H. Plana

DYNAMICAL EFFECTS OF INTERACTIONS AND THE TULLY-FISHER RELATION FOR HICKSON COMPACT GROUPS

We investigate the properties of the B-band Tully-Fisher (T-F) relation for 25 compact group galaxies, using Vmax derived from two-dimensional velocity maps. Our main result is that the majority of the Hickson Compact Group galaxies lie on the T-F relation. However, about 20% of the galaxies, including the lowest-mass systems, have higher B luminosities for a given mass, or alternatively, a mass that is too low for their luminosities. We favor a scenario in which outliers have been brightened because of either enhanced star formation or merging. Alternatively, the T-F outliers may have undergone truncation of their dark halo due to interactions. It is possible that in some cases both effects contribute. The fact that the B-band T-F relation is similar for compact group and field galaxies tells us that these galaxies show common mass-to-size relations and that the halos of compact group galaxies have not been significantly stripped inside R25. We find that 75% of the compact group galaxies studied (22 out of 29) have highly peculiar velocity fields. Nevertheless, a careful choice of inclination, position angle, and center, obtained from the velocity field, and an average of the velocities over a large sector of the galaxy enabled the determination of fairly well-behaved rotation curves for the galaxies. However, two of the compact group galaxies HCG 91a and HCG 96a, which are the most massive members in M51-like pairs, have very asymmetric rotation curves, with one arm rising and the other one falling, indicating most probably a recent perturbation by the small close companions.

HCG 31: a multiple merger in progress

Context. HCG 31 is one of the most intriguing compact groups in Hicksons catalogue. It contains a central pair of interacting dwarf galaxies and other small members that are highly peculiar. Aims. The main goal of this study is to investigate the evolutionary stage of the group and measure the internal kinematics of the individual galaxies and of the possible tidal dwarf galaxies. Methods. We obtained new Fabry-Perot data cubes, including Ha images, velocity fields, velocity dispersion maps, lambda maps, position-velocity plots and rotation curves. We have taken advantage of the high spatial (sampling of ∼0.4 arcsec) and spectral (velocity sampling of ∼3 km s -1 ) resolutions of our Fabry-Perot data. Results. Kinematic peculiarities and overlapping double velocity components are measurable throughout the velocity field of A+C, with no signature of either distinct rotating disks or a single rotating galaxy. The velocity dispersion map shows widespread low-velocity values throughout the group (consistent with the turbulent velocity of the gas), except in a narrow interface between A and C, where the merging may be occurring. The velocity curves of four candidate tidal dwarf galaxies (regions E, F, A1, and A2) show flat velocity patterns in two cases (Al and F) and gradients with amplitudes of A ∼ 30-40 km s -1 in two others (E and A2). Our measurements show good agreement with previous optical literature data, but our data set has a much improved velocity sampling and deeper coverage. Moreover, within the star-forming regions of the group, our data profit from the higher spatial resolution with respect to HI data. Conclusions. The dynamics of the A+C system, with two main velocity components of approximately the same intensities, indicate that it is in a pre-merger stage. The two disks, in a bound orbit and in the process of merging, have had at least one earlier passage. They rotate with almost parallel spin axes like a set of gear wheels. This prograde encounter and the high star-formation rates favor the formation of a new disk. Object F may turn into a tidal dwarf galaxy bound to the group.

Star-forming regions and the metallicity gradients in the tidal tails: the case of NGC 92

We present new Gemini/GMOS spectroscopic and archival imaging data of the interacting galaxy NGC 92, which is part of a compact group and displays an extended tidal tail. We have studied the physical properties of 20 star-forming complexes in this system. We found that the star-forming regions located in the tidal tail of NGC 92 have ages younger than similar to 8 Myr, which suggests that these objects were formed in situ. The spectroscopic data reveal that these regions have slightly sub-solar metallicities, suggesting that they were formed from pre-enriched material. Using the oxygen abundances derived for each system, we found that the extended tidal tail of NGC 92 has a flat metallicity distribution. Although this scenario is consistent with N-body simulations of interacting systems, where there is gas mixing triggered by the interaction, archival H alpha Fabry-Perot data cubes of NGC 92 have not shown a velocity gradient along the tail of this galaxy, which under certain assumptions could be interpreted as a lack of gas flow in the tail. Our results suggest that a fraction of the enriched gas that was originally located in the centre of the galaxy was expelled into the tidal tail when the interacting process that formed the tail happened. However, we cannot exclude the scenario in which the star formation in the tail has increased its original oxygen abundance.

The Compact Group of Galaxies HCG 31 in an Early Phase of Merging

We have obtained high spectral resolution (R = 45900) Fabry-Perot velocity maps of the Hickson Compact Group HCG 31 in order to revisit the important problem of the merger nature of the central object A+C and to derive the internal kinematics of the candidate tidal dwarf galaxies in this group. Our main findings are: (1) double kinematic components are present throughout the main body of A+C, which strongly suggests that this complex is an ongoing merger (2) regions

The Tully–Fisher relations for Hickson compact group galaxies★

A2

Gas Kinematics in Three Hickson Compact Groups: The Data*

and E, to the east and south of complex A+C, present rotation patterns with velocity amplitudes of

Gas kinematics of a sample of five Hickson Compact Groups ?;?? The data

\sim 25 km s^{-1}

Deep GeMS/GSAOI near-infrared observations of N159W in the Large Magellanic Cloud

and they counterrotate with respect to A+C, (3) region F, which was previously thought to be the best example of a tidal dwarf galaxy in HCG 31, presents no rotation and negligible internal velocity dispersion, as is also the case for region

Deep near-infrared adaptive-optics observations of a young embedded cluster at the edge of the RCW 41 H II region

A1

The Hα kinematics of interacting galaxies in 12 compact groups

. HCG 31 presents an undergoing merger in its center (A+C) and it is likely that it has suffered additional perturbations due to interactions with the nearby galaxies B, G and Q.