We present results from a study of protoglobular cluster candidates in the interacting galaxy system Arp 284 (NGC 7714/5) using data from the Hubble Space Telescope (HST). Previous studies of the Antennae and M51 have suggested that the majority of young massive star clusters dissolve within 20 Myr due to mass loss. We use the evolutionary synthesis code starburst99 to estimate ages and extinctions for approximately 175 clusters visible with HST. We also use lower resolution Galaxy Evolution Explorer and ground-based Hα data to estimate the ages of the giant H ii regions in which these clusters are found, and compare the Spitzer colours of these H ii regions to those of star-forming regions in other interacting systems. The ages are also used to aid in the interpretation of Chandra X-ray data. Clusters in the tidal tails of NGC 7714 are generally found to have ages less than 20 Myr, though observational limits make the significance of this result uncertain. Older clusters, though not numerous, have nearly the same spatial distribution within the imaged portion of NGC 7714 as young clusters. The cluster population in the bridge connecting the two galaxies appears to be older, but the data in this part of the system are too limited to draw firm conclusions. The ages of the giant H ii regions in NGC 7714 are generally older than those of their constituent clusters, possibly indicating that the young clusters we detect are surrounded by their dispersed predecessors.

We present high spatial resolution X-ray imaging data for the interacting galaxy pair NGC 7714/7715 (Arp 284) from the Chandra X-ray telescope. In addition to the unresolved starburst nucleus, a variable point source with L x ≈ 10 40 ergs s -1 was detected 1.″5 (270 pc) to the northwest of the nucleus, coincident with a blue, extremely optically luminous (M V ≈ -14.1) point source on Hubble Space Telescope images. Eleven other candidate point-like ultraluminous X-ray sources (ULXs) were also detected in the vicinity of NGC 7714/7715, two of which exceed 10 40 ergs s -1. Ten of these appear to be associated with interaction-induced features, but only two are associated with star formation regions. We also found diffuse emission with L x ≈ 3 × 10 40 ergs s -1 extending 11″ (1.9 kpc) to the north of the nucleus. Its spectrum can be fitted with either a two-temperature MEKAL function (kT = 0.59 -0.06+0.05 and 8 -3-10 keV) or a 0.6 keV MEKAL function plus a power law (Γ = 1.8 ± 0.2). The hard component may be due to high-mass X-ray binaries (HMXBs) with possible contributions from inverse Compton radiation, while the soft component is likely from a superwind. Superbubble models imply an expansion age of ≈15 Myr, supporting previous assertions of an intermediate-age nuclear stellar population in addition to a 5 Myr starburst. We also detected extended X-ray emission associated with four extranuclear H II region complexes. The emission from these H II regions and the nuclear starburst could be due to either an enhanced population of HMXBs relative to Local Group galactic averages or to diffuse gas heated by winds from supernovae, if the X-ray production efficiency L x/L mech is high (≈5%). To estimate L x/L mech, we collected published data for well-studied H II regions and superbubbles in nearby galaxies. For H II regions with ages less than 3.5 Myr, the median L x/L mech ≈ 0.02%, while for older star formation regions, L x/L mech ≈ 0.2%-7%. Thus, it is possible that gas heating by supemovae may be sufficient to account for the observed X-rays from these H II regions. In galaxies much more distant than NGC 7714, for example, the Cartwheel galaxy, H II region complexes similar to those in NGC 7714 will be unresolved by Chandra and will mimic ULXs. No X-ray emission was detected from the Type Ib supernova SN 1999dn, with an upper limit of ≈2 × 10 38 ergs s -1.

We present new CO (1-0) observations of 11 extragalactic tails and bridges in nine interacting galaxy systems, almost doubling the number of such features with sensitive CO measurements. Eight of these 11 features were undetected in CO to very low CO/H I limits, with the most extreme case being the NGC 7714/5 bridge. This bridge contains luminous H II regions and has a very high H I column density (1.6 × 1021 cm-2 in the 55″ CO beam), yet was undetected in CO to rms T*R = 2.4 mK. The H I column density is higher than standard H2 and CO self-shielding limits for solar-metallicity gas, suggesting that the gas in this bridge is metal-poor and has an enhanced NH2/ICO ratio compared with the Galactic value. Only one of the 11 features in our sample was unambiguously detected in CO, a luminous H I-rich star formation region near an optical tail in the compact group Stephan's Quintet. We detect CO at two widely separated velocities in this feature, at ∼6000 and ∼6700 km s-1. Both of these components have H I and Hα counterparts. These velocities correspond to those of galaxies in the group, suggesting that this gas is material that has been removed from two galaxies in the group. The CO/ H I/Hα ratios for both components are similar to global values for spiral galaxies.