Galaxy formation and evolution

Abstract:

We present the search and characterisation of ionised outflows in a sample of 15 star-forming systems at z $ and outflow velocities V_ with no evidence of active galactic nuclei (AGNs) observed with the JWST/NIRSpec instrument in Integral Field Spectroscopic mode (IFS) as part of the `Galaxy Assembly with NIRSpec IFS' (GA-NIFS) program. Some of the target systems are comprised of various individual galaxies, adding up to a total of 40 individual objects. Our sample encompasses the high mass end of the galaxy populations, with most of the sample having stellar masses within log_10 (M_⋆/M_⊙) = 9.5-11, while previous studies on high-z star formation driven outflows generally contain galaxies of log_10 (M_⋆/M_⊙)$<9.5$. Leveraging the spatially resolved information and rest-frame optical coverage provided by NIRSpec IFS data, we analysed the and ̋a emission lines to search for broad kinematic components associated with galactic outflows. Crucially, the IFS observations allowed us to directly isolate the regions hosting the outflows, rather than relying on integrated spectra. We identified signatures of ionised outflows in 16 individual galaxies/regions (in 13 out of 15 systems), although we consider two of them only as `candidates', as they could be related to mergers or tidal interactions. After constraining their spatial location and extent, we characterised the integrated properties of the outflowing gas and evaluated the impact on the host galaxies. We find that the outflowing gas is more dust attenuated (by A_ ̊m V mag on average) and metal enriched (sim0.13 dex) than the interstellar medium of the host galaxies, suggesting that outflows contribute to distributing dust and metals around them. The outflows identified in this study present velocity dispersions within σ_ ̊m out km s -1 ̊m out km s^-1. Considering also less luminous and less massive star-forming galaxies from previous works, there is a statistically significant correlation between outflow velocity (v_̊m out) and star formation rate (SFR). The generally low mass-loading factors (η= _ ̊m M ̊m out /SFR $<1, in nine out of 14 outflows) obtained for the ionised outflows suggest that they do not suppress star formation in the host galaxies. Moreover, their velocities are not high enough to escape their hosts and reach the circumgalactic medium. Our results indicate that ejective feedback through ionised outflows is inefficient in high-mass and luminous star-forming galaxies within the first 2 Gyr of cosmic time.

Abstract:

Massive quenched galaxies at z>3 challenge models of early galaxy evolution, as their rapid formation and abrupt quenching require efficient feedback, which is often linked to active galactic nuclei (AGNs). The quiescent galaxy at z=3.064 is a key example of this population. Previous JWST/NIRSpec integral field unit (IFU) observations revealed an AGN-driven outflow and uncovered a compact pair of AGNs separated by sim5 kpc. In addition, VLT/MUSE spectroscopy identified a third AGN candidate at a projected distance of sim30 kpc, associated with a luminous łya emitter (LAE2) characterised by high-ionisation UV lines, although rest-frame optical diagnostics were not previously available. We aim to confirm the nature of LAE2 using rest-frame optical diagnostics enabled by new JWST observations, and to characterise the physical and ionisation properties of both LAE2 and a distinct nearby łya emitter (LAE1) that lacks any detectable continuum counterpart. Through this analysis, we investigated the interplay among low-mass satellites, black-hole growth, and the ionised environment of a quenched massive galaxy at high redshift. We analysed new JWST/NIRSpec IFU observations targeting the optical nebular lines of LAE1 and LAE2, including and ∋i, complemented with VLT/MUSE IFU spectroscopy, as part of the GA-NIFS project. We extracted integrated and spatially resolved spectra, constructed emission-line maps, and used standard diagnostic diagrams to determine ionisation sources and kinematics. LAE2 exhibits rest-frame UV–optical-line ratios fully consistent with an embedded AGN. Its and emission displays a clumpy morphology and irregular, non-rotating kinematics on sub-kiloparsec scales. Except for łya, LAE1 remains undetected in all nebular lines and in JWST imaging; its łya emission is broad (σ ∼ 200 ̨ms) and asymmetric. The similarity of the LAE1 and LAE2 łya profiles in both velocity and flux suggests that LAE1 traces resonantly scattered emission powered by LAE2 rather than in situ star formation (although the latter cannot be completely ruled out). Our analysis reveals that the environment of contains both multi-black-hole activity and gas structures on tens-of-kiloparsec scales, offering new insights into how feedback, accretion, and satellite interactions influence the late evolutionary stages of quenched massive galaxies.

