Active star formation triggered by galaxy interaction

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

2. Barred spiral galaxy NGC1313 2arcmin 1. Transition stage between SBc and SBm Red : Hα ・Optical image→ Bar and two spiral arms Southern arm ・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) 3.2 kpc ・HI image→ chaotic morphology. → Tidally disrupted by a companion?? ESO Satellite HII regions 2. Star forming regions ・Star forming regions over a wide field → Satellite HII regions around Supergiant HI shell (D=3.2 kpc, Vs=42 km/s) Ryder et al. (1995) Cf. Typical size of HI shell D～100 pc Star-forming activity within the disk has never been discussed because of faint CO emission. → AKARI HI column density map Ryder et al (1995)

3. Star formation efficiency map Revealed by AKARI ■AKARI observations (24 – 160 um) Cold dust(~20K) → Gas surface density,Σgas Warm dust(~60K) → SFR surface density, ΣSFR Color: SFE Contour: 24 um ■Star formation efficiency (SFE) (ΣSFR/Σgas [yr-1]) SFE : ≦ 10-9 yr-1 for normal spiral ～ 10-8 yr-1 for starburst Kennicutt (1998) Southern arm ～ 2x10-8 yr-1 !! > Nouthern arm Satellite HII reg. ～4-5x10-9 yr-1 → Enhanced star formation at the supergiant HI shell. 4x10-9 6x10-9 1x10-8 2x10-9 8x10-9 Starburst triggered by expanding supergiant HI shell in southern arm & satellite HII regions ??

4. ALMA observations of NGC1313 Object: reveal evidence of starburst triggered by expanding supergiant HI shell. ■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) → 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. ■A kpc-scaled super shell is expected to be capable of changing in ISM environment on galactic scale (→ impact on galaxy evolution). → 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.

5. ALMA observing plan of NGC1313 Southern arm ■Target area : Supergiant HI shell in NGC1313 - Southern arm (early science phase) - All of the area along the shell (full science phase) ALMA FOV (45” @115GHz) ■Observations 12CO(J=1-0) :Dynamics and spatial distribution of molecular clouds to associate CO clouds with the supergiant HI shell. Continuum emission@450, 850um: Temperature map of cold dust to identify prestellar (TD~10 K). regions. Stutz et al. (2010) 20 pc/arcsec ■ Sensitivity requirement From Swedish ESO Submilimeter Telescope, I12CO(J=1-0)= 810 Jy/sr(ave.) @southern arm (Contursi et al. 2002) → ~40 μJy/beam (ALMA beam size 45”) From AKARI, B(450um) = 14 MJy/sr, B(850um) = 4 MJy/sr @southern arm → Tb ~ 1 mK