Browsing by Author "Tissera, Patricia B."

Now showing 1 - 15 of 15
  • Thumbnail Image
    Item
    Assembling a high-precision abundance catalogue of solar twins in GALAH for phylogenetic studies
    (2024) Walsen, Kurt; Jofre, Paula; Buder, Sven; Yaxley, Keaghan; Das, Payel; Yates, Robert M.; Hua, Xia; Signor, Theosamuele; Eldridge, Camilla; Rojas-Arriagada, Alvaro; Tissera, Patricia B.; Johnston, Evelyn; Aguilera-Gomez, Claudia; Zoccali, Manuela; Gilmore, Gerry; Foley, Robert
    Stellar chemical abundances have proved themselves a key source of information for understanding the evolution of the Milky Way, and the scale of major stellar surveys such as GALAH have massively increased the amount of chemical data available. However, progress is hampered by the level of precision in chemical abundance data as well as the visualization methods for comparing the multidimensional outputs of chemical evolution models to stellar abundance data. Machine learning methods have greatly improved the former; while the application of tree-building or phylogenetic methods borrowed from biology are beginning to show promise with the latter. Here, we analyse a sample of GALAH solar twins to address these issues. We apply The Cannon algorithm to generate a catalogue of about 40 000 solar twins with 14 high precision abundances which we use to perform a phylogenetic analysis on a selection of stars that have two different ranges of eccentricities. From our analyses, we are able to find a group with mostly stars on circular orbits and some old stars with eccentric orbits whose age-[Y/Mg] relation agrees remarkably well with the chemical clocks published by previous high precision abundance studies. Our results show the power of combining survey data with machine learning and phylogenetics to reconstruct the history of the Milky Way.
  • No Thumbnail Available
    Item
    Disentangling the Galactic Halo with APOGEE. I. Chemical and Kinematical Investigation of Distinct Metal-poor Populations
    (2018) Hayes, Christian R.; Majewski, Steven R.; Shetrone, Matthew; Fernandez-Alvar, Emma; Allende Prieto, Carlos; Schuster, William J.; Carigi, Leticia; Cunha, Katia; Smith, Verne V.; Sobeck, Jennifer; Almeida, Andres; Beers, Timothy C.; Carrera, Ricardo; Fernandez-Trincado, J. G.; Garcia-Hernandez, D. A.; Geisler, Doug; Lane, Richard R.; Lucatello, Sara; Matthews, Allison M.; Minniti, Dante; Nitschelm, Christian; Tang, Baitian; Tissera, Patricia B.; Zamora, Olga
    We find two chemically distinct populations separated relatively cleanly in the [Fe/H]-[Mg/Fe] plane, but also distinguished in other chemical planes, among metal-poor stars (primarily with metallicities [Fe/H] < -0.9) observed by the Apache Point Observatory Galactic Evolution Experiment (APOGEE) and analyzed for Data Release 13 (DR13) of the Sloan Digital Sky Survey. These two stellar populations show the most significant differences in their [X/Fe] ratios for the alpha-elements, C+N, Al, and Ni. In addition to these populations having differing chemistry, the low metallicity high-Mg population (which we denote "the HMg population") exhibits a significant net Galactic rotation, whereas the low-Mg population (or "the LMg population") has halo-like kinematics with little to no net rotation. Based on its properties, the origin of the LMg population is likely an accreted population of stars. The HMg population shows chemistry (and to an extent kinematics) similar to the thick disk, and is likely associated with in situ formation. The distinction between the LMg and HMg populations mimics the differences between the populations of low-and high-a halo stars found in previous studies, suggesting that these are samples of the same two populations.
  • No Thumbnail Available
    Item
    Exploring the outskirts of the EAGLE disc galaxies
    (2022) Varela-Lavin, Silvio; Tissera, Patricia B.; Gomez, Facundo A.; Bignone, Lucas A.; Lagos, Claudia del P.
