Eyal NeisteinDec 2012MS workshop

Modeling galaxy clustering and weak gravitational lensing

with the Millennium simulation

Eyal Neistein

TMoX group, MPE Garching

Collaborators: Mike Boylan-Kolchin, Sadegh Khochfar, Cheng Li, Francesco Shankar, Simone Weinmann

Eyal NeisteinDec 2012MS workshop

Halo occupation distribution (HOD) models

• No evolution with time, deal with only one redshift

• Populate N galaxies inside each halo of mass M

• A specific population of galaxies (usually more massive than Mmin)

• Halo properties (density profile, clustering) are being used to compute galaxy properties

Eyal NeisteinDec 2012MS workshop

HOD principlesModel assumptions:• Number of galaxies per halo, P(N|M)

• Location of satellite galaxies within their host halo follows NFW.

Jing, Mo, & Borner (1998); Ma & Fry (2000); Peacock & Smith (2000); Seljak (2000); Scoccimarro et al. (2001); Berlind & Weinberg (2002); Cooray & Sheth (2002); Yang, Mo, & van den Bosch (2003); Kravtsov et al. (2004); Tinker et al (2005,2011); Zheng et al. (2005, 2007); Zehavi et al (2005,2010)…

Zehavi et al (2010)

Main features:• Analytic model, self-contained• A simple set of parameters• A priori functional shapes• Not fully accurate (e.g., the assembly bias, Gao et al. 2005)

Eyal NeisteinDec 2012MS workshop

The HASH* approach

2. Allow a different stellar mass for central

and satellite galaxies

Neistein et al (2011a, 2011b)

- Dynamical friction for galaxies (once subhalo are stripped below the resolution)

- Location of satellite galaxies (according to the most-bound particle, or analytic model)

1. Assign a stellar mass to each subhalo from the Millennium simulation (Minfall)

* halo and subhalo

3. The stellar mass of satellite galaxies depends on both Minfall and M200:

SAM

constant stellar mass

Eyal NeisteinDec 2012MS workshop

Parameter-free approachThe observed CFs:different bins of stellar mass

Satellites:

Ste

llar

mas

s

Minfall

Centrals:

• do not assume a functional form

• check all possibilities

Eyal NeisteinDec 2012MS workshop

Searching all solutions• ~107 subhalos within the Millennium simulation• ~1014 number of pairs• ~1010 models to test• ~1024 computer operations => Hubble time?

Correlation function: we compute the number of subhalo pairs

: central-central pairs with subhalo masses M1infall, M2

infall

, : satellite-satellite, central-satellite

Weak gravitational lensing:we compute the projected density profile around each subhalo, and average it:

Eyal NeisteinDec 2012MS workshop

Models that fit the CF & SMF

Neistein et al (2011b)

median1-stdfull range

Satellites only:

Eyal NeisteinDec 2012MS workshop

Results, weak lensing

Centrals (uniform errors)Satellites (uniform errors)Centrals, 95% levelCentrals, Mandelbaum et al. (2006), HODReference line

Eyal NeisteinDec 2012MS workshop

All constraints together

- Weak lensing does not contribute- Freedom for massive satellites- Future weak lensing measurements

Eyal NeisteinDec 2012MS workshop

Comparison to HODs

Eyal NeisteinDec 2012MS workshop

Thank you, the Millennium team!

Summary

• We develop a new approach (HASH)

- stellar mass (for satellites) depends on both halo & subhalo- freedom in satellite locations- dynamical friction with a free scaling constant

>> more freedom in the models>> higher accuracy>> (almost) parameter free

• The relation between dark-matter & galaxies-weak lensing does not add much for massive galaxies-systematics are still important (assembly bias)