Browsing by Author "Monachesi, A."
CAPOS: the bulge Cluster APOgee Survey IV elemental abundances of the bulge globular cluster NGC 6558
(MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 2023-10-20) González-Díaz, D.; Fernández-Trincado, J. G.; Villanova, S.; Geisler, D.; Barbuy, B.; Minniti, D.; Beers, T. C.; Bidin, C. M.; Mauro, F.; Muñoz, C.; Tang, B. T.; Soto, M.; Monachesi, A.; Lane, R. R.; Frelijj, H.
This study presents the results concerning six red giant stars members of the globular cluster NGC 6558. Our analysis utilized high-resolution near-infrared spectra obtained through the CAPOS initiative (the APOgee Surv e y of Clusters in the Galactic Bulge), which focuses on surv e ying clusters within the Galactic Bulge, as a component of the Apache Point Observatory Galactic Evolution Experiment II surv e y (APOGEE-2). We employ the Brussels Automatic Code for Characterizing High accUracy Spectra ( BACCHUS ) code to provide line-by-line elemental-abundances for Fe-peak (Fe, Ni), alpha-(O, Mg, Si, Ca, Ti), light-(C, N), odd-Z (Al), and the s-process element (Ce) for the four stars with high-signal-to-noise ratios. This is the first reliable measure of the CNO abundances for NGC 6558. Our analysis yields a mean metallicity for NGC 6558 of ([Fe/H]) = -1.15 +/- 0.08, with no evidence for a metallicity spread. We find a Solar Ni abundance, ([Ni/Fe]) similar to + 0.01, and a moderate enhancement of alpha-elements, ranging between + 0.16 and < + 0.42, and a slight enhancement of the s-process element ([Ce/Fe]) similar to + 0.19. We also found low levels of ([Al/Fe]) similar to + 0.09, but with a strong enrichment of nitrogen, [N/Fe] > + 0.99, along with a low level of carbon, [C/Fe] < -0.12. This behaviour of Nitrogen-Carbon is a typical chemical signature for the presence of multiple stellar populations in virtually all GCs; this is the first time that it is reported in NGC 6558. We also observed a remarkable consistency in the behaviour of all the chemical species compared to the other CAPOS bulge GCs of the same metallicity.
Chemo-dynamical tagging in the outskirts: The origins of stellar substructures in the Magellanic Clouds
(ASTRONOMY & ASTROPHYSICS, 2023-12-12) Munoz, C.; Monachesi, A.; Nidever, D. L.; Majewski, S. R.; Cheng, X. L.; Olsen, K.; Choi, Y.; Zivick, P.; Geisler, D.; Almeida, A.; Munoz, R. R.; Nitschelm, C.; Roman-Lopes, A.; Lane, R. R.; Fernández-Trincado, J. G.
We present the first detailed chemical analysis from APOGEE-2S observations of stars in six regions of recently discovered substructures in the outskirts of the Magellanic Clouds extending to 20(degrees) from the Large Magellanic Cloud (LMC) center. We also present, for the first time, the metallicity and alpha-abundance radial gradients of the LMC and the Small Magellanic Cloud (SMC) out to 11(degrees) and 6(degrees), respectively. Our chemical tagging includes 13 species including light, alpha-, and Fe-peak elements. We find that the abundances of all of these chemical elements in stars populating two regions in the northern periphery, along the northern "stream-like" feature, show good agreement with the chemical patterns of the LMC, and thus likely have an LMC origin. For substructures located in the southern periphery of the LMC we find more complex chemical and kinematical signatures, indicative of a mix of LMC-like and SMC-like populations. The southern region closest to the LMC shows better agreement with the LMC, whereas that closest to the SMC shows a much better agreement with the SMC chemical pattern. When combining this information with 3D kinematical information for these stars, we conclude that the southern region closest to the LMC likely has an LMC origin, whereas that closest to the SMC has an SMC origin and the other two southern regions have a mix of LMC and SMC origins. Our results add to the evidence that the southern substructures of the LMC periphery are the product of close interactions between the LMC and SMC, and thus likely hold important clues that can constrain models of their detailed dynamical histories.
Galaxy evolution in compact groups - I. Revealing a transitional galaxy population through a multiwavelength approach
(MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 2023-07-28) Montaguth, G. P.; Torres-Flores, S.; Monachesi, A.; Gómez, F. A.; Lima-Dias, C.; Cortesi, A.; de Oliveira, C. M.; Telles, E.; Panda, S.; Grossi, M.; Lopes, P. A. A.; Hernandez-Jimenez, J. A.; Kanaan, A.; Ribeiro, T.; Schoenell, W.
Compact groups (CGs) of galaxies show members with morphological disturbances, mainly products of galaxy-galaxy interactions, thus making them ideal systems to study galaxy evolution, in high-density environment. To understand how this environment affects the properties of galaxies, we select a sample of 340 CGs in the Stripe 82 region, for a total of 1083 galaxies, and a sample of 2281 field galaxies as a control sample. By performing a multiwavelength morphological fitting process using Southern Photometric Local Universe Survey data, we divide our sample into early-type galaxies (ETGs), late-type galaxies (LTGs), and transition galaxies using the r-band Sersic index and the colour (u - r). We find a bimodal distribution in the plane of the effective radius - Sersic index, where a secondary 'peculiar' galaxy population of smaller and more compact galaxies is found in CGs, which is not observed in the control sample. This indicates that galaxies are undergoing a morphological transformation in CGs. In addition, we find significant statistical differences in the distribution of specific star-formation rate (sSFR) when we compare both environments for LTGs and ETGs. We also find a higher fraction of quenched galaxies and a lower median sSFR in CGs than in the control sample, suggesting the existence of environmental effects favouring the cessation of star formation, regardless of galaxy type. Our results support the notion that CGs promote morphological and physical transformations, highlighting their potential as ideal systems for galaxy pre-processing.
Saying Hallo to M94's Stellar Halo: Investigating the Accretion History of the Largest Pseudobulge Host in the Local Universe
(ASTROPHYSICAL JOURNAL, 2023-04-01) Gozman, K.; Bell, E. F.; Smercina, A.; Price, P.; Bailin, J.; de Jong, R. S; D'Souza, R; Jang, I. S.; Monachesi, A.; Slater, C.
It is not yet settled how the combination of secular processes and merging gives rise to the bulges and pseudobulges of galaxies. The nearby (D similar to 4.2 Mpc) disk galaxy M94 (NGC 4736) has the largest pseudobulge in the local universe, and offers a unique opportunity for investigating the role of merging in the formation of its pseudobulge. We present a first ever look at M94's stellar halo, which we expect to contain a fossil record of M94's past mergers. Using Subaru's Hyper Suprime-Cam, we resolve and identify red giant branch (RGB) stars in M94's halo, finding two distinct populations. After correcting for completeness through artificial star tests, we can measure the radial profile of each RGB population. The metal-rich RGB stars show an unbroken exponential profile to a radius of 30 kpc that is a clear continuation of M94's outer disk. M94's metal-poor stellar halo is detectable over a wider area and clearly separates from its metal-rich disk. By integrating the halo density profile, we infer a total accreted stellar mass of similar to 2.8 x 10(8) M-circle dot, with a median metallicity of [M/H] = -1.4. This indicates that M94's most-massive past merger was with a galaxy similar to, or less massive than, the Small Magellanic Cloud. Few nearby galaxies have had such a low-mass dominant merger; therefore we suggest that M94's pseudobulge was not significantly impacted by merging.