Table of contents

We suggest that low optical depth in the Lyman continuum (LyC) may relate the Lyα emission, C ii and Si ii absorption, and C ii* and Si ii* emission seen in high-redshift galaxies. We base this analysis on Hubble Space Telescope Cosmic Origins Spectrograph spectra of four Green Pea (GP) galaxies, which may be analogs of z > 2 Lyα emitters (LAEs). In the two GPs with the strongest Lyα emission, the Lyα line profiles show reduced signs of resonant scattering. Instead, the Lyα profiles resemble the Hα line profiles of evolved star ejecta, suggesting that the Lyα emission originates from a low column density and similar outflow geometry. The weak C ii absorption and presence of non-resonant C ii* emission in these GPs support this interpretation and imply a low LyC optical depth along the line of sight. In two additional GPs, weak Lyα emission and strong C ii absorption suggest a higher optical depth. These two GPs differ in their Lyα profile shapes and C ii* emission strengths, however, indicating different inclinations of the outflows to our line of sight. With these four GPs as examples, we explain the observed trends linking Lyα, C ii, and C ii* in stacked LAE spectra, in the context of optical depth and geometric effects. Specifically, in some galaxies with strong Lyα emission, a low LyC optical depth may allow Lyα to escape with reduced scattering. Furthermore, C ii absorption, C ii* emission, and Lyα profile shape can reveal the optical depth, constrain the orientation of neutral outflows in LAEs, and identify candidate LyC emitters.

Fermi Bubbles are enigmatic γ-ray features of the Galactic bulge. Both putative activity (within few × Myr) connected to the Galactic center super-massive black hole and, alternatively, nuclear star formation have been claimed as the energizing source of the Bubbles. Likewise, both inverse-Compton emission by non-thermal electrons ("leptonic" models) and collisions between non-thermal protons and gas ("hadronic" models) have been advanced as the process supplying the Bubbles' γ-ray emission. An issue for any steady state hadronic model is that the very low density of the Bubbles' plasma seems to require that they accumulate protons over a multi-gigayear timescale, much longer than other natural timescales occurring in the problem. Here we present a mechanism wherein the timescale for generating the Bubbles' γ-ray emission via hadronic processes is ∼few × 10⁸ yr. Our model invokes the collapse of the Bubbles' thermally unstable plasma, leading to an accumulation of cosmic rays and magnetic field into localized, warm (∼10⁴ K), and likely filamentary condensations of higher-density gas. Under the condition that these filaments are supported by non-thermal pressure, the hadronic emission from the Bubbles is L_γ ≃ 2 × 10³⁷ erg s⁻¹$\dot{M}_\mathrm{in}/(0.1 \, {M_\odot }$ yr⁻¹$) \ T_\mathrm{FB}^2/(3.5 \times 10^7$ K)² M_fil/M_pls, equal to their observed luminosity (normalizing to the star-formation-driven mass flux into the Bubbles and their measured plasma temperature and adopting the further result that the mass in the filaments, M_fil is approximately equal to the that of the Bubbles' plasma, M_pls).

CO₂ is one of the most abundant components of ices in the interstellar medium; however, its formation mechanism has not been clearly identified. Here we report an experimental observation of an Eley–Rideal-type reaction on a water ice surface, where CO gas molecules react by direct collisions with surface OH radicals, made by photodissociation of H₂O molecules, to produce CO₂ ice on the surface. The discovery of this source of CO₂ provides a new mechanism to explain the high relative abundance of CO₂ ice in space.

We present the energy spectrum of an antiproton cosmic ray (CR) component calculated on the basis of the nonlinear kinetic model of CR production in supernova remnants (SNRs). The model includes the reacceleration of antiprotons already existing in the interstellar medium as well as the creation of antiprotons in nuclear collisions of accelerated protons with gas nuclei and their subsequent acceleration by SNR shocks. It is shown that the production of antiprotons in SNRs produces a considerable effect in their resultant energy spectrum, making it essentially flatter above 10 GeV so that the spectrum at TeV energies increases by a factor of 5. The calculated antiproton spectrum is consistent with the PAMELA data, which correspond to energies below 100 GeV. As a consistency check, we have also calculated within the same model the energy spectra of secondary nuclei and show that the measured boron-to-carbon ratio is consistent with the significant SNR contribution.

