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: We present ALMA deep spectroscopy for a lensed galaxy at $z_{\rm spec}=8.496$ with $\log(M_{\rm star}/M_{\odot})\sim7.8$ whose optical nebular lines and stellar continuum are detected by JWST/NIRSpec and NIRCam Early Release Observations in SMACS0723. Our ALMA spectrum shows [OIII]88$\mu$m and [CII]158$\mu$m line detections at $4.0\sigma$ and $4.5\sigma$, respectively. The redshift and position of the [OIII] line coincide with those of the JWST source, while the [CII] line is blue-shifted by 90 km s$^{-1}$ with a spatial offset of $0.''5$ ($\approx0.5$ kpc in source plane) from the JWST source. The NIRCam F444W image, including [OIII]$\lambda$5007 and H$\beta$ line emission, spatially extends beyond the stellar components by a factor of $>8$. This indicates that the $z=8.5$ galaxy has already experienced strong outflows whose oxygen and carbon produce the extended [OIII]$\lambda$5007 and the offset [CII] emission, which would promote ionizing photon escape and facilitate reionization. With careful slit-loss corrections and removals of emission spatially outside the galaxy, we evaluate the [OIII]88$\mu$m/$\lambda$5007 line ratio, and derive the electron density $n_{\rm e}$ by photoionization modeling to be $220^{+170}_{-100}$ cm$^{-3}$, which is comparable with those of $z\sim2-3$ galaxies. We estimate an [OIII]88$\mu$m/[CII]158$\mu$m line ratio in the galaxy of $>4$, as high as those of known $z\sim6-9$ galaxies. This high [OIII]88$\mu$m/[CII]158$\mu$m line ratio is generally explained by the high $n_{\rm e}$ as well as the low metallicity ($Z_{\rm gas}/Z_{\odot}=0.04^{+0.02}_{-0.02}$), high ionization parameter ($\log U > -2.27$), and low carbon-to-oxygen abundance ratio ($\log$(C/O) $=[-0.52:-0.24]$) obtained from the JWST/NIRSpec data; further [CII] follow-up observations will constrain the covering fraction of photodissociation regions.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: We present ALMA Band 7 observations of a remarkably bright galaxy candidate at $z_{\rm phot}$=$16.7^{+1.9}_{-0.3}$ ($M_{\rm UV}$=$-21.6$), S5-z17-1, identified in JWST Early Release Observation data of Stephen's Quintet. We do not detect the dust continuum at 866 $\mu$m, ruling out the possibility that S5-z17-1 is a low-$z$ dusty starburst with a star-formation rate (SFR) of $\gtrsim 30\,M_{\odot}$ yr$^{-1}$. We detect a 5.1$\sigma$ line feature at $338.726\pm0.007$ GHz exactly coinciding with the JWST source position, with a 2% likelihood of the signal being spurious. The most likely line identification would be [OIII]52$\mu$m at $z=16.01$ or [CII]158$\mu$m at $z=4.61$, whose line luminosities do not violate the non-detection of the dust continuum in both cases. Together with three other $z\gtrsim$ 11-13 candidate galaxies recently observed with ALMA, we conduct a joint ALMA and JWST spectral energy distribution (SED) analysis and find that the high-$z$ solution at $z\sim$11-17 is favored in every candidate as a very blue (UV continuum slope of $\approx-2.3$) and luminous ($M_{\rm UV}$ $\approx$ [$-$24:$-$21]) system. Still, we find in some candidates that reasonable SED fits ($\Delta$ $\chi^{2}\lesssim4$) are reproduced by type-II quasar and/or quiescent galaxy templates with strong emission lines at $z\sim3$-5, where such populations predicted from their luminosity functions and EW([OIII]+H$\beta$) distributions are abundant in survey volumes used for the $z\sim$11-17 candidates. While these recent ALMA observation results have strengthened the likelihood of the high-$z$ solutions, lower-$z$ possibilities are not completely ruled out in some of the $z\sim$11-17 candidates.