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Aims.JWST/NIRCam provides rest-frame near-IR photometry of galaxies up toz = 2.5 with exquisite depth and accuracy. This affords us an unprecedented view of the evolution of the UV/optical/near-IR color distribution and its interpretation in terms of the evolving dust attenuation,A_V. Methods.We used the value-added data products (photometric redshift, stellar mass, rest-frameU − VandV − Jcolors, andA_V) provided by the public DAWN JWST Archive. These data products derive from fitting the spectral energy distributions obtained from multiple NIRCam imaging surveys, augmented with preexisting HST imaging data. Our sample consists of a stellar-mass-complete sample of ≈28 000M_⋆ >  10⁹ M_⊙galaxies in the redshift range 0.5 <  z <  2.5. Results.TheV − Jcolor distribution of star-forming galaxies evolves strongly, in particular for high-mass galaxies (M_⋆ >  3 × 10¹⁰ M_⊙), which have a pronounced tail of very red galaxies reachingV − J >  2.5 atz >  1.5 that does not exist atz <  1. Such redV − Jcan only be explained by dust attenuation, with typical values forM_⋆ ≈ 10¹¹ M_⊙galaxies in the rangeA_V ≈ 1.5 − 3.5 atz ≈ 2. This redshift evolution went largely unnoticed before. Today, however, photometric redshift estimates for the reddest (V − J >  2.5), most attenuated galaxies have markedly improved thanks to the new, precise photometry, which is in much better agreement with the 25 available spectroscopic redshifts for such galaxies. The reddest population readily stands out as the independently identified population of galaxies detected at submillimeter wavelengths. Despite the increased attenuation,U − Vcolors across the entire mass range are slightly bluer at higherz. A well-defined and tight color sequence exists at redshifts 0.5 <  z <  2.5 forM_⋆ >  3 × 10¹⁰ M_⊙quiescent galaxies, in bothU − VandV − J, but inV − Jit is bluer rather than redder compared to star-forming galaxies. In conclusion, whereas the rest-frame UV-optical color distribution evolves remarkably little fromz = 0.5 toz = 2.5, the rest-frame optical/near-IR color distribution evolves strongly, primarily due to a very substantial increase with redshift in dust attenuation for massive galaxies. 

The M81 galaxy group is surrounded by an HI debris field scattered by the tidal interactions of its galaxies, a situation that has obvious similarities to the Magellanic stream and illuminates the formation of in-situ stars in stellar halos during galaxy collisions. Using observations of stars across the M81 group from the Subaru Hyper Suprime-Cam, and observations of the neutral HI from the Very Large Array, we find that within this HI debris the density of young stars broadly correlates with the density of gas, as expected given the Schmidt-Kennicutt star formation law and the results of previous work. Yet, there are regions that have systematically different behaviors in distributions of stars and gas. We focus on two stretches of HI coming off NGC 3077: the Southern tidal bridge (between M81 and NGC 3077) and the Northern tidal bridge (from NGC 3077 in the direction of M82). The Southern bridge has a narrow strip of young stars down its center, and the Northern bridge is mostly devoid of stars. While the driver(s) for this kind of behavior remain uncertain, our analysis of star formation in galaxy group-scale mergers from the TNG50 hydrodynamical galaxy simulations shows that the differences between projected line-of-sight distances of the gas may be an important consideration. 

Abstract We present the discovery of Aquarius III, an ultra-faint Milky Way satellite galaxy identified in the second data release of the DECam Local Volume Exploration survey. Based on deeper follow-up imaging with DECam, we find that Aquarius III is a low-luminosity ( $M_V=-{2.5}_{-0.5}^{+0.3};$ $L_V={850}_{-260}^{+380}{L}_{\odot }$), extended ( $r_{1/2}={41}_{-8}^{+9}$pc) stellar system located in the outer halo (D_⊙= 85 ± 4 kpc). From medium-resolution Keck/DEIMOS spectroscopy, we identify 11 member stars and measure a mean heliocentric radial velocity of $v_{\mathrm{sys}}=-{13.1}_{-0.9}^{+1.0}\mathrm{km}{\mathrm{s}}^{-1}$for the system and place an upper limit ofσ_v< 3.5 km s⁻¹(σ_v< 1.6 km s⁻¹) on its velocity dispersion at the 95% (68%) credible level. Based on calcium-triplet metallicities of the six brightest red giant members, we find that Aquarius III is very metal-poor ([Fe/H]= − 2.61 ± 0.21) with a statistically significant metallicity spread ( ${\sigma }_{\left[\mathrm{Fe}/\mathrm{H}\right]}={0.46}_{-0.14}^{+0.26}$dex). We interpret this metallicity spread as strong evidence that the system is a dwarf galaxy as opposed to a star cluster. Combining our velocity measurement with Gaia proper motions, we find that Aquarius III is currently situated near its orbital pericenter in the outer halo (r_peri= 78 ± 7 kpc) and that it is plausibly on first infall onto the Milky Way. This orbital history likely precludes significant tidal disruption from the Galactic disk, notably unlike other satellites with comparably low velocity dispersion limits in the literature. Thus, if further velocity measurements confirm that its velocity dispersion is truly belowσ_v≲ 2 km s⁻¹, Aquarius III may serve as a useful laboratory for probing galaxy formation physics in low-mass halos. 

Antarctic minke whales (Balaenoptera bonaerensis, AMW) are an abundant, ice-dependent species susceptible to rapid climatic changes occurring in parts of the Antarctic. Here, we used remote biopsy samples and estimates of length derived from unoccupied aircraft system (UAS) to characterize for the first time the sex ratio, maturity, and pregnancy rates of AMWs around the Western Antarctic Peninsula (WAP). DNA profiling of 82 biopsy samples (2013–2020) identified 29 individual males and 40 individual females. Blubber progesterone levels indicated 59% of all sampled females were pregnant, irrespective of maturity. When corrected for sexual maturity, the median pregnancy rate was 92.3%, indicating that most mature females become pregnant each year. We measured 68 individuals by UAS (mean = 8.04 m) and estimated that 66.5% of females were mature. This study provides the first data on the demography of AMWs along the WAP and represents the first use of non-lethal approaches to studying this species. Furthermore, these results provide baselines against which future changes in population status can be assessed in this rapidly changing marine ecosystem. 

Abstract We present the second public data release (DR2) from the DECam Local Volume Exploration survey (DELVE). DELVE DR2 combines new DECam observations with archival DECam data from the Dark Energy Survey, the DECam Legacy Survey, and other DECam community programs. DELVE DR2 consists of ∼160,000 exposures that cover >21,000 deg 2 of the high-Galactic-latitude (∣ b ∣ > 10°) sky in four broadband optical/near-infrared filters ( g , r , i , z ). DELVE DR2 provides point-source and automatic aperture photometry for ∼2.5 billion astronomical sources with a median 5 σ point-source depth of g = 24.3, r = 23.9, i = 23.5, and z = 22.8 mag. A region of ∼17,000 deg 2 has been imaged in all four filters, providing four-band photometric measurements for ∼618 million astronomical sources. DELVE DR2 covers more than 4 times the area of the previous DELVE data release and contains roughly 5 times as many astronomical objects. DELVE DR2 is publicly available via the NOIRLab Astro Data Lab science platform.