    Observations show that the surface brightness of disc galaxies can be well-described by a single exponential (TI), up-bending (TIII), or down-bending (TII) profiles in the outskirts. Here we characterize the mass surface densities of simulated late-type galaxies from the eagle project according to their distribution of mono-age stellar populations, the star formation activity, and angular momentum content. We find a clear correlation between the inner scale lengths and the stellar spin parameter, lambda, for all three disc types with lambda > 0.35. The outer scale lengths of TII and TIII discs show a positive trend with lambda, albeit weaker for the latter. TII discs prefer fast rotating galaxies. With regards to the stellar age distribution, negative and U-shape age profiles are the most common for all disc types. Positive age profiles are determined by a more significant contribution of young stars in the central regions, which decrease rapidly in the outer parts. TII discs prefer relative higher contributions of old stars compared to other mono-age populations across the discs whereas TIII discs become progressively more dominated by intermediate age (2-6 Gyr) stars for increasing radius. The change in slope of the age profiles is located after the break of the mass surface density. We find evidence of larger flaring for the old stellar populations in TIII systems compared to TI and TII, which could indicate the action of other processes. Overall, the relative distributions of mono-age stellar populations and the dependence of the star formation activity on radius are found to shape the different disc types and age profiles.
  • No Thumbnail Available
    Item
    Lopsided galaxies in a cosmological context: a new galaxy-halo connection
    (2023) Varela-Lavin, Silvio; Gomez, Facundo A.; Tissera, Patricia B.; Besla, Gurtina; Garavito-Camargo, Nicolas; Marinacci, Federico; Laporte, Chervin F. P.
    Disc galaxies commonly show asymmetric features in their morphology, such as warps and lopsidedness. These features can provide key information regarding the recent evolution of a given disc galaxy. In the nearby Universe, up to & SIM;30 per cent of late-type galaxies display a global non-axisymmetric lopsided mass distribution. However, the origin of this perturbation is not well understood. In this work, we study the origin of lopsided perturbations in simulated disc galaxies extracted from the TNG50 simulation of the IllustrisTNG project. We statistically explore different excitation mechanisms for this perturbation, such as direct satellite tidal interactions and distortions of the underlying dark matter distributions. We also characterize the main physical conditions that lead to lopsided perturbations. 50 per cent of our sample galaxy have lopsided modes m = 1 greater than & SIM;0.12. We find a strong correlation between internal galaxy properties, such as central stellar surface density and disc radial extension with the strength of lopsided modes. The majority of lopsided galaxies have lower central surface densities and more extended discs than symmetric galaxies. As a result, such lopsided galaxies are less self-gravitationally cohesive, and their outer disc region is more susceptible to different types of external perturbations. However, we do not find strong evidence that tidal interactions with satellite galaxies are the main driving agent of lopsided modes. Lopsided galaxies tend to live in asymmetric dark matter haloes with high spin, indicating strong galaxy-halo connections in late-type lopsided galaxies.
  • No Thumbnail Available
    Item
    Lopsidedness as a tracer of early galactic assembly history
    (2023) Dolfi, Arianna; Gomez, Facundo A.; Monachesi, Antonela; Varela-Lavin, Silvio; Tissera, Patricia B.; Sifon, Cristobal; Galaz, Gaspar
    Large-scale asymmetries (i.e. lopsidedness) are a common feature in the stellar density distribution of nearby disc galaxies both in low- and high-density environments. In this work, we characterize the present-day lopsidedness in a sample of 1435 disc-like galaxies selected from the TNG50 simulation. We find that the percentage of lopsided galaxies (10 percent-30 percent) is in good agreement with observations if we use similar radial ranges to the observations. However, the percentage (58 percent) significantly increases if we extend our measurement to larger radii. We find a mild or lack of correlation between lopsidedness amplitude and environment at z = 0 and a strong correlation between lopsidedness and galaxy morphology regardless of the environment. Present-day galaxies with more extended discs, flatter inner galactic regions, and lower central stellar mass density (i.e. late-type disc galaxies) are typically more lopsided than galaxies with smaller discs, rounder inner galactic regions, and higher central stellar mass density (i.e. early-type disc galaxies). Interestingly, we find that lopsided galaxies have, on average, a very distinct star formation history within the last 10 Gyr, with respect to their symmetric counterparts. Symmetric galaxies have typically assembled at early times (similar to 8-6 Gyr ago) with relatively short and intense bursts of central star formation, while lopsided galaxies have assembled on longer time-scales and with milder initial bursts of star formation, continuing building up their mass until z = 0. Overall, these results indicate that lopsidedness in present-day disc galaxies is connected to the specific evolutionary histories of the galaxies that shaped their distinct internal properties.
