A profile in FIRE: resolving the radial distributions of satellite galaxies in the Local Group with simulations

While many tensions between Local Group (LG) satellite galaxies and LCDM cosmology have been alleviated through recent cosmological simulations, the spatial distribution of satellites remains an important test of physical models and physical versus numerical disruption in simulations. Using the FIRE-2 cosmological zoom-in baryonic simulations, we examine the radial distributions of satellites with Mstar > 10^5 Msun around 8 isolated Milky Way- (MW) mass host galaxies and 4 hosts in LG-like pairs. We demonstrate that these simulations resolve the survival and physical destruction of satellites with Mstar >~ 10^5 Msun. The simulations broadly agree with LG observations, spanning the radial profiles around the MW and M31. This agreement does not depend strongly on satellite mass, even at distances <~ 100 kpc. Host-to-host variation dominates the scatter in satellite counts within 300 kpc of the hosts, while time variation dominates scatter within 50 kpc. More massive host galaxies within our sample have fewer satellites at small distances, likely because of enhanced tidal destruction of satellites via the baryonic disks of host galaxies. Furthermore, we quantify and provide fits to the tidal depletion of subhalos in baryonic relative to dark matter-only simulations as a function of distance. Our simulated profiles imply observational incompleteness in the LG even at Mstar >~ 10^5 Msun: we predict 2-10 such satellites to be discovered around the MW and possibly 6-9 around M31. To provide cosmological context, we compare our results with the radial profiles of satellites around MW analogs in the SAGA survey, finding that our simulations are broadly consistent with most SAGA systems.Comment: 18 pages, 10 figures, plus appendices. Main results in figures 2, 3, and 4. Accepted versio

Planes of satellites around Milky Way/M31-mass galaxies in the FIRE simulations and comparisons with the Local Group

We examine the prevalence, longevity, and causes of planes of satellite dwarf galaxies, as observed in the Local Group. We use 14 Milky Way/Andromeda-(MW/M31) mass host galaxies from the FIRE-2 simulations. We select the 14 most massive satellites by stellar mass within 300 kpc of each host and correct for incompleteness from the foreground galactic disc when comparing to the MW. We find that MW-like planes as spatially thin and/or kinematically coherent as observed are uncommon, but they do exist in our simulations. Spatially thin planes occur in 1-2 per cent of snapshots during $z=0-0.2$, and kinematically coherent planes occur in 5 per cent of snapshots. These planes are generally transient, surviving for less than 500 Myr. However, if we select hosts with an LMC-like satellite near first pericentre, the fraction of snapshots with MW-like planes increases dramatically to 7-16 per cent, with lifetimes of 0.7-1 Gyr, likely because of group accretion of satellites. We find that M31's satellite distribution is much more common: M31's satellites lie within about 1 sigma of the simulation median for every plane metric we consider. We find no significant difference in average satellite planarity for isolated hosts versus hosts in LG-like pairs. Baryonic and dark matter-only simulations exhibit similar levels of planarity, even though baryonic subhaloes are less centrally concentrated within their host haloes. We conclude that planes of satellites are not a strong challenge to LCDM cosmology.Comment: 15 pages, 8 figures. Main results in Figures 2 and 7. Accepted by MNRA

The massive CPN−1CP^{N-1} model for frustrated spin systems

We study the classical ${SU(N)\otimes U(1)/SU(N-1)\otimes U(1)}$ Non Linear Sigma model which is the continuous low energy effective field theory for $N$ component frustrated spin systems. The $\beta$ functions for the two coupling constants of this model are calculated around two dimensions at two loop order in a low temperature expansion. Our study is completed by a large $N$ analysis of the model. The $\beta$ functions for the coupling constants and the mass gap are calculated in all dimensions between 2 and 4 at order ${1/N}$. As a main result we show that the standard procedure at the basis of the $1/N$ expansion leads to results that partially contradict those of the weak coupling analysis. We finally present the procedure that reconciles the weak coupling and large $N$ analysis, giving a consistent picture of the expected scaling of frustrated magnets.Comment: 55 pages, Late

