26 research outputs found
Determinazione della struttura a spirale della Via Lattea alle frequenze radio
Lo scopo principale di questo breve scritto è la ricerca e la riscoperta delle prime tecniche di detezione e rilevazione della struttura a spirale della Via Lattea, in particolare si ripercorrono brevemente i risultati e gli studi compiuti durante il XX secolo per mettere in luce i principali componenti che costituiscono la nostra galassia. L'analisi della disposizione sul disco sottile di regioni di idrogeno neutro e ionizzato e nubi di monossido di carbonio ha permesso di stabilire fin dalla seconda metà del 1900 la natura a spirale della Via Lattea, mentre lo studio della densità superficiale di idrogeno neutro alle radiofrequenze ne fornisce una visione più approfondita. L'attenzione si rivolge in seguito verso uno studio recente portato avanti da un gruppo di scienziati coreani che grazie all'uso di un cospicuo set di dati riesce a definire la struttura principale e le ulteriori ramificazioni; tuttavia la brillante deduzione risulta priva di difetti e necessita quindi una revisione accurata. Poiché già sul finire del secolo sorgono diverse problematiche, che non possono essere trascurate, legate alla corretta disposizione dei bracci di spirale, è necessario visionare con occhio critico gli ultimi modelli e le teorie proposte sulla struttura a spirale della Via Lattea.ope
Ultra diffuse galaxies in the Hydra I cluster from the LEWIS Project: Phase-Space distribution and globular cluster richness
Although ultra diffuse galaxies (UDGs) are found in large numbers in clusters
of galaxies, the role of the cluster environment in shaping their low surface
brightness and large sizes is still uncertain. Here we examine a sample of UDGs
in the Hydra I cluster (D = 51 Mpc) with new radial velocities obtained as part
of the LEWIS (Looking into the faintest with MUSE) project using VLT/MUSE data.
Using a phase-space, or infall diagnostic, diagram we compare the UDGs to other
known galaxies in the Hydra I cluster and to UDGs in other clusters. The UDGs,
along with the bulk of regular Hydra I galaxies, have low relative velocities
and are located near the cluster core, and thus consistent with very early
infall into the cluster. Combining with literature data, we do not find the
expected trend of GC-rich UDGs associated with earlier infall times. This
result suggests that quenching mechanisms other than cluster infall should be
further considered, e.g. quenching by strong feedback or in cosmic sheets and
filaments. Tidal stripping of GCs in the cluster environment also warrants
further modelling.Comment: 6 pages, 2 figures, MNRAS, 525, 9
Looking into the faintEst WIth MUSE (LEWIS): on the nature of ultra-diffuse galaxies in the Hydra-I cluster.I. Project description and preliminary results
Looking into the faintEst WIth MUSE (LEWIS) is an ESO large observing
programme aimed at obtaining the first homogeneous integral-field spectroscopic
survey of 30 extremely low-surface brightness (LSB) galaxies in the Hydra I
cluster of galaxies, with MUSE at ESO-VLT. The majority of LSB galaxies in the
sample (22 in total) are ultra-diffuse galaxies (UDGs). The distribution of
systemic velocities Vsys ranges between 2317 km/s and 5198 km/s and is centred
on the mean velocity of Hydra I (Vsys = 3683 46 km/s). Considering the
mean velocity and the velocity dispersion of the cluster, 17 out of 20 targets
are confirmed cluster members. To assess the quality of the data and
demonstrate the feasibility of the science goals, we report the preliminary
results obtained for one of the sample galaxies, UDG11. For this target, we
derived the stellar kinematics, including the 2-dimensional maps of
line-of-sight velocity and velocity dispersion, constrained age and
metallicity, and studied the globular cluster (GC) population hosted by the
UDG. Results are compared with the available measurements for UDGs and dwarf
galaxies in literature. By fitting the stacked spectrum inside one effective
radius, we find that UDG11 has a velocity dispersion km/s,
it is old ( Gyr), metal-poor ([M/H]=-1.170.11 dex) and has a total
dynamical mass-to-light ratio M, comparable to those observed for
classical dwarf galaxies. The spatially resolved stellar kinematics maps
suggest that UDG11 does not show a significant velocity gradient along either
major or minor photometric axes. We find two GCs kinematically associated with
UDG11. The estimated total number of GCs in UDG11, corrected for the
spectroscopic completeness limit, is , which
corresponds to a GC specific frequency of .Comment: Accepted for publication in Astronomy and Astrophysic
The dynamical state of bars in cluster dwarf galaxies: The cases of NGC 4483 and NGC 4516
