Abstract
We present the first results of the Multi-Instrument Kinematic Survey of Galactic Globular Clusters (GGCs), a project aimed at exploring the internal kinematics of a representative sample of ...GGCs from the radial velocity of individual stars, covering the entire radial extension of each system. This is achieved by exploiting the formidable combination of multi-object and integral field unit spectroscopic facilities of the ESO Very Large Telescope. As a first step, here we discuss the results obtained for 11 clusters from high and medium resolution spectra acquired through a combination of FLAMES and KMOS observations. We provide the first kinematical characterization of NGC 1261 and NGC 6496. In all the surveyed systems, the velocity dispersion profile declines at increasing radii, in agreement with the expectation from the King model that best fits the density/luminosity profile. In the majority of the surveyed systems, we find evidence of rotation within a few half-mass radii from the center. These results are in general overall agreement with the predictions of recent theoretical studies, suggesting that the detected signals could be the relic of significant internal rotation set at the epoch of the cluster’s formation.
In the context of the ESO-VLT Multi-Instrument Kinematic Survey (MIKiS) of Galactic globular clusters (GGCs), we present the line-of-sight rotation curve and velocity dispersion profile of M5 (NGC ...5904), as determined from the radial velocity of more than 800 individual stars observed out to 700″ (∼5 half-mass radii) from the center. We found one of the cleanest and most coherent rotation patterns ever observed for globular clusters, with a very stable rotation axis (having constant position angle of 145° at all surveyed radii) and a well-defined rotation curve. The density distribution turns out to be flattened in the direction perpendicular to the rotation axis, with a maximum ellipticity of ∼0.15. The rotation velocity peak (∼3 km s−1 in projection) is observed at ∼0.6 half-mass radii, and its ratio with respect to the central velocity dispersion (∼0.3–0.4 at 4 projected half-mass radii) indicates that ordered motions play a significant dynamical role. This result strengthens the growing empirical evidence of the kinematic complexity of GGCs and motivates the need of fundamental investigations of the role of angular momentum in collisional stellar dynamics.
In the last few years, antibiotic resistance and, analogously, anticancer drug resistance have increased considerably, becoming one of the main public health problems. For this reason, it is crucial ...to find therapeutic strategies able to counteract the onset of multi-drug resistance (MDR). In this review, a critical overview of the innovative tools available today to fight MDR is reported. In this direction, the use of membrane-disruptive peptides/peptidomimetics (MDPs), such as antimicrobial peptides (AMPs), has received particular attention, due to their high selectivity and to their limited side effects. Moreover, similarities between bacteria and cancer cells are herein reported and the hypothesis of the possible use of AMPs also in anticancer therapies is discussed. However, it is important to take into account the limitations that could negatively impact clinical application and, in particular, the need for an efficient delivery system. In this regard, the use of nanoparticles (NPs) is proposed as a potential strategy to improve therapy; moreover, among polymeric NPs, cationic ones are emerging as promising tools able to fight the onset of MDR both in bacteria and in cancer cells.
Context. The Milky Way bulge is the nearest galactic bulge and the most readily accessible laboratory for studies of stellar populations in spheroids based on individual stellar abundances and ...kinematics. These studies are challenged by the strongly variable and often large extinction on a small spatial scale.Aims. We use the Vista Variables in the Via Lactea (VVV) ESO public survey data to measure extinction values in the complete area of the Galactic bulge covered by the survey at high resolution.Methods. We derive reddening values using the method described in Paper I. This is based on measuring the mean (J − Ks) color of red clump giants in small subfields of 2′ × 2′ to 6′ × 6′ in the following bulge area: − 10.3° ≤ b ≤ + 5.1° and − 10.0° ≤ l ≤ + 10.4°. To determine the reddening values E(J − Ks) for each region, we measure the RC color and compare it to the (J − Ks) color of RC stars measured in Baade’s Window, for which we adopt E(B − V) = 0.55. This allows us to construct a reddening map sensitive to small-scale variations minimizing the problems arising from differential extinction.Results. The significant reddening variations are clearly observed on spatial scales as small as 2′. We find good agreement between our extinction measurements and Schlegel maps in the outer bulge, but, as already stated in the literature the Schlegel maps are unreliable for regions within |b| ≲ 6°. In the inner regions, we compare our results with maps derived from DENIS and Spitzer surveys. While we find good agreement with other studies in the corresponding overlapping regions, our extinction map is of higher quality owing to both its higher resolution and a more complete spatial coverage of the bulge. We investigate the importance of differential reddening and demonstrate the need for high spatial resolution extinction maps for detailed studies of bulge stellar populations and structure.Conclusions. We present the first extinction map covering uniformly ~315 sq. deg. of the Milky Way bulge at high spatial resolution. We consider a 30 arcmin window at a latitude of b = −4°, which corresponds to a frequently studied low extinction window, the so-called Baade’s Window, and find that its AKs values can vary by up to 0.1 mag. Larger extinction variations are observed at lower Galactic latitudes. The extinction variations on scales of up to 2′−6′ must be taken into account when analyzing the stellar populations of the Galactic bulge.
