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Observations of a quasar at redshift 7.54, when the Universe was just five per cent of its current age, suggest that the Universe was significantly neutral at this epoch. A massive black hole in the early Universe Despite extensive searches, only one quasar has been known at redshifts greater than 7, at 7.09. Eduardo Bañados and colleagues report observations of a quasar at a redshift of 7.54, when the Universe was just 690 million years old, with a black-hole mass 800 million times the mass of the Sun. The spectrum shows that the quasar's Lyman α emission is being substantially absorbed by an intergalactic medium containing significantly neutral hydrogen, indicating that reionization was not complete at that epoch. Quasars are the most luminous non-transient objects known and as a result they enable studies of the Universe at the earliest cosmic epochs. Despite extensive efforts, however, the quasar ULAS J1120 + 0641 at redshift z  = 7.09 has remained the only one known at z  > 7 for more than half a decade 1 . Here we report observations of the quasar ULAS J134208.10 + 092838.61 (hereafter J1342 + 0928) at redshift z  = 7.54. This quasar has a bolometric luminosity of 4 × 10 13 times the luminosity of the Sun and a black-hole mass of 8 × 10 8 solar masses. The existence of this supermassive black hole when the Universe was only 690 million years old—just five per cent of its current age—reinforces models of early black-hole growth that allow black holes with initial masses of more than about 10 4 solar masses 2 , 3 or episodic hyper-Eddington accretion 4 , 5 . We see strong evidence of absorption of the spectrum of the quasar redwards of the Lyman α emission line (the Gunn–Peterson damping wing), as would be expected if a significant amount (more than 10 per cent) of the hydrogen in the intergalactic medium surrounding J1342 + 0928 is neutral. We derive such a significant fraction of neutral hydrogen, although the exact fraction depends on the modelling. However, even in our most conservative analysis we find a fraction of more than 0.33 (0.11) at 68 per cent (95 per cent) probability, indicating that we are probing well within the reionization epoch of the Universe.

ABSTRACT We describe the design, construction, and commissioning of FIRE, a 0.82-2.51 μ m echelle spectrograph for the 6.5 m Magellan Baade telescope. FIRE may be operated in two modes. Its primary mode is a prism cross-dispersed echelle, which delivers R = 6000 spectra for an 0.6″ slit, with continuous wavelength coverage over the full instrument bandpass in a single setup. Alternatively, the echelle grating may be replaced with a flat mirror to obtain high-throughput R = 400 longslit spectra through the prisms alone-again with full Y/J/H/K coverage. This contribution outlines the details of the optical design and execution, mechanical and thermal design, detector systems, and data analysis software. We also present performance metrics from commissioning observations. These have established that the instrument is achieving its design goals, particularly with regard to throughput, as is required for observations of faint, high-redshift QSOs and the lowest mass brown dwarfs.

We introduce a data-reduction package written in Interactive Data Language (IDL) for the Magellan Echellete Spectrograph (MAGE). MAGE is a medium-resolution ( R ∼ 4100 R ∼ 4100 ), cross-dispersed, optical spectrograph, with coverage from ∼ 3000 – 10000     Å . The MAGE Spectral Extractor (MASE) incorporates the entire image reduction and calibration process, including bias subtraction, flat fielding, wavelength calibration, sky subtraction, object extraction, and flux calibration of point sources. We include examples of the user interface and reduced spectra. We show that the wavelength calibration is sufficient to achieve∼5 km s-1 ∼ 5     km   s - 1 rms accuracy and relative flux calibrations better than 10%. A lightweight version of the full reduction pipeline has been included for real-time source extraction and signal-to-noise estimation at the telescope.

We present photometric and spectroscopic observations of supernova (SN) 2002cx, which reveal it to be unique among all observed Type Ia supernovae (SNe Ia). SN 2002cx exhibits an SN 1991T–like premaximum spectrum, an SN 1991bg–like luminosity, and expansion velocities roughly half those of normal SNe Ia. Photometrically, SN 2002cx has a broad peak in theRband and a plateau phase in theIband, and slow late‐time decline. TheB−Vcolor evolution is nearly normal, but theV−RandV−Icolors are very red. Early‐time spectra of SN 2002cx evolve very quickly and are dominated by lines from Fe‐group elements; features from intermediate‐mass elements (Ca, S, Si) are weak or absent. Mysterious emission lines are observed around 7000 Å at about 3 weeks after maximum brightness. The nebular spectrum of SN 2002cx is also unique, consisting of narrow iron and cobalt lines. The observations of SN 2002cx are inconsistent with the observed spectral/photometric sequence and provide a major challenge to our understanding of SNe Ia. No existing theoretical model can successfully explain all observed aspects of SN 2002cx.

