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  • 1
    Electronic Resource
    Electronic Resource
    The afterglow, redshift and extreme energetics of the γ-ray burst of 23 January 1999 (1999)
    [s.l.] : Macmillan Magazines Ltd.
    Nature 398 (1999), S. 389-394 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Long-lived emission, known as afterglow, has now been detected from about a dozen γ-ray bursts. Distance determinations place the bursts at cosmological distances, with redshifts, z, ranging from ∼1 to 3. The energy required to produce these bright γ-ray flashes is enormous: up ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/18821
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    Paper (German National Licenses)
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  • 2
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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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  • 3
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    On the possible environmental effect in distributing heavy elements beyond individual gaseous haloes (2015)
    Oxford University Press
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    Publication Date: 2015-04-10
    Description: We present a study of extended galaxy halo gas through H i and O vi absorption over two decades in projected distance at z   0.2. The study is based on a sample of 95 galaxies from a highly complete (〉80 per cent) survey of faint galaxies ( L  〉 0.1 L * ) with archival quasar absorption spectra and 53 galaxies from the literature. A clear anticorrelation is found between H i (O vi ) column density and virial radius normalized projected distance, d / R h . Strong H i (O vi ) absorption systems with column densities greater than 10 14.0 (10 13.5 ) cm –2 are found for 48 of 54 (36 of 42) galaxies at d 〈 R h indicating a mean covering fraction of $\langle \kappa _{\rm H\,\small {i}}\rangle =0.89$ ( $\langle \kappa _{\rm O\,\small {vi}}\rangle =0.86$ ). O vi absorbers are found at d    R h , beyond the extent observed for lower ionization species. At d / R h  = 1–3 strong H i (O vi ) absorption systems are found for only 7 of 43 (5 of 34) galaxies ( $\langle \kappa _{\rm H\,\small {i}}\rangle =0.16$ and $\langle \kappa _{\rm O\,\small {vi}}\rangle =0.15$ ). Beyond d  = 3 R h , the H i and O vi covering fractions decrease to levels consistent with coincidental systems. The high completeness of the galaxy survey enables an investigation of environmental dependence of extended gas properties. Galaxies with nearby neighbours exhibit a modest increase in O vi covering fraction at d  〉  R h compared to isolated galaxies ( $\kappa _{\rm O\,\small {vi}}\approx 0.13$ versus 0.04) but no excess H i absorption. These findings suggest that environmental effects play a role in distributing heavy elements beyond the enriched gaseous haloes of individual galaxies. Finally, we find that differential H i and O vi absorption between early- and late-type galaxies continues from d  〈  R h to d   3 R h .
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    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 4
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    Non-linearity and environmental dependence of the star-forming galaxies main sequence (2015)
    Oxford University Press
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    Publication Date: 2015-11-27
    Description: Using data from four deep fields (COSMOS, AEGIS, ECDFS, and CDFN), we study the correlation between the position of galaxies in the star formation rate (SFR) versus stellar mass plane and local environment at z 〈 1.1. To accurately estimate the galaxy SFR, we use the deepest available Spitzer /MIPS 24 and Herschel /PACS data sets. We distinguish group environments ( M halo ~ 10 12.5–14.2 M ) based on the available deep X-ray data and lower halo mass environments based on the local galaxy density. We confirm that the main sequence (MS) of star-forming galaxies is not a linear relation and there is a flattening towards higher stellar masses ( M * 〉 10 10.4–10.6 M ), across all environments. At high redshift (0.5 〈 z 〈 1.1), the MS varies little with environment. At low redshift (0.15 〈 z 〈 0.5), group galaxies tend to deviate from the mean MS towards the region of quiescence with respect to isolated galaxies and less-dense environments. We find that the flattening of the MS towards low SFR is due to an increased fraction of bulge-dominated galaxies at high masses. Instead, the deviation of group galaxies from the MS at low redshift is caused by a large fraction of red disc-dominated galaxies which are not present in the lower density environments. Our results suggest that above a mass threshold (~10 10.4 –10 10.6 M ) stellar mass, morphology and environment act together in driving the evolution of the star formation activity towards lower level. The presence of a dominating bulge and the associated quenching processes are already in place beyond z ~1. The environmental effects appear, instead, at lower redshifts and have a long time-scale.
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    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 5
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    Reversal or no reversal: the evolution of the star formation rate-density relation up to z ~ 1.6 (2013)
    Oxford University Press
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    Publication Date: 2013-12-06
    Description: We investigate the evolution of the star formation rate (SFR)–density relation in the Extended Chandra Deep Field South and the Great Observatories Origin Deep Survey fields up to z  ~ 1.6. In addition to the ‘traditional method’, in which the environment is defined according to a statistical measurement of the local galaxy density, we use a ‘dynamical’ approach, where galaxies are classified according to three different environment regimes: group, ‘filament-like’ and field. Both methods show no evidence of an SFR–density reversal. Moreover, group galaxies show a mean SFR lower than other environments up to z  ~ 1, while at earlier epochs group and field galaxies exhibit consistent levels of star formation (SF) activity. We find that processes related to a massive dark matter halo must be dominant in the suppression of the SF below z  ~ 1, with respect to purely density-related processes. We confirm this finding by studying the distribution of galaxies in different environments with respect to the so-called main sequence (MS) of star-forming galaxies. Galaxies in both group and ‘filament-like’ environments preferentially lie below the MS up to z  ~ 1, with group galaxies exhibiting lower levels of star-forming activity at a given mass. At z  〉 1, the star-forming galaxies in groups reside on the MS. Groups exhibit the highest fraction of quiescent galaxies up to z  ~ 1, after which group, ‘filament-like’ and field environments have a similar mix of galaxy types. We conclude that groups are the most efficient locus for SF quenching. Thus, a fundamental difference exists between bound and unbound objects, or between dark matter haloes of different masses.
