Dramatic change in environments of galaxy disks and intergalactic space Suzuki et al. (2007,2010a) M101 銀河 Suzuki et al. (2010b) M101 Stephan’s Quintet (HCG92) Suzuki et al. 2007, 2010 Suzuki et al (submitted) High-velocity (150 km/s) HI gas infall → Four active star-forming regions Gas & dust stripping from galaxies → Intergalactic star-forming regions AKARI → Investigation of star formation acitivity on a kpc scale in nearby galaxies. AKARI → Investigation of star formation acitivity on a kpc scale in nearby galaxies. Toyoaki Suzuki (ISAS/JAXA)

Star-forming activity within the disk has never been discussed because of faint CO emission. → AKARI Star-forming activity within the disk has never been discussed because of faint CO emission. → AKARI 2 arcmin ESO 1. Transition stage between SBc and SBm ・ Optical image → Bar and two spiral arms ・ Metal poor : 12+log(O/H) = 8.2 (Hadfield et al. 2007) Cf. 8.1 for SMC, 8.4 for LMC ・ No significant gradient of O/H abundance (Walsh & Roy, 1997) ・ Metal poor : 12+log(O/H) = 8.2 (Hadfield et al. 2007) Cf. 8.1 for SMC, 8.4 for LMC ・ No significant gradient of O/H abundance (Walsh & Roy, 1997) 2. Star forming regions ・ Star forming regions over a wide field → Satellite HII regions around Supergiant HI shell ・ Star forming regions over a wide field → Satellite HII regions around Supergiant HI shell Ryder et al. (1995) Red : Hα Satellite HII regions (D=3.2 kpc, Vs=42 km/s) Cf. Typical size of HI shell D ～ 100 pc Ryder et al (1995) HI column density map ・ HI image → chaotic morphology. → Tidally disrupted by a companion?? ・ HI image → chaotic morphology. → Tidally disrupted by a companion?? Southern arm 3.2 kpc

→ Enhanced star formation at the supergiant HI shell. → Enhanced star formation at the supergiant HI shell. Starburst triggered by expanding supergiant HI shell in southern arm & satellite HII regions ?? Starburst triggered by expanding supergiant HI shell in southern arm & satellite HII regions ?? SFE : ≦ yr -1 for normal spiral ～ yr -1 for starburst SFE : ≦ yr -1 for normal spiral ～ yr -1 for starburst Kennicutt (1998) ■ Star formation efficiency (SFE) (Σ SFR /Σ gas [yr -1 ]) ■ Star formation efficiency (SFE) (Σ SFR /Σ gas [yr -1 ]) 4x x x x x10 -8 Contour: 24 um ■ AKARI observations (24 – 160 um) Cold dust (~20K) → Gas surface density, Σ gas Warm dust (~60K) → SFR surface density, Σ SFR ■ AKARI observations (24 – 160 um) Cold dust (~20K) → Gas surface density, Σ gas Warm dust (~60K) → SFR surface density, Σ SFR Southern arm ～ 2x10 -8 yr -1 !! > Nouthern arm Satellite HII reg. ～ 4-5x10 -9 yr -1 Southern arm ～ 2x10 -8 yr -1 !! > Nouthern arm Satellite HII reg. ～ 4-5x10 -9 yr -1 Color: SFE

■ Super shells have long been suggested as drivers of molecular cloud formation (and then star formation). However, conclusive observational evidence of super shell-associated molecular clouds is just a few of the examples because of poor spatial resolution. e.g. Dawson et al. (2010) ■ Super shells have long been suggested as drivers of molecular cloud formation (and then star formation). However, conclusive observational evidence of super shell-associated molecular clouds is just a few of the examples because of poor spatial resolution. e.g. Dawson et al. (2010) Object: reveal evidence of starburst triggered by expanding supergiant HI shell. Object: reveal evidence of starburst triggered by expanding supergiant HI shell. ■ A kpc-scaled super shell is expected to be capable of changing in ISM environment on galactic scale ( → impact on galaxy evolution). ■ A kpc-scaled super shell is expected to be capable of changing in ISM environment on galactic scale ( → impact on galaxy evolution). → ALMA gives chance to observe super shells in nearby galaxies. Those in face-on galaxies are less affected by contamination from unrelated emission, which can be problem in the case of our galaxy. → ALMA gives chance to observe super shells in nearby galaxies. Those in face-on galaxies are less affected by contamination from unrelated emission, which can be problem in the case of our galaxy. → NGC1313 that has the largest super HI shell (3 kpc) is a best candidate for ALMA observation. Very active star formation in the southern arm and satellite HII regions may be triggered by expanding supergiant HI shell. → NGC1313 that has the largest super HI shell (3 kpc) is a best candidate for ALMA observation. Very active star formation in the southern arm and satellite HII regions may be triggered by expanding supergiant HI shell.