The Serpens South infrared dark cloud consists of several filamentary ridges, some of which fragment into dense clumps. On the basis of CCS (J_N = 4₃–3₂), HC₃N (J = 5–4), N₂H⁺ (J = 1–0), and SiO (J = 2–1, v = 0) observations, we investigated the kinematics and chemical evolution of these filamentary ridges. We find that CCS is extremely abundant along the main filament in the protocluster clump. We emphasize that Serpens South is the first cluster-forming region where extremely strong CCS emission is detected. The CCS-to-N₂H⁺ abundance ratio is estimated to be about 0.5 toward the protocluster clump, whereas it is about 3 in the other parts of the main filament. We identify six dense ridges with different V_LSR. These ridges appear to converge toward the protocluster clump, suggesting that the collisions of these ridges may have triggered cluster formation. The collisions presumably happened within a few ×  10⁵ yr because CCS is abundant only for a short time. The short lifetime agrees with the fact that the number fraction of Class I objects, whose typical lifetime is 0.4  ×  10⁵ yr, is extremely high, about 70% in the protocluster clump. In the northern part, two ridges appear to have partially collided, forming a V-shape clump. In addition, we detected strong bipolar SiO emission that is due to the molecular outflow blowing out of the protostellar clump, as well as extended weak SiO emission that may originate from the filament collisions.

The depth of penetration of Jupiter's zonal winds into the planet's interior is unknown. A possible way to determine the depth is to measure the effects of the winds on the planet's high-order zonal gravitational coefficients, a task to be undertaken by the Juno spacecraft. It is shown here that the equatorial winds alone largely determine these coefficients which are nearly independent of the depth of the non-equatorial winds.

Using the first 50% of data collected for the Spitzer Large Area Survey with Hyper-Suprime-Cam observations on the 1.8 deg² Cosmological Evolution Survey we estimate the masses and star formation rates of 3398 M_* > 10¹⁰ M_☉ star-forming galaxies at 4 < z < 6 with a substantial population up to M_* ≳ 10^11.5 M_☉. We find that the strong correlation between stellar mass and star formation rate seen at lower redshift (the "main sequence" of star-forming galaxies) extends to z ∼ 6. The observed relation and scatter is consistent with a continued increase in star formation rate at fixed mass in line with extrapolations from lower-redshift observations. It is difficult to explain this continued correlation, especially for the most massive systems, unless the most massive galaxies are forming stars near their Eddington-limited rate from their first collapse. Furthermore, we find no evidence for moderate quenching at higher masses, indicating quenching either has not occurred prior to z ∼ 6 or else occurs rapidly, so that few galaxies are visible in transition between star-forming and quenched.

We survey the methods proposed in the literature for detecting moons of extrasolar planets in terms of their ability to distinguish between prograde and retrograde moon orbits, an important tracer of the moon formation channel. We find that most moon detection methods, in particular, sensitive methods for detecting moons of transiting planets, cannot observationally distinguishing prograde and retrograde moon orbits. The prograde and retrograde cases can only be distinguished where the dynamical evolution of the orbit due to, e.g., three body effects is detectable, where one of the two cases is dynamically unstable, or where new observational facilities, which can implement a technique capable of differentiating the two cases, come online. In particular, directly imaged planets are promising targets because repeated spectral and photometric measurements, which are required to determine moon orbit direction, could also be conducted with the primary interest of characterizing the planet itself.

The occurrence of planets in binary star systems has been investigated via a variety of techniques that sample a wide range of semi-major axes, but with a preponderance of such results applicable to planets with semi-major axes less than a few astronomical units. We utilize a new method—the presence or absence of heavy elements in the atmospheres of white dwarf stars—to elucidate the frequency in main sequence binary star systems of planets with semi-major axes greater than a few astronomical units. We consider only binaries where a putative planetary system orbits one member (no circumbinary planets). For main sequence binaries where the primary star is of spectral type A or F, data in the published literature suggests that the existence of a secondary star with a semi-major axis less than about 1000 AU suppresses the formation and/or long-term stability of an extended planetary system around the primary. For these spectral types and initial semi-major axis ⩾1000 AU, extended planetary systems appear to be as common around stars in binary systems as they are around single stars.

