The Tully-Fisher relation of distant field galaxies

We examine the evolution of the Tully-Fisher relation (TFR) using a sample of 89 field spirals, with 0.1 < z < 1, for which we have measured confident rotation velocities (Vrot). By plotting the residuals from the local TFR versus redshift, or alternatively fitting the TFR to our data in several redshift bins, we find evidence that luminous spiral galaxies are increasingly offset from the local TFR with redshift, reaching a brightening of -1.0+-0.5 mag, for a given Vrot, by approximately z = 1. Since selection effects would generally increase the fraction of intrinsically-bright galaxies at higher redshifts, we argue that the observed evolution is probably an upper limit. Previous studies have used an observed correlation between the TFR residuals and Vrot to argue that low mass galaxies have evolved significantly more than those with higher mass. However, we demonstrate that such a correlation may exist purely due to an intrinsic coupling between the Vrot scatter and TFR residuals, acting in combination with the TFR scatter and restrictions on the magnitude range of the data, and therefore it does not necessarily indicate a physical difference in the evolution of galaxies with different Vrot. Finally, if we interpret the luminosity evolution derived from the TFR as due to the evolution of the star formation rate (SFR) in these luminous spiral galaxies, we find that SFR(z) is proportional to (1+z)^(1.7+-1.1), slower than commonly derived for the overall field galaxy population. This suggests that the rapid evolution in the SFR density of the universe observed since approximately z = 1 is not driven by the evolution of the SFR in individual bright spiral galaxies. (Abridged.)Comment: 14 pages, 10 figures, accepted by MNRA

MegaMorph: classifying galaxy morphology using multi-wavelength S\'ersic profile fits

Aims. This work investigates the potential of using the wavelength-dependence of galaxy structural parameters (S\'ersic index, n, and effective radius, Re) to separate galaxies into distinct types. Methods. A sample of nearby galaxies with reliable visual morphologies is considered, for which we measure structural parameters by fitting multi-wavelength single-S\'ersic models. Additionally, we use a set of artificially redshifted galaxies to test how these classifiers behave when the signal-to-noise decreases. Results. We show that the wavelength-dependence of n may be employed to separate visually-classified early- and late-type galaxies, in a manner similar to the use of colour and n. Furthermore, we find that the wavelength variation of n can recover galaxies that are misclassified by these other morphological proxies. Roughly half of the spiral galaxies that contaminate an early-type sample selected using (u-r) versus n can be correctly identified as late-types by N, the ratio of n measured in two different bands. Using a set of artificially-redshifted images, we show that this technique remains effective up to z ~ 0.1. N can therefore be used to achieve purer samples of early-types and more complete samples of late-types than using a colour-n cut alone. We also study the suitability of R, the ratio of Re in two different bands, as a morphological classifier, but find that the average sizes of both early- and late-type galaxies do not change substantially over optical wavelengths.Comment: 6 pages, 2 figures, 2 tables, Accepted for publication in A&

Evolution of field spiral galaxies up to redshifts z=1

We have gained VLT/FORS spectra and HST/ACS images of a sample of 220 distant field spiral galaxies. Spatially resolved rotation curves were extracted and fitted with synthetic velocity fields that take into account all geometric and observational effects, like blurring due to the slit width and seeing influence. The maximum rotation velocity Vmax could be determined for 124 galaxies that cover the redshift range 0.1<z<1.0. The luminosity-rotation velocity distribution of this sample is offset from the Tully-Fisher relation (TFR) of local low-mass spirals, whereas the distant high-mass spirals are compatible with the local TFR. We show that the slope of the local and the intermediate-z TFR would be in compliance if its scatter decreased by more than a factor of 3 between z~0.5 and z~0. On the other hand, the distant low-luminosity disks have much lower stellar M/L ratios than their local counterparts, while high-luminosity disks barely evolved in M/L over the covered redshift range. This could be the manifestation of the "downsizing" effect, i.e. the succesive shift of the peak of star formation from high-mass to low-mass galaxies towards lower redshifts. This trend might be canceled out in the TF diagram due to the simultaneous evolution of multiple parameters. We also estimate the ratios between stellar and total masses, finding that these remained constant since z=1, as would be expected in the context of hierarchically growing structure. (Abridged)Comment: 20 pages, 5 figures, ApJ, accepte

Star formation rates and chemical abundances of emission line galaxies in intermediate-redshift clusters

We examine the evolutionary status of luminous, star-forming galaxies in intermediate-redshift clusters by considering their star formation rates and the chemical and ionsiation properties of their interstellar emitting gas. Our sample consists of 17 massive, star-forming, mostly disk galaxies with M_{B}<-20, in clusters with redshifts in the range 0.31< z <0.59, with a median of =0.42. We compare these galaxies with the identically selected and analysed intermediate-redshift field sample of Mouhcine et al. (2006), and with local galaxies from the Nearby Field Galaxy Survey of Jansen et al. (2000). From our optical spectra we measure the equivalent widths of OII, Hbeta and OIII emission lines to determine diagnostic line ratios, oxygen abundances, and extinction-corrected star formation rates. The star-forming galaxies in intermediate-redshift clusters display emission line equivalent widths which are, on average, significantly smaller than measured for field galaxies at comparable redshifts. However, a contrasting fraction of our cluster galaxies have equivalent widths similar to the highest observed in the field. This tentatively suggests a bimodality in the star-formation rates per unit luminosity for galaxies in distant clusters. We find no evidence for further bimodalities, or differences between our cluster and field samples, when examining additional diagnostics and the oxygen abundances of our galaxies. This maybe because no such differences exist, perhaps because the cluster galaxies which still display signs of star-formation have recently arrived from the field. In order to examine this topic with more certainty, and to further investigate the way in which any disparity varies as a function of cluster properties, larger spectroscopic samples are needed.Comment: 10 pages, 6 figures, MNRAS in pres

