COZMIC. II. Cosmological Zoom-in Simulations with Fractional non-CDM Initial Conditions

Abstract We present 24 cosmological dark matter (DM)-only zoom-in simulations of a Milky Way analog with initial conditions appropriate for scenarios where non-cold dark matter (NCDM) is a fraction of the total DM abundance (f-NCDM models) as the second installment of the COZMIC suite. We initialize our simulations using transfer functions, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi class="MJX-tex-calligraphic" mathvariant="script">T</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">f</mml:mi> <mml:mo>−</mml:mo> <mml:mi mathvariant="normal">NCDM</mml:mi> </mml:mrow> </mml:msub> <mml:mo stretchy="false">(</mml:mo> <mml:mi>k</mml:mi> <mml:mo stretchy="false">)</mml:mo> <mml:mo>≡</mml:mo> <mml:msqrt> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi>P</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">f</mml:mi> <mml:mo>−</mml:mo> <mml:mi mathvariant="normal">NCDM</mml:mi> </mml:mrow> </mml:msub> <mml:mo stretchy="false">(</mml:mo> <mml:mi>k</mml:mi> <mml:mo stretchy="false">)</mml:mo> <mml:mo>/</mml:mo> <mml:msub> <mml:mrow> <mml:mi>P</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">CDM</mml:mi> </mml:mrow> </mml:msub> <mml:mo stretchy="false">(</mml:mo> <mml:mi>k</mml:mi> <mml:mo stretchy="false">)</mml:mo> </mml:mrow> </mml:msqrt> </mml:math> (where P ( k ) is the linear matter power spectrum), with an initial suppression similar to thermal-relic warm dark matter (WDM) followed by a constant-amplitude plateau. We simulate suppression wavenumbers [22.8, 32.1, 41.8, 52.0, 57.1, 95.3] Mpc −1 , corresponding to thermal-relic WDM masses m WDM ∈ [3, 4, 5, 6, 6.5, 10] keV, and plateau amplitudes δ ∈ [0.2, 0.4, 0.6, 0.8]. We model the subhalo mass function in terms of the suppression wave number and δ . Integrating these models into a forward model of the MW satellite galaxy population yields new limits on f-NCDM scenarios, with suppression wavenumbers greater than 46 and 40 Mpc −1 for δ = 0.2 and 0.4, respectively, at 95% confidence. The current data do not constrain δ &gt; 0.4. We map these limits to scenarios where a fraction f WDM of DM behaves as a thermal relic, which yields the following bounds on cosmologies with a mixture of WDM and CDM: m WDM &gt; 3.6, 4.1, 4.6, 4.9, 5.4 keV for f WDM = 0.5, 0.6, 0.7, 0.8, 0.9, respectively, at 95% confidence. The current data do not constrain WDM fractions f WDM &lt; 0.5. Our results affirm that low-mass halo abundances are sensitive to partial suppression in P ( k ), indicating the possibility of using galactic substructure to reconstruct P ( k ) on small scales.