Object of the Week May 5th, 2019 - NGC 4435/4438 "The Eyes"

[Uwe Glahn]

NGC 4435 (Arp 120)
RA: 12h27m40.5s
Dec: +13°04'47"
Mag: 10.8V

NGC 4438 (VV 188, Arp 120)
RA: 12h27m45.6s
Dec: +13°00'31"
Mag: 10.0V

Reason why I choose these spectacular pair of galaxies is because of their bright tidal tails. The tails are perhaps one of the easiest in the northern sky.

But let's start at the beginning. As often, the discoverer both galaxies was William Herschel in 1784. Interestingly the name "The Eyes" was founded in 1955 by the Amateur Astronomer Leland S. Copeland who wrote an article in the February edition of the magazine Sky and Telescope about Markarian's Chain and called the pair NGC 4435/4438 the "Eyes".
Vorontsov-Velyaminov and Arp (only for NGC 4438) also included the pair in their professional catalogs.

NGC 4435 itself seems to be free of tidal action for the first view but shows a long, very faint tail to the NW which could also be foregrounded galactic cirrus. The galaxy appears to be almost devoid of dust and gas because of a former collision.
In contrast and on even not so deep photographs NGC 4438 shows strong and bright tidal tails. Modern studies names as a collision partner not only NGC 4435 but Messier 86. Professional hydrogen emission maps shows connections between M 86 and NGC 4438 but even very deep amateur photographs shows H-Alpha bridges between all three partners.

Through the telescopes "The Eyes" are the center of Markarian's Chain and visible from small binoculars up. To my big surprise I could detect the tidal tail of NGC 4438 with my old 8-inch years ago. With the 27-inch the tail is brighter and more detailed but the real astonishing observation was through the 8-inch. But what could you see and from what aperture could you detect the faint tidal?

As always, give it a go and let us know.

photograph: chart32, Acquisition: Philipp Keller; Processing: Bernd Flach-Wilken
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link to the page (http://www.chart32.de/index.php/component/k2/item/98)

photograph: Mark Hanson
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link to the page (https://www.hansonastronomy.com/m86-group)

sketch: 27", 172x - 293x, NELM 6m5+, Seeing III
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[Ivan Maly]

Nice informative write-up, Uwe, thanks. Here is what I have (20" F/5, 13 mm Ethos, SQM 21.3, March 2017):

"NGC 4435 and 4438. Herschel 400, reobservation. "The Eyes", Arp 120. 2 cores. Separated thick extension of -38 to SW. Thin streak begins from the parallel [declination] of the N tip of -35 and runs between the cores. Joined to it at the N end, another streak runs not quite to the core of -38."

Just earlier this week from a darker site (SQM 21.7) I looked at them casually while scanning the area with the same eyepiece and my F/4 20-inch, and was struck by how bright, wide, and diffuse the area of the N tip of the tidal feature looked. This is brought out in the Keller/Flach-Wilken image.

[Raul Leon]

Hi here's my observation from 5/26/2017: ngc 4438 and ngc 4435 galaxies in Virgo; magnitude:10.1 and 10.5 ; aka known as "the Eyes". Appearing as two ghostly eyes these two interacting galaxies have bright cores. Ngc 4438 is brighter and more elongated and has a tidal tail that I believe I saw in times of good seeing. I used a 8mm Ethos at 198x with my 14.5 Starstructure Dob f/4.3 3527

[akarsh]

Last week, during Texas Star Party, I was up at Jimi Lowrey's observatory to observe with his marvelous 48" telescope. One of the observations that stood out from the Tuesday night of TSP 2023 (16th May 2023) was NGC 4438.

Here is annotated DSS2 image marking the features Jimi and I observed:
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and also an annotated Hubble image:
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Tidal tails marked T1 and T2 were readily seen and I have logged them once earlier through Jimi's 48", I think last year. T3 was the new observation -- Jimi reminded me to look for it, and it was not particularly difficult. A Yellow filter really brought it out. The T3 tail is believed to be pulled out by the dwarf galaxy VCC 1040, according to this 2005 paper (https://www.aanda.org/articles/aa/abs/2005/23/aa1664-04/aa1664-04.html). Dwarf galaxy VCC 1040 was held almost continuously with averted vision after placing it in my averted-vision sweet-spot. Incidentally, VCC 1040 is blueshifted.

While observing the core region of NGC 4438 at moderate power (~600x), I detected the dust lane marked D1 going up (southwest). Putting in high power (~800x) made it more prominent and it could be seen turning counterclockwise to the left (west/northwest). At this same high power, I picked up a much weaker sensation of a dark lane on the opposite (western) side of the core as a thin and short dark section, which is identified with a portion of "D2" that I've marked the location of. Since the core region was overexposed on DSS2, we were not guided by an image, and I was pleased to see that the observations matched the HST image perfectly when we pulled it up later.

My notes on T1 and T2 read: "The tidal tail is seen both going north and south of the galaxy. The south side curves counter-clockwise and ends in a brighter clump that is collinear with a widely spaced conspicuous double star. The northern tail is faint, nearly straight, and diffuse." As for T3, "A 'jet' emanates from the core due south-ish, by which I refer to the brighter section of the tidal extension going south."

The image prompted me to look for "D3", which was picked up as a sort of darker region, as though the sky background in the eyepiece were marginally blacker in that portion, west of the galaxy. I logged it as follows "A dark region curves along the core of the galaxy to the west ... indicative that we are detection the 'loop' of the tidal tail. Wow."

[akarsh]

While I'm on this thread, I might as well share the report of the tidal tail of NGC 4438 in my 18" f/4.5
This was from ~5500ft altitude Bortle 2-ish skies near Big Pine, CA but the transparency was poor. In my notes, I wrote down "~70% of the sky is engulfed in haze. Could not give the eyes a second shot but was happy to have called out the location of the brightest segment [of the tidal tail]". The accompanying illustrative sketch I made shows the northern tail of NGC 4438 as a thin streak emanating from the main body of NGC 4438 in the same orientation as its elongation, with a brighter region towards its tip where it ends. The southern tail was not detected. I was using 200x power (10mm Delos).

[Howard B]

Wow, what a great observation Akarsh - I sure wish I could have joined you guys at Jimi's! I had a go at 4438 a couple weeks ago but my skies were pretty awful, but that just made me more determined to try again - hopefully at the GSSP next month.

My best observation, which doesn't reveal nearly as much as what you saw, was in June 2021 with my 28-inch scope:

"Super nice with lots of tidal tail action. The main galaxies(NGC 4435 and 4438) are bright and well-matched in size, core brightness, and stellar nuclei (I hope that's the plural of "nucleus"...) but 4438's tidal tails steal the show. Somewhat indistinct close to 4435, each tail has a distinctly brighter section, almost like two additional galaxies. Beautiful! 192x and 253x, 21.84SQM."

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