The Wide-field Spectroscopic Telescope (WST) is a concept for a dedicated 12-m spectroscopic survey facility designed to address some of the most important questions in astrophysics in the 2040s. The WST will provide unprecedented spectroscopic survey capabilities by operating simultaneously over a 2-degree diameter field of view with 54 low-resolution spectrographs fed by 30,000 fibres, 8-16 high-resolution spectrographs fed by 2,000 fibres, and a large panoramic low-resolution integral-field spectrograph. Supported by Horizon Europe, the concept study has refined the science cases, facility architecture, operations model, sustainability strategy, and technology roadmap. The resulting reference design demonstrates that the WST is both scientifically transformative and technically feasible, while identifying the developments required to mitigate the remaining risks. The WST is designed as an ESO flagship facility for the post-ELT construction era and a key spectroscopic complement to the major imaging, time-domain, and multi-messenger facilities of the coming decades.

We revisit the relation between disc stellar mass and disc velocity dispersion (M_*-σ_e) and extend it to thin and thick subcomponents using orbit-based dynamical models of 161 SAMI galaxies and counterpart measurements for 31 disc galaxies in the NewHorizon simulation. On the observational side, we apply Schwarzschild orbit superposition to recover orbital circularity distributions and component kinematics. On the simulation side, we sample thin and thick discs by circularity and, separately, by stellar age to test classification dependence. Our analysis reveals three main results. (1) Discs follow a tight M_*-σ_e relation, nearly parallel to the bulge relation. (2) For both circularity- and age-based definitions, the thick-disc component is systematically hotter than the thin-disc component, and the thin-thick dispersion ratio varies only weakly with mass. However, age cuts yield a smaller kinematic contrast, indicating that stellar age and orbital circularity do not map one-to-one and that no single global age threshold reproduces the circularity-based split. (3) Method and data systematics are present, with Schwarzschild modelling returning slightly higher disc σ_e than spectroscopic bulge-disc decompositions, and simulated discs showing lower σ_e at fixed mass than observed. All these results are consistent with a baseline set by vertical-equilibrium scalings, with secular heating accumulating over time and modulating the dispersion at fixed mass. Occasional minor interactions may add localised heating but do not appear to be essential for explaining the qualitative, global trends reported here. Future tests with chemo-dynamical modelling and higher-resolution, chemistry-tracking simulations will provide stronger constraints on disc substructures in external galaxies.

The relationship between a galaxy's specific angular momentum j and its mass M, parameterised by j ∝ M^α and known as the Fall relation, has emerged as a fundamental scaling relation reflecting key physical and morphological properties of galaxies. This relation has been well studied for galaxies with masses above 10^9 M_⊙. However, whether or not it holds for the low-mass dwarf galaxies, especially given their varied morphologies, remains uncertain. Here we use Hα observations of 49 star-forming dwarf galaxies from the SHαDE survey, as well as 20 high-mass `control' galaxies, to investigate the stellar j_*-M_* relation down to masses below 10^6 M_⊙. We find that the star-forming dwarf galaxies follow the same j_*-M_* relation as high-mass disk-like galaxies, with α= 0.53 ±0.4, demonstrating that the relation holds across 5 orders of magnitude in mass. We then select a matching sample from the IllustrisTNG cosmological simulation and create mock observations resembling the SHαDE survey. We find that the simulated dwarf galaxy population follows the extrapolated j_*-M_* relation with a flattening and significant scatter towards lower j_* values. Following the evolution of these galaxies, we find that dwarf galaxies experience a gradual loss in j_* with time, while high-mass galaxies experience a sudden jump in j_* before settling into a stable state. This dynamical evolution leads to a redshift dependence in α, with α= 0.45 at z = 2 and 0.55 at z = 0. Despite the apparent simplicity in the present-day j_*-M_* relation over a wide mass range, the evolution of j leading to this relation is complex and dynamic.

