1,647 research outputs found
No. 617 Stuart Ruckman
No full textTranscript (12, 40 pages) of two interviews by Matt Driscoll with Stuart Ruckman on April 9, 2010, and July 7, 2011Ruckman (b. 1966) was born in Salt Lake City, Utah. Stuart shares how his family, particularly his father, played a significant role in introducing him to the outdoors. Some of his initial explorations included a hike to the top of Mount Olympus when he was five years old, backpacking trips in the Wasatch and Uinta Mountains, and a successful summit attempt on the Grand Teton when he was twelve. Stuart discovered technical rock climbing due to the influence of his older brother Bret, five years Stuart\u27s senior. Bret learned under Dennis Turville, a well-respected Salt Lake climbing instructor. Stuart shares his observations on the Salt Lake climbing community of the late 1970s and 1980s, noting the intimacy of the community, while also pointing out the significant influence of a handful of climbers, including Merrill Bitter, Les Ellison, and Brian Smoot. He briefly describes the proliferation of new-route development in the Wasatch during his first decade in climbing. In collaboration with his brother Bret, Stuart published comprehensive guidebooks on climbing in the Wasatch Mountains. Stuart\u27s contributions as a first-ascensionist and co-author of Rock Climbing the Wasatch Range attest to his lasting impact on Utah climbing. Interview is part of the Outdoor Recreation History Project. Interviewer: Matt Driscol
The role of Pop III stars and early black holes in the 21-cm signal from Cosmic Dawn
No full textModeling the 21-cm global signal from the Cosmic Dawn is challenging due to the many poorly constrained physical processes that come into play. We address this problem using the semi-analytical code 'Cosmic Archaeology Tool' (CAT). CAT follows the evolution of dark matter haloes tracking their merger history and provides an ab initio description of their baryonic evolution, starting from the formation of the first (Pop III) stars and black holes (BHs) in mini-haloes at z > 20. The model is anchored to observations of galaxies and AGN at z < 6 and predicts a reionization history consistent with constraints. In this work, we compute the evolution of the mean global 21-cm signal between 4 ≤ z ≤ 40 based on the rate of formation and emission properties of stars and accreting BHs. We obtain an absorption profile with a maximum depth δTb = -95 mK at z ~ 26.5 (54 MHz). This feature is quickly suppressed turning into an emission signal at z = 20 due to the contribution of accreting BHs that efficiently heat the intergalactic medium (IGM) at z < 27. The high-z absorption feature is caused by the early coupling between the spin and kinetic temperature of the IGM induced by Pop III star formation episodes in mini-haloes. Once we account for an additional radio background from early BHs, we are able to reproduce the timing and the depth of the EDGES signal only if we consider a smaller X-ray background from accreting BHs, but not the shape
Dark-ages Reionization and Galaxy Formation Simulation – XIV. Gas accretion, cooling, and star formation in dwarf galaxies at high redshift
No full textDark-ages reionization and galaxy formation simulation - XII. Bubbles at dawn
No full textThe direct detection of regions of ionized hydrogen (H II) has been suggested as a promising probe of cosmic reionization. Observing the redshifted 21-cm signal of hydrogen from the epoch of reionization (EoR) is a key scientific driver behind new-generation, low-frequency radio interferometers.We investigate the feasibility of combining low-frequency observations with the Square Kilometre Array and near infra-red survey data of the Wide-Field Infrared Survey Telescope to detect cosmic reionization by imaging HII bubbles surrounding massive galaxies during the cosmic dawn. While individual bubbles will be too small to be detected, we find that by stacking redshifted 21-cm spectra centred on known galaxies, it will be possible to directly detect the EoR at z ~ 9-12, and to place qualitative constraints on the evolution of the spin temperature of the intergalactic medium (IGM) at z ≳ 9. In particular, given a detection of ionized bubbles using this technique, it is possible to determine if the IGM surrounding them is typically in absorption or emission. Determining the globally averaged neutral fraction of the IGM using this method will prove more difficult due to degeneracy with the average size of HII regions
Dark-ages reionization and galaxy formation simulation - XIII. AGN quenching of high-redshift star formation in ZF-COSMOS-20115
No full textMassive quiescent galaxies (MQGs) are thought to have formed stars rapidly at early times followed by a long period of quiescence. The recent discovery of aMQG, ZF-COSMOS-20115 at z ~ 4, only 1.5 Gyr after the big bang, places new constraints on galaxy growth and the role of feedback in early star formation. Spectroscopic follow-up confirmed ZF-COSMOS- 20115 as a MQG at z = 3.717 with an estimated stellar mass of ~1011 M⊙, showing no evidence of recent star formation. We use the MERAXES semi-analytic model to investigate how ZF-COSMOS-20115 analogues build stellar mass, and why they become quiescent. We identify three analogue galaxies with similar properties to ZF-COSMOS-20115. We find that ZF-COSMOS-20115 is likely hosted by a massive halo with virial mass of ~1013M⊙, having been through significant mergers at early times. These merger events drove intense growth of the nucleus, which later prevented cooling and quenched star formation. Therefore, ZFCOSMOS- 20115 is unlikely to have experienced strong or extended star formation events at z < 3.7.We find that the analogues host the most massive black holes in our simulation and were luminous quasars at z ~ 5, indicating that ZF-COSMOS-20115 and other MQGs may be the descendants of high-redshift quasars. In addition, themodel suggests that ZF-COSMOS-20115 formed in a region of intergalactic medium that was reionized early
