Evolution of Damped Lyman α Systems
from Hierarchical Structure Formation Models
Katsuya Okoshi (The University of Electro-communications)Okoshi, Nagashima, Gouda and Yoshioka 2004 ApJ, 603,12
Okoshi and Nagashima 2005 ApJ, 623,99
Okoshi,Nagashima and Gouda 2006 submitted to ApJ

Galaxy Formation based on
Hierarchical Structure Formation

Merging Histories of Dark HalosFormation of QSO Absorption Systems

QSO Lyα emission

DLA
QSO
ObserverLyα forestQSO Absorption Systems
Types

redshift Log N(HI) Origin

Lyα cloud

0-4.5

13-17

Intergalactic cloud or/andgalactic gasLLS

1-4.0

17-20？？？

DLA

0-4.5

20-22

galactic disk gas （?）

C IV

1-3.5

--------

halo hot gas (105 K)

Mg II0-2.2--------

halo warm gas (103 K)

１．Introduction
なぜDLA Systemに注目するのか？
1. High HI column density system

NHI ＞ 10 20.3 cm-2

Optically Thick (!) Systems NHI ＞ 10 17 cm-2
Star Formation Process の解明(cf. Surface density in the disk of the Milky Way;
Ngas=55 ±10 Mpc-2=10 21.8 cm-2 )2. More abundant systems at high redshift
多数のシステムが見つかりやすい ( Typical L*-galaxy の10倍以上）

3. Precise measurements of metal abundance in GAS (notSTAR)
Mild metallicity evolution (0 <z< 4.5）

DLAの個数密度典型的な(massive spiral)銀河と比較すると・・・c⎛ dN ⎞32
1/ 2= Φ g , 0 (1 + z ) πR g
≈
0.
02
Ω
⎟
⎜
1/ 25/ 2
Ω(1+)
Hz⎝ dz ⎠ typical
0galaxy( z = 3; Φ g , 0 = 0 . 01 h 3 Mpc − 3 , R g = 10 h − 1kpc )⎛ dN ⎞⎛ dN ⎞≈ 10 ⎜⎜⎟⎟⎝ dz ⎠ DLA⎝ dz ⎠ typicalgalaxy

Redshift Distribution

Prochaska et al. 2004

3. Precise measurements of metal abundance in GAS (not STAR)
125 DLAsからGas Metallcityを測定

Mild metallicity evolution (0 <z< 4.5）
(e.g., Prochaska et al.2003)
４. Dust-poor system (cf typical galaxy)
Small amount of dust (e.g. E(B-V)<0.01: Murphy & Liske 2004)
No evidence for a statistically significant dust bias inMgII-selected DLA surveys at 0.5 < z(abs) <3.5
(Ellison et al. 2001, 2004)>> ‘Unbiased’ Tracer : Metallicity Evolution of Pre-galactic System>> Stringent Constraints on Galaxy Formation

Prochaska et al. 2003

5. HI ガスの貯蔵庫
DLA contains a significant fraction of the HI gas in the universe!

Ω(HI) ~ 10-3 at 0 < z < 4(β=1.4-1.6; Rao et al. 2005; Prochaska et al. 2004)

HI ガスのほとんどが、DLAに存在している！

Gas Density

Prochaska et al. 2005

Metal abundanceN(HI) distribution

Number density

QSO Absorption System

QSOとの相関
銀河との相関Gas abundance
dynamics

Semi-Analytic Approach to Structure Formation
Luminosity Function, Cold-gas Mass, CMR,…

Galaxy Formation

Key Process?

QSO Absorption Systems Formation( DLA, Lyman-α clouds, metal systems,..)

