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A two-dimensional spectroscopic investigation of a large, luminous filament of the cosmic web near QSO UM287 reveals that the brightest emission region is an extended rotating hydrogen disk with a velocity profile that is characteristic of gas in a 10 13 -solar-mass dark-matter halo, with a geometry that is strongly suggestive of cold flow accretion. A giant disk in the cosmic web The recent discovery of a large, luminous filament of cold gas near the radio-quiet quasar QSO UM287 provided a glimpse of the three-dimensional structure of the cosmic web, a network of filaments with galaxies located at nodes where the filaments intersect. A two-dimensional spectroscopic investigation of this filament now reveals that the brightest emission region is an extended rotating hydrogen disk with a velocity profile characteristic of gas in a 10 13 -solar-mass dark-matter halo, with a geometry strongly suggestive of a cold accretion flow. Such a disk has been predicted by models of cold accretion flows from the cosmic web filaments into forming galaxies. This structure provides a useful model for understanding the processes connecting galaxy formation and the intergalactic and circumgalactic medium. The specifics of how galaxies form from, and are fuelled by, gas from the intergalactic medium remain uncertain. Hydrodynamic simulations suggest that ‘cold accretion flows’—relatively cool (temperatures of the order of 10 4 kelvin), unshocked gas streaming along filaments of the cosmic web into dark-matter halos 1 , 2 , 3 —are important. These flows are thought to deposit gas and angular momentum into the circumgalactic medium, creating disk- or ring-like structures that eventually coalesce into galaxies that form at filamentary intersections 4 , 5 . Recently, a large and luminous filament, consistent with such a cold accretion flow, was discovered near the quasi-stellar object QSO UM287 at redshift 2.279 using narrow-band imaging 6 . Unfortunately, imaging is not sufficient to constrain the physical characteristics of the filament, to determine its kinematics, to explain how it is linked to nearby sources, or to account for its unusual brightness, more than a factor of ten above what is expected for a filament. Here we report a two-dimensional spectroscopic investigation of the emitting structure. We find that the brightest emission region is an extended rotating hydrogen disk with a velocity profile that is characteristic of gas in a dark-matter halo with a mass of 10 13 solar masses. This giant protogalactic disk appears to be connected to a quiescent filament that may extend beyond the virial radius of the halo. The geometry is strongly suggestive of a cold accretion flow.

A Mira image Mira is one of a class of low to slightly more than solar mass stars in the late stages of stellar evolution. These stars have a direct impact on star and planet formation in their host galaxy via the winds that they send out. Martin et al . report the discovery of an ultraviolet-emitting bow shock and turbulent wake extending over 2 degrees on the sky, arising from Mira's large space velocity and the interaction between its wind and the interstellar medium. This wind wake is a tracer of the past 30,000 years of Mira's mass loss history. Mira is one of a class of low-to-intermediate mass stars in the late stages of stellar evolution. This paper reports the discovery of an ultraviolet-emitting bow shock and turbulent wake extending over 2 degrees on the sky, arising from Mira's large space velocity and the interaction between its wind and the interstellar medium. This wind wake is a tracer of the last 30,000 years of Mira's mass-loss history. Mira is one of the first variable stars ever discovered 1 and it is the prototype (and also the nearest example) of a class of low-to-intermediate-mass stars in the late stages of stellar evolution. These stars are relatively common and they return a large fraction of their original mass to the interstellar medium (ISM) (ref. 2 ) through a processed, dusty, molecular wind. Thus stars in Mira’s stage of evolution have a direct impact on subsequent star and planet formation in their host galaxy. Previously, the only direct observation 3 of the interaction between Mira-type stellar winds and the ISM was in the infrared. Here we report the discovery of an ultraviolet-emitting bow shock and turbulent wake extending over 2 degrees on the sky, arising from Mira’s large space velocity and the interaction between its wind and the ISM. The wake is visible only in the far ultraviolet and is consistent with an unusual emission mechanism whereby molecular hydrogen is excited by turbulent mixing of cool molecular gas and shock-heated gas. This wind wake is a tracer of the past 30,000 years of Mira’s mass-loss history and provides an excellent laboratory for studying turbulent stellar wind–ISM interactions.

