Constraining the ages of the fireballs in the wake of the dIrr galaxy VCC 1217/IC 3418

¹ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA, Leiden The Netherlands
e-mail: fumagalli@strw.leidenuniv.nl
² Dipartimento di Fisica G. Occhialini, Università di Milano-Bicocca, Piazza della Scienza 3, 20126 Milano, Italy
e-mail: giuseppe.gavazzi@mib.infn.it
³ INAF – Osservatorio Astronomico di Roma, via Frascati 33, 0040 Monte Porzio Catone (RM), Italy
e-mail: roberto.scaramella@oa-roma.inaf.it
⁴ INAF, IASF-Milano, via Bassini 15, 20133 Milano, Italy
e-mail: paolo@lambrate.inaf.it

Received: 23 July 2010
Accepted: 5 November 2010

Abstract

Context. A complex of Hα emitting blobs with strong FUV excess is associated to the dIrr galaxy VCC 1217/IC 3418 (Hester et al. 2010, ApJ, 716, L14), and extends up to 17 Kpc in the southeast direction. These outstanding features can be morphologically divided into diffuse filaments and compact knots, where most of the star formation activity traced by Hα takes place.

Aims. We investigate the properties of the galaxy and the blobs using a multiwavelength approach to constrain their origin.

Methods. We collected publicly available data in UV and Hα and observed the scene in the optical U,g,r,i bands with LBT. The photometric data allows evaluation of the star formation rate and performance of a SED fitting separately for the galaxy and the blobs in order to constrain their stellar population age. Moreover we analyzed the color and luminosity profile of the galaxy and its spectrum to investigate its recent interaction with the Virgo cluster.

Results. Our analysis confirms that the most plausible mechanism for the formation of the blobs is ram pressure stripping by the Virgo cluster IGM. The galaxy colors, luminosity profile and SED are consistent with a sudden gas depletion in the last few hundred Myr. The SED fitting of the blobs constrains their ages in  < 400 Myr.