Metal, HI gas, galaxy correlation, …

2. Model
Dark HalosのMerging Process
Probability Function f( M,z | M’,z’)dM:
Halo (mass M’ redshift z’) has a progenitor (M,z)>> Press-Schechter Mass Function n(M,z | M’,z’)
Dark halos

Density perturbations

ガスの進化過程について(A) Life time
Life time of halo is equal to cooing time of gas

2 ρ gas rcool
kTt life = τ cool ( rcool ) =3 μ m p n e2 rcool Λ ( T )( ρ gas ( r ) ∝ n e ( r ) ∝ r − 2 )(B) Star Formation Process•M∗ =M coldτ∗α∗Vc⎛⎞ατ∗ = τ ⎜⎟ (1 + z ) z⎝ 300 km / s ⎠0∗αz = −1.5(∝ tdyn) :accelerated efficiency model
0: constant efficiency modelτ ∗0 ≅ 2 − 5Gyr (M / L B − Vcrelation)τ ∗0 , α ∗ , α z

(C) Supernovae Feedback
Energy input by SN explosions•dM rehaeat
4 ηSN ESN • ⎛⎞
MβM
=ε=∗
⎜
∗⎟
5 Vc2dt⎝⎠⎛ V ⎞β ( V c ) = ⎜⎜ c ⎟⎟⎝ V hot ⎠− α hot: input efficiency: fraction of stars M ≥ 8M Θη SN51
ESN : energy release per a SN ( = 10 erg)
εα hot : α hot = 2(D) Population Synthesis
Total Luminosity•L ∗ = ∫ M Z cold dt∗Stellar population synthesis model

(F) Chemical Evolution
Basic Equation for 2 phase model (Cold and Hot gas components)••
dM c= − M ∗ + F (t )(1 − f ) + g (t ) − β M ∗dt
dM ∗ M c=τ∗dt•dM h= β M ∗ − g (t ) + F(t )f + A(t )dt
M c02 drcoolg (t ) = 4πρ h (rcool )rcool≅τdt••
dM c Z c= (1 − f )(FZ (t ) + R Z (t )) − Z c M ∗ + Z h g (t ) − Z cβ M ∗dt•
dM h Z h= f (FZ (t ) + R Z (t )) + Z cβ M ∗ − Z h g (t ) + Z d A(t )dt

β : SN feedback

g: cooling gas inflow

F: gas inflow from stars Fz: metal mass produced by new stars
Rz: metal mass inflow A: gas mass accreted from diffuse matter(=0)

Here we apply ‘Instantaneous Recyclic Approximation’.

銀河のMerging Processes
Dark halosのmerging processHot gas は新しくできた一つのhaloの中で共有する。
最もmassiveな銀河を’central galaxy’とし、それ以外の銀河を‘satellites’と呼ぶ。
このとき、これらの銀河どうしがmergeする。
Criteria for merging processes of galaxies
Satellite-Central merger : t (elapse) > t (dynamical friction)
Satellite-Satellite merger: t > t (random collision)

Type of merging processes (satellites v central galaxy)
Two types: Major and Minor merge
Major merge

m small / m l arg e > f bu lg e
＞ Star burst, Bulge formation (all stars reside in central bulge)
Minor merge

m small / m l arg e < f bu lg e

＞ Disk formation ( stars in satellites >> disk components)

Reference Models
standard models in galaxy formation model(ΩLCDM0, ΩΛ, h , σ 8 )( 0.3, 0.7, 0.7, 1 )( V hot ( km / s ), α hot , τ ∗0 , α ∗ )

LC
LD

(280,
(280,2.5,2.5,1.5, -2 ) (Reference Model)
4, -2 )

Astrophysical parameters are given by as follows:
1. Galaxy luminosity function (B- and K- bands)

α hot , V hot(<< SN feedback process)2. Cold-gas mass fractionα ∗,τ0∗すべて local galaxyに関する観測量で決める

DLAの同定
1．HI Central column density

2. Inclination of gaseous disksrd
3.Disk size
Exponential profile

R(DLA) = r(NHI=1020.3 cm-2)

R(DLA)

NHI<NHI>
1020.3

4. Average of HI column density
0

R(DLA) r

§３．RESULTS[A] GLOBAL PROPERTIES OF DLA SYSTEMS

Metallicity of cold gas in DLA systems
solid line: Our best model
dotted line: stellar metallicity
dashed line: a model with τ*∝dynamicaltimescale of disks (LD model)
observational data: Prochaska and Wolfe
2000, Savaglio 2001
・The metallicity shows mild evolution.
・The star formation timescale should benearly constantHI column density distribution
solid line: Our best modelobservational data:
Prochaska and Wolfe 2000
・Our model reproduces the HI column
density distribution.