The Tully-Fisher relation of intermediate redshift field and cluster galaxies from Subaru spectroscopy

We have carried out spectroscopic observations in 4 cluster fields using Subaru's FOCAS multi-slit spectrograph and obtained spectra for 103 bright disk field and cluster galaxies at $0.06 \le z \le 1.20$. Seventy-seven of these show emission lines, and 33 provide reasonably-secure determinations of the galaxies' rotation velocity. The rotation velocities, luminosities, colours and emission-line properties of these galaxies are used to study the possible effects of the cluster environment on the star-formation history of the galaxies. Comparing the Tully-Fisher relations of cluster and field galaxies at similar reshifts we find no measurable difference in rest-frame $B$-band luminosity at a given rotation velocity (the formal difference is $0.18\pm0.33$mag). The colours of the cluster emission line galaxies are only marginally redder in rest-frame $B-V$ (by $0.06\pm0.04$mag) than the field galaxies in our sample. Taken at face value, these results seem to indicate that bright star-forming cluster spirals are similar to their field counterparts in their star-formation properties. However, we find that the fraction of disk galaxies with absorption-line spectra (i.e., with no current star formation) is larger in clusters than in the field by a factor of $\sim3$--5. This suggests that the cluster environment has the overall effect of switching off star formation in (at least) some spiral galaxies. To interpret these observational results, we carry out simulations of the possible effects of the cluster environment on the star-formation history of disk galaxies and thus their photometric and spectroscopic properties. Finally, we evaluate the evolution of the rest-frame absolute $B$-band magnitude per unit redshift at fixed rotation velocity.Comment: 21 pages, 13 figures, accepted for publication in MNRA

Inpatient case fatality rates improvements in children under 5: Diarrhoeal disease, pneumonia and severe acute malnutrition

Data on the number of admissions and deaths in children aged under 5 years from diarrhoea, pneumonia and severe acute malnutrition are routinely collected through the District Health Information System. These data, and the associated case fatality rates, are available for all public sector hospitals in South Africa (SA), and can be compared over time, as well as across different settings. This article presents these data for the period 2011/12 - 2016/17. It reflects on the remarkable improvements in these case fatality rates, and the likely reasons for their declines across all provinces. The article concludes by identifying the actions that need to be taken to ensure that SA achieves the Sustainable Development Goal aim of ending preventable child deaths by 2030

The sizes of disc galaxies in intermediate-redshift clusters

We examine how the location of star formation within disc galaxies depends on environment at intermediate redshift. This is achieved by comparing emission-line (r_em) and restframe B-band (r_B) scalelengths for matched samples of 50 field and 19 cluster star-forming, disc galaxies, with 0.25 < z < 1.0 and M_B < -19.5 mag. We find that at a given r_B the majority of our cluster galaxies have r_em smaller than those in the field, by 25 percent on average. These results are compared with studies of local galaxies, which find a very similar behaviour. From the relations of r_em and r_B versus B-band absolute magnitude (M_B) we infer that the difference between the intermediate-z cluster and field samples is mostly attributable to variation in r_em at a given M_B, while the r_B versus M_B relation is similar for the two samples.Comment: 5 pages, 5 figures, accepted for publication in MNRAS Letter

Galaxy bimodality versus stellar mass and environment

We analyse a z<0.1 galaxy sample from the Sloan Digital Sky Survey focusing on the variation of the galaxy colour bimodality with stellar mass and projected neighbour density Sigma, and on measurements of the galaxy stellar mass functions. The characteristic mass increases with environmental density from about 10^10.6 Msun to 10^10.9 Msun (Kroupa IMF, H_0=70) for Sigma in the range 0.1--10 per Mpc^2. The galaxy population naturally divides into a red and blue sequence with the locus of the sequences in colour-mass and colour-concentration index not varying strongly with environment. The fraction of galaxies on the red sequence is determined in bins of 0.2 in log Sigma and log mass (12 x 13 bins). The red fraction f_r generally increases continuously in both Sigma and mass such that there is a unified relation: f_r = F(Sigma,mass). Two simple functions are proposed which provide good fits to the data. These data are compared with analogous quantities in semi-analytical models based on the Millennium N-body simulation: the Bower et al. (2006) and Croton et al. (2006) models that incorporate AGN feedback. Both models predict a strong dependence of the red fraction on stellar mass and environment that is qualitatively similar to the observations. However, a quantitative comparison shows that the Bower et al. model is a significantly better match; this appears to be due to the different treatment of feedback in central galaxies.Comment: 19 pages, 17 figures; accepted by MNRAS, minor change