A Megacam Survey of Outer Halo Satellites. Vi. The Spatially Resolved Star-Formation History of the Carina Dwarf Spheroidal Galaxy*

Santana, Felipe A.; Muñoz, Ricardo R.; Boer, T. J. L. de; Simon, Joshua D.; Geha, Marla; Côté, Patrick; Guzmán, Andrés E.; Stetson, P. B.; Djorgovski, S. G.

doi:10.3847/0004-637x/829/2/86

Cited by 21 publications

(14 citation statements)

References 66 publications

(139 reference statements)

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“…This effect can eventually lead to an overall median age gradient where young stars form in the center of the galaxy and old stars are preferentially found in the outskirts. Qualitatively, this agrees with the observed age and metallicity gradients seen in most dwarf galaxies locally, where younger (more metal-rich) stars lie in the center and older (more metal-poor) stars in the outskirts (Battaglia et al 2006;Faria et al 2007;Beccari et al 2014;McMonigal et al 2014;del Pino et al 2015;Santana et al 2016;Kacharov et al 2017;McQuinn et al 2017;Okamoto et al 2017;Cicuéndez et al 2018;Cicuéndez & Battaglia 2018).…”

supporting

confidence: 88%

A predicted correlation between age gradient and star formation history in FIRE dwarf galaxies

Graus

Bullock

Fitts

et al. 2019

Monthly Notices of the Royal Astronomical Society

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We explore the radial variation of star formation histories in dwarf galaxies simulated with Feedback In Realistic Environments (FIRE) physics. The sample contains 9 lowmass field dwarfs with M star = 10 5 − 10 7 M from previous FIRE results, and a new suite of 17 higher mass field dwarfs with M star = 10 7 − 10 9 M introduced here. We find that age gradients are common in our dwarfs, with older stars dominant at large radii. The strength of the gradient correlates with overall galaxy age such that earlier star formation produces a more pronounced gradient. The relation between formation time and strength of the gradient is driven by both mergers and star-formation feedback. Mergers can both steepen and flatten the age gradient depending on the timing of the merger and star formation history of the merging galaxy. In galaxies without significant mergers, early feedback pushes stars to the outskirts at early times. Interestingly, among galaxies without mergers, those with large dark matter cores have flatter age gradients because these galaxies have more late-time feedback. If real galaxies have age gradients as we predict, stellar population studies that rely on sampling a limited fraction of a galaxy can give a biased view of its global star formation history. We show that central fields can be biased young by a few Gyrs while outer fields are biased old. Fields positioned near the 2D half-light radius will provide the least biased measure of a dwarf galaxy's global star formation history.

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supporting

confidence: 88%

A predicted correlation between age gradient and star formation history in FIRE dwarf galaxies

Graus

Bullock

Fitts

et al. 2019

Monthly Notices of the Royal Astronomical Society

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“…Jablonka et al 2015) Conversely, there are hints that lower mass classical dSphs, such as Sextans and Carina, could have a larger dispersion at fixed metallicity. In the case of Carina this is expected because of its star formation history, characterized by at least three distinct bursts (Hurley-Keller et al 1998;Santana et al 2016) that are so far interpreted as resulting from interactions with the Milky Way (Fabrizio et al 2011(Fabrizio et al , 2016Pasetto et al 2011). In Sextans, the observed dispersion in [α/Fe], when data from Aoki et al (2009) and Tafelmeyer et al (2010) are considered, has been attributed to the effect of the smaller number of supernovae enriching the ISM from which the observed stars were born, and to the coexistence of pockets of ISM with various abundances.…”

Section: The α Elementsmentioning

confidence: 99%

Homogeneity in the early chemical evolution of the Sextans dwarf Spheroidal galaxy

