We present the discovery of a very faint stellar system, SMASH 1, that is potentially a satellite of the Large Magellanic Cloud. Found within the Survey of the MAgellanic Stellar History (SMASH), SMASH 1 is a compact (r(h) 9.1(-3.4)(+5.9)pc) and very low luminosity (M-V = -1.0 +/- 0.9, L-V = 10(2.3 +/- 0.4) L-circle dot) stellar system that is revealed by its sparsely populated main sequence and a handful of red giant branch candidate member stars. The photometric properties of these stars are compatible with a metal-poor ([Fe/H] = -2.2) and old (13 Gyr) isochrone located at a distance modulus of similar to 18.8, i.e., a distance of similar to 57 kpc. Situated at 11 degrees.3 from the LMC in projection, its three-dimensional distance from the Cloud is similar to 13 kpc, consistent with a connection to the LMC, whose tidal radius is at least 16 kpc. Although the nature of SMASH 1 remains uncertain, its compactness favors it being a stellar cluster and hence dark-matter free. If this is the case, its dynamical tidal radius is only less than or similar to 19 pc at this distance from the LMC, and smaller than the system's extent on the sky. Its low luminosity and apparent high ellipticity (epsilon = 0.62(-0.21)(+0.17)) with its major axis pointing toward the LMC may well be the tell-tale sign of its imminent tidal demise.

We present a primary transit observation for the ultra-hot (T-eq similar to 2400 K) gas giant expolanet WASP-121b, made using the Hubble Space Telescope Wide Field Camera 3 in spectroscopic mode across the 1.12-1.64 mu m wavelength range. The 1.4 mu m water absorption band is detected at high confidence (5.4 sigma) in the planetary atmosphere. We also reanalyze ground-based photometric light curves taken in the B, r', and z' filters. Significantly deeper transits are measured in these optical bandpasses relative to the near-infrared wavelengths. We conclude that scattering by high-altitude haze alone is unlikely to account for this difference and instead interpret it as evidence for titanium oxide and vanadium oxide absorption. Enhanced opacity is also inferred across the 1.12-1.3 mu m wavelength range, possibly due to iron hydride absorption. If confirmed, WASP-121b will be the first exoplanet with titanium oxide, vanadium oxide, and iron hydride detected in transmission. The latter are important species in M/L dwarfs and their presence is likely to have a significant effect on the overall physics and chemistry of the atmosphere, including the production of a strong thermal inversion.

We report the first detection of extended neutral hydrogen (H I) gas in the interstellar medium (ISM) of a massive elliptical galaxy beyond z similar to 0. The observations utilize the doubly lensed images of QSO HE 0047-1756 at z(QSO) = 1.676 as absorption-line probes of the ISM in the massive (M-star approximate to 10(11) M-circle dot) elliptical lens at z = 0.408, detecting gas at projected distances of d = 3.3 and 4.6 kpc on opposite sides of the lens. Using the Space Telescope Imaging Spectrograph, we obtain UV absorption spectra of the lensed QSO and identify a prominent flux discontinuity and associated absorption features matching the Lyman series transitions at z = 0.408 in both sightlines. The H I column density is log N(H I)= 19.6-19.7 at both locations across the lens, comparable to what is seen in 21 cm images of nearby ellipticals. The H I gas kinematics are well-matched with the kinematics of the Fe II absorption complex revealed in ground-based echelle data, displaying a large velocity shear of approximate to 360 km s(-1) across the galaxy. We estimate an ISM Fe abundance of 0.3-0.4 solar at both locations. Including likely dust depletions increases the estimated Fe abundances to solar or supersolar, similar to those of the hot ISM and stars of nearby ellipticals. Assuming 100% covering fraction of this Fe-enriched gas, we infer a total Fe mass of M-cool(Fe) similar to (5-8) x 10(4) M-circle dot in the cool ISM of the massive elliptical lens, which is no more than 5% of the total Fe mass observed in the hot ISM.

