arXiv subjects

Phoebe Upton Sanderbeck

Publications and source records attributed to Phoebe Upton Sanderbeck.

6 recordsLinked to original sources

arXiv2026

The Lifetimes of High-redshift Quasars Suggest Magnetic Disk Support

It has recently been suggested that a variety of data on active galactic nuclei (AGN) can be explained if AGN disks are supported against gravitational fragmentation by magnetic fields that are advected into the disk from the surrounding galaxy. Here we derive the maximum timescales over which accretion onto a black hole (BH) powering an AGN can be maintained at a given rate, both with and without magnetic disk support. We then compare these timescales to the lifetimes of episodes of sustained luminous accretion that are inferred from measurements of the photoionized proximity zones around high-redshift quasars. While some of the shortest inferred quasar lifetimes are consistent with pure gas pressure support, we find that some additional magnetic support is likely required to explain the longest inferred quasar lifetimes of > 10$^4$ yr. For these longest-lived AGN, we find that magnetic pressure in their disks can be up to a hundred times higher than the gas pressure. In addition, the lack of inferred quasar lifetimes that are definitively > 10$^6$ yr is consistent with gas pressure and advected magnetic fields being the principal sources of disk support. This adds to the body of evidence that magnetic fields play an important role in sustaining the rapid growth of supermassive BHs in the early universe.

astro-ph.GA↗

arXiv2025

Forecasts for Broadband Intensity Mapping of the Ultraviolet-Optical Background with CASTOR and SPHEREx

Broadband tomography statistically extracts the redshift distribution of frequency dependent emission from the cross correlation of intensity maps with a reference catalog of galaxy tracers. We make forecasts for the performance of future all-sky UV experiments doing broadband tomography. We consider the Cosmological Advanced Survey Telescope for Optical-UV Research (CASTOR) and the Spectro-Photometer for the History of the Universe, Epoch of Reionization, and Ices Explorer (SPHEREx). The dominant uncertainty is from variability in the photometric zero point, which scales with limiting magnitude and so mirror size. With this scaling, and assuming a galaxy number density characteristic of future spectroscopic datasets, we find that CASTOR measures the UV background SED $2-10$ times better than existing data. The applicable redshift range will expand from the current $z < 1$ to $z \approx 0-3$ with CASTOR and $z =5-9$ with SPHEREx. We show that CASTOR can provide competitive constraints on the EBL monopole to those available from galaxy number counts and direct measurement techniques. At high redshift especially, these results will help understand galaxy formation and reionization. Our modelling code and chains are publicly available.

astro-ph.CO↗

arXiv2021

Nucleosynthetic signatures of primordial origin around supermassive black holes

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.

astro-ph.CO↗

arXiv2021

Effect of Separate Initial Conditions on the Lyman-$α$ Forest in Simulations

Using a set of high resolution simulations, we quantify the effect of species specific initial transfer functions on probes of the IGM via the Lyman-$α$ forest. We focus on redshifts $2-6$, after H~{\sc i} reionization. We explore the effect of these initial conditions on measures of the thermal state of the low density IGM: the curvature, Doppler width cutoff, and Doppler width distribution. We also examine the matter and flux power spectrum, and potential consequences for constraints on warm dark matter models. We find that the curvature statistic is at most affected at the $\approx2\%$ level at $z=6$. The Doppler width cutoff parameters are affected by $\approx5\%$ for the intercept, and $\approx8\%$ for the fit slope, though this is subdominant to sample variation. The Doppler width distribution shows a $\approx30\%$ effect at $z=3$, however the distribution is not fully converged with simulation box size and resolution. The flux power spectrum is at most affected by $\approx5\%$ at high redshift and small scales. We discuss numerical convergence with simulation parameters.

astro-ph.CO↗

arXiv2020

Inhomogeneous HeII reionization in Hydrodynamic Simulations

The reionization of the second electron of helium shapes the physical state of intergalactic gas at redshifts between 2 < z < 5. Because performing full in situ radiative transfer in hydrodynamic simulations is computationally expensive for large volumes, the physics of HeII reionization is often approximated by a uniform UV background model that does not capture the patchiness of reionization. We have devised a model that implements the effects of HeII reionization using semi-analytic calculations of the thermal state of intergalactic gas-- a way to bypass a full radiative transfer simulation while still realizing the physics of HeII reionization that affects observables such as the Lyman alpha forest. Here we present a publicly-available code that flexibly models inhomogeneous HeII reionization in simulations at a negligible computational cost. Because many of the parameters of HeII reionization are uncertain, our model is customizable from a set of free parameters. We show results from this code in MP-Gadget, where this model is implemented. We demonstrate the resulting temperature evolution and temperature-density relation of intergalactic gas-- consistent with recent measurements and previous radiative transfer simulations. We show that the impact of HeII reionization gives rise to subtle signatures in the one-dimensional statistics of the Lyman alpha forest at the level of several per cent, in agreement with previous findings. The flexible nature of these simulations are ideal for studies of HeII reionization and future observations of the HeII Lyman alpha forest.

astro-ph.CO↗

arXiv2019

Estimates for the impact of Ultraviolet Background fluctuations on galaxy clustering measurements

Spatial fluctuations in ultraviolet backgrounds can subtly modulate the distribution of extragalactic sources, a potential signal and systematic for large-scale structure surveys. While this modulation has been shown to be significant for 3D Ly alpha forest surveys, its relevance for other large-scale structure probes has been hardly explored, despite being the only astrophysical process that likely can affect clustering measurements on the scales of >~Mpc. We estimate that the background fluctuations, modulating the amount of H I, have a fractional effect of (0.03-0.3) x (k/[10^-2 Mpc^-1])^-1 on the power spectrum of 21 cm intensity maps at z = 1-3. We find a smaller effect for H alpha and Ly alpha intensity mapping surveys of (0.001-0.1) x (k/[10^-2 Mpc^-1])-1 and even smaller effect for more traditional surveys that correlate the positions of individual H alpha or Ly alpha emitters. We also estimate the effect of backgrounds on low-redshift galaxy surveys in general based on a simple model in which background fluctuations modulate the rate halo gas cools, modulating star formation: We estimate a maximum fractional effect on the power of ~0.01 (k/[10-2 Mpc-1])-1 at z = 1. We compare sizes of these imprints to cosmological parameter benchmarks for the next generation of redshift surveys: We find that ionizing backgrounds could result in a bias on the squeezed triangle non-Gaussianity parameter fNL that can be larger than unity for power spectrum measurements with a SPHEREx-like galaxy survey, and typical values of intensity bias. Marginalizing over a shape of the form k-1PL, where PL is the linear matter power spectrum, removes much of this bias at the cost of ~ 40% larger statistical errors.

astro-ph.CO↗