ASTRONOMY & ASTROPHYSICS FEBRUARY I 1998, PAGE 367 SUPPLEMENT SERIES Astron. Astrophys. Suppl. Ser. 127, 367-395 (1998) The “Virgo photometry catalogue”; a catalogue of 1180 galaxies in the direction of the Virgo Cluster’s core C.K. Young1,2 and M.J. Currie3 1Beijing Astronomical Observatory, Chinese Academy of Sciences, Beijing 100080, China 2Department of Physics, University of Oxford, Nuclear and Astrophysics Laboratory, Keble Road, Oxford OX1 3RH, UK 3Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire OX11 0QX, UK Received February 25; accepted May 22, 1997 Abstract. We present a new catalogue of galaxies in merged images; our segmentation software being able to the direction of the Virgo Cluster’s core: the Virgo cope with the vast majority of image mergers. Photometry Catalogue (VPC)1. This catalogue contains 1180 galaxies (including background objects) within a 23 Key words: galaxies: clusters: individual: Virgo — square-degree area of the sky centred on R.A.1950.0 = catalogues — galaxies: fundamental parameters — h m ◦ 0 12 26 and dec.1950.0 =13 08 . The VPC galaxy sample galaxies: photometry comprises of non-stellar objects brighter than BJ25 =19.0; the completeness limits being BJ25 ≈ 18.5 for the northern half of the survey area and BJ25 ≈ 18.0 for the southern half. Independently-calibrated photographic surface pho- 1. Introduction tometry is presented for over 1000 galaxies in the U, BJ The Virgo Cluster, being the dominant nearby clus- and RC bands. Parameters listed for catalogued galax- ter of galaxies, has long attracted much attention. ies include: equatorial coordinates, morphological types, It is irregular and exhibits significant substructure. surface-brightness profile parameters (which preserve the Binggeli et al. (1987) divided Virgo into two main clusters: majority of the original surface photometry information), a dominant cluster, Cluster A, which is rich in early type U, BJ & RC isophotal magnitudes, BJ and [transformed] galaxies and contains the giant elliptical NGC 4486 (oth- B total magnitudes, (U − BJ)and(BJ−RC) equal-area erwise known as M 87) and a secondary cluster, Cluster and total colours, apparent angular radii, ellipticities, po- B, dominated by late spirals, in the direction of the giant sition angles, heliocentric radial velocities and alternative elliptical NGC 4472 (M 49). Their Clusters A and B corre- designations. All total magnitudes and total colours are spond to de Vaucouleurs’s concentric E ∪ S and S’ Clouds extrapolated according to a new system denoted t in or- respectively (see e.g. de Vaucouleurs & Corwin 1986). The der to distinguish it from the T system already in use. VPC covers the central region of Cluster A/Clouds E&S. The VPC is based primarily on four (one U,twoBJ It does not cover the central region of Cluster B/Cloud and one RC) UK-Schmidt plates, all of which were digi- S’, but there may of course still be many objects from this tised using the Royal Observatory Edinburgh’s (ROE) secondary cluster within the VPC survey area. COSMOS measuring machine. All magnitudes, colours The equatorial coordinates of the centre of what is gen- and surface-brightness parameters are derived from nu- erally held to be the Virgo Cluster proper (i.e. of Cluster merical integrations of segmented plate-scan data, except A or the E/S Clouds) are approximately 12h26m in right for (in 109 cases) saturated or (in 51 cases) inextricably- ascension (1950.0) and +13◦000 in declination (1950.0). The entire complex including substructures, is generally Send offprint requests to: C.K. Young by e-mailing thought of as subtending a radius of about 6◦ on the ce- [email protected] lestial sphere, though its true extent has yet to be estab- 1 Appendices B, C and E, which contain the surface lished. photometry, the main catalogue and the summary cata- logue respectively, are only available in electronic form. Radial velocities of the constituent galaxies vary from TheycanbeobtainedfromLeCentredeDonn´ees the most negative ones known (and the only negative ones astronomiques de Strasbourg (CDS) via anonymous ftp known for galaxies outside the neighbourhood of the Local to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u- Group) to a maximum of about +3000 km s−1,asisev- strasbg.fr/Abstract.html ident from Binggeli et al.’s (1985) Virgo Cluster Catalog 368 C.K. Young and M.J. Currie: Virgo photometry catalogue (VCC). There appears to be a ∼4000 km s−1-deep veloc- tion. We will also be investigating the luminosity functions ity void behind the cluster, as the background system is of Virgo dwarfs, with the triple benefits of: galaxy samples at +7000 km s−1 (see e.g. Drinkwater et al. 1996). selected according to objective