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Register a new userSynchronous Evolution of Galaxies in Groups: NGC 524 Group
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Authors
Olga K. Silchenko
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By means of panoramic spectroscopy at the SAO RAS BTA telescope, we investigated the properties of stellar populations in the central regions of five early-type galaxies -- the NGC 524 group members. The evolution of the central regions of galaxies looks synchronized: the average age of stars in the bulges of all the five galaxies lies in the range of 3--6 Gyr. Four of the five galaxies revealed synchronized bursts of star formation in the nuclei 1--2 Gyr ago. The only galaxy, in which the ages of stellar population in the nucleus and in the bulge coincide (i.e. the nuclear burst of star formation did not take place) is NGC 502, the farthest from the center of the group of all the galaxies studied.
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Members of the NGC 524 group of galaxies are studied using data obtained on the 6m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences, with the SCORPIO reducer in an imaging mode. Surface photometry has been carried out and parameters of the large-scale galactic components - disks and bulges - have been determined for the six largest galaxies of the group. A lower than expected percentage of bars and high percentage of ring structures were found. Integrated B-V colours for a hundred of dwarf galaxies in the vicinity (within 30 kpc) of the six largest galaxies of the group have been measured. A considerable number of blue irregular galaxies with ongoing star formation is found among dwarf satellites of the lenticular galaxies of the group. The luminosity function for the dwarf galaxies of the group suggests that the total mass of the group is not very high, and that the X-ray emitting gas observed around NGC 524 relates to the central galaxy and not to the group as a whole.
We present a compilation of galaxies in the NGC 1023 Group, an accumulation of late-type galaxies at a distance of 10 Mpc. Members at high and intermediate luminosities were identified from their spectroscopic velocities. Members at low luminosities were identified from their morphologies on wide-field CCD images. The faint-end slope is in the range -1.27 < alpha < -1.12. There is evidence for two dwarf galaxy populations: one in the halo of NGC 1023 that is dominated by dwarf elliptical galaxies, and one in the infall region surrounding NGC 1023 that contains mainly dwarf irregular galaxies. Similar distinctive populations are observed in the Local Group.
Understanding the astrophysical processes acting within galaxy groups and their effects on the evolution of the galaxy population is one of the crucial topic of modern cosmology, as almost 60% of galaxies in the Local Universe are found in groups. We imaged in the far (FUV 1539 A) and near ultraviolet (NUV 2316 A) with GALEX three nearby groups, namely LGG93, LGG127 and LGG225. We obtained the UV galaxy surface photometry and, for LGG225, the only group covered by the SDSS, the photometry in u, g, r, i, z bands. We discuss galaxy morphologies looking for interaction signatures and we analyze the SED of galaxies to infer their luminosity-weighted ages. The UV and optical photometry was also used to perform a kinematical and dynamical analysis of each group and to evaluate the stellar mass. A few member galaxies in LGG225 show a distorted UV morphology due to ongoing interactions. (FUV-NUV) colors suggest that spirals in LGG93 and LGG225 host stellar populations in their outskirts younger than that of M31 and M33 in the LG or with less extinction. The irregular interacting galaxy NGC3447A has a significantly younger stellar population (few Myr old) than the average of the other irregular galaxies in LGG225 suggesting that the encounter triggered star formation. The early-type members of LGG225, NGC3457 and NGC3522, have masses of the order of a few 10^9 Mo, comparable to the Local Group ellipticals. For the most massive spiral in LGG225, we estimate a stellar mass of ~4x10$^{10}$ Mo, comparable to M33 in the LG. Ages of stellar populations range from a few to ~7 Gyr for the galaxies in LGG225. The kinematical and dynamical analysis indicates that LGG127 and LGG225 are in a pre-virial collapse phase, i.e. still undergoing dynamical relaxation, while LGG93 is likely virialized. (Abridged)
The NGC 1023 group is one of the most studied nearby groups. We want to give an insight into the evolution of its innermost region by means of ultraviolet observations and proper models. We used the FUV and NUV GALEX archival data as well as a large set of SPH simulations with chemo-photometric implementation. From the UV observations we found that several, already known, dwarf galaxies very close to NGC 1023 are also detected in UV and two more objects (with no optical counterpart) can be added to the group. Using these data we construct exhaustive models to account for their formation. We find that the whole SED of NGC 1023 and its global properties are well matched by a simulation which provides a minor merger with a companion system 5 times less massive. The strong interaction phase started 7.7 Gyr ago and the final merger 1.8 Gyr ago.
We have studied unbarred S0 galaxies, NGC 3599 and NGC 3626, the members of the X-ray bright group Leo II, by means of 3D spectroscopy, long-slit spectroscopy, and imaging, with the aim to identify epoch and mechanismsof their transformation from spirals. Both galaxies have appeared to bear a complex of features resulting obviously from minor merging: decoupled gas kinematics, nuclear starforming rings, and multi-tiered oval large-scale stellar disks. The weak-emission line nucleus of NGC 3599 bears all signs of the Seyfert activity, according to the line-ratio diagnostics of the gas excitation mechanism. After all, we conclude that the transformation of these lenticular galaxies has had place about 1-2 Gyr ago, through the gravitational mechanisms not related to hot intragroup medium of Leo II.
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