Reservoirs of dense atomic gas (primarily hydrogen) contain approximately 90 per cent of the neutral gas at a redshift of 3, and contribute to between 2 and 3 per cent of the total baryons in the Universe 1 – 4 . These ‘damped Lyman α systems’—so called because they absorb Lyman α photons within and from background sources—have been studied for decades, but only through absorption lines present in the spectra of background quasars and γ-ray bursts 5 – 10 . Such pencil beams do not constrain the physical extent of the systems. Here we report integral-field spectroscopy of a bright, gravitationally lensed galaxy at a redshift of 2.7 with two foreground damped Lyman α systems. These systems are greater than 238 kiloparsecs squared in extent, with column densities of neutral hydrogen varying by more than an order of magnitude on scales of less than 3 kiloparsecs. The mean column densities are between 10 20.46 and 10 20.84  centimetres squared and the total masses are greater than 5.5 × 10 8 –1.4 × 10 9 times the mass of the Sun, showing that they contain the necessary fuel for the next generation of star formation, consistent with relatively massive, low-luminosity primeval galaxies at redshifts greater than 2. Spectroscopy of a gravitationally lensed galaxy at a redshift of 2.7 with spatially resolved maps of two foreground damped Lyman α systems indicates a vast mass of neutral hydrogen gas, consistent with a star-forming region.

Stellar mergers are a brief but common phase in the evolution of binary star systems 1 , 2 . These events have many astrophysical implications; for example, they may lead to the creation of atypical stars (such as magnetic stars 3 , blue stragglers 4 and rapid rotators 5 ), they play an important part in our interpretation of stellar populations 6 and they represent formation channels of compact-object mergers 7 . Although a handful of stellar mergers have been observed directly 8 , 9 , the central remnants of these events were shrouded by an opaque shell of dust and molecules 10 , making it impossible to observe their final state (for example, as a single merged star or a tighter, surviving binary 11 ). Here we report observations of an unusual, ring-shaped ultraviolet (‘blue’) nebula and the star at its centre, TYC 2597-735-1. The nebula has two opposing fronts, suggesting a bipolar outflow of material from TYC 2597-735-1. The spectrum of TYC 2597-735-1 and its proximity to the Galactic plane suggest that it is an old star, yet it has abnormally low surface gravity and a detectable long-term luminosity decay, which is uncharacteristic for its evolutionary stage. TYC 2597-735-1 also exhibits Hα emission, radial-velocity variations, enhanced ultraviolet radiation and excess infrared emission—signatures of dusty circumstellar disks 12 , stellar activity 13 and accretion 14 . Combined with stellar evolution models, the observations suggest that TYC 2597-735-1 merged with a lower-mass companion several thousand years ago. TYC 2597-735-1 provides a look at an unobstructed stellar merger at an evolutionary stage between its dynamic onset and the theorized final equilibrium state, enabling the direct study of the merging process. Observations and stellar evolution models of a blue ring nebula and its central star (TYC 2597-735-1) suggest that the remnant star merged with a lower-mass companion several thousand years ago.

Theory suggests that there are two primary modes of accretion through which dark-matter halos acquire the gas to form and fuel galaxies: hot- and cold-flow accretion. In cold-flow accretion, gas streams along cosmic web filaments to the centre of the halo, allowing for the efficient delivery of star-forming fuel. Recently, two quasar-illuminated H i Lyman ɑ (Lyα)-emitting objects were reported to have properties of cold, rotating structures1,2. However, the spatial and spectral resolution available was insufficient to constrain the radial flows associated with connecting filaments. With the Keck Cosmic Web Imager (KCWI)3, we now have eight times the spatial resolution, permitting the detection of these inspiralling flows. To detect these inflows, we introduce a suite of models that incorporate zonal radial flows, demonstrate their performance on a numerical simulation that exhibits cold-flow accretion, and show that they are an excellent match to KCWI velocity maps of two Lyα emitters observed around high-redshift quasars. These multi-filament inflow models kinematically isolate zones of radial inflow that correspond to extended filamentary emission. The derived gas flux and inflow path is sufficient to fuel the inferred central galaxy star-formation rate and angular momentum. Thus, our kinematic emission maps provide strong evidence that the inflow of gas from the cosmic web is building galaxies at the peak of star formation.Theoretical modelling of velocity maps of high-redshift Lyman α emitters indicates sufficient gas inflow to fuel the central galaxy’s star-formation rate and angular momentum, implying that cold gas accretion is building galaxies at the peak of star formation.