Dynamical mass estimates down to the planet-mass regime can help to understand planet formation. We present Atacama Large Millimeter/submillimeter Array (ALMA) 1.3 mm observations of FW Tau C, a proposed similar to 10M(Jup) planet-mass companion at similar to 330 au from the host binary FW Tau AB. We spatially and spectrally resolve the accretion disk of FWTau C in (CO)-C-12 (2-1). By modeling the Keplerian rotation of gas, we derive a dynamical mass of similar to 0.1 M-circle dot. Therefore, FW Tau C is unlikely a planet, but rather a low-mass star with a highly inclined disk. This also suggests that FW Tau is a triple system consisting of three similar to 0.1. M-circle dot stars.

We present spectra of five ultra-diffuse galaxies (UDGs) in the vicinity of the Coma cluster obtained with the Multi-object Double Spectrograph on the Large Binocular Telescope. We confirm four of these as members of the cluster, quintupling the number of spectroscopically confirmed systems. Like the previously confirmed large (projected half-light radius > 4.6 kpc) UDG, DF44, the systems we targeted all have projected half-light radii > 2.9 kpc. As such, we spectroscopically confirm a population of physically large UDGs in the Coma cluster. The remaining UDG is located in the field, about 45 Mpc behind the cluster. We observe Balmer and Ca II H and K absorption lines in all of our UDG spectra. By comparing the stacked UDG spectrum against stellar population synthesis models, we conclude that, on average, these UDGs are composed of metal-poor stars ([Fe/H] less than or similar to -1.5). We also discover the first UDG with [O II] and [O III] emission lines within a clustered environment, demonstrating that not all cluster UDGs are devoid of gas and sources of ionizing radiation.

We present IRAM/NOEMA and JVLA observations of the quasar J1342+0928 at z = 7.54 and report detections of copious amounts of dust and [C Pi] emission in the interstellar medium (ISM) of its host galaxy. At this redshift, the age of the universe is 690 Myr, about 10% younger than the redshift of the previous quasar record holder. Yet, the ISM of this new quasar host galaxy is significantly enriched by metals, as evidenced by the detection of the [C 158 mu m cooling line and the underlying far-infrared (FIR) dust continuum emission. To the first order, the FIR properties of this quasar host are similar to those found at a slightly lower redshift (z similar to 6), making this source by far the FIR-brightest galaxy known at z greater than or similar to 7.5. The [C Pi]emission is spatially unresolved, with an upper limit on the diameter of 7 kpc. Together with the measured FWHM of the [C Pi]line, this yields a dynamical mass of the host of <1.5 x 10(11) M-circle dot Using standard assumptions about the dust temperature and emissivity, the NOEMA measurements give a dust mass of (0.6-4.3) x 10(8) M-circle dot The brightness of the [C Pi] luminosity, together with the high dust mass, imply active ongoing star formation in the quasar host. Using [C Pi]-SFR scaling relations, we derive star formation rates of 85-545 M-circle dot yr(-1) in the host, consistent with the values derived from the dust continuum. Indeed, an episode of such past high star formation is needed to explain the presence of similar to 10(8) M-circle dot of dust implied by the observations.

We test the galactic outflow model by probing associated galaxies of four strong intergalactic C IV absorbers at z = 5-6 using the Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS) ramp narrowband filters. The four strong C IV absorbers reside at z = 5.74, 5.52, 4.95, and 4.87, with column densities ranging from N-C IV = 10(13.8) to 10(14.8) cm(-2). At z = 5.74, we detect an i-dropout Ly alpha emitter (LAE) candidate with a projected impact parameter of 42 physical kpc from the C IV absorber. This LAE candidate has a Ly alpha-based star formation rate (SFRLy alpha) of 2 M-circle dot yr(-1) and a UV-based SFR of 4 M-circle dot yr(-1). Although we cannot completely rule out that this i-dropout emitter may be an [O II] interloper, its measured properties are consistent with the C IV powered galaxy at z = 5.74. For C IV absorbers at z = 4.95 and z = 4.87, although we detect two LAE candidates with impact parameters of 160 and 200 kpc, such distances are larger than that predicted from the simulations. Therefore, we treat them as nondetections. For the system at z = 5.52, we do not detect LAE candidates, placing a 3 sigma upper limit of SFRLy alpha approximate to 1.5 M-circle dot yr(-1). In summary, in these four cases, we only detect one plausible C IV source at z = 5.74. Combining the modest SFR of the one detection and the three nondetections, our HST observations strongly support that smaller galaxies (SFRLy alpha less than or similar to 2 M-circle dot yr(-1)) are main sources of intergalactic C IV absorbers, and such small galaxies play a major role in the metal enrichment of the intergalactic medium at z greater than or similar to 5.

