We present a new method – called HINORA (HIgh-NOise RANdom SAmple Consensus) – for the identification of regular structures in 3D point distributions. Motivated by the possible existence of the so-called Council of Giants, that is, a ring of 12 massive galaxies surrounding the Local Group in the Local Sheet with a radius of 3.75 Mpc, we apply HINORA to the Local Volume Galaxy catalogue confirming its existence. When varying the lower limit of K-band luminosity of the galaxy entering the catalogue, we further report on the existence of another ring-like structure in the Local Volume that now contains the Milky Way and M31. However, this newly found structure is dominated by low-mass (satellite) galaxies. While we here simply present the novel method as well as its first application to observational data, follow-up work using numerical simulations of cosmic structure formation shall shed light into the origin of such regular patterns in the galaxy distribution. Further, the method is equally suited to identify similar (or even different) structures in various kinds of astrophysical data (e.g. locating the actual ‘baryonic-acoustic oscillation spheres’ in galaxy redshift surveys).

Contemporary interdisciplinary collaboration practices offer visions of new modes of assembly. This article traces a curatorial model of interdisciplinary collaboration, exploring how artists activate curation as a methodology of creation. I refer specifically to the creative practice of the award-winning Queer trans/mogrifying multidisciplinary artist and futurist Sage Ni'Ja Whitson, and their series The Unarrival Experiments. I reflect on Whitson's curatorial practice as a sacred methodology rooted in Yorùbá cosmologies, theatrical jazz aesthetic, and concepts of dark matter, superfluidity, and unarrival. I trace how Whitson's use of curatorial frameworks supports ease in the impossible, builds layers of multiplicity and simultaneity, resists institutional hegemony and power structures, and crafts systems of queer kinship and care for communities, ancestors, and futures. I outline the criteria of coexistence through which they imbue curatorial practices into their collaborations, generating what I describe as a “third space.” For Whitson, this fertile space of sustained difference is a portal to an alternate institution of darkness, interdependent sovereignty, and superfluidity. I conclude by unfolding the possibilities of Whitson's third space as a forward-facing methodology of how to move through the impossible together and envision new collective futures.

In gravitational imaging, the mass model for the main lensing galaxy is one of the main sources of systematic uncertainty. We use subhalo detection models with increasing levels of angular complexity in the lens mass model to analyse 100 HST mock observations. We find that perturbations of just 1% are enough to cause a 20% false positive subhalo detection rate, with order 3 multipoles having the strongest effect. The area in an observation where a substructure can be detected drops by a factor of 10 if multipoles up to 3 per cent amplitude are included in the lens model. The mass of the smallest detectable substructure however is not affected. We find a detection limit of M>108.2 M⊙ at 5σ in all models. In order for strong lensing searches for dark matter objects to remain reliable in the future, angular structure beyond the elliptical power-law must be included.

The gravitational lensing signal produced by a galaxy or a galaxy cluster is determined by its total matter distribution, providing us with a way to directly constrain their dark matter content. State-of-the-art numerical simulations successfully reproduce many observed properties of galaxies and can be used as a source of mock observations and predictions. Many gravitational lensing studies aim at constraining the nature of dark matter, discriminating between cold dark matter and alternative models. However, many past results are based on the comparison to simulations that did not include baryonic physics. Here we show that the presence of baryons can significantly alter the predictions: we look at the structural properties (profiles and shapes) of elliptical galaxies and at the inner density slope of subhaloes. Our results demonstrate that future simulations must model the interplay between baryons and alternative dark matter, to generate realistic predictions that could significantly modify the current constraints.

Strong gravitational lensing by galaxies provides us with a powerful laboratory for testing dark matter models. Various particle models for dark matter give rise to different small-scale distributions of mass in the lens galaxy, which can be differentiated with sensitive observations. Th. The sensitivity of a gravitational lens observation to the presence (or absence) of low-mass dark structures in the lens galaxy is determined mainly by the angular resolution of the instrument and the spatial structure of the source. Here, I discuss results from the analysis of a global VLBI observation of a gravitationally lensed radio jet. With an angular resolution better than 5 milli-arcseconds and a highly extended, spatially resolved source, we are able to place competitive constraints on the particle mass in fuzzy dark matter models using this single observation. I also discuss preliminary results from our analysis of warm dark matter models using this lens system.

Stellar bars drive the galaxy secular evolution. While rotating around the galaxy centre with a given angular frequency, the bar pattern speed, they sweep material and modify the galaxy structure. In the LCDM model, bars are expected to slow down by exchanging angular momentum with the other omponents and/or through dynamical friction exerted by the dark matter halo. The only direct method to derive the bar pattern speed, the Tremaine-Weinberg method, revealed that real bars rotate fast, stressing a tension between the observations, conducted to date in the local universe, and the LCDM model. Measuring the bar pattern speed to bars up to z∼1-2 will reveal if the expected bar evolutionary path is actually taking place and/or to confirm if the dark matter is able to exert friction. Using high resolution N-body simulations we tested the applicability of the Tremaine-Weinberg method to deep spectroscopy of the NIRSpec@JWST for a sample of bars at z∼1-2. Our analysis can be used to prepare an observational proposal to get dedicated data.

