The properties of the star-forming interstellar medium at z = 0.84-2.23 from HiZELS : mapping the internal dynamics and metallicity gradients in high-redshift disc galaxies.

We present adaptive optics assisted, spatially resolved spectroscopy of a sample of nine Hα-selected galaxies at z = 0.84-2.23 drawn from the HiZELS narrow-band survey. These galaxies have star formation rates of 1-27 M⊙ yr-1 and are therefore representative of the typical high-redshift star-forming population. Our ˜kpc-scale resolution observations show that approximately half of the sample have dynamics suggesting that the ionized gas is in large, rotating discs. We model their velocity fields to infer the inclination-corrected, asymptotic rotational velocities. We use the absolute B-band magnitudes and stellar masses to investigate the evolution of the B-band and stellar-mass Tully-Fisher relationships. By combining our sample with a number of similar measurements from the literature, we show that, at fixed circular velocity, the stellar mass of star-forming galaxies has increased by a factor of 2.5 between z = 2 and 0, whilst the rest-frame B-band luminosity has decreased by a factor of ˜ 6 over the same period. Together, these demonstrate a change in mass-to-light ratio in the B band of Δ(M/LB)/(M/LB)z=0 ˜ 3.5 between z = 1.5 and 0, with most of the evolution occurring below z = 1. We also use the spatial variation of [N II]/Hα to show that the metallicity of the ionized gas in these galaxies declines monotonically with galactocentric radius, with an average Δ log(O/H)/ΔR = -0.027 ± 0.005 dex kpc-1. This gradient is consistent with predictions for high-redshift disc galaxies from cosmologically based hydrodynamic simulations

Calibrating [O II] star formation rates at z < 1 from dual Hα-[O II] imaging from HiZELS

We investigate the relationship between Hα and [O II](λ3727) emission in faint star-forming galaxies at z = 1.47 with dust uncorrected star formation rates (SFRs) down to 1.4 M⊙ yr-1, using data in two narrow bands from wide-field camera/United Kingdom Infrared Telescope and Subaru prime focus camera/Subaru. A stacking analysis allows us to investigate Hα emission flux from bright [O II] emitters as well as faint ones for which Hα is not individually detected, and to compare them with a large sample of local galaxies. We find that there is a clear, positive correlation between the average Hα and [O II] luminosities for [O II] emitters at z = 1.47, with its slope being consistent with the local relation. [O II] emitters at z = 1.47 have lower mean observed ratios of Hα/[O II] suggesting a small but systematic offset (at 2.8σ significance) towards lower values of dust attenuation, AHα ˜ 0.35, than local galaxies. This confirms that [O II] selection tends to pick up galaxies which are significantly less dusty on average than Hα-selected ones, with the difference being higher at z = 1.47 than at z = 0. The discrepancy of the observed line ratios between [O II] emitters at z = 1.47 and the local galaxies may in part be due to the samples having different metallicities. However, we demonstrate that metallicity is unlikely to be the main cause. Therefore, it is important to take into account that the relations for the dust correction which are derived using Hα emitter samples, and frequently used in many studies of high-z galaxies, may overestimate the intrinsic SFRs of [O II]-selected galaxies, and that surveys of [O II] emission galaxies are likely to miss dusty populations

Infrared Magnitude-Redshift Relations for Luminous Radio Galaxies

Infrared magnitude-redshift relations for the 3CR and 6C samples of radio galaxies are presented for a wide range of plausible cosmological models, including those with non-zero cosmological constant OmegaLambda. Variations in the galaxy formation redshift, metallicity and star formation history are also considered. The results of the modelling are displayed in terms of magnitude differences between the models and no-evolution tracks, illustrating the amount of K-band evolution necessary to account for the observational data. Given a number of plausible assumptions, the results of these analyses suggest that: (i) cosmologies which predict T_0xH_0>1 (where T_0 denotes the current age of the universe) can be excluded; (ii) the star formation redshift should lie in the redshift interval 5<z<20, values towards the lower end of the range being preferred in cosmologies with larger values of T_0xH_0; (iii) the Einstein-de Sitter model provides a reasonable fit to the data; (iv) models with finite values of OmegaLambda can provide good agreement with the observations only if appropriate adjustments of other parameters such as the galaxy metallicities and star-formation histories are made. Without such modifications, even after accounting for stellar evolution, the high redshift radio galaxies are more luminous (ie. more massive) than those nearby in models with finite OmegaLambda, including the favoured model with Omega=0.3, OmegaLambda=0.7. For cosmological models with larger values of T_0xH_0, the conclusions are the same regardless of whether any adjustments are made or not. The implications of these results for cosmology and models of galaxy formation are discussed.Comment: 14 pages, LaTeX, 9 figures, accepted for publication in MNRAS. Replacement corrects some annoying typo