The physical conditions of the circumgalactic medium are investigated by means of intervening absorption-line systems in the spectrum of background quasi-stellar objects (QSOs) out to the epoch of cosmic reionization 1 – 4 . A correlation between the ionization state of the absorbing gas and the nature of the nearby galaxies has been suggested by the sources detected in either Ly α or [C  ii ] 158 μm near to, respectively, highly ionized and neutral absorbers 5 , 6 . This is also probably linked to the global changes in the incidence of absorption systems of different types and the process of cosmic reionization 7 – 12 . Here we report the detection of two [C  ii ]-emitting galaxies at redshift z  ≈ 5.7 that are associated with a complex, high-ionization C  iv absorption system. These objects are part of an overdensity of galaxies and have compact sizes (<2.4 kpc) and narrow linewidths (full width at half maximum (FWHM) ≈ 62–64 km s −1 ). Hydrodynamic simulations predict that similar narrow [C  ii ] emission may arise from the heating of small (≲3 kpc) clumps of cold neutral medium or a compact photodissociation region 13 , 14 . The lack of counterparts in the rest-frame ultraviolet (UV) indicates severe obscuration of the sources that are exciting the [C  ii ] emission. These results may suggest a connection between the properties of the [C  ii ] emission, the rare overdensity of galaxies and the unusual high ionization state of the gas in this region. Investigation of the physical conditions of the circumgalactic medium led to detection of two compact [C ii]-emitting galaxies with narrow linewidths at a redshift of 5.7, associated with a complex, high-ionization C iv absorption system.

The spectrum of a quasar at redshift 7.04 reveals absorption from a large column of foreground neutral hydrogen with no corresponding heavy elements; this absorbing gas is either diffuse and intergalactic but has not yet been ionized by starlight at this early epoch, or it is gravitationally bound to a proto-galaxy that has a chemical abundance <1/10,000 the solar level. Getting closer to the first stars Lower abundances of heavy elements, relative to those found in typical astrophysical environments, have been observed in Milky Way halo stars and in two quasar absorption systems at redshifts of z = 3. Such objects are widely interpreted as relics from the early Universe. This paper reports measurements of chemical abundances in the infrared spectra of a distant quasar at a redshift of z = 7.04, corresponding to a time when the Universe was only 5.6% of its present age. This epoch is thought to approach the time when the first stars—which produced the first heavy elements—were formed. The spectra reveal a large column of neutral hydrogen, but no heavy elements to sensitive upper limits, establishing these clouds as among the most chemically pristine neutral gas reservoirs known. This suggests that we may finally be witnessing the earliest generations of star formation. In typical astrophysical environments, the abundance of heavy elements ranges from 0.001 to 2 times the solar value. Lower abundances have been seen in selected stars in the Milky Way’s halo 1 , 2 , 3 and in two quasar absorption systems at redshift z = 3 (ref. 4 ). These are widely interpreted as relics from the early Universe, when all gas possessed a primordial chemistry. Before now there have been no direct abundance measurements from the first billion years after the Big Bang, when the earliest stars began synthesizing elements. Here we report observations of hydrogen and heavy-element absorption in a spectrum of a quasar at z =  7.04, when the Universe was just 772 million years old (5.6 per cent of its present age). We detect a large column of neutral hydrogen but no corresponding metals (defined as elements heavier than helium), limiting the chemical abundance to less than 1/10,000 times the solar level if the gas is in a gravitationally bound proto-galaxy, or to less than 1/1,000 times the solar value if it is diffuse and unbound. If the absorption is truly intergalactic 5 , 6 , it would imply that the Universe was neither ionized by starlight nor chemically enriched in this neighbourhood at z  ≈ 7. If it is gravitationally bound, the inferred abundance is too low to promote efficient cooling 7 , 8 , and the system would be a viable site to form the predicted but as yet unobserved massive population III stars.