Average mass evolution of each phase:cold gas (dashed line), stars(soild line),
metals(dotted line)
Metallicity weighted by mass
cold gas in DLAs (long-dashed line)
cold gas in all galaxies (dot-dahed line)
・ The average HI mass M(HI) is ~109M
・ Chemical enrichment in DLAs is similar to thatin all galaxies論点：
DLAのhost galaxyはどのような特徴をもつのか?
Compact object:galactic disk, minihalo, …?
Diffuse gas:filament, clump, …?

⇒ Low redshifts (0<z<1)の様々な観測的特徴に注目。
⇒ typical galaxiesと比較しながら、DLAのhostgalaxyを探る。

[B] Low-redshift DLA systems
We focus on DLA systems at redshift 0<z<1 ⇒ What are DLA galaxies ？
・Luminosity, HI column density, size etc. ← photometric counterparts(e.g. Rao et al.2003, Rao 2005 Proceedings of IAU conference No.199)

14 DLA galaxies

Low Luminous galaxies with
Small Impact parametersORMassive Spiral Galaxies !?

Our results agree with some observation trends.
But, our model underpredicts the luminosities andthe sizes of low-z DLAs.
⇒ Some observational biases?

1+zL/L*b [kpc]Next, we take into account a selection effect of DLA galaxies(1) Surface brightness dimming effect: fail to identify DLA galaxies fainterthan observational brightness limits (>25 mag arcsec^-1)

Observational Trend:
Luminous galaxies with large impact parameters ?
H

Direct Search for optical counterparts of DLAs

(Rao et al. 2003, ApJ, 595, 94)Next, we add a new selection effect of DLA galaxies(2) Masking effect: fail to identify DLA galaxies hidden or contaminatedby a point spread function of background QSOs

・We find that our results show better agreementwith the observations(e.g. the luminosities and the sizes) .
・A missing rate of DLA galaxies by the masking
effect attains at 60-80%
in the sample when a angular size limit is as
small as 1 arcsec.

Missing !

Radio Surveys
Another way to explore DLAs APART FROM THE SELECTION EFFECTSzArecibo Dual-Beam Survey (ADBS) [US]Blind search for HI 21 cm emission covering ~430 deg2 of sky
The radio samples are 250-300 HI-selected galaxies(a)Detections of optical counterparts (Rosenberg et al.2005)
the 2MASS J-,H-,K-band observations ⇒ L(J)-M(HI) relation??
(b) High N(HI) samples (Rosenberg & Schneider 2003)
Implication for DLA systems ⇒ σ-M(HI) relationzHI Parkes All Sky Survey (HIPASS) [Australia]
Blind search the whole southern sky for HI 21cm emission(a) Extragalactic radio objects (Zwaan et al. 2003, 2005)~4300 extragalactic HI objects(about 80% optical counterparts are confirmed: Doyle et al.2005)⇒ HI Mass Function, Ω(HI), Dark galaxies..
(b) Halo clouds (HVC) (Putman et al. 2003)⇒ Missing satellites of the Local Group⇒ CIV, MgII system

Blind HI surveys
HI Parkes All Sky Survey(Meyer et al. 2004)

4315

265

7566

Arecibo Dual-Beam Survey(Rosenberg & Schneider 2000-2005)
Slice Survey (Spitzak & Schneider 1998)

Arecibo HI Sky Survey (Solar et al.1994)

Disk Size vs HI mass

We find a tight correlation between the HI masses and the cross sections:σ∝M(HI)p; p=0.97 ± 0.01

HI gas の拡がり, HI mass

Luminosty(Star Formation) ?

