OR: Spring Galaxies including the Hydra I Cluster.
by Steve Gottlieb
On Tuesday March 28th, with the new moon observing window starting to close, Mark McCarthy and I observed at Kevin Ritschel's ranch in the rolling hills southeast of Hollister (southern part of the Diablo Range). The drive south from Berkeley in the afternoon was pretty brutal due to accidents and slowdowns and the usual 2 ½ drive took me an extra hour. Still, I arrived about an hour before sunset and had plenty of time to set up my 24-inch f/3.7 Starstructure and eat dinner while it was getting dark. Mark arrived about a half hour after me and set up his 20-inch before I was finished. About a half hour after sunset I started scanning in the west looking for Mercury but instead noticed an extremely thin arc, nearly lost in some low clouds and haze along the western horizon -- it was the crescent moon just 25 hours old. Quite an exquisitely thin sight and totally unexpected. About 15 minutes later I found Mercury, which was surprisingly bright and high -- both of us were initially unsure it was Mercury as it was so (relatively) high in the west. But a quick look in Mark's scope (just a non stellar "blob") confirmed it was Mercury. Turns out it was close to its maximum elongation (about 10° elevation when we viewed it). By 9:00 it was fully dark, but we could see some illuminated clouds along the western horizon and northern horizons. Mark measured an SQM reading of only 21.2 or so (subpar for
this site), but I believe it hit 21.5 or 21.6 sometime after midnight. Early on we took a peek at comet 41P/Tuttle-Giacobini-Kresak near the Ursa Major/Draco border in Mark's scope.
This relatively bright and large comet seemed around 8th magnitude and contained a very prominent nucleus. I also took a quick look at the planetaries I worked on three different programs in the evening -- each for a couple of hours. First up was a number of IC galaxies in Gemini, Cancer, Canis Minor and Hydra. The middle part of the evening was a survey of the central region of Hydra I galaxy cluster, which includes NGCs 3285, 3305, 3307, 3308, 3309, 3311, 3312, 3314, 3315 and 3316. I took notes on 19 galaxies for a planned article in Sky & Tel next spring. The cluster is a near twin of the downtown section of the Virgo cluster -- just 3 times as distant! Late at night I focussed on a number of new (for me) Arp galaxies. All in all, about 50 objects were viewed over 7 ½ hours. Here are the highlights. — Steve Gottlieb |
This member of the Flat Galaxy Catalogue appeared as a very faint, extremely thin ghostly streak, over 10:1 NW-SE, ~1.1'x0.1’, with a low fairly even surface brightness. It increased in length with averted vision, so the outer tips were a bit fainter. A mag 15.5 star is 30" NE of center.
I took a look at this close galaxy pair at both 260x and 520x. The brighter eastern galaxy appeared faint, small, round, 12" - 15" diameter, quasi-stellar or stellar nucleus.
Situated within a N-S string of mag 9 to 10.5 star including a mag 10.2 star 1.5' NW. IC 491 forms a very close pair (non-physical) with
IC 496 was resolved into a close pair (physical), separated by just 19" E-W. The brighter western component (
This edge-on appeared fairly faint, moderately large, very elongated 6:1 NNW-SSE, 0.9'x0.15', slightly brighter core. Bulges very slightly but no nucleus seen. Situated in a busy star field with a mag 15.5 star 1.2' S (collinear with the major axis). A mag 10.9 star lies 2.5' NW. This galaxy lies at a distance of ~200 million light years, which implies a true diameter of ~100,000 l.y. for the galaxy.
NGC 3067, about 70 million l.y. distant, appeared fairly bright, moderately large, elongated 5:2 WNW-ESE. The brighter elongated central section was mottled and appeared to have a sharp light cut-off (dust lane) on the northern flank. The eastern end of the galaxy has a lower surface brightness, probably due to dust. 3C 232 = Ton 469, a distant quasar with a redshift of z = .531 (light-travel time of 5.3 billion years), lies 1.9' due north. It was easily visible at 375x as a very faint mag 16 star. A brighter mag 15 star is 1.4' WSW of the quasar. This QSR was involved in one of Halton Arp's controversies. A neutral Hydrogen "bridge" appears to connect the quasar and NGC 3067. Arp proposed the QSR was ejected from NGC 3067, a theory which was rejected by mainstream astronomers.
This interacting pair in Leo resides at a distance of ~375 million light years. The brighter and larger northeastern component (
Arp 198 is an overlapping pair consisting of face-on spiral and a thin edge-on that extends right to the nucleus of the face-on. Halton Arp classified this pair under his
category "Galaxies: Material ejected from Nuclei.” Clearly, he interpreted it as a face-on spiral with a jet extending to the west (right). But this SDSS image clearly reveals it as
an overlapping pair very close to a star! There is no sign of distortion in At 260x and 375x, the pair appeared as a very faint, fairly small, very elongated glow, ~0.4'x0.1', extending to the southwest of a mag 12.3 star. The faint glow had an unusual
"spike" appearance, with a very small "knot" (core of VV 267a = UGC 6073b, the face-on spiral) at most 10" diameter at the northeast end close to the mag 12 star [28" SW of the
star]. The spike or tail (
Arp 156 is considered to be a gas-rich post-merger with a major-axis dust lane. This Draco galaxy is pretty distant at ~480 million l.y. It appeared fairly faint, moderately
large, oval 4:3 or 3:2, contains a brighter core with much fainter asymmetric extensions ~40"x 30" NW-SE. The SE extension seemed cut off (due to dust?). A mag 12 star is 1.2' SW
and a mag 10.7 star is 1.9' S. Also nearby is a mag 9.3 star (
I logged 19 galaxies in the central region of the Hydra I cluster — in preparation for an article in Sky & Telescope next year. This cluster is one of the closest fairly rich
clusters to our Local Group, after the Virgo cluster, the Fornax cluster and the Antlia cluster. It has are some interesting similarities with the well-known Virgo cluster. The
cluster is roughly 3 times the distance of the Virgo cluster and extends about ? the size in the sky — so both cluster have a similar linear dimension as well as a comparable number
of members. Furthermore, both clusters have an giant X-ray emitting galaxy near the core — The cluster surrounds a naked-eye mag 4.9 star, which makes finding the cluster pretty easy in a dark sky, but also makes viewing some of the nearby galaxies pretty tough.
Although
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