Lucchesi,

Lardo,

Primas

et al. 2020

Preprint

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We present the high-resolution spectroscopic analysis of two new extremely metal-poor stars (EMPS) candidates in the dwarf spheroidal galaxy Sextans. These targets were pre-selected from medium resolution spectra centered around the Ca ii triplet in the near-infrared and followed-up at higher resolution with VLT/UVES. We confirm their low metallicities with [Fe/H]=−2.95 and [Fe/H]=−3.01, placing them among the most metal-poor stars known in Sextans. The abundances of 18 elements, including C, Na, the α, Fe-peak, and neutron capture elements, are determined. In particular, we present the first measurements of Zn in a classical dwarf at extremely low metallicity. There has been previous hints of a large scatter in the abundance ratios of the Sextans stellar population around [Fe/H]∼ −3 when compared to other galaxies. We took the opportunity of this work to re-analyse the full sample of EMPS and find a Milky-Way -like plateau and a normal dispersion at fixed metallicity.

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“…According to Clarkson et al (2011), the bulge field BSS frequency (S BSS ), defined as the number of BSS scaled to the number of RC stars, is between 0.3 and 1.23, while for the clusters Ferraro et al (2003) found 0.1 S BSS 1. However, based on a photometric study of a sample of globular clusters and dwarf spheroidals, Santana et al (2013Santana et al ( , 2016 found that the number of BSS grows almost linearly with the total stellar mass of the system; therefore, the BSS frequency in dwarf spheroidals is much higher than in clusters. In addition, when considering that the dynamical state of the bulge is expected to be more similar to that of dwarf spheroidals than of clusters, it is plausible that the bulge BSS frequency provided by Clarkson et al (2011) could be an underestimation.…”

Section: Stellar Ages Determinationmentioning

confidence: 99%

Mapping the stellar age of the Milky Way bulge with the VVV

Surot

Valenti

Hidalgo

et al. 2019

A&A

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Context. Recent observational programs are providing a global view of the Milky Way bulge that serves as a template for detailed comparison with models and extragalactic bulges. A number of surveys (VVV, GIBS, GES, ARGOS, BRAVA, APOGEE) are producing comprehensive and detailed extinction, metallicity, kinematics, and stellar density maps of the Galactic bulge with unprecedented accuracy. However, the still missing key ingredient is the distribution of stellar ages across the bulge. Aims. To overcome this limitation, we aim to age-date the stellar population in several bulge fields with the ultimate goal of deriving an age map of the bulge. This paper presents the methodology and the first results obtained for a field along the bulge minor axis, at b = −6°. Methods. We use a new PSF-fitting photometry of the VISTA Variables in the Vía Láctea (VVV) survey data to construct deep color–magnitude diagrams of the bulge stellar population down to ∼2 mag below the main sequence turnoff. To address the contamination by foreground disk stars we adopt a statistical approach by using control-disk fields located at different latitudes (spanning approximately the bulge’s range) and longitudes −30° and +20°. We generate synthetic photometric catalogs of complex stellar populations with different age and metallicity distributions, including the observational errors and completeness. The comparison between the color–magnitude diagrams of synthetic and observed disk-decontaminated bulge populations provides constraints on the stellar ages in the observed field. Results. We find the bulk of the bulge stellar population in the observed field along the minor axis to be older than ∼7.5 Gyr. In particular, when the metallicity distribution function spectroscopically derived by GIBS is used, the best fit to the data is obtained with a combination of synthetic populations with ages in between ∼7.5 Gyr and 11 Gyr. However, the fraction of stars younger than ∼10 Gyr strongly depends upon the number of blue straggler stars present in the bulge. Simulations show that the observed color–magnitude diagram of the bulge in the field along the minor axis is incompatible with the presence of a conspicuous population of intermediate-age and young (≲5 Gyr) stars.

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A Megacam Survey of Outer Halo Satellites. Vi. The Spatially Resolved Star-Formation History of the Carina Dwarf Spheroidal Galaxy*

Cited by 21 publications

References 66 publications

A predicted correlation between age gradient and star formation history in FIRE dwarf galaxies

A predicted correlation between age gradient and star formation history in FIRE dwarf galaxies

Homogeneity in the early chemical evolution of the Sextans dwarf Spheroidal galaxy

Mapping the stellar age of the Milky Way bulge with the VVV

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