Transcript Combining GAIA patches

5.10.2007, Tuorla Observatory
Galaxy groups in ΛCDM simulations and
SDSS DR5
P. Nurmi, P. Heinämäki, S. Niemi, J. Holopainen
Tuorla Observatory
E. Saar, M. Einasto, E. Tempel, J. Einasto
Tartu Observatory
V.J. Martínez
Observatori Astronòmic, Universitat de València
Louhi: Cray XT4
The 2.5-meter SDSS survey telescope
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5.10.2007, Tuorla Observatory
The main idea of the study ?
To compare the properties of galaxy groups in SDSS DR5
and ΛCDM in different volume limited samples
Richness = N of galaxies in the galaxy group
Luminosity functions of galaxy groups
Velocity dispersion
Virial radius
Maximum projected linear size
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5.10.2007, Tuorla Observatory
The main idea of the study ?
ΛCDM simulations
SDSS DR5 data
?
Rvir
Typical halo with several subhalos (galaxies)
Abell 2151: The Hercules Galaxy Cluster
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5.10.2007, Tuorla Observatory
Scientific context: large-scale galaxy
clustering ?
Two-point correlation functions calculated
from the halos in ΛCDM-simulations and
galaxies from SDSS agree very well (Conroy et
al. 2006, ApJ 647)-> dots = SDSS, solid line =
ART simulations 512³ in (80 Mpc/h)³
Similar results from Virgo Consortium
simulations in larger scales (Springel et al.
2005, Nature, 435)-> 2160³ in (500 Mpc/h)³
Also the galaxy formation physics incorporated
in the SPH simulation give a good account of
observed galaxy clustering (Weinberg et al.
2005, ApJ 601). [144³ in (50 Mpc/h)³ cube]
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5.10.2007, Tuorla Observatory
Scientific context: small-scale galaxy
clustering -> missing dwarf problem ?
Basically all cosmological simulations predict that there are at least one order of magnitude more small
subhalos (dwarf galaxies) around Milky Way like galaxies than what is observed (e.g. Via Lactea simulation
Diemand et al. 2007, ApJ 657)->234 million particles in (90 Mpc/h)³ multimass simulation, mp=20900 Msun
Recently discovered (from SDSS data) ultra-faint dwarfs with M/L~1000 help to solve this discrepancy, but not
fully (factor of 4 difference). However, If reionization occurred around redshift 9 − 14 , and dwarf galaxy formation
was strongly suppressed thereafter, the circular velocity function of Milky Way satellite galaxies
approximately matches that of CDM subhalos in Via Lactea simulation. (Simon and Geha 2007, astroph. 0706.0516)
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5.10.2007, Tuorla Observatory
Scientific context: large-scale galaxy
clustering ?
Multiplicity function measurements provide one
of the key constraints on the relation between
galaxy populations and dark matter halos.
The closest study similar to us is Berlind et al.
(2006, ApJSS, 167), where they used N-body
simulations to find the best linking lengths
(projected and line-of-sight) that would find
galaxy groups in SDSS data in the best way. They
also used different recipes to populate halos with
galaxies were different. The main output is their
calculated multiplicity function:
All three multiplicity functions are well fitted by
power-law relations, with best-fit slopes of
-2.72±0.16, -2.48±0.14, and -2.49±0.28.
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5.10.2007, Tuorla Observatory
Scientific context: our contribution ?
Although the idea of galaxy-halo connection is well justified ,
the question how tight the connection is and what properties are
related, remains open.
Especially, here we study the connection between galaxy
groups and halo-subhalo populations. This question is closely
related to the question how galaxies and galaxy groups are
formed and structured.
We also study the properties of galaxy groups in detail and
compare velocity dispersions, virial radius values and maximum
projected linear sizes (not yet ready).
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5.10.2007, Tuorla Observatory
Cosmological N-body
Simulations
The parameters of the cosmological model
astro-ph/0603449 v1: March 20, 2006
Wilkinson Microwave Anisotropy Probe (WMAP) Three Year Results: Implications for Cosmology
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Cosmological N-body Simulations
Our simulations: 6 different simulations with 3 different resolutions and
2 different simulation codes (AMIGA and GADGET-2):
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5.10.2007, Tuorla Observatory
How to populate halos with galaxies
(a major problem to DM-simulations) ?
We can use a simplified
procedure (varying M/L
function) that is based on the
analytical fit that gives
luminosity when halo mass is
given (Vale & Ostriker 2004,
MNRAS, 353).
We test if this is statistically
satisfied by using another
method in which suitable
galaxies that resemble DM
halos and subhalos are
selected from the Millenium
run semi-analytic galaxy
catalogue.
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5.10.2007, Tuorla Observatory
SDSS DR5 galaxy group sample
Observational ingredient is based on the galaxy group catalogue by Tago et al.
2007).
From this data we select three volume limited samples based on the group
distance; d<100 Mpc/h, d<200 Mpc/h and d<300 Mpc/h; and SDSS completeness
limit mr(lim)=17.5. This gives us three luminosity limits for galaxies that are
included in the analysis.
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5.10.2007, Tuorla Observatory
Comparison 1: Richness ?
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5.10.2007, Tuorla Observatory
Comparison 2a: Luminosity ?
(all galaxies that have L > Llim(d) are included, for observations Lgroup is
corrected for invisible galaxies)
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5.10.2007, Tuorla Observatory
Comparison 2b: Luminosity ?
(all galaxies are included, lower limit for Lgroup is chosen)
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Comparison 3: Boundness ?
(simulations)
Fractions N ≥ 2:
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5.10.2007, Tuorla Observatory
Summary
The galaxy-halo-subhalo connection is very strong beyond
dwarf galaxy mass region.
If we assume that galaxy groups in Tago et al. (2007) always
resemble halo-subhalo systems in the ΛCDM-simulations, then
their multiplicity functions agree very well.
Also, the agreement with group luminosity functions is good (at
least in large samples that include galaxy groups with large
luminosities).
The simple analytical approach to populate halos with galaxies
works surprisingly well in a statistical study.
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