The discovery of the most UV–Ly α luminous star-forming galaxy: a young, dust- and metal-poor starburst with QSO-like luminosities

ABSTRACT We report the discovery of BOSS-EUVLG1 at z = 2.469, by far the most luminous, almost un-obscured star-forming galaxy known at any redshift. First classified as a QSO within the Baryon Oscillation Spectroscopic Survey, follow-up observations with the Gran Telescopio Canarias reveal that its large luminosity, MUV ≃ −24.40 and log(LLyα/erg s–1) ≃ 44.0, is due to an intense burst of star formation, and not to an active galactic nucleus or gravitational lensing. BOSS-EUVLG1 is a compact (reff ≃ 1.2 kpc), young (4–5 Myr) starburst with a stellar mass log(M*/M⊙) = 10.0 ± 0.1 and a prodigious star formation rate of ≃1000 M⊙ yr−1. However, it is metal- and dust-poor [12 + log(O/H) = 8.13 ± 0.19, E(B – V) ≃ 0.07, log(LIR/LUV) < −1.2], indicating that we are witnessing the very early phase of an intense starburst that has had no time to enrich the ISM. BOSS-EUVLG1 might represent a short-lived (<100 Myr), yet important phase of star-forming galaxies at high redshift that has been missed in previous surveys. Within a galaxy evolutionary scheme, BOSS-EUVLG1 could likely represent the very initial phases in the evolution of massive quiescent galaxies, even before the dusty star-forming phase.

Inundation, flow dynamics, and damage in the 9 January 2018 Montecito debris-flow event, California, USA: Opportunities and challenges for post-wildfire risk assessment

Shortly before the beginning of the 2017–2018 winter rainy season, one of the largest fires in California (USA) history (Thomas fire) substantially increased the susceptibility of steep slopes in Santa Barbara and Ventura Counties to debris flows. On 9 January 2018, before the fire was fully contained, an intense burst of rain fell on the portion of the burn area above Montecito, California. The rainfall and associated runoff triggered a series of debris flows that mobilized ∼680,000 m3 of sediment (including boulders >6 m in diameter) at velocities up to 4 m/s down coalescing urbanized alluvial fans. The resulting destruction (including 23 fatalities, at least 167 injuries, and 408 damaged homes) underscores the need for improved understanding of debris-flow runout in the built environment, and the need for a comprehensive framework to assess the potential loss from debris flows following wildfire. We present observations of the inundation, debris-flow dynamics, and damage from the event. The data include field measurements of flow depth and deposit characteristics made within the first 12 days after the event (before ephemeral features of the deposits were lost to recovery operations); an inventory of building damage; estimates of flow velocity; information on flow timing; soil-hydrologic properties; and post-event imagery and lidar. Together, these data provide rare spatial and dynamic constraints for testing debris-flow runout models, which are needed for advancing post-fire debris-flow hazard assessments. Our analysis also outlines a framework for translating the results of these models into estimates of economic loss based on an adaptation of the U.S. Federal Emergency Management Agency’s Hazus model for tsunamis.

Can’t touch this

Australia’s laid-back, sun-drenched beach lifestyle has been a celebrated and prominent part of its official popular culture for nigh on a century, and the images and motifs associated with this culture have become hallmarks of the country’s collective identity. Though these representations tend towards stereotype, for many Australians the idea of a summer holiday at the beach is one that is intensely personal and romanticised – its image is not at all urbanised. As Douglas Booth observed, for Australians the beach has become a ‘sanctuary at which to abandon cares – a place to let down one’s hair, remove one’s clothes […] a paradise where one could laze in peace, free from guilt, drifting between the hot sand and the warm sea, and seek romance’.1 Beach holidays became popular in the interwar years of the twentieth century, but the most intense burst of activity – both in touristic promotion and in the development of tourism infrastructure – accompanied the postwar economic boom, when family incomes were able to meet the cost of a car and, increasingly, a cheap block of land by the beach upon which a holiday home could be erected with thrift and haste. In subtropical southeast Queensland, the postwar beach holiday became the hallmark of the state’s burgeoning tourism industry; the state’s southeast coastline in particular benefiting from its warm climate and proximity to the capital, Brisbane. It was here – along the evocatively named Gold Coast (to Brisbane’s south) and Sunshine Coast (to its north) [1] – that many families experienced their first taste of what is now widely celebrated as the beach lifestyle [2]. As one reflection has it: In the era before motels and resorts, a holiday at the Gold and Sunshine coasts usually meant either pitching a tent and camping by the beach or staying in a simple cottage owned by family or friends […] Simplicity, informality, individuality […] were the hallmarks of these humble places.2