Experimental investigation of the flow evolution in the tributary of a 90° open channel confluence

Open channel and river confluences have received a lot of attention in hydraulic literature, because of the interesting flow phenomena observed. Features such as flow acceleration, curvature, separation, mixing and recovery are combined in the confluence area into a complex 3D flow pattern. Typically, the analysis of these features is started at the upstream corner of the confluence area, and the upstream main and tributary branches are considered to be the (uniform) upstream boundary conditions. However, several indications in literature suggest the existence of flow features upstream of the confluence corner. This paper confirms, by means of measurements in a laboratory, 90° confluence flume, considerable streamline curvature in the tributary branch, upstream of the confluence. Furthermore, it shows and quantifies velocity redistribution as well as local water surface super-elevation and depression in the tributary branch. Consequently, flow fea-ture analysis in confluences should start a considerable distance upstream of the confluence

The stellar mass function of star-forming galaxies and the mass-dependent SFR function since z = 2.23 from HiZELS

We explore a large uniformly selected sample of Hα selected star-forming galaxies (SFGs) at z = 0.40, 0.84, 1.47, 2.23 to unveil the evolution of the star formation rate (SFR) function and the stellar mass function. We find strong evolution in the SFR function, with the typical SFR of SFGs declining exponentially in the last 11 Gyr as SFR*(T[Gyr]) = 104.23/T + 0.37 M⊙ yr−1, but with no evolution in the faint-end slope, α ≈ −1.6. The stellar mass function of SFGs, however, reveals little evolution: α ≈ −1.4, M* ∼ 1011.2 ± 0.2 M⊙ and just a slight increase of ∼2.3× in Φ* from z = 2.23 to z = 0.4. The stellar mass density within SFGs has been roughly constant since z = 2.23 at ∼107.65 ± 0.08 M⊙ Mpc−3, comprising ≈100 per cent of the stellar mass density in all galaxies at z = 2.23, and declining to ≈20 per cent by z = 0.40, driven by the rise of the passive population. We find that SFGs with ∼1010.0 ± 0.2 M⊙ contribute most to the SFR density (ρSFR) per d log10M, and that there is no significant evolution in the fractional contribution from SFGs of different masses to ρSFR or ρSFR(d log10M)−1 since z = 2.23. Instead, we show that the decline of SFR* and of ρSFR is primarily driven by an exponential decline in SFRs at all masses. Our results have important implications not only on how SFGs need to be quenched across cosmic time, but also on the driver(s) of the exponential decline in SFR* from ∼66 M⊙ yr−1 to 5 M⊙ yr−1 since z ∼ 2.23

Morphological classification of radio galaxies: Capsule Networks versus Convolutional Neural Networks

Next-generation radio surveys will yield an unprecedented amount of data, warranting analysis by use of machine learning techniques. Convolutional neural networks are the deep learning technique that has proven to be the most successful in classifying image data. Capsule networks are a more recently developed technique that use capsules comprised of groups of neurons, that describe properties of an image including the relative spatial locations of features. The current work explores the performance of different capsule network architectures against simpler convolutional neural network architectures, in reproducing the classifications into the classes of unresolved, FRI and FRII morphologies. We utilise images from a LOFAR survey which is the deepest, wide-area radio survey to date, revealing more complex radio-source structures compared to previous surveys, presenting further challenges for machine learning algorithms. The 4- and 8-layer convolutional networks attain an average precision of 93.3% and 94.3% respectively, compared to 89.7% obtained with the capsule network, when training on original and augmented images. Implementing transfer learning achieves a precision of 94.4%, that is within the confidence interval of the 8-layer convolutional network. The convolutional networks always outperform any variation of the capsule network, as they prove to be more robust to the presence of noise in images. The use of pooling appears to allow more freedom for the intra-class variability of radio galaxy morphologies, as well as reducing the impact of noise

