Effect of Reionization on Structure Formation in the Universe

Abstract

I use simulations of cosmological reionization to quantify the effect of photoionization on the gas fraction in low mass objects, in particular the characteristic mass scale below which the gas fraction is reduced compared to the universal value. I show that this characteristic scale can be up to an order of magnitude lower than the linear theory Jeans mass, and that even if one defines the Jeans mass at a higher overdensity, it does not track the evolution of this characteristic suppression mass. Instead, the filtering mass, which corresponds directly to the scale over which baryonic perturbations are smoothed in linear perturbation theory, provides a remarkably good fit to the characteristic mass scale. Thus, it appears that the effect of reionization on structure formation in both the linear and nonlinear regimes is described by a single characteristic scale, the filtering scale of baryonic perturbations. In contrast to the Jeans mass, the filtering mass depends on the full thermal history of the gas instead of the instantaneous value of the sound speed, so it accounts for the finite time required for pressure to influence the gas distribution in the expanding universe. In addition to the characteristic suppression mass, I study the full shape of the probability distribution to find an object with a given gas mass among all the objects with the same total mass, and I show that the numerical results can be described by a simple fitting formula that again depends only on the filtering mass. This simple description of the probability distribution may be useful for semi-analytical modeling of structure formation in the early universe.

Galaxy formation in the Planck cosmology – I. Matching the observed evolution of star formation rates, colours and stellar masses

“…In order to model this, we use results from Gnedin (2000) who defines a filtering halo mass, MF (z), below which the baryonic fraction is reduced with respect to the universal value according to:…”

Constraints on the star formation efficiency of galaxies during the epoch of reionization

“…In the following discussion, we assume the critical halo mass Mc below which star formation is "photo-suppressible" to be 5.0 × 10 9 M , consistent with the mass scale for efficient photoionization feedback (Gnedin 2000;Finlator et al 2011), while all other parameters take the same values as in the fiducial model, unless otherwise stated. To see how photoionization heating might influence the reionization history, we compare our revised models to the baseline model given a specific combinations of Mmin,z=7 = 3.6 × 10 8 M and fesc = 0.1, 0.2, 0.2 for Model I, II, III, respectively (see the white crosses in Fig.…”

Redshift evolution of stellar mass versus gas fraction relation in 0 <z< 2 regime: observational constraint for galaxy formation models

“…They considered radiative cooling (Wiersma et al 2009;Schaye et al 2015), photo-heating by cosmic microwave background, UV and X-ray background radiation (Haardt & Madau 2001 (Springel et al 2005b). With the L-GALAXIES, they implemented radiative cooling with the cooling function of Sutherland & Dopita (1993), photoionisation heating (Gnedin 2000;Kravtsov et al 2004), star formation (Kauffmann 1996;Kennicutt 1989), and the feedbacks from SNe and AGN (Croton et al 2006). We obtain their MH 2 /M⋆ values from Fig.…”

“…Larson 1974;Dekel & Silk 1986), photoionisation by cosmic ultraviolet background radiation (e.g. Ikeuchi 1986; Efstathiou 1992; Navarro & Steinmetz 1997; ⋆ E-mail:kana.matsui@nao.ac.jp; babajn@elsi.jp Gnedin 2000;Okamoto et al 2008), and preheating of the intergalactic medium (IGM) by gravitational pancaking (e.g. Mo et al 2005;Lu et al 2015) have been considered, while for high-mass galaxies, active galactic nucleus (AGN) feedback (e.g.…”