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Register a new userIntra-Group Light in Hickson Compact Groups - A Wavelet Approach
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Cristiano Da Rocha
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A diffuse component of intra-group light can be observed in compact groups of galaxies. This component is presumably due to stellar material tidally stripped from the member galaxies of the group, which gets trapped in the group potential. It represents an efficient tool for the determination of the stage of dynamical evolution of such structures and for mapping the gravitational potential of the group. Detecting this kind of low surface brightness structure (about 1% above the sky level) is a difficult task, which is subject to many problems like the modeling of stars and galaxy and sky subtraction. To overcome these problems, we apply a new method, the wavelet technique OV_WAV, with which these low surface brightness structures can be revealed and analyzed by separating different components according to their spatial characteristic sizes (allowing the study of the point sources, galaxies and diffuse envelope separately). We have analyzed 3 of the of the Hickson Compact Groups Catalogue (HCG 79, HCG 88 and HCG 95) and were able to detect this diffuse component in two of the studied groups: HCG 79, where the diffuse light corresponds to $46pm11%$ of the total B band luminosity and HCG 95, where the fraction is $11pm26%$. HCG 88 had no component detected, as expected by its estimated early evolutionary stage.
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We have analyzed the intra-group light component of 3 Hickson Compact Groups (HCG 79, HCG 88 and HCG 95) with detections in two of them: HCG 79, with $46pm11%$ of the total $B$ band luminosity and HCG 95 with $11pm26%$. HCG 88 had no component detected. This component is presumably due to tidally stripped stellar material trapped in the group potential and represents an efficient tool to determine the stage of dynamical evolution and to map its gravitational potential. To detect this low surface brightness structure we have applied the wavelet technique OV_WAV, which separates the different components of the image according to their spatial characteristic sizes.
We observed 5 Hickson Compact Groups with the ESO/MPI 2.2m telescope and WFI to investigate the dwarf galaxy content and distribution in these galaxy groups. Our deep imaging and careful selection of the candidate galaxies revealed a rich population of mainly passively evolving dwarf galaxies, which is spatially much more extended than the originally defined Hickson Compact groups. The composite luminosity function of the 5 groups shows a bimodal structure with a very steep rise in the low luminosity regime. The faint end slope is close to the predictions of CDM theory for the slope of the Dark Matter halo mass function.
Deep $B$ and $R$ images of three Hickson Compact Groups, HCG 79, HCG 88 and HCG 95, were analyzed using a new wavelet technic to measure possible intra-group diffuse light present in these systems. The method used, OV_WAV, is a wavelet technic particularly suitable to detect low-surface brightness extended structures, down to a $S/N = 0.1$ per pixel, which corresponds to a 5-$sigma$-detection level in wavelet space. The three groups studied are in different evolutionary stages, as can be judged by their very different fractions of the total light contained in their intra-group halos: $46pm11$% for HCG 79 and $11pm26$% for HCG 95, in the $B$ band, and HCG 88 had no component detected down to a limiting surface brightness of $29.1 B mag arcsec^{-2}$. For HCG 95 the intra-group light is red, similar to the mean colors of the group galaxies themselves, suggesting that it is formed by an old population with no significant on-going star formation. For HCG 79, however, the intra-group material has significantly bluer color than the mean color of the group galaxies, suggesting that the diffuse light may, at least in part, come from stripping of dwarf galaxies which dissolved into the group potential well.
This study presents the mass distribution for a sample of 18 late-type galaxies in nine Hickson Compact Groups. We used rotation curves from high resolution 2D velocity fields of Fabry-Perot observations and J-band photometry from the 2MASS survey, in order to determine the dark halo and the visible matter distributions. The study compares two halo density profile, an isothermal core-like distribution and a cuspy one. We also compare their visible and dark matter distributions with those of galaxies belonging to cluster and field galaxies coming from two samples: 40 cluster galaxies of Barnes et al (2004) and 35 field galaxies of Spano et al. (2008). The central halo surface density is found to be constant with respect to the total absolute magnitude similar to what is found for the isolated galaxies. This suggests that the halo density is independent to galaxy type and environment. We have found that core-like density profiles fit better the rotation curves than cuspy-like ones. No major differences have been found between field, cluster and compact group galaxies with respect to their dark halo density profiles.
I present observations of the Hickson Compact Group 88 (HCG88) obtained during the commissioning of a new 28-inch telescope at the Wise Observatory. This galaxy group was advertised to be non-interacting, or to be in a very early interaction stage, but this is not the case. The observations reported here were done using a luminance filter, essentially a very broad R filter, reaching a low surface brightness level of about 26 mag per square arcsec. Additional observations were obtained in a narrow spectral band approximately centered on the rest-frame H-alpha line from the group. Contrary to previous studies, my observations show that at least two of the major galaxies have had significant interactions in the past, although probably not between themselves. I report the discovery of a faint extended tail emerging from the brightest of the group galaxies, severe isophote twisting and possible outer shells around another galaxy, and map the HII regions in all the galaxies.
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