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Register a new userThe KMOS$^mathrm{3D}$ Survey: rotating compact star forming galaxies and the decomposition of integrated line widths
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Using integral field spectroscopy we investigate the kinematic properties of 35 massive centrally-dense and compact star-forming galaxies (${log{overline{M}_*}}=11.1$, $log{(Sigma_mathrm{1kpc})}>9.5$, $log{(M_ast/r_e^{1.5})}>10.3$) at $zsim0.7-3.7$ within the KMOS$^mathrm{3D}$survey. We spatially resolve 23 compact star-forming galaxies (SFGs) and find that the majority are dominated by rotational motions with velocities ranging from {$95-500$ km s$^{-1}$}. The range of rotation velocities is reflected in a similar range of integrated H$alpha$ linewidths, $75-400$ km s$^{-1}$, consistent with the kinematic properties of mass-matched extended galaxies from the full KMOS$^mathrm{3D}$ sample. The fraction of compact SFGs that are classified as `rotation-dominated or `disk-like also mirrors the fractions of the full KMOS$^mathrm{3D}$ sample. We show that integrated line-of-sight gas velocity dispersions from KMOS$^mathrm{3D}$ are best approximated by a linear combination of their rotation and turbulent velocities with a lesser but still significant contribution from galactic scale winds. The H$alpha$ exponential disk sizes of compact SFGs are on average $2.5pm0.2$ kpc, $1-2times$ the continuum sizes, in agreement with previous work. The compact SFGs have a $1.4times$ higher AGN incidence than the full KMOS$^mathrm{3D}$ sample at fixed stellar mass with average AGN fraction of 76%. Given their high and centrally concentrated stellar masses as well as stellar to dynamical mass ratios close to unity, the compact SFGs are likely to have low molecular gas fractions and to quench on a short time scale unless replenished with inflowing gas. The rotation in these compact systems suggests that their direct descendants are rotating passive galaxies.
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We investigate what drives the redshift evolution of the typical electron density ($n_e$) in star-forming galaxies, using a sample of 140 galaxies drawn primarily from KMOS$^{rm 3D}$ ($0.6lesssim{z}lesssim{2.6}$) and 471 galaxies from SAMI ($z<0.113$). We select galaxies that do not show evidence of AGN activity or outflows, to constrain the average conditions within H II regions. Measurements of the [SII]$lambda$6716/[SII]$lambda$6731 ratio in four redshift bins indicate that the local $n_e$ in the line-emitting material decreases from 187$^{+140}_{-132}$ cm$^{-3}$ at $zsim$ 2.2 to 32$^{+4}_{-9}$ cm$^{-3}$ at $zsim$ 0; consistent with previous results. We use the H$alpha$ luminosity to estimate the root-mean-square (rms) $n_e$ averaged over the volumes of star-forming disks at each redshift. The local and volume-averaged $n_e$ evolve at similar rates, hinting that the volume filling factor of the line-emitting gas may be approximately constant across $0lesssim{z}lesssim{2.6}$. The KMOS$^{rm 3D}$ and SAMI galaxies follow a roughly monotonic trend between $n_e$ and star formation rate, but the KMOS$^{rm 3D}$ galaxies have systematically higher $n_e$ than the SAMI galaxies at fixed offset from the star-forming main sequence, suggesting a link between the $n_e$ evolution and the evolving main sequence normalization. We quantitatively test potential drivers of the density evolution and find that $n_e$(rms) $simeq{n_{H_2}}$, suggesting that the elevated $n_e$ in high-$z$ H II regions could plausibly be the direct result of higher densities in the parent molecular clouds. There is also tentative evidence that $n_e$ could be influenced by the balance between stellar feedback, which drives the expansion of H II regions, and the ambient pressure, which resists their expansion.
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.
