Gyr Age Research Articles

Dissecting the Gaia HR diagram – II. The vertical structure of the star formation history across the solar cylinder

ABSTRACT Starting from the Gaia DR3 HR diagram, we derive the star formation history (SFH) as a function of distance from the Galactic plane within a cylinder centred on the Sun with a 200 pc radius and spanning 1.3 kpc above and below the Galaxy’s midplane. We quantify both the concentration of the more recent star formation in the Galactic plane, and the age-related increase in the scale height of the Galactic disc stellar component, which is well-described by power laws with indices ranging from 1/2 to 2/3. The vertically-integrated star formation rate falls from $(1.147 \pm 0.039)\times 10^{-8}\, \text{M}_\odot \, \text{yr}^{-1} \, \text{pc}^{-2}$ at earlier times down to $(6.2 \pm 3.0) \times 10^{-9}\, \text{M}_\odot \, \text{yr}^{-1} \, \text{pc}^{-2}$ at present times, but we find a significant peak of star formation in the 2–3 Gyr age bin. The total mass of stars formed per unit area over time is $118.7 \pm 6.2\, \text{M}_\odot \, \text{pc}^{-2}$, which is nearly twice the present stellar mass derived from kinematics within 1 kpc from the Galactic plane, implying a high degree of matter recycling in successive generations of stars. The method is then modified by adopting an age-dependent correlation between the SFH across the different slices, which results in less noisy and more symmetrical results without significantly changing the previously mentioned quantities. This appears to be a promising way to improve SFH recovery in external galaxies.

Long-term Evolution of Warps in Debris Disks—Application to the Gyr-old System HD 202628

We present the results of N-body simulations meant to reproduce the long-term effects of mutually inclined exoplanets on debris disks, using the HD 202628 system as a proxy. HD 202628 is a Gyr-old solar-type star that possesses a directly observable, narrow debris ring with a clearly defined inner edge and nonzero eccentricity, hinting at the existence of a sculpting exoplanet. The eccentric nature of the disk leads us to examine the effect on it over Gyr timescales from an eccentric and inclined planet, placed on its orbit through scattering processes. We find that, in systems with dynamical timescales akin to that of HD 202628, a planetary companion is capable of completely tilting the debris disk. This tilt is preserved over the Gyr age of the system. Simulated observations of our models show that an exoplanet around HD 202628 with an inclination misalignment ≳10° would cause the disk to be observably diffuse and broad, which is inconsistent with Atacama Large Millimeter Array (ALMA) observations. With these observations, we conclude that, if there is an exoplanet shaping this disk, it likely had a mutual inclination of less than 5° with the primordial disk. The conclusions of this work can be applied either to debris disks appearing as narrow rings (e.g., Fomalhaut and HR 4796) or to disks that are vertically thick at ALMA wavelengths (e.g., HD 110058).

Integral Field Spectroscopy of the cometary starburst galaxy NGC 4861

ABSTRACT Using the PMAS Integral Field Unit on the Calar Alto 3.5 m telescope, we observed the southern component (Markarian 59) of the ‘cometary’ starburst galaxy NGC 4861. Mrk 59 is centred on a giant nebula and concentration of stars 1 kpc in diameter. Strong $\rm H\,\alpha$ emission points to a star-formation rate (SFR) at least 0.47 $\rm M_{\odot }\, yr^{-1}$. Mrk 59 has a very high [O iii] $\rm \lambda 5007/H\,\beta$ ratio, reaching 7.35 in the central nebula, with a second peak at a star-forming hotspot further north. Fast outflows are not detected but nebular motion and galaxy rotation produce relative velocities up to 40 km $\rm s^{-1}$. Spectral analysis of different regions with ‘Fitting Analysis using Differential evolution Optimization’ (FADO) finds that the stars in the central and ‘spur’ nebulae are very young, $\rm \le 125~Myr$ with a large $\rm \lt 10~Myr$ contribution. Older stars ($\rm \sim 1~Gyr$) make up the northern disk component, while the other regions show mixtures of 1 Gyr age with very young stars. This and the high specific SFR $\rm \sim 3.5~Gyr^{-1}$ imply a bimodal star formation history, with Mrk 59 formed in ongoing starbursts fuelled by a huge gas inflow, turning the galaxy into an asymmetric ‘green pea’ or blue compact dwarf. We map the He ii λ4686 emission, and identify a broad component from the central nebula, consistent with the emission of ∼300 Wolf–Rayet stars. About a third of the He ii λ4686 flux is a narrow line emitted from a more extended area covering the central and spur nebulae, and may have a different origin.

