Nitrous oxide (N2O) is a potent greenhouse gas (GHG) and ozone destructing agent; yet global estimates of N2O emissions are uncertain. Marine N2O stems from nitrification and denitrification ...processes which depend on organic matter cycling and dissolved oxygen (O2). We introduce N2O as an obligate intermediate product of denitrification and as an O2‐dependent by‐product from nitrification in the Bern3D ocean model. A large model ensemble is used to probabilistically constrain modern and to project marine N2O production for a low (Representative Concentration Pathway (RCP)2.6) and high GHG (RCP8.5) scenario extended to A.D. 10,000. Water column N2O and surface ocean partial pressure N2O data serve as constraints in this Bayesian framework. The constrained median for modern N2O production is 4.5 (±1σ range: 3.0 to 6.1) Tg N yr−1, where 4.5% stems from denitrification. Modeled denitrification is 65.1 (40.9 to 91.6) Tg N yr−1, well within current estimates. For high GHG forcing, N2O production decreases by 7.7% over this century due to decreasing organic matter export and remineralization. Thereafter, production increases slowly by 21% due to widespread deoxygenation and high remineralization. Deoxygenation peaks in two millennia, and the global O2 inventory is reduced by a factor of 2 compared to today. Net denitrification is responsible for 7.8% of the long‐term increase in N2O production. On millennial timescales, marine N2O emissions constitute a small, positive feedback to climate change. Our simulations reveal tight coupling between the marine carbon cycle, O2, N2O, and climate.
Key Points
A new parameterization for marine N2O production by nitrification and denitrification is developed
Modern marine N2O emissions are constrained by observations to 4.3 (2.8 to 5.9) Tg N yr‐1
Probabilistic projections yield massive reductions in O2 and a long‐term increase in N2O emissions
Aims.
We perform a comprehensive determination of the systemic proper motions of 74 dwarf galaxies and dwarf galaxy candidates in the Local Group based on
Gaia
early data release 3. The outputs of ...the analysis for each galaxy, including probabilities of membership, will be made publicly available. The analysis is augmented by a determination of the orbital properties of galaxies within 500 kpc.
Methods.
We adopt a flexible Bayesian methodology presented in the literature, which takes into account the location of the stars on the sky, on the colour-magnitude diagram, and on the proper motion plane. We applied some modifications, in particular to the way the colour-magnitude diagram and spectroscopic information are factored in, for example, by including stars in several evolution phases. The bulk motions were integrated in three gravitational potentials: two where the Milky Way was treated in isolation and has a mass 0.9 & 1.6 × 10
12
M
⊙
, and a time-varying potential, which includes the infall of a massive Large Magellanic Cloud (LMC).
Results.
We were able to determine bulk proper motions for 73 systems, and we consider 66 to be reliable measurements. For the first time, systemic motions are presented for galaxies out to a distance of 1.4 Mpc in the NGC 3109 association. The inclusion of the infall of a massive LMC significantly modifies the orbital trajectories of the objects, with respect to orbit integration in static Milky-Way-only potentials, and this leads to six galaxies likely being associated with the LMC, three possibly being associated with it, and one recently captured object. We discuss the results of the orbit integration in the context of the relation of the galaxies to the system of Milky Way satellites, implications for the too-big-to-fail problem, the impact on star formation histories, and tidal disruption.
A proper understanding of the Milky Way (MW) dwarf galaxies in a cosmological context requires knowledge of their 3D velocities and orbits. However, proper motion (PM) measurements have generally ...been of limited accuracy and are available only for more massive dwarfs. We therefore present a new study of the kinematics of the MW dwarf galaxies. We use the Gaia DR2 for those dwarfs that have been spectroscopically observed in the literature. We derive systemic PMs for 39 galaxies and galaxy candidates out to 420 kpc, and generally find good consistency for the subset with measurements available from other studies. We derive the implied Galactocentric velocities, and calculate orbits in canonical MW halo potentials of low (0.8 × 1012 M⊙) and high mass (1.6 × 1012 M⊙). Comparison of the distributions of orbital apocenters and 3D velocities to the halo virial radius and escape velocity, respectively, suggests that the satellite kinematics are best explained in the high-mass halo. Tuc III, Crater II, and additional candidates have orbital pericenters small enough to imply significant tidal influences. Relevant to the missing satellite problem, the fact that fewer galaxies are observed to be near apocenter than near pericenter implies that there must be a population of distant dwarf galaxies yet to be discovered. Of the 39 dwarfs: 12 have orbital poles that do not align with the MW plane of satellites (given reasonable assumptions about its intrinsic thickness); 10 have insufficient PM accuracy to establish whether they align; and 17 satellites align, of which 11 are co-orbiting and (somewhat surprisingly, in view of prior knowledge) 6 are counter-orbiting. Group infall might have contributed to this, but no definitive association is found for the members of the Crater-Leo group.
