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Register a new userThe KMOS Galaxy Evolution Survey (KGES): the angular momentum of star-forming galaxies over the last ~10 Gyr
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We present the KMOS Galaxy Evolution Survey (KGES), a $K$-band Multi-Object Spectrograph (KMOS) study of the H$alpha$ and [NII] emission from 288 $K$ band-selected galaxies at $1.2 lesssim z lesssim 1.8$, with stellar masses in the range $log_{10}(M_{*}/rm{M}_{odot})approx$9-11.5. In this paper, we describe the survey design, present the sample, and discuss the key properties of the KGES galaxies. We combine KGES with appropriately matched samples at lower redshifts from the KMOS Redshift One Spectroscopic Survey (KROSS) and the SAMI Galaxy Survey. Accounting for the effects of sample selection, data quality, and analysis techniques between surveys, we examine the kinematic characteristics and angular momentum content of star-forming galaxies at $zapprox1.5$, $approx1$ and $approx0$. We find that stellar mass, rather than redshift, most strongly correlates with the disc fraction amongst star-forming galaxies at $z lesssim 1.5$, observing only a modest increase in the prevalence of discs between $zapprox1.5$ and $zapprox0.04$ at fixed stellar mass. Furthermore, typical star-forming galaxies follow the same median relation between specific angular momentum and stellar mass, regardless of their redshift, with the normalisation of the relation depending more strongly on how disc-like a galaxys kinematics are. This suggests that massive star-forming discs form in a very similar manner across the $approx$ 10 Gyr encompassed by our study and that the inferred link between the angular momentum of galaxies and their haloes does not change significantly across the stellar mass and redshift ranges probed in this work.
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We present a MUSE and KMOS dynamical study 405 star-forming galaxies at redshift z=0.28-1.65 (median redshift z=0.84). Our sample are representative of star-forming, main-sequence galaxies, with star-formation rates of SFR=0.1-30Mo/yr and stellar masses M=10^8-10^11Mo. For 49+/-4% of our sample, the dynamics suggest rotational support, 24+/-3% are unresolved systems and 5+/-2% appear to be early-stage major mergers with components on 8-30kpc scales. The remaining 22+/-5% appear to be dynamically complex, irregular (or face-on systems). For galaxies whose dynamics suggest rotational support, we derive inclination corrected rotational velocities and show these systems lie on a similar scaling between stellar mass and specific angular momentum as local spirals with j*=J/M*propto M^(2/3) but with a redshift evolution that scales as j*propto M^{2/3}(1+z)^(-1). We identify a correlation between specific angular momentum and disk stability such that galaxies with the highest specific angular momentum, log(j*/M^(2/3))>2.5, are the most stable, with Toomre Q=1.10+/-0.18, compared to Q=0.53+/-0.22 for galaxies with log(j*/M^(2/3))<2.5. At a fixed mass, the HST morphologies of galaxies with the highest specific angular momentum resemble spiral galaxies, whilst those with low specific angular momentum are morphologically complex and dominated by several bright star-forming regions. This suggests that angular momentum plays a major role in defining the stability of gas disks: at z~1, massive galaxies that have disks with low specific angular momentum, appear to be globally unstable, clumpy and turbulent systems. In contrast, galaxies with high specific angular have evolved in to stable disks with spiral structures.
We analyse maps of the spatially-resolved nebular emission of $approx$1500 star-forming galaxies at $zapprox0.6$-$2.2$ from deep KMOS and MUSE observations to measure the average shape of their rotation curves. We use these to test claims for declining rotation curves at large radii in galaxies at $zapprox1$-$2$ that have been interpreted as evidence for an absence of dark matter. We show that the shape of the average rotation curves, and the extent to which they decline beyond their peak velocities, depends upon the normalisation prescription used to construct the average curve. Normalising in size by the galaxy stellar disk-scale length after accounting for seeing effects ($R_{rm{d}}^{prime}$), we construct stacked position-velocity diagrams that trace the average galaxy rotation curve out to $6R_{rm{d}}^{prime}$ ($approx$13 kpc, on average). Combining these curves with average HI rotation curves for local systems, we investigate how the shapes of galaxy rotation curves evolve over $approx$10 Gyr. The average rotation curve for galaxies binned in stellar mass, stellar surface mass density and/or redshift is approximately flat, or continues to rise, out to at least $6R_{rm{d}}^{prime}$. We find a trend between the outer slopes of galaxies rotation curves and their stellar mass surface densities, with the higher surface density systems exhibiting flatter rotation curves. Drawing comparisons with hydrodynamical simulations, we show that the average shapes of the rotation curves for our sample of massive, star-forming galaxies at $zapprox0$-$2.2$ are consistent with those expected from $Lambda$CDM theory and imply dark matter fractions within $6R_{rm{d}}$ of at least $approx60$ percent.