Dark-ages reionization and galaxy formation simulation – XVI. The thermal memory of reionization
No full textIntergalactic medium temperature is a powerful probe of the epoch of reionization, as information is retained long after reionization itself. However, mean temperatures are highly degenerate with the timing of reionization, with the amount heat injected during the epoch, and with the subsequent cooling rates. We post-process a suite of semi-analytic galaxy formation models to characterize how different thermal statistics of the intergalactic medium can be used to constrain reionization. Temperature is highly correlated with redshift of reionization for a period of time after the gas is heated. However as the gas cools, thermal memory of reionization is lost, and a power-law temperature–density relation is formed, T = T0(1 + δ)1 − γ with γ ≈ 1.5. Constraining our model against observations of electron optical depth and temperature at mean density, we find that reionization likely finished at
with a soft spectral slope of
. By restricting spectral slope to the range [0.5, 2.5] motivated by population II synthesis models, reionization timing is further constrained to
. We find that, in the future, the degeneracies between reionization timing and background spectrum can be broken using the scatter in temperatures and integrated thermal history
The detectability of Lyα emission from galaxies during the epoch of reionization
No full textWe study the visibility of the Lyα emission line during the epoch of reionization. Combining galactic outflow models with large-scale seminumeric simulations of reionization, we quantify the probability distribution function of the fraction of Lyα photons transmitted through the intergalactic medium (IGM). Our study focuses on galaxies populating dark matter haloes with masses of Mhalo= 1010M⊙ at z= 8.6, which is inspired by the recent reported discovery of a galaxy at z= 8.6 with strong Lyα line emission. For reasonable assumptions, we find that the combination of winds and reionization morphology results in per cent (50 per cent), for the majority of galaxies, even when the Universe is ~80 per cent (60 per cent) neutral by volume. Thus, the observed strong Lyα emission from the reported z= 8.6 galaxy is consistent with a highly neutral IGM, and cannot be used to place statistically significant constraints on the volume-averaged neutral fraction of hydrogen in the IGM. We also investigate the implications of the recent tentative evidence for an observed decrease in the 'Lyman alpha emitter fraction' among drop-out galaxies between z= 6 and 7. If confirmed, we show that a rapid evolution in will be required to explain this observation via the effects of reionization. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS
Redemption in the work of Francis Stuart
No full textThe idea of redemption is central to an understanding of the work
of Francis Stuart. Through an examination of its development and
expression, it is possible to demonstrate the integrity of his work and
its distinctive qualities. Such a demonstration is necessary because
Stuart's writing has been subjected to comparatively little scholarly
inquiry, although reviews of his work, especially that produced since
1949, suggest that it is impressive and important.
First, a general background to Stuart's work, a discussion of the
special problems associated with reading it, and a summary of his corpus
is provided. This indicates that the idea of redemption is important to
his earliest writing. The state of redemption is shown to be a
necessary apotheosis for Stuart's outcast heroes; it involves spiritual
suffering through which may be found a sense of reintegration and a
higher reality. This is expressed through interrelated themes such as
those of gambler, artist and ordinary man; mystic and criminal; sacred
and profane love; and spirituality and the mundane. The nature of the
redemptive experience is further elaborated by distinctive, complex
motifs, especially the hare, the ark and the woman-Christ. Their
recurrence provides an important element in the unity of Stuart's work.
Because Stuart's idea of the outcast raises important biographical
questions, an examination of the relationship between Stuart's life and
his work is made. Finally, the way in which the idea of redemption
exists in the language structures of Stuart's novels is examined, with
especial reference to his most recent work, The High Consistory. The
thesis shows that the development of the these of redemption
demonstrates the integrity of Stuart's work
Dark-ages reionization and galaxy formation simulation – IV. UV luminosity functions of high-redshift galaxies
No full textDark-ages reionization and galaxy-formation simulation – VII. The sizes of high-redshift galaxies
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