ABSTRACT
We use Gaia DR2 systemic proper motions of 45 satellite galaxies to constrain the mass of the Milky Way using the scale-free mass estimator of Watkins et al. (2010). We first determine the ...anisotropy parameter β, and the tracer satellites’ radial density index γ to be β = $-0.67^{+0.45}_{-0.62}$ and γ = 2.11 ± 0.23. When we exclude possible former satellites of the Large Magellanic Cloud, the anisotropy changes to β = $-0.21^{+0.37}_{-0.51}$. We find that the index of the Milky Way’s gravitational potential α, which is dependent on the mass itself, is the parameter with the largest impact on the mass determination. Via comparison with cosmological simulations of Milky Way-like galaxies, we carried out a detailed analysis of the estimation of the observational uncertainties and their impact on the mass estimator. We found that the mass estimator is biased when applied naively to the satellites of simulated Milky Way haloes. Correcting for this bias, we obtain for our Galaxy a mass of $0.58^{+0.15}_{-0.14}\times 10^{12}$ M⊙ within 64 kpc, as computed from the inner half of our observational sample, and $1.43^{+0.35}_{-0.32}\times 10^{12}$ M⊙ within 273 kpc, from the full sample; this latter value extrapolates to a virial mass of $M_\mathrm{vir\, \Delta =97}=1.51^{+0.45}_{-0.40} \times 10^{12}\,{\rm M}_{\odot }$ corresponding to a virial radius of Rvir = 308 ± 29 kpc. This value of the Milky Way mass lies in-between other mass estimates reported in the literature, from various different methods.
A wealth of tiny galactic systems populates the surroundings of the Milky Way. However, some of these objects might have originated as former satellites of the Magellanic Clouds, in particular of the ...Large Magellanic Cloud (LMC). Examples of the importance of understanding how many systems are genuine satellites of the Milky Way or the LMC are the implications that the number and luminosity-mass function of satellites around hosts of different mass have for dark matter theories and the treatment of baryonic physics in simulations of structure formation. Here we aim at deriving the bulk motions and estimates of the internal velocity dispersion and metallicity properties in four recently discovered distant southern dwarf galaxy candidates, Columba I, Reticulum III, Phoenix II, and Horologium II. We combined Gaia DR2 astrometric measurements, photometry, and new FLAMES/GIRAFFE intermediate-resolution spectroscopic data in the region of the near-IR Ca II triplet lines; this combination is essential for finding potential member stars in these low-luminosity systems. We find very likely member stars in all four satellites and are able to determine (or place limits on) the bulk motions and average internal properties of the systems. The systems are found to be very metal poor, in agreement with dwarf galaxies and dwarf galaxy candidates of similar luminosity. Of these four objects, we can only firmly place Phoenix II in the category of dwarf galaxies because of its resolved high velocity dispersion ( 9.5 −4.4+6.8 km s−1 9.5 −4.4 +6.8 km s −1 $ 9.5_{-4.4}^{+6.8}\, {\rm {km\,s}}^{-1} $ ) and intrinsic metallicity spread (0.33 dex). For Columba I we also measure a clear metallicity spread. The orbital pole of Phoenix II is well constrained and close to that of the LMC, suggesting a prior association. The uncertainty on the orbital poles of the other systems is currently very large, so that an association cannot be excluded, except for Columba I. Using the numbers of potential former satellites of the LMC identified here and in the literature, we obtain for the LMC a dark matter mass of M200 = 1.9 −0.9+1.3 × 1011 M⊙ M 200 = 1.9 −0.9 +1.3 × 10 11 M ⊙ $ M_{200}=1.9_{-0.9}^{+1.3}\times10^{11}\, M_{\odot} $ .
Abstract
Dwarf spheroidal galaxies (dSphs) appear to be some of the most dark matter (DM)-dominated objects in the Universe. Their dynamical masses are commonly derived using the kinematics of stars ...under the assumption of equilibrium. However, these objects are satellites of massive galaxies (e.g. the Milky Way) and thus can be influenced by their tidal fields. We investigate the implication of the assumption of equilibrium focusing on the Sculptor dSph by means of ad hoc N-body simulations tuned to reproduce the observed properties of Sculptor following the evolution along some observationally motivated orbits in the Milky Way gravitational field. For this purpose, we used state-of-the-art spectroscopic and photometric samples of Sculptor’s stars. We found that the stellar component of the simulated object is not directly influenced by the tidal field, while ${\approx } 30\!-\!60{{\ \rm per\ cent}}$ of the mass of the more diffuse DM halo is stripped. We conclude that, considering the most recent estimate of the Sculptor proper motion, the system is not affected by the tides and the stellar kinematics represents a robust tracer of the internal dynamics. In the simulations that match the observed properties of Sculptor, the present-day dark-to-luminous mass ratio is ≈6 within the stellar half-light radius (≈0.3 kpc) and >50 within the maximum radius of the analysed data set (≈1.5○, ≈2 kpc).
