Las Campanas Observatory

Abstract We present and analyze panchromatic (0.35–14 μ m) spectroscopy of the Type II supernova 2023ixf, including near- and mid-infrared spectra obtained 33.6 days after explosion during the plateau phase, with the James Webb Space Telescope (JWST). This is the first in a series of papers examining the evolution of SN 2023ixf with JWST during the initial 1000 days after explosion and monitoring the formation and growth of molecules and dust in ejecta and the surrounding environment. The JWST infrared spectra are overwhelmingly dominated by H lines, whose profiles reveal ejecta structures, including flat tops, blue notches, and red shoulders, unseen in the optical spectra. We characterize the nature of these structures, concluding that they likely result from a combination of ejecta geometry, viewing angle, and opacity effects. We find no evidence for the formation of dust precursor molecules such as carbon monoxide (CO), nor do we observe an infrared excess attributable to dust. These observations imply that the detections of molecules and dust in SN 2023ixf at later epochs arise either from freshly synthesized material within the ejecta or circumstellar material at radii not yet heated by the supernova at this epoch.

Abstract We present panchromatic 0.4–21 μ m observations of the nearby (∼7.2 Mpc) Type II supernova (SN) 2024ggi, obtained during the plateau phase at ∼55 days past explosion. Our data set includes JWST spectra spanning 1.7–14 μ m, mid-infrared (MIR) imaging at 7.7 and 21 μ m, and near-simultaneous ground-based optical and near-infrared (NIR) spectra covering 0.32−1.8 μ m. The NIR and MIR spectral features of SN 2024ggi are dominated by H i emission. We present line IDs and a toy PHOENIX/1D model that reproduces the observations well, especially the continuum redward of 0.9 μ m. We compare SN 2024ggi to SN 2022acko and SN 2023ixf, two other Type II SNe that were also observed by JWST, and highlight key similarities and differences in their spectral features. No evidence for a MIR excess or dust is found at these epochs, with the model matching the observed flux out to 21 μ m. We discuss the model’s shortcomings, focusing on the density profile, which suppresses line blanketing and produces features in the optical that are too narrow. Our results show the power of panchromatic studies in both exploring the nature of the SN ejecta and constraining detailed models of SNe.

Abstract Spectral morphological analysis is crucial for determining the fundamental physical properties of stars, particularly for rare and astrophysically important O-type stars. Due to heavy interstellar extinction in the optical range, most Galactic O stars remain obscured, making near-infrared (NIR) spectroscopy the only viable approach to achieve a reasonably complete sample of this stellar population and to extend current classification schemes. Our aim is to build a comprehensive spectral classification atlas of O-type stars in the NIR, providing robust morphological criteria to support and enhance future research on massive stars in heavily obscured environments. To this end, we obtained high-resolution ( R ∼ 4000–11,000) NIR spectra for the majority of standard stars from the latest installment of the Galactic O-Star Spectroscopic Survey, using spectrographs at Gemini North and Las Campanas Observatory to ensure broad spectral coverage and high data quality. We present an atlas featuring spectral sequences for nine dwarfs (O4 to B0), nine giants (O3.5 to O9.5), and 20 supergiants (O2 to B0), systematically organised and accompanied by clear morphological criteria for subtype classification across the Y , J , H , and K bands (0.930–1.115, 1.160–1.290, 1.460–1.760, and 2.050–2.200 μ m, respectively). This atlas provides a unified framework for reliable NIR classification of O-type stars and paves the way for detailed studies of massive stars in regions heavily affected by extinction.

ABSTRACT We use Magellan/MIKE echelle spectroscopy to conduct an in-depth chemodynamical analysis of the most luminous star-forming region within the metal-poor starburst dwarf galaxy CGCG 007-025. Leveraging the exceptional high resolution (R $\sim$ 50 000) and broad wavelength coverage, we apply Bayesian inference to simultaneously model the fluxes of 30 emission lines spanning the wavelength range 3400–9200 Å. Employing a two-region ionization model, we characterize various gas properties including electron temperature, electron density, and chemical abundances across different elements. Our direct-method inferred metallicity yields $\rm 12+\log (O/H)=7.77\pm 0.03$, placing the galaxy in the metal-poor regime. Furthermore, Metal-to-Oxygen ratios such as log(S/O), log(Ne/O), or log(Ar/O) are in full agreement with the values derived for the Milky Way, consistent with expectations from stellar evolutionary models. The brightest emission lines are kinematically complex, with modelling requiring up to four distinct components. The exceptional resolution and signal-to-noise ratio of the data unveil asymmetric and wide ($\sigma _{\mathrm{ He}\, {{\small II}}} \approx$ 35 km s−1) He ii$\lambda$4686 emission. The flux ratio of this nebular line, together with the absence of other high ionization species such as [Ne v]$\lambda$3426, indicates the presence of fast radiative shocks. This data set underscores the capability of echelle spectroscopy in delivering comprehensive chemodynamical analyses of starbursts in the Local Volume.

