Euclid

Abstract:

Abstract Cosmic filaments have been recognised as influencing galaxy evolution, but their connection to galactic cold gas reservoirs is elusive, particularly at low redshifts. We investigate the influence of filaments on neutral hydrogen (H i) detections in galaxies at 0.02 < z < 0.09, using the MeerKAT International GHz Tiered Extragalactic Exploration (MIGHTEE) survey in the COSMOS and XMM-LSS fields. We measure the fraction of optical galaxies from the Dark Energy Spectroscopic Instrument (DESI) Survey detected in H i emission as a function of stellar mass, morphology, local density, and the distance to the nearest filament. We find that galaxies closer to filaments have higher stellar masses, higher local densities, and a larger early-type fraction, all of which affect the H i detection. After controlling for these dependencies, filaments have measurable effects on H i detection. Late-type galaxies in low-local density environments show reduced H i detection fractions close to filaments across all stellar mass ranges, suggesting potential gas depletion through ram pressure stripping and cosmic web detachment. Massive early-type galaxies show an enhanced H i detection fraction in filaments compared to the voids, suggesting possible gas replenishment through filamentary accretion or gas-rich mergers. Our results suggest that cosmic filaments influence galactic H i gas reservoirs through various competing processes, whose relative importance varies with stellar mass and local density.

Abstract:

Abstract Radio continuum surveys provide samples of active galactic nuclei (AGN) and star forming galaxies (SFGs) to high redshifts, free of biases due to dust obscuration. However, radio detected sources require multi-wavelength counterparts to understand their intrinsic properties (e.g. redshift, stellar mass) and to study the evolution of star formation and AGN activity. In this work we present host galaxy counterparts for the MeerKAT International GHz Tiered Extragalactic Exploration (MIGHTEE) survey continuum Data Release 1 in regions with the best ancillary data (totalling 7.5 sq. deg). We combine statistical cross-matching and visual inspection to identify Ks-band selected host galaxies, and additionally combine multiple radio components into single physical objects, where needed. This results in a combined radio catalogue of ~66 000 sources, with host counterparts and redshifts identified for ~95 per cent of sources in the COSMOS field, ~91 per cent in XMM-LSS and ~90 per cent in CDFS-DEEP. This includes a significant fraction of sources with spectroscopic redshifts within the COSMOS field (~50 per cent), with ~30 and ~20 per cent in the XMM-LSS and CDFS-DEEP fields respectively. Using the cross-matched catalogue, we make an initial identification of radio-excess and star forming galaxies based on comparisons of the radio luminosities to host star formation rates. Using this split as a proxy for radio loud AGN or SFGs, we present expectations for the redshift distributions of these sources, finding broad agreement with those from deep radio luminosity functions and simulated catalogues.

Abstract:

A primary target of the Euclid space mission is to constrain early-universe physics by searching for deviations from a primordial Gaussian random field. A significant detection of primordial non-Gaussianity would rule out the simplest models of cosmic inflation and transform our understanding of the origin of the Universe. This paper forecasts how well field-level inference of galaxy redshift surveys can constrain the amplitude of local primordial non-Gaussianity, f NL^local, within a Bayesian hierarchical framework, in the upcoming Euclid data. We designed and simulated mock datasets and performed Markov chain Monte Carlo analyses using a full-field forward modelling approach. By including the formation history of the cosmic matter field in the analysis, the method takes into account all available probes of primordial non-Gaussianity, and goes beyond statistical summary estimators of f NL^local. Probes include, for example, two-point and higher-order statistics, peculiar velocity fields, and scale-dependent galaxy biases. Furthermore, the method simultaneously handles systematic survey effects, such as selection effects, survey geometries, and galaxy biases. The forecast shows that, using simulated Euclid data, the method can achieve a precision of σ(f NL^local) = 2.6 (68.3% confidence level), assuming a grid resolution of ΔL = 31.25 h ⁻¹ Mpc and a cut-off scale of k NF = 0.1 h Mpc⁻¹. We also provide data products, including realistic simulations with non-zero values of f NL^local and maps of adiabatic curvature fluctuations. The results underscore the feasibility and advantages of field-level inference to constrain f NL^local in galaxy redshift surveys. Our approach consistently captures all the information available in the large-scale structure to constrain f NL^local, and resolves the degeneracy between early-universe physics and late-time gravitational effects, while mitigating the impact of systematic and observational effects.

Abstract:

Massive early-type galaxies (ETGs; M > 10¹¹ M⊙) are believed to form primarily through mergers of less massive progenitors, which leave behind numerous traces of violent formation histories, such as stellar streams and shells. A particularly striking signature of these mergers is the formation of supermassive black hole (SMBH) binaries, which can create depleted stellar cores through interactions with stars on radial orbits – a process known as core scouring. The secondary SMBH in such systems may still carry a dense stellar envelope and thereby remain observable for some time as a secondary nucleus while it sinks towards the shared gravitational potential of the merged galaxy. Direct observations of secondary nuclei on sub-kiloparsec scales remain rare, with only a few notable cases, such as NGC 5419. Investigating such features and building up statistics requires both high spatial resolution and wide-field coverage, a capability uniquely provided by Euclid. In this study, we leverage Euclid’s Q1 Early Release data to systematically search for secondary nuclei in ETGs. We present a preliminary sample of 666 candidate systems distributed over 504 hosts (some of which contain multiple secondary nuclei). The vast majority of these fall at separations of 3 kpc to 15 kpc, indicative of normal mergers. However, 44 fall at projected separations of less than 2 kpc. We argue that this most interesting subset of secondary nucleus candidates – those at very close angular separations – are unlikely to be a consequence of chance alignments. We show that their stellar masses are mostly too large for them to be globular clusters and that a significant subset are unresolved even at Euclid’s spatial resolution, rendering them too small to be dwarf galaxies. These objects may represent the highest-density nuclei of a previously merged galaxy currently sinking into the centre of the new common gravitational potential, and thus they likely host a secondary SMBH. We also demonstrate that convolutional neural networks offer a viable avenue to detect multiple nuclei in the 30 times larger sky coverage of the future Euclid DR1. Finally, we argue that our method can detect the remnants of a recoil event from two merged SMBHs, as two of our secondary nuclei candidates are unresolved at the Euclid spatial resolution, appear at projected physical separations of less than 2 kpc, and appear in hosts of M > 10¹¹ M⊙, which makes them viable candidates.