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    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 6
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    The evolution of star formation activity in galaxy groups (2014)
    Oxford University Press
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    Publication Date: 2014-10-22
    Description: We study the evolution of the total star formation (SF) activity, total stellar mass ( M * ) and halo occupation distribution (HOD) in massive haloes by using one of the largest X-ray selected sample of galaxy groups with secure spectroscopic identification in the major blank field surveys (ECDFS, CDFN, COSMOS, AEGIS). We provide an accurate measurement of star formation rate (SFR) for the bulk of the star-forming galaxies using very deep mid-infrared Spitzer MIPS and far-infrared Herschel PACS observations. For undetected IR sources, we provide a well-calibrated SFR from spectral energy distribution (SED) fitting. We observe a clear evolution in the level of SF activity in galaxy groups. The total SF activity in the high-redshift groups (0.5 〈  z  〈 1.1) is higher with respect to the low-redshift (0.15 〈  z  〈 0.5) sample at any mass by 0.8 ± 0.12 dex. A milder difference (0.35 ± 0.1 dex) is observed between the low-redshift bin and the groups at z  ~ 0. We show that the level of SF activity is declining more rapidly in the more massive haloes than in the more common lower mass haloes. We do not observe any evolution in the HOD and total stellar mass–halo mass relations in groups. The picture emerging from our findings suggests that the galaxy population in the most massive systems is evolving faster than galaxies in lower mass haloes, consistently with a ‘halo downsizing’ scenario.
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    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 7
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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).
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    Electronic ISSN: 1365-2966
    Topics: Physics
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  • 8
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    Discovery of a transparent sightline at {rho} lsim 20 kpc from an interacting pair of galaxies (2014)
    Oxford University Press
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    Publication Date: 2014-02-20
    Description: We report the discovery of a transparent sightline at projected distances of 20 kpc to an interacting pair of mature galaxies at z  = 0.12. The sightline of the UV-bright quasar PG 1522+101 at z em  = 1.328 passes at  = 11.5 kpc from the higher mass galaxy ( M *  = 10 10.6 M ) and  = 20.4 kpc from the lower mass one ( M *  = 10 10.0 M ). The two galaxies are separated by 9 kpc in projected distance and 30 km s –1 in line-of-sight velocity. Deep optical images reveal tidal features indicative of close interactions. Despite the small projected distances, the quasar sightline shows little absorption associated with the galaxy pair with a total H i column density no greater than $\log \, N({\rm H\,\small {I}})/{\rm cm}^{-2}=13.65$ . This limiting H i column density is already two orders of magnitude less than what is expected from previous halo gas studies. In addition, we detect no heavy-element absorption features associated with the galaxy pair with 3 limits of $\log \,N({\rm Mg\,\small {II}})/{\rm cm}^{-2} 〈 12.2$ and $\log \,N({\rm O\,\small {VI}})/{\rm cm}^{-2} 〈 13.7$ . The probability of seeing such little absorption in a sightline passing at a small projected distance from two non-interacting galaxies is 0.2 per cent. The absence of strong absorbers near the close galaxy pair suggests that the cool gas reservoirs of the galaxies have been significantly depleted by the galaxy interaction. These observations therefore underscore the potential impact of galaxy interactions on the gaseous haloes around galaxies.
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    Electronic ISSN: 1365-2966
    Topics: Physics
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  • 9
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    The GEEC2 spectroscopic survey of Galaxy groups at 0.8 〈 z 〈 1 (2014)
    Oxford University Press
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    Publication Date: 2014-08-06
    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.
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    Topics: Physics
    Published by Oxford University Press
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  • 10
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    The lack of star formation gradients in galaxy groups up to z ~ 1.6 (2013)
    Oxford University Press
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    Publication Date: 2013-09-06
    Description: In the local Universe, galaxy properties show a strong dependence on environment. In cluster cores, early-type galaxies dominate, whereas star-forming galaxies are more and more common in the outskirts. At higher redshifts and in somewhat less dense environments (e.g. galaxy groups), the situation is less clear. One open issue is that of whether and how the star formation rate (SFR) of galaxies in groups depends on the distance from the centre of mass. To shed light on this topic, we have built a sample of X-ray selected galaxy groups at 0 〈  z  〈 1.6 in various blank fields [Extended Chandra Deep Field South (ECDFS), Cosmological Evolution Survey (COSMOS), Great Observatories Origin Deep Survey (GOODS)]. We use a sample of spectroscopically confirmed group members with stellar mass M *  〉 10 10.3 M in order to have a high spectroscopic completeness. As we use only spectroscopic redshifts, our results are not affected by uncertainties due to projection effects. We use several SFR indicators to link the star formation (SF) activity to the galaxy environment. Taking advantage of the extremely deep mid-infrared Spitzer MIPS and far-infrared Herschel 1 PACS observations, we have an accurate, broad-band measure of the SFR for the bulk of the star-forming galaxies. We use multi-wavelength Spectral Energy Distribution (SED) fitting techniques to estimate the stellar masses of all objects and the SFR of the MIPS and PACS undetected galaxies. We analyse the dependence of the SF activity, stellar mass and specific SFR on the group-centric distance, up to z  ~ 1.6, for the first time. We do not find any correlation between the mean SFR and group-centric distance at any redshift. We do not observe any strong mass segregation either, in agreement with predictions from simulations. Our results suggest that either groups have a much smaller spread in accretion times with respect to the clusters and that the relaxation time is longer than the group crossing time.
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    Topics: Physics
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