DLA systems と galaxies との違いはあるのか？

DLA systems(QSO Absorption lines)

LuminosityGalaxies(Emission lines)

HI gas density

2MASS, SDSS, 2dFGRS,..
⇒ Emission lines(Hα,Lyα)

Blind Radio Surveys
HIPASS, ADBS,…
⇒ Emission lines(21cm)⇒ Stellar Mass
(Luminosity Function)⇒ HI Mass(HI Mass Function)

Optical Surveys

Luminosity vs M(HI) relation

Our result agrees with the L(J)-M(HI) relation

No significant difference between DLAs and All galaxies!

HI Mass Function (HIMF)

Our results are consistent withthe observations at M>108M

DLA systems⇒ HI-Selected galaxies
at M>108M

Prediction: SFR -M(HI) relation

The SFR is correlated more tightly with the HI mass
SFR ∝ M(HI)α α=1.22±0.05

Recent Observational Results


Optical Surveys for HI-selected Galaxies
SINGG (Survey for Ionization in Neutral-Gas Galaxies)
H-alpha emission lines from HIPASS galaxies(e.g. Meurer et al. 2006 ApJS, 165, 307)
93 HIPASS targets ⇒ Star FormationRates

HIPSS Catalogue: Optical Counterparts of HI Selected Galaxies(Doyle et al. 2005)

Optical Counterparts of ADBS samples

Good Agreement with the SFR-M(HI) Relation
More samples of low-M(HI) systems !
HI-selected galaxies provide good clues for determining theSFRs

Our model suggests that the average SFRs 0.01 M /yr.

[C] Radio properties of DLA systems at redshift z=0
Another way to explore DLA systems apart from selection effects.
Detection of DLA galaxies by Blind 21cm surveys (e.g. Rosenberg & Schneider 2003)⇒ about 50 HI-rich galaxies with HI column densities comparable to those in DLA systems
We find that
(1) A tight correlation between the HI masses and the cross sections: Log σ∝Log M(HI)(2) HI-rich galaxies with 10^9M mainly contribute to the population of DLA systems at z=0⇒ Our result is entirely consistent with the observational properties of HI-selected galaxies in the radiosurvey.
[D] Star formation rates (SFRs)
a clue to exploring what types of galaxies
consist of DLAs
⇒ Our model suggests that the average SFRs
are as low as 0.01 M /yr.

Dashed box: observational data (Rosenberg & Scheider 2003)

Conclusions
zWe investigate evolution of Damped Lyman α systems taking into accountmerging processes of dark halos from hierarchical galaxy formation models
Our results are simultaneously consistent with the observational properties:
DLA systems: Metallicity evolution, N(HI)-distribution
Optically selected-galaxies:
Luminosity functions, HI-gas mass fraction
Radio selected-galaxies:
HI-disk size, Luminosities(J-band), HIMF, Ω(HI)LSB dwarf galaxies primarily contribute to the population of DLA systems
at z<1: size ~3kpc, Sb ~22 to 27 mag arcsec-1,SFR ~10-2 Myr-1
DLA corresponds to HI-selected galaxies at M(HI)>108M in blindRadio Surveys (ADBS, HIPASS)(NB: sub-DLA corresponds to HIPASS galaxies at M(HI)~107M）（Okoshi et al.2007)⇒ Our prediction: more tight relation: SFR-M(HI) relation

High redshisft (z>2) vs Low redshift (z<2)

Different Population??

Number density
vsCross sectionDifficulties for realizing high-z DLA disks
How one can form rotaionally supported disks ~ 20 h-1kpc at z>2 ?