We present new results on the evolution of rest-frame blue/UV sizes and Sersic indices of H$alpha$-selected star-forming galaxies over the last 11 Gyrs. We investigate how the perceived evolution can be affected by a range of biases and systematics such as cosmological dimming and resolution effects. We use GALFIT and an artificial redshifting technique, which includes the luminosity evolution of H$alpha$-selected galaxies, to quantify the change on the measured structural parameters with redshift. We find typical sizes of 2 to 3 kpc and Sersic indices of n~1.2, close to pure exponential disks all the way from z=2.23 to z=0.4. At z=0 we find typical sizes of 4-5 kpc. Our results show that, when using GALFIT, cosmological dimming has a negligible impact on the derived effective radius for galaxies with <10 kpc, but we find a ~20% bias on the estimate of the median Sersic indices, rendering galaxies more disk-like. Star-forming galaxies have grown on average by a factor of 2-3 in the last 11 Gyrs with $r_epropto(1+z)^{-0.75}$. By exploring the evolution of the stellar mass-size relation we find evidence for a stronger size evolution of the most massive star-forming galaxies since z~2, as they grow faster towards z~0 when compared to the lower stellar mass counterparts. As we are tracing the rest-frame blue/UV, we are likely witnessing the growth of disks where star formation is ongoing in galaxies while their profiles remain close to exponential disks, n<1.5, across the same period.
We present an analysis of the physical and dynamical states of two sets of EAGLE zoom simulations of galaxy haloes, one at high redshift ($z=2-3$) and the other at low redshift ($z=0$), with masses of $approx 10^{12} M_{odot}$. Our focus is how the circumgalactic medium (CGM) of these $L^*$ star-forming galaxies change over the last 10 Gyr. We find that the high-$z$ CGM is almost equally divided between the cool ($T<10^5$ K) and hot ($Tgeq 10^5$ K) phases, while the low-$z$ hot CGM phase contains $5times$ more mass. The high-$z$ hot CGM contains 60% more metals than the cool CGM, while the low-$z$ cool CGM contains 35% more metals than the hot CGM content. The metals are evenly distributed radially between the hot and cool phases throughout the high-$z$ CGM. At high $z$, the CGM volume is dominated by hot outflows, cool gas is mainly inflowing, but cool metals are flowing outward. At low $z$, the cool metals dominate the interior and the hot metals are more prevalent at larger radii. The low-$z$ cool CGM has tangential motions consistent with rotational support out to $0.2 R_{200}$, often exhibiting $r approx 40$ kpc disc-like structures. The low-$z$ hot CGM has several times greater angular momentum than the cool CGM, and a more flattened radial density profile than the high-$z$ hot CGM. This study verifies that, just as galaxies demonstrate significant evolutionary stages over cosmic time, the gaseous haloes surrounding them also undergo considerable changes of their own both in physical characteristics of density, temperature and metallicity, and dynamic properties of velocity and angular momentum.
The [CII] 158 micron line is one of the strongest IR emission lines, which has been shown to trace the star-formation rate (SFR) of galaxies in the nearby Universe and up to $z sim 2$. Whether this is also the case at higher redshift and in the early Universe remains debated. The ALPINE survey, which targeted 118 star-forming galaxies at $4.4 < z< 5.9$, provides a new opportunity to examine this question with the first statistical dataset. Using the ALPINE data and earlier measurements from the literature we examine the relation between the [CII] luminosity and the SFR over the entire redshift range from $z sim 4-8$. ALPINE galaxies, which are both detected in [CII] and dust continuum, show a good agreement with the local L([CII])-SFR relation. Galaxies undetected in the continuum with ALMA are found to be over-luminous in [CII], when the UV SFR is used. After accounting for dust-obscured star formation, by an amount SFR(IR)$approx$SFR(UV) on average, which results from two different stacking methods and SED fitting, the ALPINE galaxies show an L([CII])-SFR relation comparable to the local one. When [CII] non-detections are taken into account, the slope may be marginally steeper at high-z, although this is still somewhat uncertain. When compared in a homogeneous manner, the $z>6 $ [CII] measurements (detections and upper limits) do not behave very differently from the $z sim 4-6$ data. We find a weak dependence of L([CII])/SFR on the Lyman-alpha equivalent width. Finally, we find that the ratio L([CII])/LIR $sim (1-3) times 10^{-3}$ for the ALPINE sources, comparable to that of normal galaxies at lower redshift. Our analysis, which includes the largest sample ($sim 150$ galaxies) of [CII] measurements at $z>4$ available so far, suggests no or little evolution of the L([CII])-SFR relation over the last 13 Gyr of cosmic time.
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