About NGC 3314

NGC 3314 lies in Hydra (to be precise, at equinox 2000 coordinates 10 37 12.8 -27 41 04), and at least one of the galaxies is a member of the Hydra I cluster of galaxies (also known as Abell 1060). Its existence is no great secret, since this part of the sky was depicted in the cover shot of every CDROM box for the southern Digitized Sky Survey, and its nature is noted in the caption for the Abell 1060 photograph distributed by the Royal Observatory Edinburgh (look under "Galaxy Clusters" - the picture referred to is available below). However, long-exposure photographs saturated the inner parts, making this look like a galaxy blowing off material in the manner of M82 and so hiding its real nature. I first learned of it from seeing some photographs taken with the 1.5-meter telescope at Cerro Tololo by Dan Weedman and Malcolm Smith, with a range of exposure times so that the dark spiral dust lanes stood out in some pictures.

The two galaxies involved have been designated as NGC 3314a (the foreground spiral) and NGC 3314b (the more inclined background object). Their redshifts are quite different - 2851 km/s for NGC 3314a and 4641 km/s for NGC 3314b. The mean value for the cluster Abell 1060 is about 3400 km/s (corresponding to a distance of about 42 megaparsecs = 140 million light-years), with a dispersion for clear members of about +/-600 km/s. Thus the velocities of both galaxies are consistent with being cluster members in the outer envelope of its velocity range. However, maps in the 21-cm emission of neutral hydrogen by Pauline McMahon and colleagues using the Very Large Array show that NGC 3314a is one of several spiral galaxies at very similar redshift and almost connected by tenuous streamers of gas, suggesting that these galaxies form a distinct group in front of Abell 1060. Either way, we are pleased that there's no direct evidence of interaction between NGC 3314a and b which would complicate our ability to interpret measurements of the dust in NGC 3314a.

Starburst Galaxy M82, courtesy of Lowell Observatory

Cerro Tololo's domes in twilight

How far away are the two galaxies, from us and from each other? I won't pretend to know the distance to Hydra I to better than 10 Mpc. More to the point, let's be good HST types and call the Hubble constant 80 km/s/Mpc. The best evidence puts NGC 3314 in a group at mean redshift 2810 km/s, for a redshift distance of distance 35 Mpc. Abell 1060 has mean redshift 3418 km/s for a distance of 43 Mpc. Not that I'd put too much faith in the exact numbers, but unless we're being fooled by the dynamics, the two galaxies are 5-8 Mpc apart. So in light-years, I'd call that 115 and 140 million from us, and something like 25 million apart.

How big is NGC 3314? Current catalog entries aren't too helpful because they deal with the blended light of the two galaxies in odd ways. From the HST data, the bright part of the combined image subtends an area 1.0 by 1.7 arcminutes which projects to 12 by 21 kiloparsecs at the distance of Abell 1060. By themselves, NGC 3314a would be about 1.3 by 1.3 minutes and NGC 3314b about 0.7 by 1.7.

How bright? Similarly, existing catalogs give rough magnitudes for the two components, which depend strongly on how you take the image apart (and what you assume about the effects of dust). Again from the HST data, we derive a total magnitude for the part shown in the Heritage image of 13.5 in blue light, or about 12.8 in the visual band.

In a large amateur telescope, this is a very interesting region. The cluster center lies only 12 minutes of arc away, between the giant elliptical galaxies NGC 3309 and 3311, and just to their east is the giant spiral NGC 3312 (probably a cohort of NGC 3314a, along with the small ringlike galaxy to the east of NGC 3312). The cluster includes a total of ten galaxies bright enough to be listed in the NGC catalog, within 1/2 degree of its center. You can see some of these in this 0.35-degree portion of the Southern Sky Survey, extracted by Skyview (noting the copyright data for these images). NGC 3314 is at lower left, on the southeastern fringes of the cluster region. NGC 3314 appears just to the southeast of a brighter star (magnitude 12), which is superimposed on the outer fringe of NGC 3314b. We took special care to keep this star out of the field of the CCD (and on another CCD of WFPC2) in planning the HST observations, to avoid problems with scattered light overwhelming part of the galaxies.