Of more than a thousand known cataclysmic variables (CVs), where a white dwarf is accreting from a hydrogen-rich star, only a dozen have orbital periods below 75 minutes 1 – 9 . One way to achieve these short periods requires the donor star to have undergone substantial nuclear evolution before interacting with the white dwarf 10 – 14 , and it is expected that these objects will transition to helium accretion. These transitional CVs have been proposed as progenitors of helium CVs 13 – 18 . However, no known transitional CV is expected to reach an orbital period short enough to account for most of the helium CV population, leaving the role of this evolutionary pathway unclear. Here we report observations of ZTF J1813+4251, a 51-minute-orbital-period, fully eclipsing binary system consisting of a star with a temperature comparable to that of the Sun but a density 100 times greater owing to its helium-rich composition, accreting onto a white dwarf. Phase-resolved spectra, multi-band light curves and the broadband spectral energy distribution allow us to obtain precise and robust constraints on the masses, radii and temperatures of both components. Evolutionary modelling shows that ZTF J1813+4251 is destined to become a helium CV binary, reaching an orbital period under 20 minutes, rendering ZTF J1813+4251 a previously missing link between helium CV binaries and hydrogen-rich CVs. A 51-minute-orbital-period, fully eclipsing binary system consisting of a star with a comparable temperature to that of the Sun but a 100 times greater density, accreting onto a white dwarf is reported.

Over a dozen millisecond pulsars are ablating low-mass companions in close binary systems. In the original ‘black widow’, the eight-hour orbital period eclipsing pulsar PSR J1959+2048 (PSR B1957+20) 1 , high-energy emission originating from the pulsar 2 is irradiating and may eventually destroy 3 a low-mass companion. These systems are not only physical laboratories that reveal the interesting results of exposing a close companion star to the relativistic energy output of a pulsar, but are also believed to harbour some of the most massive neutron stars 4 , allowing for robust tests of the neutron star equation of state. Here we report observations of ZTF J1406+1222, a wide hierarchical triple hosting a 62-minute orbital period black widow candidate, the optical flux of which varies by a factor of more than ten. ZTF J1406+1222 pushes the boundaries of evolutionary models 5 , falling below the 80-minute minimum orbital period of hydrogen-rich systems. The wide tertiary companion is a rare low-metallicity cool subdwarf star, and the system has a Galactic halo orbit consistent with passing near the Galactic Centre, making it a probe of formation channels, neutron star kick physics 6 and binary evolution. ZTF J1406+1222 is a wide hierarchical triple system that hosts a low-metallicity subdwarf star and a ‘black widow’ millisecond pulsar that has a highly varying optical flux and a 62-minute period.

We have designed, constructed, and tested an InGaAs near-infrared camera to explore whether low-cost detectors can make small (≤ 1 m) telescopes capable of precise (< 1 mmag) infrared photometry of relatively bright targets. The camera is constructed around the 640 × 512 pixel APS640C sensor built by FLIR Electro-Optical Components. We designed custom analog-to-digital electronics for maximum stability and minimum noise. The InGaAs dark current halves with every 7°C of cooling, and we reduce it to 840 e- s-1 pixel-1 (with a pixel-to-pixel variation of ± 200 e- s-1 pixel-1) by cooling the array to -20°C. Beyond this point, glow from the readout dominates. The single-sample read noise of 149 e- is reduced to 54 e- through up-the-ramp sampling. Laboratory testing with a star field generated by a lenslet array shows that two-star differential photometry is possible to a precision of 631 ± 205 ppm (0.68 mmag) hr-1/2 at a flux of 2.4 × 104 e- s-1. Employing three comparison stars and decorrelating reference signals further improves the precision to 483 ± 161 ppm (0.52 mmag) hr-1/2. Photometric observations of HD80606 and HD80607 (J = 7.7 and 7.8) in the Y band shows that differential photometry to a precision of 415 ppm (0.45 mmag) hr-1/2 is achieved with an effective telescope aperture of 0.25 m. Next-generation InGaAs detectors should indeed enable Poisson-limited photometry of brighter dwarfs with particular advantage for late-M and L types. In addition, one might acquire near-infrared photometry simultaneously with optical photometry or radial velocity measurements to maximize the return of exoplanet searches with small telescopes.

ABSTRACT We characterize the near-IR sky background from 308 observations with the Folded-port InfraRed Echellette (FIRE) spectrograph at Magellan. A subset of 105 observations selected to minimize lunar and thermal effects gives a continuous, median spectrum from 0.83 to 2.5 μm, which we present in Table 2. The data are used to characterize the broadband continuum emission between atmospheric OH features and correlate its properties with observing conditions such as lunar angle and time of night. We find that the Moon contributes significantly to the inter-line continuum in Y and J bands, whereas the observed H-band continuum is dominated by the blended Lorentzian wings of multiple OH line profiles, even at R = 6000. Lunar effects may be mitigated in Y and J through careful scheduling of observations, but the most ambitious near-IR programs will benefit from allocation during dark observing time if those observations are not limited by read noise. In Y and J, our measured continuum exceeds space-based average estimates of the zodiacal light, but it is not readily identified with known terrestrial foregrounds. If further measurements confirm such a fundamental background, it would impact requirements for OH-suppressed instruments operating in this regime.