We present an analysis of the levels and evolution of star formation activity in a representative sample of 30 massive galaxy clusters at 0.15 < z < 0.30 from the Local Cluster Substructure Survey, ...combining wide-field Spitzer/MIPS 24 mum data with extensive spectroscopy of cluster members. The specific SFRs of massive (M > ~ 10 super(10) M sub(middot in circle)) star-forming cluster galaxies within r sub(200) are found to be systematically ~28% lower than their counterparts in the field at fixed stellar mass and redshift, a difference significant at the 8.7sigma level. This is the unambiguous signature of star formation in most (and possibly all) massive star-forming galaxies being slowly quenched upon accretion into massive clusters, their star formation rates (SFRs) declining exponentially on quenching timescales in the range 0.7-2.0 Gyr. We measure the mid-infrared Butcher-Oemler effect over the redshift range 0.0-0.4, finding rapid evolution in the fraction (functionof sub(SF)) of massive (M sub(K) < - 23.1) cluster galaxies within r sub(200) with SFRs > 3 M sub(middot in circle) yr super(-1), of the form functionof sub(SF) alpha (1 + z) super(7.6 + or - 1.1). We dissect the origins of the Butcher-Oemler effect, revealing it to be due to the combination of a ~3 x decline in the mean specific SFRs of star-forming cluster galaxies since z ~ 0.3 with a ~1.5 x decrease in number density. Two-thirds of this reduction in the specific SFRs of star-forming cluster galaxies is due to the steady cosmic decline in the specific SFRs among those field galaxies accreted into the clusters. The remaining one-third reflects an accelerated decline in the star formation activity of galaxies within clusters. The slow quenching of star formation in cluster galaxies is consistent with a gradual shut down of star formation in infalling spiral galaxies as they interact with the intracluster medium via ram-pressure stripping or starvation mechanisms. The observed sharp decline in star formation activity among cluster galaxies since z ~ 0.4 likely reflects the increased susceptibility of low-redshift spiral galaxies to gas removal mechanisms as their gas surface densities decrease with time. We find no evidence for the build-up of cluster S0 bulges via major nuclear starburst episodes.
We study the case of a bright (L > L
) barred spiral galaxy from the rich cluster A3558 in the Shapley supercluster core (z = 0.05) undergoing ram-pressure stripping. Integral-field spectroscopy with ...Wide Field Spectrograph (WiFeS) at the 2.3-m Australian National University telescope, complemented by imaging in ultraviolet (GALEX), B and R European Southern Observatory (ESO) 2.2-m WFI, Hα (Magellan), K (United Kingdom Infrared Telescope), 24 and 70 μm (Spitzer), allows us to reveal the impact of ram pressure on the interstellar medium. With these data we study in detail the kinematics and the physical conditions of the ionized gas and the properties of the stellar populations. We observe one-sided extraplanar ionized gas along the full extent of the galaxy disc, extending ∼13 kpc in projection from it. Narrow-band Hα imaging resolves this outflow into a complex of knots and filaments, similar to those seen in other cluster galaxies undergoing ram-pressure stripping. The gas velocity field is complex with the extraplanar gas showing signature of rotation, while the stellar velocity field is regular and the K-band image shows a symmetric stellar distribution. We use line-ratio diagnostics to ascertain the origin of the observed emission. In all parts of the galaxy, we find a significant contribution from shock excitation, as well as emission powered by star formation. Shock-ionized gas is associated with the turbulent gas outflow and highly attenuated by dust (A
v
= 1.5-2.3 mag). All these findings cover the whole phenomenology of early-stage ram-pressure stripping. Intense, highly obscured star formation is taking place in the nucleus, probably related to the bar, and in a region 12 kpc south-west (SW) from the centre. These two regions account for half of the total star formation in the galaxy, which overall amounts to 7.2 ± 2.2 M yr−1. In the SW region we identify a starburst characterized by a ∼5× increase in the star formation rate over the last ∼100 Myr, possibly related to the compression of the interstellar gas by the ram pressure. The scenario suggested by the observations is supported and refined by ad hoc N-body/hydrodynamical simulations which identify a rather narrow temporal range for the onset of ram-pressure stripping around t ∼ 60 Myr ago, and an angle between the galaxy rotation axis and the intracluster medium wind of ∼45°. The ram pressure is therefore acting at an intermediate angle between face-on and edge-on. Taking into account that the galaxy is found ∼1 Mpc from the cluster centre in a relatively low density region, this study shows that ram-pressure stripping still acts efficiently on massive galaxies well outside the cluster cores, as also recently observed in the Virgo cluster.
