Chandra Observations of the Interacting NGC 4410 Galaxy Group

We present high resolution X-ray imaging data from the ACIS-S instrument on the Chandra telescope of the nearby interacting galaxy group NGC 4410. Four galaxies in the inner portion of this group are clearly detected by Chandra, including the peculiar low luminosity radio galaxy NGC 4410A. In addition to a nuclear point source, NGC 4410A contains diffuse X-ray emission, including an X-ray ridge extending out to about 12" (6 kpc) to the northwest of the nucleus. This ridge is coincident with an arc of optical emission-line gas, which has previously been shown to have optical line ratios consistent with shock ionization. This structure may be due to an expanding superbubble of hot gas caused by supernovae and stellar winds or by the active nucleus. The Chandra observations also show four or five possible compact ultra-luminous X-ray (ULX) sources (L(x) >= 10^39 erg/s) associated with NGC 4410A. At least one of these candidate ULXs appears to have a radio counterpart, suggesting that it may be due to an X-ray binary with a stellar-mass black hole, rather than an intermediate mass black hole. In addition, a faint diffuse intragroup X-ray component has been detected between the galaxies (L(x) ~ 10^41 erg/s). This supports the hypothesis that the NGC 4410 group is in the process of evolving via mergers from a spiral-dominated group (which typically have no X-ray-emitting intragroup gas) to an elliptical-dominated group (which often have a substantial intragroup medium).Comment: 27 pages, 14 figures; Accepted by Astronomical Journal; color images at http://www.etsu.edu/physics/bsmith/research/n4410.htm

Nuclear activity and massive star formation in the low luminosity AGN NGC4303: Chandra X-ray observations

We present evidence of the co-existence of either an AGN or an ultraluminous X-ray source (ULX), together with a young super stellar cluster in the 3 central parsecs of NGC4303. The galaxy contains a low luminosity AGN and hosts a number of starburst regions in a circumnuclear spiral, as well as in the nucleus itself. A high spatial resolution Chandra image of this source reveals that the soft X-ray emission traces the ultraviolet nuclear spiral down to a core, which is unresolved both in soft and hard X-rays. The astrometry of the X-ray core coincides with the UV core within the Chandra positioning accuracy. The total X-ray luminosity of the core, 1.5*10^{39} erg/s, is similar to that from some LINERs or from the weakest Seyferts detected so far. The soft X-rays in both the core and the extended structure surrounding it can be well reproduced by evolutionary synthesis models (which include the emission expected from single stars, the hot diffuse gas, supernova remnants and binary systems), consistent with the properties of the young stellar clusters identified in the UV. The hard X-ray tail detected in the core spectrum, however, most likely requires the presence of an additional source. This additional source could either be a weak active nucleus black hole or an ultraluminous X-ray object. The implications of these results are discussed.Comment: 37 pages, 7 figures, ApJ accepte

Star Formation in the Radio Galaxy NGC 4410A

The NGC4410 group of galaxies provides us a rare opportunity to study a nearby (97 h75^-1 Mpc) example of a radio galaxy (NGC4410A) embedded in an extended X-ray source, with evidence for star formation that can be readily spatially distinguished from regions dominated by the AGN and shocks. We present broadband and narrowband optical images along with optical and IUE ultraviolet spectroscopy for the radio galaxy NGC 4410A and its companion NGC 4410B. Our H-alpha+[NII] images reveal six luminous HII regions (L_H-alpha ~ 1e40 erg/s distributed in an arc near NGC 4410A. Partially completing the ring is a prominent stellar loop containing diffuse ionized gas. This filamentary gas, in contrast to the H II regions, shows spectroscopic signatures of shock ionization. The star formation in this system may have been triggered by a collision or interaction between the two galaxies, perhaps by an expanding density wave, as in classical models of ring galaxies. Alternatively, the star formation may have been induced by the impact of a radio jet on the interstellar matter. Extended Ly-alpha is detected in the ultraviolet IUE spectrum. The ultraviolet continuum, which is presumably radiated by the nucleus of NGC4410A, is not extended. NGC4410A appears to be interacting with its neighbors in the NGC4410 group, and could be an example of a spiral galaxy transforming into an elliptical.Comment: 33 pages, 9 figures. Accepted for publication in April, 2002 A

Chandra X-Ray Imaging of the Interacting Starburst Galaxy System NGC 7714/5: Tidal ULXs, Emergent Wind, and Resolved HII Regions

We present Chandra X-ray images for the interacting galaxy pair NGC 7714/5. In addition to the unresolved starburst nucleus, a variable point source with L(X) ~ 10^40 erg/s was detected 1.5" (270 pc) northwest of the nucleus, coincident with a blue, extremely optically-luminous (M(V) ~ -14.1) point source on HST images. Eleven more candidate point-like ultraluminous X-ray sources (ULXs) are seen, two >= 10^40 erg/s. Ten of these are associated with interaction-induced features but only two with star formation. We found diffuse emission with L(X) ~ 3 X 10^40 erg/s extending 11" (1.9 kpc) to the north of the nucleus. Its spectrum can be fit with a 2-temperature Mekal function (0.6/8 keV) or a 0.6 keV Mekal function plus a power law. The hard component may be due to high mass X-ray binaries (HMXBs) with contributions from inverse Compton radiation, while the soft component is likely from a superwind. We also detected extended X-ray emission from four extra-nuclear HII region complexes. This emission may be due to HMXBs 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 HII regions and superbubbles in nearby galaxies. For young HII regions (<3.5 Myrs), the median L(X)/L(mech) ~ 0.02%, while for older regions, L(X)/L(mech) ~ 0.2-7%. Thus gas heating by supernovae may be sufficient to account for the HII region emission. In galaxies much more distant than NGC 7714, for example, the Cartwheel galaxy, HII region complexes similar to those in NGC 7714 will be unresolved by Chandra and will mimick ULXs.Comment: Accepted by the Astronomical Journal. Figures also available at http://www.etsu.edu/physics/bsmith/research/n7714_chandra.htm