Studying Luminous Red Galaxies to probe H(z) at high redshift

Luminous Red Galaxies (LRGs) have old, red stellar populations often interpreted as evidence of a formation scenario in which these galaxies form in a single intense burst of star formation at high redshift. By measuring the average age of LRGs at two different redshifts, one can potentially measure the redshift interval corresponding to a time interval and thus measure the Hubble parameter H(z) ≈ −(1 + z)−1 Δ z/Δt (as in Jimenez & Loeb). The goal of this project is to measure directly the expansion rate of the universe at the redshift range 0.1 < z < 1.0 within 3% precision. We explore the age-dating of Sloan Digital Sky Survey LRGs using the stellar population models of Lick absorption line indices after stacking spectra in redshift bins to increase the signal-to-noise. We also use the method of full spectral fitting to measure the ages of LRGs observed with the Southern Africa Large Telescope (SALT).

Synoptic- and Frontal-Scale Influences on Tropical Transition Events in the Atlantic Basin. Part II: Tropical Transition of Hurricane Karen

A finescale simulation of the tropical transition of Atlantic Hurricane Karen in October 2001 is examined to determine the processes leading to the development of upshear convection and its effects on the process of tropical transition. The analysis shows that, as in marine extratropical cyclones, the area upshear of the pretransition cyclone is characterized by reduced stability. Lower-tropospheric frontogenesis leads to an intense burst of convection there and instigates three important processes that combine to produce a full-fledged tropical cyclone. First, the convection generates intense low-level vorticity on the western half of the cyclone, which quickly dominates the cyclone’s vorticity field eventually organizing the circulation into a small-scale, intense vortex. Second, the diabatically enhanced circulation hastens the isolation of the cyclone’s developing warm core by intensifying cold air advection on the northern and western sides of the storm and by placing evaporatively cooled air into the boundary layer to the south of the cyclone. Third, upshear convection vertically redistributes potential vorticity (PV) from the tropopause to the surface and introduces a component to the upper-level winds, which advects strong, shear-inducing PV gradients away from the column above the cyclone. These three processes transform the initial extratropical cyclone into a frontless vortex with tropical storm–force winds and a warm core in a low-shear environment. These features are sufficient, given a warm enough ocean surface, to allow self-amplification of the storm as a tropical cyclone. The results further blur the distinction between tropical and extratropical cyclones as many of the processes identified as important to transition are similar to those that characterize ordinary marine cyclones and the extratropical occlusion process with the key distinctions being that here the convection is stronger and the initial upper-level feature is weaker. Thus, tropical transition of strong extratropical precursors follows the canonical midlatitude cyclone life cycle with upshear convection serving as the catalyst that both induces and organizes processes that favor tropical cyclogenesis in the postmature phase.

Sensory Signals of Unloading in One Leg Follow Stance Onset in Another Leg: Transfer of Load and Emergent Coordination in Cockroach Walking

The transfer of load from one leg to another is an essential component in walking, but sense organs that signal this process have rarely been identified. We used high-speed digital imaging and neurophysiological recordings to characterize activities of tibial campaniform sensilla, receptors that detect forces via cuticular strains, in the middle legs of cockroaches during walking. Previous studies demonstrated that the distal tibial sensilla discharge when body load is suddenly decreased in freely standing animals. Sensory recordings during walking showed that distal receptors in the middle leg fired an intense burst near the end of the stance phase. We tested the hypothesis that initiation of distal firing resulted from the action of other legs entering stance. Analysis of leg movements in slow walking showed that sensory bursts in the middle leg closely followed stance onset of the ipsilateral hind leg while the ipsilateral front leg entered stance earlier in phase. Similar phases of leg movement were found in slow walking in experiments in which animals had no implanted recording wires. Those studies also demonstrated that the opposite middle leg entered stance earlier in phase. Measurements of leg positions in walking showed that the hind leg tarsus was placed closest to the middle leg, in keeping with a “targeting” strategy. Triggering of distal bursts in the middle leg by mechanical action of the hind leg could facilitate the onset of swing in the middle leg through local reflex effects and contribute to emergent coordination of leg movements in metachronal gaits.