Dwarf barred galaxies are the perfect candidates for hosting slowly-rotating bars. They are common in dense environments and they have a relatively shallow potential well, making them prone to heating by interactions. When an interaction induces bar formation, the bar should rotate slowly. They reside in massive and centrally-concentrated dark matter halos, which slow down the bar rotation through dynamical friction. While predictions suggest that slow bars should be common, measurements of bar pattern speed, using the Tremaine-Weinberg method, show that bars are mostly fast in the local Universe. We present a photometric and kinematic characterisation of bars hosted by two dwarf galaxies in the Virgo Cluster, NGC 4483 and NGC 4516. We derive the bar length and strength using the Next Generation Virgo Survey imaging and the circular velocity, bar pattern speed, and rotation rate using spectroscopy from the Multi Unit Spectroscopic Explorer. Including the previously studied galaxy IC 3167, we compare the bar properties of the three dwarf galaxies with those of their massive counterparts from literature. Bars in the dwarf galaxies are shorter and weaker, and rotate slightly slower with respect to those in massive galaxies. This could be due to a different bar formation mechanism and/or to a large dark matter fraction in the centre of dwarf galaxies. We show that it is possible to push the application of the Tremaine-Weinberg method to the galaxy low mass regime
A Milky Way-like barred spiral galaxy at a redshift of 3
International audienceThe majority of massive disk galaxies in the local Universe show a stellar barred structure in their central regions, including our Milky Way. Bars are supposed to develop in dynamically cold stellar disks at low redshift, as the strong gas turbulence typical of disk galaxies at high redshift suppresses or delays bar formation. Moreover, simulations predict bars to be almost absent beyond in the progenitors of Milky Way-like galaxies. Here we report observations of ceers-2112, a barred spiral galaxy at redshift , which was already mature when the Universe was only 2 Gyr old. The stellar mass () and barred morphology mean that ceers-2112 can be considered a progenitor of the Milky Way, in terms of both structure and mass-assembly history in the first 2 Gyr of the Universe, and was the closest in mass in the first 4 Gyr. We infer that baryons in galaxies could have already dominated over dark matter at , that high-redshift bars could form in approximately 400 Myr and that dynamically cold stellar disks could have been in place by redshift (more than 12 Gyrs ago)
Implementation of preventive and predictive BRCA testing in patients with breast, ovarian, pancreatic, and prostate cancer: a position paper of Italian Scientific Societies
TASSO DI ROTAZIONE DELLA BARRA: UNO STRUMENTO PER INDAGARE LA FORMAZIONE E LA DINAMICA DELLE GALASSIE BARRATE
Nell’Universo Locale, più di due-terzi delle galassie a disco ospitano una struttura ellittica che ruota al centro del disco, chiamata barra. La lunghezza R_bar, la forza S_bar, e la velocità angolare Ω_bar della barra evolvono nel tempo modificando le proprietà fotometriche e cinematiche dell’intera galassia. La velocità angolare della barra è il più importante tra i vari parametri che caratterizzano la barra: controlla la posizione delle risonanze, modifica la dinamica stellare e dipende dal contenuto di materia oscura. Solitamente, è parametrizzata attraverso il tasso di rotazione, un parametro adimensionale e indipendente dalla distanza della galassia, che distingue le barre in lente, veloci, e ultraveloci. Lavori teorici e simulazioni N-corpi permettono di indagare la formazione delle galassie barrate e l’evoluzione delle proprietà della barra, mentre studi osservativi consentono di esplorare le attuali proprietà delle galassie barrate. Le barre veloci possono formarsi spontaneamente a causa di instabilità interne che forzano le stelle a muoversi su orbite allungate. In alternativa, la formazione della barra può avvenire a seguito dell’interazione mareale con una galassia vicina. Quest’ultime sono generalmente più lente rispetto alle barre formate spontaneamente. Lavori teorici e simulazioni cosmologiche hanno dimostrato che le barre rallentano a seguito dell’interazione con un denso alone di materia oscura, mentre lavori teorici sulle orbite stellari, mostrano che le barre ultraveloci non dovrebbero esistere in quanto le orbite stellari non possono efficacemente sorreggere la struttura della barra. Studi osservativi mostrano che le barre risultano essere veloci, parte di esse è classificata come ultraveloce, mentre le poche barre lente osservate finora presentano grandi incertezze e non possono essere affidabilmente considerate lente. In questa tesi, ci proponiamo l’obiettivo di studiare la natura e la dinamica delle galassie barrate analizzandone la struttura interna attraverso modelli dinamici e simulazioni. Nel Capitolo 2 discutiamo il caso delle barre ultraveloci, la cui esistenza sfida la nostra conoscenza della struttura orbitale nelle galassie barrate. Analizziamo le proprietà delle barre ultraveloci osservate nella Calar Alto Legacy Integral Field Area (CALIFA) survey allo scopo di indagare se le barre ultraveloci sono un artefatto causato da una sovrastima della misura di R_bar o una nuova classe di barre. Troviamo che la maggior parte delle galassie possiede una struttura ad anello, pseudo-anello o bracci di spirale prominenti che possono alterare la misura di R_bar. Concludiamo che adottando una corretta misura di R_bar, le barre ultraveloci non sono più osservabili. Nel