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In this paper we examine the allowed amount of intergalactic (IG) dust, which is constrained by extinction and reddening of distant Type Ia supernovae (SNe Ia) and the thermal history of the intergalactic medium (IGM) affected by dust photoelectric heating. Based on the observational cosmic star formation history, we find an upper bound of ¥ö, the mass ratio of the IG dust to the total metal in the Universe, as ξ ≤ 0.1 for 10 Å ≤ a ≤ 0.1 μm and ξ ≤ 0.1(a/0.1 μm) for 0.1 ≤ a ≤ 1 μm, where a is a characteristic grain size of the IG dust. This upper bound of ξ ∼ 0.1 suggests that the dust-to-metal ratio in the IGM is smaller than the current Galactic value. The corresponding allowed density of the IG dust increases from ∼10-34 g cm-3 at ζ = 0 to ∼10-33 g cm-3 at z ∼ 1, and keeps almost the value toward higher redshift. This causes IG extinction of ≤0.2 mag at the observer's B band for ζ ∼ 1 sources and that of ≤1 mag for higher redshift sources. Furthermore, if E(B–V) ∼ 0.1 mag at the observer's frame against z ≥ 1 sources is detected, we can conclude that a typical size of the IG dust is ≤100 Å. The signature of the 2175-Å feature of small graphite may be found as a local minimum at z ∼ 2.5 in a plot of the observed E(B–V) as a function of the source redshift. Finally, the IGM mean temperature at z ≤ 1 can be still higher than 104 K, provided the size of the IG dust is ≤100 Å. [ABSTRACT FROM AUTHOR]

ABSTRACT We study the prospects for observing H[sub 2] and HD emission during the assembly of primordial molecular cloud cores. The primordial molecular cloud cores, which resemble those at the present epoch, can emerge around 1 +z∼ 20 according to recent numerical simulations. A core typically contracts to form the first generation of stars and the contracting core emits H[sub 2] and HD line radiation. These lines show a double-peak feature. The higher peak is the H[sub 2] line of the J= 2–0 (v= 0) rotational transition, and the lower peak is the HD line of the J= 4–3 (v= 0) rotational transition. The ratio of the peaks is about 20, this value characterizing the emission from primordial galaxies. The expected emission flux at the redshift of 1 +z∼ 20 (e.g. Ω[sub M]= 0.3 and Ω[sub Λ]= 0.7) , in the J= 2–0 (v= 0) line of H[sub 2] occurs at a rate ∼2 × 10[sup -7] Jy , and in the J= 4–3 (v= 0) line of HD at a rate ∼8 × 10[sup -9] Jy . The former has a frequency of 5.331 79 × 10[sup 11] Hz and the latter is at 5.333 88 × 10[sup 11] Hz , respectively. Because the frequency resolution of the Atacama Large Millimetre Array (ALMA) is about 40 kHz, the double peak is resolvable. While an individual object is not observable even by ALMA, the expected assembly of primordial star clusters on subgalactic scales can result in fluxes at the 2000–50 μJy level. These are marginally observable. The first peak of H[sub 2] is produced when the core gas cools due to HD cooling, while the second peak of HD occurs because the medium maintains thermal balance by H[sub 2] cooling which must be enhanced by three-body reactions to form H[sub 2] itself. [ABSTRACT FROM AUTHOR]

We study the prospects for observing H[sub 2] emission during the assembly of primordial molecular cloud kernels. The primordial molecular cloud cores, which resemble those at the present epoch, can emerge around 1+z∼20 according to recent numerical simulations. The kernels form inside the cores, and the first stars will appear inside the kernels. A kernel typically contracts to form one of the first generation stars with an accretion rate that is as large as ∼0.01 M[sub ⊙] yr[sup -1]. This occurs owing to the primordial abundances, which result in a kernel temperature of order 1000 K, and the collapsing kernel emits H[sub 2] line radiation at a rate ∼10[sup 35] erg s[sup -1]. Predominantly J=5-3 (v=0) rotational emission of H[sub 2] is expected. At redshift 1+z∼20 , the expected flux is ∼0.01 μJy for a single kernel. While an individual object is not observable by any facilities available in the near future, the expected assembly of primordial star clusters on subgalactic scales can result in fluxes at the sub-mJy level. This is marginally observable with ASTRO-F and ALMA. We also examine the rotational J=2-0 (v=0) and vibrational δv=1 emission lines. The former may possibly be detectable with ALMA. [ABSTRACT FROM AUTHOR]

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, D, in the IGM. As the rate of the dust photoelectric heating depends on the size of dust, we find the following results: if the grain size is ... 100 Å, D at z ∼ 3 is ... 1/100 Galactic value corresponding to Ω[sup IGM, sub dust] ... 10[sup -5] On the other hand, if the grain size is as small as ∼10 Å, D is ...1/1000 Galactic value corresponding to Ω[sup IGM, sub dust] ... 10[sup -6]. [ABSTRACT FROM AUTHOR]

It has recently been argued that the unidentified SCUBA objects (USOs) are a thick disc population of free-floating dense, compact galactic gas clumps at a temperature of about 7 K. The characteristic mass-scale is constrained to be on the order of a Jupiter mass, and the size is about 10 au. A typical Galactic USO is located at a distance from the Sun of about 300 pc. We have calculated the molecular emission lines from these low-temperature clouds. We consider three molecules: HD, LiH, and CO. HD is optically thin in the cloud, LiH is a molecule with a large electric dipole moment, and CO is an abundant molecule that is observed in dusty clouds. Our estimate for the typical object shows that LiH may be detectable by the future submillimetre (submm) array project, ALMA; its expected flux is at the mJy level and the linewidth is about 10[SUP5] Hz. Although typical galactic USOs are chemically and dynamically transient, the younger USOs will be recognizable via LiH emission if about a hundred USOs are observed. If USOs are confirmed to be of galactic origin, the total baryonic budget will need to be reevaluated. [ABSTRACT FROM AUTHOR]