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We study 31 little red dots (LRD) detected by JADES/NIRCam and covered by the SMILES/MIRI survey, of which ∼70% are detected in the two bluest MIRI bands and 40% in redder MIRI filters. The median/quartiles redshifts are $z={6.9}_{5.9}^{7.7}$ (55% spectroscopic). The spectral slopes flatten in the rest-frame near-infrared, consistent with a 1.6 μ m stellar bump but bluer than direct pure emission from active galactic nuclei (AGN) tori. The apparent dominance of stellar emission at these wavelengths for many LRDs expedites stellar mass estimation: the median/quartiles are $\mathrm{log}{M}_{\star }/{M}_{\odot }={9.4}_{9.1}^{9.7}$ . The number density of LRDs is 10 ^−4.0±0.1 Mpc ^−3 , accounting for 14% ± 3% of the global population of galaxies with similar redshifts and masses. The rest-frame near-/mid-infrared (2–4 μ m) spectral slope reveals significant amounts of warm dust (bolometric attenuation ∼3–4 mag). Our spectral energy distribution modeling implies the presence of 10 mag. We find a wide variety in the nature of LRDs. However, the best-fitting models for many of them correspond to extremely intense and compact starburst galaxies with mass-weighted ages 5–10 Myr, very efficient in producing dust, with their global energy output dominated by the direct (in the flat rest-frame ultraviolet and optical spectral range) and dust-recycled emission from OB stars with some contribution from an obscured AGN (in the infrared).

Entering the era of large-scale galaxy surveys, which will deliver unprecedented amounts of photometric and spectroscopic data, there is a growing need for more efficient, data-driven, and less model-dependent techniques to analyze the spectral energy distribution of galaxies. In this work, we demonstrate that by taking advantage of manifold learning approaches, we can estimate spectroscopic features of large samples of galaxies from their broadband photometry when spectroscopy is available only for a fraction of the sample. This will be done by applying the self-organizing map algorithm on broadband colors of galaxies and mapping partially available spectroscopic information into the trained maps. In this pilot study, we focus on estimating the 4000 Å break in a magnitude-limited sample of galaxies in the Cosmic Evolution Survey (COSMOS) field. We also examine this method to predict the H δ _A index given our available spectroscopic measurements. We use observed galaxy colors ( u,g,r,i,z,Y,J,H ), as well as spectroscopic measurements for a fraction of the sample from the LEGA-C and z COSMOS spectroscopic surveys to estimate this feature for our parent photometric sample. We recover the D4000 feature for galaxies that only have broadband colors with uncertainties about twice the uncertainty of the employed spectroscopic surveys. Using these measurements, we observe a positive correlation between D4000 and the stellar mass of the galaxies in our sample with weaker D4000 features for higher-redshift galaxies at fixed stellar masses. These can be explained by the downsizing scenario for the formation of galaxies and the decrease in their specific star formation rate as well as the aging of their stellar populations over this time period.

In this work, we present the longest photometric monitoring of up to 1200 hr of the strongly variable brown dwarf binaries Luhman 16 AB and provide evidence of ±5% variability on a timescale of several to hundreds of hours for this object. We show that short-period rotational modulation around 5 hr ( k = 1 wavenumber) and 2.5 hr ( k = 2 wavenumber) dominate the variability under 10 hr, where the planetary-scale wave model composed of k = 1 and k = 2 waves provides good fits to both the periodograms and light curve. In particular, models consisting of three to four sine waves could explain the variability of the light-curve durations up to 100 hr. We show that the relative range of the k = 2 periods is narrower compared to the k = 1 periods. Using simple models of zonal banding in solar system giants, we suggest that the difference in period range arises from the difference in wind-speed distribution at low and mid-to-high latitudes in the atmosphere. Last, we show that Luhman 16 AB also exhibits long-period ±5% variability, with periods ranging from 15 hr up to 100 hr over the longest monitoring of this object. Our results for the k = 1 and k = 2 waves and long-period evolution are consistent with previous 3D atmosphere simulations, demonstrating that both latitude-dependent waves and slow-varying atmospheric features are potentially present in Luhman 16 AB atmospheres and are a significant contribution to the light-curve modulation over hundreds of rotations.

