Small but mighty: Dark matter substructure

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Small but mighty: Dark matter substructure TeVPA 2017, Columbus OH August 11, 2017 Francis-Yan Cyr-Racine Postdoctoral Fellow Department of Physics,

1 Small but mighty: Dark matter substructure TeVPA 2017, Columbus OH August 11, 2017 Francis-Yan Cyr-Racine Postdoctoral Fellow Department of Physics, Harvard University With Ana Díaz Rivero, Cora Dvorkin, Chuck Keeton, Leonidas Moustakas, Jesús Zavala, Mark Vogelsberger Tansu Daylan, Doug Finkbeiner

2 In dark matter science, hope for the best Let s hope we can find dark matter in the lab And many, many more Francis-Yan Cyr-Racine, Harvard 8/11/17 2

(2003) Merging Clusters Lyman-alpha forest

3 but prepare for the worst! Gravitational signatures might be all we can observe! Gravitational Lensing Dwarf galaxies Stellar Streams Suyu et al. (2013) de Odenkirchen et al. (2003) Merging Clusters Lyman-alpha forest Credits: Bullock, Geha, Powell Credits: Bill Keel Markevitch et al., Clowe et al. Francis-Yan Cyr-Racine, Harvard 8/11/17 3

4 What dark matter physics can we probe through astronomy? 1) Interactions affecting the DM transfer function (initial conditions) 2) Interaction affecting the dynamics of structure formation (self-interaction) Vogelsberger, Zavala, Cyr-Racine +, arxiv:

5 Physical impacts of modified matter power spectrum and dark matter self-interaction. 10 M. Vogelsberger et al.to 1) Change the abundance of small-scale substructure 2) Change to the inner structure of subhalos See also: Schewtschenko et al. (2015, 2016), Boehm etfigure 6. DM density projections of the zoom MW-like halo simulations for four different DM models. The suppression of substructure, relative to the CDM Vogelsberger, Zavala, Cyr-Racine +, arxiv: have a primordial power spectrum suppressed at small scales. The projection has a al. (2014), Buckley et al. (2014), Elbert et al. (2017). model, is evident for the ETHOS models ETHOS-1 to ETHOS-3, which side length and depth of 500 kpc. Francis-Yan Cyr-Racine, Harvard 5 evaporation and photo-heating alone may not be enough to bring 8/11/17 subdominant impact compared to the effect of DM collisions. This

6 Galaxy-scale Gravitational Lenses Credits: Leonidas Moustakas 6

7 Direct Substructure Detection Gravitational Imaging of Perturbed Einstein Rings Vegetti et al. Nature, (2012) Figure 1: The detection of a dark-matter dominated satellite in the gravitational lens system 7 B at redshift The data shown here are at 2.2 micron and were taken with the

Top middle: the same for the perturbed model. Top right: the difference between the two models.

8 Direct Substructure Detection Gravitational Imaging of Perturbed Einstein Rings Figure 6. Top left: the sky emission model in band 6 for the best-fit smooth lens parameters for the SDP.81 data. Top middle: the same for the perturbed model. Top right: the difference between the two models. The bottom panels show the same for band 7. The bright feature in the difference plots is mainly caused by the astrometric anomaly of the arc. In each row, the images have been scaled to the peak flux of the smooth model. Hezaveh et al., (2016) 8

9 Direct Substructure Detection: A transdimensional approach A more accurate way to capture model covariances Daylan, Cyr-Racine, et al., arxiv: See also Brewer at al. (2015) 9

10 A different approach to substructure lensing: 2-point correlation function Instead of describing lensing perturbations in terms of individual subhalo, look at the correlation function of the projected density field Fisher Forecast P (k) [pc 2 ] Hezaveh et al., (2016) k [pc 1 ]

11 Substructure lensing: 2-point function Philosophy: in a CDM halo, many subhalos are encountered along any given line of sight. 10 M. Vogelsberger et al. 500 kpc Gaussian?? Clearly not Gaussian Vogelsberger, Zavala, Cyr-Racine+, arxiv: Francis-Yan Cyr-Racine, Harvard Figure 6. DM density projections of the zoom MW-like halo simulations for four different DM models. The suppression model, is evident for the ETHOS models ETHOS-1 to ETHOS-3, which have a primordial power spectrum suppressed a side length and depth of 500 kpc. 8/11/17 11

12 My philosophy: even if the convergence field is not entirely Gaussian, looking at the substructure power spectrum is interesting. Key Question: Substructure lensing: 2-point function What will we learn about low-mass subhalos from measuring the substructure convergence power spectrum? 12

13 Substructure Convergence Power Spectrum Díaz Rivero, Cyr-Racine, & Dvorkin, arxiv: Goal: Use the halo model to compute from first principle the substructure convergence power spectrum. Z sub (r) 1 A apple sub (r) = Z d 2 s NX sub i=1 apple i (r r i,m i, q i ), Z Y d 2 r i P r (r i ) ( i (apple sub (s) apple sub )(apple sub (s + r) apple sub ) P sub (k) = Z 13 Z d 2 r e ik r sub (r)

14 Substructure Power Spectrum: tnfw As a warm up, let s consider a population of truncated NFW subhalos Díaz Rivero, Cyr-Racine, & Dvorkin, arxiv:

15 Substructure Power Spectrum: tnfw The power spectrum depends mostly on three quantities: - Low-k amplitude - Truncation scale apple sub hm 2 i/hmi, - Asymptotic slope - - Díaz Rivero, Cyr-Racine, & Dvorkin, arxiv:

16 Substructure Power Spectrum: truncated cored profile Let s now consider an SIDM-inspired truncated cored profile: Díaz Rivero, Cyr-Racine, & Dvorkin, arxiv:

17 Substructure Power Spectrum: truncated cored profile Key probe of the inner subhalo density profile: asymptotic slope ALMA (Hezaveh et al. 2016) Díaz Rivero, Cyr-Racine, & Dvorkin, arxiv:

18 Measuring the substructure power spectrum: cartoon Cyr-Racine, Keeton & Moustakas, in prep. Substructure convergence perturbation Lensing potential and deflection field 18

19 Measuring the substructure power spectrum: cartoon Fiducial image Image residuals 19

20 Measuring the substructure power spectrum: cartoon There is definitely signal in the lensing residual! Warning: Completely idealized, proof-ofconcept result!! 20

21 Substructure Lensing: Conclusions Substructure lensing allows the study of small-scale dark matter structures that may hold key information about dark matter physics. The n-point functions of the projected density field allow for a more general description of dark matter substructure. The substructure power spectrum mostly depends on the abundance of substructure, their truncation, and their inner density profile. In principle, it appears possible to measure the substructure convergence power spectrum. A thorough study is on the way. 21

Statistics of flux ratios in strong lenses: probing of dark matter on small scales

Statistics of flux ratios in strong lenses: probing of dark matter on small scales Daniel Gilman (UCLA) With: Simon Birrer, Tommaso Treu, Anna Nierenberg, Chuck Keeton, Andrew Benson image: ESA/Hubble,