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  • 1
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    Do group dynamics play a role in the evolution of member galaxies? (2013)
    Oxford University Press
    Details
    Publication Date: 2013-09-26
    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.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 2
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    Efficient satellite quenching at z~1 from the GEEC2 spectroscopic survey of galaxy groups (2013)
    Oxford University Press
    Details
    Publication Date: 2013-04-13
    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.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 3
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    Star formation and environmental quenching of GEEC2 group galaxies at z ~ 1 (2014)
    Oxford University Press
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    Publication Date: 2014-02-20
    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).
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 4
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    High-voltage nanosecond pulses in a low-pressure radio-frequency discharge (2013)
    American Physical Society (APS)
    Details
    Publication Date: 2013-06-11
    Description: Author(s): M. Y. Pustylnik, L. Hou, A. V. Ivlev, L. M. Vasilyak, L. Couëdel, H. M. Thomas, G. E. Morfill, and V. E. Fortov An influence of a high-voltage (3–17 kV) 20 ns pulse on a weakly-ionized low-pressure (0.1–10 Pa) capacitively coupled radiofrequency (RF) argon plasma is studied experimentally. The plasma evolution after pulse exhibits two characteristic regimes: a bright flash, occurring within 100 ns after the p... [Phys. Rev. E 87, 063105] Published Mon Jun 10, 2013
    Keywords: Plasma Physics
    Print ISSN: 1539-3755
    Electronic ISSN: 1550-2376
    Topics: Physics
    Published by American Physical Society (APS)
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  • 5
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    International Myeloma Working Group recommendations for global myeloma care (2014)
    Nature Publishing Group (NPG)
    In: Leukemia
    Details
    Publication Date: 2014-05-08
    Description: International Myeloma Working Group recommendations for global myeloma care Leukemia 28, 981 (May 2014). doi:10.1038/leu.2013.293 Authors: H Ludwig, J S Miguel, M A Dimopoulos, A Palumbo, R Garcia Sanz, R Powles, S Lentzsch, W Ming Chen, J Hou, A Jurczyszyn, K Romeril, R Hajek, E Terpos, K Shimizu, D Joshua, V Hungria, A Rodriguez Morales, D Ben-Yehuda, P Sondergeld, E Zamagni & B Durie
    Keywords: myeloma careglobal perspectivemanagement of myeloma-related side effects
    Print ISSN: 0887-6924
    Electronic ISSN: 1476-5551
    Topics: Medicine
    Published by Nature Publishing Group (NPG)
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  • 6
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    The pre-processing of subhaloes in SDSS groups and clusters (2014)
    Oxford University Press
    Details
    Publication Date: 2014-06-08
    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.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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