hubble time, and the initial mass of the black hole is $M_\mathrm{BH} \sim 10^{-2} H^{-1} M_\mathrm{Pl}^2$. Post formation, we find that the PBH undergoes rapid mass growth beyond the self-similar limit $M_\mathrm{BH}\propto H^{-1}$, at least initially. We argue that this implies that most of the final mass of the PBH is accreted from its ambient surroundings post formation.

Phoebe Upton Sanderbeck, Simeon Bird, Zoltan Haiman

If primordial black holes (PBHs) seeded the supermassive black holes (SMBHs) at the centers of high-redshift quasars, then the gas surrounding these black holes may reveal nucleosynthetic clues to their primordial origins. We present predictions of altered primordial abundances around PBHs massive enough to seed SMBHs at z~6-7.5. We find that if PBHs with initial masses of ~10^5 M$_{\odot}$ are responsible for such SMBHs, they may produce primordial Deuterium and Helium fractions enhanced by >~ 10%, and Lithium abundance depleted by >~10%, at distances of up to ~ a comoving kiloparsec away from the black hole after decoupling. We estimate that ~ 10^8 M$_{\odot}$ of gas is enhanced (or depleted) by at least one percent. Evidence of these modified primordial Deuterium, Helium, and Lithium abundances could still be present if this circum-PBH gas remains unaccreted by the SMBH and in or near the host galaxies of high-redshift quasars. Measuring the abundance anomalies will be challenging, but could offer a novel way to reveal the primordial origin of such SMBH seeds.

Fulvio Melia, Qingbo Ma, Jun-Jie Wei, Bo Yu

Several satellite missions have uncovered a series of potential anomalies in the fluctuation spectrum of the cosmic microwave background temperature, including: (1) an unexpectedly low level of correlation at large angles, manifested via the angular correlation function, C(theta); and (2) missing power in the low multipole moments of the angular power spectrum, C_ell. Their origin is still debated, however, due to a persistent lack of clarity concerning the seeding of quantum fluctuations in the early Universe. A likely explanation for the first of these appears to be a cutoff, k_min=(3.14 +/- 0.36) x 10^{-4} Mpc^{-1}, in the primordial power spectrum, P(k). Our goal in this paper is twofold: (1) we examine whether the same k_min can also self-consistently explain the missing power at large angles, and (2) we confirm that the of this cutoff in P(k) does not adversely affect the remarkable consistency between the prediction of Planck-LCDM and the Planck measurements at ell > 30. We use the publicly available code CAMB to calculate the angular power spectrum, based on a line-of-sight approach. The code is modified slightly to include the additional parameter (i.e., k_min) characterizing the primordial power spectrum. In addition to this cutoff, the code optimizes all of the usual standard-model parameters. In fitting the angular power spectrum, we find an optimized cutoff, k_min = 2.04^{+1.4}_{-0.79} x 10^{-4} Mpc^{-1}, when using the whole range of ell's, and k_min=3.3^{+1.7}_{-1.3} x 10^{-4} Mpc^{-1}, when fitting only the range ell < 30, where the Sachs-Wolfe effect is dominant. These are fully consistent with the value inferred from C(theta), suggesting that both of these large-angle anomalies may be due to the same truncation in P(k).

Tomer D. Yavetz, Xinyu Li, Lam Hui

We present a wave generalization of the classic Schwarzschild method for constructing self-consistent halos -- such a halo consists of a suitable superposition of waves instead of particle orbits, chosen to yield a desired mean density profile. As an illustration, the method is applied to spherically symmetric halos. We derive an analytic relation between the particle distribution function and the wave superposition amplitudes, and show how it simplifies in the high energy (WKB) limit. We verify the stability of such constructed halos by numerically evolving the Schr\"odinger-Poisson system. The algorithm provides an efficient and accurate way to simulate the time-dependent halo substructures from wave interference. We use this method to construct halos with a variety of density profiles, all of which have a core from the ground-state wave function, though the core-halo relation need not be the standard one.