Galaxy formation and evolution

Abstract:

James Webb Space Telescope (JWST) has revealed a population of ‘Little Red Dots’ (LRDs): compact, red objects at redshifts with ‘v’-shaped spectral energy distributions, broad permitted lines, and, often, hydrogen Balmer absorption. We use NIRSpec/IFS data from the BlackTHUNDER survey to study the H α line in the LRD Abell2744-QSO1 at , which is a confirmed active galactic nucleus (AGN) due to time-variable equivalent width (EW) in its broad emission lines. The H α spectral profile is non-Gaussian, requiring at least two Gaussian components. We also detect a narrow-line Gaussian component, and strong H α absorption (EW relative to the continuum ), confirming a connection between the strong Balmer break and line absorption. The absorber is at rest with respect to broad H α , suggesting that the gas cannot be interpreted as an inflow or outflow, forming instead a long-lived structure. Its velocity dispersion is , consistent with the value inferred from the analysis of the Balmer break. Based on H α , we infer a black hole mass of , smaller but close to the previous estimates based on H β . The Eddington ratio is 0.09. Combining the high signal-to-noise ratio of the narrow H α line with the spectral resolution of the G395H grating, we infer a narrow-line intrinsic dispersion , which places a stringent constraint on the black hole-to-dynamical mass ratio of this system to be , confirming the overmassive nature of the black hole and potentially leaving little room for a host galaxy.

Abstract:

We present a novel method for classifying two-dimensional orbits in rotating bar potentials based on an empirical proxy for the second integral of motion, calibrated angular momentum (CAM), which is defined as the ratio of the time-averaged angular momentum ( Lz¯ ) to its temporal dispersion ( σLz ) in the corotating frame. We show that CAM is determined by the ratio of the azimuthal to radial actions ( Jϕ′/Jr′ ) in the analytical Freeman bar model. We then construct a new parameter space defined by CAM versus the rms radius (Rrms) and apply this framework to orbits in several representative rotating bar potentials. In the CAM–Rrms plane, periodic orbits generate well-defined branches separating distinct regions corresponding to different orbital families. Several of these branches enclose isolated areas that can be associated with specific orbital families, such as the x2 orbital family. We further validate the method using orbits from test-particle simulations, which show a well-ordered and nonoverlapping distribution of orbital families in the CAM–Rrms plane. Since CAM is fundamentally linked to intrinsic orbital properties and readily applied to three-dimensional orbits in N-body simulations, our results establish the CAM–Rrms plane as a robust and efficient framework for orbit classification in rotating bars that complements conventional methods.

Abstract:

We present a new stellar-dynamical measurement of the supermassive black hole (SMBH) mass in the nearby spiral galaxy NGC 4258 (M106), a critical benchmark for extragalactic mass measurements. We use archival James Webb Space Telescope (JWST) Near-Infrared Spectrograph (NIRSpec) integral field unit data (G235H/F170LP grating) to extract high-resolution two-dimensional stellar kinematics from the CO bandhead absorption features within the central 3″ × 3″. We extract the stellar kinematics after correcting for instrumental artifacts and separating the stellar light from the nonthermal active galactic nucleus (AGN) continuum. We employ Jeans anisotropic models to fit the observed kinematics, exploring a grid of 12 models to systematically test the impact of different assumptions for the point-spread function, stellar mass-to-light ratio profile, and orbital anisotropy. All 12 models provide broadly acceptable fits, albeit with minor differences. The ensemble median and 68% (1σ) bootstrap confidence interval of our 12 models yield a black hole mass of MBH=(4.08−0.33+0.19)×107 M⊙. This paper showcases the utility of using the full model ensemble to robustly account for systematic uncertainties, rather than relying on formal errors from a single preferred model, as has been common practice. Our result is just 5% larger than, and consistent with, the benchmark SMBH mass derived from water-maser dynamics, validating the use of NIRSpec stellar kinematics for robust SMBH mass determination. Our analysis demonstrates JWST’s ability to resolve the SMBH’s sphere of influence and deliver precise dynamical masses, even in the presence of significant AGN continuum emission.

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.