Rare systems with multiple sources strongly lensed by a single galaxy provide the most robust way to explore the geometry of the Universe and to study the inner mass structure of lens galaxies. We present here a study of the SDSS J0100+1818 deflector, analyzing its total and baryonic mass distributions. The system comprises an ultra-massive early-type galaxy, surrounded by ten multiple images of three background sources. Exploiting high-resolution HST photometry and VLT/X-shooter spectroscopy we conduct a strong lensing analysis with the software GLEE to reconstruct the complex surface brightness distributions of the background sources over approximately 7200 HST pixels. These results are presented in our recent paper, Bolamperti et al. (2023). Finally, we present some preliminary results from new VLT/MUSE observations, that will allow us to build a new strong lensing+dynamics joint model and measure the values of the total matter density and of the cosmological constant parameters, Ωm and ΩΛ.

We present high-precision strong lensing models for the galaxy clusters MACS J0416.1–0403 at z=0.396 and Abell 2744 at z=0.307. The models are constrained by two of the largest data-sets of secure multiple images ever used in lensing. These are identified from the photometric images observed by the Hubble space telescope and JWST in combination with spectroscopic data obtained by the Multi-Unit Spectroscopic Explorer at the Very Large Telescope. The same spectro-photometric data are used to create pure and complete samples of cluster member galaxies. Our models allow an extremely precise estimation of the cluster total mass distribution and produce accurate magnification maps that are fundamental to study the physical properties (mass, size, luminosity, etc.) of the lensed high-redshift galaxies.

The luminosity of the brightest stars (tip) of the red giant branch (TRGB) in the color–magnitude diagrams of old stars was used early on to introduce the ‘multiple stellar populations’ concept, in 1944, by Walter Baade. However, the precision and accuracy of the TRGB for distance estimation has not been known well for long. In the modern era, equipped with high spatial resolution imaging telescopes, the TRGB is considered an excellent standard candle for any type of resolved galaxies, thus representing a powerful probe for cosmology. The TRGB has several advantages over the classical Cepheids. I review how we can apply the TRGB in cosmology. Four science cases, from large to small scales, are presented: (1) the Hubble flow with Type Ia supernovae; (2) Virgo Cluster infall and dark matter; (3) dark galaxies; and (4) dark matter-free galaxies.

While the direct detection of the dark-matter particle remains very challenging, the physical properties of dark matter could potentially be constrained indirectly – by comparing the population characteristics of substructures in real galaxies with predictions from the phenomenological dark-matter models, such as cold, warm or self-interacting dark matter. Whereas these models are practically indistinguishable with respect to the expected abundance and statistical properties of massive galactic substructures, the critical difference lies in the low-mass regime ≲ 108M⊙. Galaxy-galaxy strong gravitational lensing provides a unique opportunity to search for gravitational signatures of such low-mass substructures in galaxies acting as a strong gravitational lens on a more distant background galaxy, serendipitously located along the same line of sight. In [Bayer et∼al.(2023)Bayer, Chatterjee, Koopmans, Vegetti, McKean, Treu, Fassnacht, and Glazebrook, Bayer et∼al.(2023)Bayer, Koopmans, McKean, Vegetti, Treu, Fassnacht, and Glazebrook, Bayer et∼al.(2023)Bayer, Vernardos, and Koopmans], we have recently introduced a novel approach to investigate the collective perturbative effect of low-mass substructures in the inner regions of massive elliptical lens galaxies and observationally constrain their power spectrum (on 1-10 kpc scales) based on the Fourier analysis of the associated surface-brightness anomalies in the lensed images (i.e., Einstein rings and gravitational arcs) observed with the Hubble Space Telescope. Here, we present a concise summary of the methodology, the encountered modelling challenges and the inferred observational constraints on the sub-galactic matter power spectrum. The future comparison of these results with predictions from hydrodynamical simulations might either verify the cold-dark-matter paradigm or require its substantial revision. Moreover, we demonstrate that the grid-based smooth lens modelling might model away surface-brightness anomalies caused by the presence of substructures in the lens galaxy and incorrectly interpret them as surface-brightness structure in the lensed background galaxy itself. If not properly understood and accounted for, such signal suppression might lead to severely biased constraints on the properties of substructures in galactic haloes.

Over the last two decades, strong gravitational lensing has emerged as a potential method for studying the nature and distribution of dark matter on sub-galactic scales. In addition to the main lens substructure, line-of-sight dark matter haloes contribute greatly to the subtle perturbations of lensed images. Line-of-sight haloes, unlike dark matter subhaloes, imprint distinct anisotropic and quadrupole signatures in the maps that depict the divergence and curl of the effective deflection field, respectively, giving rise to quadrupole moments of the image-plane averaged two-point correlation function of these maps. In terms of central density evolution and dark matter halo distribution, the shapes and amplitudes of the two-point function multipoles alter dramatically in the presence of warm dark matter and self-interacting dark matter. This method, in conjunction with upcoming large-scale surveys, provides the prospect of improving the constraints on dark matter at a critical time in strong gravitational lensing research.

