We are investigating the co-evolution of galaxies within groups combining multi-wavelength photometric and 2D kinematical observations. Here we focus on S0s showing star formation in ring/arm-like ...structures. We use smooth particle hydrodynamical simulations (SPH) with chemo-photometric implementation which provide dynamical and morphological information together with the spectral energy distribution (SED) at each evolutionary stage. As test cases, we simulate the evolution of two such S0s: NGC 1533 and NGC 3626.
The merging of two halos with mass ratio 2:1, initially just composed of DM and gas, well match their observed SEDs, their surface brightness profiles and their overall kinematics. The residual star formation today “rejuvenating” the ring/arm like structures in these S0s is then a mere consequence of a major merger, i.e. this is a phase during the merger episode. The peculiar kinematical features, e.g. gas-stars counter rotation in NGC 3626, depends on the halos initial impact parameters. Furthermore, our simulations allow to follow, in a fully consistent way, the transition of these S0s through the green valley in the NUV-r vs. Mr colour magnitude diagram, which they cross in about 3–5Gyrs, before reaching their current position in the red sequence. We conclude that a viable mechanism driving the evolution of S0s in groups is of gravitational origin.
A study of the gas content in 1038 interacting galaxies, essentially selected from Arp, Arp & Madore, Vorontsov-Velyaminov catalogues and some of the published literature, is presented here. The data ...on the interstellar medium have been extracted from a number of sources in the literature and compared with a sample of 1916 normal galaxies. The mean values for each of the different ISM tracers (FIR, 21 cm, CO lines, X-ray) have been estimated by means of survival analysis techniques, in order to take into account the presence of upper limits. From the data it appears that interacting galaxies have a higher gas content than normal ones. Galaxies classified as ellipticals have both a dust and gas content one order of magnitude higher than normal. Spirals have in most part a normal dust and HI content but an higher molecular gas mass. The X-ray luminosity also appears higher than that of normal galaxies of same morphological type, both including or excluding AGNs. We considered the alternative possibilities that the molecular gas excess may derive from the existence of tidal torques which produce gas infall from the surrounding regions or from a different metallicity which affects the X conversion factor between the observed CO line luminosity and the H2 calculated mass. According to our tests, it appears that interacting galaxies possess a higher molecular mass than normal galaxies but with a similar star formation efficiency.
The NGC1023 group is one of the most studied nearby groups. Our aim is to give an insight into the evolution of its innermost region by means of ultraviolet observations and proper models. We use ...far-ultraviolet and near-ultraviolet GALEX archival data as well as a large set of smoothed particle hydrodynamics simulations with chemo-photometric implementation. From the UV observations we find that several, already known, dwarf galaxies very close to NGC1023 are also detected in the ultraviolet 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 spectral energy distribution of NGC1023 and its global properties are well matched by a simulation that provides a minor merger with a companion system 5 times less massive. The strong interaction phase started 7.7Gyr ago and the final merger 1.8Gyr ago.
We present the Galaxy Evolution Explorer (GALEX) far-ultraviolet (FUV) and near-ultraviolet (NUV) imaging of three nearby shell galaxies, namely NGC 2865, NGC 5018 and NGC 7135 located in low-density ...environments.
The system of shells and fine structures visible in the optical is detected in the NUV image of NGC 2865 and in both NUV and FUV images of NGC 7135. The NUV image of NGC 5018 does not present shell structures. We detect absorption features in the nuclear region of all three galaxies. NGC 2865 has a nearly flat colour profile with (FUV−NUV) ≈ 2 throughout the whole galaxy. NGC 7135 is blue in the centre (FUV−NUV) ≈ 0 and as red as (FUV−NUV) ≈ 1.5 in the outskirts, including the faint shell-like feature.
The three shell galaxies are members of poor groups of galaxies. We compare GALEX NUV observations with available H i large-scale measurements, and determine the UV magnitudes of likely companions. Most of the known (and possible) companions are gas-rich late-type galaxies, suggesting that our shell galaxies inhabit the ideal environment for hosting rejuvenating episodes driven by accretion events.