Early Results from GLASS-JWST. XVI. Discovering a Bluer z ∼ 4–7 Universe through UV Slopes

We use the GLASS-JWST Early Release Science NIRCam parallel observations to provide a first view of the UV continuum properties of NIRCam/F444W selected galaxies at 4 < z < 7. By combining multiwavelength NIRCam observations, we constrain the UV continuum slope for a sample of 401 galaxies with stringent quality controls. We find that >99% of the galaxies are blue star-forming galaxies with very low levels of dust (Av β ∼ 0.01 ± 0.33). We find no statistically significant correlation for UV slope with redshift or UV magnitude. However, we find that in general galaxies at higher redshifts and fainter UV magnitudes have steeper UV slopes. We find a statistically significant correlation for UV slope with stellar mass, with galaxies with higher stellar mass showing shallower UV slopes. Individual fits to some of our galaxies reach the bluest UV slopes of β ∼ −3.1 allowed by stellar population models used in this analysis. Therefore, it is likely that stellar population models with a higher amount of Lyman continuum leakage, active galactic nucleus effects, and/or Population III contributions are required to accurately reproduce the rest-UV and optical properties of some of our bluest galaxies. This dust-free early view confirms that our current cosmological understanding of gradual mass + dust buildup of galaxies with cosmic time is largely accurate to describe the ∼0.7–1.5 Gyr age window of the universe. The abundance of a large population of UV faint dust-poor systems may point to a dominance of low-mass galaxies at z > 6 playing a vital role in cosmic reionization.

The Star Formation History of the Milky Way’s Nuclear Star Cluster

We report the first star formation history study of the Milky Ways nuclear star cluster (NSC), which includes observational constraints from a large sample of stellar metallicity measurements. These metallicity measurements were obtained from recent surveys from Gemini and the Very Large Telescope of 770 late-type stars within the central 1.5 pc. These metallicity measurements, along with photometry and spectroscopically derived temperatures, are forward modeled with a Bayesian inference approach. Including metallicity measurements improves the overall fit quality, as the low-temperature red giants that were previously difficult to constrain are now accounted for, and the best fit favors a two-component model. The dominant component contains 93% ± 3% of the mass, is metal-rich (), and has an age of Gyr, which is ∼3 Gyr younger than earlier studies with fixed (solar) metallicity; this younger age challenges coevolutionary models in which the NSC and supermassive black holes formed simultaneously at early times. The minor population component has low metallicity () and contains ∼7% of the stellar mass. The age of the minor component is uncertain (0.1–5 Gyr old). Using the estimated parameters, we infer the following NSC stellar remnant population (with ∼18% uncertainty): 1.5 × 105 neutron stars, 2.5 × 105 stellar-mass black holes (BHs), and 2.2 × 104 BH–BH binaries. These predictions result in 2–4 times fewer neutron stars compared to earlier predictions that assume solar metallicity, introducing a possible new path to understand the so-called “missing-pulsar problem”. Finally, we present updated predictions for the BH–BH merger rates (0.01–3 Gpc−3yr−1).

PHANGS–JWST First Results: A Combined HST and JWST Analysis of the Nuclear Star Cluster in NGC 628

We combine archival Hubble Space Telescope and new James Webb Space Telescope imaging data covering the ultraviolet to mid-infrared regime to morphologically analyze the nuclear star cluster (NSC) of NGC 628, a grand-design spiral galaxy. The cluster is located in a 200 pc × 400 pc cavity lacking both dust and gas. We find roughly constant values for the effective radius (r eff ∼ 5 pc) and ellipticity (ϵ ∼ 0.05), while the Sérsic index (n) and position angle (PA) drop from n ∼ 3 to ∼2 and PA ∼ 130° to 90°, respectively. In the mid-infrared, r eff ∼ 12 pc, ϵ ∼ 0.4, and n ∼ 1–1.5, with the same PA ∼ 90°. The NSC has a stellar mass of , as derived through B − V, confirmed when using multiwavelength data, and in agreement with the literature value. Fitting the spectral energy distribution (SED), excluding the mid-infrared data, yields a main stellar population age of (8 ± 3) Gyr with a metallicity of Z = 0.012 ± 0.006. There is no indication of any significant star formation over the last few gigayears. Whether gas and dust were dynamically kept out or evacuated from the central cavity remains unclear. The best fit suggests an excess of flux in the mid-infrared bands, with further indications that the center of the mid-infrared structure is displaced with respect to the optical center of the NSC. We discuss five potential scenarios, none of them fully explaining both the observed photometry and structure.

