Cosmological interpretation of the color-magnitude diagrams of galaxy clusters

We investigate the color-magnitude diagram (CMD) of cluster galaxies in the hierarchical $\Lambda$-CDM cosmological scenario using both single stellar populations and simple galaxy models. First, we analyze the effect of bursts and mergers and companion chemical pollution and rejuvenation of the stellar content on the integrated light emitted by galaxies. The dispersion of the galaxy magnitudes and colors on the $M_V-(B-V)$ plane is mainly due to mixing of ages and metallicities of the stellar populations, with mergers weighting more than bursts of similar mass fractions. The analysis is made using the Monte-Carlo technique applied to ideal model galaxies reduced to single stellar populations with galaxy-size mass to evaluate mass, age and metallicity of each object. We show that separately determining the contributions by bursts and mergers leads to a better understanding of observed properties of CMD of cluster galaxies. Then we repeat the analysis using suitable chemo-photometric models of galaxies whose mass is derived from the cosmological predictions of the galaxy content of typical clusters. Using the halo mass function and the Monte-Carlo technique, we derive the formation redshift of each galaxy and its photometric history. These are used to simulate the CMD of the cluster galaxies. The main conclusion is that most massive galaxies have acquired the red color they show today in very early epochs and remained the same ever since. The simulations nicely reproduce the Red Sequence, the Green Valley and the Blue Cloud, the three main regions of the CMD in which galaxies crowd.Comment: Accepted for publication in Ap

The mass assembly in galaxies and clusters: a new perspective from the luminosity profiles

Context: Galaxy clusters are the largest virialized structures in the observable Universe. Knowledge of their properties provides many useful astrophysical and cosmological information. Aim: Our aim is to derive the luminosity and stellar mass profiles of the nearby galaxy clusters of the Omega-WINGS survey, to study the main scaling relations valid for such systems and to compare them with those valid for early-type galaxies (ETGs). Methods: We merged data from the WINGS and Omega-WINGS databases, sorted the sources according to the distance from the brightest cluster galaxy (BCG), and calculated the integrated luminosity profiles in the B and V bands, taking into account extinction, photometric and spatial completeness, K correction, and background contribution. Then, by exploiting the spectroscopic sample we derived the stellar mass profiles of the clusters. Results: We obtained the luminosity profiles of 46 galaxy clusters, reaching the virial radius in 30 cases, and the stellar mass profiles of 42 of our objects. We successfully fitted all the integrated luminosity growth profiles with one or two embedded Sérsic components, deriving the main clusters parameters. We checked the main scaling relation among the clusters parameters in comparison with those obtained for a selected sample of ETGs of the same clusters. Conclusions: We found that the nearby galaxy clusters are non-homologous structures such as ETGs and exhibit a color-magnitude (CM) red-sequence relation very similar to that observed for galaxies in clusters. These properties are not expected in the current cluster formation scenarios. In particular the existence of a CM relation for clusters, shown here for the first time, suggests that the baryonic structures grow and evolve in a similar way at all scales. We also provided an explanation of the properties of the fundamental plane relation of both clusters and ETGs in terms of a fine-tuning between the time-averaged star formation rate and the structural and dynamical characteristics of the system. Finally, we showed that the light profiles of clusters mirrors, in at least half cases, the light profile of the corresponding BCGs

The parallelism between galaxy clusters and early-type galaxies: I. The light and mass profiles

We have analyzed the parallelism between the properties of galaxy clusters and early-type galaxies (ETGs) by looking at the similarity between their light profiles. We find that the equivalent luminosity profiles of all these systems in the \vfilt\ band, once normalized to the effective radius \re\ and shifted in surface brightness, can be fitted by the S\'ersic's law \Sers\ and superposed with a small scatter ($\le0.3$ mag). By grouping objects in different classes of luminosity, the average profile of each class slightly deviates from the other only in the inner and outer regions (outside $0.1\leq r/R_e\leq 3$), but the range of values of $n$ remains ample for the members of each class, indicating that objects with similar luminosity have quite different shapes. The "Illustris" simulation reproduces quite well the luminosity profiles of ETGs, with the exception of in the inner and outer regions where feedback from supernovae and active galactic nuclei, wet and dry mergers, are at work. The total mass and luminosity of galaxy clusters as well as their light profiles are not well reproduced. By exploiting simulations we have followed the variation of the effective half-light and half-mass radius of ETGs up to $z=0.8$, noting that progenitors are not necessarily smaller in size than current objects. We have also analyzed the projected dark+baryonic and dark-only mass profiles discovering that after a normalization to the half-mass radius, they can be well superposed and fitted by the S\'ersic's law.Comment: 25 pages, 19 figure