Distant FR I radio galaxies in the Hubble Deep Field: implications for the cosmological evolution of radio-loud AGN

Deep and high resolution radio observations of the Hubble Deep Field and flanking fields have shown the presence of two distant edge-darkened FR I radio galaxies, allowing for the first time an estimate of their high redshift space density. If it is assumed that the space density of FR I radio galaxies at z>1 is similar to that found in the local universe, then the chance of finding two FR I radio galaxies at these high radio powers in such a small area of sky is 1 than at present, effectively ruling out the possibility that FR I radio sources undergo no cosmological evolution. We suggest that FR I and FR II radio galaxies should not be treated as intrinsically distinct classes of objects, but that the cosmological evolution is simply a function of radio power with FR I and FR II radio galaxies of similar radio powers undergoing similar cosmological evolutions. Since low power radio galaxies have mainly FR I morphologies and high power radio galaxies have mainly FR II morphologies, this results in a generally stronger cosmological evolution for the FR IIs than the FR Is. We believe that additional support from the V/Vmax test for evolving and non-evolving populations of FR IIs and FR Is respectively is irrelevant, since this test is sensitive over very different redshift ranges for the two classes.Comment: LaTeX, 6 pages, 3 figs. To appear in MNRA

A relationship between specific star formation rate and metallicity gradient within z ∼ 1 galaxies from KMOS-HiZELS

We have observed a sample of typical z ∼ 1 star-forming galaxies, selected from the HiZELS survey, with the new K-band Multi-Object Spectrograph (KMOS) near-infrared, multi-integral field unit instrument on the Very Large Telescope (VLT), in order to obtain their dynamics and metallicity gradients. The majority of our galaxies have a metallicity gradient consistent with being flat or negative (i.e. higher metallicity cores than outskirts). Intriguingly, we find a trend between metallicity gradient and specific star formation rate (sSFR), such that galaxies with a high sSFR tend to have relatively metal poor centres, a result which is strengthened when combined with data sets from the literature. This result appears to explain the discrepancies reported between different high-redshift studies and varying claims for evolution. From a galaxy evolution perspective, the trend we see would mean that a galaxy's sSFR is governed by the amount of metal-poor gas that can be funnelled into its core, triggered either by merging or through efficient accretion. In fact, merging may play a significant role as it is the starburst galaxies at all epochs, which have the more positive metallicity gradients. Our results may help to explain the origin of the fundamental metallicity relation, in which galaxies at a fixed mass are observed to have lower metallicities at higher star formation rates, especially if the metallicity is measured in an aperture encompassing only the central regions of the galaxy. Finally, we note that this study demonstrates the power of KMOS as an efficient instrument for large-scale resolved galaxy surveys

A 10 deg^2 Lyman α survey at z=8.8 with spectroscopic follow-up: strong constraints on the luminosity function and implications for other surveys

Candidate galaxies at redshifts of z ∼ 10 are now being found in extremely deep surveys, probing very small areas. As a consequence, candidates are very faint, making spectroscopic confirmation practically impossible. In order to overcome such limitations, we have undertaken the CF-HiZELS survey, which is a large-area, medium-depth near-infrared narrow-band survey targeted at z = 8.8 Lyman α (Lyα) emitters (LAEs) and covering 10 deg2 in part of the SSA22 field with the Canada–France–Hawaii Telescope (CFHT). We surveyed a comoving volume of 4.7 × 106 Mpc3 to a Lyα luminosity limit of 6.3 × 1043 erg s−1. We look for Lyα candidates by applying the following criteria: (i) clear emission-line source, (ii) no optical detections (ugriz from CFHTLS), (iii) no visible detection in the optical stack (ugriz > 27), (iv) visually checked reliable NBJ and J detections and (v) J − K ≤ 0. We compute photometric redshifts and remove a significant amount of dusty lower redshift line-emitters at z ∼ 1.4 or 2.2. A total of 13 Lyα candidates were found, of which two are marked as strong candidates, but the majority have very weak constraints on their spectral energy distributions. Using follow-up observations with SINFONI/VLT, we are able to exclude the most robust candidates as LAEs. We put a strong constraint on the Lyα luminosity function at z ∼ 9 and make realistic predictions for ongoing and future surveys. Our results show that surveys for the highest redshift LAEs are susceptible of multiple contaminations and that spectroscopic follow-up is absolutely necessary