Day 131

Wednesday.  I've accumulated a whole bunch of things to do, and I didn't get a whole lot done the past two days.  

1111.1716

New insights on the star formation histories of candidate intermediate-age early-type galaxies from K'-band imaging of globular clusters

Georgiev, Goudfrooij, Puzia

Globular clusters can be used as relevant proxies of the SF histories of galaxies.  Found photometric ages are older than spectroscopic ages by ~2Gyr, but the photometric and spectroscopic metallicities are in good agreement.  This indicates the presence of hot HB (horizontal branch) stars in the massive clusters, and renders the spectroscopic ages from Balmer line strengths to be underestimated.  Using the relation between the most massive GC mass and the galaxy's SFR, find that the galaxies' peak SFR was attained at the epoch of the formation of the oldest (i.e., metal-poor) CGs.  Age and metallicity distributions of the metal-rich GCs are broad, indicating prolonged galaxy star formation histories.  Peak ages of the metal-rich GCs in the sample galaxies are xxx for yyy, respectively.  The peak value of the age and metallicity distributions of the GCs correlates with host galaxy integrated age and metallicity.  Hence the conclusion in the first sentence.

1111.1717

Cold gas accretion by high-velocity clouds and their connection to QSO absorption-line systems

Richter

Meausre and model H I HVC distribution between MW and M31; estimate H I HVC population around galaxies extends to a radius of up to 110 kpc for the most massive galaxies.  The mean (projected) covering fraction of HVCs with log N(HI)>17.5 in galaxy halos is small, <f_HVC>=0.2, typically.  The H I disks of galaxies and their surrounding HVC population can account for 30-100% of the H I QSO absorption-line systems with log N(HI)>17.5 at z=0.  Estimate neutral-gas accretion rate density of galaxies at z=0 in the form of HVCs is dM/HI/dt/dV=0.022 M_sun/yr/Mpc^3.

1111.1718

Constraining the formation of inner bars.  Photometry, kinematics and stellar populations in NGC 357

de Lorenzo-Caceres, Vazdekis, Aguerri, Corsini, Debattista

Study double-barred spirals, find (1) bulge, inner and outer bar are nearly coeval and old; (2) the bulge and inner bar of same metallicity and overabundance, where the outer bar tends to be less metal-rich and more alpha-enhanced, indicating (3) the redistribution of the existing stars is driving the formation of the inner structures.

1111.1720

Why are central radio relics so rare?

Vazza, Brueggen, van Weeren, Bonafede, Dolag, Brunetti

Simulations support this--all models cause >50% of the detectable relic emission at projected distances > 800 kpc.  Central radio relics caused by shocks that propagated along the LOS are rare events for geometrical reasons, and they have a low surface brightness making them elusive for current instruments.  Radial distribution of observed relics == radial trend of dissipated kinetic energy in shocks, that increases with distance from the cluster centre up until half of the virial radius.

1111.1721

How many radio relics await discovery?

Nuza, Hoeft, van Weeren, Gottloeber, Yepes

Radio relics == steep-spectrum diffuse radio emission coming from periphery of galaxy clusters, belived to trace shock waves induced by cluster mergers.  Abundance of radio relics studied.  Number of known relics is still small.  Actual number of newly discovered relics will crucially depend on the existence of sufficiently complete galaxy cluster catalogues.

1111.1729

The galaxy stellar mass function of x-ray detected groups: environmental dependence of galaxy evolution in the COSMOS survey

Giodini, Finoguenov, .. et al

Find fraction of SF galaxies increasing with z in all environments, but at a faster pace in the denser ones.  at z=0.2-0.4 groups with M200<6e13 Msun (low mass groups) tend to have a characteristic mass for SF galaxies which is 50% higher than in higher mass groups--interpreted as a reduced action of environmental processes in such systems.  Low mass groups have a higher fraction (by 50%) of the stellar mass locked in SF galaxies than higher mass systems (i.e., 2/3 of their stellar mass), suggesting SF galaxies in groups convert more efficiently baryons into stars.

1111.1736

Bars rejuvenating bulges?  Evidence from stellar population analysis

Coelho, Gadotti

575 bulges with spectra from SDSS.  Bulges in barred and unbarred galaxies occupy similar loci in the age vs. metallicity plane.  However, the distribution of bulge ages in barred galaxies show an excess of populations ounger than ~4Gyr, significant to 99.94%.  Presence of bars affect the mean stellar ages of bulges.  Lends strong support to models in which bars trigger SF activity in the centers of galaxies.