The hot gas content of fossil galaxy clusters

We investigate the properties of the hot gas in four fossil galaxy systems detected at high significance in the Planck Sunyaev-Zeldovich (SZ) survey. XMM-Newton observations reveal overall temperatures of kT ~ 5-6 keV and yield hydrostatic masses M500,HE > 3.5 x 10e14 Msun, confirming their nature as bona fide massive clusters. We measure the thermodynamic properties of the hot gas in X-rays (out to beyond R500 in three cases) and derive their individual pressure profiles out to R ~ 2.5 R500 with the SZ data. We combine the X-ray and SZ data to measure hydrostatic mass profiles and to examine the hot gas content and its radial distribution. The average Navarro-Frenk-White (NFW) concentration parameter, c500 = 3.2 +/- 0.4, is the same as that of relaxed `normal' clusters. The gas mass fraction profiles exhibit striking variation in the inner regions, but converge to approximately the cosmic baryon fraction (corrected for depletion) at R500. Beyond R500 the gas mass fraction profiles again diverge, which we interpret as being due to a difference in gas clumping and/or a breakdown of hydrostatic equilibrium in the external regions. Overall our observations point to considerable radial variation in the hot gas content and in the gas clumping and/or hydrostatic equilibrium properties in these fossil clusters, at odds with the interpretation of their being old, evolved and undisturbed. At least some fossil objects appear to be dynamically young.Comment: 4 pages, 2 figures. Accepted for publication in A&

The competitive NMDA antagonist CPP protects substantia nigra neurons from MPTP-induced degeneration in primates

Degeneration of nigrostriatal dopaminergic neurons is the primary histopathological feature of Parkinson's disease. The neurotoxin MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) induces a neurological syndrome in man and non-human primates very similar to idiopathic Parkinson's disease by selectively destroying dopaminergic nigrostriatal neurons. This gives rise to the hypothesis that Parkinson's disease may be caused by endogenous or environmental toxins. Endogenous excitatory amino acids (EAAs) such as L-glutamate could be involved in neurodegenerative disorders including Parkinson's disease. We report in this study that the competitive NMDA antagonist CPP (3-((+/-)-2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid) protects nigral tyrosine hydroxylase (TH) positive neurons from degeneration induced by systemic treatment with MPTP in common marmosets. This indicates that EAAs are involved in the pathophysiological cascade of MPTP-induced neuronal cell death and that EAA antagonists may offer a neuroprotective therapy for Parkinson's disease

Asymptotic Conformal Yano--Killing Tensors for Schwarzschild Metric

The asymptotic conformal Yano--Killing tensor proposed in J. Jezierski, On the relation between metric and spin-2 formulation of linearized Einstein theory [GRG, in print (1994)] is analyzed for Schwarzschild metric and tensor equations defining this object are given. The result shows that the Schwarzschild metric (and other metrics which are asymptotically ``Schwarzschildean'' up to O(1/r^2) at spatial infinity) is among the metrics fullfilling stronger asymptotic conditions and supertranslations ambiguities disappear. It is also clear from the result that 14 asymptotic gravitational charges are well defined on the ``Schwarzschildean'' background.Comment: 8 pages, latex, no figure

The North Ecliptic Pole Supercluster

We have used the ROSAT All-Sky Survey to detect a known supercluster at z=0.087 in the North Ecliptic Pole region. The X-ray data greatly improve our understanding of this supercluster's characteristics, approximately doubling our knowledge of the structure's spatial extent and tripling the cluster/group membership compared to the optical discovery data. The supercluster is a rich structure consisting of at least 21 galaxy clusters and groups, 12 AGN, 61 IRAS galaxies, and various other objects. A majority of these components were discovered with the X-ray data, but the supercluster is also robustly detected in optical, IR, and UV wavebands. Extending 129 x 102 x 67 (1/h50 Mpc)^3, the North Ecliptic Pole Supercluster has a flattened shape oriented nearly edge-on to our line-of-sight. Owing to the softness of the ROSAT X-ray passband and the deep exposure over a large solid angle, we have detected for the first time a significant population of X-ray emitting galaxy groups in a supercluster. These results demonstrate the effectiveness of X-ray observations with contiguous coverage for studying structure in the Universe.Comment: Accepted for publication in The Astrophysical Journal; 5 pages with 2 embedded figures; uses emulateapj.sty; For associated animations, see http://www.ifa.hawaii.edu/~mullis/nep3d.html; A high-resolution color postscript version of the full paper is available at http://www.ifa.hawaii.edu/~mullis/papers/nepsc.ps.g

