Browsing by Author "Ferreras, Ignacio"

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    The binary nucleus in VCC 128: A candidate supermassive black hole in a dwarf elliptical galaxy
    (2006) Debattista, Victor P.; Ferreras, Ignacio; Pasquali, Anna; Seth, Anil; De Rijcke, Sven; Morelli, Lorenzo
    Hubble Space Telescope (HST) Wide Field Planetary Camera 2 (WFPC2) images of the Virgo Cluster dwarf elliptical galaxy VCC 128 reveal an apparently double nucleus. The two components, which are separated by similar to 32 pc in projection, have the same magnitude and color. We present a spectrum of this double nucleus and show that it is inconsistent with one or both components being emission-line background objects or foreground stars. The most likely interpretation is that, as suggested by Lauer et al. for the double nucleus in NGC 4486B, we are seeing a nuclear disk surrounding a supermassive black hole. This is only the second time an early-type dwarf (dE/dSph) galaxy has been suggested to host a supermassive black hole.
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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.