  • No Thumbnail Available
    Item
    Machine learning for galactic archaeology: a chemistry-based neural network method for identification of accreted disc stars
    (2022) Tronrud, Thorold; Tissera, Patricia B.; Gomez, Facundo A.; Grand, Robert J. J.; Pakmor, Ruediger; Marinacci, Federico; Simpson, Christine M.
    We develop a method ('Galactic Archaeology Neural Network', gann) based on neural network models (NNMs) to identify accreted stars in galactic discs by only their chemical fingerprint and age, using a suite of simulated galaxies from the Auriga Project. We train the network on the target galaxy's own local environment defined by the stellar halo and the surviving satellites. We demonstrate that this approach allows the detection of accreted stars that are spatially mixed into the disc. Two performance measures are defined - recovery fraction of accreted stars, f(recov) and the probability that a star with a positive (accreted) classification is a true-positive result, P(TP). As the NNM output is akin to an assigned probability (P-a), we are able to determine positivity based on flexible threshold values that can be adjusted easily to refine the selection of presumed-accreted stars. We find that gann identifies accreted disc stars within simulated galaxies, with high f(recov) and/or high P(TP). We also find that stars in Gaia-Enceladus-Sausage (GES) mass systems are over 50 per cent recovered by our NNMs in the majority (18/24) of cases. Additionally, nearly every individual source of accreted stars is detected at 10 per cent or more of its peak stellar mass in the disc. We also demonstrate that a conglomerated NNM, trained on the halo and satellite stars from all of the Auriga galaxies provides the most consistent results, and could prove to be an intriguing future approach as our observational capabilities expand.
  • No Thumbnail Available
    Item
    Milky Way-like galaxies: stellar population properties of dynamically defined discs, bulges and stellar haloes
    (2022) Ortega-Martinez, Sara; Obreja, Aura; Dominguez-Tenreiro, Rosa; Pedrosa, Susana E.; Rosas-Guevara, Yetli; Tissera, Patricia B.
    The formation of galaxies can be understood in terms of the assembly patterns of each type of galactic component. To perform this kind of analysis, it is necessary to define some criteria to separate those components. Decomposition methods based on dynamical properties are more physically motivated than photometry-based ones. We use the unsupervised Gaussian Mixture model of galactic structure finder to extract the components of a sub-sample of galaxies with Milky Way-like masses from the eagle simulations. A clustering in the space of first- and second-order dynamical moments of all identified substructures reveals five types of galaxy components: thin and thick discs, stellar haloes, bulges and spheroids. We analyse the dynamical, morphological and stellar population (SP) properties of these five component types, exploring to what extent these properties correlate with each other, and how much they depend on the total galaxy stellar and dark matter halo masses. All galaxies contain a bulge, a stellar halo and a disc. In total, 60 per cent of objects host two discs (thin and thick), and 68 per cent host also a spheroid. The dynamical disc-to-total ratio does not depend on stellar mass, but the median rotational velocities of the two discs do. Thin discs are well separated in stellar ages, [Fe/H] and alpha-enhancement from the three dispersion-dominated components, while thick discs are in between. Except for thin discs, all components show correlations among their SP properties: older ages mean lower metallicities and larger alpha-enhancement. Finally, we quantify the weak dependence of SP properties on each component's dynamics.
  • No Thumbnail Available
    Item
    Modelling H2 and its effects on star formation using a joint implementation of gadget-3 and KROME
    (2021) Sillero, Emanuel; Tissera, Patricia B.; Lambas, Diego G.; Bovino, Stefano; Schleicher, Dominik R.; Grassi, Tommaso; Bruzual, Gustavo; Charlot, Stephane
    We present p-gadget3-k, an updated version of gadget-3, that incorporates the chemistry package krome. p-gadget3-k follows the hydrodynamical and chemical evolution of cosmic structures, incorporating the chemistry and cooling of H-2 and metal cooling in non-equilibrium. We performed different runs of the same ICs to assess the impact of various physical parameters and prescriptions, namely gas metallicity, molecular hydrogen formation on dust, star formation recipes including or not H-2 dependence, and the effects of numerical resolution. We find that the characteristics of the simulated systems, both globally and at kpc-scales, are in good agreement with several observable properties of molecular gas in star-forming galaxies. The surface density profiles of star formation rate (SFR) and H-2 are found to vary with the clumping factor and resolution. In agreement with previous results, the chemical enrichment of the gas component is found to be a key ingredient to model the formation and distribution of H-2 as a function of gas density and temperature. A star formation algorithm that takes into account the H-2 fraction together with a treatment for the local stellar radiation field improves the agreement with observed H-2 abundances over a wide range of gas densities and with the molecular Kennicutt-Schmidt law, implying a more realistic modelling of the star formation process.