We present the discovery of Ursa Major III/UNIONS 1, the least luminous known satellite of the Milky Way, which is estimated to have an absolute V -band magnitude of $+{2.2}_{-0.3}^{+0.4}$ mag, equivalent to a total stellar mass of ${16}_{-5}^{+6}$ M _⊙ . Ursa Major III/UNIONS 1 was uncovered in the deep, wide-field Ultraviolet Near Infrared Optical Northern Survey (UNIONS) and is consistent with an old ( τ > 11 Gyr), metal-poor ([Fe/H] ∼ −2.2) stellar population at a heliocentric distance of ∼10 kpc. Despite its being compact ( r _h = 3 ± 1 pc) and composed of few stars, we confirm the reality of Ursa Major III/UNIONS 1 with Keck II/DEIMOS follow-up spectroscopy and identify 11 radial velocity members, eight of which have full astrometric data from Gaia and are co-moving based on their proper motions. Based on these 11 radial velocity members, we derive an intrinsic velocity dispersion of ${3.7}_{-1.0}^{+1.4}$ km s ^−1 but some caveats preclude this value from being interpreted as a direct indicator of the underlying gravitational potential at this time. Primarily, the exclusion of the largest velocity outlier from the member list drops the velocity dispersion to ${1.9}_{-1.1}^{+1.4}$ km s ^−1 , and the subsequent removal of an additional outlier star produces an unresolved velocity dispersion. While the presence of binary stars may be inflating the measurement, the possibility of a significant velocity dispersion makes Ursa Major III/UNIONS 1 a high-priority candidate for multi-epoch spectroscopic follow-ups to deduce the true nature of this incredibly faint satellite.

We present wide-field, high resolution maps of the color excess for 14 globular clusters toward the Southern Galactic bulge. The maps were derived using Gaia EDR3 astrometry and stellar photometry from the Blanco DECam Bulge Survey, which is a deep, wide-field ugriz Y photometric survey of the southern Galactic bulge. Comparisons with WISE 12 μ m images of thermal continuum emission demonstrate that the maps presented here trace interstellar extinction by dust down to 5″ scales. We use the reddening-corrected photometry of proper motion-selected cluster stars to build color–magnitude diagrams for the target globular clusters, which show residual broadening in excess of that expected from the photometric errors alone. This residual broadening is likely to be driven by star-to-star elemental abundance variations.

We use the Illustris-1 simulation to explore the capabilities of the Hubble Space Telescope (HST) and James Webb Space Telescope (JWST) data to analyze the stellar populations in high-redshift galaxies, taking advantage of the combined depth, spatial resolution, and wavelength coverage. For that purpose, we use simulated broadband ACS, WFC3, and NIRCam data and two-dimensional stellar population synthesis (2D-SPS) to derive the integrated star formation history (SFH) of massive ( M _* > 10 ^10 M _⊙ ) simulated galaxies at 1 < z < 4 that evolve into a local M _* > 10 ^11 M _⊙ galaxy. In particular, we explore the potential of HST and JWST data sets reaching a depth similar to those of the CANDELS and ongoing CEERS observations, respectively, and concentrate on determining the capabilities of this data set for characterizing the first episodes in the SFH of local M _* > 10 ^11 M _⊙ galaxies by studying their progenitors at z > 1. The 2D-SPS method presented in this paper has been calibrated to robustly recover the cosmic times when the first star formation episodes occurred in massive galaxies, i.e., the first stages in their integrated SFHs. In particular, we discuss the times when the first 1%–50% of their total stellar mass formed in the simulation. We demonstrate that we can recover these ages with typical median systematic offset of less than 5% and scatter around 20%–30%. According to our measurements on Illustris data, we are able to recover that local M _* > 10 ^11 M _⊙ galaxies would have started their formation by z = 16, forming the first 5% of their stellar mass present at z ∼ 1 by z = 4.5, 10% by z = 3.7, and 25% by z = 2.7.