This paper provides an update of our previous scaling relations between galaxy-integrated molecular gas masses, stellar masses, and star formation rates (SFRs), in the framework of the star formation main sequence (MS), with the main goal of testing for possible systematic effects. For this purpose our new study combines three independent methods of determining molecular gas masses from CO line fluxes, far-infrared dust spectral energy distributions, and ∼1 mm dust photometry, in a large sample of 1444 star-forming galaxies between z = 0 and 4. The sample covers the stellar mass range log(M _*/M _⊙) = 9.0–11.8, and SFRs relative to that on the MS, δMS = SFR/SFR(MS), from 10^−1.3 to 10^2.2. Our most important finding is that all data sets, despite the different techniques and analysis methods used, follow the same scaling trends, once method-to-method zero-point offsets are minimized and uncertainties are properly taken into account. The molecular gas depletion time t _depl, defined as the ratio of molecular gas mass to SFR, scales as (1 + z)^−0.6 × (δMS)^−0.44 and is only weakly dependent on stellar mass. The ratio of molecular to stellar mass μ _gas depends on ( 1 + z ) 2.5 × ( δ MS ) 0.52 × ( M * ) − 0.36 , which tracks the evolution of the specific SFR. The redshift dependence of μ _gas requires a curvature term, as may the mass dependences of t _depl and μ _gas. We find no or only weak correlations of t _depl and μ _gas with optical size R or surface density once one removes the above scalings, but we caution that optical sizes may not be appropriate for the high gas and dust columns at high z.

We present a census of ionized gas outflows in 599 normal galaxies at redshift 0.6 < z < 2.7, mostly based on integral field spectroscopy of Hα, [N ii], and [S ii] line emission. The sample fairly homogeneously covers the main sequence of star-forming galaxies with masses 9.0 < log(M _*/M _⊙) < 11.7, and probes into the regimes of quiescent galaxies and starburst outliers. About one-third exhibits the high-velocity component indicative of outflows, roughly equally split into winds driven by star formation (SF) and active galactic nuclei (AGNs). The incidence of SF-driven winds correlates mainly with SF properties. These outflows have typical velocities of ∼450 km s⁻¹, local electron densities of n _e ∼ 380 cm⁻³, modest mass loading factors of ∼0.1–0.2 at all galaxy masses, and energetics compatible with momentum driving by young stellar populations. The SF-driven winds may escape from log(M _*/M _⊙) ≲ 10.3 galaxies, but substantial mass, momentum, and energy in hotter and colder outflow phases seem required to account for low galaxy formation efficiencies in the low-mass regime. Faster AGN-driven outflows (∼1000–2000 km s⁻¹) are commonly detected above log(M _*/M _⊙) ∼ 10.7, in up to ∼75% of log(M _*/M _⊙) ≳ 11.2 galaxies. The incidence, strength, and velocity of AGN-driven winds strongly correlates with stellar mass and central concentration. Their outflowing ionized gas appears denser (n _e ∼ 1000 cm⁻³), and possibly compressed and shock-excited. These winds have comparable mass loading factors as the SF-driven winds but carry ∼10 (∼50) times more momentum (energy). The results confirm our previous findings of high-duty-cycle, energy-driven outflows powered by AGN above the Schechter mass, which may contribute to SF quenching.

We present binary galaxy merger simulations with varying mass ratios and different progenitor morphologies. The simulations include mergers of gas-rich disks (Sp-Sp), of early-type galaxies and disks (E-Sp, mixed mergers), and mergers of early-type galaxies (E-E, dry mergers). We follow the dynamics of gas, stars, and dark matter, and include radiative cooling, star formation and black hole (BH) accretion, and the associated feedback processes as in Springel et al. We study the mass assembly of the BHs and discuss technical issues of the implemented model in detail. For Sp-Sp mergers, the peak star formation rate and BH accretion rate decrease and the growth timescales of the central BHs and newly formed stars increase with higher progenitor mass ratios. The peak BH accretion rate typically occurs shortly after the time of BH merging for low progenitor mass ratios (e.g., 3:1 and lower), whereas for higher progenitor mass ratios there is no clear correlation between the peak BH accretion rate and the BH merging time. The termination of star formation by BH feedback in disk mergers is significantly less important for higher progenitor mass ratios (e.g., 3:1 and higher). In addition, the inclusion of BH feedback efficiently suppresses star formation in dry E-E mergers and mixed E-Sp mergers. All merger remnants, independent of their progenitors, follow the observed relations between the central BH mass and the stellar velocity dispersion (M _BH – σ), the bulge mass (M _BH – M _*), and the bulge binding energy (M _BH – M _*σ²), with the dominant source of scatter arising from variations in the initial gas mass fraction. The normalizations for all relations and the simulated slope of the M _BH – σ and M _BH – M _*σ² relations are in good agreement with the observations, whereas the simulated slope of the M _BH – M _* relation is slightly steeper compared to the observations. This indicates that the simple BH feedback model self-regulates the mass growth of the BHs in accordance with the observed relations for a very wide range of merger progenitors.

We present the 0.6 < z < 2.6 evolution of the ionized gas velocity dispersion in 175 star-forming disk galaxies based on data from the full integral field spectroscopic survey. In a forward-modeling Bayesian framework including instrumental effects and beam-smearing, we fit simultaneously the observed galaxy velocity and velocity dispersion along the kinematic major axis to derive the intrinsic velocity dispersion σ ₀. We find a reduction of the average intrinsic velocity dispersion of disk galaxies as a function of cosmic time, from σ ₀ ∼ 45 km s⁻¹ at z ∼ 2.3 to σ ₀ ∼ 30 km s⁻¹ at z ∼ 0.9. There is substantial intrinsic scatter ( ) around the best-fit σ ₀–z relation beyond what can be accounted for from the typical measurement uncertainties (δσ ₀ ≈ 12 km s⁻¹), independent of other identifiable galaxy parameters. This potentially suggests a dynamic mechanism such as minor mergers or variation in accretion being responsible for the scatter. Putting our data into the broader literature context, we find that ionized and atomic+molecular velocity dispersions evolve similarly with redshift, with the ionized gas dispersion being ∼10–15 km s⁻¹ higher on average. We investigate the physical driver of the on average elevated velocity dispersions at higher redshift and find that our galaxies are at most marginally Toomre-stable, suggesting that their turbulent velocities are powered by gravitational instabilities, while stellar feedback as a driver alone is insufficient. This picture is supported through comparison with a state-of-the-art analytical model of galaxy evolution.

The most recent observational evidence seems to indicate that giant molecular clouds are predominantly gravitationally unbound objects. In this paper we show that this is a natural consequence of a scenario in which cloud–cloud collisions and stellar feedback regulate the internal velocity dispersion of the gas, and so prevent global gravitational forces from becoming dominant. Thus, whilst the molecular gas is for the most part gravitationally unbound, local regions within the denser parts of the gas (within the clouds) do become bound and are able to form stars. We find that the observations, in terms of distributions of virial parameters and cloud structures, can be well modelled provided that the star formation efficiency in these bound regions is of the order of 5–10 per cent. We also find that in this picture the constituent gas of individual molecular clouds changes over relatively short time-scales, typically a few Myr.