  • Thumbnail Image
    Item
    On the Evolutionary History of a Simulated Disk Galaxy as Seen by Phylogenetic Trees
    (2024) Silva, Danielle de Brito; Jofre, Paula; Tissera, Patricia B.; Yaxley, Keaghan J.; Jara, Jenny Gonzalez; Eldridge, Camilla J. L.; Sillero, Emanuel; Yates, Robert M.; Hua, Xia; Das, Payel; Aguilera-Gomez, Claudia; Johnston, Evelyn J.; Rojas-Arriagada, Alvaro; Foley, Robert; Gilmore, Gerard
    Phylogenetic methods have long been used in biology and more recently have been extended to other fields-for example, linguistics and technology-to study evolutionary histories. Galaxies also have an evolutionary history and fall within this broad phylogenetic framework. Under the hypothesis that chemical abundances can be used as a proxy for the interstellar medium's DNA, phylogenetic methods allow us to reconstruct hierarchical similarities and differences among stars-essentially, a tree of evolutionary relationships and thus history. In this work, we apply phylogenetic methods to a simulated disk galaxy obtained with a chemodynamical code to test the approach. We found that at least 100 stellar particles are required to reliably portray the evolutionary history of a selected stellar population in this simulation, and that the overall evolutionary history is reliably preserved when the typical uncertainties in the chemical abundances are smaller than 0.08 dex. The results show that the shapes of the trees are strongly affected by the age-metallicity relation, as well as the star formation history of the galaxy. We found that regions with low star formation rates produce shorter trees than regions with high star formation rates. Our analysis demonstrates that phylogenetic methods can shed light on the process of galaxy evolution.
  • No Thumbnail Available
    Item
    Planes of Satellites around Simulated Disk Galaxies. II. Time-persistent Planes of Kinematically Coherent Satellites in ?CDM
    (2023) Santos-Santos, Isabel; Gamez-Marin, Matias; Dominguez-Tenreiro, Rosa; Tissera, Patricia B.; Bignone, Lucas; Pedrosa, Susana E.; Artal, Hector; Gomez-Flechoso, M. Angeles; Rufo-Pastor, Victor; Martinez-Serrano, Francisco; Serna, Arturo
    We use two zoom-in ?CDM hydrodynamical simulations of massive disk galaxies to study the possible existence of fixed satellite groups showing a kinematically coherent behavior across evolution (angular momentum conservation and clustering). We identify three such groups in the two simulations, defining kinematically coherent persistent planes (KPPs) that last at least from virialization to z = 0 (more than 7 Gyr). This proves that orbital pole clustering is not necessarily set in at low redshift, representing a long-lived property of galaxy systems. KPPs are thin and oblate, represent similar to 25%-40% of the total number of satellites in the system, and are roughly perpendicular to their corresponding central disk galaxies during certain periods, consistently with Milky Way z = 0 data. KPP satellite members are statistically distinguishable from satellites outside KPPs: they show higher specific orbital angular momenta, orbit more perpendicularly to the central disk galaxy, and have larger pericentric distances than the latter. We numerically prove, for the first time, that KPPs and the best-quality positional planes share the same space configuration across time, such that KPPs act as "skeletons" preventing the latter from being washed out in short timescales. In one of the satellite-host systems, we witness the late capture of a massive dwarf galaxy endowed with its own satellite system, also organized into a KPP configuration prior to its capture. We briefly explore the consequences this event has on the host's KPP and on the possible enhancement of the asymmetry in the number of satellites rotating in one sense or the opposite within the KPP.
