The star formation history of the Sextans dwarf spheroidal galaxy: a true fossil of the pre-reionization era

Bettinelli, M.; Hidalgo, S. L.; Cassisi, S.; Aparicio, A.; Piotto, G.

doi:10.1093/mnras/sty226

Cited by 34 publications

(40 citation statements)

References 59 publications

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“…The lack of metals before the onset of type Ia SNe in Sextans could be also explained by a short main episode of star formation. Bettinelli et al (2018) found that the main episode of star formation lasted only ∼0.6 Gyr and ended ∼12.9 Gyr ago, which supports the hypothesis that Sextans quickly drained most of its gas reservoir.…”

Section: The Imf and The Alpha Kneesupporting

confidence: 74%

Neutron-capture elements in dwarf galaxies

Reichert

Hansen

Hanke

et al. 2020

A&A

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Context. We present a large homogeneous set of stellar parameters and abundances across a broad range of metallicities, involving 13 classical dwarf spheroidal (dSph) and ultra-faint dSph (UFD) galaxies. In total, this study includes 380 stars in Fornax, Sagittarius, Sculptor, Sextans, Carina, Ursa Minor, Draco, Reticulum II, Bootes I, Ursa Major II, Leo I, Segue I, and Triangulum II. This sample represents the largest, homogeneous, high-resolution study of dSph galaxies to date. Aims. With our homogeneously derived catalog, we are able to search for similar and deviating trends across different galaxies. We investigate the mass dependence of the individual systems on the production of α-elements, but also try to shed light on the long-standing puzzle of the dominant production site of r-process elements. Methods. We used data from the Keck observatory archive and the ESO reduced archive to reanalyze stars from these 13 classical dSph and UFD galaxies. We automatized the step of obtaining stellar parameters, but ran a full spectrum synthesis (1D, local thermal equilibrium) to derive all abundances except for iron to which we applied nonlocal thermodynamic equilibrium corrections where possible. Results. The homogenized set of abundances yielded the unique possibility of deriving a relation between the onset of type Ia supernovae and the stellar mass of the galaxy. Furthermore, we derived a formula to estimate the evolution of α-elements. This reveals a universal relation of these systems across a large range in mass. Finally, we show that between stellar masses of 2.1 × 107 M⊙ and 2.9 × 105 M⊙, there is no dependence of the production of heavy r-process elements on the stellar mass of the galaxy. Conclusions. Placing all abundances consistently on the same scale is crucial to answering questions about the chemical history of galaxies. By homogeneously analyzing Ba and Eu in the 13 systems, we have traced the onset of the s-process and found it to increase with metallicity as a function of the galaxy’s stellar mass. Moreover, the r-process material correlates with the α-elements indicating some coproduction of these, which in turn would point toward rare core-collapse supernovae rather than binary neutron star mergers as a host for the r-process at low [Fe/H] in the investigated dSph systems.

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Section: The Imf and The Alpha Kneesupporting

confidence: 74%

Neutron-capture elements in dwarf galaxies

Reichert

Hansen

Hanke

et al. 2020

A&A

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“…For our comparison with observations we use the results of Leaman et al (2013) and Kacharov et al (2017) to compile stellar metallicity gradient information for a total of 10 Local Group dwarfs. We then use t 50 values determined from the star formation histories created in Weisz et al (2014a,b), and Bettinelli et al (2018). Table 2 summarises the t 50 values, gradient strengths, γ z , and the effective radii taken from McConnachie (2012), Munoz et al (2018), andSimon (2019) -for the ten galaxies we analyse.…”

Section: Observational Comparisonmentioning

confidence: 99%

“…Properties of 10 observed Local Group galaxies: (1) lookback time to the formation of 50% of stars determined from published SFHs(Weisz et al 2014a,b;Bettinelli et al …”

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confidence: 99%

A relationship between stellar metallicity gradients and galaxy age in dwarf galaxies

Mercado

Bullock

Boylan-Kolchin

et al. 2020

Monthly Notices of the Royal Astronomical Society

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We explore the origin of stellar metallicity gradients in simulated and observed dwarf galaxies. We use FIRE-2 cosmological baryonic zoom-in simulations of 26 isolated galaxies as well as existing observational data for 10 Local Group dwarf galaxies. Our simulated galaxies have stellar masses between 105.5 and 108.6 M⊙. Whilst gas-phase metallicty gradients are generally weak in our simulated galaxies, we find that stellar metallicity gradients are common, with central regions tending to be more metal-rich than the outer parts. The strength of the gradient is correlated with galaxy-wide median stellar age, such that galaxies with younger stellar populations have flatter gradients. Stellar metallicty gradients are set by two competing processes: (1) the steady ‘puffing’ of old, metal-poor stars by feedback-driven potential fluctuations and (2) the accretion of extended, metal-rich gas at late times, which fuels late-time metal-rich star formation. If recent star formation dominates, then extended, metal-rich star formation washes out pre-existing gradients from the ‘puffing’ process. We use published results from ten Local Group dwarf galaxies to show that a similar relationship between age and stellar metallicity-gradient strength exists among real dwarfs. This suggests that observed stellar metallicity gradients may be driven largely by the baryon/feedback cycle rather than by external environmental effects.

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“…Altogether, observations of the known UFD population orbiting the Milky Way suggest that these very low-mass systems have old stellar populations, with little star-formation activity since z ∼ 1−2 (e.g. Okamoto et al 2008Okamoto et al , 2012de Jong et al 2008;Sand et al 2009Sand et al , 2010Sand et al , 2012Brown et al 2012;Martin et al 2015;Bettinelli et al 2018).…”

Section: Ufd Galaxy Samplementioning

confidence: 99%

The suppression of star formation on the smallest scales: what role does environment play?

Wimberly

Cooper

Fillingham

et al. 2018

Monthly Notices of the Royal Astronomical Society

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The predominantly ancient stellar populations observed in the lowest mass galaxies (i.e. ultrafaint dwarfs) suggest that their star formation was suppressed by reionization. Most of the well-studied ultra-faint dwarfs, however, are within the central half of the Milky Way dark matter halo, such that they are consistent with a population that was accreted at early times and thus potentially quenched via environmental processes. To study the potential role of environment in suppressing star formation on the smallest scales, we utilize the Exploring the Local Volume in Simulations suite of N-body simulations to constrain the distribution of infall times for low-mass subhaloes likely to host the ultra-faint population. For the ultra-faint satellites of the Milky Way with star formation histories inferred from Hubble Space Telescope imaging, we find that environment is highly unlikely to play a dominant role in quenching their star formation. Even when including the potential effects of pre-processing, there is a 0.1 per cent probability that environmental processes quenched all of the known ultra-faint dwarfs early enough to explain their observed star formation histories. Instead, we argue for a mass floor in the effectiveness of satellite quenching at roughly M ∼ 10 5 M , below which star formation in surviving galaxies is globally suppressed by reionization. We predict a large population of quenched ultra-faint dwarfs in the Local Field (1 < R/R vir < 2), with as many as ∼250 to be discovered by future wide-field imaging surveys.

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The star formation history of the Sextans dwarf spheroidal galaxy: a true fossil of the pre-reionization era

Cited by 34 publications

References 59 publications

Neutron-capture elements in dwarf galaxies

Neutron-capture elements in dwarf galaxies

A relationship between stellar metallicity gradients and galaxy age in dwarf galaxies

The suppression of star formation on the smallest scales: what role does environment play?

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