The Evolving Chronology of Moon Formation

Defining the age of the Moon has proven to be an elusive task because it requires reliably dating lunar samples using radiometric isotopic systems that record fractionation of parent and daughter elements during events that are petrologically associated with planet formation. Crystallization of the magma ocean is the only event that unambiguously meets this criterion because it probably occurred within tens of millions of years of Moon formation. There are three dateable crystallization products of the magma ocean: mafic mantle cumulates, felsic crustal cumulates, and late-stage crystallization products known as urKREEP (uniform residuum K, rare earth elements, and P). Although ages for these materials in the literature span 200 million years, there is a preponderance of reliable ages around 4.35 billion years recorded in all three lunar rock types. This age is also observed in many secondary crustal rocks, indicating that they were produced contemporaneously (within uncertainty of the ages), possibly during crystallization and overturn of the magma ocean. ▪The duration of planet formation is key information in understanding the mechanisms by which the terrestrial planets formed.▪Ages of the oldest lunar rocks range widely, reflecting either the duration of Moon formation or disturbed ages caused by impact metamorphism.▪Ages determined for compositionally distinct crust and mantle materials produced by lunar magma ocean differentiation cluster near 4.35 Gyr.▪The repeated occurrence of 4.35 Gyr ages implies that Moon formation occurred late in Solar System history, likely by giant impact into Earth.

Stability Constrained Characterization of the 23 Myr Old V1298 Tau System: Do Young Planets Form in Mean Motion Resonance Chains?

A leading theoretical expectation for the final stages of planet formation is that disk migration should naturally drive orbits into chains of mean motion resonances (MMRs). In order to explain the dearth of MMR chains observed at Gyr ages (<1%), this picture requires such configurations to destabilize and scramble period ratios following disk dispersal. Strikingly, the only two known stars with three or more planets younger than ≲100 Myr, HR 8799 and V1298 Tau, have been suggested to be in such MMR chains, given the orbits’ near-integer period ratios. We incorporate recent transit and radial velocity (RV) observations of the V1298 Tau system, and investigate constraints on the system’s orbital architecture imposed by requiring dynamical stability on timescales much shorter than the system’s age. We show that the recent RV mass measurement of V1298 Tau b places it within a factor of 2 of the instability limit, and that this allows us to set significantly lower limits on the eccentricity (e b ≤0.17 at 99.7% confidence). Additionally, we rule out a resonant chain configuration for V1298 Tau at ≳99% confidence. Thus, if the ∼23 Myr old V1298 Tau system did form as a resonant chain, it must have undergone instability and rearrangement shortly after disk dispersal. We expect that similar stability constrained characterization of future young multiplanet systems will be valuable in informing planet formation models.

Precise Dynamical Masses of ε Indi Ba and Bb: Evidence of Slowed Cooling at the L/T Transition

We report individual dynamical masses of 66.92 ± 0.36 M Jup and 53.25 ± 0.29 M Jup for the binary brown dwarfs ε Indi Ba and Bb, measured from long-term (≈10 yr) relative orbit monitoring and absolute astrometry monitoring data on the Very Large Telescope (VLT). Relative astrometry with NACO fully constrains the Keplerian orbit of the binary pair, while absolute astrometry with FORS2 measures the system’s parallax and mass ratio. We find a parallax consistent with the Hipparcos and Gaia values for ε Indi A, and a mass ratio for ε Indi Ba to Bb precise to better than 0.2%. ε Indi Ba and Bb have spectral types T1-1.5 and T6, respectively. With an age of Gyr from ε Indi A’s activity, these brown dwarfs provide some of the most precise benchmarks for substellar cooling models. Assuming coevality, the very different luminosities of the two brown dwarfs and our moderate mass ratio imply a steep mass–luminosity relationship () that can be explained by a slowed cooling rate in the L/T transition, as previously observed for other L/T binaries. Finally, we present a periodogram analysis of the near-infrared photometric data, but find no definitive evidence of periodic signals with a coherent phase.

