The Stellar Mass, Star Formation Rate and Dark Matter Halo Properties of LAEs at z∼2z\sim2

We present average stellar population properties and dark matter halo masses of $z \sim 2$ \lya emitters (LAEs) from SED fitting and clustering analysis, respectively, using $\simeq$ $1250$ objects ($NB387\le25.5$) in four separate fields of $\simeq 1$ deg$^2$ in total. With an average stellar mass of $10.2\, \pm\, 1.8\times 10^8\ {\mathrm M_\odot}$ and star formation rate of $3.4\, \pm\, 0.4\ {\mathrm M_\odot}\ {\rm yr^{-1}}$, the LAEs lie on an extrapolation of the star-formation main sequence (MS) to low stellar mass. Their effective dark matter halo mass is estimated to be $4.0_{-2.9}^{+5.1} \times 10^{10}\ {\mathrm M_\odot}$with an effective bias of$1.22^{+0.16}_{-0.18}$which is lower than that of$z \sim 2$LAEs ($1.8\, \pm\, 0.3$), obtained by a previous study based on a three times smaller survey area, with a probability of$96\%. However, the difference in the bias values can be explained if cosmic variance is taken into account. If such a low halo mass implies a low HI gas mass, this result appears to be consistent with the observations of a high \lya escape fraction. With the low halo masses and ongoing star formation, our LAEs have a relatively high stellar-to-halo mass ratio (SHMR) and a high efficiency of converting baryons into stars. The extended Press-Schechter formalism predicts that at z=0$our LAEs are typically embedded in halos with masses similar to that of the Large Magellanic Cloud (LMC); they will also have similar SHMRs to the LMC, if their SFRs are largely suppressed after$z \sim 2$ as some previous studies have reported for the LMC itself.Comment: 34 pages, 15 figures, 6 tables. Accepted for publication in PAS

The dominant origin of diffuse Lyα halos around Lyα emitters explored by spectral energy distribution fitting and clustering analysis

The physical origin of diffuse Lyα halos (LAHs) around star-forming galaxies is still a matter of debate. We present the dependence of LAH luminosity [L(Lyα)_H] on the stellar mass (M⋆), star formation rate, color excess [E(B − V)⋆], and dark matter halo mass (M_h) of the parent galaxy for ∼900 Lyα emitters (LAEs) at z ∼ 2 divided into ten subsamples. We calculate L(Lyα)_H using the stacked observational relation between L(Lyα)H and central Lyα luminosity of Momose et al. (2016, MNRAS, 457, 2318), which we find agrees with the average trend of VLT/MUSE-detected individual LAEs. We find that our LAEs have relatively high L(Lyα)_H despite low M⋆ and M_h, and that L(Lyα)_H remains almost unchanged with M⋆ and perhaps with M_h. These results are incompatible with the cold stream (cooling radiation) scenario and the satellite-galaxy star-formation scenario, because the former predicts fainter L(Lyα)_H and both predict steeper L(Lyα)_H vs. M⋆ slopes. We argue that LAHs are mainly caused by Lyα photons escaping from the main body and then scattering in the circum-galactic medium. This argument is supported by LAH observations of Hα emitters (HAEs). When LAHs are taken into account, the Lyα escape fractions of our LAEs are about ten times higher than those of HAEs with similar M⋆ or E(B − V)⋆, which may partly arise from lower H I gas masses implied from lower M_h at fixed M⋆, or from another Lyα source in the central part

The dominant origin of diffuse Lyα halos around Lyα emitters explored by spectral energy distribution fitting and clustering analysis

