Diversity of dwarf galaxy rotation curves: baryons, dark matter or non-circular motions? Isabel Santos-Santos Postdoctoral Research Fellow (UVic) + Julio Navarro, The Apostle Collaboration
Diversity of rotation curve shapes in observed disc galaxies V max ≈ 80 km/s • Dwarf galaxies present a wide diversity of rotation curve shapes • CDM predicts a single profile for a given velocity scale, unlike observed rotation curves • Some galaxies are consistent with CDM, others are not: either “ cuspier ” or “cored” Diversity of dwarf Galaxy rotation curves problem (Oman+15)==“ Cusp-core problem ” ( see Moore94, de Blok+08, Oh+15) Isabel Santos Santos 2
Diversity of rotation curve shapes in observed disc galaxies Diversity can be quantified by comparing: Isabel Santos Santos 3
Diversity of rotation curve shapes in observed disc galaxies SPARC (Lelli+17) Velocity at 2 kpc [km/s] LITTLE THINGS (Oh+11,Iorio+17) Santos-Santos+19 in prep Maximum velocity See Oman+15,Santos-Santos+18 Isabel Santos Santos 4
Diversity of rotation curve shapes in observed disc galaxies Dwarf galaxy mass range: Vmax ~50-100 km/s SPARC (Lelli+17) Velocity at 2 kpc [km/s] LITTLE THINGS (Oh+11,Iorio+17) Santos-Santos+19 in prep Maximum velocity See Oman+15,Santos-Santos+18 Isabel Santos Santos 5
Diversity of rotation curve shapes in observed disc galaxies Dwarf galaxy mass range: Vmax ~50-100 km/s SPARC (Lelli+17) LITTLE THINGS (Oh+11,Iorio+17) Velocity inner radii: at 2 kpc Possible solutions to the “Rotation curve diversity problem” a) Galaxy formation can modify DM mass profiles? b) DM is not CDM (e.g., self-interacting, SIDM)? c) Uncertainties in data modeling and gas non-circular motions? Velocity outer radii: maximum velocity See Oman+15,Santos-Santos+18 Isabel Santos Santos 6
A) Galaxy formation can modify DM profile: baryon-induced cores Benitez-Llambay+18 Log (Mgas/Mdark) Supernova explosions may lead to • massive gas outflows that cause variations in the gravitational potential and the consequent reduction of dark matter in the inner regions (e.g., Navarro+96, Pontzen Log (Mdark/Msun) & Governato12) Log (r/kpc) • This creates cores in the dark matter that may be reversed if baryons are re-accreted (Benitez- Llambay+18, Read+16) • It can lead to large rotation curve SFR diversity (see Santos-Santos+18 with NIHAO simulated galaxies) Time/Gyr Isabel Santos Santos 7
A) Galaxy formation can modify DM profile: baryon-induced cores Santos-Santos+18 Benitez-Llambay+18 Supernova explosions may lead to • massive gas outflows that cause variations in the gravitational potential and the consequent reduction of dark matter in the inner regions (e.g., Navarro+96, Pontzen & Governato12) • This creates cores in the dark matter that may be reversed if baryons are re-accreted (Benitez- Llambay+18, Read+16) • It can lead to large rotation curve diversity (see Santos-Santos+18 with NIHAO simulated galaxies) Isabel Santos Santos 8
B) Self-interacting dark matter (SIDM) Vtot Vcirc [km/s] SIDM → “heat transfer” from Vbar the outside in → reduction of dark matter in the inner regions (e.g.Kamada+16) If baryons accumulate ρ [M sun /kpc 3 ] to the center, core size decreases → rotation curve diversity (Kaplinghat+14, Ren+18) SIDM-only SIDM with baryons R [kpc] R [kpc] Santos-Santos+19 in prep Isabel Santos Santos 9
C) Non-circular motions? Simulated galaxies “observed” (Oman+19, see also Hayashi&Navarro06,Read+16,Pineda+17) • Synthetic observations of the HI velocity field, using same tools as in observations • Rotation curves derived using 3D-BAROLO (DiTeodoro+Fraternali15) “tilted - ring” model If there are non-circular motions in the gas, velocities are generally underestimated • Oman+19 Cusp? or Core? Circular velocity curve Azimuthal gas vel. pressure support corrected Kinematic model pressure support corrected, different orientations of line-of-sight Φ Isabel Santos Santos 10
How do these scenarios match the diversity? V2kpc [km/s] Vmax [km/s] Santos-Santos+19 in prep Isabel Santos Santos 11
How do these scenarios match the diversity? V2kpc [km/s] V2kpc [km/s] Vmax [km/s] Santos-Santos+19 in prep Isabel Santos Santos 12
How do these scenarios match the diversity? V2kpc [km/s] V2kpc [km/s] Vmax [km/s] Vmax [km/s] Santos-Santos+19 in prep Isabel Santos Santos 13
How do these scenarios match the diversity? V2kpc [km/s] V2kpc [km/s] Vmax [km/s] Vmax [km/s] Santos-Santos+19 in prep Isabel Santos Santos 14
How do these scenarios match the diversity? Santos-Santos+19 in prep Isabel Santos Santos 15
How to tell these scenarios apart?: correlations V2 bar /V2 Baryon contribution to total velocity at 2kpc Santos-Santos+19 in prep Isabel Santos Santos 16
How to tell these scenarios apart? correlations V2 bar /V2 Baryon contribution to total velocity at 2kpc V2 DM /V2 NFW Dark matter core size at 2kpc Santos-Santos+19 in prep Isabel Santos Santos 17
How to tell these scenarios apart? correlations V2 bar /V2 Baryon contribution to total velocity at 2kpc V2 DM /V2 NFW Dark matter core size at 2kpc Santos-Santos+19 in prep Isabel Santos Santos 18
How to tell these scenarios apart? correlations Dark matter core size at 2kpc Baryon contribution to total velocity at 2kpc Santos-Santos+19 in prep Isabel Santos Santos 19
How to tell these scenarios apart? correlations 2 = V 2 - V bar V dm 2 Dark matter core size at 2kpc Baryon contribution to total velocity at 2kpc Santos-Santos+19 in prep Isabel Santos Santos 20
Summary/future work: A model that explains diversity has to explain correlations as well • Baryon-induced cores • can reproduce the largest cores • lacks the most extreme cuspy cases (i.e., galaxies with low baryonic contribution in their inner regions) • SIDM+observed galaxies Produce cored galaxies in general, but not as extreme as observed. • • There is no trend between the size of the core and the importance of baryons. Mock observations of CDM+baryons (no core) simulated galaxies • • reproduce the range of diversity in core size and the trend with baryonic contribution, though more statistics is needed. • Isabel Santos Santos 21
Summary/future work: A model that explains diversity has to explain correlations as well • Baryon-induced cores • can reproduce the largest cores • lacks the most extreme cuspy cases (i.e., galaxies with low baryonic contribution in their inner regions) • SIDM+observed galaxies Produce cored galaxies in general, but not as extreme as observed. • • There is no trend between the size of the core and the importance of baryons. Mock observations of CDM+baryons (no core) simulated galaxies • • reproduce the range of diversity in core size and the trend with baryonic contribution, though more statistics is needed. • • Exploring other possibilities: i. CDM+hydro simulations with a variety of SF density thresholds ii. CDM+hydro simulations with different feedback schemes iii. SIDM+hydro simulations, with baryonic outflows Isabel Santos Santos 22
Thank you.
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