Transformation of a Virgo Cluster dwarf irregular galaxy by ram pressure stripping: IC3418 and its fireballs
- Yale University Astronomy Department, P.O. Box 208101, New Haven, CT 06520-8101 (United States)
- Bennington College, Bennington, VT (United States)
- Department of Astronomy and Yonsei University Observatory, Yonsei University, 120-749 Seoul (Korea, Republic of)
- Department of Astronomy, Columbia University, 550 West 120th Street, New York, NY 10027 (United States)
- CDS, Observatoire astronomique de Strasbourg, UMR7550, 11 rue de l'université, F-67000 Strasbourg (France)
We present optical imaging and spectroscopy and H I imaging of the Virgo Cluster galaxy IC 3418, which is likely a 'smoking gun' example of the transformation of a dwarf irregular into a dwarf elliptical galaxy by ram pressure stripping. IC 3418 has a spectacular 17 kpc length UV-bright tail comprised of knots, head-tail, and linear stellar features. The only Hα emission arises from a few H II regions in the tail, the brightest of which are at the heads of head-tail UV sources whose tails point toward the galaxy ('fireballs'). Several of the elongated tail sources have Hα peaks outwardly offset by ∼80-150 pc from the UV peaks, suggesting that gas clumps continue to accelerate through ram pressure, leaving behind streams of newly formed stars which have decoupled from the gas. Absorption line strengths, measured from Keck DEIMOS spectra, together with UV colors, show star formation stopped 300 ± 100 Myr ago in the main body, and a strong starburst occurred prior to quenching. While neither Hα nor H I emission are detected in the main body of the galaxy, we have detected 4 × 10{sup 7} M {sub ☉} of H I from the tail with the Very Large Array. The velocities of tail H II regions, measured from Keck LRIS spectra, extend only a small fraction of the way to the cluster velocity, suggesting that star formation does not happen in more distant parts of the tail. Stars in the outer tail have velocities exceeding the escape speed, but some in the inner tail should fall back into the galaxy, forming halo streams.
- OSTI ID:
- 22348273
- Journal Information:
- Astrophysical Journal, Vol. 780, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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