Directly observing “Pop III” or zero-metallicity galaxies has long been a goal in our quest to find the first galaxies that formed in the Universe. These objects, however, have remained elusive even with 2.5 years of JWST observations. We present spectroscopy on the lowest metallicity systems yet confirmed with JWST, including the most extreme Lyman-alpha emitters at MUV = −15 (0.01L*) detected with MUSE at z =3 −7 as well as a photometrically-selected sample at z =4 −9 from the JADES survey. While these objects show significantly lower metallicities than more UV-luminous objects at the same redshifts, we find a consistent metallicity floor at ≍ 2% Zȯ. This indicates rapid chemical enrichment must be taking place in systems with light-weighted ages less than 5 Myr. However, many typical selections involving photometric redshifts and/or UV continuum slopes are biased against identification of even lower metallicities. Therefore, it is currently not possible to establish if this “floor” is real or an observational artifact. Spectroscopy of larger samples selected in less restrictive ways will be required to fully determine the answer.

Based on RR Lyrae with accurate proper motions and classification in Gaia DR3, we determine the Milky Way mass distribution from fitting dynamical models to the gravitational force field and the Galactic rotation curve. Applying Gaussian Mixture Model to the intrinsic velocity distribution, we present the result of a multi-component kinematic model of RR Lyrae in the inner regions 5 ≲ r ≲ 20 kpc. Considering the early accretion history of the MW and thus the stellar halo may not be in equilibrium, we separate the halo population into an isotropic stellar halo and the radially-anisotropic population relevant to a merge event. With a Bayesian approach, we fit the potential model parameters, including the density flattening of the dark matter (DM) halo. Our best-fitting dynamical model suggests a nearly spherical spheroid shape of , a DM halo mass of , total MW mass of .

Understanding the epoch of reionization (EoR) is one of the frontier goals of modern astronomy. Lyα emission from the high-redshift galaxies has proved to be a useful tool for probing cosmic reionization. The launch of JWST has enabled the ultraviolet and optical spectroscopic studies of Lyα emitters (LAE) in the EoR. In this contribution, we present the results based on the stacking analysis of JWST/NIRSpec spectra of galaxies taken as part of the JWST GTO program JADES. The sample consists of > 250 galaxies at redshifts of ∼5-10. We divide this sample into six different sub-samples of galaxies based on the strengths of Lyα emission and redshifts and create composite spectra. We then estimate emission line ratios of optical and UV emission lines, and various physical quantities such as dust extinction, electron temperatures, ionization parameters, and ionizing photon production efficiencies to characterize the populations of LAEs and non-LAEs.

We investigated chromospheric activities of pre-main-sequence (PMS) stars. First, we studied the Ca II infrared triplet emission lines with Subaru/HDS and other spectroscopic instruments. Most PMS stars have narrow Ca II lines whose intensities are as large as the maximum of the zero-age main-sequence (ZAMS) stars. The chromosphere of PMS stars is suggested to be filled by the Ca II emitting region. Second, we found many faint chromospheric emission lines such as Mg I and Fe I for more than half of the ZAMS stars. Third, we searched the periodic light variation caused by a starspot for the 26 PMS stars. Their TESS light variations and Ca II emission line strengths show the positive correlation, and are located on the extensions of the superflare stars. In summary, PMS stars have very active chromosphere driven by strong dynamo process due to the fast rotation and the long convection timescale.

In this contribution, I will review a few of the key characteristics of the stellar populations and interstellar medium (ISM) of high-redshift galaxies as revealed by James Webb Space Telescope (JWST) spectroscopy. Specifically, I will discuss recent evidence for nitrogen enhancement and proposed mechanisms to explain it, the existence of galaxies with very blue UV continuum slopes, and the ionization state of emission-line galaxies. I will then focus on some recent work to understand the connection between ionization parameter, gas density, and metallicity, showing that the gas density is an important factor in modulating the ionization parameter across a large range of redshift.

Ram-pressure stripping (RPS) is a process known to remove gas from satellite galaxies. Recent observational studies have found an increased ratio of active galactic nuclei (AGN) among the population of RPS galaxies compared to regular galaxies in the field. To test whether ram pressure (RP) can trigger an AGN, we perform a suite of hydrodynamical wind-tunnel simulations of a massive (Mstar = 1011 Mȯ) galaxy, with inclusion of star formation, stellar feedback and high resolution up to 39 pc. We find that RP increases the inflow of gas to the galaxy centre, which in turn can result in the enhanced BH accretion, as measured by the Bondi-Hoyle model. We also estimate pressure of outflows from our accretion rates and show that AGN feedback would play an important role on the early stages of stripping, while RP itself is not so strong.

