分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: The primordial He abundance $Y_\mathrm{P}$ is a powerful probe of cosmology. Currently, $Y_\mathrm{P}$ is best determined by observations of metal-poor galaxies, while there are only a few known local extremely metal-poor ($<0.1 Z_\odot$) galaxies (EMPGs) having reliable He/H measurements with HeI$\lambda$10830 near-infrared (NIR) emission. Here we present deep Subaru NIR spectroscopy for 10 EMPGs. Combining the existing optical data, He/H values of 5 out of the 10 EMPGs are reliably derived by the Markov chain Monte Carlo algorithm. Adding the existing 3 EMPGs and 51 moderately metal-poor ($0.1-0.4 Z_\odot$) galaxies with reliable He/H estimates, we obtain $Y_\mathrm{P}=0.2370^{+0.0034}_{-0.0033}$ by linear regression in the $\mathrm{(He/H)}-\mathrm{(O/H)}$ plane, where we increase the number of EMPGs from 3 to 8 anchoring He/H of the most metal-poor gas in galaxies. Although our $Y_\mathrm{P}$ measurement and previous measurements are consistent, our result is slightly ($\sim 1\sigma$) smaller due to our EMPGs. With our $Y_\mathrm{P}$ and the existing primordial deuterium $D_\mathrm{P}$ measurement, we constrain the effective number of neutrino species $N_\mathrm{eff}$ and the baryon-to-photon ratio $\eta$ showing $\gtrsim 1-2\sigma$ tensions with the Standard Model and Planck Collaboration et al. (2020). Motivated by the tensions, we allow the degeneracy parameter of electron-neutrino $\xi_e$ to vary as well as $N_\mathrm{eff}$ and $\eta$. We obtain $\xi_e = 0.05^{+0.03}_{-0.02}$, $N_\mathrm{eff}=3.11^{+0.34}_{-0.31}$, and $\eta\times10^{10}=6.08^{+0.06}_{-0.06}$ from the $Y_\mathrm{P}$ and $D_\mathrm{P}$ measurements with a prior of $\eta$ taken from Planck Collaboration et al. (2020). Our constraints suggest a lepton asymmetry and allow for a high value of $N_\mathrm{eff}$ within the $1\sigma$ level, which could mitigate the Hubble tension.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: We present kinematics of 6 local extremely metal-poor galaxies (EMPGs) with low metallicities ($0.016-0.098\ Z_{\odot}$) and low stellar masses ($10^{4.7}-10^{7.6} M_{\odot}$). Taking deep medium-high resolution ($R\sim7500$) integral-field spectra with 8.2-m Subaru, we resolve the small inner velocity gradients and dispersions of the EMPGs with H$\alpha$ emission. Carefully masking out sub-structures originated by inflow and/or outflow, we fit 3-dimensional disk models to the observed H$\alpha$ flux, velocity, and velocity-dispersion maps. All the EMPGs show rotational velocities ($v_{\rm rot}$) of 5--23 km s$^{-1}$ smaller than the velocity dispersions ($\sigma_{0}$) of 17--31 km s$^{-1}$, indicating dispersion-dominated ($v_{\rm rot}/\sigma_{0}=0.29-0.80<1$) systems affected by inflow and/or outflow. Except for two EMPGs with large uncertainties, we find that the EMPGs have very large gas-mass fractions of $f_{\rm gas}\simeq 0.9-1.0$. Comparing our results with other H$\alpha$ kinematics studies, we find that $v_{\rm rot}/\sigma_{0}$ decreases and $f_{\rm gas}$ increases with decreasing metallicity, decreasing stellar mass, and increasing specific star-formation rate. We also find that simulated high-$z$ ($z\sim 7$) forming galaxies have gas fractions and dynamics similar to the observed EMPGs. Our EMPG observations and the simulations suggest that primordial galaxies are gas-rich dispersion-dominated systems, which would be identified by the forthcoming James Webb Space Telescope (JWST) observations at $z\sim 7$.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: A new model grid containing 228,016 synthetic red supergiant explosions (Type II supernovae) is introduced. Time evolution of spectral energy distributions from 1 A to 50,000 A (100 frequency bins in a log scale) is computed at each time step up to 500 days after explosion in each model. We provide light curves for the filters of the Vera C. Rubin Observatory's Legacy Survey of Space and Time (LSST), Zwicky Transient Facility (ZTF), Sloan Digital Sky Servey (SDSS), and the Neil Gehrels Swift Observatory, but light curves for any photometric filters can be constructed by convolving any filter response functions to the synthetic spectral energy distributions. We also provide bolometric light curves and photosphere information such as photospheric velocity evolution. The parameter space covered by the model grid is five progenitor masses (10, 12, 14, 16, and 18 Msun at the zero-age main sequence, solar metallicity), ten explosion energies (0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, and 5.0 x 10^51 erg), nine 56Ni masses (0.001, 0.01, 0.02, 0.04, 0.06, 0.08, 0.1, 0.2, and 0.3 Msun), nine mass-loss rates (1e-5.0, 1e-4.5, 1e-4.0, 1e-3.5, 1e-3.0, 1e-2.5, 1e-2.0, 1e-1.5, and 1e-1.0 Msun/yr with a wind velocity of 10 km/s), six circumstellar matter radii (1, 2, 4, 6, 8, and 10 x 10^14 cm), and ten circumstellar structures (beta = 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, and 5.0). 56Ni is assumed to be uniformly mixed up to the half mass of a hydrogen-rich envelope. This model grid can be a base for rapid characterizations of Type II supernovae with sparse photometric sampling expected in LSST through a Bayesian approach, for example. The model grid is available at https://doi.org/10.5061/dryad.pnvx0k6sj.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: Type Ia supernovae are thought to be carbon-oxygen white dwarf stars that explode after accreting material from a companion star, but despite extensive studies the nature of the companion star is still poorly understood, as is the explosion mechanism. In the single degenerate scenario, the companion is a non-degenerate star that loses material through winds and/or binary interaction, and a few Type Ia supernovae have shown evidence for hydrogen-rich circumstellar material. We present here the study of SN 2020eyj, a unique Type Ia supernova showing delayed interaction with helium-rich, but hydrogen-poor, circumstellar material. This material surrounding SN 2020eyj is revealed by its unusual light curve and infrared emission, narrow helium emission lines and, for the first time ever in a Type Ia supernova, also a radio counterpart. The circumstellar material likely originates from the companion star, providing the first direct evidence for a, so far hypothesized, single degenerate progenitor system composed of a white dwarf and a helium donor star.