Abstract
As part of the ESO-VLT Multi-Instrument Kinematic Survey of Galactic globular clusters (GCs), we present a detailed investigation of the internal kinematics of NGC 5986. The analysis is ...based on about 300 individual radial velocities of stars located at various distances from the cluster center, up to 300″ (about four half-mass radii). Our analysis reveals the presence of a solid-body rotation extending from the cluster center to the outermost regions probed by the data, and a velocity dispersion profile initially declining with the distance from the cluster’s center, but flattening and staying constant at ∼5 km s
−1
for distances larger than about one half-mass radius. This is the first GC for which evidence of the joint presence of solid-body rotation and flattening in the outer velocity dispersion profile has been found. The combination of these two kinematical features provides a unique opportunity to shed light on fundamental aspects of GC dynamics and to probe the extent to which internal relaxation, star escape, angular momentum transport and loss, and the interaction with the Galaxy tidal field can affect a cluster’s dynamical evolution and determine its current kinematical properties. We present the results of a series of
N
-body simulations illustrating the possible dynamical paths leading to kinematic features like those observed in this cluster and the fundamental dynamical processes that underpin them.
We report on the identification of the optical counterpart to the recently detected INTEGRAL transient IGR J1824-24525 in the Galactic globular cluster M28. From analysis of a multi-epoch Hubble ...Space Telescope data set, we have identified a strongly variable star positionally coincident with the radio and Chandra X-ray sources associated with the INTEGRAL transient. The star has been detected during both a quiescent and an outburst state. In the former case it appears as a faint, unperturbed main-sequence star, while in the latter state it is about two magnitudes brighter and slightly bluer than main-sequence stars. We also detected H alpha excess during the outburst state, suggestive of active accretion processes by the neutron star.
ABSTRACT
We exploit a combination of high-resolution Hubble Space Telescope and wide-field ESO-VLT observations to study the slope of the global mass function (αG) and its radial variation (α(r)) in ...the two dense, massive and post core-collapse globular clusters M15 and M30. The available data set samples the clusters’ main sequence down to ∼0.2 M⊙ and the photometric completeness allows the study of the mass function between 0.40 M⊙ and 0.75 M⊙ from the central regions out to their tidal radii. We find that both clusters show a very similar variation in α(r) as a function of clustercentric distance. They both exhibit a very steep variation in α(r) in the central regions, which then attains almost constant values in the outskirts. Such a behaviour can be interpreted as the result of long-term dynamical evolution of the systems driven by mass-segregation and mass-loss processes. We compare these results with a set of direct N-body simulations and find that they are only able to reproduce the observed values of α(r) and αG at dynamical ages (t/trh) significantly larger than those derived from the observed properties of both clusters. We investigate possible physical mechanisms responsible for such a discrepancy and argue that both clusters might be born with a non-standard (flatter/bottom-lighter) initial mass function.
Abstract
We present the results of the spectroscopic and photometric follow-up of two field galaxies that were selected as possible stellar counterparts of local high-velocity clouds. Our analysis ...shows that the two systems are distant (D > 20 Mpc) dwarf irregular galaxies unrelated to the local H i clouds. However, the newly derived distance and structural parameters reveal that the two galaxies have luminosities and effective radii very similar to the recently identified ultra diffuse galaxies (UDGs). At odds with classical UDGs, they are remarkably isolated, having no known giant galaxy within ∼2.0 Mpc. Moreover, one of them has a very high gas content compared to galaxies of similar stellar mass, with a H i
to stellar mass ratio
$M_{\rm H\, {\small {I}}}/M_{\rm \star }\sim 90$
, typical of almost-dark dwarfs. Expanding on this finding, we show that extended dwarf irregulars overlap the distribution of UDGs in the MV
versus log r
e plane and that the sequence including dwarf spheroidals, dwarf irregulars and UDGs appears as continuously populated in this plane. This may suggest an evolutionary link between dwarf irregulars and UDGs.
We used a combination of Hubble Space Telescope and ground-based data to probe the dynamical state of the low-mass Galactic globular cluster NGC 6101. We have rederived the structural parameters of ...the cluster by using star counts and we find that it is about three times more extended than thought before. By using three different indicators, namely the radial distribution of blue straggler stars (BSSs), that of main-sequence binaries, and the luminosity (mass) function, we demonstrated that NGC 6101 shows no evidence of mass segregation, even in the innermost regions. Indeed, both the BSS and the binary radial distributions fully resemble those of any other cluster population. In addition, the slope of the luminosity (mass) function does not change with the distance, as expected for non-relaxed stellar systems. NGC 6101 is one of the few globulars where the absence of mass segregation has been observed so far. This result provides additional support for the use of the "dynamical clock" calibrated on the radial distribution of the blue stragglers as a powerful indicator of the cluster dynamical age.
The parameter A+, defined as the area enclosed between the cumulative radial distribution of blue straggler stars (BSSs) and that of a reference population, is a powerful indicator of the level of ...BSS central segregation. As part of the Hubble Space Telescope UV Legacy Survey of Galactic globular clusters (GCs), here we present the BSS population and the determination of A+ in 27 GCs observed out to about one half-mass radius. In combination with 21 additional clusters discussed in a previous paper, this provides us with a global sample of 48 systems (corresponding to ∼32% of the Milky Way GC population), for which we find a strong correlation between A+ and the ratio of cluster age to the current central relaxation time. Tight relations have also been found with the core radius and the central luminosity density, which are expected to change with the long-term cluster dynamical evolution. An interesting relation is emerging between A+ and the ratio of the BSS velocity dispersion relative to that of main sequence turn-off stars, which measures the degree of energy equipartition experienced by BSSs in the cluster. These results provide further confirmation that BSSs are invaluable probes of GC internal dynamics and that A+ is a powerful dynamical clock.