The Chandra Deep Field North Survey. IX. Extended X-ray Sources

The ~1 Ms Chandra Deep Field North observation is used to study the extended X-ray sources in the region surrounding the Hubble Deep Field North (HDF-N), yielding the most sensitive probe of extended X-ray emission at cosmological distances to date. A total of six such sources are detected, the majority of which align with small numbers of optically bright galaxies. Their angular sizes, band ratios, and X-ray luminosities -- assuming they lie at the same distances as the galaxies coincident with the X-ray emission -- are generally consistent with the properties found for nearby groups of galaxies. One source is notably different and is likely to be a poor-to-moderate X-ray cluster at high redshift (i.e., z > 0.7). We are also able to place strong constraints on the optically detected cluster of galaxies ClG 1236+6215 at z=0.85 and the wide-angle-tail radio galaxy VLA J123725.7+621128 at z~1-2. With rest-frame 0.5--2.0 keV X-ray luminosities of <(3-15)e42 ergs s^{-1}, the environments of both sources are either likely to have a significant deficit of hot intra-cluster gas compared to local clusters of galaxies, or they are X-ray groups. We find the surface density of extended X-ray sources in this observation to be 167 (+97,-67) deg^{-2} at a limiting soft-band flux of approximately 3e-16 ergs s^{-1} cm^{-2}. No evolution in the X-ray luminosity function of clusters is needed to explain this value. (Abridged)Comment: 16 pages, 14 figures (8 color), LaTeX emulateapj5.sty, accepted for publication by the Astronomical Journal. Manuscript with full resolution embedded images available at http://www.astro.psu.edu/users/niel/hdf/hdf-chandra.htm

Constraining q_0 with Cluster Gas Mass Fractions: A Feasibility Study

As the largest gravitationally bound objects in the universe, clusters of galaxies may contain a fair sample of the baryonic mass fraction of the universe. Since the gas mass fraction from the hot ICM is believed to be constant in time, the value of the cosmological deceleration parameter $q_0$ can be determined by comparing the calculated gas mass fraction in nearby and distant clusters (Pen 1997). To test the potential of this method, we compare the gas fractions derived for a sample of luminous ($L_X > 10^{45}$erg s$^{-1}$), nearby clusters with those calculated for eight luminous, distant ($0.3 < z < 0.6$) clusters using ASCA and ROSAT observations. For consistency, we evaluate the gas mass fraction at a fixed physical radius of 1 $h_{50}^{-1}$ Mpc (assuming $q_0=0.0$). We find a best fit value of $q_0 = 0.07$ with -0.47 < q_0 < 0.67 at 95% confidence. We also determine the gas fraction using the method of Evrard, Metzler, & Navarro (1997) to find the total mass within $r_{500}$, the radius where the mean overdensity of matter is 500 times the critical density. In simulations, this method reduces the scatter in the determination of gravitational mass without biasing the mean. We find that it also reduces the scatter in actual observations for nearby clusters, but not as much as simulations suggest. Using this method, the best fit value is $q_0 = 0.04$ with -0.50 < q_0 < 0.64. The excellent agreement between these two methods suggests that this may be a useful technique for determining $q_0$. The constraints on $q_0$ should improve as more distant clusters are studied and precise temperature profiles are measured to large radii.Comment: 8 pages, 4 figures, uses emulateapj.sty, onecolfloat.st

Prospects for high-z cluster detections with Planck, based on a follow-up of 28 candidates using MegaCam@CFHT

The Planck catalogue of SZ sources limits itself to a significance threshold of 4.5 to ensure a low contamination rate by false cluster candidates. This means that only the most massive clusters at redshift z>0.5, and in particular z>0.7, are expected to enter into the catalogue, with a large number of systems in that redshift regime being expected around and just below that threshold. In this paper, we follow-up a sample of SZ sources from the Planck SZ catalogues from 2013 and 2015. In the latter maps, we consider detections around and at lower significance than the threshold adopted by the Planck Collaboration. To keep the contamination rate low, our 28 candidates are chosen to have significant WISE detections, in combination with non-detections in SDSS/DSS, which effectively selects galaxy cluster candidates at redshifts $z\gtrsim0.5$. By taking r- and z-band imaging with MegaCam@CFHT, we bridge the 4000A rest-frame break over a significant redshift range, thus allowing accurate redshift estimates of red-sequence cluster galaxies up to z~0.8. After discussing the possibility that an overdensity of galaxies coincides -by chance- with a Planck SZ detection, we confirm that 16 of the candidates have likely optical counterparts to their SZ signals, 13 (6) of which have an estimated redshift z>0.5 (z>0.7). The richnesses of these systems are generally lower than expected given the halo masses estimated from the Planck maps. However, when we follow a simplistic model to correct for Eddington bias in the SZ halo mass proxy, the richnesses are consistent with a reference mass-richness relation established for clusters detected at higher significance. This illustrates the benefit of an optical follow-up, not only to obtain redshift estimates, but also to provide an independent mass proxy that is not based on the same data the clusters are detected with, and thus not subject to Eddington bias.Comment: 13 pages, 7 figures. Accepted for publication in A&