Dr Anastasia Ponomareva

Abstract:

Measuring galaxy rotation curves is critical for inferring the properties of dark-matter haloes in the Lambda Cold Dark Matter (ΛCDM) paradigm. We present H i rotation curves and mass models for 20 galaxies from the MIGHTEE survey. Using extended H i kinematics, we construct resolved mass models that include stellar, gaseous, and dark-matter components. Stellar masses are derived using 3.6 μm imaging under fixed mass-to-light ratio (ϒ* = M/L) assumptions and are complemented, for the first time for a H I-selected sample, by spatially resolved M/L, obtained from multi-wavelength SED fitting. We examine the ratio of baryonic to observed rotation velocity (Vbar/Vobs) at the characteristic radius R2.2. Adopting a fixed ϒ⋆ = 0.5 M⊙/L⊙ yields a clear dependence of V2.2/Vobs on galaxy luminosity, while adopting ϒ⋆ = 0.2 M⊙/L⊙ substantially weakens this trend. In contrast, the resolved M/L analysis preserves the luminosity dependence while modifying the stellar contribution on a galaxy-by-galaxy basis, providing a more accurate representation of the underlying relation. We model the dark-matter haloes using Navarro–Frenk–White profiles and find that the different assumptions for a fixed a M/L systematically shift galaxies relative to the theoretical stellar-to-halo mass and baryonic-to-halo mass relations, while the spatially varying M/L yields the closest agreement with theoretical benchmarks within ΛCDM. We therefore demonstrate that future investigations of the dark matter properties of galaxies using rotation curves need to account for varying M/L across individual galaxy profiles and between galaxies in order to obtain accurate measurements of the dark matter, and therefore test ΛCDM.

Abstract:

Untargeted neutral hydrogen ( > 1.5 kpc) to be ultra-diffuse galaxies (UDGs). Furthermore, we extracted surveys are well suited to identifying low surface brightness galaxies (LSBGs) that are gas rich, and they offer a complementary view to optically selected populations. We examined the LSBG population as identified via stellar and gaseous content using the MIGHTEE XMM-LSS early science data and the publicly available catalogs of optically identified LSBGs. There is currently little overlap between these datasets, with only three galaxies commonly detected. We performed surface brightness photometry of selected MIGHTEE detections to find 29 LSBGs, and 26 of these meet the size requirement (R_ eff spectra at the location of all optically identified galaxies, placing upper limits on the mass ratio in these systems. While the population overall tends toward bluer colors, the and the optically selected samples mostly overlap in mean effective surface brightness, effective radii, and color. Although it is not straightforward to discern why the LSBGs were missed in optical searches, this work highlights the utility of surveys in finding these faint systems. The LSBGs are gas rich compared to the general population. Furthermore, three out of four UDGs with available kinematics show no systematic offset from the baryonic Tully-Fisher relation, although we are biased away from sources with low rotational velocities due to the low spectral resolution of the data. This work demonstrates the utility of observations for finding and characterizing the low surface brightness Universe.

Abstract:

Understanding the cold atomic hydrogen gas (H i) within cosmic filaments has the potential to pin down the relationship between the low density gas in the cosmic web and how the galaxies that lie within it grow using this material. We report the discovery of a cosmic filament using 14 H i-selected galaxies that form a very thin elongated structure of 1.7 Mpc. These galaxies are embedded within a much larger cosmic web filament, traced by optical galaxies, that spans at least Mpc. We find that the spin axes of the H i galaxies are significantly more strongly aligned with the cosmic web filament () than cosmological simulations predict, with the optically selected galaxies showing alignment to a lesser degree (). This structure demonstrates that within the cosmic filament, the angular momentum of galaxies is closely connected to the large-scale filamentary structure. We also find strong evidence that the galaxies are orbiting around the spine of the filament, making this one of the largest rotating structures discovered thus far, and from which we can infer that there is transfer of angular momentum from the filament to the individual galaxies. The abundance of H i galaxies along the filament and the low dynamical temperature of the galaxies within the filament indicates that this filament is at an early evolutionary stage where the imprint of cosmic matter flow on galaxies has been preserved over cosmic time.

Abstract:

The relationship between the already formed stellar mass in a galaxy and the gas reservoir of neutral atomic hydrogen, is a key element in our understanding of how gas is turned into stars in galaxy haloes. In this paper, we measure the relation based on a stellar-mass selected sample at and the MeerKAT International GHz Tiered Extragalactic Exploration-H i Data Release 1 spectral data. Using a powerful Bayesian stacking technique, for the first time we are also able to measure the underlying bivariate distribution of H i mass and stellar mass of galaxies with M, finding that an asymmetric underlying H i distribution is strongly preferred by our complete samples. We define the concepts of the average of the logarithmic H i mass, , and the logarithmic average of the H i mass, , and find that the difference between and can be as large as 0.5 dex for the preferred asymmetric H i distribution. We observe shallow slopes in the underlying scaling relations, suggesting the presence of an upper H i mass limit beyond which a galaxy can no longer retain further H i gas. From our bivariate distribution we also infer the H i mass function at this redshift and find tentative evidence for a decrease of 2–10 times in the comoving space density of the most H i massive galaxies up to .

Abstract:

Atomic hydrogen constitutes the gas reservoir from which molecular gas and star formation in galaxies emerges. However, the weakness of the line means it has been difficult to directly detect in all but the very local Universe. Here, we present results from the first search using the MeerKAT International Tiered Extragalactic Exploration (MIGHTEE) Survey for high-redshift () H i emission from individual galaxies. By searching for 21-cm emission centred on the position and redshift of optically selected emission-line galaxies we overcome difficulties that hinder untargeted searches. We detect 11 galaxies at , forming the first sample of detections with an interferometer, with the highest redshift detection at . We find they have much larger H i masses than their low-redshift H i-selected counterparts for a given stellar mass. This can be explained by the much larger cosmological volume probed at these high redshifts, and does not require any evolution of the H i mass function. We make the first-ever measurement of the baryonic Tully–Fisher relation (bTFr) with H i at and find consistency with the local bTFr, but with tentative evidence of a flattening in the relation at these redshifts for higher-mass objects. This may signify evolution, in line with predictions from hydrodynamic simulations, or that the molecular gas mass in these high-mass galaxies could be significant. This study paves the way for future studies of H i beyond the local Universe, using both searches targeted at known objects and via pure H i selection.