Context. O Vz stars are identified by optical spectra where the He II λ4686 absorption line is more intense than any other He line, suggesting they may be less luminous, less evolved, and closer to the zero-age main sequence (ZAMS). Despite ongoing debate, these stars remain candidates for understanding the early evolutionary stages of O-type stars. Aims. We study O Vz stars in the star-forming regions NGC 346 in the Small Magellanic Cloud and 30 Doradus in the Large Magellanic Cloud by determining their physical parameters and exploring the influence of low metallicity on the development of the Vz spectral peculiarity. Methods. We identified a sample of O Vz and O V stars in NGC 346 using spectra obtained with the Magellan Echellette spectrograph at Las Campanas Observatory. The stars were classified based on the relationship between the equivalent width of the relevant He lines. Quantitative spectroscopic analysis was performed using the IACOB-BROAD, IACOB-GBAT/FASTWIND tools. The O V and O Vz stars from 30 Doradus, previously identified in an earlier study, were reclassified following the same criteria. Results. In NGC 346, 8 O Vz stars (29%) and 20 O V stars (71%) were identified. After a revised classification in 30 Doradus, 28 O,Vz stars (33%) and 56 O V stars (67%) were identified. Despite differences in sample sizes and metallicity, the proportion of O Vz stars is similar in both regions. O Vz stars in NGC 346 exhibit lower projected rotational velocities (v sin i < 70 km s−1), higher effective temperatures (37–40 kK) and similar surface gravities (logg = 3.7 − 4.1) compared to O V stars. Contrary to prior assumptions, O Vz stars are not consistently closer to the ZAMS. In the Hertzsprung-Russell diagram, O Vz stars appear in both young and evolved regions, suggesting that the Vz phenomenon is related to stellar wind properties.

Abstract There is a broad consensus from theory that stellar feedback in galaxies at high redshifts is essential to their evolution, alongside conflicting evidence in the observational literature about its prevalence and efficacy. To this end, we utilize deep, high-resolution [C II] emission-line data taken as part of the [C II] resolved interstellar medium (ISM) in star-forming galaxies with the Atacama Large Millimeter/submillimeter Array (CRISTAL) survey. Excluding sources with kinematic evidence for gravitational interactions, we perform a rigorous stacking analysis of the remaining 15 galaxies to search for broad emission features that are too weak to detect in the individual spectra, finding only weak evidence that a broad component is needed to explain the composite spectrum. Additionally, such evidence is mostly driven by CRISTAL-02, which is already known to exhibit strong outflows in multiple ISM phases. Interpreting modest residuals in the stack at v ∼ 300 km s−1 as an outflow, we derive a mass outflow rate of M ̇ out = 26 ± 11 M ⊙ yr−1 and a cold outflow mass-loading factor of η m = 0.49 ± 0.20. This result holds for the subsample with the highest star formation rate surface density (ΣSFR > 1.93 M ⊙ yr−1 kpc−2), but no such broad component is present in the composite of the lower-star-formation-rate density subsample. Our results imply that the process of star-formation-driven feedback may already be in place in typical galaxies at z = 5, but on average are not strong enough to completely quench ongoing star formation.