  • No Thumbnail Available
    Item
    The Eighteenth Data Release of the Sloan Digital Sky Surveys: Targeting and First Spectra from SDSS-V
    (2023) Almeida, Andres; Anderson, Scott F.; Argudo-Fernandez, Maria; Badenes, Carles; Barger, Kat; Barrera-Ballesteros, Jorge K.; Bender, Chad F.; Benitez, Erika; Besser, Felipe; Bird, Jonathan C.; Bizyaev, Dmitry; Blanton, Michael R.; Bochanski, John; Bovy, Jo; Brandt, William Nielsen; Brownstein, Joel R.; Buchner, Johannes; Bulbul, Esra; Burchett, Joseph N.; Diaz, Mariana Cano; Carlberg, Joleen K.; Casey, Andrew R.; Chandra, Vedant; Cherinka, Brian; Chiappini, Cristina; Coker, Abigail A.; Comparat, Johan; Conroy, Charlie; Contardo, Gabriella; Cortes, Arlin; Covey, Kevin; Crane, Jeffrey D.; Cunha, Katia; Dabbieri, Collin; Davidson, James W.; Davis, Megan C.; de Andrade Queiroz, Anna Barbara; De Lee, Nathan; Mendez Delgado, Jose Eduardo; Demasi, Sebastian; Di Mille, Francesco; Donor, John; Dow, Peter; Dwelly, Tom; Eracleous, Mike; Eriksen, Jamey; Fan, Xiaohui; Farr, Emily; Frederick, Sara; Fries, Logan; Frinchaboy, Peter; Gaensicke, Boris T.; Ge, Junqiang; Gonzalez Avila, Consuelo; Grabowski, Katie; Grier, Catherine; Guiglion, Guillaume; Gupta, Pramod; Hall, Patrick; Hawkins, Keith; Hayes, Christian R.; Hermes, J. J.; Hernandez-Garcia, Lorena; Hogg, David W.; Holtzman, Jon A.; Ibarra-Medel, Hector Javier; Ji, Alexander; Jofre, Paula; Johnson, Jennifer A.; Jones, Amy M.; Kinemuchi, Karen; Kluge, Matthias; Koekemoer, Anton; Kollmeier, Juna A.; Kounkel, Marina; Krishnarao, Dhanesh; Krumpe, Mirko; Lacerna, Ivan; Lago, Paulo Jakson Assuncao; Laporte, Chervin; Liu, Chao; Liu, Ang; Liu, Xin; Lopes, Alexandre Roman; Macktoobian, Matin; Majewski, Steven R.; Malanushenko, Viktor; Maoz, Dan; Masseron, Thomas; Masters, Karen L.; Matijevic, Gal; McBride, Aidan; Medan, Ilija; Merloni, Andrea; Morrison, Sean; Myers, Natalie; Meszaros, Szabolcs; Negrete, C. Alenka; Nidever, David L.; Nitschelm, Christian; Oravetz, Daniel; Oravetz, Audrey; Pan, Kaike; Peng, Yingjie; Pinsonneault, Marc H.; Pogge, Rick; Qiu, Dan; Ramirez, Solange V.; Rix, Hans-Walter; Rosso, Daniela Fernandez; Runnoe, Jessie; Salvato, Mara; Sanchez, Sebastian F.; Santana, Felipe A.; Saydjari, Andrew; Sayres, Conor; Schlaufman, Kevin C.; Schneider, Donald P.; Schwope, Axel; Serna, Javier; Shen, Yue; Sobeck, Jennifer; Song, Ying-Yi; Souto, Diogo; Spoo, Taylor; Stassun, Keivan G.; Steinmetz, Matthias; Straumit, Ilya; Stringfellow, Guy; Sanchez-Gallego, Jose; Taghizadeh-Popp, Manuchehr; Tayar, Jamie; Thakar, Ani; Tissera, Patricia B.; Tkachenko, Andrew; Toledo, Hector Hernandez; Trakhtenbrot, Benny; Fernandez-Trincado, Jose G.; Troup, Nicholas; Trump, Jonathan R.; Tuttle, Sarah; Ulloa, Natalie; Vazquez-Mata, Jose Antonio; Alfaro, Pablo Vera; Villanova, Sandro; Wachter, Stefanie; Weijmans, Anne-Marie; Wheeler, Adam; Wilson, John; Wojno, Leigh; Wolf, Julien; Xue, Xiang-Xiang; Ybarra, Jason E.; Zari, Eleonora; Zasowski, Gail
    The eighteenth data release (DR18) of the Sloan Digital Sky Survey (SDSS) is the first one for SDSS-V, the fifth generation of the survey. SDSS-V comprises three primary scientific programs or "Mappers": the Milky Way Mapper (MWM), the Black Hole Mapper (BHM), and the Local Volume Mapper. This data release contains extensive targeting information for the two multiobject spectroscopy programs (MWM and BHM), including input catalogs and selection functions for their numerous scientific objectives. We describe the production of the targeting databases and their calibration and scientifically focused components. DR18 also includes & SIM;25,000 new SDSS spectra and supplemental information for X-ray sources identified by eROSITA in its eFEDS field. We present updates to some of the SDSS software pipelines and preview changes anticipated for DR19. We also describe three value-added catalogs (VACs) based on SDSS-IV data that have been published since DR17, and one VAC based on the SDSS-V data in the eFEDS field.
