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Integrated global assessment of the natural forest carbon potential
(2023-12-07) Mo, Lidong
Forests are a substantial terrestrial carbon sink, but anthropogenic changes in land use and climate have considerably reduced the scale of this system1. Remote-sensing estimates to quantify carbon losses from global forests2-5 are characterized by considerable uncertainty and we lack a comprehensive ground-sourced evaluation to benchmark these estimates. Here we combine several ground-sourced6 and satellite-derived approaches2,7,8 to evaluate the scale of the global forest carbon potential outside agricultural and urban lands. Despite regional variation, the predictions demonstrated remarkable consistency at a global scale, with only a 12% difference between the ground-sourced and satellite-derived estimates. At present, global forest carbon storage is markedly under the natural potential, with a total deficit of 226 Gt (model range = 151-363 Gt) in areas with low human footprint. Most (61%, 139 Gt C) of this potential is in areas with existing forests, in which ecosystem protection can allow forests to recover to maturity. The remaining 39% (87 Gt C) of potential lies in regions in which forests have been removed or fragmented. Although forests cannot be a substitute for emissions reductions, our results support the idea2,3,9 that the conservation, restoration and sustainable management of diverse forests offer valuable contributions to meeting global climate and biodiversity targets.
Analysis of ground-sourced and satellite-derived models reveals a global forest carbon potential of 226 Gt outside agricultural and urban lands, with a difference of only 12% across these modelling approaches.
Stellar Properties for a Comprehensive Collection of Star-forming Regions in the SDSS APOGEE-2 Survey
(ASTRONOMICAL JOURNAL, 2023-01-01) Román-Zúñiga, CG; Kounkel, M; Hernández, J; Ramírez, KP; [et al.]
The Sloan Digital Sky Survey IV APOGEE-2 primary science goal was to observe red giant stars throughout the Galaxy to study its dynamics, morphology, and chemical evolution. The APOGEE instrument, a high-resolution 300fiber H-band (1.55-1.71 mu m) spectrograph, is also ideal to study other stellar populations in the Galaxy, among which are a number of star-forming regions and young open clusters. We present the results of the determination of six stellar properties (Teff, log g, [Fe/H], L/L-circle dot, M/M-circle dot, and age) for a sample that is composed of 3360 young stars, of subsolar to supersolar types, in 16 Galactic star formation and young open cluster regions. Those sources were selected by using a clustering method that removes most of the field contamination. Samples were also refined by removing targets affected by various systematic effects of the parameter determination. The final samples are presented in a comprehensive catalog that includes all six estimated parameters. This overview study also includes parameter spatial distribution maps for all regions and Hertzsprung-Russell (log L/L-circle dot vs. T-eff) diagrams. This study serves as a guide for detailed studies on individual regions and paves the way for the future studies on the global properties of stars in the pre-main-sequence phase of stellar evolution using more robust samples.
Light elements Na and Al in 58 bulge spheroid stars from APOGEE
(MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 2023-09-29) Barbuy, B; Friaça, ACS; Ernandes, H; Moura, T; Masseron, T; Cunha, K; Smith, VV; Souto, D; Pérez-Villegas, A; Souza, SO; Chiappini, C; Queiroz, ABA; Fernández-Trincado, JG; [et al.]
We identified a sample of 58 candidate stars with metallicity [Fe/H]less than or similar to-0.8 that likely belong to the old bulge spheroid stellar population, and analyse their Na and Al abundances from Apache Point Observatory Galactic Evolution Experiment (APOGEE) spectra. In a previous work, we inspected APOGEE-Stellar Parameter and Chemical Abundance Pipeline abundances of C, N, O, Mg, Al, Ca, Si, and Ce in this sample. Regarding Na lines, one of them appears very strong in about 20percent of the sample stars, but it is not confirmed by other Na lines, and can be explained by sky lines, which affect the reduced spectra of stars in a certain radial velocity range. The Na abundances for 15 more reliable cases were taken into account. Al lines in the H band instead appear to be very reliable. Na and Al exhibit a spread in abundances, whereas no spread in N abundances is found, and we found no correlation between them, indicating that these stars could not be identified as second-generation stars that originated in globular clusters. We carry out the study of the behaviour of Na and Al in our sample of bulge stars and literature data by comparing them with chemodynamical evolution model suitable for the Galactic bulge. The Na abundances show a large spread, and the chemodynamical models follow the main data, whereas for aluminum instead, the models reproduce very satisfactorily the nearly secondary-element behaviour of aluminum in the metallicity range below [Fe/H]less than or similar to-1.0. For the lower-metallicity end ([Fe/H<-2.5), hypernovae are assumed to be the main contributor to yields.