The cyclopropenyl cation (c-C₃H₃⁺) is the smallest aromatic hydrocarbon molecule and considered to be a pivotal intermediate in ion–molecule reactions in space. An astronomical identification has been prohibited so far, because of a lack of gas-phase data. Here we report the first high resolution infrared laboratory gas-phase spectrum of the ν₄ (C–H asymmetric stretching) fundamental band of c-C₃H₃⁺. The c-C₃H₃⁺ cations are generated in supersonically expanding planar plasma by discharging a propyne/helium gas pulse, yielding a rotational temperature of ∼35 K. The absorption spectrum is recorded in the 3.19 μm region using sensitive continuous-wave cavity ring-down spectroscopy. The analysis of about 130 ro-vibrational transitions results in precise spectroscopic parameters. These constants allow for an accurate comparison with high-level theoretical predictions, and provide the relevant information needed to search for this astrochemically relevant carbo-cation in space.

Relative to calcium, both strontium and barium are markedly enriched in Earth's continental crust compared to the basaltic crusts of other differentiated rocky bodies within the solar system. Here, we both re-examine available archived Keck spectra to place upper bounds on n(Ba)/n(Ca) and revisit published results for n(Sr)/n(Ca) in two white dwarfs that have accreted rocky planetesimals. We find that at most only a small fraction of the pollution is from crustal material that has experienced the distinctive elemental enhancements induced by Earth-analog plate tectonics. In view of the intense theoretical interest in the physical structure of extrasolar rocky planets, this search should be extended to additional targets.

We present far-UV spectroscopy from the Cosmic Origins Spectrograph on the Hubble Space Telescope of a cool, star-forming filament in the core of A1795. These data, which span 1025 Å < λ_rest < 1700 Å, allow for the simultaneous modeling of the young stellar populations and the intermediate-temperature (10^5.5 K) gas in this filament, which is far removed (∼30 kpc) from the direct influence of the central active galactic nucleus. Using a combination of UV absorption line indices and stellar population synthesis modeling, we find evidence for ongoing star formation, with the youngest stars having ages of $7.5^{+2.5}_{-2.0}$ Myr and metallicities of 0.4$^{+0.2}_{-0.1}$ Z_☉. The latter is consistent with the local metallicity of the intracluster medium. We detect the O vi λ1038 line, measuring a flux of f_{O VI, 1038} = 4.0 ± 0.9 × 10⁻¹⁷ erg s⁻¹ cm⁻². The O vi λ1032 line is redshifted such that it is coincident with a strong Galactic H₂ absorption feature, and is not detected. The measured O vi λ1038 flux corresponds to a cooling rate of 0.85 ± 0.2 (stat) ± 0.15 (sys) M_☉ yr⁻¹ at ∼10^5.5 K, assuming that the cooling proceeds isochorically, which is consistent with the classical X-ray luminosity-derived cooling rate in the same region. We measure a star formation rate of 0.11 ± 0.02 M_☉ yr⁻¹ from the UV continuum, suggesting that star formation is proceeding at $13^{+3}_{-2}$% efficiency in this filament. We propose that this inefficient star formation represents a significant contribution to the larger-scale cooling flow problem.

There have been several ideas proposed to explain how the Sun's corona is heated and how the solar wind is accelerated. Some models assume that open magnetic field lines are heated by Alfvén waves driven by photospheric motions and dissipated after undergoing a turbulent cascade. Other models posit that much of the solar wind's mass and energy is injected via magnetic reconnection from closed coronal loops. The latter idea is motivated by observations of reconnecting jets and also by similarities of ion composition between closed loops and the slow wind. Wave/turbulence models have also succeeded in reproducing observed trends in ion composition signatures versus wind speed. However, the absolute values of the charge-state ratios predicted by those models tended to be too low in comparison with observations. This Letter refines these predictions by taking better account of weak Coulomb collisions for coronal electrons, whose thermodynamic properties determine the ion charge states in the low corona. A perturbative description of nonlocal electron transport is applied to an existing set of wave/turbulence models. The resulting electron velocity distributions in the low corona exhibit mild suprathermal tails characterized by "kappa" exponents between 10 and 25. These suprathermal electrons are found to be sufficiently energetic to enhance the charge states of oxygen ions, while maintaining the same relative trend with wind speed that was found when the distribution was assumed to be Maxwellian. The updated wave/turbulence models are in excellent agreement with solar wind ion composition measurements.