The physical origin of diffuse Lyα halos (LAHs) around star-forming galaxies is still a matter of debate. We present the dependence of LAH luminosity [L(Lyα)_H] on the stellar mass (M⋆), star formation rate, color excess [E(B − V)⋆], and dark matter halo mass (M_h) of the parent galaxy for ∼900 Lyα emitters (LAEs) at z ∼ 2 divided into ten subsamples. We calculate L(Lyα)_H using the stacked observational relation between L(Lyα)H and central Lyα luminosity of Momose et al. (2016, MNRAS, 457, 2318), which we find agrees with the average trend of VLT/MUSE-detected individual LAEs. We find that our LAEs have relatively high L(Lyα)_H despite low M⋆ and M_h, and that L(Lyα)_H remains almost unchanged with M⋆ and perhaps with M_h. These results are incompatible with the cold stream (cooling radiation) scenario and the satellite-galaxy star-formation scenario, because the former predicts fainter L(Lyα)_H and both predict steeper L(Lyα)_H vs. M⋆ slopes. We argue that LAHs are mainly caused by Lyα photons escaping from the main body and then scattering in the circum-galactic medium. This argument is supported by LAH observations of Hα emitters (HAEs). When LAHs are taken into account, the Lyα escape fractions of our LAEs are about ten times higher than those of HAEs with similar M⋆ or E(B − V)⋆, which may partly arise from lower H I gas masses implied from lower M_h at fixed M⋆, or from another Lyα source in the central part

Ferromagnetism in multi--band Hubbard models: From weak to strong Coulomb repulsion

We propose a new mechanism which can lead to ferromagnetism in Hubbard models containing triangles with different on-site energies. It is based on an effective Hamiltonian that we derive in the strong coupling limit. Considering a one-dimensional realization of the model, we show that in the quarter-filled, insulating case the ground-state is actually ferromagnetic in a very large parameter range going from Tasaki's flat-band limit to the strong coupling limit of the effective Hamiltonian. This result has been obtained using a variety of analytical and numerical techniques. Finally, the same results are shown to apply away from quarter-filling, in the metallic case.Comment: 12 pages, revtex, 12 figures,needs epsf and multicol style file

The stellar mass, star formation rate and dark matter halo properties of LAEs at z ∼ 2

We present average stellar population properties and dark matter halo masses of z ∼ 2 Lyα emitters (LAEs) from spectral energy distribution fitting and clustering analysis, respectively, using ≃ 1250 objects (NB387 ≤ 25.5) in four separate fields of ≃ 1 deg^2 in total. With an average stellar mass of 10.2 ± 1.8 × 10^8 M⊙ and star formation rate of 3.4 ± 0.4 M⊙ yr^(−1), the LAEs lie on an extrapolation of the star-formation main sequence (MS) to low stellar mass. Their effective dark matter halo mass is estimated to be 4.0^(+5.1)_(−2.9)×10^(10) M⊙ with an effective bias of 1.22^(+0.16)_(−0.18, which is lower than that of z ∼ 2 LAEs (1.8 ± 0.3) obtained by a previous study based on a three times smaller survey area, with a probability of 96%. However, the difference in the bias values can be explained if cosmic variance is taken into account. If such a low halo mass implies a low H I gas mass, this result appears to be consistent with the observations of a high Lyα escape fraction. With the low halo masses and ongoing star formation, our LAEs have a relatively high stellar-to-halo mass ratio (SHMR) and a high efficiency of converting baryons into stars. The extended Press–Schechter formalism predicts that at z = 0 our LAEs are typically embedded in halos with masses similar to that of the Large Magellanic Cloud (LMC); they will also have similar SHMRs to the LMC, if their star formation rates are largely suppressed after z ∼ 2 as some previous studies have reported for the LMC itself

EMPRESS. II. Highly Fe-Enriched Metal-poor Galaxies with ∼1.0\sim 1.0 (Fe/O)⊙_\odot and 0.020.02 (O/H)⊙_\odot : Possible Traces of Super Massive (>300M⊙>300 M_{\odot}) Stars in Early Galaxies