Abstract The stellar initial mass function (IMF) is a fundamental ingredient in galaxy evolution, linking observed integrated light to stellar masses, star-formation rates, and chemical enrichment histories. Constraining the full IMF shape beyond the Milky Way remains challenging, as most studies focus either on the low-mass end of quiescent galaxies or the high-mass end of star-forming galaxies. Here, we present the first simultaneous analysis of both ends of the IMF in 214 star-forming galaxies from the Hector survey ( z tilde z ∼ $z \sim$ 0.01–0.07). We estimate the low-mass end slope ( alpha Subscript normal l normal o normal w α l o w $\alpha_{\mathrm{low}}$ ) using a stellar population approach that fits IMF-sensitive absorption features with extended star formation histories, while the high-mass end slope ( alpha Subscript normal h normal i normal g normal h α h i g h $\alpha_{\mathrm{high}}$ ) is derived via the Kennicutt diagnostic, which compares the observed H alpha α $\alpha$ equivalent width and g minus r g − r $g-r$ colour with stellar population synthesis model predictions. We find substantial diversity in IMF shapes, with galaxies spanning combinations of bottom-heavy/light and top-heavy/light slopes. A weak but statistically robust correlation between the low- and high-mass IMF slopes is observed, but partial correlation analysis indicates that this apparent link is largely driven by their mutual dependence on stellar mass and metallicity. Both IMF slopes show significant correlations with stellar mass, star formation activity (traced by H alpha α $\alpha$ luminosity and surface density), and stellar metallicity ([M/H]). In general, higher stellar mass, stronger star formation activity, and higher metallicity are associated with both bottom-heavy and top-heavy IMFs. We find that the full IMF shape seems to be modulated by total stellar mass. Partial correlation analysis reveals that alpha Subscript normal l normal o normal w α l o w $\alpha_{\mathrm{low}}$ is primarily driven by [M/H], whereas alpha Subscript normal h normal i normal g normal h α h i g h $\alpha_{\mathrm{high}}$ is mainly linked to stellar mass and recent star formation. Because alpha Subscript normal l normal o normal w α l o w $\alpha_{\mathrm{low}}$ traces the IMF over long-term averages and alpha Subscript normal h normal i normal g normal h α h i g h $\alpha_{\mathrm{high}}$ captures only recent ( less than or equivalent to 10 ≲ 10 $\lesssim10$ Myr) star formation, the processes shaping each end likely occur over different and possibly decoupled timescales. Our findings challenge the universality of the IMF and emphasise the need for galaxy evolution and stellar population models to incorporate a flexible IMF prescription. Accounting for these variations is essential to build an IMF-consistent picture of galaxy evolution across cosmic time.

To explore the environmental mechanisms causing quenching in nearby star-forming galaxies, we study the variation with local and large-scale environments of a star formation concentration index, C-index equivalent to log (r(50,H alpha)/r(50,cont)), that traces the spatially resolved distribution of H alpha emission. Our analysis combines (i) GAMA spectroscopic redshift survey data to optically select galaxy groups and reconstruct the cosmic web, (ii) eROSITA data to identify X-ray-emitting groups, and (iii) SAMI Galaxy Survey data to characterise spatially resolved star formation. We find that galaxies in X-ray + optical groups exhibit the lowest median C-index and the highest fraction of centrally concentrated star-forming galaxies relative to optical groups and the field (independently of group or stellar mass). Star-forming galaxies in more X-ray luminous groups at fixed dynamical mass show more concentrated star formation. At large scales, nodes show the lowest median C-index and the highest fraction of centrally concentrated star-forming galaxies relative to filaments and voids, which have similar C-index distributions. C-index correlates most strongly with the distance to the closest node, leaving no significant role for other local or large-scale environment metrics. Finally, regular star-forming galaxies tend to have spins aligned parallel to filaments, consistent with smooth gas accretion, while centrally concentrated galaxies tend have spins aligned perpendicular to filaments, likely driven by mergers and associated with bulge growth. These results suggest that multi-scale environmental processes, i.e. locally and at large-scale, act to concentrate star formation toward galaxy centres, via gas-related mechanisms in nodes and ram-pressure stripping in X-ray + optical groups.

