Galaxy formation and evolution

Abstract:

We present numerical simulations of discrete relativistic ejecta from an X-ray binary (XRB) with initial conditions directly informed by observations. XRBs have been observed to launch powerful discrete plasma ejecta during state transitions, which can propagate up to parsec distances. Understanding these ejection events unveils new understanding of jet-launching, jet power, and jet–interstellar medium (ISM) interaction among other implications. Multifrequency quasi-simultaneous radio observations of ejecta from the black hole XRB MAXI J1820+070 produced both size and calorimetry constraints, which we use as initial conditions of a relativistic hydrodynamic simulation. We qualitatively reproduce the observed deceleration of the ejecta in a homogeneous ISM. Our simulations demonstrate that the ejecta must be denser than the ISM, the ISM be significantly low density, and the launch be extremely powerful, in order to propagate to the observed distances. The blob propagates and clears out a high-pressure low-density cavity in its wake, providing an explanation for this pre-existing low-density environment, as well as ‘bubble-like’ environments in the vicinity of XRBs inferred from other studies. As the blob decelerates, we observe the onset of instabilities and a long-lived reverse shock – these mechanisms convert kinetic to internal energy in the blob, responsible for in situ particle acceleration. We transform the outputs of our simulation into pseudo-radio images, incorporating the coverage of the MeerKAT and e-MERLIN telescopes from the original observations with real-sky background. Through this, we maximize the interpretability of the results and provide direct comparison to current data, as well as provide prediction capabilities.

Abstract:

We measured the harmonic-space power spectrum of Galaxy clustering auto-correlation from the Evolutionary Map of the Universe Pilot Survey 1 data (EMU PS1) and its cross-correlation with the lensing convergence map of cosmic microwave background (CMB) from Planck Public Release 4 at the linear scale range from to 500. We applied two flux density cuts at and mJy on the radio galaxies observed at 944MHz and considered two source detection algorithms. We found the auto-correlation measurements from the two algorithms at the 0.18 mJy cut to deviate for due to the different criteria assumed on the source detection and decided to ignore data above this scale. We report a cross-correlation detection of EMU PS1 with CMB lensing at 5.5 , irrespective of flux density cut. In our theoretical modelling we considered the SKADS and T-RECS redshift distribution simulation models that yield consistent results, a linear and a non-linear matter power spectrum, and two linear galaxy bias models. That is a constant redshift-independent galaxy bias and a constant amplitude galaxy bias . By fixing a cosmology model and considering a non-linear matter power spectrum with SKADS, we measured a constant galaxy bias at mJy ( mJy) with ( ) and a constant amplitude bias with ( ). When is a free parameter for the same models at mJy ( mJy) with the constant model we found ( ), while with the constant amplitude model we measured ( ), respectively. Our results agree at with the measurements from Planck CMB and the weak lensing surveys and also show the potential of cosmology studies with future radio continuum survey data.

Abstract:

We present a comprehensive analysis of galaxy close-pair fractions and major merger rates to evaluate the importance of mergers in the hierarchical growth of galaxies over cosmic time. This study focuses on the previously poorly understood redshift range of using JADES observations. Our mass-complete sample includes primary galaxies with stellar masses of , having major companions (mass ratio ) selected by pkpc projected separation and redshift proximity criteria. Pair fractions are measured using a statistically robust method incorporating photometric redshift posteriors and available spectroscopic data. The pair fraction evolves with redshift and shows dependence on the stellar mass: at there is an increase up to , followed by a turnover, while at higher stellar masses there is a flattening and weak decline with increasing redshift. Similarly, the derived galaxy major merger rate increases and flattens beyond to per galaxy, showing a weak scaling with stellar mass, driven by the evolution of the galaxy stellar mass function. A comparison between the cumulative mass accretion from major mergers and the mass assembled through star formation indicates that major mergers contribute approximately to the total mass growth over the studied redshift range, which is in agreement with the ex situ mass fraction estimated from our simple numerical model. These results highlight that major mergers contribute little to the direct stellar mass growth compared to in situ star formation but could still play an indirect role by driving star formation itself.