CLASSY VII Lyα Profiles: The Structure and Kinematics of Neutral Gas and Implications for LyC Escape in Reionization-era Analogs
(ASTROPHYSICAL JOURNAL, 2023-10-01) Hu, WD; Martin, CL; Gronke, M; Gazagnes, S; Hayes, M; Chisholm, J; Heckman, T; Mingozzi, M; [et al.]
Ly alpha line profiles are a powerful probe of interstellar medium (ISM) structure, outflow speed, and Lyman-continuum escape fraction. In this paper, we present the Ly alpha line profiles of the Cosmic Origins Spectrograph (COS) Legacy Archive Spectroscopic SurveY, a sample rich in spectroscopic analogs of reionization-era galaxies. A large fraction of the spectra show a complex profile, consisting of a double-peaked Ly alpha emission profile in the bottom of a damped, Ly alpha absorption trough. Such profiles reveal an inhomogeneous ISM. We successfully fit the damped Ly alpha absorption and the Ly alpha emission profiles separately, but with complementary covering factors, a surprising result because this approach requires no Ly alpha exchange between high-N-H I and low-N-H I paths. The combined distribution of column densities is qualitatively similar to the bimodal distributions observed in numerical simulations. We find an inverse relation between Ly alpha peak separation and the [O III]/[O II] flux ratio, confirming that the covering fraction of Lyman-continuum-thin sightlines increases as the Ly alpha peak separation decreases. We combine measurements of Ly alpha peak separation and Ly alpha red peak asymmetry in a diagnostic diagram, which identifies six Lyman-continuum leakers in the COS Legacy Archive Spectrocopy SurveY (CLASSY) sample. We find a strong correlation between the Ly alpha trough velocity and the outflow velocity measured from interstellar absorption lines. We argue that greater vignetting of the blueshifted Ly alpha peak, relative to the redshifted peak, is the source of the well-known discrepancy between shell-model parameters and directly measured outflow properties. The CLASSY sample illustrates how scattering of Ly alpha photons outside the spectroscopic aperture reshapes Ly alpha profiles because the distances to these compact starbursts span a large range.
The stellar halo in Local Group Hestia simulations
(ASTRONOMY & ASTROPHYSICS, 2023-09-11) Khoperskov, S; Minchev, I; Libeskind, N; Haywood, M; Di Matteo, P; Belokurov, V; Steinmetz, M; Gomez, FA; [et al.]
Recent progress in understanding the assembly history of the Milky Way (MW) is driven by the tremendous amount of high-quality data delivered by Gaia (ESA), revealing a number of substructures potentially linked to several ancient accretion events. In this work we aim to explore the phase-space structure of accreted stars by analysing six M31 /MW analogues from the HESTIA suite of cosmological hydrodynamics zoom-in simulations of the Local Group. We find that all HESTIA galaxies experience a few dozen mergers but only between one and four of those have stellar mass ratios > 0 :2, relative to the host at the time of the merger. Depending on the halo definition, the most massive merger contributes from 20% to 70% of the total stellar halo mass. Individual merger remnants show diverse density distributions at z = 0, significantly overlapping with each other and with the in situ stars in the L-z - E, (V-R , V-phi) and (R; v(phi)) coordinates. Moreover, merger debris often shifts position in the Lz E space with cosmic time due to the galactic mass growth and the non-axisymmetry of the potential. In agreement with previous works, we show that even individual merger debris exhibit a number of distinct L-z-E features. In the (V-R,V-phi) plane, all HESTIA galaxies reveal radially hot, non-rotating or weakly counter-rotating, Gaia-Sausage-like features, which are the remnants of the most recent significant mergers. We find an age gradient in L-z - E space for individual debris, where the youngest stars, formed in the inner regions of accreting systems, deposit to the innermost regions of the host galaxies. The bulk of these stars formed during the last stages of accretion, making it possible to use the stellar ages of the remnants to date the merger event. In action space ( J(r),J(z),J(phi)), merger debris do not appear as isolated substructures, but are instead scattered over a large parameter area and overlap with the in situ stars. We suggest that accreted stars can be best identified using root J(r) > 0.2-0.3 (10(4) kpc km s (-1))(0.5). We also introduce a new, purely kinematic space ( J(z) /J(r)-orbital eccentricity), where di fferent merger debris can be disentangled better from each other and from the in situ stars. Accreted stars have a broad distribution of eccentricities, peaking at epsilon approximate to 0.6 0.9, and their mean eccentricity tends to be smaller for systems accreted more recently.