Abstract:

Type Ia supernova (SN Ia) standardization parameters exhibit evidence for systematic variation across the host galaxy star formation rate–stellar mass (SFR) plane, motivating the incorporation of galaxy SFR information in cosmological inference. SFRs are commonly estimated via spectral energy distribution (SED) fitting with far-infrared (FIR) measurements to account for dust-obscured star formation. Such FIR coverage will, however, be limited for upcoming time-domain surveys such as the Rubin Observatory Legacy Survey of Space and Time (LSST), necessitating the use of alternative SFR tracers. Here, we reconstruct the SFR– plane using 1.4 GHz diagnostics, to test the consistency of host classifications against FIR-constrained SED-based estimates. Within this plane, SN Ia host galaxies are divided into three regions: Region 1 (low mass), Region 2 (high-mass star forming), and Region 3 (high-mass passive). We find that per cent of SN hosts retain identical region assignments when using radio versus FIR-constrained SED-derived SFRs. Measuring SN Ia nuisance parameters () within each subregion, we find consistent values between the two SFR– plane reconstructions, indicating limited sensitivity to SFR estimator choice, with the largest deviations in Region 3 at . Across the three 1.4 GHz SFR– subregions, we confirm the region-dependent variation in SN Ia standardization parameters – particularly – reported in our earlier SED-based analysis. With near-complete radio coverage of the LSST footprint anticipated from current and forthcoming radio continuum surveys (e.g. Square Kilometre Array), radio SFR calibrations will become an increasingly useful and scalable approach to host galaxy classification, supporting the construction of robust SN Ia subsamples for precision cosmology.

Abstract:

Context. Ultra-compact massive galaxies (UCMGs) often exhibit elevated stellar-to-dynamical mass ratios when dynamical masses are estimated using standard virial prescriptions. This discrepancy has been interpreted as evidence for structural non-homology driven primarily by their compactness. Aims. This study investigates how the stellar-to-dynamical mass ratio depends on compactness (C), internal kinematics (σ*), stellar population properties (mass-weighted age, metallicity, and [Mg/Fe]), and star formation histories. The analysis is based on a homogeneous catalogue of 482 UCMGs from the INSPIRE and E-INSPIRE surveys, extending to significantly smaller sizes than previously analysed samples. Methods. I first derive the compactness–mass relation assuming a constant virial coefficient (K = 5). I then correct stellar masses for initial mass function (IMF) variations and recompute stellar-to-dynamical mass ratios using an empirical prescription in which the virial coefficient varies as a function of radius and stellar mass. Finally, I test whether the relation is modulated by stellar kinematics and population properties, including the degree of relicness (DoR), which quantifies the extremeness of the star formation history. Results. A statistically significant anti-correlation between compactness and the IMF-corrected stellar-to-dynamical mass ratio is recovered when a constant virial coefficient is adopted, even within the relatively narrow range of C spanned by nearby UCMGs. The relation substantially flattens when a structure-dependent K is adopted, in agreement with previous literature. Beyond this one-dimensional behaviour, the data define a structural–dynamical manifold in the (logC,Clog σ*) space. Velocity dispersion sets the dominant axis of variation, and the corresponding plane accounts for ∼62% of the variance in stellar-to-dynamical mass ratio. Including stellar age increases the explained variance to ∼63%, revealing a secondary evolutionary modulation. In contrast, DoR, metallicity, and [Mg/Fe] do not retain independent explanatory power once stellar age is included. Conclusions. The stellar-to-dynamical mass ratio in UCMGs is governed primarily by the depth of the gravitational potential, traced by stellar velocity dispersion, rather than by compactness alone. At fixed size, systems with higher σ* exhibit systematically lower stellar-to-dynamical mass ratio, indicating that dynamical structure regulates the apparent mass imbalance in the ultra-compact regime. Compactness largely reflects this dynamical scaling, while stellar age introduces a coherent secondary modulation linking the structural manifold to the evolutionary state of the galaxy. Non-homology in UCMGs therefore encodes coupled dynamical and assembly processes rather than purely geometric compactness.