ALBERT

Description: LAEs and LBGs represent the most common groups of star-forming galaxies at high-z, and the differences between their inherent stellar populations (SPs) are a key factor in understanding early galaxy formation and evolution. We have run a set of SP burst-like models for a sample of 1,558 sources at 3.4 〈 z 〈 6.8 from the Survey for High-z Absorption Red and Dead Sources (SHARDS) over the GOODS-N field. This work focuses on the differences between the three different observational subfamilies of our sample: LAE-LBGs, no-Lyα LBGs and pure LAEs. Single and double SP synthetic spectra were used to model the SEDs, adopting a Bayesian information criterion to analyse under which situations a second SP is required. We find that the sources are well modelled using a single SP in $sim 79{{ m per cent}}$ of the cases. The best models suggest that pure LAEs are typically young low mass galaxies ($tsim 26^{+41}_{-25}$ Myr; $M_{mathrm{star}}sim 5.6^{+12.0}_{-5.5}imes 10^{8} M_{odot }$), undergoing one of their first bursts of star formation. On the other hand, no-Lyα LBGs require older SPs (t ∼ 71 ± 12 Myr), and they are substantially more massive (Mstar ∼ 3.5 ± 1.1 × 109 M⊙). LAE-LBGs appear as the subgroup that more frequently needs the addition of a second SP, representing an old and massive galaxy caught in a strong recent star-forming episode. The relative number of sources found from each subfamily at each z supports an evolutionary scenario from pure LAEs and single SP LAE-LBGs to more massive LBGs. Stellar Mass Functions are also derived, finding an increase of M* with cosmic time and a possible steepening of the low mass slope from z ∼ 6 to z ∼ 5 with no significant change to z ∼ 4. Additionally, we have derived the SFR-Mstar relation, finding a $mathrm{SFR}propto M_{mathrm{star}}^{ eta }$ behaviour with negligible evolution from z ∼ 4 to z ∼ 6.

Description: Context. The CARMENES exoplanet survey of M dwarfs has obtained more than 18 000 spectra of 329 nearby M dwarfs over the past five years as part of its guaranteed time observations (GTO) program. Aims. We determine planet occurrence rates with the 71 stars from the GTO program for which we have more than 50 observations. Methods. We use injection-and-retrieval experiments on the radial-velocity time series to measure detection probabilities. We include 27 planets in 21 planetary systems in our analysis. Results. We find 0.06−0.03+0.04 giant planets (100 M⊕ 〈 Mpl sin i 〈 1000 M⊕) per star in periods of up to 1000 d, but due to a selection bias this number could be up to a factor of five lower in the whole 329-star sample. The upper limit for hot Jupiters (orbital period of less than 10 d) is 0.03 planets per star, while the occurrence rate of planets with intermediate masses (10 M⊕ 〈 Mpl sin i 〈 100 M⊕) is 0.18−0.05+0.07 planets per star. Less massive planets with 1 M⊕ 〈 Mpl sin i 〈 10 M⊕ are very abundant, with an estimated rate of 1.32−0.31+0.33 planets per star for periods of up to 100 d. When considering only late M dwarfs with masses M⋆ 〈 0.34 M⊙, planets more massive than 10 M⊕ become rare. Instead, low-mass planets with periods shorter than 10 d are significantly overabundant. Conclusions. For orbital periods shorter than 100 d, our results confirm the known stellar mass dependences from the Kepler survey: M dwarfs host fewer giant planets and at least two times more planets with Mpl  sin i 〈 10 M⊕ than G-type stars. In contrast to previous results, planets around our sample of very low-mass stars have a higher occurrence rate in short-period orbits of less than 10 d. Our results demonstrate the need to take into account host star masses in planet formation models.