The Stellar Metallicities of Massive Quiescent Galaxies at 1.0 < z < 1.3 from KMOS + VANDELS

We present a rest-frame UV–optical (λ = 2500–6400 Å) stacked spectrum representative of massive quiescent galaxies at 1.0 < z < 1.3 with log(M */M ⊙) > 10.8. The stack is constructed using VANDELS survey data, combined with new KMOS observations. We apply two independent full-spectral-fitting approaches, measuring a total metallicity [Z/H] = −0.13 ± 0.08 with Bagpipes and [Z/H] = 0.04 ± 0.14 with Alf, a fall of ∼0.2–0.3 dex compared with the local universe. We also measure an iron abundance [Fe/H] = −0.18 ± 0.08, a fall of ∼0.15 dex compared with the local universe. We measure the alpha enhancement via the magnesium abundance, obtaining [Mg/Fe] = 0.23 ± 0.12, consistent with galaxies of similar mass in the local universe, indicating no evolution in the average alpha enhancement of log(M */M ⊙) ∼ 11 quiescent galaxies over the last ∼8 Gyr. This suggests the very high alpha enhancements recently reported for several bright z ∼ 1–2 quiescent galaxies are due to their extreme masses, log(M */M ⊙) ≳ 11.5, in accordance with the well-known downsizing trend, rather than being typical of the z ≳ 1 population. The metallicity evolution we observe with redshift (falling [Z/H], [Fe/H], constant [Mg/Fe]) is consistent with recent studies. We recover a mean stellar age of Gyr, corresponding to a formation redshift . Recent studies have obtained varying average formation redshifts for z ≳ 1 massive quiescent galaxies, and, as these studies report consistent metallicities, we identify models with different star formation histories as the most likely cause. Larger spectroscopic samples from upcoming ground-based instruments will provide precise constraints on ages and metallicities at z ≳ 1. Combining these with precise stellar mass functions for z > 2 quiescent galaxies from the James Webb Space Telescope will provide an independent test of formation redshifts derived from spectral fitting.

Estimation of ages and masses via carbon and nitrogen abundances for 556 007 giants from LAMOST

Estimating ages for a large number of giants is of great importance for studying Galactic evolution. In this work, we determine stellar ages and masses for 556 007 giants from LAMOST Data Release 5 (DR5) with empirical relations estimated from chemical [C/N] abundance ratios. Our sample reveals the two well-known sequences in the age–[α/M] relation. The high-α sequence is composed of stars older than 8 Gyr and low-α sequence is composed of stars with age ranging from 0 Gyr to 13.8 Gyr. Our sample also shows a flat age–[M/H] relation up until 12 Gyr. We compare these distributions with Galactic Chemical Evolution models for reference. When looking at the spatial distribution of stars in 2 Gyr age bins, we find that young stars are concentrated towards the Galactic plane and older stars extend to higher height above and below the disk. We find a smooth transition of median Galactic height for different age bins, which suggests a strong age-dependence on Galactic scale height.

The winds of young Solar-type stars in the Hyades

ABSTRACT Stellar winds govern the spin-down of Solar-type stars as they age, and play an important role in determining planetary habitability, as powerful winds can lead to atmospheric erosion. We calculate 3D stellar wind models for five young Solar-type stars in the Hyades cluster, using TOUPIES survey stellar magnetograms and state-of-the-art Alfvén wave-driven wind modelling. The stars have the same 0.6 Gyr age and similar fundamental parameters, and we account for the uncertainty in and underestimation of absolute field strength inherent in Zeeman–Doppler imaging by adopting both unscaled and scaled (by a factor of five) field strengths. For the unscaled fields, the resulting stellar wind mass-loss is 2–4 times greater and the angular momentum loss 2–10 times greater than for the Sun today, with the scaled results correspondingly greater. We compare our results with a range published of wind models and for the Alfvén wave-driven modelling see evidence of mass-loss saturation at ${\sim 10} \dot{M}_{\odot }$.

The sustained post-outburst brightness of Nova Per 2018, the evolved companion, and the long orbital period

Nova Per 2018 (= V392 Per) halted the decline from maximum when it was 2 mag brighter than quiescence and since 2019 has been stable at such a plateau. The ejecta have already fully diluted into the interstellar space. We obtained BVRIgrizY photometry and optical spectroscopy of V392 Per during the plateau phase and compared it with equivalent data gathered prior to the nova outburst. We find the companion star (CS) to be a G9 IV/III and the orbital period to be 3.4118 days, making V392 Per the longest known period for a classical nova. The location of V392 Per on the theoretical isochrones is intermediate between that of classical novae and novae erupting within symbiotic binaries, in a sense bridging the gap. The reddening is derived to be EB − V = 0.72 and the fitting to isochrones returns a 3.6 Gyr age for the system and 1.35 M⊙, 5.3 R⊙, and 15 L⊙ for the companion. The huge Ne overabundance in the ejecta and the very fast decline from nova maximum both point to a massive white dwarf (WD) (MWD ≥ 1.1−1.2 M⊙). The system is viewed close to pole-on conditions and the current plateau phase is caused by irradiation of the CS by the WD still burning at the surface.

