The Structural evolution of substructure

We investigate the evolution of substructure in cold dark matter (CDM) halos using N-body simulations of tidal stripping of substructure halos within a static host potential. We find that halos modeled following the Navarro, Frenk, & White (NFW) mass profile lose mass continuously because of tides from the massive host, leading to the total disruption of satellite halos with small tidal radii. Although mass is predominantly stripped from the outer regions, tidal heating also causes the halo to expand and the central density to decrease after each pericentric passage, when mass loss preferentially occurs. As a result, simple models based on the tidal-limit approximation underestimate significantly the tidal mass loss over several orbits. The equilibrium structure of stripped NFW halos depends mainly on the fraction of mass lost and can be expressed in terms of a simple correction to the original NFW profile. We apply these results to substructure in the Milky Way and conclude that the dark matter halos surrounding its dwarf spheroidal (dSph) satellites have circular velocity curves that peak well beyond the luminous radius at velocities significantly higher than expected from the stellar line-of-sight velocity dispersion. Our modeling suggests that the true tidal radii of dSphs lie well beyond the putative tidal cutoff observed in the surface brightness profile, suggesting that the latter are not really tidal in origin but rather features in the light profile of limited dynamical relevance. For Draco in particular, our modeling implies that its tidal radius is much larger than derived by Irwin & Hatzidimitriou, lending support to the interpretation of recent Sloan Digital Sky Survey data by Odenkirchen et al. Similarly, our model suggests that Carina’s halo has a peak circular velocity of order � 55 km s � 1 , which may help explain how this small galaxy has managed to retain enough gas to undergo several bursts of star formation. Our results imply a close correspondence between the most massive substructure halos expected in a CDM universe and the known satellites of the Milky Way and suggest that only substructure halos with peak circular velocities below 35 km s � 1 lack readily detectable luminous counterparts. Subject headings: cosmology: theory — dark matter — galaxies: evolution — galaxies: halos — galaxies: structure — methods: N-body simulations

[1]  P. Steinhardt,et al.  Cosmology - The cosmic triangle: Revealing the state of the universe , 1999, astro-ph/9906463.

[2]  G. Quinlan.  The time-scale for core collapse in spherical star clusters , 1996, astro-ph/9606182.

[3]  J. Ostriker,et al.  Halo Formation in Warm Dark Matter Models , 2000, astro-ph/0010389.

[4]  G. Lake,et al.  Dark matter haloes within clusters , 1998, astro-ph/9801192.

[5]  Dark matter in draco and the local group: implications for direct detection experiments , 2001, astro-ph/0106271.

[6]  S. White,et al.  Tidal interactions between spherical galaxies , 1985 .

[7]  Francisco Prada,et al.  Where Are the Missing Galactic Satellites? , 1999, astro-ph/9901240.

[8]  A. Burkert.  Do Dwarf Spheroidal Galaxies Contain Dark Matter? , 1996, astro-ph/9610192.

[9]  Spergel,et al.  Observational evidence for self-interacting cold dark matter , 1999, Physical review letters.

[10]  University of Durham,et al.  The effects of photoionization on galaxy formation - II. Satellite galaxies in the Local Group , 2001, astro-ph/0108218.

[11]  D. Syer,et al.  Survival of substructure within dark matter haloes , 1997, astro-ph/9712222.

[12]  G. Lake,et al.  Density Profiles and Substructure of Dark Matter Halos: Converging Results at Ultra-High Numerical Resolution , 1999, astro-ph/9910166.

[13]  Exploring Halo Substructure with Giant Stars. II. Mapping the Extended Structure of the Carina Dwarf Spheroidal Galaxy , 1999, astro-ph/9911191.

[14]  Mark I. Wilkinson,et al.  First Clear Signature of an Extended Dark Matter Halo in the Draco Dwarf Spheroidal , 2001 .

[15]  G. Lake,et al.  Resolving the Structure of Cold Dark Matter Halos , 1997, astro-ph/9709051.

[16]  Halo Cores and Phase-Space Densities: Observational Constraints on Dark Matter Physics and Structure Formation , 2000, astro-ph/0004381.