We report on the detection of the millisecond pulsar PSR J0437−4715 with the Murchison Wide-field Array (MWA) at a frequency of 192 MHz. Our observations show rapid modulations of pulse intensity in time and frequency that arise from diffractive scintillation effects in the interstellar medium (ISM), as well as prominent drifts of intensity maxima in the time–frequency plane that arise from refractive effects. Our analysis suggests that the scattering screen is located at a distance of ∼80–120 pc from the Sun, in disagreement with a recent claim that the screen is closer (∼10 pc). Comparisons with higher frequency data from Parkes reveal a dramatic evolution of the pulse profile with frequency, with the outer conal emission becoming comparable in strength to that from the core and inner conal regions. As well as demonstrating the high time resolution science capabilities currently possible with the MWA, our observations underscore the potential to conduct low-frequency investigations of timing-array millisecond pulsars, which may lead to increased sensitivity in the detection of nanoHertz gravitational waves via the accurate characterization of ISM effects.

Observations have shown that the spatial distribution of satellite galaxies is not random, but rather is aligned with the major axes of central galaxies (CGs). The strength of the alignment is dependent on the properties of both the satellites and centrals. Theoretical studies using dissipationless N-body simulations are limited by their inability to directly predict the shape of CGs. Using hydrodynamical simulations including gas cooling, star formation, and feedback, we carry out a study of galaxy alignment and its dependence on the galaxy properties predicted directly from the simulations. We found that the observed alignment signal is well produced, as is the color dependence: red satellites and red centrals both show stronger alignments than their blue counterparts. The reason for the stronger alignment of red satellites is that most of them stay in the inner region of the dark matter halo where the shape of the CG better traces the dark matter distribution. The dependence of alignment on the color of CGs arises from the halo mass dependence, since the alignment between the shape of the central stellar component and the inner halo increases with halo mass. We also find that the alignment of satellites is most strongly dependent on their metallicity, suggesting that the metallicity of satellites, rather than color, is a better tracer of galaxy alignment on small scales. This could be tested in future observational studies.

Fluctuation dynamos are generic to astrophysical systems. The only analytical model of the fluctuation dynamo is the Kazantsev model which assumes a velocity field that is delta-correlated in time. We derive a generalized model of fluctuation dynamos with finite correlation time, τ, using renovating flows. For τ → 0, we recover the standard Kazantsev equation for the evolution of longitudinal magnetic correlation, M_L. To the next order in τ, the generalized equation involves third and fourth spatial derivatives of M_L. It can be recast to one with at most second derivatives of M_L using the Landau–Lifschitz approach. Remarkably, we then find that the magnetic power spectrum remains the Kazantsev spectrum of M(k)∝k^3/2, in the large k limit, independent of τ.

Asteroids of size larger than 150 m generally do not have rotation periods smaller than 2.2 hr. This spin cutoff is believed to be due to the gravitationally bound rubble-pile structures of the asteroids. Rotation with periods exceeding this critical value will cause asteroid breakup. Up until now, only one object, 2001 OE84, has been found to be an exception to this spin cutoff. We report the discovery of a new super-fast rotator, (335433) 2005 UW163, spinning with a period of 1.290 hr and a light curve variation of r' ∼ 0.8 mag from the observations made at the P48 telescope and the P200 telescope of the Palomar Observatory. Its $H_{r^{\prime }} = 17.69 \pm 0.27$ mag and multi-band colors (i.e., g' − r' = 0.68 ± 0.03 mag, r' − i' = 0.19 ± 0.02 mag and SDSS i − z = −0.45 mag) show it is a V-type asteroid with a diameter of 0.6 + 0.3/ − 0.2 km. This indicates (335433) 2005 UW163 is a super-fast rotator beyond the regime of the small monolithic asteroid.

We present Very Large Array observations at 7 mm that trace the thermal emission of large dust grains in the HD 169142 protoplanetary disk. Our images show a ring of enhanced emission of radius ∼25–30 AU, whose inner region is devoid of detectable 7 mm emission. We interpret this ring as tracing the rim of an inner cavity or gap, possibly created by a planet or a substellar companion. The ring appears asymmetric, with the western part significantly brighter than the eastern one. This azimuthal asymmetry is reminiscent of the lopsided structures that are expected to be produced as a consequence of trapping of large dust grains. Our observations also reveal an outer annular gap at radii from ∼40 to ∼70 AU. Unlike other sources, the radii of the inner cavity, the ring, and the outer gap observed in the 7 mm images, which trace preferentially the distribution of large (millimeter/centimeter sized) dust grains, coincide with those obtained from a previous near-infrared polarimetric image, which traces scattered light from small (micron-sized) dust grains. We model the broadband spectral energy distribution and the 7 mm images to constrain the disk physical structure. From this modeling we infer the presence of a small (radius ∼0.6 AU) residual disk inside the central cavity, indicating that the HD 169142 disk is a pre-transitional disk. The distribution of dust in three annuli with gaps in between them suggests that the disk in HD 169142 is being disrupted by at least two planets or substellar objects.

