Exploring Bright Galaxy Groups in Leo

Whenever I watch a TV show or movie filmed in pre-COVID times I cringe at scenes featuring packed restaurants, bars and concert crowds. What used to be normal activities now seem so alien. Hopefully, that will change soon. There's no denying the right crowd engenders energy and excitement; gathering in groups to meet and share ideas is the essence of being human. I can't wait to feel that vibe again.

Likewise in the sky. When we come across a field thick with stars or spilling over with galaxies our thrill-meter goes up. Seeing three, four, or five deep-sky objects in the same view feels like reaching the summit with a sweeping view of peaks all around. Grander, really. With galaxy groups, we're looking at stellar congregations up to a million or more light-years across, separated by tens of thousands to millions of light-years. What magic frames so much space in the tidy circle of the eyepiece?

We're going to visit three such groups in Leo, all nicely placed in the southeastern sky around 10 p.m. local time in the latter half of March. The waxing Moon will interfere starting about the 20th but will get out the way again by month's end. My observations were made with a 15-inch reflector under Bortle 4 skies, rated as rural/suburban transition.

I deliberately selected brighter groups (and the brighter galaxies within those groups in some cases), so all of these should also be visible in an 8-inch telescope and a few in apertures as small as 6-inches.

When you observe these clumps, picture them as distant versions of our own Local Group. Each group is also a member of either the Leo I or Leo II galactic clouds, larger assemblages of galaxies at distances of approximately 35 million light-years and 75 million light-years, respectively. Like nested matryoshka dolls these fold into the Virgo Supercluster which is part of even vaster structure, the Laniakea Supercluster.

NGC 3227 Bunch — Leo II Group

One of the easiest groups to find, the NGC 3227 bunch is located ¾° east of 2nd-magnitude Gamma (γ) Leonis, also known as Algieba. In a good sky, even a 6-inch scope will show two galaxies in contact — the spiral NGC 3227 and its companion NGC 3226, a dwarf elliptical. Also known as Arp 94 from astronomer Halton Arp's Atlas of Peculiar Galaxies, this interacting pair makes for a compelling sight. NGC 3227 is the brighter of the two at magnitude 10.3 and clearly elongated northwest-southeast with a prominent near-stellar nucleus.

Use magnifications north of 200× to appreciate its blazing intensity and to picture what lurks here, a supermassive black hole some 14 million times more massive than the Sun — more than three times the heft of the Milky Way's dark heart.

NGC 3227 is a Seyfert galaxy with an active, quasar-like nucleus that flickers in X-rays on time scales of hours to months. Tidal interactions with NGC 3226 to the northwest have spawned blue knots of star formation within their common envelope. NGC 3226 is about half as large as its partner and a little fainter at magnitude 11.4. At first glance it appears round but reveals a faint, outer envelope angled northeast-southwest with averted vision. It also possesses a bright, nonstellar nucleus.

A third much fainter member of the group, NGC 3213 (magnitude 13.5, size 1.1′ × 0.9′), sits 33′ off to the southwest of the duo at the fringe of Algieba's glare zone. Use magnifications of 200× and higher to catch this midge. Another unrelated, more remote galaxy, NGC 3222 (magnitude 12.8, 1.3′ × 1.1′), lies 12′ west of the NGC 3226-27 pair. All four fit in a 1° field with room to spare.

NGC 3190 bunch — Leo I group

If NGC 3226-27 is your first stop you don't have to go far to find our next batch of furry galactic catkins. The NGC 3190 group appears just 2° north of Gamma (γ) Leonis on a line to Zeta (ζ) Leonis in a field peppered with bright telescopic stars ranging from magnitude 7.5 to 10.5. This tight clump of four galaxies spans just 17′wide, which means you can use magnifications of 200× or more and keep them all in the same field of view.

The galaxy NGC 3193 (magnitude 10.9, 2.0′ × 2.0′) is a classic elliptical — round and fuzzy with a brighter core and near-stellar nucleus. A 9.6-magnitude star pins its northern border. While the spiral NGC 3190 (magnitude 11.1, 4.4′ × 1.5′) appears a tad fainter it was my favorite with an obviously elongated disk and a bright, extended nuclear region that swaddled a bloated, starlike nucleus. NGC 3185 (magnitude 12, 2.3′ × 1.6′) was a small, faint oval oriented northwest-southeast with a stellar core and slightly brighter inner disk.

I'd hoped to see the barred spiral NGC 3187's (magnitude 13.4, 3.6′ × 1.6′) wacky spiral arms, flung out on either side like a swing dancer, but this is a faint, diffuse object, and the best I could do was make out a misty, elongated disk tipped northwest-southeast at 257× with averted vision. Both NGC 3127 and neighboring NGC 3190 exhibited warped disks, evidence of tidal interactions common among galaxies in compact clusters.

