2. SAMPLE

2.1. Selection

The sample of objects in this Atlas includes galaxies in the GALEX Nearby Galaxies Survey (NGS) (Gil de Paz et al. 2004; Bianchi et al. 2003a, 2003b) plus galaxies serendipitously found in NGS fields or in fields with similar or greater depth obtained as part of other GALEX imaging surveys that have optical diameters at the µ_B = 25 mag arcsec^-2 isophote larger than 1 arcmin according to the Third Reference Catalog of Bright Galaxies (RC3 hereafter; de Vaucouleurs et al. 1991). Note also that 1arcmin is the apparent diameter for which the RC3 catalog is reasonably complete (Harold G. Corwin, private communication).

As mentioned above the answers to some of the most fundamental open questions on galaxy evolution in general and on the UV properties of galaxies in particular are largely dependent on the (sometimes very large) corrections for dust extinction that must be applied. With this in mind the NGS survey was constructed to optimally sample the UV as provided by GALEX and the FIR (where most of the UV light absorbed by dust is re-emitted) as seen by the Spitzer Space Telescope that would give us a bolometric view of galaxies in the Local Universe. Thus, we began building the NGS sample using Spitzer's Reserved Observations Catalog (ROC v2.0), which guarantees that both UV and infrared data will be eventually made publicly available to the community for all these galaxies. This includes the Spitzer Infrared Nearby Galaxies Survey legacy project (SINGS; Kennicutt et al. 2003), but also data from Guaranteed Time Observations (GTO) programs like The Mid-IR Hubble Atlas of Galaxies (PI: G. Fazio), Starburst Activity in Nearby Galaxies (PI: G. Rieke), Probing a sample of Interacting and Ultra-luminous Galaxies (PI: G. Fazio), etc. The total number of (targeted) NGS galaxies represents approximately one fourth of the total sample of 1034 galaxies in the present Atlas. The vast majority of the UV images of the galaxies observed as part of NGS have exposure times of 1 GALEX orbit or more (~ 1700 s). See section 3 for a detailed description of the GALEX spacecraft and instrument.

In order to cover a wider range of physical properties (see Section 3.1) and taking advantage of the large field-of-view of the GALEX instrument (1.2degrees in diameter) we added to the Atlas sample all galaxies in the RC3 catalog with D25 diameter larger than 1arcmin that were serendipitously observed within NGS fields and/or within other GALEX surveys of similar or greater depth that were available to the GALEX team, namely the Medium Deep, Deep, and Ultra-deep Imaging Surveys (MIS, DIS, and UIS, respectively). We also added galaxies that were targeted by GALEX because they had been observed by previous UV missions like UIT or FOCA (as an additional calibration test for GALEX) and galaxies from dedicated observations of the central 12 deg² of the Virgo cluster (Boselli et al. 2005).

Of the original 1136 galaxies compiled 26 were found in images that have failed the quality assurance (QA) test of the image aspect solution that is included as part of the standard GALEX pipeline. A total of 55 additional galaxies were excluded either because were observed in regions of high background, high Galactic extinction, during very short orbits and/or they showed extremely low surface brightness in the UV. After excluding these galaxies and those objects with no published redshift (21) we ended up with a total of 1034 galaxies; 893 of them having both FUV and NUV high-quality observations.

2.2. Positions, sizes, morphological types, and distances

In Table 1 we give some basic parameters for the galaxies included in this Atlas, including their positions, sizes, distances, Galactic color excesses [E(B - V)], and morphological and spectroscopic types.

The coordinates shown (columns 2 and 3) correspond to those given by NED, which are known to be more accurate than those in the RC3 catalog from which a significant fraction of these galaxies were selected (Harold G. Corwin, private communication). A few objects (29) had NED coordinates that were clearly offset from the position of the galaxy both in the UV and the DSS images. In these cases, the new, correct positions were determined by eye after inspecting the corresponding UV images and the Table 1 corrected accordingly. Finally, for two of the objects in the Atlas (UGC 08650 and UGC 11859) a missing/incomplete World Coordinate System (WCS) solution was recomputed using the positions of nearby stars in the USNO-B catalog (Monet et al. 2003). Sizes are the major (column 4) and minor (column 5) axis diameters at the B-band 25 mag arcsec^-2 isophote (computed from the corresponding D25 and R25 values in the RC3 catalog). For those few objects in our sample not included in the RC3 catalog we used the major and minor axis diameters available in NED. Position angles (PA; column 6) missing or incorrect in the RC3 catalog were determined by eye for a total of 90 of the galaxies in the sample after inspecting the corresponding UV images. Note that the PA is undefined in those galaxies for which the D25 isophote is approximately circular according to the RC3.