We present new determinations of the iron abundance for 220 stars belonging to the stellar system Terzan 5 in the Galactic bulge. The spectra have been acquired with FLAMES at the Very Large ...Telescope of the European Southern Observatory and DEIMOS at the Keck II Telescope. This is by far the largest spectroscopic sample of stars ever observed in this stellar system. From this data set, a subsample of targets with spectra unaffected by TiO bands was extracted and statistically decontaminated from field stars. Once combined with 34 additional stars previously published by our group, a total sample of 135 member stars covering the entire radial extent of the system has been used to determine the metallicity distribution function of Terzan 5. The iron distribution clearly shows three peaks: a super-solar component at Fe/H Asymptotically = to 0.25 dex, accounting for ~29% of the sample, a dominant sub-solar population at Fe/H Asymptotically = to -0.30 dex, corresponding to ~62% of the total, and a minor (6%) metal-poor component at Fe/H Asymptotically = to -0.8 dex. Such a broad, multi-modal metallicity distribution demonstrates that Terzan 5 is not a genuine globular cluster but the remnant of a much more complex stellar system.
The GIRAFFE Inner Bulge Survey (GIBS) Zoccali, M; Vasquez, S; Gonzalez, O A ...
Astronomy and astrophysics (Berlin),
3/2017, Volume:
599
Journal Article
Peer reviewed
Open access
Context. Several recent studies have demonstrated that the Galactic bulge hosts two components with different mean metallicities, and possibly different spatial distribution and kinematics. As a ...consequence, both the metallicity distribution and the radial velocity of bulge stars vary across different lines of sight. Aims. We present here the metallicity distribution function of red clump stars in 26 fields spread across a wide area of the bulge, with special emphasis on fields close to Galactic plane, at latitudes b= -2degrees and b= -1degrees, that have not been explored before. Methods. This paper includes new metallicities from a sample of approximately 5000 K giant stars, observed at spectral resolution R~ 6500, in the Calcium II Triplet region. These represent the main dataset from the GIRAFFE Inner Bulge Survey. As part of the same survey we have previously published results for a sample of approximately 600 K giant stars, at latitude b~ -4degrees, derived from higher resolution spectra (R= 22 500). Results. The combined sample allows us to trace and characterize the metal poor and metal rich bulge populations down to the inner bulge. We present a density map for each of the two components. Contrary to expectations from previous works, we found the metal poor population to be more centrally concentrated than the metal rich one, and with a more axisymmetric spatial distribution. The metal rich population, on the other hand, is arranged in a boxy distribution, consistent with an edge-on bar. By coupling metallicities and radial velocities we show that the metal poor population has a velocity dispersion that varies rather mildly with latitude. On the contrary, the metal rich population has a low velocity dispersion far from the plane (b= -8.5degrees), yet has a steeper gradient with latitude, becoming higher than the metal poor one in the innermost field (b= -1degrees). Conclusions. This work provides new observational constraints on the actual chemodynamical properties of the Galactic bulge, that will help discrimination between different formation models.
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 abundance analysis for 30 M giant stars in two inner Galactic bulge fields at (l, b) = (0degrees, -1degrees.75) and at (l, b) = (1degrees, -2degrees.65), based on R = 25,000 infrared ...spectroscopy (1.5-1.8 mu m) using NIRSPEC at the Keck II telescope. We find iron abundances of left angle bracketFe/Hright angle bracket = -0.16 + or - 0.03 dex with a 1sigma dispersion of 0.12 + or - 0.02 and left angle bracketFe/H right angle bracket = -0.21 + or - 0.02 dex, with a 1sigma dispersion of 0.09 + or - 0.016 for the (l, b) = (0degrees, -1degrees.75) and (l, b) = (1degrees, -2degrees.65) fields, respectively. In agreement with all prior studies, we find enhanced alpha /Fe of +0.3 dex. We confirm the lack of any major vertical abundance or composition gradient in the innermost ~600 pc between Baade's Window, at (l, b) = (1degrees, -3degrees.9), and ~150 pc from the Galactic plane. We also confirm that the known enhancement of alpha elements observed between 500 and 1000 pc from the nucleus is also present over the volume of the inner bulge and may therefore be presumed to be characteristic of all bulge/bar stars within 1 kpc of the Galactic center.
Globular star clusters are compact and massive stellar systems old enough to have witnessed the entire history of our Galaxy, the Milky Way. Although recent results suggest that their formation may ...have been more complex than previously thought, they still are the best approximation to a stellar population formed over a relatively short timescale (less than 1 Gyr) and with virtually no dispersion in the iron content. Indeed, only one cluster-like system ( Centauri) in the Galactic halo is known to have multiple stellar populations with a significant spread in iron abundance and age. Similar findings in the Galactic bulge have been hampered by the obscuration arising from thick and varying layers of interstellar dust. Here we report that Terzan 5, a globular-cluster-like system in the Galactic bulge, has two stellar populations with different iron contents and ages. Terzan 5 could be the surviving remnant of one of the primordial building blocks that are thought to merge and form galaxy bulges.
PDF