We present a study of the evolution of two types of coronal holes (CHs) in the solar minimum of 24/25, which was preceded by a prolonged minimum of 23/24 and a weak 24 solar cycle. The goal of the study is to clarify whether the behavior of CHs during this period is also unusual? The study is based on the material of observations obtained by SDO/AIA/193. The Heliophysics Events Knowledgebase was used to localize the CHs and calculate their areas. Analysis of the evolution of the areas of polar and non-polar CHs in solar minimum 24/25 revealed a number of features. The hemispheric asymmetry is evident both in solar activity indices and in the localization of maxima of polar and non-polar CH areas. The hemispheric area imbalance is minimal for polar CHs and pronounced in the regions of non-polar CHs and sunspots. This is consistent with the general concept of polar CHs as the main source of the Sun’s dipole magnetic field. The areas of polar CHs significantly exceed the areas of non-polar CHs and make a significant contribution to the total area of all CHs in the solar disk. It is concluded that the dynamics of polar and nonpolar CHs suggests that the 24/25 minimum is rather close to earlier minima than to the 23/24 minimum.

Cosmological simulations predict dark matter shapes that deviate from spherical symmetry. The exact shape depends on the prescription of the simulation and the interplay between dark matter and baryons. This signature is most pronounced in the diffuse galactic haloes that can be observationally probed with planetary nebulae and globular clusters (GCs). The kinematic observations of these halo tracers support intrinsic triaxial shape for the mass generating the gravitational potential. With discrete axisymmetric modelling of GCs as the halo tracers of NGC 5128 we investigate the overall mass distribution of this nearby giant elliptical galaxy. Our modelling approach constrains c200, (M/L)*,B and inclination. We derive a preliminary M200 ∼ 1 × 1012 M⊙ and flattening qDM ∼ 1.3 indicative of prolate/triaxial halo for NGC 5128.

A striking feature of the solar cycle is that at the beginning, sunspots appear around mid-latitudes, and over time the latitudes of emergences migrate towards the equator. The maximum level of activity varies from cycle to cycle. For strong cycles, the activity begins early and at higher latitudes with wider sunspot distributions than for weak cycles. The activity and the width of sunspot belts increase rapidly and begin to decline when the belts are still at high latitudes. However, in the late stages of the cycles, the level of activity, and properties of the butterfly wings all have the same statistical properties independent of the peak strength of the cycles. We have modelled these features using Babcock–Leighton type dynamo model and shown that the toroidal flux loss from the solar interior due to magnetic buoyancy is an essential nonlinearity that leads to all the cycles decline in the same way.

Using the superb capabilities of JWST, we investigate the structure of thin and thick disks in galaxies beyond the local universe for the first time. We found evidence of sequential formation, where most galaxies initially form a thick disk, followed by the formation of a thin disk. Thin disk formation occurred around 8 Gyr ago in high-mass galaxies, earlier than 4 Gyr ago in low-mass galaxies, aligning with the onset of thin disk formation in the Milky Way. We propose that this downsizing thin disk formation—delayed in low-mass galaxies—can be naturally explained by stability-regulated disk formation by evolving gas fractions. As gas fractions decrease over time, turbulence in the gas disk declines, allowing a thin disk to form. High-mass galaxies, which efficiently convert gas into stars, achieve lower gas fractions, supporting earlier thin disk formation.

The REBELS ALMA large program has obtained, to date, the largest number of [C ii] and dust continuum observations of massive galaxies at z 6-8. We present results from a now complete JWST NIRSpec/IFU program (GO-1626, PI Stefanon) targeting 12 of these galaxies at 0.6-5.3μm. Due to the incredible sensitivity of the NIRSpec prism, key optical emission lines between [O ii] and [S ii] are detected for the majority of the sample, enabling metallicity constraints from a range of different calibrations. One surprising finding of this dataset is the near-solar oxygen abundances for several of these galaxies. We focus on an extension of the mass-metallicity relations at high-z to higher stellar masses, in comparison to the typical galaxies observed in e.g., JADES and CEERS. These relations provide fundamental information on how stellar mass is assembled in galaxies, and how star formation enriches and dilutes the interstellar medium.

Ionized nebulae are key to understanding the chemical composition and evolution of the Universe. Among these nebulae, H ii regions and planetary nebulae are particularly important as they provide insight into the present and past chemical composition of the interstellar medium, along with the nucleosynthetic processes involved in the chemical evolution of the gas. However, the heavy-element abundances derived from collisionally excited lines (CELs) and recombination lines (RLs) do not align. This longstanding abundance discrepancy problem calls into question our absolute abundance determinations. Which of the lines (if any) provides the correct heavy element abundances? Recently, it has been shown that there are temperature inhomogeneities concentrated within the highly ionized gas of the H ii regions, causing the reported discrepancy. However, planetary nebulae do not exhibit the same trends as the H ii regions, suggesting a different origin for the abundance discrepancy. In this proceedings, we briefly discuss the state-of-the-art of the abundance discrepancy problem in both H ii regions and planetary nebulae.

