Resonant line transfer in a fog: using Lyman-alpha to probe tiny structures in atomic gas

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Table 1

Summary of the regimes found in a static, clumpy medium.

Name	Requirement^a	N_cl^b	x_p^c	Description

Free-streaming	τ_0,total ≲ 1	∝ f_c	~ 0	Photons stream through clumps
Porous	(τ_0,total ≳ 1) ∧ (f_c ≲ 1)	~ 0	~ 0	Escape through holes without interaction
Random-walk		∝ f_c²	~ 0	Scatter off clumps until escape
Homogeneous {		∝ f_c	~ x_esc ^A	Excursion-like escape
Homogeneous {		∝ f_c	~ x_∗ ^B	Escape in a single flight

Notes. The regimes are described in detail in Sect. 2.3.

^(a)

Parameter space of regime. Visualized in Fig. 1.

^(b)

Average number of clumps a photon encounters before escape.

^(c)

Dominant frequency of escape.

^(A)

Escape frequency from a homogeneous slab (Eq. (5)).

^(B)

Boundary between core and wing of the line. x_∗ ~ 3.26 for T = 10⁴K.

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