Galaxy formation and evolution

Abstract:

Abstract Understanding how the internal kinematics of massive galaxies evolve is key to constraining the physical processes that drive their assembly. We investigate the evolution of rotational support in massive ( log M * / M ⊙ ≥ 10.6 ) early-type galaxies (ETGs) over the past ∼7 Gyr. We use MUSE integral-field spectroscopic (IFS) data for 212 ETGs at intermediate redshift (0.25 <  z  < 0.75) from the MAGNUS sample. We compare their kinematics to a carefully matched local sample of 787 ETGs ( z ≤ 0.05) from the MaNGA survey. Using the specific stellar angular momentum proxy, λ R , we quantify the balance between ordered rotation and random motions. We derive intrinsic λ R values by applying a uniform correction for seeing and point-spread function (PSF) effects to both samples. We find a significant evolutionary trend: The intermediate-redshift ETGs are systematically more rotationally supported than their local counterparts. The median PSF-corrected λ R for the MAGNUS sample is 0.48 ± 0.05, substantially higher than the median of 0.34 ± 0.03 for the matched MaNGA sample. This corresponds to a positive slope in the λ R − z relation of d λ R / d z  = 0.25 ± 0.04 for the combined sample. The decline in rotational support is most pronounced for the most massive ( log M * / M ⊙ > 11.3 ) and highest-velocity-dispersion ( σ e  ≳ 200 km s −1 ) galaxies. Our results provide robust evidence that massive ETGs have undergone significant kinematic evolution, losing angular momentum as they evolve towards the present day, consistent with theoretical models where processes such as dry mergers play a crucial role in shaping the dynamical state of galaxies.

Abstract:

Eccentric binary black holes (BBHs) formed through dynamical interactions can significantly contribute to gravitational wave (GW) detections. In this work, we present a simulated catalog of dynamically formed, stellar-mass BBHs in the local universe, incorporating contributions from the Galactic field (flyby interactions), Galactic nucleus (eccentric Kozai-Lidov evolution), and globular clusters (N-body interactions). Our results predict a wide, highly eccentric BBH population in the Milky Way, with source counts of ∼25, 9, 3, 1, and <1 for a 4-year LISA mission (∼36, 13, 5, 2, and 1 for a 10-year extended mission), for SNR>1, 3, 8, 20, and 50, respectively. Extending this model to cosmological populations, we show that different dynamical channels can produce distinct eccentricity distributions in the LVK band and can contribute hundreds of additional low-SNR mHz sources. Specifically, our model yields a merger rate of Γ∼9 Gpc-3 yr-1 and ∼150 extragalactic mHz BBHs with SNR>1. However, due to the lower mass and weaker GW signals of stellar-mass BBHs, this number declines sharply at higher detection thresholds (e.g., ∼1 for SNR>8). We further highlight the impact of eccentric BBH signals on the LISA global fit, showing that their individual harmonics can be independently detected in the Milky Way, and may mimic circular binaries with systematically biased chirp masses. Lastly, we show that post-Newtonian waveforms converge reliably for eccentric BBHs with masses of ≲103M⊙ in the mHz band. Overall, eccentric BBHs represent a prevalent and promising target for future space-based GW observatories.