ALBERT

Description: We examine galaxy groups from the present epoch to z  ~ 1 to explore the impact of group dynamics on galaxy evolution. We use group catalogues from the Sloan Digital Sky Survey (SDSS), the Group Environment and Evolution Collaboration (GEEC) and the high-redshift GEEC2 samples to study how the observed member properties depend on the galaxy stellar mass, group dynamical mass and dynamical state of the host group. We find a strong correlation between the fraction of non-star-forming (quiescent) galaxies and galaxy stellar mass, but do not detect a significant difference in the quiescent fraction with group dynamical mass, within our sample halo mass range of ~10 13 –10 14.5 M , or with dynamical state. However, at z  ~ 0.4 we do find some evidence that the quiescent fraction in low-mass galaxies [log 10 ( M star /M )  10.5] is lower in groups with substructure. Additionally, our results show that the fraction of groups with non-Gaussian velocity distributions increases with redshift to z  ~ 0.4, while the amount of detected substructure remains constant to z  ~ 1. Based on these results, we conclude that for massive galaxies [log 10 ( M star /M )  10.5], evolution is most strongly correlated to the stellar mass of a galaxy with little or no additional effect related to either the group dynamical mass or the dynamical state. For low-mass galaxies, we do find some evidence of a correlation between the quiescent fraction and the amount of detected substructure, highlighting the need to probe further down the stellar mass function to elucidate the role of environment in galaxy evolution.

Description: We present new analysis from the Group Environment Evolution Collaboration 2 (GEEC2) spectroscopic survey of galaxy groups at 0.8 〈  z  〈 1. Our previous work revealed an intermediate population between the star-forming and quiescent sequences and a strong environmental dependence in the fraction of quiescent galaxies. Only ~5 per cent of star-forming galaxies in both the group and field sample show a significant enhancement in star formation, which suggests that quenching is the primary process in the transition from the star-forming to the quiescent state. To model the environmental quenching scenario, we have tested the use of different exponential quenching time-scales and delays between satellite accretion and the onset of quenching. We find that with no delay, the quenching time-scale needs to be long in order to match the observed quiescent fraction, but then this model produces too many intermediate galaxies. Fixing a delay time of 3 Gyr, as suggested from the local Universe, produces too few quiescent galaxies. The observed fractions are best matched with a model that includes a delay that is proportional to the dynamical time and a rapid quenching time-scale (~0.25 Gyr), but this model also predicts intermediate galaxies H strength higher than that observed. Using stellar synthesis models, we have tested other scenarios, such as the rejuvenation of star formation in early-type galaxies and a portion of quenched galaxies possessing residual star formation. If environment quenching plays a role in the GEEC2 sample, then our work suggests that only a fraction of intermediate galaxies may be undergoing this transition and that quenching occurs quite rapidly in satellite galaxies (0.25 Gyr).

Description: We present the data release of the Gemini-South GMOS spectroscopy in the fields of 11 galaxy groups at 0.8 〈  z  〈 1, within the COSMOS field. This forms the basis of the Galaxy Environment Evolution Collaboration 2 (GEEC2) project to study galaxy evolution in haloes with M ~ 10 13 M across cosmic time. The final sample includes 162 spectroscopically confirmed members with R  〈 24.75, and is 〉50 per cent complete for galaxies within the virial radius, and with stellar mass M star 〉 10 10.3 M . Including galaxies with photometric redshifts, we have an effective sample size of ~400 galaxies within the virial radii of these groups. We present group velocity dispersions, dynamical and stellar masses. Combining with the GCLASS sample of more massive clusters at the same redshift, we find the total stellar mass is strongly correlated with the dynamical mass, with log M 200  = 1.20(log M star  – 12) + 14.07. This stellar fraction of ~1 per cent is lower than predicted by some halo occupation distribution models, though the weak dependence on halo mass is in good agreement. Most groups have an easily identifiable most massive galaxy (MMG) near the centre of the galaxy distribution, and we present the spectroscopic properties and surface brightness fits to these galaxies. The total stellar mass distribution in the groups, excluding the MMG, compares well with an NFW (Navarro Frenk & White) profile with concentration 4, for galaxies beyond ~0.2 R 200 . This is more concentrated than the number density distribution, demonstrating that there is some mass segregation.

Description: We investigate pre-processing using the observed quenched fraction of group and cluster galaxies in the Yang et al. Sloan Digital Sky Survey (SDSS)-seventh data release (DR7) group catalogue in the redshift range of 0.01 〈 z  〈 0.045. We categorize group galaxies as virialized, infall or backsplash and we apply a combination of the Dressler–Shectman statistic and group member velocities to identify subhaloes. On average, the fraction of galaxies that reside in subhaloes is a function of host halo mass, where more massive systems have a higher fraction of subhalo galaxies both in the overall galaxy and infall populations. Additionally, we find that within the range 2 r 200 〈 3 the quiescent fraction is higher in the subhalo population with respect to both the field and non-subhalo populations. At these large radii (2 r 200 〈 3), the majority of galaxies (~80 per cent) belong to the infall population and therefore, we attribute the enhanced quenching to infalling subhalo galaxies, indicating that pre-processing has occurred in the subhalo population. We conclude that pre-processing plays a significant role in the observed quiescent fraction, but only for the most massive ( M halo 〉 10 14.5 M ) systems in our sample.

