Galaxy formation and evolution

Abstract:

We present gas-phase abundances of carbon (C), α-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 z = 4–7 have a median stellar mass of log (M*/M⊙) = 8.46 and a median star-formation rate of log (SFR/M⊙ yr−1) = 0.30, placing them close to the star-formation main sequence. We find that the stacked spectrum of all our 564 sources has relatively low [C/O] = −0.70, moderate [Ne/O] = −0.09, and low [Ar/O] = −0.28 values at a low gas-phase metallicity of 12 + log (O/H) = 7.71 (Z ∼ 0.1 Z⊙), 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 [Si/O] = −0.63, which is lower than that of stars in the Milky Way disc and lower than expected by chemical evolution models, suggesting silicon depletion onto dust grains. Likewise, this Si/O value is lower than that we newly derive for two individual z > 6 galaxies (GN-z11 and RXCJ2248) with negligible dust attenuation. By performing spectral stacking in bins of M*, SFR, specific SFR (sSFR), and ultra-violet (UV) continuum slope βUV, we identify [Fe iii] line detections in the high-sSFR bin and the blue-βUV 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 .

Abstract:

The evolution of galaxies is known to be connected to their position within the large-scale structure and their local environmental density. We investigate the relative importance of these using the underlying dark matter density field extracted from the Constrained Simulations in BORG (CSiBORG) suite of constrained cosmological simulations. We define cosmic web environment through both dark matter densities averaged on a scale up to 16 Mpc , and through cosmic web location identified by applying DisPerSE to the CSiBORG haloes. We correlate these environmental measures with the properties of observed galaxies in large surveys using optical data (from the NASA-Sloan Atlas) and 21-cm radio data (from ALFALFA). We find statistically significant correlations between environment and colour, neutral hydrogen gas () mass fraction, star formation rate, and Sérsic index. Together, these correlations suggest that bluer, star-forming, rich, and disc-type galaxies tend to reside in lower density areas, further from filaments, while redder, more elliptical galaxies with lower star formation rates tend to be found in higher density areas, closer to filaments. We find analogous trends with the quenching of galaxies, but notably find that the quenching of low-mass galaxies has a greater dependence on environment than the quenching of high-mass galaxies. We find that the relationship between galaxy properties and the environmental density is stronger than that with distance to filament, suggesting that environmental density has a greater impact on the properties of galaxies than their location within the larger-scale cosmic web.