Galaxy formation and evolution

Abstract:

Early-type galaxies (ETGs) show a bimodal distribution in key structural properties like stellar specific angular momentum, kinematic morphology, shape, and nuclear surface brightness profiles. Slow rotator ETGs, mostly found in the densest regions of galaxy clusters, become common when the stellar mass exceeds a critical value of around M ∗ crit ≈2×1011 M ⊙, or more precisely when lg(R e/kpc)≳12.4−lg(M ∗/M ⊙). These galaxies have low specific angular momentum, spheroidal shapes, and stellar populations that are old, metal-rich, and α-enhanced. In contrast, fast rotator ETGs form a continuous sequence of properties with spiral galaxies. In these galaxies, the age, metallicity, and α-enhancement of the stellar population correlate best with the effective stellar velocity dispersion σ e ∝ M ∗ / R e (i.e., properties are similar for R e ∝ M ∗), or with other proxies approximating their bulge mass fraction. This sequence spans from star-forming spiral disks to quenched, passive, spheroid-dominated fast rotator ETGs. Notably, at a fixed σ e, younger galaxies show lower metallicity. The structural differences and environmental distributions of ETGs suggest two distinct formation pathways: slow rotators undergo early intense star formation followed by rapid quenching via their dark halos and supermassive black holes, and later evolve through dry mergers during hierarchical cluster assembly; fast rotators, on the other hand, develop more gradually through gas accretion and minor mergers, becoming quenched by internal feedback above a characteristic lg(σ e crit/km s−1) ≳ 2.3 (in the local Universe) or due to environmental effects.

Abstract:

Strong gravitational lensing has emerged as one of the most versatile tools to explore a range of open questions in astrophysics and cosmology. In this chapter, we focus on the significant contribution of strong lensing in the fields of galaxy structure and evolution. This includes the distribution of luminous and dark matter in galaxies, dark matter substructure, the initial mass function in intermediate redshift massive galaxies and the nature of high redshift galaxies. The impact of this probe has been significant, despite the rarity of known gravitational lens systems. In the imminent era of wide-area sensitive sky surveys, that will reveal 105 strong lensing systems, the full potential of strongly lensed galaxies as an essential and versatile probe of the nature of galaxies will be realized.

Abstract:

Abstract:

We combine the power of blind integral field spectroscopy from the Hobby–Eberly Telescope (HET) Dark Energy Experiment (HETDEX) with sources detected by the Low Frequency Array (LOFAR) to construct the HETDEX-LOFAR Spectroscopic Redshift Catalog. Starting from the first data release of the LOFAR Two-metre Sky Survey, including a value-added catalog with photometric redshifts, we extracted 28,705 HETDEX spectra. Using an automatic classifying algorithm, we assigned each object a star, galaxy, or quasar label along with a velocity/redshift, with supplemental classifications coming from the continuum and emission-line catalogs of the internal, fourth data release from HETDEX (HDR4). We measured 9087 new redshifts; in combination with the value-added catalog, our final spectroscopic redshift sample is 9710 sources. This new catalog contains the highest substantial fraction of LOFAR galaxies with spectroscopic redshift information; it improves archival spectroscopic redshifts and facilitates research to determine the [O ii] emission properties of radio galaxies from 0.0 < z < 0.5, and the Lyα emission characteristics of both radio galaxies and quasars from 1.9 < z < 3.5. Additionally, by combining the unique properties of LOFAR and HETDEX, we are able to measure star formation rates (SFRs) and stellar masses. Using the Visible Integral-field Replicable Unit Spectrograph, we measure the emission lines of [O iii], [Ne iii], and [O ii] and evaluate line-ratio diagnostics to determine whether the emission from these galaxies is dominated by active galactic nuclei or star formation and fit a new SFR–L 150MHz relationship.