Using a MeerKAT observation of the galaxy cluster A3562 (a member of the Shapley Supercluster), we have discovered a narrow, long and straight, very faint radio filament, which branches out at a ...straight angle from the tail of a radio galaxy located in projection near the core of the cluster. The radio filament spans 200 kpc and aligns with a sloshing cold front seen in the X-rays, staying inside the front in projection. The radio spectral index along the filament appears uniform (within large uncertainties) atα' −1.5. We propose that the radio galaxy is located outside the cold front, but dips its tail under the front. The tangential wind that blows there may stretch the radio plasma from the radio galaxy into a filamentary structure. Some reacceleration is needed in this scenario to maintain the radio spectrum uniform. Alternatively, the cosmic ray electrons from that spot in the tail can spread along the cluster magnetic field lines, straightened by that same tangential flow, via anomalously fast diffusion. Our radio filament can provide constraints on this process. We also uncover a compact radio source at the Brightest Cluster Galaxy (BCG) that is 2–3 orders of magnitude
OBJECTIVETo test the hypothesis that cognitively unimpaired individuals with Alzheimer disease (AD) neuropathology differ from individuals with AD dementia on biomarkers of neurodegeneration, ...synaptic dysfunction, and glial activation.
METHODSIn a cross-sectional study, adult participants >70 years old (n = 79, age 77.1 ± 5.3 years) underwent comprehensive cognitive evaluation and CSF collection, which was assayed for markers of amyloid, phosphorylated tau (p-tau), neurodegeneration (neurofilament light protein NFL and total tau), synaptic dysfunction (neurogranin), and glial activation (chitinase-3–like protein 1 YKL-40). Participants were divided into 3 groups based on diagnosis and p-tau/β-amyloid42 (Aβ42)those with low p-tau/Aβ42 and unimpaired cognition were classified as controls (n = 25); those with high p-tau/Aβ42 diagnosed with AD-dementia or AD–mild cognitive impairment were classified as AD-Dementia (n = 40); and those with high p-tau/Aβ42 but unimpaired cognition were classified as mismatches (n = 14). A similar, secondary analysis was performed with no age exclusion criteria (n = 411).
RESULTSIn both the primary and secondary analyses, biomarker levels between groups were compared with the use of analysis of covariance while controlling for age and demographic variables. Despite p-tau/Aβ42 and Aβ42/Aβ40 levels comparable to those of the AD-Dementia group, mismatches had significantly lower levels of NFL and total tau. While not significantly lower than the AD-Dementia group on YKL-40 and neurogranin, mismatches were also not significantly different from controls.
CONCLUSIONSThese results provide evidence that, in the absence of significant neurodegenerative processes, individuals who harbor AD neuropathology may remain cognitively unimpaired. This finding provides insight into the biological processes phenotypic of dementia and supports monitoring multiple biomarkers in individuals positive for AD neuropathology.
Postmortem studies of Parkinson's disease (PD) suggest that Lewy body pathology accumulates in a predictable topographical sequence, beginning in the olfactory bulb, followed by caudal brainstem, ...substantia nigra, limbic cortex, and neocortex. Diffusion‐weighted imaging (DWI) is sensitive, if not specific, to early disease‐related white matter (WM) change in a variety of traumatic and degenerative brain diseases. Although numerous cross‐sectional studies have reported DWI differences in cerebral WM in PD, only a few longitudinal studies have investigated whether DWI change exceeds that of normal aging or coincides with regional Lewy body accumulation. This study mapped regional differences in the rate of DWI‐based microstructural change between 29 PD patients and 43 age‐matched controls over 18 months. Iterative within‐ and between‐subject tensor‐based registration was completed on motion‐ and eddy current‐corrected DWI images, then baseline versus follow‐up difference maps of fractional anisotropy, mean, radial, and axial diffusivity were analyzed in the Biological Parametric Mapping toolbox for MATLAB. This analysis showed that PD patients had a greater decline in WM integrity in the rostral brainstem, caudal subcortical WM, and cerebellar peduncles, compared with controls. In addition, patients with unilateral clinical signs at baseline experienced a greater rate of WM change over the 18‐month study than patients with bilateral signs. These findings suggest that rate of WM microstructural change in PD exceeds that of normal aging and is maximal during early stage disease. In addition, the neuroanatomic locations (rostral brainstem and subcortical WM) of accelerated WM change fit with current theories of topographic disease progression.
We present two new examples of galaxies undergoing transformation in the Shapley supercluster core. These low-mass (
$\mathcal {M}_{\star }\sim 0.4\text{--}1\times 10^{10}$
M⊙) galaxies are members ...of the two clusters SC 1329−313 (z ∼ 0.045) and SC 1327−312 (z ∼ 0.049). Integral-field spectroscopy complemented by imaging in the ugriK bands and in Hα narrow band is used to disentangle the effects of tidal interaction (TI) and ram-pressure stripping (RPS). In both galaxies, SOS 61086 and SOS 90630, we observe one-sided extraplanar ionized gas extending respectively ∼30 and ∼41 kpc in projection from their discs. The galaxies' gaseous discs are truncated, and the kinematics of the stellar and gas components are decoupled, supporting the RPS scenario. The emission of the ionized gas extends in the direction of a possible companion for both galaxies suggesting a TI. The overall gas velocity field of SOS 61086 is reproduced by ad hoc N-body/hydrodynamical simulations of RPS acting almost face-on and starting ∼250 Myr ago, consistent with the age of the young stellar populations. A link between the observed gas stripping and the cluster–cluster interaction experienced by SC 1329−313 and A3562 is suggested. Simulations of ram pressure acting almost edge-on are able to fully reproduce the gas velocity field of SOS 90630, but cannot at the same time reproduce the extended tail of outflowing gas. This suggests that an additional disturbance from a TI is required. This study adds a piece of evidence that RPS may take place in different environments with different impacts and witnesses the possible effect of cluster–cluster merger on RPS.
