Galaxy formation and evolution

Abstract:

Abstract We present the most complete modelling of the MOJAVE 1.5 Jansky Quarter Century active galactic nuclei (AGN) jet population, using likelihood-free simulation-based inference. Due to the complex impact of a flux-limit on observed AGN data sets, careful modelling of the parent population is required. In particular, when observing and fitting to multiple data distributions likelihoods become non-intuitive. Parameter degeneracies further complicate the problem and make it suitable for likelihood-free, simulation-based inference. This method relies on a normalising flow learning the likelihood surface or posteriors directly. We extensively validate the flow to show that previous parameter estimates for the AGN jet speed distributions underestimated parameter errors significantly and do not capture the non-gaussianity of the parameter posteriors. The new results enable a better statistical comparison to other AGN population studies, but also a more accurate comparison of supermassive black hole jets with their lower mass counterparts, X-ray binaries (XRB). We find that the AGN follow a Lorentz factor distribution of the shape N(Γ)∝Γb with $b= -1.32_{-0.19}^{+0.20}$. This slope is consistent with the XRB Lorentz factor distribution at 2σ. Simulation-based inference as a method is generally well-suited to many astrophysical problems, and this paper shows the convenient applicability of this methodology to parent population studies of jetted AGN with multiple observables specifically.

Abstract:

Ground-based gravitational-wave (GW) observatories have detected approximately 200 binary black hole (BH) mergers. The astrophysical origin of these events is debated, with evidence suggesting that at least a subset originated from dynamic environments characterized by frequent close encounters. Accretion disks in active galactic nuclei (AGNs) are of particular interest, as certain observed features could be more readily produced within such environments. In this paper, we investigate the expected properties of mergers in these environments, and their dependence on various parameters, using 1D N-body simulations combined with a comprehensive semianalytical model. In our fiducial model, the distributions of masses (m1 and m2) and mass ratios (q ≡ m2/m1 ≤ 1) are similar to those observed. However, they depend strongly on the lifetime and density of the AGN disk and on the number and accretion efficiency of BHs, with higher masses predicted as these quantities increase. The most massive mergers, such as GW231123, can be produced either by efficient gas accretion or by hierarchical mergers among ≥3 generations of BHs. The observed negative correlation between q and the average effective spin (χeff), along with the positive correlation between χeff and the chirp mass (Mchirp), can be explained by a combination of efficient gas accretion, which promotes spin alignment, and hierarchical mergers, which produce high-∣χeff∣ and low-q binaries. Hierarchical mergers can also explain the negative correlation between q and the dispersion of χeff, as well as the positive correlation between ∣χeff∣and Mchirp. We present a comprehensive study on how the expected distribution of each of these quantities depends on model parameters and assumptions, which will aid the interpretation of observed GW population properties.

Abstract:

Simulations predict that bars in galaxies should slow down over time. This is often attributed to the exchange of angular momentum between the bar and other regions of the galaxy, such as the outer disk and dark matter halo, which implies that galaxies with a more massive halo or disk should be able to slow down the bar more efficiently. However, observational evidence for this process has been limited. In this work, we provide observational support for the slowing down of bars as predicted by simulations. We combine bar kinematics measurements obtained with the Tremaine–Weinberg method and host galaxy mass estimates derived from Jeans anisotropic models for a sample of 30 galaxies from the MaNGA survey. We find a statistically significant anticorrelation (>4σ) between the bar pattern speed and both the stellar and total dynamical mass, which suggests that the slowest bars reside in the most massive galaxies. However, while the slope of the best-fit line between the pattern speed and dark matter mass is negative, it is not statistically significant (2.43σ). We also find that bars with lower pattern speeds have more extended NFW dark matter profiles with lower central densities. Additionally, we find statistically significant correlations (>3σ) between the corotation radius and the stellar mass, dark matter mass, and total dynamical mass. Finally, we find no significant correlations that involve the dark matter fraction or (Formula presented) R, likely due to the inherent challenges associated with measuring these specific parameters accurately.

Abstract:

ABSTRACT We examine the spatial correlation of emission from polycyclic aromatic hydrocarbons (PAH) (3.3, 7.7, and 11.3 $\mathrm{\mu m}$) with the far-ultraviolet (FUV), near-ultraviolet (NUV), and H$\alpha$ emission from star-forming complexes (SFCs) in different regions of NGC 628. We use the James Webb Space Telescope to detect PAH emission, along with the Ultraviolet Imaging Telescope and Multi-Unit Spectroscopic Explorer observations to sample the UV and H$\alpha$ emission, respectively. We investigate the correlation of PAH luminosities with FUV, NUV, and H$\alpha$ luminosities for the extracted SFCs. We find that the arm and spur SFCs show bright PAH emission, except for those with only NUV emission, located primarily in bubbles and superbubbles. We also examine these correlations in the phantom void, the largest superbubble in NGC 628. We investigate the trend for FUV-NUV and the Initial mass function (IMF) index $\alpha _2$ derived from the ratio of B stars with PAH band ratios (F335M/F1130W, F770W/F1130W, and F335M/F770W). We find that PAH band ratios increase as the IMF becomes more top-heavy and the SFCs become bluer, consistent with enhanced PAH excitation and ionization in stronger UV radiation fields. However, $\alpha _2$ of spur SFCs shows a flat trend with PAH band ratios compared to arms. Upon closer examination, two SFCs in the shell region of the phantom void showed a flatter IMF compared to the SFC located near the elongated bubble. This is likely due to gas accumulation, possibly through feedback mechanisms in the shell region, while the SFC near the elongated bubble may have formed in a region affected by shear.

Abstract:

Little red dots (LRDs) are compact, red sources discovered by JWST at high redshift (z ≳ 4), marked by distinctive “V-shaped” spectral energy distributions (SEDs) and often interpreted as rapidly accreting active galactic nuclei (AGNs). Their true nature remains unclear though, and their evolutionary connection to their lower-redshift counterparts is still poorly constrained. Thus, we present WISEA J123635.56+621424.2 (here dubbed the Saguaro), a z = 2.0145 galaxy in GOODS-North, as a possible analog of high-redshift LRDs and a potential missing link in their evolutionary path toward lower-redshift systems. It features a compact LRD-like nucleus surrounded by a face-on spiral host. Its connections to LRDs include the following: (1) its nuclear spectrum shows a clear “V-shaped” SED, and (2) when redshifted to z = 7, surface brightness dimming makes the host undetectable, thus mimicking an LRD. This suggests that high-redshift LRDs may be embedded in extended hosts. To test this, we stack rest-frame UV images of 99 photometrically selected LRDs, revealing faint, diffuse emission. Stacking in redshift bins reveals mild radial growth, consistent with the expected galaxy size evolution. A simple analytic model confirms that surface brightness dimming alone can explain their compact appearance. Lastly, we show that the Saguaro is not unique by describing similar objects from the literature at z ≲ 3.5. Taken together, our results support a scenario in which LRDs may not be a distinct population, but could be the visible nuclei of galaxies undergoing a short-lived, (perhaps) AGN-dominated evolutionary phase, with their compact, red appearance driven largely by observational biases.