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Register a new userDetection of multiple stellar populations in extragalactic massive clusters with JWST
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The discovery both through spectroscopy and photometry of multiple stellar populations in Galactic globular clusters, and in Magellanic Clouds massive intermediate-age and old clusters, has led to a major change in our views about the formation of these objects. To date, none of the proposed scenarios is able to explain quantitatively all chemical patterns observed in individual clusters, and an extension of the study of multiple populations to resolved extragalactic massive clusters beyond the Magellanic Clouds would be welcome, for it would enable to investigate and characterize the presence of multiple populations in different environments and age ranges. To this purpose, the James Webb Space Telescope can potentially play a major role. On the one hand, the JWST promises direct observations of proto-globular cluster candidates at high redshift; on the other hand, it can potentially push to larger distances the sample of resolved clusters with detected multiple populations. In this paper we have addressed this second goal. Using theoretical stellar spectra and stellar evolution models, we have investigated the effect of multiple population chemical patterns on synthetic magnitudes in the JWST infrared NIRCam filters. We have identified the colours (F150W-F460M), (F115W-F460M) and pseudocolours C_{F150W,F460M,F115W}=(F150W-F460M)-(F460M-F115W), C_{F150W,F277W,F115W}=(F150W-F277W)-(F277W-F115W), as diagnostics able to reveal the presence of multiple populations along the red giant branches of old and intermediate age clusters. Using the available on-line simulator for the NIRCam detector, we have estimated that multiple populations can be potentially detected --depending on the exposure times, exact filter combination used, plus the extent of the abundance variations and the cluster [Fe/H]--out to a distance of about 5Mpc (approximately the distance to the M83 group).
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The internal dynamics of multiple stellar populations in Globular Clusters (GCs) provides unique constraints on the physical processes responsible for their formation. Specifically, the present-day kinematics of cluster stars, such as rotation and velocity dispersion, seems to be related to the initial configuration of the system. In recent work (Milone et al. 2018), we analyzed for the first time the kinematics of the different stellar populations in NGC0104 (47Tucanae) over a large field of view, exploiting the Gaia Data Release 2 proper motions combined with multi-band ground-based photometry. In this paper, based on the work by Cordoni et al. (2019), we extend this analysis to six GCs, namely NGC0288, NGC5904 (M5), NGC6121 (M4), NGC6752, NGC6838 (M71) and further explore NGC0104. Among the analyzed clusters only NGC0104 and NGC5904 show significant rotation on the plane of the sky. Interestingly, multiple stellar populations in NGC5904 exhibit different rotation curves.
This is the second paper in our series about the search for multiple populations in Magellanic Cloud star clusters using the Hubble Space Telescope. Here we report the detection of multiple stellar populations in the colour-magnitude diagrams of the intermediate-age clusters Lindsay 1, NGC 416 and NGC 339. With ages between 6.0 and 7.5 Gyr, these clusters are the youngest ones in which chemical abundance spreads have been detected so far. This confirms that the appearance of multiple populations is not restricted to only ancient globular clusters, but may also be a common feature in clusters as young as 6 Gyr. Our results are in agreement with a recent spectroscopic study of Lindsay 1. We found that the fraction of enriched stars in NGC 416 is ~45% whereas it is ~25% in NGC 339 and ~36% in Lindsay 1. Similar to NGC 121, these fractions are lower than the average value for globular clusters in the Milky Way.
The internal dynamics of multiple stellar populations in Globular Clusters (GCs) provides unique constraints on the physical processes responsible for their formation. Specifically, the present-day kinematics of cluster stars, such as rotation and velocity-dispersion, could be related to the initial configuration of the system. In recent work, we provided the first study of the kinematics of different stellar populations in NGC$,$0104 over a large field of view in the plane of the sky, exploiting Gaia Data Release 2 (DR2) proper motions combined with multi-band ground-based photometry. In this paper, we combine Gaia DR2 proper motions with Very Large Telescope radial velocities to investigate the kinematics along the line of sight and in the plane of the sky of multiple populations in seven GCs, namely NGC$,$0104, NGC$,$0288, NGC$,$5904, NGC$,$6121, NGC$,$6254, NGC$,$6752 and NGC$,$6838. Among the analyzed clusters only NGC$,$0104 and NGC$,$5904 show significant rotation. Separating our sample into two groups of first- and second-population stars (1P and 2P) we find that overall these two populations exhibit a similar rotation pattern in NGC$,$0104. However, some hints of different rotation are observed in the external regions of this cluster. Interestingly, 1P and 2P stars in NGC$,$5904 show different rotation curves, with distinct phases and such difference is significant at the $sim$2.5-$sigma$ level. The analysis of the velocity-dispersion profiles of multiple populations confirms that 2P stars of NGC$,$0104 show stronger anisotropy than the 1P.
We investigate the multiple stellar populations of the globular clusters M3, M5, M13, and M71 using $g^prime$ and intermediate-band CN-$lambda 3883$ photometry obtained with the WIYN 0.9-m telescope on Kitt Peak. We find a strong correlation between red giant stars CN$-g^prime$ colors and their spectroscopic sodium abundances, thus demonstrating the efficacy of the two-filter system for stellar population studies. In all four clusters, the observed spread in red giant branch CN$-g^prime$ colors is wider than that expected from photometric uncertainty, confirming the well-known chemical inhomogeneity of these systems. M3 and M13 show clear evidence for a radial dependence in the CN-band strengths of its red giants, while the evidence for such a radial dependence of CN strengths in M5 is ambiguous. Our data suggest that the dynamically old, relatively metal-rich M71 system is well mixed, as it shows no evidence for chemical segregation. Finally, we measure the radial gradients in the integrated CN$-g^prime$ color of the clusters and find that such gradients are easily detectable in the integrated light. We suggest that photometric observations of color gradients within globular clusters throughout the Local Group can be used to characterize their multiple populations, and thereby constrain the formation history of globular clusters in different galactic environments.
Multiple stellar populations (MPs) are a distinct characteristic of Globular Clusters (GCs). Their general properties have been widely studied among main sequence, red giant branch (RGB) and horizontal branch (HB) stars, but a common framework is still missing at later evolutionary stages. We studied the MP phenomenon along the AGB sequences in 58 GCs, observed with the Hubble Space Telescope in ultraviolet (UV) and optical filters. By using UV-optical color-magnitude diagrams, we selected the AGB members of each cluster and identified the AGB candidates of the metal-enhanced population in type II GCs. We studied the photometric properties of AGB stars and compared them to theoretical models derived from synthetic spectra analysis. We observe the following features: i) the spread of AGB stars in photometric indices sensitive to variations of light-elements and helium is typically larger than that expected from photometric errors; ii) the fraction of metal-enhanced stars in the AGB is lower than in the RGB in most of the type II GCs; iii) the fraction of 1G stars derived from the chromosome map of AGB stars in 15 GCs is larger than that of RGB stars; v) the AGB/HB frequency correlates with the average mass of the most helium-enriched population. These findings represent a clear evidence of the presence of MPs along the AGB of Galactic GCs and indicate that a significant fraction of helium-enriched stars, which have lower mass in the HB, does not evolve to the AGB phase, leaving the HB sequence towards higher effective temperatures, as predicted by the AGB-manque scenario.
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