Galaxy formation and evolution

Abstract:

Does the environment of a galaxy directly influence the kinematics of its bar? We present observational evidence that bars in high-density environments exhibit significantly slower rotation rates than bars in low-density environments. Galactic bars are central, extended structures composed of stars, dust and gas, present in approximately 30–70 per cent of luminous spiral galaxies in the local Universe. Recent simulation studies have suggested that the environment can influence the bar rotation rate, , which is used to classify bars as either fast () or slow (). We use estimates of obtained with the Tremaine–Weinberg method applied to Integral Field Unit spectroscopy from Mapping Nearby Galaxies at Apache Point Observatory and Calar Alto Legacy Integral Field Area. After cross-matching these with the projected neighbour density, , we retain 286 galaxies. The analysis reveals that bars in high-density environments are significantly slower (median ) compared to bars in low-density environments (median ); Anderson–Darling p-value of (). This study marks the first empirical test of the hypothesis that fast bars are formed by global instabilities in isolated galaxies, while slow bars are triggered by tidal interactions in dense environments, in agreement with predictions from numerous N-body simulations. Future studies would benefit from a larger sample of galaxies with reliable Integral Field Unit data, required to measure bar rotation rates. Specifically, more data are necessary to study the environmental influence on bar formation within dense settings (i.e. groups, clusters and filaments).

Abstract:

We study the luminosity function (LF) and clustering properties of 888 Hα emitters (HAEs) at 3.75 < z < 6 in the GOODS-N field. The sample, built from JWST CONGRESS and FRESCO NIRCam grism surveys using a novel redshift assignment algorithm, spans ∼62 arcmin2 and reaches LHα ∼ 1041.2 erg s−1. We identify two prominent filamentary protoclusters at z ≈ 4.41 and z ≈ 5.19, hosting 98 and 144 HAEs, respectively. The observed Hα LFs show similar shallow faint-end slopes for both protocluster and field galaxies at 3.75 < z < 5, and for the protocluster at 5 < z < 6 (α ≈ −1.2 to −1.3). In contrast, the field LF at 5 < z < 6 has a much steeper slope ( α=−1.87−0.23+0.30 ), suggesting that protocluster galaxies at z > 5 are more evolved, resembling the populations at 3.75 < z < 5. The observed star formation rate density from Hα integrated down to 0.45 M⊙ yr−1, is 0.050−0.003+0.002M⊙yr−1Mpc−3 at 3.75 < z < 5 and 0.046−0.004+0.006M⊙yr−1Mpc−3 at 5 < z < 6, with protoclusters contributing about 25% and 55%, respectively. This implies a large fraction of star formation at z > 4 occurs in protoclusters. For the first time, we conduct the star formation-rate-limited three-dimensional clustering analysis at z > 4. We find that the filamentary geometry of protoclusters flattens the power-law shape of the HAE autocorrelation functions, with slopes much shallower than the typically assumed value. The autocorrelation function of field HAEs has a correlation length of r0=4.61−0.68+1.00h−1Mpc at z ≈ 4−5 and r0=6.23−1.13+1.68h−1Mpc at z ≈ 5−6. Comparing the observed correlation functions with the UniverseMachine simulation, we infer the dark matter (sub-)halo masses of HAEs to be log(Mh/M⊙)=11.0−11.2 at z ≈ 4−6, with a scatter of 0.4 dex.