When giant planets form, they grow by accreting gas and dust. HD 142527 is a young star that offers a scaled-up view of this process. It has a broad, asymmetric ring of gas and dust beyond ∼100 AU and a wide inner gap. Within the gap, a low-mass stellar companion orbits the primary star at just ∼12 AU, and both the primary and secondary are accreting gas. In an attempt to directly detect the dusty counterpart to this accreted gas, we have observed HD 142527 with the Gemini Planet Imager in polarized light at Y band (0.95–1.14 μm). We clearly detect the companion in total intensity and show that its position and photometry are generally consistent with the expected values. We also detect a point source in polarized light that may be spatially separated by ∼ a few AU from the location of the companion in total intensity. This suggests that dust is likely falling onto or orbiting the companion. Given the possible contribution of scattered light from this dust to previously reported photometry of the companion, the current mass limits should be viewed as upper limits only. If the dust near the companion is eventually confirmed to be spatially separated, this system would resemble a scaled-up version of the young planetary system inside the gap of the transition disk around LkCa 15.

Subarcsecond images of the rotational line emissions of CCH, CS, H₂CO, and CH₃OH have been obtained toward the low-mass protostar IRAS 04368+2557 in L1527 as one of the early science projects of the Atacama Large Millimeter/submillimeter Array. The intensity distributions of CCH and CS show a double-peaked structure along the edge-on envelope with a dip toward the protostar position, whereas those of H₂CO and CH₃OH are centrally peaked. By analyzing the position–velocity diagrams along the envelope, CCH and CS are found to reside mainly in the envelope, where the gas is infalling with conservation of its angular momentum. They are almost absent inward of the centrifugal barrier (a half of the centrifugal radius). Although H₂CO exists in the infalling rotating envelope, it also resides in the disk component inside the centrifugal barrier to some extent. On the other hand, CH₃OH seems to exist around the centrifugal barrier and in the disk component. Hence, the drastic chemical change occurs at the centrifugal barrier. A discontinuous infalling motion as well as the gas-grain interaction would be responsible for the chemical change. This result will put an important constraint on initial chemical compositions for chemical evolution of protostellar disks.

We investigated the possible feedback of type I bursts on the accretion process during the spectral evolution of the atoll source 4U 1608–52. By fitting the burst spectrum with a blackbody and an adjustable, persistent spectral component, we found that the latter is significantly state-dependent. In the banana state, the persistent flux increases along the burst evolution, while in the island state this trend holds only when the bursts are less luminous and start to reverse at higher burst luminosities. We speculate that, by taking into account both the Poynting–Robertson drag and radiation pressure, these phenomena may arise from the interactions between the radiation field of the type I burst and the inner region of the accretion disk.

Even though only a handful of sub-stellar companions have been found via direct imaging, each of these discoveries has had a tremendous impact on our understanding of the star formation process and the physics of cool atmospheres. Young stars are prime targets for direct imaging searches for planets and brown dwarfs due to the favorable brightness contrast expected at such ages and also because it is often possible to derive relatively good age estimates for these primaries. Here we present the direct imaging discovery of HD 284149 b, a 18–50 M_Jup companion at a projected separation of 400 AU from a young ($25^{+25}_{10}$ Myr) F8 star, with which it shares common proper motion.

Application of the most robust method of measuring black hole masses, spatially resolved kinematics of gas and stars, is presently limited to nearby galaxies. The Atacama Large Millimeter/sub-millimeter Array (ALMA) and 30m class telescopes (the Thirty Meter Telescope, the Giant Magellan Telescope, and the European Extremely Large Telescope) with milli-arcsecond resolution are expected to extend such measurements to larger distances. Here, we study the possibility of exploiting the angular magnification provided by strong gravitational lensing to measure black hole masses at high redshifts (z ∼ 1–6), using resolved gas kinematics with these instruments. We show that in ∼15% and ∼20% of strongly lensed galaxies, the inner 25 and 50 pc could be resolved, allowing the mass of ≳ 10⁸ M_☉ black holes to be dynamically measured with ALMA, if moderately bright molecular gas is present at these small radii. Given the large number of strong lenses discovered in current millimeter surveys and future optical surveys, this fraction could constitute a statistically significant population for studying the evolution of the M–σ relation at high redshifts.