Localized qubits in curved spacetimes

We provide a systematic and self-contained exposition of the subject of localized qubits in curved spacetimes. This research was motivated by a simple experimental question: if we move a spatially localized qubit, initially in a state |\psi_1>, along some spacetime path \Gamma from a spacetime point x_1 to another point x_2, what will the final quantum state |\psi_2> be at point x_2? This paper addresses this question for two physical realizations of the qubit: spin of a massive fermion and polarization of a photon. Our starting point is the Dirac and Maxwell equations that describe respectively the one-particle states of localized massive fermions and photons. In the WKB limit we show how one can isolate a two-dimensional quantum state which evolves unitarily along \Gamma. The quantum states for these two realizations are represented by a left-handed 2-spinor in the case of massive fermions and a four-component complex polarization vector in the case of photons. In addition we show how to obtain from this WKB approach a fully general relativistic description of gravitationally induced phases. We use this formalism to describe the gravitational shift in the COW 1975 experiment. In the non-relativistic weak field limit our result reduces to the standard formula in the original paper. We provide a concrete physical model for a Stern-Gerlach measurement of spin and obtain a unique spin operator which can be determined given the orientation and velocity of the Stern-Gerlach device and velocity of the massive fermion. Finally, we consider multipartite states and generalize the formalism to incorporate basic elements from quantum information theory such as quantum entanglement, quantum teleportation, and identical particles. The resulting formalism provides a basis for exploring precision quantum measurements of the gravitational field using techniques from quantum information theory.Comment: 53 pages, 7 figures; v2: published version with further corrections. v3: some references and equation typesetting fixe

The Many Landscapes of Recombination in <em>Drosophila melanogaster</em>

<div><p>Recombination is a fundamental biological process with profound evolutionary implications. Theory predicts that recombination increases the effectiveness of selection in natural populations. Yet, direct tests of this prediction have been restricted to qualitative trends due to the lack of detailed characterization of recombination rate variation across genomes and within species. The use of imprecise recombination rates can also skew population genetic analyses designed to assess the presence and mode of selection across genomes. Here we report the first integrated high-resolution description of genomic and population variation in recombination, which also distinguishes between the two outcomes of meiotic recombination: crossing over (CO) and gene conversion (GC). We characterized the products of 5,860 female meioses in <em>Drosophila melanogaster</em> by genotyping a total of 139 million informative SNPs and mapped 106,964 recombination events at a resolution down to 2 kilobases. This approach allowed us to generate whole-genome CO and GC maps as well as a detailed description of variation in recombination among individuals of this species. We describe many levels of variation in recombination rates. At a large-scale (100 kb), CO rates exhibit extreme and highly punctuated variation along chromosomes, with hot and coldspots. We also show extensive intra-specific variation in CO landscapes that is associated with hotspots at low frequency in our sample. GC rates are more uniformly distributed across the genome than CO rates and detectable in regions with reduced or absent CO. At a local scale, recombination events are associated with numerous sequence motifs and tend to occur within transcript regions, thus suggesting that chromatin accessibility favors double-strand breaks. All these non-independent layers of variation in recombination across genomes and among individuals need to be taken into account in order to obtain relevant estimates of recombination rates, and should be included in a new generation of population genetic models of the interaction between selection and linkage.</p> </div

Relationship between CO rate (c) and nucleotide polymorphism (π).

<p>π indicates pairwise nucleotide variation (/bp) at noncoding sites (intergenic and introns). π values for X-linked are adjusted to be comparable to autosomal regions. Based on 100-kb adjacent windows, there is a significant positive correlation between <i>c</i> and π (Spearman's <i>R</i> = 0.560, <i>P</i><1×10⁻¹²) also detected after removing telomeric/centromeric regions (<i>R</i> = 0.497, <i>P</i><1×10⁻¹²).</p

Crossing over rate variation along chromosome arms in <i>D. melanogaster</i>.

<p>Rate of crossing over (<i>c</i>) based on data from all crosses and indicated in centimorgans (cM) per megabase (Mb) per female meiosis (red line). <i>c</i> is shown along chromosomes for 100-kb windows and a movement between adjacent windows of 50 kb. Blue lines indicate 90% confidence interval for <i>c</i> at each window.</p

Estimates of the gene conversion initiation rate (γ) along chromosome arms in <i>D. melanogaster</i>.

<p>γ (/bp/female meiosis) based all crosses and shown for adjacent 100-kb windows.</p

Top DNA motifs found enriched in sequences encompassing CO events.

<p>We focused on 1,909 CO events delimited by 500 bp or less (CO₅₀₀ sequences). Only motifs with E-vale<1×10⁻¹⁰ are shown and ranked by E-value. Presence indicates the total number of motifs per 100 CO₅₀₀ sequences, including the possible multiple presence in a single sequence. Motif M_CO4 contains the 7-nucleotide motif CCTCCCT first associated with hotspot determination in humans <a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1002905#pgen.1002905-Myers2" target="_blank">[87]</a> while motif M_CO16 contains a 10-mer sequence (CCNTCGCCGC) that overlaps with the longer 13-mer CCNCCNTNNCCNC associated with crossover activity in human hot spots <a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1002905#pgen.1002905-Myers1" target="_blank">[86]</a>. For display purposes, sequence motifs are chosen between forward and reverse to maximize the presence of A and/or C nucleotides.</p