Description: In the last decades, changing climate conditions have had a severe impact on sea ice at the western Antarctic Peninsula (WAP), an area rapidly transforming under global warming. To study the development of spring sea ice and environmental conditions in the pre-satellite era we investigated three short marine sediment cores for their biomarker inventory with a particular focus on the sea ice proxy IPSO25 and micropaleontological proxies. The core sites are located in the Bransfield Strait in shelf to deep basin areas characterized by a complex oceanographic frontal system, coastal influence and sensitivity to large-scale atmospheric circulation patterns. We analyzed geochemical bulk parameters, biomarkers (highly branched isoprenoids, glycerol dialkyl glycerol tetraethers, sterols), and diatom abundances and diversity over the past 240 years and compared them to observational data, sedimentary and ice core climate archives, and results from numerical models. Based on biomarker results we identified four different environmental units characterized by (A) low sea ice cover and high ocean temperatures, (B) moderate sea ice cover with decreasing ocean temperatures, (C) high but variable sea ice cover during intervals of lower ocean temperatures, and (D) extended sea ice cover coincident with a rapid ocean warming. While IPSO25 concentrations correspond quite well to satellite sea ice observations for the past 40 years, we note discrepancies between the biomarker-based sea ice estimates, the long-term model output for the past 240 years, ice core records, and reconstructed atmospheric circulation patterns such as the El Niño–Southern Oscillation (ENSO) and Southern Annular Mode (SAM). We propose that the sea ice biomarker proxies IPSO25 and PIPSO25 are not linearly related to sea ice cover, and, additionally, each core site reflects specific local environmental conditions. High IPSO25 and PIPSO25 values may not be directly interpreted as referring to high spring sea ice cover because variable sea ice conditions and enhanced nutrient supply may affect the production of both the sea-ice-associated and phytoplankton-derived (open marine, pelagic) biomarker lipids. For future interpretations we recommend carefully considering individual biomarker records to distinguish between cold sea-ice-favoring and warm sea-ice-diminishing environmental conditions.

Description: Context. The direct imaging of exoplanets in reflected starlight will represent a major advance in the study of cold and temperate exoplanet atmospheres. Understanding how basic planet and atmospheric properties may affect the measured spectra is key to their interpretation. Aims. We have investigated the information content in reflected-starlight spectra of exoplanets. We apply our analysis to Barnard’s Star b candidate super-Earth, for which we assume a radius 0.6 times that of Neptune, an atmosphere dominated by H2–He, and a CH4 volume mixing ratio of 5 × 10−3. The main conclusions of our study are however planet-independent. Methods. We set up a model of the exoplanet described by seven parameters including its radius, atmospheric methane abundance, and basic properties of a cloud layer. We generated synthetic spectra at zero phase (full disc illumination) from 500 to 900 nm and a spectral resolution R ~ 125–225. We simulated a measured spectrum with a simplified, wavelength-independent noise model at a signal-to-noise ratio of 10. With a retrieval methodology based on Markov chain Monte Carlo sampling, we analysed which planet and atmosphere parameters can be inferred from the measured spectrum and the theoretical correlations amongst them. We considered limiting cases in which the planet radius is either known or completely unknown, and intermediate cases in which the planet radius is partly constrained. Results. If the planet radius is known, we can generally discriminate between cloud-free and cloudy atmospheres, and constrain the methane abundance to within two orders of magnitude. If the planet radius is unknown, new correlations between model parameters occur and the accuracy of the retrievals decreases. Without a radius determination, it is challenging to discern whether the planet has clouds, and the estimates on methane abundance degrade. However, we find the planet radius is constrained to within a factor of two for all the cases explored. Having a priori information on the planet radius, even if approximate, helps improve the retrievals. Conclusions. Reflected-starlight measurements will open a new avenue for characterizing long-period exoplanets, a population that remains poorly studied. For this task to be complete, direct-imaging observations should be accompanied by other techniques. We urge exoplanet detection efforts to extend the population of long-period planets with mass and radius determinations.

Description: The very first galaxies that started the cosmic dawn likely resided in so-called “minihalos’’, with masses of ∼105–108M⊙, accreting their gas from the intergalactic medium through H2 cooling. Such molecularly-cooled galaxies (MCGs), mostly formed in pristine environments, hosted massive, metal-free stars, and were eventually sterilized by the build-up of a disassociating (Lyman-Werner; LW) background. Therefore, their properties might be very different from the galaxies we see in the later Universe. Although MCGs are probably too faint to be observed directly, we could nevertheless infer their properties from the imprint they leave in the cosmic 21-cm signal. Here we quantify this imprint by extending the public simulation code 21cmFAST to allow for a distinct population of MCGs. We allow MCGs to have different properties from other galaxies, including unique scaling relations for their stellar to halo mass ratios, ionizing escape fractions, and spectral energy distributions. We track inhomogeneous recombinations, disassociative LW feedback, and photo-heating from reionization. After demonstrating how MCGs can shape the 21-cm signal, we explore to what extent current observations can already place constraints on their properties. The CMB optical depth from Planck sets an upper limit on the product of the ionizing escape fraction and the stellar mass in MCGs. When including also the timing of the putative EDGES absorption signal, we find an additional strong degeneracy between the stellar mass and the X-ray luminosity of MCGs. If proven to be of cosmic origin, the timing of the EDGES signal would have been set by MCGs.