The stellar initial mass function (IMF) is a fundamental ingredient in galaxy evolution, linking observed integrated light to galaxy properties. Constraining the full IMF shape beyond the Milky Way remains challenging, as most studies focus either on the low-mass end of quiescent galaxies or the high-mass end of star-forming galaxies. Here we present the first simultaneous analysis of both ends of the IMF in 214 star-forming galaxies from the Hector survey. We estimate the low-mass end slope using a stellar population approach that fits IMF-sensitive absorption features with extended star formation histories, while the high-mass end slope is derived via the Kennicutt diagnostic, which compares the observed H-alpha equivalent width and g-r colour with stellar population synthesis model predictions. We find substantial diversity in IMF shapes and a weak but statistically robust correlation between the low- and high-mass IMF slopes. Both IMF slopes show significant correlations with stellar mass, star formation activity, and stellar metallicity ([M/H]). In general, higher stellar mass, stronger star formation activity, and higher metallicity are associated with both bottom-heavy and top-heavy IMFs. Partial correlation analysis reveals that the low-mass end slope is primarily driven by [M/H], whereas the high-mass end is mainly linked to stellar mass and recent star formation. Because the low-mass end slope traces the IMF over long-term averages and the high-mass end slope captures only recent star formation, the processes shaping each end likely occur over different and possibly decoupled timescales. Our findings challenge the universality of the IMF and emphasise the need for galaxy evolution and stellar population models to incorporate a flexible IMF prescription. Accounting for these variations is essential to build an IMF-consistent picture of galaxy evolution across cosmic time.

The spin parameter λ_R_e is a proxy for the specific stellar angular momentum of galaxies and is a useful metric for classifying kinematic morphology. This study aims to quantify the relative importance of galaxy properties in explaining λ_R_e, using data from the Sydney-AAO Multi-object Integral-field spectrograph (SAMI) Galaxy Survey. We apply partial correlation analysis and partial least squares regression to assess the relative contributions of different parameters in explaining λ_R_e. We find that morphology indicators, bulge-to-total ratio within one effective radius (B/T_e) and ellipticity (ε_e), show the strongest correlations with λ_R_e and play a leading role in the regression analysis. This result statistically confirms the established fast-rotator sequence, in which fast-rotating early-type galaxies form a continuous structural and kinematic sequence with spiral galaxies, with λ_R_e decreasing as bulge prominence increases. The light-weighted age and stellar mass also exhibit significant correlations, but their contributions are secondary to the morphology indicators in multivariate analyses. We also examine whether the observed trends in λ_R_e can be reproduced using galaxy properties alone. The morphology indicators (B/T_e, ε_e) reproduce the overall distribution of observed λ_R_e with a scatter of about 0.12, while the inclusion of Age_LW and M_⋆ provides only modest additional improvement. However, these relations do not reproduce the slow-rotator regime well. Overall, our results show that photometric structural parameters best explain λ_R_e and suggest that statistical inference of galaxy spin from non-IFS observables may become feasible with improved models and a broader set of parameters.

The cosmological principle asserting the large-scale uniformity of the Universe is a testable assumption of the standard cosmological model. We explore the constraints on anisotropic expansion provided by measuring directional variation in the Hubble constant, H 0 , derived from differential zeropoint measurements of the Tully-Fisher distance estimator. We fit various models for directional variation in H 0 using the Tully-Fisher dataset from the all-sky Cosmicflows-4 catalog. The best-fit dipole variation has an amplitude of 0.063 ± 0.016 mag in the direction ( ℓ , b ) = (142 ± 30°,52 ± 10°). If this were due to anisotropic expansion it would imply a 3% variation in H 0 (i.e. Δ H 0 = 2.10 ± 0.53 km s -1 Mpc -1 if H 0 = 70 km s -1 Mpc -1 ) with a significance of 3.9 σ . A model including this H 0 dipole is only weakly favored relative to a model with a constant H 0 and a bulk motion of the volume sampled by Cosmicflows-4 consistent with the standard ΛCDM cosmology. However, we show from simulations that the expected Tully-Fisher data from the WALLABY and DESI surveys should allow detection of a 1% H 0 dipole anisotropy at 5.8 σ confidence and distinguish it from the typical bulk flow predicted by ΛCDM over the volume of these surveys.