TOI-677b: A Warm Jupiter (P = 11.2 days) on an Eccentric Orbit Transiting a Late F-type Star

Abstract We report the discovery of TOI-677 b, first identified as a candidate in light curves obtained within Sectors 9 and 10 of the Transiting Exoplanet Survey Satellite (TESS) mission and confirmed with radial velocities. TOI-677 b has a mass of = , a radius of = , and orbits its bright host star (V = 9.8 mag) with an orbital period of d, on an eccentric orbit with . The host star has a mass of = , a radius of = , an age of Gyr and solar metallicity, properties consistent with a main-sequence late-F star with K. We find evidence in the radial velocity measurements of a secondary long-term signal, which could be due to an outer companion. The TOI-677 b system is a well-suited target for Rossiter–Mclaughlin observations that can constrain migration mechanisms of close-in giant planets.

Asteroseismology of the Multiplanet System K2-93

Abstract We revisit the analysis of the bright multiplanet system K2-93, discovered with data taken by the K2 mission. This system contains five identified planets ranging in size from sub-Neptune to Jupiter size. The K2 data available at the discovery of the system only showed single transits for the three outer planets, which allowed weak constraints to be put on their periods. As these planets are interesting candidates for future atmospheric studies, a better characterization of the host star and tighter constraints on their orbital periods are essential. Using new data from the K2 mission taken after the discovery of the system, we perform an asteroseismic characterization of the host star. We are able to place strong constraints on the stellar parameters and obtain a value for the stellar mass of , a stellar radius of 1.30 ± 0.01 R ⊙, and an age of Gyr. Put together with the additional transits identified for two of the three outer planets, we constrain the orbital periods of the outer planets and provide updated estimates for the stellar reflex velocities induced by the planets.

KELT-24b: A 5MJ Planet on a 5.6 day Well-aligned Orbit around the Young V = 8.3 F-star HD 93148

Abstract We present the discovery of KELT-24 b, a massive hot Jupiter orbiting a bright (V = 8.3 mag, K = 7.2 mag) young F-star with a period of 5.6 days. The host star, KELT-24 (HD 93148), has a T eff = K, a mass of M * = M ⊙, a radius of R * = 1.506 ± 0.022 R ⊙, and an age of Gyr. Its planetary companion (KELT-24 b) has a radius of R P = 1.272 ± 0.021 R J and a mass of M P = M J, and from Doppler tomographic observations, we find that the planet’s orbit is well-aligned to its host star’s projected spin axis ( ). The young age estimated for KELT-24 suggests that it only recently started to evolve from the zero-age main sequence. KELT-24 is the brightest star known to host a transiting giant planet with a period between 5 and 10 days. Although the circularization timescale is much longer than the age of the system, we do not detect a large eccentricity or significant misalignment that is expected from dynamical migration. The brightness of its host star and its moderate surface gravity make KELT-24b an intriguing target for detailed atmospheric characterization through spectroscopic emission measurements since it would bridge the current literature results that have primarily focused on lower mass hot Jupiters and a few brown dwarfs.

Populating H2 and CO in galaxy simulation with dust evolution

There are two major theoretical issues for the star formation law (the relation between the surface densities of molecular gas and star formation rate on a galaxy scale): (i) At low metallicity, it is not obvious that star-forming regions are rich in H$_2$ because the H$_2$ formation rate depends on the dust abundance; and (ii) whether or not CO really traces H$_2$ is uncertain, especially at low metallicity. To clarify these issues, we use a hydrodynamic simulation of an isolated disc galaxy with a spatial resolution of a few tens parsecs. The evolution of dust abundance and grain size distribution is treated consistently with the metal enrichment and the physical state of the interstellar medium. We compute the H$_2$ and CO abundances using a subgrid post-processing model based on the dust abundance and the dissociating radiation field calculated in the simulation. We find that when the metallicity is $\lesssim 0.4$ Z$_\odot$ ($t<1$ Gyr), H$_2$ is not a good tracer of star formation rate because H$_2$-rich regions are limited to dense compact regions. At $Z\gtrsim 0.8$ Z$_\odot$, a tight star formation law is established for both H$_2$ and CO. At old ($t \sim 10$ Gyr) ages, we also find that adopting the so-called MRN grain size distribution with an appropriate dust-to-metal ratio over the entire disc gives reasonable estimates for the H$_2$ and CO abundances. For CO, improving the spatial resolution of the simulation is important while the H$_2$ abundance is not sensitive to sub-resolution structures at $Z\gtrsim 0.4$ Z$_\odot$.