The bright and distant past A dwarf nova is a type of cataclysmic variable containing a collapsed white dwarf star that accretes matter from its close companion in a binary system, a red dwarf. An instability periodically dumps material onto the white dwarf, increasing the luminosity by up to a hundredfold. Classical novae are thousands of times brighter than dwarf novae, and are accompanied by the formation of shells around the system. Theory predicts that dwarf novae will eventually gain sufficient mass to undergo classical nova eruptions. This suspected link between dwarf and classical novae now has an observational basis with the discovery of an ancient nova shell around the dwarf nova Z Camelopardalis. The nature of the shell suggests that a few thousand years ago, Z Cam underwent a classical nova eruption and for some days was one of the brightest stars in the sky. Classical novae are thousands of times brighter than dwarf novae, and are accompanied by the formation of shells around the system. This paper reports the discovery of a shell an order of magnitude more extended than those detected around many other classical novae surrounding the prototypical dwarf nova Z Camelopardalis, thereby observationally linking the objects. Cataclysmic variables (classical novae and dwarf novae) are binary star systems in which a red dwarf transfers hydrogen-rich matter, by way of an accretion disk, to its white dwarf companion 1 . In dwarf novae, an instability 2 is believed to episodically dump much of the accretion disk onto the white dwarf. The liberation of gravitational potential energy then brightens these systems by up to 100-fold every few weeks or months 2 . Thermonuclear-powered eruptions thousands of times more luminous 3 , 4 occur in classical novae 5 , accompanied by significant mass ejection 6 and formation of clearly visible shells 7 , 8 from the ejected material. Theory predicts that the white dwarfs in all dwarf novae must eventually accrete enough mass to undergo classical nova eruptions 9 . Here we report a shell, an order of magnitude more extended than those detected around many classical novae, surrounding the prototypical dwarf nova Z Camelopardalis. The derived shell mass matches that of classical novae, and is inconsistent with the mass expected from a dwarf nova wind or a planetary nebula. The shell observationally links the prototypical dwarf nova Z Camelopardalis with an ancient nova eruption and the classical nova process.

Stars of the Leo ring A massive ring of neutral hydrogen (H i ) was detected during radio observations in the 1980s, orbiting the M105 and NGC 3384 galaxies in the constellation Leo. Called the Leo ring, it remains a mysterious structure, thought to be a remnant primordial cloud left over from when the Leo I group galaxies formed. Until now the Leo ring has been detected only in the radio region of the spectrum (H i emission), suggesting an absence of stars. Now observations from the GALEX (Galaxy Evolution Explorer) orbiting space telescope have detected ultraviolet light originating from parts of the ring, indicating recent massive star formation in substructures. If such structures were common in the early Universe, they may have produced a large, as yet undetected population of faint, metal-poor, halo-lacking dwarf galaxies. The Leo ring is a massive, 200-kpc-wide structure orbiting the galaxies M105 and NGC3384 with a 4-Gyr period. This paper reports ultraviolet light originating from gaseous substructures, which is attributed to recent massive star formation. If structures like the Leo ring were common in the early Universe, they may have produced a large, yet undetected population of faint, metal-poor, halo-lacking dwarf galaxies. Few intergalactic, plausibly primordial clouds of neutral atomic hydrogen (H  i ) have been found in the local Universe, suggesting that such structures have either dispersed, become ionized or produced a stellar population on gigayear timescales. The Leo ring 1 , 2 , a massive ( M H  i  ≈ 1.8 × 10 9 , denoting the solar mass), 200-kpc-wide structure orbiting the galaxies M105 and NGC 3384 with a 4-Gyr period, is a candidate primordial cloud. Despite repeated atttempts 3 , 4 , it has previously been seen only from H  i emission, suggesting the absence of a stellar population. Here we report the detection of ultraviolet light from gaseous substructures of the Leo ring, which we attribute to recent massive star formation. The ultraviolet colour of the detected complexes is blue, implying the onset of a burst of star formation or continuous star formation of moderate (∼10 8 -yr) duration. Measured ultraviolet–visible photometry favours models with low metallicity ( Z  ≈  /50– /5, denoting the solar metallicity), that is, a low proportion of elements heavier than helium, although spectroscopic confirmation is needed. We speculate that the complexes are dwarf galaxies observed during their formation, but distinguished by their lack of a dark matter component 5 . In this regard, they resemble tidal dwarf galaxies, although without the enrichment preceding tidal stripping. If structures like the Leo ring were common in the early Universe, they may have produced a large, yet undetected, population of faint, metal-poor, halo-lacking dwarf galaxies.

