We explore the dependence of UV upturn colours in early type cluster galaxies on the properties of their parent clusters (such as velocity dispersion and X-ray luminosity) and on the positions and kinematics of galaxies within them. We use a sample of 24 nearby clusters with highly complete spectroscopy and optical/infrared data to select a suitable sample of red sequence galaxies, whose FUV and NUV magnitudes we measure from archival GALEX data. Our results show that the UV upturn colour has no dependence on cluster properties and has the same range in all clusters. There is also no dependence on the projected position within clusters or on line-of-sight velocity. Therefore, our conclusion is that the UV upturn phenomenon is an intrinsic feature of cluster early type galaxies, irrespective of their cluster environment.

Using GALEX, UVOT and optical photometry, we explore the prevalence and strength of the UV-upturn in the spectra of quiescent early type galaxies in several nearby clusters. Even for galaxies with completely passive optical colours, there is a large spread in vacuum UV colour consistent with almost all having some UV upturn component. Combining GALEX and UVOT data below 3000Å, we generate for the first time comparatively detailed UV SEDs for Coma cluster galaxies. Fitting the UV upturn component with a blackbody, twenty six of these show a range of characteristic temperatures (10000-21000K) for the UV upturn population. Assuming a single temperature to explain GALEX-optical colours could underestimate the fraction of galaxies with UV upturns and mis-classify some as systems with residual star formation. The UV upturn phenomenon is not an exclusive feature found only in giant galaxies; we identify galaxies with similar (or even bluer) FUV −V colours to the giants with upturns over a range of fainter luminosities. The temperature and strength of the UV upturn are correlated with galaxy mass. Under the plausible hypothesis that the sources of the UV upturn are blue horizontal branch stars, the most likely mechanism for this is the presence of a substantial (between 4% and 20%) Helium rich (Y > 0.3) population of stars in these galaxies, potentially formed at z ∼ 4 and certainly at z > 2; this plausibly sets a lower limit of ∼ 0.3 − 0.8 × 10 10 M to the in situ stellar mass of ∼ L * galaxies at this redshift.

PurposeThis study aims (1) to numerically investigate the characteristics of a human cough jet in a quiescent environment, such as the variation with time of the velocity field, streamwise jet penetration and maximum jet width. Two different turbulence modelling approaches, the unsteady Reynolds-averaged Navier–Stokes (URANS) and large eddy simulation (LES), are used for comparison purposes. (2) To validate the numerical results with the experimental data.Design/methodology/approachTwo different approaches, the URANS and LES, are used to simulate a human cough jet flow. The numerical results for the velocity magnitude contours and the spatial average of the two-dimensional velocity magnitude over the corresponding particle image velocimetry (PIV) field of view are compared with the relevant PIV measurements. Similarly, the numerical results for the streamwise velocity component at the hot-wire probe location are compared with the hot-wire anemometry (HWA) measurements. Furthermore, the numerical results for the streamwise jet penetration are compared with the data from the previous experimental work.FindingsBased on the comparison with the URANS approach and the experimental data, the LES approach can predict the temporal development of a human cough jet reasonably well. In addition, the maximum width of the cough jet is found to grow practically linearly with time in the far-field, interrupted-jet stage, while the corresponding axial distance from the mouth of the jet front increases with time in an approximately quadratic manner.Originality/valueCurrently, no numerical study of human cough flow has been conducted using the LES approach due to the following challenges: (1) the computational cost is much higher than that of the URANS approach; (2) it is difficult to specify the turbulent fluctuations at the mouth for the cough jet properly; (3) it is necessary to define the appropriate conditions for the droplets to obtain statistically valid results. Therefore, this work fills this research gap.

We have analysed the strength of the UV upturn in red sequence galaxies with luminosities reaching to below the L * point within four clusters at z = 0.3, 0.55 & 0.7. We find that the incidence and strength of the upturn remains constant up to z = 0.55. In comparison, the prevalence and strength of the UV upturn is significantly diminished in the z = 0.7 cluster, implying that the stellar population responsible for the upturn in a typical red sequence galaxy is only just developing at this redshift and is essentially fully-developed by ∼ 1 Gyr later. Of all the mainstream models that seek to explain the UV upturn phenomenon, it is those that generate the upturn through the presence of a Helium-enhanced stellar subpopulation on the (hot) horizontal branch that are most consistent with this behaviour. The epoch (z = 0.7) where the stars responsible for the upturn first evolve from the red giant branch places constraints on their age and chemical abundances. By comparing our results with the prediction made by the YEPS Helium-enhanced spectrophotometic models, we find that a solar metallicity sub-population that displays a consistent upturn between 0 < z < 0.55 but then fades by z = 0.7 would require a Helium abundance of Y 0.45, if formed at z f ∼ 4. Later formation redshifts and/or higher metallicity would further increase the Helium enhancement required to produce the observed upturn in these clusters and vice versa.

We measure the near-UV (rest-frame ∼2400 Å) to optical color for early-type galaxies in 12 clusters at 0.3 < z < 1.0. We show that this is a suitable proxy for the more common far-ultraviolet bandpass used to measure the ultraviolet upturn and find that the upturn is detected to z = 0.6 in these data, in agreement with previous work. We find evidence that the strength of the upturn starts to wane beyond this redshift and largely disappears at z = 1. Our data are most consistent with models where early-type galaxies contain minority stellar populations with non-cosmological helium abundances, up to around 46%, formed at z ≥ 3, resembling globular clusters with multiple stellar populations in our Galaxy. This suggests that elliptical galaxies and globular clusters share similar chemical evolution and star formation histories. The vast majority of the stellar mass in these galaxies also must have been in place at z > 3.