We study the stellar mass-gas metallicity relation (MZR) which shows a significant scatter for a fixed stellar mass. By defining global environments, nodes, filaments, and voids within the Horizon Run 5 cosmological hydrodynamical simulation, we explore when and where the enrichment of galaxies occurs, analysing key evolution parameters such as star-formation rate and changes in gas-fraction and gas-metallicity per unit time. At high redshift (z > 4.5), there are minimal deviations from the MZR due to environment, however, larger deviations emerge as redshift decreases. Low stellar mass galaxies in nodes, M-star < 10(9.8) M-circle dot, start showing deviations at z = 3.5, whilst other environments do not. For, z < 2, filaments and voids begin to show deviations above and below the MZR, respectively. By z = 0.625, the last epoch of HR5, deviations exist for all stellar masses and environments, with a maximum value of 0.13 dex at M-star approximate to 10(9.35) M-circle dot, between the median gas metallicities of node and void galaxies. To explain this environmental variance we discuss gas accretion, AGN, ram-pressure-stripping and strangulation as regulators of Z(g). Concurrently, at high metallicities, for z < 2, while massive galaxies in nodes show increasing Z(g) and decreasing [O/Fe], void galaxies show a turnover where Z(g) falls with decreasing [O/Fe]. This directly points to the importance of cold-gas accretion in retaining lower Z(g) in massive void galaxies for z < 2, whilst its absence in nodes allowed Z(g) to access higher values.

Thin stellar streams, such as those resulting from the tidal disruption of globular clusters, have long been known and used as probes of the gravitational potential of our Galaxy, both its visible and dark contents. In particular, the presence of under-density regions, or gaps, along these streams is commonly interpreted as being due to the close passage of dark matter sub-halos. In this work, we investigate the perturbations induced on streams by the passage of dense stellar systems, such as globular clusters themselves, to test the possibility that they may cause the formation of gaps as well. In particular, we focus on the study of the stream of Palomar 5, a well-known globular cluster in the Galactic halo, which has particularly long tidal tails. For this purpose, we used a particle-test code to simulate Palomar 5's tidal tails when subjected to the Galaxy's gravitational field plus its whole system of globular clusters. Our study shows that the tails of Palomar 5 can be strongly perturbed by the close passage of other clusters, in particular of NGC 2808, NGC 7078, NGC 104, and that these perturbations induce the formation of gaps in the tails. These results show that globular clusters are capable of inducing gaps in streams–as other baryonic components such as giant molecular clouds and the galactic bar have been shown to do in other works. Therefore, when searching to construct the distribution function of dark matter sub halos within the Milky Way, the gap contribution from globular clusters must be included.

The variation of metal production over time and its dilution in the interstellar medium depend on the star formation and gas accretion rates. Measuring age-chemistry relations across the Milky Way disk provides key constraints on the gas accretion and star formation histories, and offers insight into the birth locations of stars. We present a study based on a sample of nearly 30000 dwarf stars from the APOGEE DR17 survey within 2 kpc of the Sun, for which we measure accurate ages. Various parameter combinations are tested to optimize stellar age determination from isochrones. The resulting age-chemistry relations for a selected subsample of 12000 stars are interpreted with the aid of a chemical evolution model. The data reveal a well-defined, tight thick disk sequence, characterized by high [alpha/Fe], subsolar metallicities, and ages older than 8 Gyr. The thin disk, with lower [alpha/Fe] and younger ages, exhibits a wide spread in metallicity at all ages, with apparent structures. Dividing the sample by guiding radius into inner, intermediate, and outer disks shows distinct chemical evolution patterns. The inner disk displays a monotonic, homogeneous chemical evolution with little dispersion, while the outer disk shows little metallicity increase over the past 8 Gyr. The solar neighborhood appears as a mixture, not only due to stellar migration but also because the chemical evolution of the ISM in this intermediate region results from the mixing of gas from the inner and outer disks. In particular, we demonstrate that the solar vicinity experienced a decrease in the mean ISM metallicity 7-9 Gyr ago. A plausible explanation involves a radial inflow of lower-metallicity gas from the outer disk at that time, which diluted the gas leftover by the thick disk formation, contributing to the observed metallicity gradient in the intermediate region.

We investigate the formation history of intrahalo light (IHL) using the high-resolution (∼1 kpc), large-scale (∼1 Gpc) cosmological hydrodynamical simulation Horizon Run 5 (HR5). IHL particles are identified by carefully considering both their binding energies and positions with respect to the tidal radii of individual galaxies. By analyzing more than 1200 galaxy groups and clusters with ≳10 ^13 M _⊙ and tracing their individual IHL particles back in time, we classify the origin of each IHL particle at each epoch, based on the status of the originating galaxy, into one of three categories: brightest halo galaxy (BHG) formation/merger, satellite galaxy stripping, and preprocessing. Our study reveals that IHL production through BHG formation/merger is the predominant production channel, contributing over 60% of the total IHL mass across all redshifts. The second most significant IHL production channel is preprocessing, providing more than 20% in the final HR5 snapshot. Stripping is negligible at z > 4 but becomes gradually more important as the halos mature at z < 4. Finally, we verify that the IHL production through the disruption of dwarf galaxies and in situ formation is negligible, contributing less than ∼3% and ∼0.5% to the total IHL production, respectively.