Description: Atmospheric radiative transfer models (RTMs) are software tools that help researchers in understanding the radiative processes occurring in the Earth's atmosphere. Given their importance in remote sensing applications, the intercomparison of atmospheric RTMs is therefore one of the main tasks used to evaluate model performance and identify the characteristics that differ between models. This can be a tedious tasks that requires good knowledge of the model inputs/outputs and the generation of large databases of consistent simulations. With the evolution of these software tools, their increase in complexity bears implications for their use in practical applications and model intercomparison. Existing RTM-specific graphical user interfaces are not optimized for performing intercomparison studies of a wide variety of atmospheric RTMs. In this paper, we present the Atmospheric Look-up table Generator (ALG) version 2.0, a new software tool that facilitates generating large databases for a variety of atmospheric RTMs. ALG facilitates consistent and intuitive user interaction to enable the running of model executions and storing of RTM data for any spectral configuration in the optical domain. We demonstrate the utility of ALG in performing intercomparison studies of radiance simulations from broadly used atmospheric RTMs (6SV, MODTRAN, and libRadtran) through global sensitivity analysis. We expect that providing ALG to the research community will facilitate the usage of atmospheric RTMs to a wide range of applications in Earth observation.

Description: We present new observations of the transmission spectrum of the hot Jupiter WASP-6b both from the ground with the Very Large Telescope FOcal Reducer and Spectrograph (FORS2) from 0.45 to 0.83 μm, and space with the Transiting Exoplanet Survey Satellite from 0.6 to 1.0 μm and the Hubble Space Telescope (HST) Wide Field Camera 3 from 1.12 to 1.65 μm. Archival data from the HST Space Telescope Imaging Spectrograph (STIS) and Spitzer are also re-analysed on a common Gaussian process framework, of which the STIS data show a good overall agreement with the overlapping FORS2 data. We also explore the effects of stellar heterogeneity on our observations and its resulting implications towards determining the atmospheric characteristics of WASP-6b. Independent of our assumptions for the level of stellar heterogeneity we detect Na i, K i, and H2O absorption features and constrain the elemental oxygen abundance to a value of [O/H] ≃ −0.9 ± 0.3 relative to solar. In contrast, we find that the stellar heterogeneity correction can have significant effects on the retrieved distributions of the [Na/H] and [K/H] abundances, primarily through its degeneracy with the sloping optical opacity of scattering haze species within the atmosphere. Our results also show that despite this presence of haze, WASP-6b remains a favourable object for future atmospheric characterization with upcoming missions such as the James Webb Space Telescope.

Description: We present a Bayesian method to identify multiple (chemodynamic) stellar populations in dwarf spheroidal galaxies (dSphs) using velocity, metallicity, and positional stellar data without the assumption of spherical symmetry. We apply this method to a new Keck/Deep Imaging Multi-Object Spectrograph (DEIMOS) spectroscopic survey of the Ursa Minor (UMi) dSph. We identify 892 likely members, making this the largest UMi sample with line-of-sight velocity and metallicity measurements. Our Bayesian method detects two distinct chemodynamic populations with high significance (in logarithmic Bayes factor, ln B ∼ 33). The metal-rich ([Fe/H] = −2.05 ± 0.03) population is kinematically colder (radial velocity dispersion of $sigma _v=4.9_{-1.0}^{+0.8} , mathrm{km} , mathrm{s}^{-1}$) and more centrally concentrated than the metal-poor ($[{ m Fe/H}]=-2.29_{-0.06}^{+0.05}$) and kinematically hotter population ($sigma _v =11.5_{-0.8}^{+0.9}, mathrm{km} , mathrm{s}^{-1}$). Furthermore, we apply the same analysis to an independent Multiple Mirror Telescope (MMT)/Hectochelle data set and confirm the existence of two chemodynamic populations in UMi. In both data sets, the metal-rich population is significantly flattened (ϵ = 0.75 ± 0.03) and the metal-poor population is closer to spherical ($epsilon =0.33_{-0.09}^{+0.12}$). Despite the presence of two populations, we are able to robustly estimate the slope of the dynamical mass profile. We found hints for prolate rotation of order ${sim}2 , mathrm{km} , mathrm{s}^{-1}$ in the MMT data set, but further observations are required to verify this. The flattened metal-rich population invalidates assumptions built into simple dynamical mass estimators, so we computed new astrophysical dark matter annihilation (J) and decay profiles based on the rounder, hotter metal-poor population and inferred $log _{10}{(J(0{^{circ}_{.}}5)/{ m GeV^{2} , cm^{-5}})}approx 19.1$ for the Keck data set. Our results paint a more complex picture of the evolution of UMi than previously discussed.