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The Properties of DLAs at z ~ 3

The Properties of DLAs at z ~ 3. Luo Zhijian Key Lab for Astrophysics, Shanghai Normal University Shu Chenggang ( ShNU ) Lu Y.( UMASS ) Mo H. J. ( UMASS ) Huang J. S. ( CfA ). OUTLINE. 1. What are DLAs? 2. Previous DLA Studies 3. Modeling 4. Predictions 5. Summary. 1.What are DLAs.

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The Properties of DLAs at z ~ 3

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  1. The Properties of DLAs at z ~3 Luo Zhijian Key Lab for Astrophysics, Shanghai Normal University Shu Chenggang (ShNU) Lu Y.(UMASS) Mo H. J. (UMASS) Huang J. S. (CfA)

  2. OUTLINE 1. What are DLAs? 2. Previous DLA Studies 3. Modeling 4. Predictions 5. Summary

  3. 1.What are DLAs Damped Lyman-alpha systems (DLAs) Found in quasar spectra

  4. The observed spectra consist of neutral hydrogen Lyman alpha absorption lines which are broadened by radiation damping.

  5. N>1020.3cm-2: A historical threshold set by the HI properties of nearby spiral galaxies • Physical reason: this column density divides neutral gas from ionized gas.

  6. The very large HI column density marks that they likely be hosted by gas-rich systems. DLAs are the important neutral-gas reservoirs for star formation at high redshifts They are the prime candidates for the high-redshift progenitors of the present spiral galaxies.

  7. 2. DLA Studies DLA Statistics

  8. N(HI) vs. metallicity Z Molecular hydrogen DLA SFR per unit area Noterdaeme et al. 2008 Wolfe et al. 2003 Krumholz et al. 2009

  9. Cosmological simulations the insufficient mass resolution the failure to reproduce correctly disk sizes angular moment problem under-estimated the rate of incidence of DLAs Theoretic Works

  10. Semi-analytical models (SAMs) Some observational results could not be explained very well N(HI) always smaller than 1022cm-2 N(HI) vs. Metallicity ……

  11. The reasons for the discrepancy are various Two important factors: 1) Previous works simply assume that all Hydrogen gas is the atomic form without considering the molecular fraction. 2) A simple Kennicutt (1998) star formation law is often adopted to describe the star formation process.

  12. It is necessary to make a new attempt to re-examine the observed properties of DLAs by introducing 1) The atomic to molecular transition in the interstellar mediums. 2) A new form of star formation rate which is determined by the molecular fraction. (Wong & Blitz 2002; Gao & Solomon 2004, Blitz & Rosolowsky 2004, 2006; Wu et al. 2005; Blitz & Rosolowsky 2006; Krumholz et al. 2008,2009)

  13. i) Supposed that DLAs are hosted by disk galaxies that form at the center of the dark haloes at z ~ 3 ii) Adopted the galaxy formation model suggested by Mo, Mao & White (1998, MMW) to trace their formation and evolution. As an illustration, DLA properties are assumed at z ~3 and a LCDM model consistent with the 5-year WMAP results is adopted 3.Modeling

  14. Modelling a single galaxy Disk Halo Exponential form

  15. c) Fraction of molecular in the disk and star formation prescription Krumholz, McKee & Tumlinson (2009, hereafter KMT09)

  16. d) Outflow model i) No outflow model (NOM) ii) Fixed outflow model (FOM) iii) Physical outflow model (POM)

  17. e) Chemical evolution We assume that star formation and chemical evolution in each DLA last for a period of 0 ~1 Gyr from redshifts z~3.

  18. Modelling DLA population Generated a sample of galaxies by a Monte-Carlo simulation at z ~ 3. a) Halo mass function (Sheth-Tormen form)

  19. b) Distribution of the spin parameter

  20. Selecting DLAs: random lines penetrating modelled disks Log N(HI) > 20.3  DLA candidates disk inclination ▲ Star Formation ▲ Chemical evolution random line of sight

  21. 4. Model Predictions 1）Vc and  • small Vc < 100km/s •  larger  , extended • peak ~ 0.060 • median ~ 0.072

  22. 2） Impact Parameters A high enough column density N(HI) >1020.3cm-2 which is identified as a DLA is expected to easily occur at the center regions of galaxies. Peak : around 2.5kpc; Median: around 3.7kpc Hosts : small galaxies

  23. 3） Rate of incidence n(z) The model prediction: n(z) ~ 0.259 Obs: n(z=3)~0.241 (SDSS DR5 Prochaska et al. 2005) 4） Mass density of Neutral Gas

  24. 5） HI Column Density Distribution Function Definition: the number of absorbers per unit N(HI) and per unit X. Model with large c can reproduce most of the observational features

  25. 6） Metallicities vs HI column densities Lines(upper limit of Observated DLAs, Schaye 2001): Model : the trend of anti-correlationc=20

  26. 7） Molecular Hydrogen Column Density NOM FOM Filled squares: the DLAs in N08 (Noterdaeme et al. 2008). Triangles: Data of the Galactic disk with N(HI) > 1020.3 cm-2(Savage et al. 1977) POM

  27. 8) SFR density Match observations done by Wolfe et al. (2004) based on the CII* absorption lines.

  28. We investigated the properties of DLAs at z ~3 Galaxy formation model: MMW (1998) Considered the transition between atomic and molecular gas on disks Adopted a new form of star formation rate (Krumholz, McKee & Tumlinson 2009). Included the ISM outflow models Generated a population galaxies by Monte Carlo simulations and select modeled DLAs according to the observed selection criterion 5.Summary

  29. the selected DLAs could reproduce Number density per unit redshift n(z) HI frequency distribution f(N_HI) Total mass density of neutral hydrogen. Anti-correlation between Z and N(HI) Correlation between atomic and molecular hydrogen column density SFR density at z~3

  30. The End Thanks

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