Tidal torques provide 5-10 % of the angular momentum for
rotational support
The radius of gas sphere at turn-around is ~200 h-1kpc

Spherical top-hat flactuation ⇒ collapse timescale

Need for some information about
Spatial distribution : tidal tail, caustics or panckaes

Theoretical Models [準解析的手法とNumerical Simulations]• Nagamine, Springel, Hernquist (SPH)
DLAs ⇒ Compact objects MDLA=1011.2M
Too high metallicity ⇒ Strong Wind Model (Low resolution?)• Bouche, Gardner, Katz, Hernquist, Weinberg
DLAs ⇒ (massive) galaxies with large disks
Halo mass M~1010 M以下のハローに対して、cross-section vscircular velocityの関係（σ∝Vc＾β）を外挿して考察

Too large cross-sections (Low resolution?)• Maller, Somerville, Primack (SAM)

DLAs ⇒ galaxies with Mestel-type disks N(HI)∝R-1
α＊は考慮されていないため、metallicity evolutionは再現できず。

dN/dN(HI)やLarge cross-sectionも説明できず。

Results of Numerical Simulations

SPH: Nagamine et al. 2004

これまでの結果
z

DLAs correspond to HI-selected galaxies at M(HI)>108M in blindRadio Surveys (ADBS, HIPASS)⇒ Our prediction: more tight relation: SFR-M(HI) relation

zDLAs are LSB dwarf galaxies (~3kpc) at z<1
Our results are entirely consistent with the observational resultsof the counterparts:(a) DLAs [HST]: Lanzetta et al.2002
Rao et al. 2003, Hopkins et al.2005(b) HI selected galaxies [BRS]: Rosenberg et al. 2005

COMPACT OBJECTSHigh redshift z では？

Detection of Lyman alpha emission from DLA-host galaxies
Moller, Fynbo & Fall 2004, A&A 422,L33

FORS1/G600B spectrum of the z=2.0395 Damped Ly line. The 1 noise
spectrum (per 5 Å resolution element) is shown as a dashed line (blue). Theemission line is detected at 9.3 sigma .

2D spectra of a DLA at z=2.0395

DLA galaxies at high redshift detected in emission

High-z DLA galaxies are also very COMAPCT !?
⇒MORE samples are required to study high-z DLA galaxies⇒ The difficulties of detecting the emission lines;
Compactness, Low Surface Brightness,…

Half-light radius & Optical to NIR color of high-z DLA galaxies(Moller et al. 2002, ApJ, 574,51)

Relation between DLAs and LBGs

Fig. 1. PSS0808+5215 redshift histogram. Redshift histogram of the2.6 < z < 3.4 LBGs in the PSS0808+5215 field. Objects are binned withΔz = 0.03. The redshifts of the two known DLAs are indicated by thevertical dashed lines

Cooke et al. 2006

Observational Strategy
The Detection of emissions from DLA host-galaxies at HIGH Z(e.g. Moller,Fynbo, Ledoux’s works)‘Large Observatories Joint Comprehensive Search’「どのような観点からどのような観測量に注目するか」を吟味しなければならない！

[The Aim of this Strategy]•The nature of high-z DLAs （金属量の切り口で）•Lyman Break Galaxies•The hosts of Gamma-ray Bursts （吸収線プロファイルの切り口で）（空間相関の切り口で）モデルの予測が必要な側面があるStrategy for detecting emission lines from DLA galaxies at high z(Moller 2004 private communication)

Luminous galaxies ⇒ High metallicity Z

LyαFlux vs Metallicity relation predicted by our model
DLA galaxies (Moller et al.) (blue dots)
Detection limits of Subaru Telescopes (red-dashed lines)

Okoshi, Minowa, Moller, Fynbo, Ledoux、Bouche et al. 2005-2006

Key points• Low redshift z=0:
HI-selected galaxies at M(HI) <108M
The nature of DLAs and subDLAs
Star formation laws•

High redshift z>2:
Large samples !!(e.g., Spectra of GRB afterglow )Metalの空間分布 （e.g., SNe explosions)
Metal systems (e.g., MgII, CIV systems)
Lyman-break galaxiesとの相関
Sub-structure problems
UV background radiation (Proximity effects)
He II reionization
Angular-momentum problems etc…..