A search for peculiar stars in the open cluster Hogg 16

The study of chemically peculiar (CP) stars in open clusters provides valuable information about their evolutionary status. Their detection can be performed using the $\Delta a$ photometric system, which maps a characteristic flux depression at $\lambda \sim 5200$ \AA. This paper aims at studying the occurrence of CP stars in the earliest stages of evolution of a stellar population by applying this technique to Hogg 16, a very young Galactic open cluster (about 25 Myr). We identified several peculiar candidates: two B-type stars with a negative $\Delta a$ index (CD-60 4701, CPD-60 4706) are likely emission-line (Be) stars, even though spectral measurements are necessary for a proper classification of the second one; a third object (CD-60 4703), identified as a Be candidate in literature, appears to be a background B-type supergiant with no significant $\Delta a$ index, which does not rule out the possibility that it is indeed peculiar as the normality line of $\Delta a$ for supergiants has not been studied in detail yet. A fourth object (CD-60 4699) appears to be a magnetic CP star of 8 M$_\odot$, but obtained spectral data seem to rule out this hypothesis. Three more magnetic CP star candidates are found in the domain of early F-type stars. One is a probable nonmember and close to the border of significance, but the other two are probably pre-main sequence cluster objects. This is very promising, as it can lead to very strong constraints to the diffusion theory. Finally, we derived the fundamental parameters of Hogg 16 and provide for the first time an estimate of its metal content.Comment: Accepted for publication in New Astronomy. 9 pages, 4 figures, and 4 tables. A complete data table is available via CDS or upon request from the corresponding autho

The mass assembly in galaxies and clusters: a new perspective from the luminosity profiles

Context: Galaxy clusters are the largest virialized structures in the observable Universe. Knowledge of their properties provides many useful astrophysical and cosmological information. Aim: Our aim is to derive the luminosity and stellar mass profiles of the nearby galaxy clusters of the Omega-WINGS survey, to study the main scaling relations valid for such systems and to compare them with those valid for early-type galaxies (ETGs). Methods: We merged data from the WINGS and Omega-WINGS databases, sorted the sources according to the distance from the brightest cluster galaxy (BCG), and calculated the integrated luminosity profiles in the B and V bands, taking into account extinction, photometric and spatial completeness, K correction, and background contribution. Then, by exploiting the spectroscopic sample we derived the stellar mass profiles of the clusters. Results: We obtained the luminosity profiles of 46 galaxy clusters, reaching the virial radius in 30 cases, and the stellar mass profiles of 42 of our objects. We successfully fitted all the integrated luminosity growth profiles with one or two embedded Sérsic components, deriving the main clusters parameters. We checked the main scaling relation among the clusters parameters in comparison with those obtained for a selected sample of ETGs of the same clusters. Conclusions: We found that the nearby galaxy clusters are non-homologous structures such as ETGs and exhibit a color-magnitude (CM) red-sequence relation very similar to that observed for galaxies in clusters. These properties are not expected in the current cluster formation scenarios. In particular the existence of a CM relation for clusters, shown here for the first time, suggests that the baryonic structures grow and evolve in a similar way at all scales. We also provided an explanation of the properties of the fundamental plane relation of both clusters and ETGs in terms of a fine-tuning between the time-averaged star formation rate and the structural and dynamical characteristics of the system. Finally, we showed that the light profiles of clusters mirrors, in at least half cases, the light profile of the corresponding BCGs.Contesto: Gli ammassi di galassie sono le più grandi strutture virializzate dell’Universo osservabile e comprenderne le proprietà può fornire molte informazioni utili sia in ambito astrofisico che cosmologico. Scopo: Lo scopo del nostro lavoro è di derivare i profili di luminosità e massa per un campione di ammassi di galassie dell’Universo locale tratti dalla survey Omega-WINGS, di studiarne le principali relazioni di scala e di compararle con quelle valide per le galassie “early-type” (ETG). Metodo: Abbiamo unito i dati delle survey WINGS e Omega-WINGS, ordinato le sorgenti in funzione della loro distanza dalla galassia d’ammasso più brillante (BCG) e calcolato i profili di luminosità integrata nelle bande B e V, tenendo conto di estinzione, completezza spaziale e fotometrica, correzione K e sorgenti di campo. Infine, sfruttando il campione spettroscopico, abbiamo derivato i profili di massa stellare degli ammassi. Risultati: Abbiamo ottenuto i profili di luminosità di 46 ammassi di galassie, raggiungendo il raggio viriale in 30 casi, e i profili di massa di 42 di questi. Successivamente, abbiamo interpolato tutti i profili di luminosità con una o due componenti di Sérsic innestate l’una dentro l’altra, e abbiamo così derivato i parametri degli ammassi. Questi parametri sono stati usati per ottenere delle relazioni da paragonare a quelle valide per un campione di ETG degli ammassi stessi. Conclusioni: Abbiamo scoperto che gli ammassi di galassie analizzati sono strutture non omologhe (come le ETG) e che mostrano una sequenza di oggetti rossi nel diagramma colore-magnitudine (CM) molto simile a quella delle galassie d’ammasso. Queste proprietà non sono attese dal corrente scenario di formazione delle strutture cosmiche. In particolare, l’esistenza di una relazione CM per gli ammassi, identificata qua per la prima volta, suggerisce che le strutture di materia barionica crescano ed evolvano in maniera analoga a tutte le scale. Abbiamo inoltre fornito una spiegazione alle proprietà del piano fondamentale delle ETG e degli ammassi in termini di taratura fine tra il tasso di formazione stellare medio e le caratteristiche strutturali e dinamiche del sistema. Infine, abbiamo mostrato come in almeno metà dei casi il profilo di luminosità dell’ammasso rispecchi quello della rispettiva BCG

