Cosmology

Abstract:

We present a follow-up analysis examining the dynamics and structures of 41 massive, large star-forming galaxies at z ∼ 0.67 - 2.45 using both ionized and molecular gas kinematics. We fit the galaxy dynamics with models consisting of a bulge, a thick, turbulent disk, and an NFW dark matter halo, using code that fully forward-models the kinematics, including all observational and instrumental effects. We explore the parameter space using Markov Chain Monte Carlo (MCMC) sampling, including priors based on stellar and gas masses and disk sizes. We fit the full sample using extracted 1D kinematic profiles. For a subset of 14 well-resolved galaxies, we also fit the 2D kinematics. The MCMC approach robustly confirms the results from least-squares fitting presented in Paper I: the sample galaxies tend to be baryon-rich on galactic scales (within one effective radius). The 1D and 2D MCMC results are also in good agreement for the subset, demonstrating that much of the galaxy dynamical information is captured along the major axis. The 2D kinematics are more affected by the presence of noncircular motions, which we illustrate by constructing a toy model with constant inflow for one galaxy that exhibits residual signatures consistent with radial motions. This analysis, together with results from Paper I and other studies, strengthens the finding that massive, star-forming galaxies at z ∼ 1 - 2 are baryon-dominated on galactic scales, with lower dark matter fractions toward higher baryonic surface densities. Finally, we present details of the kinematic fitting code used in this analysis.

Abstract:

We present a new set of index-based measurements of [α/Fe] for a sample of 2093 galaxies in the SAMI Galaxy Survey. Following earlier work, we fit a global relation between [α/Fe] and the galaxy velocity dispersion σ for red sequence galaxies, [α/Fe]=(0.378±0.009)log10(σ/100)+(0.155±0.003)⁠. We observe a correlation between the residuals and the local environmental surface density, whereas no such relation exists for blue cloud galaxies. In the full sample, we find that elliptical galaxies in high-density environments are α-enhanced by up to 0.057 ± 0.014 dex at velocity dispersions σ < 100 km s−1, compared with those in low-density environments. This α-enhancement is morphology-dependent, with the offset decreasing along the Hubble sequence towards spirals, which have an offset of 0.019 ± 0.014 dex. At low velocity dispersion and controlling for morphology, we estimate that star formation in high-density environments is truncated ∼1 Gyr earlier than in low-density environments. For elliptical galaxies only, we find support for a parabolic relationship between [α/Fe] and σ, with an environmental α-enhancement of at least 0.03 dex. This suggests strong contributions from both environment and mass-based quenching mechanisms. However, there is no evidence for this behaviour in later morphological types.

Abstract:

We present Lyα and ultraviolet (UV)-continuum luminosity functions (LFs) of galaxies and active galactic nuclei (AGNs) at z = 2.0-3.5 determined by the untargeted optical spectroscopic survey of the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX). We combine deep Subaru imaging with HETDEX spectra resulting in 11.4 deg2 of fiber spectra sky coverage, obtaining 18,320 galaxies spectroscopically identified with Lyα emission, 2126 of which host type 1 AGNs showing broad (FWHM > 1000 km s-1) Lyα emission lines. We derive the Lyα (UV) LF over 2 orders of magnitude covering bright galaxies and AGNs in (-27 < MUV < -20) by the 1/Vmax estimator. Our results reveal that the bright-end hump of the Lyα LF is composed of type 1 AGNs. In conjunction with previous spectroscopic results at the faint end, we measure a slope of the best-fit Schechter function to be αSch=-1.70-0.14+0.13, which indicates that αSch steepens from z = 2-3 toward high redshift. Our UV LF agrees well with previous AGN UV LFs and extends to faint-AGN and bright-galaxy regimes. The number fraction of Lyα-emitting objects (XLAE) increases from MUV∗ ∼ -21 to bright magnitude due to the contribution of type 1 AGNs, while previous studies claim that XLyα decreases from faint magnitudes to MUV∗, suggesting a valley in the XLyα-magnitude relation at MUV∗. Comparing our UV LF of type 1 AGNs at z = 2-3 with those at z = 0, we find that the number density of faint (MUV > -21) type 1 AGNs increases from z ∼ 2 to 0, as opposed to the evolution of bright (MUV < -21) type 1 AGNs, suggesting AGN downsizing in the rest-frame UV luminosity.