Context. The variations in the production of metals with time and their dilution in the interstellar medium are a function of the star formation and gas accretion rates. Thus, measuring age-chemistry relations across the Milky Way disk is our most important constraint on the gas accretion history, the past star formation history, but also provides crucial information on the place of birth of the stars. Aims. We present a new study of these relations based on a sample of almost 30 000 dwarf stars from the APOGEE survey DR17 within 2 kpc of the Sun for which we measured accurate ages. Methods. Various combinations of parameters were tested to find the best determination of stellar ages from stellar isochrones. The resulting age-chemistry relations for a selected subsample of 12 000 stars were interpreted with the help of a chemical evolution model. Results. The data show a very well-defined and tight thick disk sequence, characterized by high [alpha/Fe] content, subsolar metallicities, and ages greater than 8 Gyr. The thin disk, characterized by a lower alpha-content and by ages younger than 8 Gyr, shows a large metallicity spread at all ages, with apparent structures. When detailed in inner (R-guide < 7 kpc), intermediate (7.6 kpc 10 kpc) disk using guiding radius, the data show distinct chemical evolutions. We find in particular that the inner disk is typical of a monotonic, homogeneous evolution, with little dispersion, while the outer disk shows little increase in metallicity over the last 8 Gyr. The evolution at the solar radius seems to be a mix not only because some stars have migrated from the inner and outer disk, but more importantly because the chemical evolution of the interstellar medium (ISM) in the intermediate region results from mixed gas from the inner and outer disk. In particular, we demonstrate that in the solar neighborhood the evolution shows a decrease in the mean metallicity of the ISM that occurred 7-9 Gyr ago. One possible explanation assumes a radial inflow from the outer disk of lower metallicity gas at this epoch that diluted the gas left over by the formation of the thick disk, giving rise to the metallicity gradient observed in this intermediate region.

We test whether Lyα emitters (LAEs) and Lyman-break galaxies (LBGs) can be good tracers of high- z large-scale structures, using the Horizon Run 5 cosmological hydrodynamical simulation. We identify LAEs using the Ly α emission line luminosity and its equivalent width, and LBGs using the broadband magnitudes at z ∼ 2.4, 3.1, and 4.5. We first compare the spatial distributions of LAEs, LBGs, all galaxies, and dark matter around the filamentary structures defined by dark matter. The comparison shows that both LAEs and LBGs are more concentrated toward the dark matter filaments than dark matter. We also find an empirical fitting formula for the vertical density profile of filaments as a binomial power-law relation of the distance to the filaments. We then compare the spatial distributions of the samples around the filaments defined by themselves. LAEs and LBGs are again more concentrated toward their filaments than dark matter. We also find the overall consistency between filamentary structures defined by LAEs, LBGs, and dark matter, with the median spatial offsets that are smaller than the mean separation of the sample. These results support the idea that the LAEs and LBGs could be good tracers of large-scale structures of dark matter at high redshifts.

One intriguing approach for studying the dynamical evolution of galaxy clusters is to compare the spatial distributions among various components such as dark matter, member galaxies, gas, and intracluster light (ICL). Utilizing the recently introduced weighted overlap coefficient (WOC), we analyze the spatial distributions of components within 174 galaxy clusters ( M tot > 5 × 10 13 M ⊙ , z = 0.625) at varying dynamical states in the cosmological hydrodynamical simulation Horizon Run 5. We observe that the distributions of gas and the combination of ICL with the brightest cluster galaxy (BCG) closely resembles the dark matter distribution, particularly in more relaxed clusters, characterized by the half-mass epoch. The similarity in spatial distribution between dark matter and BCG+ICL mimics the changes in the dynamical state of clusters during a major merger. Notably, at redshifts >1, BCG+ICL traced dark matter more accurately than the gas. Additionally, we examined the one-dimensional radial profiles of each component, which show that the BCG+ICL is a sensitive component revealing the dynamical state of clusters. We propose a new method that can approximately recover the dark matter profile by scaling the BCG+ICL radial profile. Furthermore, we find a recipe for tracing dark matter in unrelaxed clusters by including the most massive satellite galaxies together with the BCG+ICL distribution. Combining the BCG+ICL and the gas distribution enhances the dark matter tracing ability. Our results imply that the BCG+ICL distribution is an effective tracer for the dark matter distribution, and the similarity of the spatial distribution may be a useful probe of the dynamical state of a cluster.