The Hector Galaxy Survey is a new optical integral field spectroscopy (IFS) survey currently using the Anglo-Australian Telescope to observe up to 15 000 galaxies at low redshift ( $z \lt 0.1$ ). The Hector instrument employs 21 optical fibre bundles feeding into two double-beam spectrographs, AAOmega and the new Spector spectrograph, to enable wide-field multi-object IFS observations of galaxies. To efficiently process the survey data, we adopt the data reduction pipeline developed for the SAMI Galaxy Survey, with significant updates to accommodate Hector's dual-spectrograph system. These enhancements address key differences in spectral resolution and other instrumental characteristics relative to SAMI and are specifically optimised for Hector's unique configuration. We introduce a two-dimensional arc fitting approach that reduces the root-mean-square (RMS) velocity scatter by a factor of 1.2-3.4 compared to fitting arc lines independently for each fibre. The pipeline also incorporates detailed modelling of chromatic optical distortion in the wide-field corrector, to account for wavelength-dependent spatial shifts across the focal plane. We assess data quality through a series of validation tests, including wavelength solution accuracy (1.2-2.7 km s $<^>{-1}$ RMS), spectral resolution (FWHM of 1.2-1.4 & Aring; for Spector), throughput characterisation, astrometric precision ( $\lesssim$ 0.03 arcsec median offset), sky subtraction residuals (1-1.6% median continuum residual), and flux calibration stability (4% systematic offset when compared to Legacy Survey fluxes). We demonstrate that Hector delivers high-fidelity, science-ready datasets, supporting robust measurements of galaxy kinematics, stellar populations, and emission-line properties and provide examples. Additionally, we address systematic uncertainties identified during the data processing and propose future improvements to enhance the precision and reliability of upcoming data releases. This work establishes a robust data reduction framework for Hector, delivering high-quality data products that support a broad range of extragalactic studies.

We explore the impact of the large-scale 3D density field, as defined by deep, wide-field galaxy surveys, on stellar spin (lambda(Re)) and the distributions of fast and slow rotators. We use the Galaxy And Mass Assembly spectroscopic redshift survey to reconstruct the cosmic web and obtain spatially resolved stellar kinematics from the SAMI (Sydney-AAO Multi-object Integral-field spectrograph) Galaxy Survey. Among various local and large-scale environment metrics, the distance to the closest filament (D-fil) correlates most significantly with lambda(Re), but it is secondary to the more dominant roles played by stellar age and mass. Fast rotators tend to have increasing lambda(Re) going from nodes to filaments to voids, independently of mass. Slow rotators and mass-matched fast rotators are found to have significantly different distributions of large-scale environment metrics but consistent distributions of local environment metrics. About 95 per cent of slow rotators have D-fil <= 2 Mpc, while covering broader ranges (similar to fast rotators) in distance to nodes and voids, local galaxy density, halo mass, and position with respect to the halo. At fixed mass, the fraction of slow rotators, f(SR), increases for smaller D-fil, especially for massive galaxies. While controlling for age or mass, only galaxies very close to filaments and nodes show a significant impact of local environment on f(SR). Our results demonstrate that the cosmic web leaves an imprint on galactic spin amplitudes, and that pre-processing by mergers occurring within filaments is likely to be an important physical mechanism for the formation of slow rotators before they reach nodes.