criteria, independently cal- Most attempts to pin down the value of the Hubble ibrated machine generated magnitude measurements and constant have long been based on distance measurements the consideration of depth effects. These studies will be for Virgo-Cluster galaxies. There are probably two main the subjects of future papers but a preliminary study of reasons for this. First, it is the nearest cluster in which the spatial distribution of 64 Virgo dwarf-ellipticals has a full complement of morphological types is represented: already been presented in Young & Currie (1995) and a i.e. giant elliptical galaxies; classical ellipticals, spirals and comparison with the existing magnitude scales for Virgo irregulars; dwarf ellipticals and irregulars; blue compact galaxies will be presented by Young et al. (in preparation). dwarfs; galaxies in the process of merging and others that defy classification. It has therefore been possible to apply 2. The observations a wider variety of different distance indicators to Virgo galaxies than it has been for other clusters at similar red- shifts such as Fornax or Leo. Second, Virgo has the added advantage of being easily observable from observatories in Table 1. The UKST plates on which the VPC is based both the Northern and Southern hemispheres. plate date (α, δ)a emulsion/filter/exposure Virgo’s popularity as a pivotal step in the cosmic dis- 1950.0 tance scale has nevertheless not been without its difficul- U9362 84:06:03 12:27,13:30 IIIaJ/UG1/3 hr. ties and controversies. Until recently, the possibility that J4882 79:03:23 12:25,13:20 IIIaJ/GG395/1 hr. the spatial extent of the Virgo Cluster may have consider- J9229 84:04:26 12:27,13:30 IIIaJ/GG395/1 hr. able line-of-sight depth was not taken seriously. Although R2936 77:02:27 12:25,13:20 IIIaF/RG630/48 min. Pierce & Tully (1988) suggested the “possible presence of a superposed foreground and background galaxies” in their the equatorial coordinates of the plate centres: in hours sample of Virgo spirals, it was not until the distance-scale and minutes of time for right ascension (α) and in degrees and minutes of arc for declination (δ). work of Tonry et al. (1990) and Tonry (1991) that any author was prepared to stand by the case for consider- able depth. However, these authors did not confront the potentially embarrassing issue of the cluster’s elongation The VPC is based on four photographic plates (one U, ratio in the line of sight; which would have to exceed 5:1 two BJ and one RC) of the same field; all of which were ex- in order to explain the depth in their derived galaxy dis- posed on the 1.2-metre UK Schmidt Telescope (UKST) at tributions. Other authors have understandably tended to Siding Spring Observatory in Australia. Details of all four explain any apparent depth effect in Virgo galaxy distribu- plates are listed in Table 1. Each plate measured 356 mm ◦ ◦ tions in terms of random observational errors and scatter square and covered an area of the sky 6.4by6.4 within an intrinsic to the distance indicators employed. imaging area of dimensions 343 mm by 343 mm. The plate The first authors not to avoid the elongation issue were scale was therefore 67.12 arcsec/mm in each case. All of Fukugita et al. (1993). These authors suggested that the the plates were hypersensitised by successive soaking in Virgo Cluster’s spiral-galaxy distribution is in fact fila- nitrogen and hydrogen gas. Those plates taken after 1982 mentary in shape, rather than approximately spherically December 3 had the added advantage of being nitrogen symmetric [as had been assumed before] with spirals ly- flushed; that is exposed under a constant stream of nitro- ing at distances from 13 Mpc all the way through to gen. The significance of this flushing process is dealt with 30 Mpc. In Young & Currie (1995) we also found a con- in Sects. 3.7 and 6.2. siderable depth effect, that we could not explain away in terms of errors or intrinsic scatter, this time in the distri- 3. Data reduction procedure bution of dwarf-elliptical galaxies in the direction of the 3.1. The densitometry Virgo Cluster’s core itself. Furthermore, we found prelim- inary evidence for a foreground concentration of galaxies The plates were digitised by the ROE’s Image and Data several Mpc in front of the main cluster, which led us to Processing Unit using its COSMOS measuring machine suggest that the depth effect may be due to the projection in mapping mode with a spot/pixel size of 32 microns. of more than one distinct galaxy concentration onto the The central 4◦.8-square field of each plate was subdi- same sight line. This would avoid the need for elongation vided into four separate scanning fields to ensure that ratios of the order of 5:1.