The infrared-dark dust content of high redshift galaxies

We present a theoretical model aimed at explaining the IRX-$\beta$ relation for high redshift (z >5) galaxies. Recent observations (Capak+2015; Bouwens+2016) have shown that early Lyman Break Galaxies, although characterized by a large UV attenuation (e.g. flat UV beta slopes), show a striking FIR deficit, i.e. they are "infrared-dark". This marked deviation from the local IRX-beta relation can be explained by the larger molecular gas content of these systems. While dust in the diffuse ISM attains relatively high temperatures (Td = 45 K for typical size a=0.1 um; smaller grains can reach Td = 60 K), a sizable fraction of the dust mass is embedded in dense gas, and therefore remains cold. If confirmed, the FIR deficit might represent a novel, powerful indicator of the molecular content of high-z galaxies which can be used to pre-select candidates for follow-up deep CO observations. Thus, high-z CO line searches with ALMA might be much more promising than currently thought.Comment: 8 pages, 4 Figures, MNRAS Submitte

Number Density of Bright Lyman-Break Galaxies at z~6 in the Subaru Deep Field

We report on the bright Lyman-break galaxies (LBGs) selected in a 767 arcmin^2 area of the Subaru Deep Field. The selection is made in the i-zR vs zB-zR plane, where zB and zR are new bandpasses with a central wavelength of 8842A and 9841A, respectively. This set of bandpasses enables us to separate well z~6 LBGs from foreground galaxies and Galactic cool stars. We detect 12 LBG candidates down to zR=25.4, and calculate the normalization of the rest-frame far-ultraviolet (FUV: 1400A) luminosity function at MFUV = -21.6 to be \phi(-21.6) = (2.6+/-0.7) x 10^{-5} mag^{-1} Mpc^{-3}. This must be the most reliable measurement ever obtained of the number density of bright z~6 LBGs, because it is more robust against both contamination and cosmic variance than previous values. The FUV luminosity density contributed from LBGs brighter than MFUV = -21.3 is (2.8+/-0.8) x 10^{24} ergs/s/Hz/Mpc^3, which is equivalent to a star formation rate density of (3.5+/-1.0) x 10^{-4} Msun/yr/Mpc^3. Combining our measurement with those at z<6 in the literature, we find that the FUV luminosity density of bright galaxies increases by an order of magnitude from z~6 to z~3 and then drops by 10^3 from z~3 to the present epoch, while the evolution of the total luminosity density is much milder. The evolutionary behavior of bright LBGs resembles that of luminous dusty star-forming galaxies and bright QSOs. The redshift of z~3 appears to be a remarkable era in the cosmic history when massive galaxies were being intensively formed.Comment: 12 pages, accepted for PASJ, a high resolution version is available at http://hikari.astron.s.u-tokyo.ac.jp/~shima/z6LBGs

Chaotic diffusion of particles with finite mass in oscillating convection flows

Deterministic diffusion in temporally oscillating convection is studied for particles with finite mass. The particles are assumed to obey a simple dissipative dynamical system and the particle diffusion is induced by the strange attractor. The diffusion constants are numerically calculated for convection models with free and rigid boundary conditions.Comment: 5 figure

Where are the z=4 Lyman Break Galaxies? Results from Conditional Luminosity Function Models of Luminosity-dependent Correlation Functions

Using the conditional luminosity function (CLF) -- the luminosity distribution of galaxies in a dark matter halo -- as a way to model galaxy statistics, we study how z=4 Lyman Break Galaxies (LBGs) are distributed in dark matter halos. For this purpose, we measure luminosity-dependent clustering of LBGs in the Subaru/XMM-Newton Deep Field by separating a sample of 16,920 galaxies to three magnitude bins in i'-band between 24.5 and 27.5. Our models fits to data show a possible trend for more luminous galaxies to appear as satellites in more massive halos. The satellite fraction of galaxies at z=4 in these magnitude bins is 0.13 to 0.3, 0.09 to 0.22, and 0.03 to 0.14, respectively, where the 1 sigma ranges account for differences coming from two different estimates of the z=4 LF from the literature. To jointly explain the LF and the large-scale linear bias factor of z=4 LBGs as a function of rest-UV luminosity requires central galaxies to be brighter in UV at z =4 than present-day galaxies in same dark matter mass halos. Moreover, UV luminosity of central galaxies in halos with total mass greater than roughly 10^{12} M_sun must decrease from z=4 to today by an amount more than the luminosity change for galaxies in halos below this mass. This mass-dependent luminosity evolution is preferred at more than 3 sigma confidence level compared to a pure-luminosity evolution scenario where all galaxies decrease in luminosity by the same amount from z=4 to today. The scenario preferred by the data is consistent with the ``down-sizing'' picture of galaxy evolution

Consumer Response to Genetically Modified Food Products in Japan

In Japan, a large U.S. export market, there has been growing public opposition against genetically modified (GM) foods. Using a dichotomous choice contingent valuation method, findings show the discount needed for Japanese Seikyou consumers to purchase GM food products is positively affected (i.e., a greater discount is required) by higher levels of self-reported risk perceptions toward GM food, higher levels of concern about food safety and the environment, higher self-reported knowledge about biotechnology, education levels, and income. Interestingly, gender does not significantly affect the discount needed for GM food. Further, it can be inferred from the results that a transformation of Japanese consumers' perceptions and attitudes is needed for GM food products to successfully enter the Japanese market.Consumer/Household Economics,

Very blue UV-continuum slopes of low luminosity z~7 galaxies from WFC3/IR: Evidence for extremely low metallicities?

