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Multi-Wavelength Studies of Spectacular Ram Pressure Stripping of a Galaxy. II. Star Formation in the Tail

With multiband photometric data in public archives, we detected four intracluster star-forming regions in the Virgo cluster. Two of them were at a projected distance of 35 kpc away from NGC4388, and the other two were 66 kpc away. Our new spectroscopic observation revealed that their recession velocities were comparable to the ram-pressure-stripped tail of NGC4388 and confirmed their association. The stellar mass of the star-forming regions ranged from 10^4 - 10^4.5 M_sun except for that of the faintest one which would be <10^3 M_sun. The metallicity was comparable to the solar abundance, and the age of the stars was ~ 10^6.8 years. Their young stellar age meant that the star formation should have started after the gas was stripped from NGC4388. This implied in situ condensation of the stripped gas. We also found that two star-forming regions lay near the leading edge of a filamentary dark cloud. The extinction of the filament was smaller than that derived from the Balmer decrement of the star-forming regions. It implied that the dust in the filament would be locally dense around the star-forming regions.