We study the mid-infrared (MIR) properties of galaxies in 30 massive galaxy clusters at 0.02 <= z <= 0.40, using panoramic Spitzer/MIPS 24 Delta *mm and near-infrared data, including 27 new ...observations from the LoCuSS and ACCESS surveys. This is the largest sample of clusters to date with such high-quality and uniform MIR data covering not only the cluster cores, but extending into the infall regions. We use these data to revisit the so-called Butcher-Oemler (BO) effect, measuring the fraction of massive infrared luminous galaxies (K < K + 1.5, L IR > 5 X 1010 L ) within r 200, finding a steady increase in the fraction with redshift from ~3% at z = 0.02 to ~10% by z = 0.30, and an rms cluster-to-cluster scatter about this trend of 0.03. The best-fit redshift evolution model of the form f SF (1 + z) n has n = 5.7+2.1 -1.8, which is stronger redshift evolution than that of L IR in both clusters and the field. We find that, statistically, this excess is associated with galaxies found at large cluster-centric radii, specifically r 500 < r < r 200, implying that the MIR BO effect can be explained by a combination of both the global decline in star formation in the universe since z ~ 1 and enhanced star formation in the infall regions of clusters at intermediate redshifts. This picture is supported by a simple infall model based on the Millennium Simulation semianalytic galaxy catalogs, whereby star formation in infalling galaxies is instantaneously quenched upon their first passage through the cluster, in that the observed radial trends of f SF trace those inferred from the simulations. The observed f SF values, however, lie systematically above the predictions, suggesting an overall excess of star formation, either due to triggering by environmental processes, or a gradual quenching. We also find that f SF does not depend on simple indicators of the dynamical state of clusters, including the offset between the brightest cluster galaxy and the peak of the X-ray emission. This is consistent with the picture described above in that most new star formation in clusters occurs in the infall regions, and is thus not sensitive to the details of cluster-cluster mergers in the core regions.
Aims. We present and release photometric redshifts for a uniquely large and deep sample of 522286 objects with $i'_{\rm AB}\le 25$ in the Canada-France Hawaii Telescope Legacy Survey (CFHTLS) “Deep ...Survey” fields D1, D2, D3, and D4, which cover a total effective area of 3.2 $\deg^2$. Methods. We use 3241 spectroscopic redshifts with $0 \leq z \leq 5$ from the VIMOS VLT Deep Survey (VVDS) as a calibration and training set to derive these photometric redshifts. Using the “Le Phare” photometric redshift code, we developed a robust calibration method based on an iterative zero-point refinement combined with a template optimisation procedure and the application of a Bayesian approach. This method removes systematic trends in the photometric redshifts and significantly reduces the fraction of catastrophic errors (by a factor of 2), a significant improvement over traditional methods. We use our unique spectroscopic sample to present a detailed assessment of the robustness of the photometric redshift sample. Results. For a sample selected at $i'_{\rm AB}\le 24$, we reach a redshift accuracy of $\sigma_{\Delta z/(1+z)}=0.029$ with $\eta=3.8\%$ of catastrophic errors (η is defined strictly as those objects with $|\Delta z|/(1+z) > 0.15$). The reliability of our photometric redshifts decreases for faint objects: we find $\sigma_{\Delta z/(1+z)}=0.025, 0.034$ and $\eta=1.9\%, 5.5\%$ for samples selected at $i'_{\rm AB}=17.5$–22.5 and 22.5–24 respectively. We find that the photometric redshifts of starburst galaxies are less reliable: although these galaxies represent only 22% of the spectroscopic sample, they are responsible for 50% of the catastrophic errors. An analysis as a function of redshift demonstrates that our photometric redshifts work best in the redshift range $0.2\le z \le 1.5$. We find an excellent agreement between the photometric and the VVDS spectroscopic redshift distributions at $i'_{\rm AB}\le 24$. Finally, we compare the redshift distributions of i' selected galaxies on the four CFHTLS deep fields, showing that cosmic variance is still present on fields of 0.7–0.9 deg2. These photometric redshifts are made publicly available at http://terapix.iap.fr (complete ascii catalogues) and http://cencos.oamp.fr/cencos/CFHTLS/ (searchable database interface).
PDF