We highlight the potential benefits of a synergistic use of SKAO and ESO facilities for galaxy evolution studies, focusing on the role that ESO spectroscopic surveys can play in supporting next-generation radio continuum and atomic hydrogen (HI) surveys. More specifically we illustrate the role that currently available or soon to be operational ESO multiplex spectrographs can play for three classes of projects: large/deep redshift survey campaigns, integral field unit/Atacama Large Millimeter/submillimeter Array (IFU/ALMA) surveys of selected regions of sky, and IFU/ALMA follow-ups of selected samples. We conclude with some general recommendations for an efficient joint exploitation of ESO-SKAO surveys.

By the 2040s, several all-sky surveys will have transformed our view of the large-scale structure. However, one of the major outstanding questions in astrophysics will remain: understanding how galaxies acquire and evolve their angular momentum and how this connects to the cosmic web. Measuring the alignments between galaxy spins and cosmic filaments across cosmic time, and understanding what this reveals about galaxy evolution, requires surveys that also characterise intrinsic alignments, i.e. correlations in galaxy shapes produced by the cosmic web itself rather than by lensing. Intrinsic alignments are a major source of systematic error in weak-lensing measurements of the fundamental parameters of the Universe. Addressing both questions together will necessitate new types of MOS surveys that combine kinematic information with high-completeness redshifts down to at least 24-25mag. To achieve our science goals, we require a new generation of wide-field spectroscopic facilities that can obtain spin-filament alignment measurements for millions of galaxies while simultaneously delivering sub-Mpc resolution of the cosmic web and spatially-resolved kinematics required to map the spin-filament connection at the level of individual galaxies within their local cosmic environment. Such a program would provide a unique legacy survey of galaxies and cosmic structures from kiloparsec to megaparsec scales, establishing ESO's leadership in bridging the physics of galaxy evolution with the systematic-control requirements for Stage-IV cosmological surveys.

Peculiar velocities are an important probe of the mass distribution in the Universe and the growth rate of structure, directly measuring the effects of gravity on the largest scales and providing a test for theories of gravity. Comparing peculiar velocities predicted from the density field mapped by a galaxy redshift survey with peculiar velocities measured using a distance estimator such as the Tully-Fisher relation yields the growth factor for large-scale structure. We present a method for forward modelling a sample of galaxy magnitudes and velocity widths that simultaneously determines the parameters of the Tully-Fisher relation and the peculiar velocity field. We apply this to the Cosmicflows-4 Tully-Fisher data set, using the peculiar velocities predicted from the 2M++ redshift survey. After validating the method on mock surveys, we measure the product of the growth rate and mass fluctuation amplitude to be f sigma(8) = 0.35 +/- 0.03 at an effective redshift of z = 0.017. This is consistent at 3 sigma with the Planck CMB prediction, even though the uncertainty does not fully account for all sources of sample variance. We find the residual bulk flow from gravitational influences outside the 2M++ survey volume to be |V| = 227 +/- 11 km s(-1), (l, b) = (303 degrees, -1 degrees) in Galactic polar coordinates and the CMB frame. Using simulations, we show that applying our methodology to the large new sample of Tully-Fisher peculiar velocities expected from the WALLABY H I survey of the southern sky can improve the constraints on the growth rate by a factor of 2-3.

