Galaxy Clusters in the Line of Sight to Background Quasars: I. Survey Design and Incidence of MgII Absorbers at Cluster Redshifts

We describe the first optical survey of absorption systems associated with galaxy clusters at z= 0.3-0.9. We have cross-correlated SDSS DR3 quasars with high-redshift cluster/group candidates from the Red-Sequence Cluster Survey. We have found 442 quasar-cluster pairs for which the MgII doublet might be detected at a transverse (physical) distance d<2 Mpc from the cluster centers. To investigate the incidence (dN/dz) and equivalent-width distribution n(W) of MgII systems at cluster redshifts, two statistical samples were drawn out of these pairs: one made of high-resolution spectroscopic quasar observations (46 pairs), and one made of quasars used in MgII searches found in the literature (375 pairs). The results are: (1) the population of strong MgII systems (W_0>2.0 Ang.) near cluster redshifts shows a significant (>3 sigma) overabundance (up to a factor of 15) when compared with the 'field' population; (2) the overabundance is more evident at smaller distances (d<1 Mpc) than larger distances (d<2 Mpc) from the cluster center; and, (3) the population of weak MgII systems (W_0<0.3 Ang.) near cluster redshifts conform to the field statistics. Unlike in the field, this dichotomy makes n(W) in clusters appear flat and well fitted by a power-law in the entire W-range. A sub-sample of the most massive clusters yields a stronger and still significant signal. Since either the absorber number density or filling-factor/cross-section affects the absorber statistics, an interesting possibility is that we have detected the signature of truncated halos due to environmental effects. Thus, we argue that the excess of strong systems is due to a population of absorbers in an overdense galaxy environment, and the lack of weak systems to a different population, that got destroyed in the cluster environment. (Abridged)Comment: Accepted for publication in the Astrophysical Journa

The ROCK inhibitor Fasudil prevents chronic restraint stress-induced depressive-like behaviors and dendritic spine loss in rat hippocampus

Indexación: Web of Science; Scopus.Background: Dendritic arbor simplification and dendritic spine loss in the hippocampus, a limbic structure implicated in mood disorders, are assumed to contribute to symptoms of depression. These morphological changes imply modifications in dendritic cytoskeleton. Rho GTPases are regulators of actin dynamics through their effector Rho kinase. We have reported that chronic stress promotes depressive-like behaviors in rats along with dendritic spine loss in apical dendrites of hippocampal pyramidal neurons, changes associated with Rho kinase activation. The present study proposes that the Rho kinase inhibitor Fasudil may prevent the stress-induced behavior and dendritic spine loss. Methods: Adult male Sprague-Dawley rats were injected with saline or Fasudil (i.p., 10 mg/kg) starting 4 days prior to and maintained during the restraint stress procedure (2.5 h/d for 14 days). Nonstressed control animals were injected with saline or Fasudil for 18 days. At 24 hours after treatment, forced swimming test, Golgi-staining, and immuno-western blot were performed. Results: Fasudil prevented stress-induced immobility observed in the forced swimming test. On the other hand, Fasudiltreated control animals showed behavioral patterns similar to those of saline-treated controls. Furthermore, we observed that stress induced an increase in the phosphorylation of MYPT1 in the hippocampus, an exclusive target of Rho kinase. This change was accompanied by dendritic spine loss of apical dendrites of pyramidal hippocampal neurons. Interestingly, increased pMYPT1 levels and spine loss were both prevented by Fasudil administration. Conclusion: Our findings suggest that Fasudil may prevent the development of abnormal behavior and spine loss induced by chronic stress by blocking Rho kinase activity.https://academic.oup.com/ijnp/article/20/4/336/263217

Spatially Resolved Outflows in a Seyfert Galaxy at z = 2.39

We present the first spatially resolved analysis of rest-frame optical and UV imaging and spectroscopy for a lensed galaxy at z = 2.39 hosting a Seyfert active galactic nucleus (AGN). Proximity to a natural guide star has enabled high signal-to-noise VLT SINFONI + adaptive optics observations of rest-frame optical diagnostic emission lines, which exhibit an underlying broad component with FWHM ~ 700 km/s in both the Balmer and forbidden lines. Measured line ratios place the outflow robustly in the region of the ionization diagnostic diagrams associated with AGN. This unique opportunity - combining gravitational lensing, AO guiding, redshift, and AGN activity - allows for a magnified view of two main tracers of the physical conditions and structure of the interstellar medium in a star-forming galaxy hosting a weak AGN at cosmic noon. By analyzing the spatial extent and morphology of the Ly-alpha and dust-corrected H-alpha emission, disentangling the effects of star formation and AGN ionization on each tracer, and comparing the AGN induced mass outflow rate to the host star formation rate, we find that the AGN does not significantly impact the star formation within its host galaxy.Comment: 16 pages, 5 figures, accepted for publication in Ap

Towards the statistical detection of the warm-hot intergalactic medium in intercluster filaments of the cosmic web.