  • No Thumbnail Available
    Item
    The evolution of the oxygen abundance gradients in star-forming galaxies in the EAGLE simulations
    (2022) Tissera, Patricia B.; Rosas-Guevara, Yetli; Sillero, Emanuel; Pedrosa, Susana E.; Theuns, Tom; Bignone, Lucas
    We analyse the evolution of the oxygen abundance gradient of star-forming galaxies with stellar mass M-* >= 10(9)M(circle dot) in the EAGLE simulation over the redshift range z = [0, 2.5]. We find that the median metallicity gradient of the simulated galaxies is close to zero at all z, whereas the scatter around the median increases with z. The metallicity gradients of individual galaxies can evolve from strong to weak and vice versa, since mostly low-metallicity gas accretes on to the galaxy, resulting in enhanced star formation and ejection of metal-enriched gas by energy feedback. Such episodes of enhanced accretion, mainly dominated by major mergers, are more common at higher z and hence contribute to increasing the diversity of gradients. For galaxies with negative metallicity gradients, we find a redshift evolution of similar to -0.03 dex kpc(-1)/delta z. A positive mass dependence is found at z <= 0.5, which becomes slightly stronger for higher redshifts and, mainly, for M-* < 10(9.)(5) M-circle dot. Only galaxies with negative metallicity gradients define a correlation with galaxy size, consistent with an inside-out formation scenario. Our findings suggest that major mergers and/or significant gas accretion can drive strong negative or positive metallicity gradients. The first ones are preferentially associated with disc-dominated galaxies, and the second ones with dispersion-dominated systems. The comparison with forthcoming observations at high redshift will allow a better understanding of the potential role of metallicity gradients as a chemical probe of galaxy formation.
  • Thumbnail Image
    Item
    The Origin of Kinematically Persistent Planes of Satellites as Driven by the Early Evolution of the Cosmic Web in ΛCDM
    (2024) Gamez-Marin, Matias; Santos-Santos, Isabel; Dominguez-Tenreiro, Rosa; Pedrosa, Susana E.; Tissera, Patricia B.; Gomez-Flechoso, M. Angeles; Artal, Hector
    Kinematically persistent planes (KPPs) of satellites are fixed sets of satellites co-orbiting around their host galaxy, whose orbital poles are conserved and clustered across long cosmic time intervals. They play the role of "skeletons," ensuring the long-term durability of positional planes. We explore the physical processes behind their formation in terms of the dynamics of the local cosmic web (CW), characterized via the so-called Lagrangian volumes (LVs) built up around two zoom-in, cosmological hydro-simulations of Milky Way-mass disk galaxy + satellites systems, where three KPPs have been identified. By analyzing the LV deformations in terms of the reduced tensor of inertia (TOI), we find an outstanding alignment between the LV principal directions and the KPP satellites' orbital poles. The most compressive local mass flows (along the e 3 eigenvector) are strong at early times, feeding the so-called e 3 -structure, while the smallest TOI axis rapidly decreases. The e 3 -structure collapse marks the end of this regime and is the timescale for the establishment of satellite orbital pole clustering when the Universe is less than or similar to 4 Gyr old. KPP protosatellites aligned with e 3 are those whose orbital poles are either aligned from early times or have been successfully bent at e 3 -structure collapse. KPP satellites associated with e 1 tend to have early trajectories already parallel to e 3 . We show that KPPs can arise as a result of the Lambda CDM-predicted large-scale dynamics acting on particular sets of protosatellites, the same dynamics that shape the local CW environment.