The number density of extragalactic 21-cm radio sources as a function of their spectral line-widths – the H i width function (H i WF) – is a tracer of the dark matter halo mass function. The ALFALFA 21-cm survey measured the H i WF in northern and southern Galactic fields finding a systematically higher number density in the north; an asymmetry which is in tension with Λ cold dark matter models which predicts the H i WF should be identical everywhere if sampled in sufficiently large volumes. We use the Sibelius-DARK N-body simulation and semi-analytical galaxy formation model GALFORM to create mock ALFALFA surveys to investigate survey systematics. We find the asymmetry has two origins: the sensitivity of the survey is different in the two fields, and the algorithm used for completeness corrections does not fully account for biases arising from spatial galaxy clustering. Once survey systematics are corrected, cosmological models can be tested against the H i WF.

The combination of kinematic and chemical information from Galactic stars has revealed in great detail the structure, dynamics and history of our own Galaxy. In external galaxies, it is impossible to map the distribution of individual stars, but high signal-to-noise integral field unit (IFU) spectroscopy data at various wavelengths, together with sophisticated dynamical models, give us the opportunity to gather information on the structure, dynamics and formation history of these systems. The Schwarzschild method models galaxies through the superposition of stellar orbits, and is equipped to deal with very detailed kinematic measurements, allowing us to take full advantage of high-quality IFU datasets of nearby galaxies. Here we present an implementation of this method called DYNAMITE. We provide an overview of the modelling technique, introduce applications to observations and simulations, and anticipate our future plans for DYNAMITE.

Gaia EDR3 has provided proper motions of Milky Way (MW) dwarf galaxies with an unprecedented accuracy, which allows us to investigate their orbital properties. We found that the total energy and angular momentum of MW dwarf galaxies are much larger than that of MW K-giant stars, Sagittarius stream stars and globular clusters. It suggests that many MW dwarf galaxies have had a recent infall into the MW halo. We confirmed that MW dwarf galaxies lie near their pericenters, which suggests that they do not behave like satellite systems derived from Lambda-Cold-Dark-Matter cosmological simulations. These new results require revisiting the origin of MW dwarf galaxies, e.g., if they came recently, they were likely to have experienced gas removal due to the ram pressure induced by MW’s hot gas, and to be affected by MW tides. We will discuss the consequences of these processes on their mass estimation.

We do know that planetary nebulae (PNe) are ionized gaseous clouds of material ejected by evolved dying stars. The intense ultraviolet radiation field of these stars leads to the dissociation of the cold molecular gas and then to the ionization/excitation of the resultant atomic gas. The chemical composition, ionization structure, physical conditions and formation process of nebular shells, rims, and halos are well comprehended. On the contrary, the origin of low-ionization structures (LISs) frequently found in PNe break the overall picture, and it still remains poorly understood. The latest discoveries of molecular hydrogen (H2) in LISs have changed how we think about their origin. Besides the detection of H2 emission, the [Fe ii] 1.644μm and [C i] 8727Å lines have also been detected in LISs. These results add new pieces to the puzzling problem of LISs opening a new window to enrich our knowledge and understanding on these microstructures.

Classical and recurrent novae are luminous eruptions taking place in binary star systems in which a white dwarf accretes material from a non-degenerate stellar companion. After the nova event, a shell of gas is expelled and expands into the surrounding environment at hundreds to thousands of km s−1. This shell, the so-called nova remnant, experiences interactions with the binary system, the accretion disk, the surrounding environment, and very notably with continuous winds from the white dwarf powered by radiation from nuclear burning on its surface. The similarities with the formation of planetary nebulae are obvious, yet the shaping of nova remnants occurs on much shorter time-scales. This results in the prevalent round to mild elliptical 3D shape of nova remnants. Here we describe the morphology, kinematics and dynamics of nova remnants based on our multi-epoch imaging and long-slit and integral field spectroscopic studies and compare them with those of planetary nebulae.

The study of resolved stellar populations in the nearest galaxies, or “near-field cosmology”, provides key constraints on the physics underlying galaxy formation and evolution. Deep, wide-field surveys of nearby groups of galaxies allow us to characterize the past and ongoing accretion processes shaping the halos of Milky Way-mass galaxies. This field is set to experience significant advancements with the current and future generations of state-of-the-art telescopes.