Modern analyses of structure formation predict a universe tangled in a ‘cosmic web’ of dark matter and diffuse baryons. These theories further predict that at low z, a significant fraction of the baryons will be shock-heated to T ∼ 105–107 K yielding a warm–hot intergalactic medium (WHIM), but whose actual existence has eluded a firm observational confirmation. We present a novel experiment to detect the WHIM, by targeting the putative filaments connecting galaxy clusters. We use HST/COS to observe a remarkable quasi-stellar object (QSO) sightline that passes within Δd = 3 Mpc from the seven intercluster axes connecting seven independent cluster pairs at redshifts 0.1 ≤ z ≤ 0.5. We find tentative excesses of total H I, narrow H I (NLA; Doppler parameters b < 50 km s−1), broad H I (BLA; b ≥ 50 km s−1) and O VI absorption lines within rest-frame velocities of Δv ≲ 1000 km s−1 from the cluster-pairs redshifts, corresponding to ∼2, ∼1.7, ∼6 and ∼4 times their field expectations, respectively. Although the excess of O VI likely comes from gas close to individual galaxies, we conclude that most of the excesses of NLAs and BLAs are truly intergalactic. We find the covering fractions, fc, of BLAs close to cluster pairs are ∼4–7 times higher than the random expectation (at the ∼2σ c.l.), whereas the fc of NLAs and O VI are not significantly enhanced. We argue that a larger relative excess of BLAs compared to those of NLAs close to cluster pairs may be a signature of the WHIM in intercluster filaments. By extending this analysis to tens of sightlines, our experiment offers a promising route to detect the WHIM

The COS Absorption Survey of Baryon Harbors (CASBaH): Warm-hot Circumgalactic Gas Reservoirs Traced by Ne VIII Absorption

We survey the highly ionized circumgalactic media (CGM) of 29 blindly selected galaxies at 0.49 < z_(gal) < 1.44 based on high-S/N ultraviolet spectra of z > 1 QSOs and the galaxy database from the COS Absorption Survey of Baryon Harbors (CASBaH). We detect the Ne VIII doublet in nine of the galaxies, and for gas with N(Ne VIII) > 10^13.3 cm^-2 (> 10^13.5 cm^-2), we derive a Ne VIII covering fraction f_c = 75 +15/-25% (44 +22/-20%) within impact parameter (rho) < 200 kpc of M_* = 10^(9.5-11.5) Msol galaxies and f_c = 70 +16/-22% (f_c = 42 +20/-17%) within rho < 1.5 virial radii. We estimate the mass in Ne VIII-traced gas to be M_gas(Ne VIII) > 10^9.5 Msol (Z/Zsol)^-1, or 6-20% of the expected baryonic mass if the Ne VIII absorbers have solar metallicity. Ionizing Ne VII to Ne VIII requires 207 eV, and photons with this energy are scarce in the CGM. However, for the median halo mass and redshift of our sample, the virial temperature is close to the peak temperature for the Ne VIII ion, and the Ne VIII-bearing gas is plausibly collisionally ionized near this temperature. Moreover, we find that photoionized Ne VIII requires cool and low-density clouds that would be highly underpressured (by approximately two orders of magnitude) relative to the putative, ambient virialized medium, complicating scenarios where such clouds could survive. Thus, more complex (e.g., non-equilibrium) models may be required; this first statistical sample of Ne VIII absorber/galaxy systems will provide stringent constraints for future CGM studies.Comment: Published in ApJL, Volume 877, Issue 2, Article L2

On the connection between the intergalactic medium and galaxies: the H I–galaxy cross-correlation at z ≲ 1

We present a new optical spectroscopic survey of 1777 ‘star-forming’ (‘SF’) and 366 ‘non-star-forming’ (‘non-SF’) galaxies at redshifts z ∼ 0-1 (2143 in total), 22 AGN and 423 stars, observed by instruments such as the Deep Imaging Multi-Object Spectrograph, the Visible Multi-Object Spectrograph and the Gemini Multi-Object Spectrograph, in three fields containing five quasi-stellar objects (QSOs) with Hubble Space Telescope (HST) ultraviolet spectroscopy. We also present a new spectroscopic survey of 173 ‘strong’ (1014 ≤ NHI≲ 1017 cm−2) and 496 ‘weak’ (1013 ≲ NHI 50 per cent of ‘weak’ H i systems reside within galaxy voids (hence not correlated with galaxies), and are confined in dark matter haloes of masses smaller than those hosting ‘strong’ systems and/or galaxies. We speculate that H i systems within galaxy voids might still be evolving in the linear regime even at scales ≲2 Mpc