We present VLT FLAMES spectroscopic observations (R similar to 6500 ) in the Ca II triplet region for 470 probable kinematic members of the Sculptor (Scl) dwarf spheroidal galaxy. The accurate ...velocities ( plus or minus 2 km/s) and large area coverage of Scl allow us to measure a velocity gradient of 7.6 super(+3.0) km s-1 deg-1 along the projected major axis of Scl, likely a signature of intrinsic rotation. We also use our kinematic data to measure the mass distribution within this system. By considering independently the kinematics of the two distinct stellar components known to be present in Scl, we are able to relieve known degeneracies and find that the observed velocity dispersion profiles are best fitted by a cored dark matter halo with core radius rc = 0.5 kpc and mass enclosed within the last measured point M(<1.8 kpc) = (3.4 plus or minus 0.7) x 10 super(8) M <1.8, assuming an increasingly radially anisotropic velocity ellipsoid. This results in a mass-to-light ratio of 158 plus or minus 33 (M/L)solar inside 1.8 kpc. An NFW profile with concentration C = 20 and mass M(<1.8 kpc) = 2.2 super(+2) x 10 super(8) M sub(solar) statistically consistent with the observations, but it tends to yield poorer fits for the metal-rich stars.
We present deep photometry in the B, V and I filters from CTIO/MOSAIC for about 270 000 stars in the Fornax dwarf spheroidal galaxy, out to a radius of rell ≈ 0.8 degrees. By combining the accurately ...calibrated photometry with the spectroscopic metallicity distributions of individual red giant branch stars we obtain the detailed star formation and chemical evolution history of Fornax. Fornax is dominated by intermediate age (1−10 Gyr) stellar populations, but also includes ancient (10−14 Gyr), and young (≤1 Gyr) stars. We show that Fornax displays a radial age gradient, with younger, more metal-rich populations dominating the central region. This confirms results from previous works. Within an elliptical radius of 0.8 degrees, or 1.9 kpc from the centre, a total mass in stars of 4.3 × 107 M⊙ was formed, from the earliest times until 250 Myr ago. Using the detailed star formation history, age estimates are determined for individual stars on the upper RGB, for which spectroscopic abundances are available, giving an age-metallicity relation of the Fornax dSph from individual stars. This shows that the average metallicity of Fornax went up rapidly from Fe/H ≤ −2.5 dex to Fe/H = −1.5 dex between 8−12 Gyr ago, after which a more gradual enrichment resulted in a narrow, well-defined sequence which reaches Fe/H ≈ −0.8 dex, ≈3 Gyr ago. These ages also allow us to measure the build-up of chemical elements as a function of time, and thus determine detailed timescales for the evolution of individual chemical elements. A rapid decrease in Mg/Fe is seen for the stars with Fe/H ≥ −1.5 dex, with a clear trend in age.
Abstract
Eridanus II (Eri II) is an ultrafaint dwarf (UFD) galaxy (
M
V
= −7.1) located at a distance close to the Milky Way virial radius. Early shallow color–magnitude diagrams (CMDs) indicated ...that it possibly hosted an intermediate-age or even young stellar population, which is unusual for a galaxy of this mass. In this paper, we present new Hubble Space Telescope/Advanced Camera for Surveys CMDs reaching the oldest main-sequence turnoff with excellent photometric precision and derive a precise star formation history (SFH) for this galaxy through CMD fitting. This SFH shows that the bulk of the stellar mass in Eri II formed in an extremely short star formation burst at the earliest possible time. The derived star formation rate profile has a width at half maximum of 500 Myr and reaches a value compatible with null star formation 13 Gyr ago. However, tests with mock stellar populations and with the CMD of the globular cluster M92 indicate that the star formation period could be shorter than 100 Myr. From the quantitative determination of the amount of mass turned into stars in this early star formation burst ( ∼2 × 10
5
M
⊙
) we infer the number of supernova (SN) events and the corresponding energy injected into the interstellar medium. For reasonable estimates of the Eri II virial mass and values of the coupling efficiency of the SN energy, we conclude that Eri II could be quenched by SN feedback alone, thus casting doubts on the need to invoke cosmic reionization as the preferred explanation for the early quenching of old UFD galaxies.
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