■ Observations 12CO(J=1-0) : Dynamics and spatial distribution of molecular clouds to associate CO clouds with the supergiant HI shell. Continuum 850um: Temperature map of cold dust to identify prestellar (T D ~10 K). regions. Stutz et al. (2010) ■ Observations 12CO(J=1-0) : Dynamics and spatial distribution of molecular clouds to associate CO clouds with the supergiant HI shell. Continuum 850um: Temperature map of cold dust to identify prestellar (T D ~10 K). regions. Stutz et al. (2010) ■ Sensitivity requirement From Swedish ESO Submilimeter Telescope, I 12CO(J=1-0) = 810 Jy/sr arm (Contursi et al. 2002) → ~40 μJy/beam (ALMA beam size 45”) ■ Sensitivity requirement From Swedish ESO Submilimeter Telescope, I 12CO(J=1-0) = 810 Jy/sr arm (Contursi et al. 2002) → ~40 μJy/beam (ALMA beam size 45”) ■ Target area : Supergiant HI shell in NGC Southern arm (early science phase) - All of the area along the shell (full science phase) ■ Target area : Supergiant HI shell in NGC Southern arm (early science phase) - All of the area along the shell (full science phase) ALMA FOV Southern arm 20 pc/arcsec From AKARI, B(450um) = 14 MJy/sr, B(850um) = 4 arm → T b ~ 1 mK

2 arcmin 3 μm4 μm7 μm11 μm 15 μm 24 μm65 μm90μm 140μm160μm

Flux intensity [ Jy ] Wavelength [ μm ] AKARI Spitzer IRAS T c = 21 K T w = 62 K M81 NGC1313 Flux intensity [ Jy ] Wavelength [ μm ] AKARI IRAS ISO HI mass surface density = 1.2x10 7 M ◎ /arcmin 2 (Ryder et al. 1995) HI mass surface density = 1.2x10 7 M ◎ /arcmin 2 (Ryder et al. 1995) H2/HI mass ratio = 0.2 (ave.) (Israel et al. 1997) H2/HI mass ratio = 0.2 (ave.) (Israel et al. 1997) ～ SMC

Cold dust 分布 : HI gas 分布 & PAH と良い相関 Warm dust 分布 : HII region と良い相関 Cold dust 分布 : HI gas 分布 & PAH と良い相関 Warm dust 分布 : HII region と良い相関 5 bands (24, 65, 90, 140, 160 um) を用いて、各 bin 毎に SED fitting (amplitudes, temperatures: all free) Ryder et al (1995) HI column density

Spiral arms & bar と diffuse ISM に有意な冪の差が見られない。 Cf. N ≒ spiral arms (M81, M101) Jeans instability による星形成が ” 銀河円盤全体 ” で支配的か ? (1) N ≒ 1.5, (2) Spiral arms : 渦巻腕周囲で星形成、 (3) Diffuse ISM: Supershells 周囲で星形成 (1) N ≒ 1.5, (2) Spiral arms : 渦巻腕周囲で星形成、 (3) Diffuse ISM: Supershells 周囲で星形成 NGC1313 Diameter:1 kpc Σ gas = 1700 Σ cold_dust_mass Σ SFR = 5.6x (log Lw-0.6/1.04) Suzuki et al. (2010) 一定と仮定 Σ SFR ∝ Σ N gas Kennicutt 1998 NGC1313 Σ SFR ∝ ρ gas τ growth H Gravitational instability (Elmegreen 1994) Jeans instability : τ growth ∝ ρ 0.5 gas Ρ gas : Gas density τ growth : Instability growth rate H : disk height Ρ gas : Gas density τ growth : Instability growth rate H : disk height → Σ SFR ∝ Σ 1.5 Gas