Galaxy formation and evolution

Abstract:

We utilize James Webb Space Telescope (JWST) Mid Infrared Instrument (MIRI) integral field unit observations to investigate the behavior and excitation of H2 in the nearby Seyfert galaxies NGC 3081 and NGC 5506, both part of the Galactic Activity, Torus, and Outflow Survey (or GATOS). We compare population levels of the S(1) to S(8) rotational H2 emission lines visible to JWST/MIRI spectroscopy to models assuming local thermodynamic equilibrium (LTE), in order to estimate the column density and thermal scaling of the molecular gas. For the nuclear regions, we incorporate Very Large Telescope Spectrograph for INtegral Field Observations in the Near Infrared (or VLT/SINFONI) K-band observations to estimate population levels for available rovibrational H2 emission lines, and compare the resultant population curves to non-LTE radiative transfer models and shock modeling. We report a differing set of prominent active galactic nuclei (AGN)-driven excitation mechanisms between the two galaxies. For NGC 3081, we find that a non-LTE radiative transfer environment is adequate to explain observations of the nuclear region, indicating that the primary mode in which the AGN transfers excitation energy is likely irradiation. We estimate the extent of AGN photoionization along the ionization bicone to be ≈330 pc. In contrast, for NGC 5506, we find a shock scenario to be a more plausible excitation mechanism, a conclusion bolstered by an observed spatial correlation between higher-energy rotational H2 and [Fe II]5.34μm emission. In addition, we identify potential nuclear H2 outflows resulting from an interaction between the ionization bicone and the rotational disk. By isolating the outflowing component of the H2 emission, we estimate the warm molecular mass outflow rate to be 0.07 M⊙ yr−1.

Abstract:

Galactic warps are common in disk galaxies. While often attributed to galaxy–galaxy tides, a nonspherical dark matter halo has also been proposed as a driver of disk warping. We investigate links among warp morphology, satellite distribution, and large-scale structure using the Sloan Digital Sky Survey catalog of warped disks compiled by W.-B. G. Zee et al. Warps are classified into 244 S- and 127 U-types, hosting 1373 and 740 satellites, respectively, and are compared to an unwarped control matched in stellar mass, redshift, and local density. As an indirect, population-level proxy for the host halo’s shape and orientation, we analyze the stacked spatial distribution of satellites. Warped hosts show a significant anisotropy: an excess at 45° < ϕ < 90° (measured from the host major axis), peaking at P(ϕ) ≃ 0.003, versus nearly isotropic controls. Satellites of S-type warps preferentially align with the nearest cosmic filament, whereas those of U-type warps are more often perpendicular. The incidence of warps increases toward filaments (rfila < 4 Mpc h−1), while the number of satellites around warped hosts remains approximately constant with filament distance, indicating a direct influence of the large-scale environment. We discuss possible links between galactic warps and the cosmic web, including anisotropic tidal fields and differences in evolutionary stage.

Abstract:

Abstract Merging black hole (BH) binaries in AGN discs formed through two-body scatterings via the “gas-capture” process may explain a significant fraction of BH mergers in AGN and a non-negligible contribution to the observed rate from LIGO-VIRGO-KAGRA. We perform Monte Carlo simulations of binary BH formation, evolution and mergers across the observed AGN mass function using a novel physically motivated treatment for the gas-capture process derived from hydrodynamical simulations of BH-BH encounters in AGN. Our models suggest that gas-captured binaries could result in merger rates of 0.73 − 7.1Gpc−3yr−1. Mergers from AGN are dominated by AGN with supermassive BH masses of ∼107M⊙, with 90 % of mergers occurring in the range ∼106M⊙ − 108M⊙. The merging mass distribution is flatter than the initial BH mass power law by a factor Δξ = 1.1 − 1.2, as larger BHs align with the disc and form binaries more efficiently. Similarly, the merging mass ratio distribution is flatter, therefore the AGN channel could explain high mass and unequal mass ratio detections such as GW190521 and GW190814. Using a simpler dynamical friction treatment for the binary formation process, the results are similar, where the primary bottleneck is the alignment time with the disc. The most influential parameters are the anticipated number of BHs and their mass function. Given the many uncertainties that remain in the AGN channel, we expect the true uncertainty extends beyond our predicted rates. Nonetheless, we conclude that AGN remain an important channel for consideration, particularly for gravitational wave detections involving one or two high mass BHs.