We use extensive spectroscopy from the MOSFIRE Deep Evolution Field (MOSDEF) survey to investigate the relationships between rest-frame optical emission line equivalent widths ($W$) and a number of galaxy and ISM characteristics for a sample of $1134$ star-forming galaxies at redshifts $1.4lesssim zlesssim 3.8$. We examine how the equivalent widths of [OII]$lambdalambda 3727, 3730$, H$beta$, [OIII]$lambdalambda 4960, 5008$, [OIII]$+$H$beta$, H$alpha$, and H$alpha$+[NII]$lambdalambda 6550, 6585$, depend on stellar mass, UV slope, age, star-formation rate (SFR) and specific SFR (sSFR), ionization parameter and excitation conditions (O32 and [OIII]/H$beta$), gas-phase metallicity, and ionizing photon production efficiency ($xi_{rm ion}$). The trend of increasing $W$ with decreasing stellar mass is strongest for [OIII] (and [OIII]+H$beta$). More generally, the equivalent widths of all the lines increase with redshift at a fixed stellar mass or fixed gas-phase metallicity, suggesting that high equivalent width galaxies are common at high redshift. This redshift evolution in equivalent widths can be explained by the increase in SFR and decrease in metallicity with redshift at a fixed stellar mass. Consequently, the dependence of $W$ on sSFR is largely invariant with redshift, particularly when examined for galaxies of a given metallicity. Our results show that high equivalent width galaxies, specifically those with high $W({rm [OIII]})$, have low stellar masses, blue UV slopes, young ages, high sSFRs, ISM line ratios indicative of high ionization parameters, high $xi_{rm ion}$, and low metallicities. As these characteristics are often attributed to galaxies with high ionizing escape fractions, galaxies with high $W$ are likely candidates for the population that dominates cosmic reionization.
We analyse the velocity dispersion properties of 472 z~0.9 star-forming galaxies observed as part of the KMOS Redshift One Spectroscopic Survey (KROSS). The majority of this sample is rotationally dominated (83 +/- 5% with v_C/sigma_0 > 1) but also dynamically hot and highly turbulent. After correcting for beam smearing effects, the median intrinsic velocity dispersion for the final sample is sigma_0 = 43.2 +/- 0.8 km/s with a rotational velocity to dispersion ratio of v_C/sigma_0 = 2.6 +/- 0.1. To explore the relationship between velocity dispersion, stellar mass, star formation rate and redshift we combine KROSS with data from the SAMI survey (z~0.05) and an intermediate redshift MUSE sample (z~0.5). While there is, at most, a weak trend between velocity dispersion and stellar mass, at fixed mass there is a strong increase with redshift. At all redshifts, galaxies appear to follow the same weak trend of increasing velocity dispersion with star formation rate. Our results are consistent with an evolution of galaxy dynamics driven by disks that are more gas rich, and increasingly gravitationally unstable, as a function of increasing redshift. Finally, we test two analytic models that predict turbulence is driven by either gravitational instabilities or stellar feedback. Both provide an adequate description of the data, and further observations are required to rule out either model.
We present the completed KMOS$^mathrm{3D}$ survey $-$ an integral field spectroscopic survey of 739, $log(M_{star}/M_{odot})>9$, galaxies at $0.6<z<2.7$ using the K-band Multi Object Spectrograph (KMOS) at the Very Large Telescope (VLT). KMOS$^mathrm{3D}$ provides a population-wide census of kinematics, star formation, outflows, and nebular gas conditions both on and off the star-forming galaxy main sequence through the spatially resolved and integrated properties of H$alpha$, [N II], and [S II] emission lines. We detect H$alpha$ emission for 91% of galaxies on the main sequence of star-formation and 79% overall. The depth of the survey has allowed us to detect galaxies with star-formation rates below 1 M$_{odot}$/ yr$^{-1}$, as well as to resolve 81% of detected galaxies with $geq3$ resolution elements along the kinematic major axis. The detection fraction of H$alpha$ is a strong function of both color and offset from the main sequence, with the detected and non-detected samples exhibiting different SED shapes. Comparison of H$alpha$ and UV+IR star formation rates (SFRs) reveal that dust attenuation corrections may be underestimated by 0.5 dex at the highest masses ($log(M_{star}/M_{odot})>10.5$). We confirm our first year results of a high rotation dominated fraction (monotonic velocity gradient and $v_mathrm{rot}$/$sigma_0 > sqrt{3.36}$) of 77% for the full KMOS$^mathrm{3D}$ H$alpha$sample. The rotation-dominated fraction is a function of both stellar mass and redshift with the strongest evolution measured over the redshift range of the survey for galaxies with $log(M_{star}/M_{odot})<10.5$. With this paper we include a final data release of all 739 observed objects.
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