An Upper Cretaceous (Campanian-Maastrichtian) actinopterygian fish assemblage from the marginal marine Adaffa Formation of Saudi Arabia

Actinopterygian remains have been recovered from Upper Cretaceous (lower Campanian to lower Maastrichtian) marginal marine deposits of the Adaffa Formation in northwestern Saudi Arabia. The fossils comprise gars (Lepisosteidae), pachycormids (cf. Protosphyraena sp.), indeterminate pycnodontiforms, enchodontid teleosts (cf. Enchodus sp.) and other indeterminate Teleostei. This assemblage is significant because it includes a novel occurrence for the Middle East (Pachycormidae) together with taxa (Lepisosteidae, Pycnodontiformes, Enchodontidae) that have been previously recorded from Late Cretaceous faunas elsewhere in the Mediterranean Tethyan region.     

High-resolution infrared spectra of NGC 6342 and 6528: two moderately reddened bulge globular clusters

Using the Near Infrared Spectrometer (NIRSPEC) spectrograph at Keck II, we have obtained infrared (IR) echelle spectra covering the range  1.5 –1.8 μm  for the moderately reddened bulge globular clusters NGC 6342 and 6528, finding  [Fe/H]=−0.60  and −0.17 dex, respectively. We measure an average α-enhancement of ≈+0.33 dex in both clusters, consistent with previous measurements on other metal-rich bulge clusters, and favouring the scenario of a rapid bulge formation and chemical enrichment. We also measure very low ¹²C/¹³C isotopic ratios (≈5 in NGC 6342 and ≈8 in NGC 6528), suggesting that extra-mixing mechanisms resulting from cool bottom processing are at work during evolution along the red giant branch (RGB).     

Connecting the Distant Universe with the Local Fossil Record

This review considers implications regarding galaxy formationand evolution that can be drawn from study of the ages,abundances, and kinematics of stellar populations in the LocalUniverse. The wide abundance range in the Galactic bulge and in thehalo of M31 is consistent with chemical evolution in a starburstwith wind outflow. We question the notionthat the Galactic halo population is assembled fromdisrupted dwarf spheroidal galaxies, based on the presenceof metal rich stars in Local Group halos.The alpha-element enhancements of bulge giants are those expected from a system forming on a timescale of less than 1 Gyr. Direct measurement of the star formationhistory from turnoff photometry in Local Group galaxiesis not in complete agreement with the universal star formation rateinferred from high redshift studies. We argue that the properties of the Local Universe constrain galaxyformation theory just as strongly as the findings gleaned fromhigh redshift galaxies. This revised version was published online in July 2006 with corrections to the Cover Date.     

The correlation of star formation quenching with internal galaxy properties and environment

We investigate the correlation of star formation quenching with internal galaxy properties and large-scale environment (halo mass) in empirical data and theoretical models. We make use of the halo-based group catalogue of Yang and collaborators, which is based on the Sloan Digital Sky Survey. Data from the Galaxy evolution explorer are also used to extract the recent star formation rate. In order to investigate the environmental effects, we examine the properties of 'central' and 'satellite' galaxies separately. For central galaxies, we are unable to conclude whether star formation quenching is primarily connected with halo mass or stellar mass, because these two quantities are themselves strongly correlated. For satellite galaxies, a nearly equally strong dependence on halo mass and stellar mass is seen. We make the same comparison for five different semi-analytic models based on three independently developed codes. We find that the models with active galactic nuclei feedback reproduce reasonably well the dependence of the fraction of central red and passive galaxies on halo mass and stellar mass. However, for satellite galaxies, the same models badly overproduce the fraction of red/passive galaxies and do not reproduce the empirical trends with stellar mass or halo mass. This satellite overquenching problem is caused by the too-rapid stripping of the satellites' hot gas haloes, which leads to rapid strangulation of star formation.