Galaxy formation and evolution

Abstract:

Recent photometric surveys with James Webb Space Telescope (JWST) have revealed a significant population of mysterious objects with red colours, compact morphologies, frequent signs of active galactic nucleus (AGN) activity, and negligible X-ray emission. These ‘little red dots’ (LRDs) have been explored through spectral and photometric studies, but their nature is still under debate. As part of the BlackTHUNDER survey, we have observed UNCOVER_20466, one of the most distant LRDs known (), with the JWST/NIRSpec Integral Field Unit (IFU). Previous JWST/NIRCam and JWST/NIRSpec MSA observations of this source revealed its LRD nature, as well as the presence of an AGN. Using our NIRSpec IFU data, we confirm that UNCOVER_20466 is an LRD (based on spectral slopes and compactness) that contains an overmassive black hole. However, our observed Balmer decrements do not suggest strong dust attenuation, resulting in a lower -based bolometric luminosity and () than previously found. This source lies on local relations between and , suggesting that this could be a progenitor of the core of a lower-redshift galaxy. We explore the possible evolution of this source, finding evidence for substantial black hole accretion in the past and a likely origin as a heavy seed at high redshift (). emission is strongly detected, implying . The extremely high / ratio is indicative of not only AGN photoionization and heating, but also extremely high densities (), suggesting that this black hole at such high redshift may be forming in an ultra-dense protogalaxy.

Abstract:

Abstract We present JWST/MIRI imaging of eight nearby Active Galactic Nuclei (AGN) from the GATOS survey to investigate the physical conditions of extended dust in their narrow line regions (NLRs). In four galaxies (ESO 428−G14, NGC 4388, NGC 3081, and NGC 5728), we detect spatially resolved dust structures extending ∼100-200 pc along the NLR. In these systems, we find a strong link between the morphology of the dust, the radio ejecta, and the coronal [Si vi] emission, implying that dust carries imprints of the processes shaping the NLR. Using spatially resolved spectral energy distributions, we show that dust in the NLR has systematically steeper slopes than star forming clumps. This dust emits at temperatures in the range $150- 220\, \rm K$, at a distance of ∼150 pc from the nucleus. Using simple models, we show that, even under optimistic assumptions of grain size and AGN luminosity, the excess MIR emission cannot be explained by AGN illumination alone. We interpret this excess heating as in-situ. We show that shocks with velocities of $v_{\rm shock} \sim 200- 400 \, \rm km/s$ in dense gas can close this gap, and in some cases even account for the total observed emission. This, combined with multiple lines of evidence for shocks in these regions, supports a scenario in which shocks not only coexist with dust but may be playing a key role in heating it. Our findings reveal shocks may be an important and previously overlooked driver of extended dust emission in the central hundreds of parsecs in AGN.

Abstract:

We present gas-phase abundances of carbon (C), -elements (O, Ne, Si, and Ar), and iron (Fe) obtained from stacked spectra of high-z star-forming galaxies with the deep Near Infrared Spectrograph medium-resolution data from the James Webb Space Telescope Advanced Deep Extragalactic Survey. Our 564 sources at –7 have a median stellar mass of and a median star-formation rate of , placing them close to the star-formation main sequence. We find that the stacked spectrum of all our 564 sources has relatively low , moderate , and low values at a low gas-phase metallicity of (), suggesting dominant yields of core-collapse supernovae evolved from massive stars. The detection of a weak [Si iii] emission line in our stacked spectrum provides a silicon-to-oxygen abundance ratio of , which is lower than that of stars in the Milky Way disc and lower than expected by chemical evolution models, suggesting silicon depletion on to dust grains. Likewise, this Si/O value is lower than that we newly derive for two individual galaxies (GN-z11 and RXCJ2248) with negligible dust attenuation. By performing spectral stacking in bins of , star-formation rate (SFR), specific SFR (sSFR), and ultraviolet continuum slope , we identify [Fe iii] line detections in the high-sSFR bin and the blue- bin, both of which exhibit supersolar Fe/O ratios, while their C/O, Ar/O, and Si/O ratios are comparable to those of the all-sources stack. Our findings support a chemically young gas composition with rapid dust depletion in the general population of high-z star-forming galaxies, while raising the possibility of anomalous, selective Fe/O enhancement at the very early epoch of star formation.

Abstract:

James Webb Space Telescope (JWST)/NIRCam slitless spectroscopy enables dynamical mass measurements for typical star-forming galaxies only a billion years after the big bang. We model the H morpho-kinematics of 163 galaxies at redshift –6 from FRESCO and CONGRESS (with JADES imaging), using the geko code, and infer rotational velocities and dispersions within . Our sample spans –10 and –11. Gas masses are inferred from empirical scaling relations and combined with stellar masses to yield baryonic masses. The resulting median inferred gas-to-baryonic mass fraction is . Using these baryonic masses together with the dynamical masses, we derive dark-matter fractions within the H half-light radius, and find a high median value of , where is defined relative to the total (DM + baryonic) mass. About two-thirds of systems are DM-dominated within –1 kpc. We find that decreases with stellar mass, consistent with predictions from simulations. The stellar Tully–Fisher relation shows a tentative offset to higher at fixed and substantial intrinsic scatter, suggesting that the relation is only beginning to emerge at . We measure a negative correlation between and baryonic surface density , weaker but broadly consistent with trends at cosmic noon and at . Qualitatively comparing with modified NFW profiles coupled to an empirical stellar-to-halo mass relation suggests that the lowest () require cored inner DM profiles, while the highest fractions favour cuspier profiles, potentially reflecting adiabatic contraction. Overall, the elevated and at are compatible with progenitors of baryon-dominated systems at and naturally anticipate overmassive black holes at fixed .