Present-Day Descendants of z=3.1 LyEmitting (LAE) Galaxies in the Millennium-II Halo Merger Trees

Jean P. Walker Soler – Rutgers UniversityEric Gawiser (Advisor) – Rutgers UniversityNicholas A. Bond – Goddard Space Flight CenterNelson Padilla (Advisor) – Pontificia Universidad Católica de

ChileHarold Francke – Pontificia Universidad Católica de Chile

Millennium Workshop 2012, December 18, 2012

Outline of the Methodology

Clustering Measurement(Observation)

Clustering Measurement(Observation)

Create Simulation Models

Create Simulation Models

Measure Clustering of Models

Measure Clustering of Models

Descendants of ModelsDescendants of Models

Dark Matter Halo Mass and Number Density

Dark Matter Halo Mass and Number Density

Motivation• We wish to understand how galaxy populations connect

with each other from one redshift to another.

• By using this selection technique, we do not use any gas physics in assigning galaxies to halos.

• While conditional mass function can predict the evolution of halos, it cannot provide sub-halo information.

• Using the Millennium-II simulation we can study how DM halo mass and age selection affect the properties of their descendants.

What is a Lyman α Emitter?

B V

O3

Selection Technique

• LAEs are identified by their strong Lyman α emission (EWrest > 40 Å).• A combination of broadband and narrowband filters allow the measurement of the equivalent width of the Lyman α line.

Basic Properties of z ~ 3.1 LAEs

• Age ~ 0.22 Gyr• MStellar ~ 5 x 109 M• E(B-V) ~ 0.046

See Acquaviva et al. 2011.

MUSYC z~3.1 LAE Selection

• (BV – NB5000) > 1

• BV is found from averaging the flux from B and V bands.

Clustering Measurement (Observation)

Clustering measurements at z=3.1 (Gawiser et al. 2007) and at z=2.1 (Guaita et al. 2010)

Figure from Guaita et al. 2010. Ga07 LAE point from Gawiser et al. 2007.

r0 = 3.6 MpcLog10(Mmed) = 10.9n = 1.5x10-3 Mpc-3

Selecting Lyman α Emitting Hosting HaloMass Selected Models

• Mass Limit• Selected a random sub-

sampling of halos with M >= 10^10.6 M.

• Median• Selected around the median

mass of 10^10.9 M.• +1σ

• Selected around the upper 1 sigma mass of 10^11.4 M.

• -1σ• Selected around the lower 1

sigma mass of 10^10 M.

Age Definitions• Formation Age-Age where the most massive sub-halo in timestep is half the mass of the most massive sub-halo in the merger tree.

• Assembly Age-Age where the sum of sub-halos in a timestep is half the mass of the most massive sub-halo in the merger tree.

• Merger Age-Determines where two central sub-halos have a ratio less than or equal to 3 and where one of their descendants becomes a satellite of the other descendant. We report when these two descendant sub-halos merge

Selecting Lyman α Emitting Hosting Halo

Age Selected Models

Formation Age: Young: Selected 5% youngest

halos.

Median: Selected 5% around the median age.

Assembly Age: Young: Selected 5% youngest

halos.

Median: Selected 5% around the median age.

Major Merger Age: Young: Selected 5% youngest

halos.

Median: Selected 5% around the median age.

Clustering of LAEs in Dark Matter Halos

γ = 1.8 Best Fit

• Median and Mass limit models have the measured clustering.

• The other models have their expected clustering.

Clustering of LAEs in Dark Matter Halos

Best FitΥ = 1.8

• Clustering of the Formation Young and Assembly Young is higher compared to their median aged models.

• Merger models are consistent with each other and measured LAE clustering.

Descendants of Mass Selected Models+1σMass LimitMedian-1σ

• Descendants of the Median and Mass Limit models have similar median halo masses at each redshift. (Mmedian = 10^12.58 M⊙ @ z=0)

• The uncertainty of the clustering measurement produce a spread in descendant median halo masses on the order of ~ 0.8 dex. (Mmedian = 10^12.95 M⊙ @ z=0 and Mmedian = 10^11.71 M⊙)

Descendants of Age Selected ModelsForm YoungForm MedianAssem YoungAssem MedianMerger YoungMerger Median

• Descendants of age based models are have small deviation based on age selection (Mmedian ~ 10^12.7 M⊙ @ z=0)

• The small deviations are negligible when compared to the uncertainty of the clustering measurements of LAEs at z=3.1.

Conclusions• The central descendants (~66%) at z=0 have masses of Log10(M/M⊙)=11.8+0.6

-1.0 and full distribution masses of Mmedian = 10^12.58+0.4

-0.9 M⊙.

• The central descendants have dark matter masses similar to L* type galaxies at z=0.

• Age-based models have very similar descendant mass distributions with a central median mass of Log10(M/M⊙)=12.0 and full distribution median mass of Mmedian = 10^12.7 M⊙.

• This method allows us to study the connections between galaxies at different redshifts as long as we make an assumption of galaxy/dark matter halo occupation.

• For details see Walker Soler et al. 2012