Browsing by Author "Napolitano, N. R."

Now showing 1 - 7 of 7
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    Discovery of Two Einstein Crosses from Massive Post-blue Nugget Galaxies at z > 1 in KiDS*
    (2020) Napolitano, N. R.; Li, R.; Spiniello, C.; Tortora, C.; Sergeyev, A.; D'Ago, G.; Guo, X.; Xie, L.; Radovich, M.; Roy, N.; Koopmans, L. V. E.; Kuijken, K.; Bilicki, M.; Erben, T.; Getman, F.; Heymans, C.; Hildebrandt, H.; Moya, C.; Shan, H. Y.; Vernardos, G.; Wright, A. H.
    We report the discovery of two Einstein Crosses (ECs) in the footprint of the Kilo-Degree Survey (KiDS): KIDS J232940-340922 and KIDS J122456+005048. Using integral field spectroscopy from the Multi Unit Spectroscopic Explorer at the Very Large Telescope, we confirm their gravitational-lens nature. In both cases, the four spectra of the source clearly show a prominence of absorption features, hence revealing an evolved stellar population with little star formation. The lensing model of the two systems, assuming a singular isothermal ellipsoid (SIE) with external shear, shows that: (1) the two crosses, located at redshift z = 0.38 and 0.24, have Einstein radius R-E = 5.2 kpc and 5.4 kpc, respectively; (2) their projected dark matter fractions inside the half effective radius are 0.60 and 0.56 (Chabrier initial mass function); (3) the sources are ultra-compact galaxies, R-e similar to 0.9 kpc (at redshift, z(s) = 1.59) and R-e similar to 0.5 kpc (z(s) = 1.10), respectively. These results are unaffected by the underlying mass density assumption. Due to size, blue color, and absorption-dominated spectra, corroborated by low specific star formation rates derived from optical-near-infrared spectral energy distribution fitting, we argue that the two lensed sources in these ECs are blue nuggets migrating toward their quenching phase.
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    INSPIRE: INvestigating Stellar Population In RElics - IV. The initial mass function slope in relics
    (2023) Martin-Navarro, Ignacio; Spiniello, C.; Tortora, C.; Coccato, L.; D'Ago, G.; Ferre-Mateu, A.; Pulsoni, C.; Hartke, J.; Arnaboldi, M.; Hunt, L.; Napolitano, N. R.; Scognamiglio, D.; Spavone, M.
    In the last decade, growing evidence has emerged supporting a non-universal stellar initial mass function (IMF) in massive galaxies, with a larger number of dwarf stars with respect to the Milky Way (bottom-heavy IMF). However, a consensus about the mechanisms that cause IMF variations is yet to be reached. Recently, it has been suggested that stars formed early-on in cosmic time, via a star formation burst, could be characterized by a bottom-heavy IMF. A promising way to confirm this is to use relics, ultra-compact massive galaxies, almost entirely composed by these 'pristine' stars. The INvestigating Stellar Population In RElics (INSPIRE) Project aims at assembling a large sample of confirmed relics, that can serve as laboratory to investigate on the conditions of star formation in the first 1-3 Gyr of the Universe. In this third INSPIRE paper, we build a high signal-to-noise spectrum from five relics, and one from five galaxies with similar sizes, masses, and kinematical properties, but characterized by a more extended star formation history (non-relics). Our detailed stellar population analysis suggests a systematically bottom-heavier IMF slope for relics than for non-relics, adding new observational evidence for the non-universality of the IMF at various redshifts and further supporting the above proposed physical scenario.
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    INSPIRE: INvestigating Stellar Population In RElics II. First data release (DR1)
    (2021) Spiniello, C.; Tortora, C.; D'Ago, G.; Coccato, L.; La Barbera, F.; Ferre-Mateu, A.; Pulsoni, C.; Arnaboldi, M.; Gallazzi, A.; Hunt, L.; Napolitano, N. R.; Radovich, M.; Scognamiglio, D.; Spavone, M.; Zibetti, S.
    Context. The INvestigating Stellar Population In RElics (INSPIRE) is an ongoing project targeting 52 ultra-compact massive galaxies at 0.1 < z < 0.5 with the X-shooter at VLT spectrograph (XSH). These objects are the ideal candidates to be `relics', massive red nuggets that have formed at high redshift (z > 2) through a short and intense star formation burst, and then have evolved passively and undisturbed until the present day. Relics provide a unique opportunity to study the mechanisms of star formation at high-z. Aims. INSPIRE is designed to spectroscopically confirm and fully characterise a large sample of relics, computing their number density in the redshift window 0:1 < z < 0:5 for the first time, thus providing a benchmark for cosmological galaxy formation simulations. In this paper, we present the INSPIRE Data Release (DR1), comprising 19 systems with observations completed in 2020. Methods. We use the methods already presented in the INSPIRE Pilot, but revisiting the 1D spectral extraction. For the 19 systems studied here, we obtain an estimate of the stellar velocity dispersion, fitting the two XSH arms (UVB and VIS) separately at their original spectral resolution to two spectra extracted in di fferent ways. We estimate [Mg /Fe] abundances via line-index strength and mass-weighted integrated stellar ages and metallicities with full spectral fitting on the combined (UVB +VIS) spectrum. Results. For each system, di fferent estimates of the velocity dispersion always agree within the errors. Spectroscopic ages are very old for 13 /19 galaxies, in agreement with the photometric ones, and metallicities are almost always (18 /19) super-solar, confirming the mass-metallicity relation. The [Mg /Fe] ratio is also larger than solar for the great majority of the galaxies, as expected. We find that ten objects formed more than 75% of their stellar mass (M-*) within 3 Gyr from the big bang and classify them as relics. Among these, we identify four galaxies that had already fully assembled their M-* by that time and are therefore `extreme relics' of the ancient Universe. Interestingly, relics, overall, have a larger [Mg /Fe] and a more metal-rich stellar population. They also have larger integrated velocity dispersion values compared to non-relics (both ultra-compact and normal-size) of similar stellar mass. Conclusions. The INSPIRE DR1 catalogue of ten known relics is the largest publicly available collection, augmenting the total number of confirmed relics by a factor of 3.3, and also enlarging the redshift window. The resulting lower limit for the number density of relics at 0.17 < z < 0.39 is rho similar to 9.1 x 10(-8) Mpc(-3).