We use the ultra-deep WFC3/IR data over the HUDF and the Early Release Science WFC3/IR data over the CDF-South GOODS field to quantify the broadband spectral properties of candidate star-forming galaxies at z~7. We determine the UV-continuum slope beta in these galaxies, and compare the slopes with galaxies at later times to measure the evolution in beta. For luminous L*(z=3) galaxies, we measure a mean UV-continuum slope beta of -2.0+/-0.2, which is comparable to the beta~-2 derived at similar luminosities at z~5-6. However, for the lower luminosity 0.1L*(z=3) galaxies, we measure a mean beta of -3.0+/-0.2. This is substantially bluer than is found for similar luminosity galaxies at z~4, just 800 Myr later, and even at z~5-6. In principle, the observed beta of -3.0 can be matched by a very young, dust-free stellar population, but when nebular emission is included the expected beta becomes >~-2.7. To produce these very blue beta's (i.e., beta~-3), extremely low metallicities and mechanisms to reduce the red nebular emission are likely required. For example, a large escape fraction (i.e., f_{esc}>~0.3) could minimize the contribution from this red nebular emission. If this is correct and the escape fraction in faint z~7 galaxies is >~0.3, it may help to explain how galaxies reionize the universe.Comment: 5 pages, 5 figures, accepted for publication in Astrophysical Journal Letter

Deep rest-frame far-UV spectroscopy of the giant Lyman-alpha emitter 'Himiko'

We present deep 10h VLT/XSHOOTER spectroscopy for an extraordinarily luminous and extended Lya emitter at z=6.595 referred to as Himiko and first discussed by Ouchi et al. (2009), with the purpose of constraining the mechanisms powering its strong emission. Complementary to the spectrum, we discuss NIR imaging data from the CANDELS survey. We find neither for HeII nor any metal line a significant excess, with 3 sigma upper limits of 6.8, 3.1, and 5.8x10^{-18} erg/s/cm^2 for CIV $\lambda$1549, HeII $\lambda$1640, CIII] $\lambda$1909, respectively, assuming apertures with 200 km/s widths and offset by -250 km/s w.r.t to the peak Lya redshift. These limits provide strong evidence that an AGN is not a major contribution to Himiko's Lya flux. Strong conclusions about the presence of PopIII star-formation or gravitational cooling radiation are not possible based on the obtained HeII upper limit. Our Lya spectrum confirms both spatial extent and flux (8.8+/-0.5x10^{-17} erg/s/cm^2) of previous measurements. In addition, we can unambiguously exclude any remaining chance of it being a lower redshift interloper by significantly detecting a continuum redwards of Lya, while being undetected bluewards

Evidence for Low Extinction in Actively Star Forming Galaxies at z>>6.5

We present a search for the [CII] 158micron fine structure line (a main cooling line of the interstellar medium) and the underlying far-infrared (FIR) continuum in three high-redshift (6.6<z<8.2) star-forming galaxies using the IRAM Plateau de Bure interferometer. We targeted two Lyman-Alpha-selected galaxies (Lyman-Alpha-Emitters, LAEs) with moderate UV-based star formation rates (SFR~20 M_sun/yr; Himiko at z=6.6 and IOK-1 at z=7.0) and a Gamma Ray Burst (GRB) host galaxy (GRB 090423 at z~8.2). Based on our 3 sigma rest-frame FIR continuum limits, previous (rest-frame) UV continuum measurements and spectral energy distribution (SED) fitting, we rule out SED shapes similar to highly obscured galaxies (e.g. Arp220, M82) and less extreme dust-rich nearby spiral galaxies (e.g. M51) for the LAEs. Conservatively assuming a SED shape typical of local spiral galaxies we derive upper limits for the FIR-based star formation rates (SFRs) of ~70 M_sun/yr, ~50 M_sun/yr and ~40 M_sun/yr for Himiko, IOK-1 and GRB 090423, respectively. For the LAEs these limits are only a factor ~3 higher than the published UV-based SFRs (uncorrected for extinction). This indicates that the dust obscuration in the z>6 LAEs studied here is lower by a factor of a few than what has recently been found in some LAEs at lower redshift (2<z<3.5) with similar UV-based SFRs. A low obscuration in our z>6 LAE sample is consistent with recent rest-frame UV studies of z~7 Lyman-Break-Galaxies (LBGs).Comment: Accepted for publication in the Astrophysical Journa