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Abstract:

Axisymmetric Jeans modelling is widely used to infer galaxy mass profiles from integral-field kinematics, but existing implementations maintain tractability by adopting highly restricted anisotropy prescriptions. I present a new spectral method that solves the axisymmetric Jeans equations as a two-dimensional boundary-value problem. Remarkably, this breaks the traditional trade-off between model flexibility and computational cost, accommodating completely general anisotropy distributions while executing significantly faster than standard restrictive techniques. The method relies on three key choices: (i) solving for the intrinsic dispersion rather than the rapidly varying pressure to improve numerical conditioning; (ii) working in logarithmic radius to efficiently resolve the large dynamic range of galaxies, uniquely matching scale-free (power law) regimes; and (iii) imposing a Robin outer boundary condition that enforces the correct asymptotic decay on a finite computational domain. Orbit integrations in realistic galaxy potentials motivate spherical alignment of the velocity ellipsoid as a physically plausible default, though the framework easily adapts to other alignments. Validated against exact analytic benchmarks – including new analytic Jeans solutions derived herein – the solver recovers intrinsic second moments with high accuracy, showing radially uniform residuals for power-law tests. In practice, it delivers orders-of-magnitude speed-ups over high-accuracy quadrature schemes and is naturally suited to massive GPU parallelization. Released in the public jampy package, this enables the routine application of highly general Jeans models to large surveys and the extensive parameter-space exploration required for rigorous uncertainty quantification.

Abstract:

Stellar halos are the only major stellar component of disk galaxies that lack systematic observational characterization, yet they encode critical information about galaxy merger histories. We present the first systematic census of stellar halos in a large, flux-limited sample of 169 high-inclination central galaxies with stellar masses 7.3≤logM⋆/M⊙≤11.0 and redshift z < 0.1, using Hyper Suprime-Cam Subaru Strategic Survey Deep optical images. Stellar halos are detected in 93 galaxies, primarily through their low isophotal ellipticities in the outskirts, improving upon conventional methods of stellar halo identification. The halo detection rate reaches ∼50% at logM⋆/M⊙>9.9 and ≳70% for Milky Way (MW)-mass galaxies. We derive halo surface brightness profiles, colors, and masses, finding that stellar halos generally follow power-law radial profiles. Higher-mass galaxies, on average, exhibit smaller power-law indices and larger halo mass fractions, indicating more extended halos and more active merger histories. A significant stellar halo color–mass correlation, driven mainly by the mass–metallicity relation, suggests dominance by a few massive accretion events. MW-mass galaxies have a median stellar halo fraction of 10% ± 5%. Among nearby galaxies with halo measurements within 25 Mpc, two-thirds (including the MW) lie below the mean stellar halo fraction–galaxy mass relation. Overall, the nearby galaxies show a median halo deficit of ∼0.3 dex, implying unusually quiescent merger histories. We show that this deficit follows a broader trend in which typical halo fractions increase with heliocentric distance, tracking the gradual rise in matter density toward the cosmic average by z ≲ 0.07.

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.