Gravitational lensing in clusters of galaxies is one of the most powerful methods to probe the dark matter mass distribution inside such systems, after mapping the baryonic component, and test the currently accepted ɅCDM cosmological paradigm. With the advent of new high-resolution facilities such as the JWST, strong lensing (SL) is capable of providing extremely accurate mass measurements in the densest regions of such structures. Weak lensing (WL) provides complementary information by measuring the total mass distribution in the outskirts of galaxy clusters, where no multiple images of background sources are produced.

In my talk, I will present updates on the WL mass reconstruction of the Frontier Fields galaxy cluster Abell 2744 (z = 0.308) based on Subaru, Magellan, and JWST data, and I will show how the results obtained, combined with accurate SL modeling of this lens, provide a consistent picture of the cluster total mass distribution. I will discuss the pipeline used for this work, the extensive checks performed on the different datasets and the scientific results obtained. Being composed of several substructures undergoing a merging process, the complex geometry of this cluster makes it an ideal laboratory to verify the consistency and reliability of the results obtained with the two methods. I will compare the predictions of the SL models extrapolated in the outer regions of the cluster with the non-parametric WL mass reconstruction to look for potential systematic effects affecting the SL analysis.

We present the first results from JWST/NIRSPEC spectroscopy of massive quiescent galaxy candidates at 3<z<4 to complete the spectroscopic survey of Schreiber et al. 2018. In the first six objects targeted (all of which were too faint to secure spectroscopic identifications from the ground) they all are confirmed as yet more massive quiescent galaxies at 3<z<4. The JWST spectra are high signal-to-noise and unambiguous. Most of them have ages of a few hundred Myr from stellar population fits to the spectra and about 1/3 show sign of AGN emission lines. One extraordinary object of stellar mass 1.6×1011 M⊙ shows a red spectrum with evidence of a 4000Å break and an age of ≳ 1Gyr at z=3.2 and forming at z>6.

A plausible formation scenario for the Galactic globular clusters 47 Tucanae (47 Tuc) and Omega Centauri $(\omega$ Cen) is that they are tidally stripped remnants of dwarf galaxies, in which case they are likely to have retained a fraction of their dark matter cores. In this study, we have used the ultra-wide band receiver on the Parkes telescope (Murriyang) to place upper limits on the annihilation rate of exotic Light Dark Matter particles $(\chi)$ via the $\chi\chi\rightarrow e^+e^-$ channel using measurements of the recombination rate of positronium (Ps). This is an extension of a technique previously used to search for Ps in the Galactic Centre. However, by stacking of spectral data at multiple line frequencies, we have been able to improve sensitivity. Our measurements have resulted in $3-\sigma$ flux density (recombination rate) upper limits of 1.7 mJy $\left(1.4\times 10^{43}\, \mathrm{s}^{-1}\right)$ and 0.8 mJy $\left(1.1 \times 10^{43} \mathrm{s}^{-1}\right)$ for 47 Tuc and $\omega$ Cen, respectively. Within the Parkes beam at the cluster distances, which varies from 10–23 pc depending on the frequency of the recombination line, and for an assumed annihilation cross-section $\langle\sigma v\rangle = 3\times 10^{-29} \mathrm{cm}^3\, \mathrm{s}^{-1}$ , we calculate upper limits to the dark matter mass and rms dark matter density of ${\lesssim} 1.2-1.3\times 10^5 f_n^{-0.5}$ $\left(m_\chi/\mathrm{MeV\, c}^{-2}\right)$ $\mathrm{M}_{\odot}$ and ${\lesssim} 48-54 f_n^{-0.5}$ $\left(m_\chi/\mathrm{MeV\, c}^{-2}\right)$ $\mathrm{M}_{\odot} \mathrm{pc}^{-3}$ for the clusters, where $f_n=R_n/R_p$ is the ratio of Ps recombination transitions to annihilations, estimated to be ${\sim}0.01$ . The radio limits for $\omega$ Cen suggest that, for a fiducial dark/luminous mass ratio of ${\sim}0.05$ , any contribution from Light Dark Matter is small unless $\langle\sigma v\rangle < 7.9\times 10^{-28}\ \left(m_\chi/\mathrm{MeV\, c}^{-2}\right)^2 \mathrm{cm}^3 \mathrm{s}^{-1}$ . Owing to the compactness and proximity of the clusters, archival 511-keV measurements suggest even tighter limits than permitted by CMB anisotropies, $\langle\sigma v\rangle < 8.6\times 10^{-31}\ (m_\chi/\mathrm{MeV\, c}^{-2})^2 \mathrm{cm}^3 \mathrm{s}^{-1}$ . Due to the very low synchrotron radiation background, our recombination rate limits substantially improve on previous radio limits for the Milky Way.