We present the morphological parameters and global properties of dust-obscured star formation in typical star-forming galaxies at z = 4–6. Among 26 galaxies composed of 20 galaxies observed by the Cycle-8 ALMA Large Program, CRISTAL, and 6 galaxies from archival data, we individually detect rest-frame 158 μm dust continuum emission from 19 galaxies, 9 of which are reported for the first time. The derived far-infrared luminosities are in the range log10LIR [L⊙] = 10.9 − 12.4, an order of magnitude lower than previously detected massive dusty star-forming galaxies (DSFGs). We find the average relationship between the fraction of dust-obscured star formation (fobs) and the stellar mass to be consistent with previous results at z = 4–6 in a mass range of log10M* [M⊙]∼9.5 − 11.0 and to show potential evolution from z = 6 − 9. The individual fobs exhibits significant diversity, and we find a potential correlation with the spatial offset between the dust and UV continuum, suggesting that inhomogeneous dust reddening may cause the source-to-source scatter in fobs. The effective radii of the dust emission are on average ∼1.5 kpc and are about two times more extended than those seen in rest-frame UV. The infrared surface densities of these galaxies (ΣIR ∼ 2.0 × 1010 L⊙ kpc−2) are one order of magnitude lower than those of DSFGs that host compact central starbursts. On the basis of the comparable contribution of dust-obscured and dust-unobscured star formation along with their similar spatial extent, we suggest that typical star-forming galaxies at z = 4 − 6 form stars throughout the entirety of their disks.

Context. Compact groups of galaxies are unique places where galaxy-galaxy interactions play a mayor role on the evolution of its members. These strong gravitational encounters can induce star formation bursts. Aims. We study the properties of one of the most luminous so-called hinge clumps that is located in the compact group of galaxies NGC 6845. Methods. Using integral field spectroscopy from GMOS/Gemini complemented with archival MUSE data, we obtained oxygen abundances, ages, star formation rates, and velocity fields, and we also modeled a single stellar population to understand the star formation history of the hinge clump in NGC 6845. Results. We found that the hinge clump sits in a tailthat has a star formation rate of 3.4 M⊙ yr−1, which is comparable with a few other extreme cases, for instance, the star clusters in the Antennae galaxy and other reported hinge clumps in the literature. This clump represents ∼15% of total star formation rate of NGC 6845A. Large-scale modeling of the observed velocity field of NGC 6845A rules out the scenario according to which this hinge clump was a satellite galaxy. Its kinematics is compatible with that of the galactic disk of NGC 6845A. Its abundance with a mean value of 0.4 Z⊙ is also consistent with the metallicity gradient of the galaxy. Conclusions. Our analysis suggest that the hinge clump is formed by multiple stellar populations and not by a single burst. This causes the wide age range. We found that the central clump is encompassed by a ring-like structure, which might suggest a second generation of star formation. In addition, the analysis of the diagnostic diagram indicates that this central region might also be ionized by shocks from stellar and supernova winds. Finally, the derived star formation rate density Σ = 9.7 M⊙ yr−1 kpc−2 of the central clump places it in starburst regime, where gas inflows should provide gas to maintain the star formation. This work shows a resolved example of an extreme localized starburst in a compact group of galaxies.

Multiplanet systems exhibit a diversity of architectures that diverge from the solar system and contribute to the topic of exoplanet demographics. Radial velocity (RV) surveys form a crucial component of exoplanet surveys, as their long observational baselines allow for searches for more distant planetary orbits. This work provides a significantly revised architecture for the multiplanet system HD 134606 using both HARPS and UCLES RVs. We confirm the presence of previously reported planets b, c, and d with periods of 12.0897−0.0018+0.0019 , 58.947−0.054+0.056 , and 958.7−5.9+6.3 days and masses of 9.14−0.63+0.65 , 11.0 ± 1, and 44.5 ± 2.9 Earth masses, respectively, with the planet d orbit significantly revised to over double that originally reported. We report two newly detected super-Earths, e and f, with periods of 4.31943−0.00068+0.00075 and 26.9−0.017+0.019 days and masses of 2.31−0.35+0.36 and 5.52−0.73+0.74 Earth masses, respectively. In addition, we identify a linear trend in the RV time series, and the cause of this acceleration is deemed to be a newly detected massive companion with a very long orbital period. HD 134606 now displays four low-mass planets in a compact region near the star, one gas giant further out in the habitable zone, an additional companion in the outer regime, and a low-mass M dwarf stellar companion at large separation, making it an intriguing target for system formation/evolution studies. The location of planet d in the habitable zone proves to be an exciting candidate for future space-based direct imaging missions, whereas continued RV observations of this system are recommended for understanding the nature of the massive, long-period companion.