Dark Matter Dominated Objects. Louie Strigari Stanford

Transcription

1 Dark Matter Dominated Objects Louie Strigari Stanford

2 Milky Way Circa 2009 Satellite Year Discovered LMC 1519 SMC 1519 Sculptor 1937 Fornax 1938 Leo II 1950 Leo I 1950 Ursa Minor 1954 Draco 1954 Carina 1977 Image: Marla Geha Sextans 1990 Sagittarius 1994 Ursa Major I 2005 Willman Ursa Major II 2006 Bootes I 2006 Canes Venatici I 2006 Canes Venatici II 2006 Coma Berenices 2006 Segue Leo IV 2006 Hercules 2006 Bootes II 2007 Leo V 2008 Segue

3 What is the minimum mass dark matter halo? What is the minimum mass ``galaxy? 10 0 Springel et al Luminosity Star Clusters? Galaxies?? ] dn / dm sub [ M O Aq-A-1 Aq-A-2 Aq-A-3 Aq-A-4 Aq-A-5 Deimand, Kuhlen, Madau, Via Lactea Half-light radius Figure: Shane Walsh M sub [ M O ] Cold Dark Matter Belokurov et al. 2006, Gilmore et al. 2007

4 Mapping satellites onto CDM subhalos Koposov et al Luminosity function [e.g. Bullock et al. 2001, Benson et al. 2002, Somerville et al. 2002, Kravtsov et al. 2004, Koposov et al. 2008, Tollerud et al. 2008, Busha et al. 2009, Bovill & Ricotti 2009, Koposov et al. 2009] Kravtsov et al Magnitude Radial/Velocity distribution [e.g. Willman et al. 2004, Kravtsov et al. 2004] Fig. 7. The cumulative velocity function of the dark matter satellites in the three galactic halos (solid lines compared to the average cumulative velocity function of dwarf galaxies around the Kinematics Milky [e.g. Way and Strigari Andromeda et galaxies al. 2007, (stars). For the objects in simulations V circ is the maximum circular velocity, 2008, while Li for et the al. Lo- 2008, Maccio et al. 2008] cal Group galaxies it is either the circular velocity measured from rotation curve or from the line-of-sight velocity dispersion assuming isotropic velocities. Both observed and simulated objects are selected within the radius of 200h 1 kpc from the center of their host. The dashed lines show the velocity function for the luminous satellites in our model described in 6. The minimum stellar mass of the luminous satellites for the three hosts ranges from 10 5 M to 10 6 M, comparable to the observed range. Fig. 8. The fraction of satellites within a certain distance from the center of their host galaxy. The solid lines show distributions of the ΛCDM satellites in the three galactic halos, while the connected stars show the distribution of dwarf galaxies around the Milky Way. The figure shows that radial distribution of observed satellites is more compact than that of the overall population of dark matter satellites. The dashed lines show distributions for the luminous satellites in our model ( 6). The population of luminous satellites is the same in this and previous figures. lation. The median distance of observed satellites within 200h 1 kpc is 60h 1 kpc and 85h 1 kpc for the MW and

5 Dwarf halo kinematics Ultra-faint satellites Simon & Geha 2007 ApJ Classical satellites Walker et al. Walker et al ApJL 2008

6 Satellite Masses Derived from spherical-symmetric analysis with variable velocity anisotropy Up to 8 parameters are free, though all not necessary for the faintest systems Strigari et al Estimated total mass-to-light ratios: Segue 1: Least luminous known galaxy (Geha et al. 2009) Tidal effects important, but not within stellar radius (Penarrubbia et al. 2008)

7 Tidal Disruption and Rotation Rotation in this sense detected in M15 GC [Drukier et al. 1998] Error projections assuming 1 km/s rotation/gradient w1 com uma II Theoretical error modeling indicates that hundreds of stars needed for detection of a gradient A [km/s] A [km/s] Rotation Amplitude A [km/s]

8 LCDM and the M300/M600 relation ionization and Satellites Galaxies 3 for fore ng a ust will on in amuses n of 0 6! hypopllite g in such proo be less s of s up rom the tars. erial owlate 4 in s litined Magnitude Mag!20!15!10! Circular Velocity V max [km/s] FIG. 1. The relationship between magnitude and v max for the r!, g!, and V! bands using abundance matching (solid red, green and black lines). The dashed lines show power law fits to the low-luminosity end. V!band, we get M V! 5log(h) = 18.2! 2.5log Busha et al Extrapolation of abundance matching technique [e.g. Kravtsov et al. 2004] implies the least luminous galaxies live in halos of about 10 8 Msun [ ( vmax ) ] 7.1. (1) 1km/s When selecting the appropriate v max for assigning a luminosity, we follow the method of Conroy et al. (2006) and choose the peak v max over the trajectory of the subhalo. Because luminosities are set using the maximal v max, changing z reion has no effect on the luminosity of an individual galaxy, although the population of subhalo hosting satellites may still M 0.3 [M O ] Maccio, Kang, Moore L V [L O ] See also Li, Helmi, De Lucia, Stoehr 2008; Koposov et al. 2009

9 The core/cusp ``problem CDM predicts NFW/Einasto cuspy profiles WDM or some alternatives predict shallower central densities Current data from MW dwarf spheroidals are unable to conclusively establish whether these galaxies have cores or cusps

10 Error projections Velocity Anisotropy Cusp X X X X 1000 LOS Core 1000 LOS SIM Log-Slope Log-Slope

11 Error projections 100 Percent Error on Log Slope km/s error per star 3 km/s error per star Number of Proper Motions

12 Observational Estimates Integrated Count Days M