The bimodality in galaxy properties has been observed at low and high redshift, with a clear distinction between star-forming galaxies in the blue cloud and passively evolving objects in the red sequence; the absence of galaxies with intermediate properties indicates that the quenching of star formation and subsequent transition between populations must happen rapidly. In this work, we present a study of over 100 transiting galaxies in the so-called “green valley” at intermediate redshifts (z ~ 0.8). By using very deep spectroscopy with the DEIMOS instrument at the Keck telescope, we are able to infer the star formation histories of these objects and measure the stellar mass flux density transiting from the blue cloud to the red sequence when the Universe was half its current age. Our results indicate that the process happened more rapidly, affecting more massive galaxies in the past, suggesting a top-down scenario whereby the massive end of the red sequence assembles first. This represents another aspect of downsizing, with the mass flux density moving towards smaller galaxies in recent times.

Much has been written about Ernest Hemingway, including discussion of his well-documented mood disorder, alcoholism, and suicide. However, a thorough biopsychosocial approach capable of integrating the various threads of the author's complex psychiatric picture has yet to be applied. Application of such a psychiatric view to the case of Ernest Hemingway in an effort toward better understanding of the author's experience with illness and the tragic outcome is the aim of this investigation. Thus, Hemingway's life is examined through a review and discussion of biographies, psychiatric literature, personal correspondence, photography, and medical records. Significant evidence exists to support the diagnoses of bipolar disorder, alcohol dependence, traumatic brain injury, and probable borderline and narcissistic personality traits. Late in life, Hemingway also developed symptoms of psychosis likely related to his underlying affective illness and superimposed alcoholism and traumatic brain injury. Hemingway utilized a variety of defense mechanisms, including self-medication with alcohol, a lifestyle of aggressive, risk-taking sportsmanship, and writing, in order to cope with the suffering caused by the complex comorbidity of his interrelated psychiatric disorders. Ultimately, Hemingway's defense mechanisms failed, overwhelmed by the burden of his complex comorbid illness, resulting in his suicide. However, despite suffering from multiple psychiatric disorders, Hemingway was able to live a vibrant life until the age of 61 and within that time contribute immortal works of fiction to the literary canon.

Accurate chemical compositions of star-forming regions are a critical diagnostic tool to characterize the star formation history and gas flows which regulate galaxy formation. However, the abundance discrepancy factor (ADF) between measurements from the \"direct\" optical electron temperature (\\(T_e\\)) method and from the recombination lines (RL) represents \\(\\sim0.2\\) dex systematic uncertainty in oxygen abundance. The degree of uncertainty for other elements is unknown. We conduct a comprehensive analysis of O\\(^{++}\\) and N\\(^+\\) ion abundances using optical and far-infrared spectra of a star-forming region within the nearby dwarf galaxy Haro 3, which exhibits a typical ADF. Assuming homogeneous conditions, the far-IR emission indicates an O abundance which is higher than the \\(T_e\\) method and consistent with the RL value, as would be expected from temperature fluctuations, whereas the far-IR N abundance is too large to be explained by temperature fluctuations. A two-phase analytical model reveals that differential dust obscuration associated with temperature inhomogeneity is likely required to explain all the emission line ratios, and that the total oxygen metallicity of two phases is consistent with the RL metallicity. Our findings underscore the critical importance of resolving the cause of abundance discrepancies and understanding the biases between different metallicity methods. This work represents a promising methodology, and we identify further approaches to address the current dominant uncertainties.