Pituitary adrenocorticotrophin and the melanocyte stimulating hormones

Scott, A. P.; Bloomfield, Glenys A.; Lowry, P. J.; Gilkes, J. J. H.; Landon, J.; Rees, Lesley

doi:10.1007/978-1-349-02718-7_13

Cited by 58 publications

(66 citation statements)

References 90 publications

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“…It is interesting to ponder whether one can even observe these first accretion (fossil) events, long before the first stars formed-the so-called "Dark Ages" (Scott and Rees 1990;Madau et al 1997). This question is of particular interest to scientists considering the impact of the Square Kilometer Array (SKA) in detecting gas phases 1 Near Field Cosmology 29 at hese early epochs (Barkana and Loeb 2007;Furlanetto and Loeb 2004).…”

Section: Earliest Epoch Of Gas Accretionmentioning

confidence: 99%

The Origin of the Galaxy and Local Group

Bland‐Hawthorn

Freeman

Matteuccí

2014

Saas-Fee Advanced Course

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Section: Earliest Epoch Of Gas Accretionmentioning

confidence: 99%

The Origin of the Galaxy and Local Group

Bland‐Hawthorn

Freeman

Matteuccí

2014

Saas-Fee Advanced Course

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“…In principle, 21‐cm emission from the intergalactic hydrogen could reveal the evolution of structure in the baryons during these cosmic ‘Dark Ages’. Because the baryons are cold, they would closely trace the evolution of the dark matter, so that 21‐cm imaging could trace the growth of structure following the Recombination Era (Hogan & Rees 1979; Scott & Rees 1990). Because of strong coupling between the hyperfine structure of the hydrogen and the cosmic microwave background (CMB), however, a mechanism that decouples the spin temperature of the hydrogen hyperfine structure from the CMB temperature must be active, otherwise the hydrogen is rendered invisible: it absorbs and re‐emits the CMB radiation at the same rate, leaving it indistinguishable from the CMB.…”

Section: Introductionmentioning

confidence: 99%

“…Because of strong coupling between the hyperfine structure of the hydrogen and the cosmic microwave background (CMB), however, a mechanism that decouples the spin temperature of the hydrogen hyperfine structure from the CMB temperature must be active, otherwise the hydrogen is rendered invisible: it absorbs and re‐emits the CMB radiation at the same rate, leaving it indistinguishable from the CMB. At redshifts z > 30, collisions between hydrogen and electrons and other hydrogen atoms are adequate to begin decoupling the spin temperature from the CMB (Scott & Rees 1990; Madau, Meiksin & Rees 1997). Except in dense regions, however, at later times collisional decoupling is inadequate.…”

Section: Introductionmentioning

confidence: 99%

The Wouthuysen-Field effect in a clumpy intergalactic medium

Higgins

Meiksin

2009

Monthly Notices of the Royal Astronomical Society

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We show that, due to the high optical depth of the intergalactic medium to Lyman-alpha photons before the Epoch of Reionization, the Lyman-alpha scattering rate responsible for the Wouthuysen-Field effect from an isolated source will be negligible unless (1) there is sufficient time for the scattering photons to establish a steady state, or (2) the scattering gas is undergoing internal expansion or has a peculiar motion of tens to hundreds of km/s away from the source. We present steady-state solutions in the radiative diffusion approximation for the radiation field trapped in a clump of gas and show that this may result in an enhancement, by a factor of up to 10^6, of the strength of the Wouthuysen-Field effect over that obtained from the free-streaming limit. Solutions to the time-dependent diffusion equation, however, suggest that the timescales required to reach such a steady state will generally exceed the source lifetimes. In the presence of internal expansion, a steady state may be established as photons are redshifted into the red wing, and significant enhancement in the scattering rate may again be produced. Alternatively, a substantial scattering rate may arise in systems with a peculiar motion away from the source that redshifts the received radiation into the resonance line centre. As a consequence, at epochs z<30, when collisional decoupling is small except in dense regions, and prior to the establishment of any large-scale diffuse radiation field of resonance line photons, the 21cm signature from the Intergalactic Medium produced by the Wouthuysen-Field effect will in general trace the peculiar velocity field of the gas in addition to its density structure.Comment: 11 pages, 7 figures. Accepted for publication in MNRA

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“…This result is important, because it implies that neutral intergalactic atomic hydrogen gas that exists during EoR may reveal itself in a line that is different (and possibly easier to detect) than the well‐studied 21‐cm hyperfine transition (e.g. Scott & Rees 1990; Loeb & Zaldarriaga 2004; Furlanetto, Oh & Briggs 2006). Motivated by this exciting result, and by observational efforts to detect this transition, we reanalyse the detectability of the fine‐structure line during the EoR.…”

Section: Introductionmentioning

confidence: 99%

On the detectability of the hydrogen 3-cm fine-structure line from the epoch of reionization

Dijkstra

Lidz

Pritchard

et al. 2008

Monthly Notices of the Royal Astronomical Society

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A soft ultraviolet radiation field, 10.2 < hν < 13.6 eV, that permeates neutral intergalactic gas during the epoch of reionization (EoR) excites the 2p (directly) and 2s (indirectly) states of atomic hydrogen. Because the 2s state is metastable, the lifetime of atoms in this level is relatively long, which may cause the 2s state to be overpopulated relative to the 2p state. It has recently been proposed that for this reason, neutral intergalactic atomic hydrogen gas may be detected in absorption in its 3‐cm fine‐structure line (2s1/2→ 2p3/2) against the cosmic microwave background out to very high redshifts. In particular, the optical depth in the fine‐structure line through neutral intergalactic gas surrounding bright quasars during the EoR may reach τFS∼ 10−5. The resulting surface brightness temperature of tens of μK (in absorption) may be detectable with existing radio telescopes. Motivated by this exciting proposal, we perform a detailed analysis of the transfer of Lyβ, γ, δ, … radiation, and reanalyse the detectability of the fine‐structure line in neutral intergalactic gas surrounding high‐redshift quasars. We find that proper radiative transfer modelling causes the fine‐structure absorption signature to be reduced tremendously to τFS≲ 10−10. We therefore conclude that neutral intergalactic gas during the EoR cannot reveal its presence in the 3‐cm fine‐structure line to existing radio telescopes.

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Pituitary adrenocorticotrophin and the melanocyte stimulating hormones

Cited by 58 publications

References 90 publications

The Origin of the Galaxy and Local Group

The Origin of the Galaxy and Local Group

The Wouthuysen-Field effect in a clumpy intergalactic medium

On the detectability of the hydrogen 3-cm fine-structure line from the epoch of reionization

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