Modelling galaxy spectra in presence of interstellar dust - III. From nearby galaxies to the distant Universe

Improving upon the standard evolutionary population synthesis technique, we present spectrophotometric models of galaxies with morphology going from spherical structures to discs, properly accounting for the effect of dust in the interstellar medium (ISM). The models contain three main physical components: the diffuse ISM made of gas and dust, the complexes of molecular clouds where active star formation occurs, and stars of any age and chemical composition. These models are based on robust evolutionary chemical description providing the total amount of gas and stars present at any age, and matching the properties of galaxies of different morphological types. We have considered the results obtained by Piovan et al. for the properties of the ISM, and those by Cassarà et al. for the spectral energy distribution (SED) of single stellar populations, both in presence of dust, to model the integral SEDs of galaxies of different morphological types, going from pure bulges to discs passing through a number of composite systems with different combinations of the two components. The first part of the paper is devoted to recall the technical details of the method and the basic relations driving the interaction between the physical components of the galaxy. Then, the main parameters are examined and their effects on the SED of three prototype galaxies are highlighted. The theoretical SEDs nicely match the observational ones both for nearby galaxies and those at high redshift

Open Day presso l’INAF IASF di Milano Report delle prime tre edizioni (2019, 2020, 2022)

Nel 2019, l’Istituto di Astrofisica Spaziale e Fisica cosmica di Milano (IASF), una delle due sedi di Milano dell’INAF (Istituto Nazionale di Astrofisica), ha inaugurato il proprio Open Day, una giornata dedicata agli studenti universitari. Il personale dello IASF ha aperto le porte agli studenti interessati a svolgere un progetto di ricerca presso la propria sede o, in generale, a scoprire una realtà professionale dedicata allo studio dell’Universo. Gli incontri si sono divisi in due parti: nella prima sono stati presentati l’Istituto, la sua storia, le attività di ricerca in corso e le Tesi a disposizione (triennali e magistrali), mentre nella seconda si è aperta una discussione libera tra i presenti durante una merenda offerta dallo IASF-Milano. Le tre edizioni svolte finora (2019, 2020 e 2022) hanno visto una buona partecipazione (circa 25-40 presenze all’anno) e hanno permesso di avvicinare ulteriormente lo IASF-Milano alle Università del territorio, dando ai partecipanti una percezione di disponibilità e accessibilità della ricerca e del personale dello IASF. Dopo una pausa dovuta alla pandemia (anno 2021), lo IASF-Milano ha riaperto le porte nel 2022 in quella che ci auguriamo possa diventare una lunga tradizione

Redshift identification of X-ray selected active galactic nuclei in the J1030 field: searching for large-scale structures and high-redshift sources

We publicly release the spectroscopic and photometric redshift catalog of the sources detected with Chandra in the field of the $z$=6.3 quasar SDSS J1030+0525. This is currently the fifth deepest X-ray field, and reaches a 0.5-2 keV flux limit $f_{\rm 0.5-2}$=6$\times$10$^{-17}$ erg s$^{-1}$ cm$^{-2}$. By using two independent methods, we measure a photometric redshift for 243 objects, while 123 (51%) sources also have a spectroscopic redshift, 110 of which coming from an INAF-Large Binocular Telescope (LBT) Strategic Program. We use the spectroscopic redshifts to determine the quality of the photometric ones, and find it in agreement with that of other X-ray surveys which used a similar number of photometric data-points. In particular, we measure a sample normalized median absolute deviation $\sigma_{NMAD}$=1.48||$z_{phot}$-$z_{spec}$||/(1+$z_{spec}$)=0.065. We use these new spectroscopic and photometric redshifts to study the properties of the Chandra J1030 field. We observe several peaks in our spectroscopic redshift distribution between $z$=0.15 and $z$=1.5, and find that the sources in each peak are often distributed across the whole Chandra field of view. This evidence confirms that X-ray selected AGN can efficiently track large-scale structures over physical scales of several Mpc. Finally, we computed the Chandra J1030 $z>$3 number counts: while the spectroscopic completeness at high-redshift of our sample is limited, our results point towards a potential source excess at $z\geq$4, which we plan to either confirm or reject in the near future with dedicated spectroscopic campaigns

Identification and characterization of six spectroscopically confirmed massive protostructures at 2.5 < z < 4.5

International audienceWe present six spectroscopically confirmed massive protostructures, spanning a redshift range of 2.5 9000 cMpc3) of more than 2.5σδ above the field density levels at these redshifts, have a total mass Mtot ≥ 1014.8M⊙ and one or more highly overdense (overdensity > 5σδ) peaks. One of the most complex protostructures discovered is a massive (Mtot = 1015.1M⊙) system at z ~ 3.47 that contains six peaks and 55 spectroscopic members. We also discover protostructures at z ~ 3.30 and z ~ 3.70 that appear to at least partially overlap on sky with the protostructure at z ~ 3.47, suggesting a possible connection. We additionally report on the discovery of three massive protostructures at z = 2.67, 2.80, and 4.14 and discuss their properties. Finally, we discuss the relationship between star formation rate and environment in the richest of these protostructures, finding an enhancement of star formation activity in the densest regions. The diversity of the protostructures reported here provide an opportunity to study the complex effects of dense environments on galaxy evolution over a large redshift range in the early universe

Protoclusters as Drivers of Stellar Mass Growth in the Early Universe, a Case Study: Taralay - a Massive Protocluster at z 4.57

International audienceSimulations predict that the galaxy populations inhabiting protoclusters may contribute considerably to the total amount of stellar mass growth of galaxies in the early universe. In this study, we test these predictions observationally, using the Taralay protocluster (formerly PCl J1001+0220) at z ~ 4.57 in the COSMOS field. With the Charting Cluster Construction with VUDS and ORELSE (C3VO) survey, we spectroscopically confirmed 44 galaxies within the adopted redshift range of the protocluster (4.48 15M⊙, sufficient to form a massive cluster by the present day. By comparing the star formation rate density (SFRD) within the protocluster (SFRDpc) to that of the coeval field (SFRDfield), we find that SFRDpc surpasses the SFRDfield by Δlog (SFRD/M⊙yr-1 Mpc-3) = 1.08 ± 0.32 (or ~12 ×). The observed contribution fraction of protoclusters to the cosmic SFRD adopting Taralay as a proxy for typical protoclusters is $33.5~{{\%}}^{+8.0~{{\%}}}_{-4.3~{{\%}}}$, a value ~2σ higher than the predictions from simulations. Taralay contains three peaks that are 5σ above the average density at these redshifts. Their SFRD is ~0.5 dex higher than the value derived for the overall protocluster. We show that 68% of all star formation in the protocluster takes place within these peaks, and that the innermost regions of the peaks encase $\sim 50~{{\%}}$ of the total star formation in the protocluster. This study strongly suggests that protoclusters drive stellar mass growth in the early universe and that this growth may proceed in an inside-out manner