1,363 research outputs found
A possible signature of primordial stellar populations in Lyman emitters
Observations with Subaru telescope have detected surprisingly strong Lyman
continuum (LyC; \AA\ in the rest-frame) from some Lyman
emitters (LAEs) at . We have examined the stellar population which
simultaneously accounts for the strength of the LyC and the spectral slope of
non-ionizing ultraviolet of the LAEs. As a result, we have found that stellar
populations with metallicity can explain the observed LyC
strength only with a very top-heavy initial mass function (IMF; ). However, the critical metallicity for such an IMF is expected to be
much lower. A very young ( Myr) and massive ( )
extremely metal-poor () or metal-free (so-called
Population III) stellar population can also reproduce the observed LyC strength
if the mass fraction of such 'primordial' stellar population is % in
total stellar mass of the LAEs.Comment: 4 pages, 2 figures, First Stars IV in Kyoto conference (May 2012)
proceedin
Evolution of Dust-to-Metal Ratio in Galaxies
This paper investigates the evolution of the dust-to-metal ratio in galaxies
based on a simple evolution model for the amount of metal and dust with infall.
We take into account grain formation in stellar mass-loss gas, grain growth by
the accretion of metallic atoms in a cold dense cloud, and grain destruction by
SNe shocks. Especially, we propose that the accretion efficiency is independent
of the star-formation history. This predicts various evolutionary tracks in the
metallicity ()--dust-to-gas ratio () plane depending on the
star-formation history. In this framework, the observed linear --
relation of nearby spiral galaxies can be interpreted as a sequence of a
constant galactic age. We emphasize that an observational study of the
-- relation of galaxies at is very useful to constrain the
efficiencies of dust growth and destruction. We also suggest that the
Lyman break galaxies at have a very low dust-to-metal ratio,
typically \ltsim 0.1. Although the effect of infall on the evolutionary
tracks in the -- plane is quite small, the dispersion of the infall
rate can disturb the -- relation with a constant galactic age.Comment: 9 pages, accepted to appear in PASJ October issu
Constraint on intergalactic dust from thermal history of intergalactic medium
This Letter investigates the amount of dust in the intergalactic medium
(IGM). The dust photoelectric heating can be the most efficient heating
mechanism in the IGM where the density is very small and there are a lot of
hard ultraviolet photons. Comparing the observational thermal history of IGM
with a theoretical one taking into account the dust photoelectric heating, we
can put an upper limit on the dust-to-gas ratio, , in the IGM. Since
the rate of the dust photoelectric heating depends on the size of dust, we find
the following results: If the grain size is \ga 100 \AA, at is \la 1/100 Galactic value corresponding to \Omega_{\rm dust}^{\rm
IGM}\la 10^{-5}. On the other hand, if the grain size is as small as
\AA, is \la 1/1000 Galactic value corresponding to \Omega_{\rm
dust}^{\rm IGM}\la 10^{-6}.Comment: 5 pages, 2 figures; accepted for publication in MNRAS pink page
The critical radiation intensity for direct collapse black hole formation: dependence on the radiation spectral shape
It has been proposed that supermassive black holes (SMBHs) are originated
from direct-collapse black holes (DCBHs) that are formed at z gtrsim 10 in the
primordial gas in the case that H2 cooling is suppressed by strong external
radiation. In this work, we study the critical specific intensity J^crit
required for DCBH formation for various radiation spectral shapes by a series
of one-zone calculations of a collapsing primordial- gas cloud. We calculate
the critical specific intensity at the Lyman-Werner (LW) bands J^crit_LW,21 (in
units of 10^-21 erg s^-1 Hz^-1 sr^-1 cm^-2) for realistic spectra of metal-poor
galaxies. We find J^crit is not sensitive to the age or metallicity for the
constant star formation galaxies with J^crit_LW,21 = 1300-1400, while J^crit
decreases as galaxies become older or more metal-enriched for the instantaneous
starburst galaxies. However, such dependence for the instantaneous starburst
galaxies is weak for the young or extremely metal-poor galaxies: J^crit_LW,21 =
1000-1400 for the young galaxies and J^crit_LW,21 approx 1400 for the extremely
metal-poor galaxies. The typical value of J^crit for the realistic spectra is
higher than those expected in the literature, which affects the estimated DCBH
number density n_DCBH. By extrapolating the result of Dijkstra, Ferrara and
Mesinger, we obtain n_DCBH sim 10^-10 cMpc^-3 at z = 10, although there is
still large uncertainty in this estimation.Comment: 11 pages, 6 figures, submitted to MNRA
Physical Properties of UDF12 Galaxies in Cosmological simulations
We have performed a large cosmological hydrodynamics simulation tailored to
the deep survey with the Hubble Space Telescope made in 2012, the so-called
UDF12 campaign. After making a light-cone output, we have applied the same
color selection criteria as the UDF12 campaign to select galaxies from our
simulation, and then, have examined the physical properties of them as a proxy
of the real observed UDF12 galaxies at . As a result, we find that the
halo mass is almost linearly proportional to the observed ultraviolet (UV)
luminosity ( at ). The dust
attenuation and UV slope well correlates with the observed UV
luminosity, which is consistent with observations quantitatively. The star
formation rate (SFR) is also linearly proportional to the stellar mass and the
specific SFR shows only a weak dependency on the mass. We also find an
increasing star formation history with a time-scale of Myr in the
high- galaxies. An average metallicity weighted by the Lyman continuum
luminosity reaches up to Solar even at , suggesting a rapid
metal enrichment. We also expect mJy at 350 GHz of the dust thermal
emission from the galaxies with , which can be detectable with
the Atacama Large Milimetre-submilimetre Array. The galaxies selected by the
UDF12 survey contribute to only of the cosmic SFR density from to , respectively. The James Webb Space Telescope will push
the detection fraction up to .Comment: re-Submitted to MNRAS; 16 pages; 14 figures; 1 tables
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