Joanna M. Piotrowska

The modern generation of wide-field galaxy surveys, such as LSST, Euclid, and Roman, will enable studies of dwarf galaxies (10 ⁶ ≤ M _* / M _⊙ ≤ 10 ⁹ ) beyond the Local Group (LG) in unprecedented detail. Improved theoretical understanding of this population is necessary to guide these observations, since predictions in this regime are generally limited to specific environments like the LG. We present predictions for the population of dwarf galaxies from the TNG50 run of the IllustrisTNG suite of cosmological hydrodynamical simulations, focusing on the environments within 1 < D /Mpc < 25 of LG analogs at z = 0. In the simulated sample, there are ∼1000 and ∼12,000 dwarf galaxies within 10 and 25 Mpc, respectively. We compare our results with the 50 Mpc Galaxy Catalog and estimate that current observations are highly incomplete at low masses: for 10 ⁶ ≤ M _* / M _⊙ ≤ 10 ⁷ (−13 ≲ M _r ≲ −10), we find completeness fractions of ∼23% within 10 Mpc and ∼4% within 25 Mpc. The simulated galaxies below the completeness limits of the observations exist in a range of environments, with notable populations of field dwarfs at all distances and satellites around centrals with masses 10 ⁸ ≲ M _* / M _⊙ ≲ 10 ¹¹ within 10–25 Mpc. We find that there are ∼8 times more quiescent dwarf galaxies in the TNG50 sample than are currently cataloged. Our results suggest that upcoming observations should uncover a substantial population of dwarf galaxies, and that ≳15% of these will be red, currently quenched galaxies in the field.

Understanding the growth of supermassive black holes (SMBHs) requires observational constraints on how their angular momentum—or spin—varies with mass, since the relative importance of coherent accretion, chaotic accretion, and mergers will be reflected in SMBH spin populations. Here we present an updated compilation of reflection-based SMBH spin measurements from the literature and assemble a set of ancillary quantities of interest for each SMBH (including redshift, Eddington ratio, and X-ray luminosity). No obvious apparent correlation between the Eddington-scaled accretion rate and the black hole spin is seen, noting that formal statistical tests are beyond the scope of this review. We discuss the limitations of using this heterogeneous mass–spin sample to test predictions of SMBH growth from semi-analytic models and cosmological simulations, emphasizing the need for a more uniform sample. We then highlight the encouraging prospects enabled by the next-generation NewAthena X-ray flagship observatory. Finally, we summarize how hierarchical Bayesian population inference applied to observed SMBH mass–spin populations will constitute a powerful framework for confirming tentative mass–spin trends in future samples.

Understanding the growth of supermassive black holes (SMBHs) requires observational constraints on how their angular momentum – or spin – varies with mass, since the relative importance of coherent accretion, chaotic accretion, and mergers will be reflected in SMBH spin populations. Here we present an updated compilation of reflection-based SMBH spin measurements from the literature and assemble a set of ancillary quantities of interest for each SMBH (including redshift, Eddington ratio, and X-ray luminosity). We find no obvious correlation between the Eddington ratio and the reflection-inferred spin in the sample. We discuss the limitations of using this heterogeneous mass–spin sample to test predictions of SMBH growth from semi-analytic models and cosmological simulations, emphasizing the need for a more uniform sample. We then highlight the encouraging prospects enabled by the next-generation NewAthena X-ray flagship observatory. Finally, we summarize how hierarchical Bayesian population inference applied to observed SMBH mass–spin populations will constitute a powerful framework for confirming tentative mass–spin trends in future samples.

Galaxy mergers are predicted to be a critical stage of merger-driven SMBH growth and galaxy evolution. Systems exhibiting multiple active galactic nuclei (AGN) are an important observational tool for constraining the prevalence and properties of merging SMBHs. Most multi-AGN selection methods focus on the identification of AGN pairs, while few focus on the more elusive triple AGN, which are a prediction of hierarchical growth and natural laboratories for studying SMBH dynamics. These systems are rare; only two confirmed cases exist locally ( z < 0.1). Here, we present a new, confirmed triple AGN system, WISEJ121857.42+103551.2/WISEJ121901.77+103515.0, with nuclear separations of 22.6 and 97 kpc, identified within a sample of spatially resolved mid-IR dual AGN. The system exhibits multiwavelength evidence for three distinct AGN hosted in an ongoing galaxy merger. To confirm the nature of this system, we present new radio observations with the Karl G. Jansky Very Large Array in A-configuration at 3, 10, and 15 GHz, providing subarcsecond resolutions, and the Very Long Baseline Array at 4.9 GHz, providing milliarcsecond resolutions. These observations confirm this system as a triple AGN, and the first triple AGN in which all three nuclei host radio AGN.

We present the first high-resolution X-ray spectrum of NGC 7213 obtained with XRISM/Resolve, supported by simultaneous XMM-Newton, NuSTAR, and SOAR optical data. The XRISM spectrum resolves the neutral Fe K α into two components: a narrow core ( FWHM = 65 0 − 220 + 240 km s − 1 ), consistent with emission at the dust sublimation radius, and a broader asymmetric line, best described by disklike emission from ∼100 R _g . This disk component mirrors the profile of the double-peaked H α line observed in the optical. In addition, we detect broadened Fe xxv and Fe xxvi emission lines, whose inferred locations bridge the gap between the inner disk and the optical broad-line region. The weak narrow Fe K α equivalent width (EW = 32 ± 6 eV) and the absence of a Compton hump imply a low-covering-fraction, Compton-thin torus. Together, these results reveal a radially stratified structure in NGC 7213, spanning nearly 4 orders of magnitude in radius, and place the source in an intermediate-accretion state ( λ _Edd = 0.1%–1%), where the inner disk and broad-line region remain, while the torus shows signs of dissipation.

