The physical orign of scale-dependent bias in cosmological simulations

Michael Blanton, Renyue Cen, Jeremiah P. Ostriker, Michael A. Strauss

    Research output: Contribution to journalArticle

    Abstract

    Using a large-scale hydrodynamic simulation with heuristic criteria for galaxy formation, we investigate how the galaxy field is related to physical parameters such as the mass density and the gas temperature. In our flat cold dark matter model with Ω0 = 0.37, we find that the relation between the galaxy and mass density fields is a function of scale. The bias b(R) ≡ σg(R)/σ(R), where σg(R) is the variance of galaxy counts in spheres of radius R and σ(R) is the same for mass, varies from 2.6 at 1 h-1 Mpc to 1.2 at 30 h-1 Mpc. Including the dependence of the galaxy density on local gas temperature as well as on local mass density can fully account for this scale dependence. Galaxy density depends on temperature because gas that is too hot cannot cool to form galaxies; this causes scale dependence of b(R) because local gas temperature is related to the gravitational potential and thus contains information about the large-scale density field. We show that temperature dependence generally causes b(R) to vary on quasi-linear and nonlinear scales, indicating that scale dependence of bias may be a generic effect in realistic galaxy formation scenarios. We find that the relationship between the galaxy and mass density fields is also a function of galaxy age. On large scales, the older galaxies are highly biased (b ≈ 1.7) and highly correlated (r ≡ 〈δδg〉/δδg ≈ 1.0) with the mass density field; younger galaxies are not biased (b ≈ 0.8) and are poorly correlated (r ≈ 0.5) with the mass. We argue that linear bias is inadequate to describe the relationship between galaxies and mass. We present a more physically based prescription that better fits our results and reproduces the scale dependence of the bias: ρg/〈ρg〉 = L(ρ/〈ρ〉)M(1 + T/40,000 K)N, where L = 1.23, M = 1.9, and N = -0.66.

    Original languageEnglish (US)
    Pages (from-to)590-603
    Number of pages14
    JournalAstrophysical Journal
    Volume522
    Issue number2 PART 1
    StatePublished - Sep 10 1999

    Fingerprint

    galaxies
    simulation
    gas temperature
    gas
    temperature
    galactic evolution
    heuristics
    causes
    hydrodynamics
    gravitational fields
    dark matter
    temperature dependence
    radii

    Keywords

    • Galaxies: formation
    • Hydrodynamics
    • Large-scale structure of universe

    ASJC Scopus subject areas

    • Space and Planetary Science

    Cite this

    Blanton, M., Cen, R., Ostriker, J. P., & Strauss, M. A. (1999). The physical orign of scale-dependent bias in cosmological simulations. Astrophysical Journal, 522(2 PART 1), 590-603.

    The physical orign of scale-dependent bias in cosmological simulations. / Blanton, Michael; Cen, Renyue; Ostriker, Jeremiah P.; Strauss, Michael A.

    In: Astrophysical Journal, Vol. 522, No. 2 PART 1, 10.09.1999, p. 590-603.

    Research output: Contribution to journalArticle

    Blanton, M, Cen, R, Ostriker, JP & Strauss, MA 1999, 'The physical orign of scale-dependent bias in cosmological simulations', Astrophysical Journal, vol. 522, no. 2 PART 1, pp. 590-603.
    Blanton M, Cen R, Ostriker JP, Strauss MA. The physical orign of scale-dependent bias in cosmological simulations. Astrophysical Journal. 1999 Sep 10;522(2 PART 1):590-603.
    Blanton, Michael ; Cen, Renyue ; Ostriker, Jeremiah P. ; Strauss, Michael A. / The physical orign of scale-dependent bias in cosmological simulations. In: Astrophysical Journal. 1999 ; Vol. 522, No. 2 PART 1. pp. 590-603.
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