NGC 3607 bunch — Leo II group

Located in the tail of Leo this group has two cores, one centered on NGC 3607 and the second on NGC 3684, some 2.7° to the southeast. NGC 3607, a spiral galaxy and the group's brightest and member at magnitude 9.9 and 4.7′ across, forms a tight trio with NGC 3608 (magnitude 10.8, 3.2′ × 2.6′) and faint NGC 3605 (magnitude 12.3, 1.5′ × 1.0′) in a north-south line. A fourth member, NGC 3626 (magnitude 11.0, 2.7′ × 1.9′), lies 50′ to the northeast.

NGC 3607 and 3608 resemble a pair of eyes at first glance, but NGC 3607 is clearly the brighter with a dense, luminous core and starlike nucleus set in a slightly elongated disk oriented northwest-southeast. The elliptical galaxy NGC 3608 is second dog here — a little smaller and fainter and extended east-west. Although NGC 3605, also an elliptical, looks like it belongs to the group due to its proximity to NGC 3607, it's actually much closer to us at 33 million light-years, making it a likely member of the Leo I group.

NGC 3626 (magnitude 11.0, 2.7′ × 1.9′), a true member, sits off by its lonesome 48′ northeast of the main bunch. It's a bright spiral extended northwest-southeast with a bright, stellar nucleus. While you're poking around you may also notice another faint galaxy sharing the field with NGC 3607-08, around 20′ to the west. This delicate puff with a brighter core is NGC 3599 (magnitude 12.0, 2.7′ × 2.1′), a spiral galaxy and another potential member of the Leo I group.

Moving east we arrive at the second core, composed of four rather dim galaxies that comfortably fit inside the field of view of my 142× Nagler eyepiece — three in an evenly-space northeast-southwest line with the faintest member, NGC 3691 (magnitude 11.8, 1.3′ × 1.0′), close by to the southeast. NGC 3686 (magnitude 11.3, 3.2′ × 2.5′), a barred spiral, is the brightest and largest member of this attractive group.

In good seeing at 257× I could discern a faint, extended nuclear region inside a mottled disk elongated northeast-southwest. A 15.5-magnitude star appears inside the barred galaxy's southern edge. The more tightly-wound spiral, NGC 3684 (magnitude 11.4, 3.1′ × 2.1′), displays a brighter core but lacks a stellar nucleus like its neighbor NGC 3681 (magnitude 11.2, 2.0′ × 2.0′) immediately southwest.

NGC 3691 was a dab of faint, uncondensed light. Farther afield, 1° west-southwest of the quartet, you'll find another group member, NGC 3655 (magnitude 11.7, 1.5′ × 1.0′) obviously elongated northeast-southwest with a bright, extended core dotted with a nonstellar nucleus.

If you're interested in additional galaxies in the region, such as the bright M105 group and the Leo Triplet, please check out my earlier blog and Howard Banich's article on page 18 of the April 2021 issue of Sky & Telescope. One of the challenges in observing these groups is taking the time to distinguish details in what looks like just another faint fuzzy. That's why fate placed galaxies in the spring and fall skies, when temperatures are conducive to spending more time at the telescope and the dreaded mosquitos are scarce.

Asteroid news

On March 21st at 16:03 UT (12:03 p.m. EDT), the potentially hazardous asteroid 2001 FO₃₂ will reach its minimum distance from Earth of about 2 million kilometers. Measuring between 440–680 meters (1,400–2,200 feet) across, this large object will become as bright as magnitude 11.7 on the morning of March 21st as it speeds across southern Sagittarius. Traveling at around 14′ per hour, you may even detect its motion in real time at magnifications of 200× or more. The asteroid quickly fades after the 21st but can be observed earlier on March 20th in Lupus at magnitude 12.0. For maps, visit astro.vanbuitenen.nl. Due to its southerly declination it's best visible from the southern U.S.

Then, on March 17th, observers in the southwestern U.S. will witness one of the best asteroidal occultations of 2021 when 10.7-magnitude 8 Flora covers a 7.2-magnitude star near the Hyades in Taurus. Your observations of the event will be of great value in determining details of Flora's shape and other parameters. The occultation will last up to 5 seconds with a 1.8-magnitude drop. It would normally be larger, according to David Dunham, with the International Occultation Timing Association (IOTA), but the star's 9.06-magnitude companion will remain visible during the occultation. You'll find finder charts and full details here.

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