NGC 3310, a galaxy merger?

Abstract

Abstract. The H i structure and kinematics of the peculiar starburst galaxy NGC 3310 (Arp 217, UGC 5786) are discussed. New evidence bearing on the origin of the starburst is presented. The bulk of H i coincides with the bright optical disk and shows differential rotation. Its velocity dispersion is, however, unusually large for a spiral galaxy (up to 40 km s −1 ), suggesting that the disk is highly perturbed as already indicated by optical emission line spectroscopy. There are, in addition, two prominent H i tails, one extending to the north-west and the other, somewhat patchy, to the south. These H i tails, the perturbed kinematics and the peculiar optical morphology strongly suggest a recent merger between two gas-rich galaxies. This seems to have been a major merger in which most of the gas in the inner parts has been preserved in neutral atomic form and either one of the progenitor disks has survived or a new disk has formed.

Tidal Debris in the Starburst Galaxy NGC 3310: A New Tidal Loop?

“…The inner shell features have blue colors, H p 72 0 indicative of recent star formation. They also lie within the main H i disk of NGC 3310 (Kregel & Sancisi 2001) and are centered on the galaxy. These features are likely to be associated with NGC 3310's disk.…”

“…It has been previously suggested that NGC 3310 collided with either a small dwarf galaxy (Balick & Heckman 1981;Schweizer & Seitzer 1988) or possibly a larger, more gas-rich galaxy (Kregel & Sancisi 2001), while the H i tidal tails mapped by Kregel & Sancisi (2001) imply that NGC 3310 may be the result of an equal mass merger. They point out that the existence of a disk in the postmerger system implies either that disks are more resilient than previously thought or that we may be seeing a disk that was formed as a result of this collision.…”

“…The central starburst region of this galaxy is well studied (Díaz et al 2000;Elmegreen et al 2002, and references within), as are its young stellar clusters (de Grijs et al 2003a(de Grijs et al , 2003b, and references within) and disk kinematics (Mulder & Combes 1996). Existing observations span the spectrum from the radio (Kregel & Sancisi 2001;Mulder et al 1995) up through the X-ray regime (Zezas et al 1998;Ptak et al 1999;Jenkins et al 2004). While studies of its main disk provide insight into the nature of this system, there is also much that can be gained from examining its faint outer regions.…”

“…NGC 3310 is surrounded by shell-like features thought to be tidal debris left in the wake of a collision with a small companion (Balick & Heckman 1981;Schweizer & Seitzer 1988). Recent H i line maps by Kregel & Sancisi (2001) suggest that a merger produced H i tidal tails, and that the merging galaxy may have been a larger gas-rich disk system. However, the origins of the optically prominent debris have yet to be established.…”

“…Several of the required parameters are poorly known at present. We adopt a minimum loop width of 2 kpc, pericentric distance of kpc set by the extent of the inner H i disk, and a rotation R ∼ 9 p velocity of 100 km s Ϫ1 from Kregel & Sancisi (2001). We observe a projected ratio of loop width, w, to radius, R, of .…”