Denis Erkal

A timing constraint on the (total) mass of the Large Magellanic Cloud

The research leading to these results has received ERC funding under the programme (FP/2007-2013)/ERC Grant Agreement no. 308024.

The number and size of subhalo-induced gaps in stellar streams

European Research Council under the European Union’s Seventh Framework Programme (FP/2007-2013) (Grant ID: 308024), Natural Sciences and Engineering Research Council of Canada, Science and Technology Facilities Council

Properties of dark subhaloes from gaps in tidal streams

Cold or Warm, the Dark Matter substructure spectrum must extend to objects with masses as low as

Linear perturbation theory for tidal streams and the small-scale CDM power spectrum

10^7 M_\odot

Forensics of subhalo–stream encounters: the three phases of gap growth

, according to the most recent Lyman-

A 10 kpc stellar substructure at the edge of the Large Magellanic Cloud: perturbed outer disc or evidence for tidal stripping?

\alpha

Clouds, Streams and Bridges: redrawing the blueprint of the Magellanic System with Gaia DR1

measurements. Around a Milky Way-like galaxy, more than a thousand of these subhaloes will not be able to form stars but are dense enough to survive even deep down in the potential well of their host. There, within the stellar halo, these dark pellets will bombard tidal streams as they travel around the Galaxy, causing small but recognizable damage to the stream density distribution. The detection and characterization of these stream ruptures will allow us to constrain the details of the subhalo-stream interaction. In this work, for the first time, we will demonstrate how the properties of a subhalo, most importantly its mass and size, can be reliably inferred from the gap it produces in a tidal stream. For a range of realistic observational setups, mimicking e.g. SDSS, DES, Gaia and LSST data, we find that it is possible to measure the {\it complete set} of properties (including the phase-space coordinates during the flyby) of dark perturbers with

Dynamics of stream–subhalo interactions

M>10^7 M_\odot

The upper bound on the lowest mass halo

, up to a 1d degeneracy between the mass and velocity.

The first all-sky view of the Milky Way stellar halo with Gaia+2MASS RR Lyrae

Tidal streams in the Milky Way are sensitive probes of the population of dark-matter subhalos predicted in cold-dark-matter (CDM) simulations. We present a new calculus for computing the effect of subhalo fly-bys on cold tidal streams based on the action-angle representation of streams. The heart of this calculus is a line-of-parallel-angle approach that calculates the perturbed distribution function of a given stream segment by undoing the effect of all impacts. This approach allows one to compute the perturbed stream density and track in any coordinate system in minutes for realizations of the subhalo distribution down to 10^5 Msun, accounting for the streams internal dispersion and overlapping impacts. We study the properties of density and track fluctuations with suites of simulations. The one-dimensional density and track power spectra along the stream trace the subhalo mass function, with higher-mass subhalos producing power only on large scales, while lower mass subhalos cause structure on smaller scales. The time-dependence of impacts and of the evolution of the stream after an impact gives rise to bispectra. We further find that tidal streams are essentially corrugated sheets in the presence of subhalo perturbations: different projections of the track all reflect the same pattern of perturbations, facilitating their observational measurement. We apply this formalism to density data for the Pal 5 stream and make a first rigorous determination of 10^{+11}_{-6} dark-matter subhalos with masses between 3x10^6 and 10^9 Msun within 20 kpc from the Galactic center (corresponding to 1.4^{+1.6}_{-0.9} times the number predicted by CDM-only simulations or to f_{sub}(r<20 kpc) ~ 0.2%). Improved data will allow measurements of the subhalo mass function down to 10^5 Msun, thus definitively testing whether dark matter clumps on the smallest scales relevant for galaxy formation.