Galaxy formation and evolution

Abstract:

Abstract JWST has revealed a population of ‘Little Red Dots’ (LRDs): compact, red objects at redshifts z = 2–9 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 z = 7.04, which is a confirmed 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 $\sim 22_{+12}^{-7}\mathring{\rm A}$), 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 $\sigma _abs = 110^{+20}_{-10}$ km s−1, consistent with the value inferred from the analysis of the Balmer break. Based on H α, we infer a black hole mass of log (M•/M⊙) = 7.2, 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 R = 3, 700 of the G395H grating, we infer a narrow-line intrinsic dispersion $\sigma _\mathrm{n}=22_{-6}^{+5}$ km s−1, which places a stringent constraint on the black-hole-to-dynamical-mass ratio of this system to be M•/Mdyn = 0.15–1.2, confirming the overmassive nature of the black hole and potentially leaving little room for a host galaxy.

Abstract:

This Letter presents an analysis of the infrared (∼3–28 μm) spectra extracted from the nuclear (r < 150 pc) regions of four low-luminosity active galactic nuclei (AGN), observed by JWST NIRSpec/integral field unit and MIRI/Medium Resolution Spectroscopy as an extension of the Galaxy Activity, Torus, and Outflow Survey. We find that, compared to higher-luminosity AGN, these low-luminosity AGN exhibit distinct properties in their emission of ionized gas, polycyclic aromatic hydrocarbons (PAHs), and molecular hydrogen (H2). Specifically, the low-luminosity AGN exhibit relatively weak high ionization potential lines (e.g., [Ne V] and [O IV]), and the line ratios suggest that fast radiative shocks (with vs of ∼100s km s−1) are the primary excitation source of ionized gas therein. Under the low-excitation conditions of their nuclear regions, these low-luminosity AGN generally exhibit a higher fraction of PAHs with large size (NC ≳ 200), reflecting the preferential destruction of smaller PAH molecules by AGN feedback. Furthermore, the H2 transitions in these low-luminosity AGN are not fully thermalized, with slow, plausibly jet-driven molecular shocks (with vs ≤ 10 km s−1) likely being the extra excitation source. Taken together with results from the literature, these findings indicate that feedback operates in both low- and high-luminosity AGN, although its impact varies with AGN luminosity. In particular, systematic variations in PAH band ratios are found across AGN, demonstrating the differing influence of feedback in AGN of varying luminosities and highlighting the potential of PAH band ratios as diagnostics for distinguishing kinetic- and radiative-mode AGN feedback.

Abstract:

Abstract We present JWST/NIRSpec IFU observations of the z = 7.152 galaxy system B14-65666, as part of the GA-NIFS survey. Line and continuum emission in this massive system (log10(M*/M⊙) = 9.8 ± 0.2) is resolved into two strong cores surrounded by diffuse emission, as seen in recent JWST/NIRCam imaging. Our dataset contains detections of [OII]λλ3726, 3729, [NeIII]λλ3869, 3968, Balmer lines, [OIII]λλ4959, 5007, HeIλ5875, and weak [OIII]λ4363. Each spectrum is fit with a model that consistently incorporates interstellar medium conditions (i.e., electron temperature, Te, electron density, ne, and colour excess, E(B − V)). The resulting line fluxes are used to constrain the gas-phase metallicity (Zg ~ 0.2 − 0.3 solar) and Hβ-based SFR for each region. Common line ratio diagrams (O32-R23, R3-R2, Ne3O2-R23) reveal that each line-emitting region lies at the intersection of low- and high-redshift galaxies, suggesting low ionisation and higher metallicity compared to the predominantly lower-mass galaxies studied with the JWST/NIRSpec IFU so far at z > 5.5. Spaxel-by-spaxel fits reveal evidence for both narrow (FWHM <400 km s−1) and broad (FWHM >500 km s−1) line emission, the latter of which likely represents tidal interaction or outflows. Comparison to ALMA [C II]158μm and [O III]88μm data shows a similar velocity structure, and we explore optical-far infrared diagnostics. The two core galaxies both lie on the mass-metallicity relation at z > 4, but show contrasting properties (e.g., M*, Zg), suggesting distinct evolutionary pathways. Combining the NIRSpec IFU and ALMA datasets, our analysis opens new windows into the merging system B14-65666.

Abstract:

Supermassive black hole (SMBH) binary systems are an unavoidable outcome of galaxy mergers. Their dynamics encode valuable information about their formation and growth, the composition of their host galactic nuclei, the evolution of galaxies, and the nature of gravity. Many SMBH binaries with separations pc-kpc have been found, but closer (subparsec) binaries remain to be confirmed. Identifying these systems may elucidate how binaries evolve past the “final parsec” until gravitational radiation drives them to coalescence. Methods to discover and characterize SMBH binaries can shed light on these important questions and potentially open new multimessenger channels. Here we show that SMBH binaries in nonactive galactic nuclei can be identified and characterized by the gravitational lensing of individual bright stars, located behind them in the host galaxy. The rotation of “caustics”—regions where sources are hugely magnified due to the SMBH binary’s orbit and inspiral—leads to quasiperiodic lensing of starlight (QPLS). The extreme lensing magnification of individual bright stars produces a significant variation in the host galaxies’ luminosity; their lightcurve traces the orbit of the SMBH binary and its evolution, analogous to the waveforms recorded by gravitational-wave (GW) detectors. QPLS probes the population of sources observable by pulsar timing arrays and space detectors (LISA, TianQin), offering advance warning triggers for merging SMBHs for coincident or follow-up GW detections. SMBH population models predict 1–50 $[190–5000](n_{\star }/{\mathrm{pc}}^{-3})$ QPLS binaries with period less than 10[40] yr with comparable masses and redshift $z<0.3$ , where $n_{\star }$ is the stellar number density. Additionally, stellar and orbital motion will lead to frequent instances of single or double flares caused by SMBHBs with longer periods. This novel signature can be searched for in a wealth of existing and upcoming time-domain photometric data: identifying quasiperiodic variability in galactic lightcurves will reveal an ensemble of binary systems and illuminate outstanding questions around them.

Abstract:

Abstract Deep radio continuum surveys provide fundamental constraints on galaxy evolution, but source confusion limits sensitivity to the faintest sources. We present a complete framework for producing high-fidelity deblended radio catalogues from the confused MIGHTEE maps using the probabilistic deblending framework XID+ and prior positions from deep multi-wavelength data in the COSMOS field. To assess performance, we construct MIGHTEE-like simulations based on the Tiered Radio Extragalactic Continuum Simulation (T-RECS) radio source population, ensuring a realistic distribution of star-forming galaxies and active galactic nuclei (AGN) for validation. Through these simulations, we show that prior catalogue purity is the dominant factor controlling deblending accuracy: a high-purity prior, containing only sources with a high likelihood of radio detection, recovers accurate flux densities and reproduces input source counts down to ~3σ (where σ = thermal noise). On the other hand, a complete prior overestimates the source counts due to spurious detections. Our optimal strategy combines the high-purity prior with a mask that removes sources detected above 50 μJy. Applied to the ~1.3 deg2 area of the MIGHTEE-COSMOS field defined by overlapping multi-wavelength data, this procedure yields a deblended catalogue of 89,562 sources. The derived 1.4 GHz source counts agree with independent P(D) analyses and indicate that we resolve the radio background to ~4.8 μJy. We also define a recommended high-fidelity sample of 20,757 sources, based on detection significance, flux density, and goodness-of-fit, which provides reliable flux densities for individual sources in the confusion-limited regime.