Fusarium head blight (FHB) is a global cereal disease caused by a complex of Fusarium species. In Europe, the main species responsible for FHB are F. graminearum, F. culmorum and F. poae. However, ...members of the F. tricinctum species complex (FTSC) have become increasingly important. FTSC fusaria can synthesize mycotoxins such as moniliformin (MON), enniatins (ENNs) and several other biologically active secondary metabolites that could compromise food quality. In this study, FTSC isolates primarily from Italian durum wheat and barley, together with individual strains from four non-graminaceous hosts, were collected to assess their genetic diversity and determine their potential to produce mycotoxins in vitro on rice cultures. A multilocus DNA sequence dataset (TEF1, RPB1 and RPB2) was constructed for 117 isolates from Italy and 6 from Iran to evaluate FTSC species diversity and their evolutionary relationships. Phylogenetic analyses revealed wide genetic diversity among Italian FTSC isolates. Among previously described FTSC species, F. avenaceum (FTSC 4) was the most common species in Italy (56/117 = 47.9%) while F. tricinctum (FTSC 3), and F. acuminatum (FTSC 2) accounted for 11.1% (13/117) and the 8.5% (10/117), respectively. The second most detected species was a new and unnamed Fusarium sp. (FTSC 12; 32/117 = 19%) resolved as the sister group of F. tricinctum. Collectively, these four phylospecies accounted for 111/117 = 94.9% of the Italian FTSC collection. However, we identified five other FTSC species at low frequencies, including F. iranicum (FTSC 6) and three newly discovered species (Fusarium spp. FTSC 13, 14, 15). Of the 59 FTSC isolates tested for mycotoxin production on rice cultures, 54 and 55 strains, respectively, were able to produce detectable levels of ENNs and MON. In addition, we confirmed that the ability to produce bioactive secondary metabolites such as chlamydosporol, acuminatopyrone, longiborneol, fungerin and butanolide is widespread across the FTSC.
•Fusarium tricinctum species complex (FTSC) are important cereal pathogens worldwide.•Phylogenetic analyses revealed Italian FTSC isolates are genetically diverse.•Four of the nine FTSC species recovered in Italy represent novel phylospecies.•Fusarium avenaceum (FTSC 4) was the predominant species on Italian cereals.•FTSC isolates produced significant levels of moniliformin and enniatin mycotoxins.
Full text
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Globular star clusters that formed at the same cosmic time may have evolved rather differently from the dynamical point of view (because that evolution depends on the internal environment) through a ...variety of processes that tend progressively to segregate stars more massive than the average towards the cluster centre. Therefore clusters with the same chronological age may have reached quite different stages of their dynamical history (that is, they may have different 'dynamical ages'). Blue straggler stars have masses greater than those at the turn-off point on the main sequence and therefore must be the result of either a collision or a mass-transfer event. Because they are among the most massive and luminous objects in old clusters, they can be used as test particles with which to probe dynamical evolution. Here we report that globular clusters can be grouped into a few distinct families on the basis of the radial distribution of blue stragglers. This grouping corresponds well to an effective ranking of the dynamical stage reached by stellar systems, thereby permitting a direct measure of the cluster dynamical age purely from observed properties.
Full text
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DOBA, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
ABSTRACT
Using Large Binocular Telescope deep imaging data from the Smallest Scale of Hierarchy Survey (SSH) and archival Hubble Space Telescope data, we reveal the presence of two elongated stellar ...features contiguous to a bar-like stellar structure in the inner regions of the dwarf irregular galaxy NGC 3741. These structures are dominated by stars younger than a few hundred Myr and collectively are about twice as extended as the old stellar component. These properties are very unusual for dwarf galaxies in the nearby Universe and difficult to explain by hydro-dynamical simulations. From the analysis of archival 21-cm observations, we find that the young stellar ‘bar’ coincides with an H i high-density region proposed by previous studies to be a purely gaseous bar; we furthermore confirm radial motions of a few km s−1, compatible with an inflow/outflow, and derive a steeply rising rotation curve and high H i surface density at the centre, indicating a very concentrated mass distribution. We propose that the peculiar properties of the stellar and gaseous components of NGC 3741 may be explained by a recent merger or ongoing gas accretion from the intergalactic medium, which caused gas inflows towards the galaxy centre and triggered star formation a few hundred Myr ago. This event may explain the young and extended stellar features, the bar-like structure, the very extended H i disc and the central H i spiral arms. The high central H i density and the steeply rising rotation curve suggest that NGC 3741 may be the progenitor or the descendant of a starburst dwarf.
Abstract
SECCO 1 is an extremely dark, low-mass (M⋆ ≃ 105 M⊙), star-forming stellar system lying in the low-velocity cloud (LVC) substructure of the Virgo cluster of galaxies, and hosting several H ...ii regions. Here, we review our knowledge of this remarkable system, and present the results of (a) additional analysis of our panoramic spectroscopic observations with MUSE, (b) the combined analysis of Hubble Space Telescope and MUSE data, and (c) new narrow-band observations obtained with OSIRIS@GTC to search for additional H ii regions in the surroundings of the system. We provide new evidence supporting an age as young as $\lesssim\! 4$ Myr for the stars that are currently ionizing the gas in SECCO 1. We identify only one new promising candidate H ii region possibly associated with SECCO 1, thus confirming the extreme isolation of the system. We also identify three additional candidate pressure-supported dark clouds in Virgo among the targets of the SECCO survey. Various possible hypotheses for the nature and origin of SECCO 1 are considered and discussed, also with the help of dedicated hydrodynamical simulations showing that a hydrogen cloud with the characteristics of SECCO 1 can likely survive for $\gtrsim\! 1$ Gyr while travelling within the LVC Intra Cluster Medium.
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