We present the Magellan/FIRE detection of highly ionized C IV lambda 1550 and O III]lambda 1666 in a deep infrared spectrum of the z = 6.11 gravitationally lensed low-mass galaxy RXC J2248.7-4431-ID3, which has previously known Ly alpha. No corresponding emission is detected at the expected location of He II lambda 1640. The upper limit on He II, paired with detection of O III] and C IV, constrains possible ionization scenarios. Production of C IV and O III] requires ionizing photons of 2.5-3.5 Ryd, but once in that state their multiplet emission is powered by collisional excitation at lower energies (similar to 0.5 Ryd). As a pure recombination line, He II emission is powered by 4 Ryd ionizing photons. The data therefore require a spectrum with significant power at 3.5 Ryd but a rapid drop toward 4.0 Ryd. This hard spectrum with a steep drop is characteristic of low-metallicity stellar populations, and less consistent with soft AGN excitation, which features more 4 Ryd photons and hence higher He II flux. The conclusions based on ratios of metal line detections to helium non-detection are strengthened if the gas metallicity is low. RXJ2248-ID3 adds to the growing handful of reionization-era galaxies with UV emission line ratios distinct from the general z = 2-3 population in a way that suggests hard ionizing spectra that do not necessarily originate in AGNs.

The solar wind undergoes significant heating as it propagates away from the Sun; the exact mechanisms responsible for this heating are not yet fully understood. We present for the first time a statistical test for one of the proposed mechanisms: stochastic ion heating. We use the amplitude of magnetic field fluctuations near the proton gyroscale as a proxy for the ratio of gyroscale velocity fluctuations to perpendicular (with respect to the magnetic field) proton thermal speed, defined as epsilon(p). Enhanced proton temperatures are observed when epsilon(p) is larger than a critical value (similar to 0.019-0.025). This enhancement strongly depends on the proton plasma beta (beta parallel to(p)); when beta parallel to(p) << 1 only the perpendicular proton temperature T-perpendicular to increases, while for beta parallel to(p) similar to 1 increased parallel and perpendicular proton temperatures are both observed. For epsilon(p) smaller than the critical value and beta parallel to(p) << 1 no enhancement of Tp is observed, while for beta parallel to(p) similar to 1 minor increases in T-parallel to are measured. The observed change of proton temperatures across a critical threshold for velocity fluctuations is in agreement with the stochastic ion heating model of Chandran et al. We find that epsilon(p) > epsilon(crit) in 76% of the studied periods, implying that stochastic heating may operate most of the time in the solar wind at 1 au.

We present the HST WFC3/F275W UV imaging observations of A2218-Flanking, a lensed compact dwarf galaxy at redshift z approximate to 2.5. The stellar mass of A2218-Flanking is log(M-*/M-circle dot) = 9.14(-0.04)(+0.07) and SFR is 12.5(-7.4)(+3.8) M-circle dot yr(-1) after correcting the magnification. This galaxy has a young galaxy age of 127. Myr and a compact galaxy size of r(1/2) = 2.4 kpc. The HST UV imaging observations cover the rest-frame Lyman continuum (LyC) emission (similar to 800 angstrom) from A2218-Flanking. We firmly detect (14s) the LyC emission in A2218-Flanking in the F275W image. Together with the HST F606W images, we find that the absolute escape fraction of LyC is f(abs,esc) > 28%-57% based on the flux density ratio between 1700 and 800 angstrom (f(1700)/f(800)). The morphology of the LyC emission in the F275W images is extended and follows the morphology of the UV continuum morphology in the F606W images, suggesting that the f(800) is not from foreground contaminants. We find that the region with a high star formation rate surface density has a lower f(1700)/f(800) (higher f(800)/f(1700)) ratio than the diffused regions, suggesting that LyC photons are more likely to escape from the region with the intensive star-forming process. We compare the properties of galaxies with and without LyC detections and find that LyC photons are easier to escape in low-mass galaxies.