Context. Now that modern imaging surveys have produced large databases of galaxy images advanced morphological studies have become possible. This has driven the need for well-defined calibration samples. Aims. We present the EFIGI catalogue, a multi-wavelength database specifically designed to densely sample all Hubble types. The catalogue merges data from standard surveys and catalogues (Principal Galaxy Catalogue, Sloan Digital Sky Survey, Value-Added Galaxy Catalogue, HyperLeda, and the NASA Extragalactic Database) and provides detailed morphological information. Methods. Imaging data were obtained from the SDSS DR4 in the u, g, r, i, and z bands for a sample of 4458 PGC galaxies, whereas photometric and spectroscopic data were obtained from the SDSS DR5 catalogue. Point-spread function models were derived in all five bands. Composite colour images of all objects were visually examined by a group of astronomers, and galaxies were assigned positions in the Hubble sequence and classified according to 16 morphological attributes describing their structure, texture, environment and appearance on a five-level scale. Results. The EFIGI Hubble sequence is in remarkably good agreement with the RC3 Revised Hubble Sequence. The main characteristics and reliability of the catalogue are examined, including photometric completeness, type mix, systematic trends and correlations. Conclusions. The final EFIGI database is a large sub-sample of the local Universe which densely samples Sd, Sdm, Sm and Im types compared to magnitude-limited catalogues. We estimate that the photometric catalogue is more than ≈80% complete for galaxies with 10 < g < 14. More than 99.5% of EFIGI galaxies have known redshifts in the HyperLeda and NED databases.
In this paper a new algorithm to compute the component tree is presented. As compared to the state of the art, this algorithm does not use excessive memory and is able to work efficiently on images whose values are highly quantized or even with images having floating values. We also describe how it can be applied to astronomical data to identify relevant objects.
Aims. The EFIGI catalogue of 4458 galaxies extracted from the PGC and SDSS DR4 was designed to provide a multiwavelength reference database of the morphological properties of nearby galaxies. The sample is limited in apparent diameter and densely samples all RC3 Hubble types. Methods. We examine the statistics of the 16 EFIGI shape attributes, describing the various dynamical components, the texture, and the contamination by the environment of each galaxy. Using the redshifts from SDSS, HyperLeda, or NED for 99.53% of EFIGI galaxies, we derive estimates of absolute major isophotal diameters and the corresponding mean surface brightness in the SDSS g-band.Results. We study the variations of the EFIGI morphological attributes with Hubble type and confirm that the visual Hubble sequence is a decreasing sequence of bulge-to-total ratio and an increasing sequence of disk contribution to the total galaxy flux. There is, nevertheless, a total spread of approximately five types for a given bulge-to-total ratio, because the Hubble sequence is primarily based on the strength and pitch angle of the spiral arms, independently from the bulge-to-total ratio. A steep decrease in the presence of dust from Sb to Sbc-Sc types appears to produce the grand spiral design of the Sc galaxies. In contrast, the scattered and giant HII regions show different strength variation patterns, with peaks for types Scd and Sm; hence, they do not appear to directly participate in the establishment of the visual Hubble sequence. The distortions from a symmetric profile also incidentally increase along the sequence. Bars and inner rings are frequent and occur in 41% and 25% of the disk galaxies respectively. Outer rings are half as frequent than inner rings, and outer pseudo-rings occur in 11% of barred galaxies. Finally, we find a smooth decrease in mean surface brightness and intrinsic size along the Hubble sequence. The largest galaxies are cD, ellipticals and Sab-Sbc intermediate spirals (20-50 kpc in D 25 ), whereas Sd and later spirals are nearly half as big. S0 are intermediate in size (15-35 kpc in D 25 ), and irregulars, compact and dwarf ellipticals are confirmed as small objects (5-15 kpc in D 25 ). Dwarf spiral galaxies of type Sa to Scd are rare in the EFIGI catalogue, we only find two such objects. Conclusions. The EFIGI sample provides us for the first time with a quantitative description of the visual Hubble sequence in terms of the specific morphological features of the various galaxy types.
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