Description: We present deep Gemini Multi-Object Spectrograph-South spectroscopy for 11 galaxy groups at 0.8 〈 z  〈 1.0, for galaxies with r AB  〈 24.75. Our sample is highly complete (〉66 per cent) for eight of the 11 groups. Using an optical–near-infrared colour–colour diagram, the galaxies in the sample were separated with a dust insensitive method into three categories: passive (red), star-forming (blue) and intermediate (green). The strongest environmental dependence is observed in the fraction of passive galaxies, which make up only ~20 per cent of the field in the mass range 10 10.3  〈 M star /M  〈 10 11.0 , but are the dominant component of groups. If we assume that the properties of the field are similar to those of the ‘pre-accreted’ population, the environment quenching efficiency ( ) is defined as the fraction of field galaxies required to be quenched in order to match the observed red fraction inside groups. The efficiency obtained is ~0.4, similar to its value in intermediate-density environments locally. While green (intermediate) galaxies represent ~20 per cent of the star-forming population in both the group and field, at all stellar masses, the average specific star formation rate of the group population is lower by a factor of ~3. The green population does not show strong H absorption that is characteristic of starburst galaxies. Finally, the high fraction of passive galaxies in groups, when combined with satellite accretion models, require that most accreted galaxies have been affected by their environment. Thus, any delay between accretion and the onset of truncation of star formation () must be 2 Gyr, shorter than the 3–7 Gyr required to fit data at z  = 0. The relatively small fraction of intermediate galaxies require that the actual quenching process occurs quickly, with an exponential decay time-scale of q 1 Gyr.

Description: We retrieved column-averaged dry air mole fractions of atmospheric carbon dioxide (XCO2) from backscattered short-wave infrared (SWIR) sunlight measured by the Japanese Greenhouse gases Observing SATellite (GOSAT). Over two years of XCO2 retrieved from GOSAT is compared with XCO2 inferred from collocated SWIR measurements by seven ground-based Total Carbon Column Observing Network (TCCON) stations. The average difference between GOSAT and TCCON XCO2 for individual TCCON sites ranges from −0.87 ppm to 0.77 ppm with a mean value of 0.1 ppm and standard deviation of 0.56 ppm. We find an average bias between all GOSAT and TCCON XCO2 retrievals of −0.20 ppm with a standard deviation of 2.26 ppm and a correlation coefficient of 0.75. One year of XCO2 was retrieved from GOSAT globally, which was compared to global 3-D GEOS-Chem chemistry transport model calculations. We find that the latitudinal gradient, seasonal cycles, and spatial variability of GOSAT and GEOS-Chem agree well in general with a correlation coefficient of 0.61. Regional differences between GEOS-Chem model calculations and GOSAT observations are typically less than 1 ppm except for the Sahara and central Asia where a mean difference between 2 to 3 ppm is observed, indicating regional biases in the GOSAT XCO2 retrievals unobserved by the current TCCON network. Using a bias correction scheme based on linear regression these regional biases are significantly reduced, approaching the required accuracy for surface flux inversions.

Description: Intractable epilepsies, that is, seizure disorders that do not respond to currently available therapies, are difficult, often tragic, neurological disorders. Na + channelopathies have been implicated in some intractable epilepsies, including Dravet syndrome ( Dravet 1978 ), but little progress has been forthcoming in therapeutics. Here we examine a Drosophila model for intractable epilepsy, the Na + channel gain-of-function mutant para bss1 that resembles Dravet syndrome in some aspects ( p arker et al. 2011a ). In particular, we identify second-site mutations that interact with para bss1 , seizure enhancers, and seizure suppressors. We describe one seizure-enhancer mutation named charlatan (chn) . The chn gene normally encodes an Neuron-Restrictive Silencer Factor/RE1-Silencing Transcription factor transcriptional repressor of neuronal-specific genes. We identify a second-site seizure-suppressor mutation, gilgamesh (gish) , that reduces the severity of several seizure-like phenotypes of para bss1 /+ heterozygotes. The gish gene normally encodes the Drosophila ortholog of casein kinase CK1g3, a member of the CK1 family of serine-threonine kinases. We suggest that CK1g3 is an unexpected but promising new target for seizure therapeutics.

Description: It has been shown that galaxy properties depend strongly on their host environment. In order to understand the relevant physical processes driving galaxy evolution it is important to study the observed properties of galaxies in different environments. Mass segregation in bound galaxy structures is an important indicator of evolutionary history and dynamical friction time-scales. Using group catalogues derived from the Sloan Digital Sky Survey Data Release 7 (SDSS DR7), we investigate mass-segregation trends in galaxy groups at low redshift. We investigate average galaxy stellar mass as a function of group-centric radius and find evidence for weak mass segregation in SDSS groups. The magnitude of the mass segregation depends on both galaxy stellar mass limits and group halo mass. We show that the inclusion of low-mass galaxies tends to strengthen mass-segregation trends, and that the strength of mass segregation tends to decrease with increasing group halo mass. We find the same trends if we use the fraction of massive galaxies as a function of group-centric radius as an alternative probe of mass segregation. The magnitude of mass segregation that we measure, particularly in high-mass haloes, indicates that dynamical friction is not acting efficiently.