From Smith et al. (2008), `Stochastic `Beads on a String' in the Accretion Tail of Arp 285', Astronomical Journal, 135, 2406.

For appendix material, click here.

This is one of the galaxies in the `Spirals, Bridges, and Tails' Interacting Galaxy Survey, published in Smith et al. (2007), Astronomical Journal, 133, 791.

Optical image of Arp 285 (NGC 2856/4) from the Arp Atlas of Peculiar Galaxies (1966). North is up and east to the left. This is a widely separated pair. The northern galaxy NGC 2856 has an unusual `tail' like feature extending out perpendicular to the disk from the middle of the disk. Toomre and Toomre (1972) suggested that this is material from bridge/companion, accreting to NGC 2856. Note that the Arp image shows clumpiness in this tail. Arp 285 is at a distance of 39 Mpc (H0 = 75 km/s/Mpc; v = 2898 km/s).

The VLA 21 cm HI maps of Arp 285, from Chengalur et al. (1994). Note that the tail to the northeast is rich in HI. The left panel is the naturally-weighted map, with a resolution of 29". The right panel in the map with uniform weighting, with 12" resolution.

A montage of the northern galaxy NGC 2856 in the GALEX, SDSS, and Spitzer bands.

Another look at the SDSS g and r images of NGC 2856, with a different display stretch. Four approximately evenly spaced clumps are visible along the northern tail in all of the SDSS images, except for the z image (longest wavelength SDSS data) and the u image (for two clumps).

The clumps in the tail are identified in this g band figure. They were selected by eye based on the g band image. The circles have radii of 5 pixels (1.61 arcseconds). Clumps 1 and 2 have bright compact cores; clumps 3 and 4 are fainter, with multiple peaks in the vicinity. From south to north, the separations between the clumps are 6.1" (1.2 kpc), 5.5" (1.0 kpc), and 4.1" (0.8 kpc).

The SDSS color map of northern galaxy NGC 2856. The tail clumps are bluer than main disk of NGC 2856 in the optical.

The tail is also clearly detected in the GALEX images, however, with the low resolution of GALEX (~6"), it is hard to distinguish individual clumps.
Left: the NUV image, from the GALEX MIS survey. This exposure was 813 seconds. Right: the FUV image, from the GALEX All-Sky Survey. This exposure was only 112 seconds.

The SARA H-alpha and R images of NGC 2856. The H-alpha is superimposed on the 8 micron and SDSS g images in the last two panels.

The 3.6 micron Spitzer image of Arp 285. Note that the northern plume is visible. These data were previously published in Smith et al. (2007), Astronomical Journal, 133, 791.

An expanded view of the 3.6 micron image of NGC 2856. Note that clumps 2, 3, and 4 in the SDSS image are also visible at 3.6 microns.

The 8.0 micron image of Arp 285. Note the bad `banding' problem that is present in this image. Note that clump 3 in the the northern plume *is* visible, however, it is unfortunately very close to a 'band'.

A zoomed in view of NGC 2856, at 8 microns. Note that clump 3 in the SDSS data is very bright at 8 microns.

Left: the Arp 285 8 micron image, after the banding has partially been corrected for using the IDL routine `fixband'.
Right: the original 8 micron image. Although the bad `band' is still visible in improved image, it is much less obvious.

Arp 285 was also observed at 24 microns with MIPS, but the image (shown above for the northern galaxy NGC 2856) is not suitable for getting clump or tidal fluxes because of artifacts from the point spread function. See Smith et al. (2007), Astronomical Journal, 133, 791 for more details.

Montage of the southern galaxy NGC 2854 in the GALEX, SDSS, and Spitzer bands.

The SARA H-alpha and R images of NGC 2854. The H-alpha is superimposed on the 8 micron and SDSS g images in the last two panels.

The smoothed NGC 2856 g SDSS image. A full connecting bridge is visible in the smoothed g and r images, but not in u, i, or z.

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To see more results from the `Spirals, Bridges, and Tails' Interacting Galaxy Survey, click here.

Last updated: 5/15/08.