Browsing by Subject "Reionization"

Now showing 1 - 4 of 4

A novel approach for measuring the escape of ionizing radiation from Lyman Alpha emitting galaxies
(2023-12) Davis, Dustin; Gebhardt, Karl; Boylan-Kolchin, Michael; Casey, Caitlin; Finkelstein, Steven; Shapley, Alice
How the bulk, intergalactic gas of the universe came to be nearly fully ionized after its earlier neutral state following the Epoch of Recombination remains an open investigation. That this (re)ionization took place between roughly z ∼ 15 and z ∼ 6 via photoionization is well accepted, but the main sources of the ionizing photons is actively debated. Star-forming galaxies are frequently suggested as the most likely driver. However, direct measurements of ionizing radiation from such galaxies in the Epoch of Reionization is not possible and existing surveys of what are thought to be similar, lower redshift galaxies have inconsistent or incompatible results due partly to their necessary methodologies and comparatively small sample sizes. In this work, I seek to address these issues. This dissertation represents an exploratory work to determine if it is possible to algorithmically identify large numbers of Lyman Alpha Emitting galaxies from the many millions of untargeted, low resolution spectra from the Hobby-Eberly Telescope Dark Energy Experiment survey and through spectral stacking measure the average escaping Lyman Continuum flux and various other physical properties of those galaxies. These small, rapidly star-forming, low-metallicity, z ∼ 3 galaxies can then be used as better proxies for higher redshift, Epoch of Reionization analogs and determine what role they may have played in the reionization of the universe.
The kinetic Sunyaev-Zel’dovich effect as a probe of the physics of cosmic reionization : the effect of self-regulated reionization
(2014-12) Park, Hyunbae; Shapiro, Paul R.
We calculate the angular power spectrum of the cosmic microwave background temperature fluctuations induced by the kinetic Sunyaev-Zel'dovich (kSZ) effect from the epoch of reionization (EOR). We use detailed N-body+radiative-transfer simulations to follow inhomogeneous reionization of the intergalactic medium. For the first time, we take into account the "self-regulation" of reionization: star formation in low-mass dwarf galaxies or minihalos is suppressed if these halos form in the regions that were already ionized or Lyman-Werner dissociated. Some previous work suggested that the amplitude of the kSZ power spectrum from the EOR can be described by a two-parameter family: the epoch of half-ionization and the duration of reionization. However, we argue that this picture applies only to simple forms of the reionization history which are roughly symmetric about the half-ionization epoch. In self-regulated reionization, the universe begins to be ionized early, maintains a low level of ionization for an extended period, and then finishes reionization as soon as high-mass atomically cooling halos dominate. While inclusion of self-regulation affects the amplitude of the kSZ power spectrum only modestly (~10%), it can change the duration of reionization by a factor of more than two. We conclude that the simple two-parameter family does not capture the effect of a physical, yet complex, reionization history caused by self-regulation. When added to the post-reionization kSZ contribution, our prediction for the total kSZ power spectrum is below the current upper bound from the South Pole Telescope. Therefore, the current upper bound on the kSZ effect from the EOR is consistent with our understanding of the physics of reionization.
Maximal X-ray feedback in the pre-reionization universe
(2023-08-04) Jeon, Junehyoung; Bromm, Volker; Finkelstein, Steven L
X-ray feedback in the pre-reionization Universe provided one of the major energy sources for reionization and the thermal evolution of the early intergalactic medium. However, X-ray sources at high redshift have remained largely inaccessible to observations. One alternative approach to study the overall effect of X-ray feedback in the early Universe is a full cosmological simulation. Toward this goal, in this paper we create an analytic model of X-ray feedback from accretion onto supermassive black holes (SMBHs), to be used as a sub-grid model in future cosmological simulations. Our analytic model provides a relation between the mass of a dark matter halo and the SMBH it hosts, where the efficiency is governed by an energy balance argument between thermal feedback and the confining gravitational potential of the halo. To calibrate the model, we couple the halo-level recipe with the Press-Schechter halo mass function and derive global mass and energy densities. We then compare our model to various observational constraints, such as the resulting soft X-ray and IR cosmic radiation backgrounds, to test our choice of model parameters. We in particular derive model parameters that do not violate any constraints, while providing maximal X-ray feedback prior to reionization. In addition, we consider the contribution of SMBH X-ray sources to reionization and the global 21 cm absorption signal.
Probing reionization with the Hubble Space Telescope (HST)
(2018-10-11) Larson, Rebecca Lynn; Finkelstein, Steven L.
We present the results of an unbiased search for Lyα emission from continuum-selected 5.6 < z < 8.7 galaxies. Our dataset consists of 160 orbits of G102 slitless grism spectroscopy obtained with HST/WFC3 as part of the Faint Infrared Grism Survey (FIGS; PI: Malhotra), which obtains deep slitless spectra of all sources in four fields, and was designed to minimize contamination in observations of previously-identified high-redshift galaxy candidates. The FIGS data can potentially spectroscopically confirm the redshifts of galaxies, and as Lyα emission is resonantly scattered by neutral gas, FIGS can also constrain the ionization state of the intergalactic medium (IGM) during the epoch of reionization. These data have sufficient depth to detect Lyα emission in this epoch, as Tilvi et al. (2016) have published the FIGS detection of previously known (Finkelstein et al., 2013) Lyα emission at z =7.51. The FIGS data use five separate roll-angles of HST to mitigate the contamination by nearby galaxies. We created a method that accounts for and removes the contamination from surrounding galaxies and also removes any dispersed continuum light from each individual spectrum (Pirzkal et al., 2017). We searched for significant (> 4σ) emission lines using two different automated detection methods, free of any visual inspection biases. Applying these methods on photometrically-selected high-redshift candidates between 5.6 < z < 8.7 we find two emission lines, one previously published by Tilvi et al. (2016), and a new line at 1.028 μm, which we identify as Lyα at z = 7.452 ± 0.003. This newly spectroscopically confirmed galaxy has the highest Lyα rest-frame equivalent width (EW [subscript Lyα]) yet published at z > 7 (140.3 ± 19.0Å).