Galaxy formation and evolution

Abstract:

The James Webb Space Telescope ( ) opened a new observational window on the primordial Universe. Here we present new JWST NIRSpec integral field spectroscopy (IFS) observations of the z=7.54 quasar ULAS J1342+0928 obtained as part of the Galaxy Assembly with NIRSpec IFS (GA-NIFS) GTO programme. The new data-set obtained with both the prism (R , with a mean (median) value of 480 (390) ̊m M_⊙ , JWST and the high-resolution grating (R emission on ∼7 kpc scales, well above the typical galaxy size at this redshift, likely associated with a past outflow event. Additionally, the high-resolution observations show a more energetic ionised outflow on nuclear scales (łesssim 0.8 kpc). The total ionised mass outflow rate ranges between ∼100 and 2200 ̊m M_⊙ , yr^ allow for a complete description of the quasar emission from the rest-frame UV to optical bands. The low-resolution data reveal the presence of O iii -1 -1 , where the significant spread is mostly due to the lack of tight constraints on the electron density and outflow geometry. This range broadly encompasses the star formation rate range (85--545 ̊m M_⊙ , yr^ -1 ), yet this only represents a lower limit to the total mass outflow rate. By employing an accretion disc modelling, for the first time on data, we manage to robustly estimate the black hole mass and the bolometric luminosity, ̊m łog(M_ JWST BH /(M_⊙))=9.1± 0.2 and ̊m łog(L_ bol /(erg , s^ -1 ))=46.8± 0.1, respectively. We derive an Eddington ratio of ̊m λ_ Edd ∼ 0.4, challenging the paradigm of widespread super-Eddington accretion in quasars at the epoch of re-ionisation. Lastly, we measure the most distant broad line ratios ( / and / ) so far. Interpreting these ratios as proxies to the broad line region metallicity, we find evidence for an early metal enrichment in quasars within 700 Myrs from the Big Bang. Fe ii UV Mg ii Fe ii opt H β

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.

Abstract:

We use JWST NIRCam and MIRI imaging at 2, 4, 10, and 21 μm to study young, dusty compact sources in four nearby galaxies at distances of ∼1–5 Mpc (M33, NGC 300, NGC 7793, and NGC 5068). This work bridges well-characterized massive young stellar objects (MYSOs) in the Magellanic Clouds from the Spitzer Space Telescope SAGE survey to new studies of embedded clusters in more distant galaxies with JWST. Guided by the SAGE-LMC catalog, we define JWST color–magnitude selection criteria (F1000W versus F1000W − F2100W) and test them using resolution-degradation experiments. We identify 216, 32, 80, and 139 dusty young objects in the four galaxies, respectively. The selected population spans sources from systems dominated by a single MYSO to compact marginally resolved sources hosting multiple MYSOs. The color selection remains stable across 1–5 Mpc, and the 10 μm luminosity function retains a slope of α ∼ −2. However, blending and surface-brightness dilution remove fainter sources, leading to incompleteness of up to ∼50% at 5.2 Mpc and biasing the sample toward brighter objects (F1000W < 19 mag). The sample spans approximate stellar masses of ∼10–2 × 10⁵ M⊙. Spatial resolution affects the interpretation of mid-IR emission: clustering increases the fraction of emission attributed to compact sources in active regions, while blending into diffuse emission dominates in quiescent environments. Comparisons with polycyclic aromatic hydrocarbon (PAH)-selected young clusters in the PHANGS galaxy NGC 5068 show that our selection recovers ∼80% of the PAH-selected sources. We show that the practical limit for studying individual MYSOs with JWST is ∼3 Mpc. The resulting catalog provides a foundation for future resolved studies of star formation rates and early cluster evolution.

Abstract:

Context. High-resolution JWST-MIRI images allow us to resolve the multi-scale nature of the emission in nearby star-forming galaxies in great detail, from compact star-forming regions to large-scale diffuse emission, providing new insights into dust emission, its composition, and the surrounding interstellar medium (ISM). Aims. We aim to understand at which scale the different processes driving dust emission in mid-infrared (7.7−21 μm) wavelengths take place and whether we can disentangle emission from dense regions from the one linked to a more diffuse component. Methods. We use and enhance the Constrained Diffusion Decomposition algorithm (CDD), an alternative to wavelet transform decomposition, to disentangle the emission from compact regions from the emission originating from diffuse sources. This allows us to quantify the mid-IR spectral properties of the ISM at intervals within a continuum of physical scales. Results. We find a transition scale for Polycyclic Aromatic Hydrocarbons (PAH) emission around 300 pc, with a weaker PAH fraction at smaller scales, highlighting the destruction of PAHs in H II regions. We also show variations in the PAH fraction in different morphological environments, with a lower fraction in bright and star-forming environments. By studying and comparing the probability distribution functions (PDFs) of H II regions and of diffuse ISM with the PDFs at different scales, we find a similar separation scale around 200 pc at which we observe a transition from a power-law PDF for dense structures to a log-normal distribution for the diffuse ISM. Conclusions. We infer the destruction of PAHs in nebular environments and the existence of a transition scale between stellar feedback in nebular regions and heating in the diffuse ISM. We also show that the CDD enables future applications to study the physical scales of emission.