NGC 3256: Kinematic anatomy of a merger

We present a detailed optical analysis of the galaxy cluster A2163 based on new multicolor wide field imaging and medium-to-high resolution (R~2000) spectroscopy. While X-ray observations have revealed that merging processes are present in this cluster, the merging scenario is complex and not well-defined. We undertook a complementary optical analysis, aiming to understand the dynamics of the system, to add constraints to the merging scenario and to test its effect on the pro...

In external galaxies, molecular composition may be influenced by extreme environments such as starbursts and galaxy mergers. To study such molecular chemistry, we observed the luminous-infrared galaxy and merger NGC 3256 using the Atacama Large Millimeter/sub-millimeter Array. We covered most of the 3-mm and 1.3-mm bands for a multi-species, multi-transition analysis. We first analyzed intensity ratio maps of selected lines such as HCN/HCO$^+$, which shows no enhancement at a...

This paper presents further results from our spectroscopic study of the globular cluster (GC) system of the group elliptical NGC 3923. From observations made with the GMOS instrument on the Gemini South telescope, an additional 50 GC and Ultra Compact Dwarf (UCD) candidates have been spectroscopically confirmed as members of the NGC 3923 system. When the recessional velocities of these GCs are combined with the 29 GC velocities reported previously, a total sample of 79 GC/UCD...

[abridged] We present interferometric maps of ammonia (NH3) of the nearby starburst galaxy NGC 253 [star formation rate: ~2.8 Mo yr^(-1)]. The observations have been taken with the Australia Telescope Compact Array and include the para-NH3 (1,1), (2,2), and the ortho-NH3 (3,3) and (6,6) inversion lines. Six major complexes of dense ammonia are identified, three of them on either side of the starburst center, out to projected galactocentric radii of \~250 pc. [...] The applica...

We present 236 new radial velocities of galaxies in the cluster A2256 measured with the WIYN Hydra multi-object spectrograph. Combined with the previous work of Fabricant, Kent, and Kurtz (1989), we have velocities for a total of 319 galaxies of which 277 are cluster members. In addition to the new radial velocities, we present a 3x3 image mosaic in the R band of the central 19'x19' region of A2256, from which we obtained photometry for 861 galaxies. These data provide strong...

The superior resolution of HST and the light gathering power of large 8-10m class telescopes are now providing information on distant globular clusters (GCs) that is comparable to that obtained in early 1990s for Local Group systems. Here I summarise what has been learnt from the imaging and limited spectroscopy of GCs in other galaxies. The GC systems of spirals and ellipticals reveal remarkable similarities. The vast bulk of GCs appear to have formed at early epochs, with m...

Multi-band images of the very isolated spiral galaxy NGC 5523 show a number of unusual features consistent with NGC 5523 having experienced a significant merger: (1) Near-infrared (NIR) images from the Spitzer Space Telescope (SST) and the WIYN 3.5-m telescope reveal a nucleated bulge-like structure embedded in a spiral disk. (2) The bulge is offset by ~1.8 kpc from a brightness minimum at the center of the optically bright inner disk. (3) A tidal stream, possibly associated ...

Using a sample of 38 radio-loud galaxy mergers at z<=0.2, we confirm the high detection rate (~84%) of HI 21-cm absorption in mergers, which is significantly higher (~4 times) than in non-mergers. The distributions of the HI column density [N(HI)] and velocity shift of the absorption with respect to the systemic redshift of the galaxy hosting the radio source in mergers are significantly different from that in non-mergers. We investigate the connection of the nuclear HI gas w...

The blue compact dwarf galaxy NGC 5253 hosts a very young central starburst. The center contains intense radio thermal emission from a massive ultracompact H II region (or "supernebula") and two massive and very young super star clusters (SSCs), which are seen at optical and infrared wavelengths. The spatial correspondence between these three objects over an area of < 0.5 arcsec is very uncertain, and it is usually assumed that one of the optically-detected SSCs coincides wit...

The intermediate age star cluster W3 (age ~ 300-500 Myr) in NGC 7252 is the most luminous star cluster known to date with a dynamical mass estimate of 8 +/- 2 x 10^7 M_sun. With an effective radius of about 17.5 pc and a velocity dispersion of 45 km/s this object may be viewed as one of the recently discovered ultra-compact dwarf galaxies (UCDs). Its intermediate age, however, precludes an origin as a stripped nucleated dwarf elliptical galaxy. The galaxy NGC 7252 is a merger...