PNG-UNITsims: Halo clustering response to primordial non-Gaussianities as a function of mass

We present the largest full N-body simulation to date with local primordial non-Gaussianities (L-PNG), the $\text{textsc}PNG-UNITsim$. It tracks the evolution of ${4096}^3$ particles within a periodic box with $L_{\mathrm{b}\mathrm{o}\mathrm{x}}=1h^{-1}\mathrm{G}\mathrm{p}\mathrm{c}$, leading to a mass resolution of $m_p=1.24\times {10}^9{h}^{-1}{M}_{\odot }$. This is enough to resolve galaxies targeted by stage-IV spectroscopic surveys. The $\text{textsc}PNG-UNIT$ has $\mathit{\text{Fixed}}$ initial conditions whose phases are also $\mathit{\text{Matched}}$ to the pre-existing $\text{textsc}UNIT$ simulation. These two features in the simulations reduce our uncertainty significantly so we use 100 $\text{textsc}FastPM$ mocks to estimate this reduction. The amplitude of the non-Gaussianities used to set the initial conditions of this new simulation is $f_{\mathrm{N}\mathrm{L}}^{\mathrm{l}\mathrm{o}\mathrm{c}\mathrm{a}\mathrm{l}}=100$. In this first study, we use mass selected dark matter haloes from the $\text{textsc}PNG-UNIT$ simulation to constrain the local PNG parameters. PNG induce a scale dependent bias, parameterised through \bp or $p$, which might depend on the type of cosmological tracer. Those cases when $p=1$ are referred to as the {\it universality relation}. We measure $p$ as a function of the halo mass. Haloes with masses between $1\times {10}^{12}$ and $2\times {10}^{13}{h}^{-1}{M}_{\odot }$ are well described by the {\it universality relation}. For haloes with masses between $2\times {10}^{10}$ and $1\times {10}^{12}{h}^{-1}{M}_{\odot }$ we find that $p<1$ at $3\sigma$. Combining all the mass bins, we find $p$ consistent with a value of $0.955\pm 0.013$, which is $3\sigma$ away from $\mathit{\text{universality}}$, as low mass haloes are more numerous. We also study the effect of using priors on $p$ when constraining $f_{\mathrm{N}\mathrm{L}}$. Using the values we obtain for $b_{\phi }$ as priors, we forecast that a DESI-like (stage-IV) survey will be able to constrain $f_{\mathrm{N}\mathrm{L}}$ better than if the universality relation is assumed.