BIFROST, an upcoming instrument for the VLTI, is part of the Asgard Suite, a VLTI visitor instrument. It comprises two spectrograph arms that are optimised for wavelength range of 1- 1.75 mu m (fed by a fiber that is placed on-axis for fringe tracking/monitoring) and 1-1.3 mu m (fed by a fiber that can positioned either onaxis or off-axis to observe a faint target) wavelength range, respectively. Volume phase holographic gratings (VPHGs) are employed to achieve high spectral resolving power up to 25,000 and a throughput above 75% for all dispersing elements. In this contribution, we discuss the optical and optomechanical design of the spectrographs, as well as a new relay optics design that minimizes the thermal background, with a factor 4 reduction in thermal background compared to the non-relay optics design. We will also present the first lab results obtained with the YJH spectrograph.

BIFROST is a new Y+J and H band beam combiner for the VLTI, and part of the Asgard suite of visitor instruments. BIFROST will unlock a new parameter space at the VLTI by including the astronomical J band and high spectral resolution (up to R approximate to 25,000). It will also have the ability to simultaneously observe on- and off-axis targets. BIFROST's beam combiner will be an integrated optics chip, fed by single mode optical fibers. BIFROST therefore requires a light injection module to couple the starlight from free space in the VLTI laboratory into the single mode fibers. The light injection module of BIFROST is also responsible for redirecting the starlight towards the fiber couplers; removing the optical path difference between the beams; co-phasing BIFROST with the rest of the Asgard suite; splitting the light off for the off-axis field; selecting the pointing of the off-axis field; optimizing the injection into the fibers; co-phasing the on- and off-axis light; supporting the passage of the full two arcsecond diameter field of view and providing sufficient space for additional BIFROST pre-injection optics. In this contribution we detail the novel design of the BIFROST light injection module, highlighting how it achieves this functionality using as few optics as possible. We also present Zemax Opticstudio tolerancing analysis, demonstrating the feasibility of building this design in the laboratory.

BIFROST is the short-wavelength, high-spectral resolution instrument in the Asgard Suite of VLTI visitor instruments. It will be optimized for spectral line studies in the Y, J, and H bands (1.05-1.75 μm) that include many strong lines & molecular features. In this presentation, we outline the BIFROST science drivers that have guided our design choices and map them against the operational modes that are being implemented. We give an overview about the status of the project and the milestones from the ongoing integration & testing phase in Exeter to shipping & commissioning on Paranal, scheduled for 2025 and 2026. We review the BIFROST subsystems and discuss how they interface with the broader Asgard Suite. Finally, we outline other BIFROST-related activities pursued by our group that are intended for implementation in BIFROST as part of future upgrades.

We propose a new method for finding galaxy protoclusters that is motivated by structure formation theory and also directly applicable to observations. We adopt the conventional definition that a protocluster is a galaxy group whose virial mass M _vir < M _cl at its epoch, where M _cl = 10 ^14 M _⊙ , but would exceed that limit when it evolves to z = 0. We use the critical overdensity for complete collapse at z = 0 predicted by the spherical top-hat collapse model to find the radius and total mass of the regions that would collapse at z = 0. If the mass of a region centered at a massive galaxy exceeds M _cl , the galaxy is at the center of a protocluster. We define the outer boundary of a protocluster as the zero-velocity surface at the turnaround radius so that the member galaxies are those sharing the same protocluster environment and showing some conformity in physical properties. We use the cosmological hydrodynamical simulation Horizon Run 5 ( HR5 ) to calibrate this prescription and demonstrate its performance. We find that the protocluster identification method suggested in this study is quite successful. Its application to the high-redshift HR5 galaxies shows a tight correlation between the mass within the protocluster regions identified according to the spherical collapse model and the final mass to be found within the clusters at z = 0, meaning that the regions can be regarded as the bona fide protoclusters with high reliability. We also confirm that the redshift-space distortion does not significantly affect the performance of the protocluster identification scheme.

The BIFROST instrument is poised to revolutionize high-spectral resolution interferometry at the VLTI by extending the accessible wavelength range down to 1.0 mu m, encompassing the Y, J, and H bands. In this paper, we discuss the optical design for BIFROST's pre-injection optics which correct for birefringence effects and longitudinal dispersion between the different beam lines. We present the optomechanical design for the light injection module that compresses the beams and injects them into single-mode fibres, while maintaining the full field-of-view of the VLTI auxiliary or unit telescopes. Our fibre switching module will allow for the injection of light into photonic devices optimised for different wavebands or applications. Finally, we outline our integration & alignment strategy and present the first characterisation results obtained in the optics lab at the University of Exeter.

ESO's Very Large Telescope Interferometer has a history of record-breaking discoveries in astrophysics and significant advances in instrumentation. The next leap forward is its new visitor instrument, called Asgard. It comprises four natively collaborating instruments: HEIMDALLR, an instrument performing both fringe tracking and stellar interferometry simultaneously with the same optics, operating in the K band; Baldr, a Strehl optimizer in the H band; BIFROST, a spectroscopic combiner to study the formation processes and properties of stellar and planetary systems in the Y-J-H bands; and NOTT, a nulling interferometer dedicated to imaging nearby young planetary systems in the L band. The suite is in its integration phase in Europe and should be shipped to Paranal in 2025. In this article, we present details of the alignment and calibration unit, the observing modes, the integration plan, the software architecture, and the roadmap to completion of the project.