[17]  D. Weinberg,et al.  Reionization and the Abundance of Galactic Satellites , 2000, astro-ph/0002214.

[18]  G. Efstathiou,et al.  The evolution of large-scale structure in a universe dominated by cold dark matter , 1985 .

[19]  George Lake,et al.  Dark Matter Substructure within Galactic Halos , 1999, astro-ph/9907411.

[20]  E. Bertschinger.  Self-similar secondary infall and accretion in an Einstein-de Sitter universe , 1985 .

[21]  Formation and Structure of Halos in a Warm Dark Matter Cosmology , 2000, astro-ph/0010525.

[22]  S. White,et al.  The Structure of cold dark matter halos , 1995, astro-ph/9508025.

[23]  Jeremiah P. Ostriker,et al.  EFFECTS OF TIDAL SHOCKS ON THE EVOLUTION OF GLOBULAR CLUSTERS , 1998 .

[24]  Michael S. Warren,et al.  Dark halos formed via dissipationless collapse. I: Shapes and alignment of angular momentum , 1992 .

[25]  John Dubinski,et al.  The structure of cold dark matter halos , 1991 .

[26]  Carlos S. Frenk,et al.  A recipe for galaxy formation , 1994 .

[27]  G. Efstathiou,et al.  The formation of dark halos in a universe dominated by cold dark matter , 1988 .

[28]  Dynamical Friction and the Evolution of Satellites in Virialized Halos: The Theory of Linear Response , 1999, astro-ph/9907088.

[29]  Merger histories in warm dark matter structure formation scenarios , 2001, astro-ph/0105316.

[30]  Substructure and Halo Density Profiles in a Warm Dark Matter Cosmology , 2000, astro-ph/0004115.

[31]  Stefan Gottloeber,et al.  Galaxies in N-Body Simulations: Overcoming the Overmerging Problem , 1997, astro-ph/9708191.

[32]  Toshiyuki Fukushige,et al.  On the Origin of Cusps in Dark Matter Halos , 1996, astro-ph/9610005.

[33]  Ivan R. King,et al.  The structure of star clusters. I. an empirical density law , 1962 .

[34]  G. Kauffmann,et al.  The formation and evolution of galaxies within merging dark matter haloes , 1993 .

[35]  L. Hernquist,et al.  N-body realizations of compound galaxies , 1993 .

[36]  M. Steinmetz,et al.  The Power Spectrum Dependence of Dark Matter Halo Concentrations , 2000, astro-ph/0012337.

[37]  Joel R. Primack,et al.  Formation of galaxies and large-scale structure with cold dark matter , 1984, Nature.

[38]  Fabio Governato,et al.  The Metamorphosis of Tidally Stirred Dwarf Galaxies , 2001, astro-ph/0103430.

[39]  M. Rees,et al.  Core condensation in heavy halos: a two-stage theory for galaxy formation and clustering , 1978 .

[40]  Resolving the Structure of Cold Dark Matter Halos , 2000, astro-ph/0006343.

[41]  J. Navarro,et al.  Halo Substructure and Disk Heating in a Λ Cold Dark Matter Universe , 2001, astro-ph/0106268.

[42]  Ivan R. King,et al.  The structure of star clusters. III. Some simple dvriamical models , 1966 .

[43]  Mike Irwin,et al.  Structural parameters for the Galactic dwarf spheroidals , 1995 .

[44]  S. White,et al.  A Universal Density Profile from Hierarchical Clustering , 1996, astro-ph/9611107.

[45]  George Lake,et al.  On the Destruction and Overmerging of Dark Halos in Dissipationless N-Body Simulations , 1996 .

[46]  Mario Mateo,et al.  DWARF GALAXIES OF THE LOCAL GROUP , 1998, astro-ph/9810070.

[47]  G. Efstathiou.  Suppressing the formation of dwarf galaxies via photoionization , 1992 .

[48]  The Dynamics of Sinking Satellites around Disk Galaxies: A Poor Man’s Alternative to High-Resolution Numerical Simulations , 2000, astro-ph/0012305.

[49]  Rachel S. Somerville,et al.  Can Photoionization Squelching Resolve the Substructure Crisis? , 2001, astro-ph/0107507.