The first 62 AGNs observed with SDSS-IV MaNGA – I. Their characterization and definition of a control sample

We report the characterization of the first $62$ MaNGA Active Galactic Nuclei (AGN) hosts in the Fifth Product Launch (MPL-5) and the definition of a control sample of non-active galaxies. This control sample - comprising two galaxies for each AGN - was selected in order to match the AGN hosts in terms of stellar mass, redshift, visual morphology and inclination. The stellar masses are in the range $9.4<\log(M/M_\odot)<11.5$, and most objects have redshifts $\leq 0.08$. The AGN sample is mostly comprised of low-luminosity AGN, with only 17 nuclei with $L([OIII]\lambda 5007)\geq 3.8\times 10^{40}$ erg s$^{-1}$ (that we call "strong AGN"). The stellar population of the control sample galaxies within the inner $1$-$3$ kpc is dominated by the old ($\sim$ $4$ - $13$ Gyr) age component, with a small contribution of intermediate age ($\sim 640$-$940$ Myr) and young stars ($\leq 40$ Myr) to the total light at $5700\AA$. While the weaker AGN show a similar age distribution to that of the control galaxies, the strong AGN show an increased contribution of younger stars and a decreased contribution of older stars. Examining the relationship between the AGN stellar population properties and $L([OIII])$, we find that with increasing $L([OIII])$, the AGN exhibit a decreasing contribution from the oldest ($>4$ Gyr) stellar population relative to control galaxies, but have an increasing contribution from the younger components with ages $\sim 40$ Myr. We also find a correlation of the mean age differences (AGN - control) with $L([OIII])$, in the sense that more luminous AGN are younger than the control objects, while the low-luminosity AGN seem to be older. These results support a connection between the growth of the galaxy bulge via formation of new stars and the growth of the Supermassive Black Hole via matter accretion in the AGN phase.

First Results from the Hertzsprung SONG Telescope: Asteroseismology of the G5 Subgiant Star μ Herculis*

Abstract We report the first asteroseismic results obtained with the Hertzsprung Stellar Observations Network Group Telescope from an extensive high-precision radial-velocity observing campaign of the subgiant μ Herculis. The data set was collected during 215 nights in 2014 and 2015. We detected a total of 49 oscillation modes with l values from zero to three, including some l = 1 mixed modes. Based on the rotational splitting observed in l = 1 modes, we determine a rotational period of 52 days and a stellar inclination angle of 63°. The parameters obtained through modeling of the observed oscillation frequencies agree very well with independent observations and imply a stellar mass between 1.11 and 1.15 M ⊙ and an age of Gyr. Furthermore, the high-quality data allowed us to determine the acoustic depths of the He ii ionization layer and the base of the convection zone.

A MEGACAM SURVEY OF OUTER HALO SATELLITES. VI. THE SPATIALLY RESOLVED STAR-FORMATION HISTORY OF THE CARINA DWARF SPHEROIDAL GALAXY*

ABSTRACT We present the spatially resolved star-formation history (SFH) of the Carina dwarf spheroidal galaxy, obtained from deep, wide-field g and r imaging and a metallicity distribution from the literature. Our photometry covers ∼2 deg2, reaching up to ∼10 times the half-light radius of Carina with a completeness higher than 50% at g ∼ 24.5, more than one magnitude fainter than the oldest turnoff. This is the first time a combination of depth and coverage of this quality has been used to derive the SFH of Carina, enabling us to trace its different populations with unprecedented accuracy. We find that Carina’s SFH consists of two episodes well separated by a star-formation temporal gap. These episodes occurred at old ( Gyr) and intermediate (2–8 Gyr) ages. Our measurements show that the old episode comprises the majority of the population, accounting for 54 ± 5% of the stellar mass within 1.3 times the King tidal radius, while the total stellar mass derived for Carina is , and the stellar mass-to-light ratio is 1.8 ± 0.2. The SFH derived is consistent with no recent star formation, which hints that the observed blue plume is due to blue stragglers. We conclude that the SFH of Carina evolved independently of the tidal field of the Milky Way, since the frequency and duration of its star-formation events do not correlate with its orbital parameters. This result is supported by the age–metallicity relation observed in Carina and the gradients calculated indicating that outer regions are older and more metal-poor.