Browsing by Author "De Propris, Roberto"

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    G2C2-IV.A novel approach to study the radial distributions of multiple populations in Galactic globular clusters
    (OXFORD UNIV PRESS, 2015) Vanderbeke, Joachim; De Propris, Roberto; De Rijcke, Sven; Baes, Maarten; West, Michael; Alonso Garcia, Javier; Kunder, Andrea
    We use the horizontal branch (HB) morphology of 48 Galactic globular clusters (GCs) to study the radial distributions of the different stellar populations known to exist in GCs. Assuming that the (extremely) blue HB stars correspond to stars enriched in helium and light elements, we compare the radial distributions of stars selected according to colour on the HB to trace the distribution of the secondary stellar populations in GCs. Unlike other cases, our data show that the populations are well mixed in 80 per cent of the cases studied. This provides some constraints on the mechanisms proposed to pollute the interstellar medium in young GCs.
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    The elemental abundance of quiescent galaxies in the LEGA-C survey: the (non-)evolution of [α/Fe] from z=0.75 to z=0
    (2023) Bevacqua, Davide; Saracco, Paolo; La Barbera, Francesco; D'Ago, Giuseppe; De Propris, Roberto; Ferreras, Ignacio; Gallazzi, Anna; Pasquali, Anna; Spiniello, Chiara
    We measure the [alpha/Fe] abundances for 183 quiescent galaxies at z = 0.60-0.75 with stellar masses ranging 10.4 <= log(10)(M-*/M-circle dot) <= 11.6 selected from the Large Early Galaxy Astrophysics Census survey. We estimate [alpha/Fe] from the ratio of the spectral indices Mgb (lambda similar to 5177 angstrom) and Fe4383, compared to predictions of simple stellar population models. We find that 91 percent of quiescents in our sample have supersolar [alpha/Fe], with an average value of [alpha/Fe] = +0.24 +/- 0.01. We find no significant correlation between [alpha/Fe] and stellar metallicity, mass, velocity dispersion, and average formation time. Galaxies that formed the bulk of their stellar mass on time-scales shorter than 1 Gyr follow the same [alpha/Fe] distribution as those which formed on longer time-scales. In comparison to local early-type galaxies and to stacked spectra of quiescent galaxies at z = 0.38 and z = 0.07, we find that the average [alpha/Fe] has not changed between z = 0.75 and the present time. Our work shows that the vast majority of massive quiescent galaxies at z similar to 0.7 are alpha-enhanced, and that no detectable evolution of the average [alpha/Fe] has taken place over the last similar to 6.5 Gyr.
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    THE FAINT END OF THE GALAXY LUMINOSITY FUNCTION IN A1689: A STEEP RED FAINT END UPTURN AT z=0.18
    (2010) Banados, Eduardo; Hung, Li-Wei; De Propris, Roberto; West, Michael J.
    We present a deep and wide I luminosity function (LF) for galaxies in A1689 (z = 0.183) from a mosaic of Hubble Space Telescope WFPC2 images covering 10' on the side. The main result of this work is the detection of a steep upturn in the dwarf galaxy LF, with alpha similar to-2. The dwarf-to-giant ratio appears to increase outward, but this is because giant galaxies are missing in the cluster outskirts, indicating luminosity segregation. The red sequence LF has the same parameters, within errors, as the total LF, showing that the faint end upturn consists of red quiescent galaxies. We speculate that the upturn is connected to the "filling-in" of the red sequence at z < 0.4 and may represent the latest installment of "downsizing" as the least massive galaxies are being quenched at the present epoch.
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    THE GALAXY ALIGNMENT EFFECT IN ABELL 1689: EVOLUTION, RADIAL, AND LUMINOSITY DEPENDENCE
    (2010) Hung, Li-Wei; Banados, Eduardo; De Propris, Roberto; West, Michael J.
    We measure alignments on scales of 1 Mpc h(71)(-1) for galaxies in Abell 1689 (z = 0.18) from an existing Hubble Space Telescope mosaic. We find evidence of galaxy alignment in the inner 500 h(71)(-1) kpc. The alignment appears to be stronger toward the center and is mostly present among the fainter galaxies, while bright galaxies are unaligned. This is consistent with a model where alignments originate from tidal locking.