Capitoli 3 e 4 analizziamo le proprietà fotometriche e cinematiche delle barre ospiti rispettivamente nella galassia lenticolare NGC4277 e nella galassia nana IC3167. NGC4277 ospita il primo caso di una barra stellare lenta, mentre IC3167 ospita una barra lenta con una forma peculiare. Nel Capitolo 5 indaghiamo la relazione tra il tasso di rotazione e la frazione di materia oscura, concentrandoci sulle due galassie barrate NGC4264 e NGC4277. Troviamo che NGC4277 contiene una frazione di materia oscura superiore a NGC4264, in accordo con le predizioni ottenute da lavori teorici che mostrano che le barre veloci vivono in dischi galattici dominati da materia barionica, mentre le barre lente sono state rallentate da un denso alone di materia oscura a causa della frizione dinamica. Nel Capitolo 6 confrontiamo le proprietà della galassia NGC4277 con simulazioni N-corpi. Abbiamo trovato che il miglior modello che riproduce le proprietà fotometriche e cinematiche di NGC4277 è caratterizzato da un denso alone di materia oscura, confermando che la barra di NGC4277 è stata rallentata per frizione dinamica. Infine, nel Capitolo 7 riassumiamo le principali conclusioni della tesi e presentiamo possibili futuri sviluppi.More than two-thirds of disc galaxies in the Local Universe host an elliptical structure tumbling at the centre of the disc that is known as a bar. The bar radius R_bar, strength S_bar, and pattern speed Ω_bar change in time through secular evolution, affecting the morphological and kinematic properties of the host galaxy. The bar pattern speed is one of the most important parameters that characterise a bar. It controls the position of the resonances, affects the stellar dynamics, and depends on the dark matter (DM) content. The bar pattern speed is usually parameterised by the rotation rate, a dimensionless and distance-independent parameter that separates bars into slow, fast, and ultrafast. Dynamical studies and simulations-based works allowed to shed the light on the formation of barred galaxies and to track the evolution of the bar properties, while observational studies based on wide and deep surveys permitted to draw a picture of the properties of barred galaxies in the present-day. Fast bars can form naturally in disc galaxies due to internal instabilities which force stars to move into more elongated orbits. The bar formation can also occur in galaxies with a nearby companion, due to tidal interaction. These bars are typically slower with respect to those naturally formed. Moreover, theoretical works and cosmological simulations show that bars slow down after the interaction with a centrally concentrated DM halo through dynamical friction. According to orbital theory, ultrafast bars are not expected to exist since the stellar orbits cannot efficiently support the bar structure. Many observational studies found that bars in the Local Universe are compatible with the fast regime, a fraction of them lie in the ultrafast regime, and the few slow bars detected so far have too large uncertainties to be considered genuinely slow. In this thesis, we aim at investigating the nature and dynamics of barred galaxies by studying ultrafast, fast, and slow bars and analysing the internal structure of their host galaxies using dynamical models and N-body simulations. In Chapter 2 we discuss the case of ultrafast bars whose existence challenges our understanding of the orbital structure of barred galaxies. We analyse the properties of the ultrafast bars detected in the Calar Alto Legacy Integral Field Area Survey (CALIFA) survey to investigate whether they are an artefact resulting from an overestimation of R_bar or a new class of bars. We find that nearly all the sample galaxies have an inner ring or pseudoring circling the bar and/or strong spiral arms, which hamper the measurement of R_bar. We conclude that ultrafast bars are no longer observed when the correct measurement of R_bar is adopted. In Chapters 3 and 4 we present the photometric and kinematic analysis of the bar hosted in the lenticular galaxy NGC4277 and dwarf galaxy IC3167, respectively. NGC4277 hosts the first case of a slow stellar bar, while IC3167 hosts a slow bar with a peculiar lopsided shape. In Chapter 5 we investigate the link between the rotation rate and the DM content in barred galaxies by concentrating on the cases of the lenticular galaxies NGC4264 and NGC4277. We find that the galaxy NGC4277 host a larger DM fraction with respect to NGC4264, in agreement with the predictions of theoretical works which have found that fast bars live in baryon-dominated discs, whereas slow bars experienced a strong drag from the dynamical friction due to a dense DM halo. In Chapter 6 we build N-body simulations to mimic the photometric and kinematic properties of the lenticular barred galaxy NGC4277. We find that the galaxy model that best reproduces the properties of NGC4277 is characterised by a massive DM halo. Our results confirm that the bar hosted in NGC4277 experienced a strong drag as a consequence of the interaction with a dense DM halo. Finally, in Chapter 7 we summarise the main conclusions of the thesis and present some future perspectives