We investigate the ability of the nuclear
GALEX (FUV−NUV) colour to provide information about rejuvenation phenomena in the stellar populations of the shell galaxies. To this aim, we derive from theory the relationship between the Mg2, Hβ, HγA, HδA Lick line-strength indices and the (FUV−NUV) colour. We extend the study to a sample of early-type galaxies in low-density environments which includes shell galaxies and/or galaxies with emission lines in their optical spectra. In the index versus (FUV−NUV) colour diagrams, most of the galaxies are well explained by passively evolving single stellar populations. On the average, ages and metallicities of the galaxies in our sample estimated from optical line-strength indices are consistent with those inferred from the (FUV−NUV) colour. We note that the GALEX (FUV−NUV) and (UV−V) colours have different response to age and metallicity. In general, all the colours but for (FUV−NUV) and (FUV−V), become nearly age-insensitive when 1-2 Gyr have elapsed from the last star-forming event. Finally, considering composite stellar population models with a recent burst of star formation, we suggest that the positions of the NGC 7135 and NGC 2865 nuclei in the (FUV−NUV)-Hβ plane could be explained in terms of a recent rejuvenation episode.
Context. The Galaxy Ultraviolet Explorer (GALEX) satellite has recently shown the presence of an extended, outer ring studded with UV-bright knots surrounding the lenticular galaxy NGC 4262. Such a ...structure-not detected in the optical-is coupled with a ring of atomic (HI) gas. Aims. We want to show that both star-forming and HI rings surrounding this SB0 galaxy share the same radial distance from the galaxy center and spatial orientation. We also model the kinematics of the ring(s) and of the galaxy body. Methods. We make use of archive FUV and NUV GALEX data plus HI observations from the literature. Results. We confirm that the UV-bright and atomic gas rings of NGC 4262 have the same extent and projected spatial orientation. Their kinematics is not coupled with that of the galaxy stars. Conclusions. It is possible that NGC 4262 has undergone a major gas stripping event in the past that was the origin of the present “necklace” of UV-bright knots.
We present a detailed photometric study of the peculiar double-ringed galaxy ESO474-G26. Near-infrared (NIR) and optical data have been used, with the main goal of constraining the formation history ...of ESO474-G26. NIR photometry is fundamental in this kind of study, because it gives better constraints on the spectral energy distribution (SED) and traces the older stellar population of the galaxy well. This galaxy presents a very complex structure with two almost orthogonal rings, one in the equatorial and another in the polar plane, around an elliptical-like object. Due to the peculiar morphology of ESO474-G26, we used both NIR images (J and K bands) to derive accurate analysis of the stellar light distribution and optical images (in the B, V and R bands) to derive colour profiles and colour maps to study the structure of the rings. The observational characteristics of ESO474-G26 are typical of galaxies that have experienced some kind of interaction during their evolution. We investigated two alternatives: a merging process and an accretion event. PUBLICATION ABSTRACT
This paper is the second of a series of papers in which we are exploring the coevolution of galaxies and groups in the local Universe, by adopting a multiwavelength approach. Here, we present the ...photometric and kinematic characterization of two groups, USGC U268 and USGC U376 (U268 and U376 hereafter), which are located in different regions of the Leo cloud. We revisit the group membership, using results from recent redshift surveys, and we investigate their substructures. U268, which is composed of 10 catalogued members and 11 new added members, has a small fraction ( 24 per cent) of early-type galaxies (ETGs). U376 has 16 catalogued members plus eight new added members, with 38 per cent of ETGs. We find that there are significant substructures in both groups, which suggests that they are likely to be accreting galaxies. U268 is located in a more loose environment than U376. For each member galaxy, broad-band integrated and surface photometry have been obtained in far-ultraviolet (FUV) and near-ultraviolet (NUV) with the Galaxy Evolution Explorer (GALEX), and in the u, g, r, i and z (Sloan Digital Sky Survey) bands. Hα imaging and two-dimensional high-resolution kinematical data have been obtained using the scanning Fabry-Pérot interferometer (PUMA) at the 2.12-m telescope at San Pedro Mártir (Baja California, Mexico). We have improved the galaxy classification and we have detected morphological and kinematical distortions that might be connected either to ongoing and/or past interaction/accretion events or to environmental-induced secular evolution. U268 appears to be more active than U376, with a large fraction of galaxies showing interaction signatures (60 per cent versus 13 per cent). The presence of bars among late-type galaxies is 10 per cent in U268 and 29 per cent in U376. The cumulative distribution of the FUV-NUV colours of galaxies in U268 is significantly different from that in U376, with galaxies in U268 being bluer than those in U376. In the (FUV-r versus M
r
) and (NUV-r versus M
r
) planes, no members of U268 are found in the red sequence; even ETGs lie in the blue sequence, or in the 'green valley'. Most (i.e. 80 per cent) of the early-type members in U376 inhabit the red sequence. A large fraction of galaxies, of different morphological types, are located in the green valley, while the blue sequence is underpopulated compared with U268.
