H I 21 cm Absorption as a Probe of High- z ISM + Possible Interest - - PowerPoint PPT Presentation

H I 21 cm Absorption as a Probe of High-z ISM + Possible Interest for AGNs

Hiroyuki Hirashita

Masanori Nakamura, Keiichi Asada Chiranjib Konar (ASIAA, Taiwan)

See also T.-C. Chang’s review & C.-C. Chiong’s talk

Outline

• 1. Introduction to DLAs
• 2. Physical State of the ISM in DLAs
• 3. Interests in AGNs at ASIAA
• 4. Summary

QSO Damped Lyα cloud Lyα absorption

• 1. Introduction to

Damped Lyα Clouds (DLAs)

• High H I column density (> 2×1020 cm–2)

Reservoir of a large amount of H I ⇒ progenitors of nearby large galaxies?

• Unique objects at high z for detailed study ISM by

using various species.

21 cm Observations of DLAs

see also Curran et al. (2010)

• detection rate: 1/10

Srianand et al. (2012) Kanekar et al. (2009): anticorrelation between metallicity and Ts

H2 in DLAs (A Probe of Cold Gas)

Ledoux, Petitjean, & Srianand (2003) log (molecular fraction) metal depletion log (dust/gas) log (molecular fraction)

Paucity of H2 large dispersion

DLA Samples are mostly tracing diffuse medium?

Paucity of 21 cm absorption detection ⇒ low τ ⇒ High Ts (warm diffuse medium) Paucity of H2 absorption detection ⇒ H is mostly atomic in the warm diffuse medium. (Hirashita et al. 2003)

• 2. Physical State of the ISM in DLAs

Damped Lyman α clouds (DLAs): NH > 2×1020 cm–2

Hirashita et al. (2003) background quasar

Experiment: One simulated galaxy with a background quasar at a random line of sight

50 pc log (molecular fraction)

Equilibrium H2 abundance (1) Formation on dust (2) Destruction by UV (1) = (2)

with i21 = 0.1, D = 0.1Dsun

Distribution of H2

Patchy and localized H2 distribution

Hirashita et al. (2003)

“Simulation” of Observation

log (dust-to-gas ratio) log (molecular fraction) ×: Ledoux et al. (2003) ◆: our simulation

Choose randomly a line of sight on the simulated galaxy ...  positive correlation  Molecular fraction increases rapidly at log (D/Dsun) ~ ‒1.5 (←self-shielding)  large scatter

Hirashita & Ferrara (2005)

Implication for 21 cm Observations

• Detection rate of 21 cm absorption is low (1/10).

Consistent with the small covering fraction of cold gas

Srianand et al. (2012) At least an order of magnitude better S/N ⇒ SKA is suitable.

• Low detection rate of H2, which is localized in

the cold medium.

• 3. Interests in AGNs at

ASIAA

Imaging Re-collimation Process

• f the M87 jet

Dynamic Range of current our EVN image is ~ 2500

• SKA will improve it > 1,000,000

Asada & Nakamura (2012)

HST-1 expansion Re-collimation? Re-ex pansion

• Is the M87 jet re-collimated to form HST-1?

Asada et al.

Imaging the counter-jets

Detection of the counter-jets is very important;

• Constraining a proper viewing angle

Jet acceleration dynamics SED analysis for core emission profile Modeling the accretion disk and BH shadow

Diffuse emission around FR II radio galaxies: episodic activity

αinn

inj ∼ αout inj : similar jet power

(Konar & Hardcastle, 2013) Newly discovered diffuse halo (Sirothia+, 2013) Hope to discover many such radio haloes with the SKA

Radio Galaxies: Their Dynamics and Episodic Jet Activities – p.17/17

• 4. Summary

(1)Small science group in ASIAA. ⇒ Collaboration is necessary. (2)Paucity of H I 21 cm detection for DLAs can be understood in terms of the prominent warm diffuse medium, consistent with the small H2 detection rate. (3)AGN science in ASIAA

• a. Collimation and dynamics of the M87 jet
• b. Survey of diffuse radio emission around radio galaxies

Deadline for abstracts: 24 August 2013