  • No Thumbnail Available
    Item
    The Photometric Metallicity and Carbon Distributions of the Milky Way's Halo and Solar Neighborhood from S-PLUS Observations of SDSS Stripe 82
    (2021) Whitten, Devin D.; Placco, Vinicius M.; Beers, Timothy C.; An, Deokkeun; Lee, Young Sun; Almeida-Fernandes, Felipe; Herpich, Fabio R.; Daflon, Simone; Barbosa, Carlos E.; Perottoni, Helio D.; Rossi, Silvia; Tissera, Patricia B.; Yoon, Jinmi; Youakim, Kris; Schoenell, William; Ribeiro, Tiago; Kanaan, Antonio
    We report photometric estimates of effective temperature, T (eff), metallicity, [Fe/H], carbonicity, [C/Fe], and absolute carbon abundances, A(C), for over 700,000 stars from the Southern Photometric Local Universe Survey (S-PLUS) Data Release 2, covering a substantial fraction of the equatorial Sloan Digital Sky Survey Stripe 82. We present an analysis for two stellar populations: (1) halo main-sequence turnoff stars and (2) K-dwarf stars of mass 0.58 < M/M (circle dot) < 0.75 in the Solar Neighborhood. Application of the Stellar Photometric Index Network Explorer (SPHINX) to the mixed-bandwidth (narrow- plus wide-band) filter photometry from S-PLUS produces robust estimates of the metallicities and carbon abundances in stellar atmospheres over a wide range of temperatures, 4250 < T (eff)(K) < 7000. The use of multiple narrow-band S-PLUS filters enables SPHINX to achieve substantially lower levels of "catastrophic failures" (i.e., large offsets in metallicity estimates relative to spectroscopic determinations) than previous efforts using a single metallicity-sensitive narrow-band filter. We constrain the exponential slope of the Milky Way's K-dwarf halo metallicity distribution function (MDF), lambda (10,[Fe/H]) = 0.85 +/- 0.21, over the metallicity range -2.5 < [Fe/H] < -1.0; the MDF of our local-volume K-dwarf sample is well-represented by a gamma distribution with parameters alpha = 2.8 and beta = 4.2. S-PLUS photometry obtains absolute carbon abundances with a precision of similar to 0.35 dex for stars with T (eff) < 6500 K. We identify 364 candidate carbon-enhanced metal-poor stars, obtain assignments of these stars into the Yoon-Beers morphological groups in the A(C)-[Fe/H] space, and we derive the CEMP frequencies.
  • No Thumbnail Available
    Item
    Understanding the Early Stages of Galaxy Formation Using Very Metal-poor Stars from the Hamburg/ESO Survey
    (2023) Carollo, Daniela; Christlieb, Norbert; Tissera, Patricia B.; Sillero, Emanuel
    We explore the chemodynamical properties of a sample of very metal-poor (VMP) stars selected from the Hamburg/ESO survey, matched with Gaia EDR3, in the phase space identified by the three integrals of motion (L-z , E, I-3). Disk and halo orbits are separated by using the criteria defined in Carollo & Chiba. We found 26 stars with [Fe/H] <= -2.5 possessing disk kinematics, of which 13 are extremely metal-poor. At these metallicities, the number of stars with disk kinematics is three times its retrograde counterpart. In the same range of metallicity we also identified 37 halo stars most tightly bound to the gravitational potential of the progenitor halo. The origins of these stars are investigated by comparing the observational results with simulated galaxies from the Aquarius Project and the IllustrisTNG simulations. We found two mechanisms of formation of VMP stars with disk kinematics: accretion from early satellites (which is dominant), and in situ formation. These stars are very old, with ages >12.5 Gyr (z > 5), and they are alpha-enriched. Accretion and in situ formation are also found for the retrograde counterparts, with accretion also being the dominant mode. Contributing accreted satellites have stellar masses in the range 10(6)-10(9) M-circle dot and are very gas-rich. The most bound halo stars are the oldest detected, with a median age of similar to 13.3 Gyr (z similar to 11), and are alpha-enriched. Our finding clearly shows that very old, VMP stars store important information on the first stages of assembly of our Galaxy and its halo.