With the aim of investigating galaxy evolution in nearby galaxy groups, we analyzed the spectral energy distribution of 24 galaxies, members of two groups in the Leo cloud, USGC U268 and USGC U376. ...We estimated the ages and stellar masses of the galaxies by fitting their total apparent magnitudes from far-ultraviolet to near-infrared with population synthesis models. The comparison of the results for a subsample of galaxies with smooth particle hydrodynamic (SPH) simulations with chemo-photometric implementation, shows that in most cases the estimated stellar masses obtained with the two different approaches are in good agreement. The kinematical and dynamical analysis indicates that USGC U268 is in a pre-virial collapse phase while USGC U376 is likely in a more evolved phase towards virialization.
The Galaxy Evolution Explorer (
GALEX
) detected ultraviolet emission in about 50 % of multi-spin early-type galaxies (ETGs), suggesting the occurrence of a recent rejuvenation episode connected to ...the formation of these kinematical features. With the aim at investigating the complex evolutionary scenario leading to the formation of counter rotating ETGs (CR-ETGs) we use our Smooth Particle Hydrodynamic (SPH) code with chemo-photometric implementation. We discuss here the UV evolutionary path of two CR-ETGs, NGC 3593 and NGC 5173, concurrently best fitting their global observed properties, i.e., morphology, dynamics, as well as their total
B
-band absolute magnitude and spectral energy distribution (SED) extended over three orders of magnitude in wavelength. These simulations correspond to our predictions about the target evolution which we follow in the color-magnitude diagram (CMD), near-UV (NUV) versus
r
-band absolute magnitude, as a powerful diagnostic tool to emphasize rejuvenation episodes.
We have compiled a catalogue of the gas content for a sample of 1916 galaxies, considered to be a fair representation of “normality”. The definition of a “normal” galaxy adopted in this work implies ...that we have purposely excluded from the catalogue galaxies having distorted morphology (such as interaction bridges, tails or lopsidedness) and/or any signature of peculiar kinematics (such as polar rings, counterrotating disks or other decoupled components). In contrast, we have included systems hosting active galactic nuclei (AGN) in the catalogue. This catalogue revises previous compendia on the ISM content of galaxies published by CITE and CITE, and compiles data available in the literature from several small samples of galaxies. Masses for warm dust, atomic and molecular gas, as well as X-ray luminosities have been converted to a uniform distance scale taken from the Catalogue of Principal Galaxies (PGC). We have used two different normalization factors to explore the variation of the gas content along the Hubble sequence: the blue luminosity (LB) and the square of linear diameter ($D^2_{25}$). Our catalogue significantly improves the statistics of previous reference catalogues and can be used in future studies to define a template ISM content for “normal” galaxies along the Hubble sequence. The catalogue can be accessed on-line and is also available at the Centre des Données Stellaires (CDS).
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