Ministerio de Economía y Competitividad Gobierno de Canarias Universidad de La Laguna CSIC Centro de Excelencia Severo Ochoa

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Expected number of massive galaxy relics in the present-day Universe.

Author/s: V. Quilis, I. Trujillo.

Reference: 2013arXiv1307.1976Q, ApJL | Link

Redshift evolution of the ratio of the relic galaxies to the total number of massive galaxies. The three different lines represent the three considered models. Coloured areas, orange (orange-red) show galaxies that have increased their masses less than a 10% (30%) since z∼2. Right panel: redshift evolution of the comoving number density of relic galaxies. The lines and colour shaded areas stand as for the right panel. The red and blue arrow show the observational upper limits from Trujillo et al. (2009) and Taylor et al.(2010), respectively. The green point display the observational data from Poggianti et al. (2013).
Redshift evolution of the ratio of the relic galaxies to the total number of massive galaxies. The three different lines represent the three considered models. Coloured areas, orange (orange-red) show galaxies that have increased their masses less than a 10% (30%) since z∼2. Right panel: redshift evolution of the comoving number density of relic galaxies. The lines and colour shaded areas stand as for the right panel. The red and blue arrow show the observational upper limits from Trujillo et al. (2009) and Taylor et al.(2010), respectively. The green point display the observational data from Poggianti et al. (2013).

The number of present-day massive galaxies that has survived untouched since their formation at high-z is an important observational constraint to the hierarchical galaxy formation models. Using three different semianalytical models based on the Millenium simulation, we quantify the expected fraction and number densities of the massive galaxies form at z>2 which have evolved in stellar mass less than 10% and 30%. We find that only a small fraction of the massive galaxies already form at z~2 have remained almost unaltered since their formation (<2% with Delta_M*/M*<0.1 and <8% with Delta_M*/M*<0.3). These fractions correspond to the following number densities of massive relics in the present-day Universe: ~1.2x10^-6 Mpc^-3 for Delta_M*/M*<0.1 and ~5.7x10^-6 Mpc^-3 for Delta_M*/M*<0.3. The observed number of relic candidates found in the nearby Universe is today pretty uncertain (with uncertainties up to a factor of ~100) preventing to establish a firm conclusion about the goodness of current theoretical expectations to predict such important number.

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