On the Origin of the Fundamental Plane and Faber-Jackson Relations: Implications for the Star Formation Problem

We provide an explanation of the properties of the fundamental plane (FP) relation and its observed projections for a sample of nearby early-type galaxies (ETGs) in terms of a fine-tuning between the time-averaged star formation rate and their structural and dynamical characteristics. Their total V luminosity is linked with and the central velocity dispersion σ through the relation {log}(L)=0.48(+/- 0.06){log}( )+1.00 (+/- 0.13){log}(σ )+7.81(+/- 0.26), with an rms = 0.215 (R = 0.64 and P-16). This fine-tuning permits us to obtain the FP in terms of two distinct “virtual planes” in the {log}({R}e){--}{log}(e> ){--}{log}(σ ) space. The first one (the virial plane; VP) represents the total galaxy mass derived from the scalar virial theorem and the mass-to-light ratio M/L, while the second plane comes from the relation L={L}0\prime {σ }-2, where {L}0\prime is a parameter connected with . This is a mathematically convenient way for expressing the independence of the galaxy light from the virial equilibrium. Each galaxy in the {log}({R}e){--}{log}(e> ){--}{log}(σ ) space is identified by the intersection of these two planes. A posteriori, we show that the properties of the FP (tilt and scatter) and the zone of exclusion visible in the FP projections are consequences of this fine-tuning. The link between the FP properties and the SFR of galaxies provides a new view of the star formation phenomenon. The star formation history of an unperturbed galaxy seems to be driven by the initial conditions in the protogalaxies and is regulated across cosmic epochs by the variation of the main galaxy parameters (mass, luminosity, structural shape, and velocity dispersion)

A search for peculiar stars in the open cluster Hogg 16

The study of chemically peculiar (CP) stars in open clusters provides valuable information about their evolutionary status. Their detection can be performed using the Δa photometric system, which maps a characteristic flux depression at λ ∼ 5200 Å. This paper aims at studying the occurrence of CP stars in the earliest stages of evolution of a stellar population by applying this technique to Hogg 16, a very young Galactic open cluster ( ∼ 25 Myr). We identified several peculiar candidates: two B-type stars with a negative Δa index (CD - 60 4701, CPD - 60 4706) are likely emission-line (Be) stars, even though spectral measurements are necessary for a proper classification of the second one; a third object (CD - 60 4703), identified as a Be candidate in literature, appears to be a background B-type supergiant with no significant Δa index, which does not rule out the possibility that it is indeed peculiar as the normality line of Δa for supergiants has not been studied in detail yet. A fourth object (CD - 60 4699) appears to be a magnetic CP star of 8  M⊙, but obtained spectral data seem to rule out this hypothesis. Three more magnetic CP star candidates are found in the domain of early F-type stars. One is a probable nonmember and close to the border of significance, but the other two are probably pre-main sequence cluster objects. This is very promising, as it can lead to very strong constraints to the diffusion theory. Finally, we derived the fundamental parameters of Hogg 16 and provide for the first time an estimate of its metal content.Facultad de Ciencias Astronómicas y Geofísica

Posterior reversible encephalopathy syndrome and COVID-19: A series of 6 cases from Lombardy, Italy

Posterior reversible encephalopathy cases are increasingly being reported in patients affected by COVID-19, but the largest series so far only includes 4 patients. We present a series of 6 patients diagnosed with PRES during COVID-19 hospitalized in 5 Centers in Lombardia, Italy. 5 out of the 6 patients required intensive care assistence and seizures developed at weaning from assisted ventilation. 3 out of 6 patients underwent cerebrospinal fluid analysis which was normal in all cases, with negative PCR for Sars-CoV-2 genome search. PRES occurrence may be less rare than supposed in COVID-19 patients and a high suspicion index is warranted for prompt diagnosis and treatment

Fabry-Stroke Italian Registry (FSIR): a nationwide, prospective, observational study about incidence and characteristics of Fabry-related stroke in young-adults. Presentation of the study protocol

TIA and stroke, both ischemic and hemorrhagic, may complicate Fabry disease at young-adult age and be the first manifestation that comes to the clinician's attention. No definite indications have yet been elaborated to guide neurologists in Fabry disease diagnostics. In current practice, it is usually sought in case of cryptogenic strokes (while Fabry-related strokes can also occur by classical pathogenic mechanisms) or through screening programs in young cerebrovascular populations. Data on recurrence and secondary prevention of Fabry's stroke are scanty