ABSTRACT We investigate the influence of star formation and instantaneous active galactic nuclei (AGN) feedback processes on the ionized gas velocity dispersion in a sample of 1285 emission-line galaxies with stellar masses $\log \, (M_*/\mathrm{ M}_{\odot }) \ge 9$ from the integral-field spectroscopy Sydney-AAO Multi-object Integral-field Galaxy Survey. We fit both narrow- and broad-emission-line components using aperture spectra integrated within one effective radius, while ensuring the elimination of velocity differences between the spectra of individual spaxels. Our analysis reveals that 386 (30 per cent) galaxies can be adequately described using a single-emission component while 356 (28 per cent) galaxies require two (broad and narrow) components. Galaxies characterized by high-mass, elevated star formation rate surface density, or type-2 AGN-like emissions tend to feature an additional broad-emission-line component, leading to their classification as double-component galaxies. We explore the correlations between M* and gas velocity dispersions, highlighting that the prominence of the broad component significantly contributes to elevating the gas velocity dispersion. Galaxies displaying AGN-like emission based on optical definitions show enhanced gas velocity dispersions. In star-forming galaxies, both stellar mass and star-formation rate surface density substantially contribute to the velocity dispersion of the narrow component. Increased star-forming activity appears to elevate the velocity dispersion of the narrow component. The broad component exhibits a weaker dependence on stellar mass and is primarily driven by galactic outflows. We suggest that strong star-forming activity leads to the formation of a broad-emission-line component, but the impact on inflating gas velocity dispersion is moderate. On the other hand, AGN-driven outflows appear to be a more important contributor to the elevated velocity dispersion of the ionized gas.

We measure the properties of optical emission lines in multiple locations across the Large Magellanic Cloud (LMC) using the Australian National University 2.3-metre telescope and the WiFeS integral field spectrograph. From these measurements we interpolate maps of the gas phase metallicity, extinction, Halpha radial velocity, and Halpha velocity dispersion across the LMC. The LMC metallicity maps show a complex structure that cannot be explained by a simple radial gradient. The bright HII region 30 Doradus stands out as a region of high extinction. The Halpha and HI gas radial velocities are mostly consistent except for a region to the south and east of the LMC centre. The Halpha velocity dispersion is almost always higher than the HI velocity dispersion, except in the region that shows the divergence in radial velocity, where the HI velocity dispersion is greater than the Halpha velocity dispersion. This suggests that the HI gas is diverging from the stellar radial velocity, perhaps as a result of inflow or outflow of HI gas. The study of dwarf galaxies like the LMC is important as they are the building blocks of larger galaxies like our own Milky Way. The maps provided in this work show details not accessible in the study of more distant dwarf galaxies.

ABSTRACT We propose an improved comprehensive method for determining the Hubble constant ($H_0$) using the Tully–Fisher relation. By fitting a peculiar velocity model in conjunction with the Tully–Fisher relation, all available data can be used to derive self-consistent Tully–Fisher parameters. In comparison to previous approaches, our method offers several improvements: it can be readily generalized to different forms of the Tully–Fisher relation and its intrinsic scatter; it uses a peculiar velocity model to predict distances more accurately; it can account for all selection effects; it uses the entire data set to fit the Tully–Fisher relation; and it is fully self-consistent. The Tully–Fisher relation zero-point is calibrated using the subset of galaxies with distances from absolute distance indicators. We demonstrate this method on the Cosmicflows-4 catalogue i-band and $W1$-band Tully–Fisher samples and show that the uncertainties from fitting the Tully–Fisher relation amount to only 0.2 km s$^{-1}$ Mpc$^{-1}$. Using all available absolute distance calibrators, we obtain $H_0=73.3$ $\pm$ 2.1 (stat) $\pm$ 3.5 (sys) km s$^{-1}$ Mpc$^{-1}$, where the statistical uncertainty is dominated by the small number of galaxies with absolute distance estimates. The substantial systematic uncertainty reflects inconsistencies between various zero-point calibrations of the Cepheid period–luminosity relation, the tip of the red giant branch standard candle, and the Type Ia supernova standard candle. However, given a reliable set of absolute distance calibrators, our method promises enhanced precision in $H_0$ measurements from large new Tully–Fisher samples such as the WALLABY survey.

