| 1. |
- de Blok, W.J.G., et al.
(författare)
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an overview of the MHONGOOSE survey: Observing nearby galaxies with MeerKAT
- 2016
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Ingår i: Proceedings of Science. - 1824-8039.
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Konferensbidrag (refereegranskat)abstract
- MHONGOOSE is a deep survey of the neutral hydrogen distribution in a representative sample of 30 nearby disk and dwarf galaxies with H I masses from ∼ 106 to ∼ 1011 M, and luminosities from MR ∼ 12 to MR ∼ −22. The sample is selected to uniformly cover the available range in log(MHI). Our extremely deep observations, down to H I column density limits of well below 1018 cm−2 — or a few hundred times fainter than the typical H I disks in galaxies — will directly detect the effects of cold accretion from the intergalactic medium and the links with the cosmic web. These observations will be the first ever to probe the very low-column density neutral gas in galaxies at these high resolutions. Combination with data at other wavelengths, most of it already available, will enable accurate modeling of the properties and evolution of the mass components in these galaxies and link these with the effects of environment, dark matter distribution, and other fundamental properties such as halo mass and angular momentum. MHONGOOSE can already start addressing some of the SKA-1 science goals and will provide a comprehensive inventory of the processes driving the transformation and evolution of galaxies in the nearby universe at high resolution and over 5 orders of magnitude in column density. It will be a Nearby Galaxies Legacy Survey that will be unsurpassed until the advent of the SKA, and can serve as a highly visible, lasting statement of MeerKAT’s capabilities.
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| 2. |
- Carlos, M., et al.
(författare)
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The chemical compositions of multiple stellar populations in the globular cluster NGC 2808
- 2023
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press. - 0035-8711 .- 1365-2966. ; 519:2, s. 1695-1712
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Tidskriftsartikel (refereegranskat)abstract
- Pseudo two-colour diagrams or Chromosome maps (ChM) indicate that NGC 2808 host five different stellar populations. The existing ChMs have been derived by the Hubble Space Telescope photometry, and comprise of stars in a small field of view around the cluster centre. To overcome these limitations, we built a ChM with U, B, I photometry from ground-based facilities that disentangle the multiple stellar populations of NGC 2808 over a wider field of view. We used spectra collected by GIRAFFE@VLT in a sample of 70 red giant branch and seven asymptotic giant branch (AGB) stars to infer the abundances of C, N, O, Al, Fe, and Ni, which combined with literature data for other elements (Li, Na, Mg, Si, Ca, Sc, Ti, Cr, and Mn), and together with both the classical and the new ground-based ChMs, provide the most complete chemical characterization of the stellar populations in NGC 2808 available to date. As typical of the multiple population phenomenon in globular clusters, the light elements vary from one stellar population to another; whereas the iron peak elements show negligible variation between the different populations (at a level of less than or similar to 0.10 dex). Our AGB stars are also characterized by the chemical variations associated with the presence of multiple populations, confirming that this phase of stellar evolution is affected by the phenomenon as well. Intriguingly, we detected one extreme O-poor AGB star (consistent with a high He abundance), challenging stellar evolution models that suggest that highly He-enriched stars should avoid the AGB phase and evolve as AGB-manque star.
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| 3. |
- Cordoni, G., et al.
(författare)
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Gaia and Hubble Unveil the Kinematics of Stellar Populations in the Type II Globular Clusters ? Centauri and M22
- 2020
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 898:2
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Tidskriftsartikel (refereegranskat)abstract
- The origin of multiple stellar populations in globular clusters (GCs) is one of the greatest mysteries of modern stellar astrophysics. N-body simulations suggest that the present-day dynamics of GC stars can constrain the events that occurred at high redshift and led to the formation of multiple populations. Here, we combine multiband photometry from the Hubble Space Telescope (HST) and ground-based facilities with HST and Gaia Data Release 2 proper motions to investigate the spatial distributions and the motions in the plane of the sky of multiple populations in the Type II GCs NGC 5139 (? Centauri) and NGC 6656 (M22). We first analyzed stellar populations with different metallicities. Fe-poor and Fe-rich stars in M22 share similar spatial distributions and rotation patterns and exhibit similar isotropic motions. Similarly, the two main populations with different iron abundance in ? Centauri share similar ellipticities and rotation patterns. When different radial regions are analyzed, we find that the rotation amplitude decreases from the center toward the external regions. Fe-poor and Fe-rich stars of ? Centauri are radially anisotropic in the central region and show similar degrees of anisotropy. We also investigate the stellar populations with different light-element abundances and find that their N-rich stars exhibit higher ellipticity than N-poor stars. In ? Centauri both stellar groups are radially anisotropic. Interestingly, N-rich, Fe-rich stars exhibit different rotation patterns than N-poor stars with similar metallicities. The stellar populations with different nitrogen of M22 exhibit similar rotation patterns and isotropic motions. We discuss these findings in the context of the formation of multiple populations.
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| 4. |
- Marino, A. F., et al.
(författare)
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Iron and s-elements abundance variations in NGC 5286 : comparison with 'anomalous' globular clusters and Milky Way satellites
- 2015
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 450:1, s. 815-845
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Tidskriftsartikel (refereegranskat)abstract
- We present a high-resolution spectroscopic analysis of 62 red giants in the Milky Way globular cluster (GC) NGC 5286. We have determined abundances of representative light proton-capture, a, Fe-peak and neutron-capture element groups, and combined them with photometry of multiple sequences observed along the colour-magnitude diagram. Our principal results are: (i) a broad, bimodal distribution in s-process element abundance ratios, with two main groups, the s-poor and s-rich groups; (ii) substantial star-to-star Fe variations, with the s-rich stars having higher Fe, e.g. <[Fe/H]>(s-rich) - <[Fe/H]>(s-poor) similar to 0.2 dex; and (iii) the presence of O-Na-Al (anti) correlations in both stellar groups. We have defined a new photometric index, c(BVI) = (B - V) -(V - I), to maximize the separation in the colour-magnitude diagram between the two stellar groups with different Fe and s-element content, and this index is not significantly affected by variations in light elements (such as the O-Na anticorrelation). The variations in the overall metallicity present in NGC 5286 add this object to the class of anomalous GCs. Furthermore, the chemical abundance pattern of NGC 5286 resembles that observed in some of the anomalous GCs, e.g. M 22, NGC 1851, M 2, and the more extreme omega Centauri, that also show internal variations in s-elements, and in light elements within stars with different Fe and s-elements content. In view of the common variations in s-elements, we propose the term s-Fe-anomalous GCs to describe this sub-class of objects. The similarities in chemical abundance ratios between these objects strongly suggest similar formation and evolution histories, possibly associated with an origin in tidally disrupted dwarf satellites.
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