The UZC-SSRS2 Group Catalog

Abstract.We study morphology and luminosity segregation of galaxies in loose groups. We analyze the two catalogs of groups identified in the Nearby Optical Galaxy (NOG) sample, by means of hierarchical and percolation "friends-of-friends" methods (HG and PG catalogs, respectively). In the first part of our analysis we consider 387 and 436 groups of HG and PG and compare morphology-(luminosity-) weighted to unweighted group properties: velocity dispersion, mean pairwise distance, and mean groupcentric distance of member galaxies. The second part of our analysis is based on two ensemble systems, one for each catalog, built by suitably combining together galaxies of all groups (1584 and 1882 galaxies for HG and PG groups). We find that earlier-type (brighter) galaxies are more clustered and lie closer to the group centers, both in position and in velocity, than later-type (fainter) galaxies. Spatial segregations are stronger than kinematical segregations. These effects are generally detected at the ∼ >3-sigma level. Luminosity segregation is shown to be independent of morphology segregation. Our main conclusions are strengthened by the detection of segregation in both hierarchical and percolation catalogs. Our results agree with a continuum of segregation properties of galaxies in systems, from low-mass groups to massive clusters.

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“…Ramella et al 2002). Spatial segregation phenomena are generally studied through the galaxy-galaxy correlation function analysis.…”

Section: Summary and Discussionmentioning

confidence: 99%

Morphology and luminosity segregation of galaxies in nearby loose groups

Girardi

Rigoni

Mardirossian

et al. 2003

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“…Huchra & Geller 1982;Tully 1987;Giuricin et al 2000;Ramella et al 2002;Eke et al 2004;Tago et al 2008), our knowledge of galaxy evolution in low density environments, of which groups are the defining galaxy association, is still scanty. In particular, whether a link between the elliptical-galaxy dominated and late-type galaxy dominated groups exists, i.e.…”

Section: Introductionmentioning

confidence: 99%

Galaxy evolution in Local Group analogs

Marino

Bianchi

Rampazzo

et al. 2010

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Context. Understanding the astrophysical processes acting within galaxy groups and their effects on the evolution of the galaxy population is one of the crucial topics of modern cosmology, as almost 60% of galaxies in the Local Universe are found in groups. Aims. We aim at learning about galaxy evolution within nearby groups dominated by late-type galaxies, specifically by studying their ultraviolet-emitting stellar population. Methods. We imaged in the far (FUV, λ eff = 1539 Å) and near ultraviolet (NUV, λ eff = 2316 Å) with the Galaxy Evolution Explorer (GALEX) three nearby groups, namely LGG 93, LGG 127 and LGG 225. We obtained the UV galaxy surface photometry and, for LGG 225, 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 spectral energy distribution of galaxies to infer their luminosity-weighted ages. The UV and optical photometry was also used to perform a luminosity-weighted kinematical and dynamical analysis of each group and to evaluate the stellar mass. Results. A few member galaxies in LGG 225 show a distorted UV morphology due to ongoing interactions. (FUV − NUV) colors suggest that spirals in LGG 93 and LGG 225 host stellar populations in their outskirts younger than that of M 31 and M 33 in the Local Group or with less extinction. The irregular interacting galaxy NGC 3447A has a significantly younger stellar population (a few Myr old) than the average of the other irregular galaxies in LGG 225 suggesting that the encounter triggered star formation. The early-type members of LGG 225, NGC 3457 and NGC 3522, have masses of the order of a few 10 9 M , comparable to the Local Group ellipticals. For the most massive spiral in LGG 225, we estimate a stellar mass of ≈4 × 10 10 M , comparable to M 33 in the Local Group. Ages of stellar populations range from a few to ≈7 Gyr for the galaxies in LGG 225. The kinematical and dynamical analysis indicates that LGG 127 and LGG 225 are in a pre-virial collapse phase, i.e. still undergoing dynamical relaxation, while LGG 93 is likely virialized. Both the photometric and the dynamical analyses suggest that LGG 225 is in a more active evolution phase than LGG 93 and LGG 127.

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“…the Virgo and Centaurus LFs provide different constraints, I favor the Centaurus cluster as its lower spatial density better reflects the density of the numerous galaxy groups present in a redshift survey; Ramella et al 2002). The upper bound of all the integrals mentioned below are obtained by converting the M(B T ) −15.5 completeness limit from Jerjen & Tammann (1997) into the R c band using the quoted colors extracted from Table 5 of de Lapparent et al (2003b).…”

Section: The Local Luminosity Functions Per Morphological Typementioning

confidence: 99%

Critical analysis of the luminosity functions per galaxy type measured from redshift surveys

Lapparent

2003

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Abstract. I perform a quantitative comparison of the shape of the optical luminosity functions as a function of galaxy class and filter, which have been obtained from redshift surveys with an effective depth ranging from z 0.01 to z 0.6. This analysis is based on the M * and α Schechter parameters which are systematically measured for all galaxy redshift surveys. I provide complete tables of all the existing measurements, which I have converted into the UBVR c I c Johnson-Cousins system wherever necessary.By using as reference the intrinsic luminosity functions per morphological type, I establish that the variations in the luminosity functions from survey to survey and among the galaxy classes are closely related to the criteria for galaxy classification used in the surveys, as these determine the amount of mixing of the known morphological types within a given class. When using a spectral classification, the effect can be acute in the case of inaccurate spectrophotometric calibrations: the luminosity functions are then biased by type contamination and display a smooth variation from type to type which might be poorly related to the intrinsic luminosity functions per morphological type. In the case of surveys using multi-fiber spectroscopy, galaxy classification based on rest-frame colors might provide better estimates of the intrinsic luminosity functions.It is noticeable that all the existing redshift surveys fail to measure the Gaussian luminosity function for Spiral galaxies, presumably due to contamination by dwarf galaxies. Most existing redshift surveys based on visual morphological classification also appear to have their Elliptical/Lenticular luminosity functions contaminated by dwarf galaxies. In contrast, the analyses using a reliable spectral classification based on multi-slit spectroscopy or medium-filter spectrophotometry, and combined with accurate CCD photometry succeed in measuring the Gaussian luminosity function for E/S0 galaxies. The present analysis therefore calls for a more coherent approach in separating the relevant giant and dwarf galaxy types, a necessary step towards measuring reliable intrinsic luminosity functions.

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The UZC-SSRS2 Group Catalog

Cited by 131 publications

References 51 publications

Morphology and luminosity segregation of galaxies in nearby loose groups

Morphology and luminosity segregation of galaxies in nearby loose groups

Galaxy evolution in Local Group analogs

Critical analysis of the luminosity functions per galaxy type measured from redshift surveys

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