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    INSPIRE: INvestigating Stellar Population In RElics III. Second data release (DR2): testing the systematics on the stellar velocity dispersion
    (2023) D'Ago, G.; Spiniello, C.; Coccato, L.; Tortora, C.; La Barbera, F.; Arnaboldi, M.; Bevacqua, D.; Ferre-Mateu, A.; Gallazzi, A.; Hartke, J.; Hunt, L. K.; Martin-Navarro, I.; Napolitano, N. R.; Pulsoni, C.; Radovich, M.; Saracco, P.; Scognamiglio, D.; Zibetti, S.
    Context. The project called INvestigating Stellar Population In RElics (INSPIRE) is based on VLT/X-shooter data from the homonymous on-going ESO Large Program. It targets 52 ultra-compact massive galaxies at 0.1 < z < 0.5 with the goal of constraining their kinematics and stellar population properties in great detail and of analysing their relic nature.
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    INSPIRE: INvestigating Stellar Population In RElics: I. Survey presentation and pilot study
    (2021) Spiniello, C.; Tortora, C.; D'Ago, G.; Coccato, L.; La Barbera, F.; Ferre-Mateu, A.; Napolitano, N. R.; Spavone, M.; Scognamiglio, D.; Arnaboldi, M.; Gallazzi, A.; Hunt, L.; Moehler, S.; Radovich, M.; Zibetti, S.
    Context. Massive elliptical galaxies are thought to form through a two-phase process. At early times (z> 2), an intense and fast starburst forms blue and disk-dominated galaxies. After quenching, the remaining structures become red, compact, and massive (i.e. red nuggets). Then, a time-extended second phase, which is dominated by mergers, causes structural evolution and size growth. Given the stochastic nature of mergers, a small fraction of red nuggets survive, without any interaction, massive and compact until today: these are relic galaxies. Since this fraction depends on the processes dominating the size growth, counting relics at low-z is a valuable way of disentangling between different galaxy evolution models.Aims. In this paper, we introduce the INvestigating Stellar Population In RElics (INSPIRE) Project, which aims to spectroscopically confirm and fully characterise a large number of relics at 0.1< z< 0.5. We focus here on the first results based on a pilot study targeting three systems, representative of the whole sample.Methods. For these three candidates, we extracted 1D optical spectra over an aperture of r=0.40 '', which comprises similar to 30% of the galaxies' light, and we obtained the line-of-sight integrated stellar velocity and velocity dispersion. We also inferred the stellar [alpha /Fe] abundance from line-index measurements and mass-weighted age and metallicity from full-spectral fitting with single stellar population models.Results. Two galaxies have large integrated stellar velocity dispersion values (sigma (star)similar to 250 km s(-1)), confirming their massive nature. They are populated by stars with super-solar metallicity and [alpha /Fe]. Both objects have formed >= 80% of their stellar mass within a short (similar to 0.5-1.0 Gyr) initial star formation episode occurred only similar to 1 Gyr after the Big Bang. The third galaxy has a more extended star formation history and a lower velocity dispersion. Thus we confirm two out of three candidates as relics.Conclusions. This paper is the first step towards assembling the final INSPIRE catalogue that will set stringent lower limits on the number density of relics at z< 0.5, thus constituting a benchmark for cosmological simulations, and their predictions on number densities, sizes, masses, and dynamical characteristics of these objects.
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    Nature versus nurture : relic nature and environment of the most massive passive galaxies at z < 0.5
    (2020) Tortora, C.; Napolitano, N. R.; Radovich, M.; Spiniello, C.; Hunt, L.; Roy, N.; Moscardini, L.; Scognamiglio, D.; Spavone, M.; D'Ago, Giuseppe; Cavuoti, S.; Longo, G.; Bellagamba, F.; Maturi, M.; Roncarelli, M.
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    Optically variable AGN in the three-year VST survey of the COSMOS field
    (2019) De Cicco, D.; Paolill, M.; Falocco, S.; Poulain, M.; Brandt, W. N.; Bauer, F. E.; Vagnetti, F.; Longo, G.; Grado, A.; Ragosta, F.; Botticella, M. T.; Pignata, G.; Vaccari, M.; Radovich, M.; Salvato, M.; Covone, G.; Napolitano, N. R.; Marchetti, L.; Schipani, P.
    Context. The analysis of the variability of active galactic nuclei (AGN) at different wavelengths and the study of possible correlations of different spectral windows are a current main field of inquiry. Optical variability has been largely used to identify AGN in multivisit surveys. The strength of a selection based on optical variability lies in the opportunity of analyzing data from surveys of large sky areas by ground-based telescopes. However, the effectiveness of optical variability selection with respect to other multiwavelength techniques has been poorly studied down to the depth that is expected from next-generation surveys.