We present Dark from Light (DfL), a novel method for inferring the dark sector in wide-field galaxy surveys that leverages a machine learning approach trained on contemporary cosmological simulations. The aim of this algorithm is to provide a fast, straightforward, and accurate route to estimating dark matter halo masses and group membership in wide-field spectroscopic galaxy surveys. This approach requires a highly limited number of input parameters (RA, Dec, z, and stellar mass plus uncertainties) and yields full probability distribution functions for the output halo masses of galaxies, groups, and clusters. To achieve this, we trained a series of random forest (RF) regression models on the IllustrisTNG and EAGLE simulations at z = 0 − 3, which provided model-dependent mappings from luminous tracers to dark matter halo properties. We incorporated the individual regression models into a virial group-finding algorithm (DfL), which outputs halo properties for observational input data. We tested the method at z = 0 − 2 for both the EAGLE and IllustrisTNG models, as well as in a cross-validation mode (where one simulation is used to train the model and the other to test). We demonstrate that known halo masses can be recovered with a mean systematic bias of ⟨b⟩= ± 0.10 dex (resulting from simulation choice), a mean statistical uncertainty of ⟨σ⟩=0.12 dex across epochs, and a central – (core) satellite classification accuracy of 96%. We establish that this approach yields halo mass recovery that is superior to standard abundance matching applied to groups identified through a friends-of-friends algorithm. Additionally, we compare the outputs of DfL to observational constraints on the M_* − M_Halo relation from strong gravitational lensing at z ∼ 0, demonstrating the promise of this novel approach. Finally, we systematically quantify how DfL performs on observational-like input data with varying stellar mass uncertainty and spectroscopic incompleteness, enabling robust error calibration in applications with observational galaxy surveys.

Green Pea galaxies are a class of compact, low-mass, low-metallicity star-forming galaxies in the relatively local Universe. They are believed to be analogs of high-redshift galaxies that reionized the Universe, and, indeed, the James Webb Space Telescope (JWST) is now uncovering such populations at record redshifts. Intriguingly, JWST finds evidence suggestive of active galactic nuclei (AGN) in many of these distant galaxies, including the elusive Little Red Dots, which broadly lack any detectable X-ray counterparts. Intuitively, one would expect to detect an AGN in their low-redshift analogs with X-rays, yet no study to date has conclusively identified an X-ray AGN within a Green Pea galaxy. Here we present the deepest X-ray campaign of a Green Pea galaxy performed to date, obtained with the goal of discerning the presence of a (potentially low-luminosity) AGN. The target—SDSS J082247.66+224144.0 (hereafter J0822+2241)—was previously found to display a comparable X-ray spectral shape to more local AGN (Γ ∼ 2) and a high luminosity (L _{2−10 keV} ∼ 10⁴² erg s⁻¹). We show that over 6.2 yr (rest frame) the 2–10 keV luminosity of J0822+2241 is constant, whereas the soft 0.5–2 keV flux has decreased significantly by ∼60%. We discuss possible scenarios to explain the X-ray properties of J0822+2241, finding transient low column density obscuration surrounding an AGN to be the only plausible scenario. J0822+2241 thus provides further evidence that low-luminosity AGN activity could have contributed to the epoch of reionization and that local analogs are useful to derive a complete multiwavelength picture of black hole growth in high-redshift, low-luminosity AGNs.

We present an investigation into the quenching of simulated galaxies across cosmic time, honing in on the role played by both intrinsic and environmental mechanisms at different epochs. In anticipation of VLT-MOONRISE, Very Large Telescope MOONS (Multi-Object Optical and Near-infrared Spectrograph) Redshift-Intensive Survey Experiment, the first wide-field spectroscopic galaxy survey to target cosmic noon, this work provides clear predictions to compare to the future observations. We investigate the quenching of centrals, high-mass satellites, and low-mass satellites from two cosmological hydrodynamical simulations: Illustris The Next Generation and Evolution and Assembly of GaLaxies and their Environment. Satellites are split according to bespoke mass thresholds, designed to separate environmental and intrinsic quenching mechanisms. To determine the best parameter for predicting quiescence, we apply a Random Forest classification analysis for each galaxy class at each epoch. The Random Forest classification determines supermassive black hole mass as the best predictor of quiescence in centrals and high-mass satellites. Alternatively, the quenching of low-mass satellites is best predicted by group halo mass, at all epochs. Additionally, we investigate the evolution in the dependence of the quenched fraction with various parameters, revealing a more complex picture. There is strong evidence for the rejuvenation of star formation from z = 2 to z = 0 in EAGLE, but not in IllustrisTNG. The starkest discrepancy between simulations rests in the mass threshold analysis. While IllustrisTNG predicts the existence of environmentally quenched satellites visible within the survey limits of MOONRISE, EAGLE does not. Hence, MOONRISE will provide critical data that is needed to evaluate current models, and constrain future models, of quenching processes.