We measure the ionized gas velocity dispersions of star-forming galaxies in the MAGPI survey (z similar to 0.3) and compare them with galaxies in the SAMI (z similar to 0.05) and KROSS (z similar to 1) surveys to investigate how the ionized gas velocity dispersion evolves. For the first time, we use a consistent method that forward models galaxy kinematics from z=0 to z=1. This method accounts for spatial substructure in emission line flux and beam smearing. We investigate the correlation between gas velocity dispersion and galaxy properties to understand the mechanisms that drive gas turbulence. We find that in both MAGPI and SAMI galaxies, the gas velocity dispersion more strongly correlates with the star-formation rate surface density (Sigma(SFR)) than with a variety of other physical properties, and the average gas velocity dispersion is similar, at the same Sigma(SFR), for SAMI, MAGPI, and KROSS galaxies. The results indicate that mechanisms related to Sigma(SFR )could be the dominant driver of gas turbulence from z similar to 1 to z similar to 0, for example, stellar feedback and/or gravitational instability. The gas velocity dispersion of MAGPI galaxies is also correlated with the non-rotational motion of the gas, illustrating that in addition to star-formation feedback, gas transportation and accretion may also contribute to the gas velocity dispersion for galaxies at z similar to 0.3. KROSS galaxies only have a moderate correlation between gas velocity dispersion and Sigma(SFR) and a higher scatter of gas velocity dispersion with respect to Sigma(SFR), in agreement with the suggestion that other mechanisms, such as gas transportation and accretion, are relatively more important at higher redshift galaxies.

ABSTRACT We use deep spectroscopy from the SAMI (Sydney-AAO Multi-object Integral) Galaxy Survey to explore the precision of the fundamental plane (FP) of early-type galaxies as a distance indicator for future single-fibre spectroscopy surveys. We study the optimal trade-off between sample size and signal-to-noise ratio (SNR), and investigate which additional observables can be used to construct hyperplanes with smaller intrinsic scatter than the FP. We add increasing levels of random noise (parametrized as effective exposure time) to the SAMI spectra to study the effect of increasing measurement uncertainties on the FP- and hyperplane-inferred distances. We find that, using direct-fit methods, the values of the FP and hyperplane best-fitting coefficients depend on the spectral SNR, and reach asymptotic values for a mean $\langle \mathrm{ SNR} \rangle =40\, \mathrm{\mathring{\rm A}}^{-1}$. As additional variables for the FP we consider three stellar-population observables: light-weighted age, stellar mass-to-light ratio, and a novel combination of Lick indices ($I_\mathrm{age}$). For an $\langle \mathrm{ SNR} \rangle =45~\mathrm{\mathring{\rm A}}^{-1}$ (equivalent to 1-h exposure on a 4-m telescope), all three hyperplanes outperform the FP as distance indicators. Being an empirical spectral index, $I_\mathrm{age}$ avoids the model-dependent uncertainties and bias underlying age and mass-to-light ratio measurements, yet yields a 10 per cent reduction of the median distance uncertainty compared to the FP. We also find that, as a by-product, the $I_\mathrm{age}$ hyperplane removes most of the reported environment bias of the FP. After accounting for the different SNR, these conclusions also apply to a 50 times larger sample from SDSS-III (Sloan Digital Sky Survey). However, in this case, only $\mathrm{ age}$ removes the environment bias.

The Wide-field Spectroscopic Telescope (WST) is proposed as a new facility dedicated to the efficient delivery of spectroscopic surveys. This white paper summarises the initial concept as well as the corresponding science cases. WST will feature simultaneous operation of a large field-of-view (3 sq. degree), a high multiplex (20,000) multi-object spectrograph (MOS) and a giant 3x3 sq. arcmin integral field spectrograph (IFS). In scientific capability these requirements place WST far ahead of existing and planned facilities. Given the current investment in deep imaging surveys and noting the diagnostic power of spectroscopy, WST will fill a crucial gap in astronomical capability and work synergistically with future ground and space-based facilities. This white paper shows that WST can address outstanding scientific questions in the areas of cosmology; galaxy assembly, evolution, and enrichment, including our own Milky Way; origin of stars and planets; time domain and multi-messenger astrophysics. WST's uniquely rich dataset will deliver unforeseen discoveries in many of these areas. The WST Science Team (already including more than 500 scientists worldwide) is open to the all astronomical community. To register in the WST Science Team please visit https://www.wstelescope.com/for-scientists/participate