On the kinematics of cold, metal-enriched galactic fountain flows in nearby star-forming falaxies

Galaxie

The bimodal absorption system imaging campaign (BASIC). I. A dual population of low-metallicity absorbers at z < 1

Instrumentatio

Feedback from supermassive black holes transforms centrals into passive galaxies by ejecting circumgalactic gas

Galaxie

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

On the kinematics of cold, metal-enriched galactic fountain flows in nearby star-forming falaxies

Galaxie

Signatures of recent star formation in ring S0 galaxies

We present a study of the stellar populations of ring and/or arm-like structures in a sample of S0 galaxies using GALEX far- and near-ultraviolet imaging and SDSS optical data. Such structures are prominent in the UV and reveal recent star formation. We quantitatively characterize these rejuvenation events, estimating the average age and stellar mass of the ring structures, as well as of the entire galaxy. The mass fraction of the UV-bright rings is a few percent of the total galaxy mass, although the UV ring luminosity reaches 70% of the galaxy luminosity. The integrated colors of these S0s locates them in the red sequence (NGC 2962) and in the so-called green valley. We suggest that the star formation episodes may be induced by different triggering mechanisms, such as the inner secular evolution driven by bars, and interaction episodes