This paper provides an update of our previous scaling relations (Genzel et al. 2015) between galaxy integrated molecular gas masses, stellar masses and star formation rates, in the framework of the star formation main-sequence (MS), with the main goal to test 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 ~1mm dust photometry, in a large sample of 1444 star forming galaxies (SFGs) between z=0 and 4. The sample covers the stellar mass range log(M*/M)=9.0-11.8, and star formation rates 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 tdepl, defined as the ratio of molecular gas mass to star formation rate, scales as (1+z) -0.6 × (δMS) -0.44 , and is only weakly dependent on stellar mass. The ratio of molecular-to-stellar mass μgas depends on (1+z) 2.5 × (δMS) 0.52 × (M*) -0.36 , which tracks the evolution of the specific star formation rate. The redshift dependence of μgas requires a curvature term, as may the mass-dependences of tdepl and μgas. We find no or only weak correlations of tdepl and μgas 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.

In the cold dark matter cosmology, the baryonic components of galaxies-stars and gas-are thought to be mixed with and embedded in non-baryonic and non-relativistic dark matter, which dominates the total mass of the galaxy and its dark-matter halo. In the local (low-redshift) Universe, the mass of dark matter within a galactic disk increases with disk radius, becoming appreciable and then dominant in the outer, baryonic regions of the disks of star-forming galaxies. This results in rotation velocities of the visible matter within the disk that are constant or increasing with disk radius-a hallmark of the dark-matter model. Comparisons between the dynamical mass, inferred from these velocities in rotational equilibrium, and the sum of the stellar and cold-gas mass at the peak epoch of galaxy formation ten billion years ago, inferred from ancillary data, suggest high baryon fractions in the inner, star-forming regions of the disks. Although this implied baryon fraction may be larger than in the local Universe, the systematic uncertainties (owing to the chosen stellar initial-mass function and the calibration of gas masses) render such comparisons inconclusive in terms of the mass of dark matter. Here we report rotation curves (showing rotation velocity as a function of disk radius) for the outer disks of six massive star-forming galaxies, and find that the rotation velocities are not constant, but decrease with radius. We propose that this trend arises because of a combination of two main factors: first, a large fraction of the massive high-redshift galaxy population was strongly baryon-dominated, with dark matter playing a smaller part than in the local Universe; and second, the large velocity dispersion in high-redshift disks introduces a substantial pressure term that leads to a decrease in rotation velocity with increasing radius. The effect of both factors appears to increase with redshift. Qualitatively, the observations suggest that baryons in the early (high-redshift) Universe efficiently condensed at the centres of dark-matter haloes when gas fractions were high and dark matter was less concentrated.

We present measurements of the [N II]/Hα ratio as a probe of gas-phase oxygen abundance for a sample of 419 star-forming galaxies at z = 0.6 − 2.7 from the KMOS 3D near-IR multi-IFU survey. The mass-metallicity relation (MZR) is determined consistently with the same sample selection, metallicity tracer, and methodology over the wide redshift range probed by the survey. We find good agreement with long-slit surveys in the literature, except for the low-mass slope of the relation at z ∼ 2.3, where this sample is less biased than previous samples based on optical spectroscopic redshifts. In this regime we measure a steeper slope than some literature results. Excluding the AGN contribution from the MZR reduces sensitivity at the high mass end, but produces otherwise consistent results. There is no significant dependence of the [N II]/Hα ratio on SFR or environment at fixed redshift and stellar mass. The IFU data allow spatially resolved measurements of [N II]/Hα, from which we can infer abundance gradients for 180 galaxies, thus tripling the current sample in the literature. The observed gradients are on average flat, with only 15 gradients statistically offset from zero at > 3σ. We have modelled the effect of beam-smearing, assuming a smooth intrinsic radial gradient and known seeing, inclination and effective radius for each galaxy. Our seeing-limited observations can recover up to 70% of the intrinsic gradient for the largest, face-on disks, but only 30% for the smaller, more inclined galaxies. We do not find significant trends between observed or corrected gradients and any stellar population, dynamical or structural galaxy parameters, mostly in agreement with existing studies with much smaller sample sizes. In cosmological simulations, strong feedback is generally required to produce flat gradients at high redshift.

We present 0 ′′ .2-resolution Atacama Large Millimeter/submillimeter Array observations at 870 µm for 25 Hα-seleced star-forming galaxies around the main-sequence at z = 2.2 − 2.5. We detect significant 870 µm continuum emission in 16 (64%) of these galaxies. The high-resolution maps reveal that the dust emission is mostly radiated from a single region close to the galaxy center. Exploiting the visibility data taken over a wide uv distance range, we measure the half-light radii of the rest-frame far-infrared emission for the best sample of 12 massive galaxies with log(M * /M ⊙ ) >11. We find nine galaxies to be associated with extremely compact dust emission with R 1/2,870µm < 1.5 kpc, which is more than a factor of 2 smaller than their rest-optical sizes, R 1/2,1.6µm =3.2 kpc, and is comparable with optical sizes of massive quiescent galaxies at similar redshifts. As they have an exponential disk with Sérsic index of n 1.6µm =1.2 in the rest-optical, they are likely to be in the transition phase from extended disks to compact spheroids. Given their high star formation rate surface densities within the central 1 kpc of ΣSFR 1kpc = 40 M ⊙ yr −1 kpc −2 , the intense circumnuclear starbursts can rapidly build up a central bulge with ΣM * ,1kpc > 10 10 M ⊙ kpc −2 in several hundred Myr, i.e. by z ∼ 2. Moreover, ionized gas kinematics reveal that they are rotation-supported with an angular momentum as large as that of typical star-forming galaxies at z = 1 − 3. Our results suggest bulges are commonly formed in extended rotating disks by internal processes, not involving major mergers.

We exploit deep integral-field spectroscopic observations with KMOS/VLT of 240 star-forming disks at 0.6 < z < 2.6 to dynamically constrain their mass budget. Our sample consists of massive ( 10 9.8 M ⊙ ) galaxies with sizes R e 2 kpc. By contrasting the observed velocity and dispersion profiles to dynamical models, we find that on average the stellar content contributes 32 +8 −7 % of the total dynamical mass, with a significant spread among galaxies (68th percentile range f star ∼ 18 − 62%). Including molecular gas as inferred from CO-and dust-based scaling relations, the estimated baryonic mass adds up to 56 +17 −12 % of total for the typical galaxy in our sample, reaching ∼ 90% at z > 2. We conclude that baryons make up most of the mass within the disk regions of high-redshift star-forming disk galaxies, with typical disks at z > 2 being strongly baryon-dominated within R e . Substantial object-to-object variations in both stellar and baryonic mass fractions are observed among the galaxies in our sample, larger than what can be accounted for by the formal uncertainties in their respective measurements. In both cases, the mass fractions correlate most strongly with measures of surface density. High Σ star galaxies feature stellar mass fractions closer to unity, and systems with high inferred gas or baryonic surface densities leave less room for additional mass components other than stars and molecular gas. Our findings can be interpreted as more extended disks probing further (and more compact disks probing less far) into the dark matter halos that host them.