We present element abundance ratios and ionizing radiation of local young low-mass (~$10^{6}$ M_sun) extremely metal poor galaxies (EMPGs) with a 2% solar oxygen abundance (O/H)_sun and a high specific star-formation rate (sSFR~300 Gyr$^{-1}$), and other (extremely) metal poor galaxies, which are compiled from Extremely Metal-Poor Representatives Explored by the Subaru Survey (EMPRESS) and the literature. Weak emission lines such as [FeIII]4658 and HeII4686 are detected in very deep optical spectra of the EMPGs taken with 8m-class telescopes including Keck and Subaru (Kojima et al. 2019, Izotov et al. 2018), enabling us to derive element abundance ratios with photoionization models. We find that neon- and argon-to-oxygen ratios are comparable to those of known local dwarf galaxies, and that the nitrogen-to-oxygen abundance ratios (N/O) are lower than 20% (N/O)_sun consistent with the low oxygen abundance. However, the iron-to-oxygen abundance ratios (Fe/O) of the EMPGs are generally high; the EMPGs with the 2%-solar oxygen abundance show high Fe/O ratios of ~90-140% (Fe/O)_sun, which are unlikely explained by suggested scenarios of Type Ia supernova iron productions, iron's dust depletion, and metal-poor gas inflow onto previously metal-riched galaxies with solar abundances. Moreover, these EMPGs have very high HeII4686/H$\beta$ ratios of ~1/40, which are not reproduced by existing models of high-mass X-ray binaries whose progenitor stellar masses are less than 120 M_sun. Comparing stellar-nucleosynthesis and photoionization models with a comprehensive sample of EMPGs identified by this and previous EMPG studies, we propose that both the high Fe/O ratios and the high HeII4686/H$\beta$ ratios are explained by the past existence of super massive ($>$300 M_sun) stars, which may evolve into intermediate-mass black holes ($\gtrsim$100 M_sun).Comment: ApJ in press. 23 pages, 7 Figures, 6 Table

Search for Outer Massive Bodies around Transiting Planetary Systems: Candidates of Faint Stellar Companions around HAT-P-7

We present results of direct imaging observations for HAT-P-7 taken with the Subaru HiCIAO and the Calar Alto AstraLux. Since the close-in transiting planet HAT-P-7b was reported to have a highly tilted orbit, massive bodies such as giant planets, brown dwarfs, or a binary star are expected to exist in the outer region of this system. We show that there are indeed two candidates for distant faint stellar companions around HAT-P-7. We discuss possible roles played by such companions on the orbital evolution of HAT-P-7b. We conclude that as there is a third body in the system as reported by Winn et al. (2009, ApJL, 763, L99), the Kozai migration is less likely while planet-planet scattering is possible.Comment: 8 pages, 3 figures, 2 tables, PASJ in pres

JWST/NIRSpec Measurements of Extremely Low Metallicities in High Equivalent Width Lyman-α\alpha Emitters

Deep VLT/MUSE optical integral field spectroscopy has recently revealed an abundant population of ultra-faint galaxies ($M_{UV} = -$15; 0.01 $L_{\star}$) at $z=$2.9$-$6.7 due to their strong Lyman-$\alpha$ emission. The implied Lyman-$\alpha$ equivalent widths are in excess of 100-200 Angstrom, challenging existing models of normal star formation and implying extremely young ages, small stellar masses, and a very low amount of metal enrichment. We use JWST/NIRSpec's microshutter array to follow-up 45 of these galaxies (11h in G235M/F170LP and 7h in G395M/F290LP), as well as 45 lower-equivalent width Lyman-$\alpha$ emitters. Our spectroscopy covers the range 1.7$-$5.1 micron in order to target strong optical emission lines: H$\alpha$, [OIII], H$\beta$, and [NII]. Individual measurements as well as stacks reveal line ratios consistent with a metal poor nature (2$-$30% $Z_{\odot}$) and intense ionizing radiation fields. The galaxies with the highest equivalent widths of Lyman-$\alpha$, in excess of 120 Angstrom, have lower gas-phase metallicities than those with lower equivalent widths. This implies a selection based on Lyman-$\alpha$ equivalent width is an efficient technique for identifying younger, less chemically enriched systems.Comment: 13 pages, 4 appendices; submitted to AAS Journal