Mixed Solvents

Constraining the redshifted 21-cm signal with the unresolved soft X-ray background

“…We simulated large cosmological volumes of 384 3 Mpc 3 of the high redshift Universe using a hybrid simulation, first introduced by Visbal et al (2012) and described in detail by ; we describe it briefly here. Using the known statistical properties of the initial density field, we generated a random realization of the initial overdensity (with periodic boundary conditions) and the supersonic relative velocities between the gas and dark matter (Tseliakhovich & Hirata 2010;Tseliakhovich et al 2011;Fialkov 2014) in a cubic volume. Given the large-scale density distribution, we then computed the gas fraction in starforming halos in each cell as a function of time.…”

Supersonic relative velocity between dark matter and baryons: A review

“…Interestingly enough, all the above-mentioned types of measurements may be affected by v bc , as we discuss in this section, but the most interesting potential signature of the relative velocities is expected to be found in the redshifted 21-cm signal from the epoch when first stars form 20 z 50 [11,30,32,84,85], as this is exactly the range of redshifts where the impact of v bc on structure formation and radiative backgrounds is strongest. At that epoch, in fact, the signal produced by neutral hydrogen in the intergalactic medium couples to the radiation emitted by first galaxies; thus if the first galaxies resided in light halos of M∼ 10 5 − 10 6 M ⊙ , the radiative backgrounds emitted by the first stars would bear the signature of v bc , which then would be imprinted in the 21-cm signal.…”

“…In other words, cosmological simulations that cover the complete range of scales are not currently feasible. To overcome this difficulty and properly simulate the 21-cm signal on large scales it is convenient to use hybrid computational method [12,30,32,84]. An alternative approach was taken in a papers by N. Dalal [70] in which semi-analytical estimates were used, where the later calculation is calibrated to dedicated numerical simulations [11].…”

“…They showed for the first time using semi-analytical methods that v bc imprints the enhanced BAO signal in the neutral hydrogen signal. However in this first pioneering paper several simplifying assumptions, which are now relaxed in more advanced studies [32,84,95], were made. For instance, the authors accounted for fluctuations in the 21-cm signal sourced by Ly-α radiative background only, ignoring X-rays and LW.…”

“…Since 2010, when the importance of the relative velocities was recognized for the first time [1], their impact on various areas of astrophysics and cosmology has been widely explored. The relative velocities were shown to leave signatures in a surprisingly wide variety of cosmological probes, as they were shown to affect abundance [1,8,11,13,12,16,25,42,43] and gas content [8,10,11,12,13,14,25,44,45, 50] of 10 5 − 10 6 M ⊙ halos at high redshifts (up to z ∼ 10), formation of the first stars [8,9,10,11,12], formation of globular clusters [19], abundance of massive black holes [42,43,83,72], generation of primordial magnetic fields [174], brightness of satellite galaxies [16], clustering of massive low-redshift galaxies [15,17,18], B-mode polarization of the CMB [20], patchiness of reionization [86,114], and fluctuations in 21-cm signal of neutral hydrogen [30,32,44,70,95].…”