Eyal Neistein Dec 2012 MS workshop Modeling galaxy clustering and weak gravitational lensing with...
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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)