Sky & Telescope - June 2022 - 40

GALAXY ICONS: SUPRIYA07 / SHUTTERSTOCK.COM
Merging Springtime Spirals
N
MRK 273 In May
2019, the author and
Banich observed
Mrk 273 in a private
viewing session with
fellow amateur and
telescope operator Jim
Chandler. This was at the
end of a weekend celebration
of the 80th anniversary
of the 82-inch
Otto Struve telescope at
McDonald Observatory,
which at dedication was
the second-largest in the
world. For two and a half
hours they were treated
to views of objects of
their choosing. Banich
sketched this view of
Mrk 273 through the
eyepiece of the 82-inch
at magnification 617×.
a galactic-wide outflow of gas driven by either AGN or starburst
activity.
To find VV 705, look 3.8° northeast of 3.5-magnitude Beta
(β) Boötis, the star marking the head of the Herdsman. My
24-inch displays a small oval tilting north-northwest with a
tiny but conspicuous nucleus offset to the eastern side. I had
no luck seeing two cores, at least not at 282×.
The 48-inch cleanly split the two tight cores at 610×,
with the brighter northern one increasing to a stellar peak. I
caught the northern tidal tail as a hairline arc bending clockwise
towards the west. The larger southern tail brightened
and widened before turning a short distance west.
The Forlorn M4
The monsters of the gas-rich mergers are ultraluminous infrared
galaxies (ULIRGs). Their prodigious quasarlike luminosity
exceeds 1 trillion Suns and 100 times the entire Milky Way.
ULIRGs form during the final merger stages (M4 and M5)
and contain voraciously feeding SMBHs.
Our last stop is Markarian 273 in Ursa Major, the
second-closest ULIRG at 520 million light-years away. (The
nearest is Arp 220, or IC 4553, in Serpens; at a distance of
250 million light-years, it emits 99% of its energy in the
far-infrared.) As a relatively nearby laboratory, this M4-class
powerhouse is a favorite target for researchers, with 854 (and
counting) references in the SIMBAD bibliographic database.
The power source is a dual AGN separated by less than 2,500
light-years. The southwest nucleus is a Type II Seyfert galaxy
with narrow emission lines, while the northern nucleus - a
scant 1″ away - contains an extreme starburst producing 60
solar masses per year. A slender tidal tail stretches south for
130,000 light-years with fainter diffuse plumes extending a
similar distance north and east.
To reach Mrk 273, you can sweep 3° east-northeast of
2.2-magnitude Mizar, Zeta Ursae Majoris, or head the same
distance northwest of M101. Unfortunately, our target lies 4′
west of the glare of 6.5-magnitude HD 119992, so park this
luminary outside your eyepiece field. My 18-inch shows a pale
gray oval running north to south, and my 24-inch provides
tantalizing glimpses of the southern tail.
In May 2019, Howard Banich and I had a stunning view
of Mrk 273 through the 82-inch Otto Struve telescope at
McDonald Observatory. At 617×, the mashed-up body intensified
to an elongated core with a vivid nucleus. But the real
thrill was its prominent tail, which looked like a jet contrail
streaming away from Mrk 273!
Keep in mind that when we observe these spiral mergEXTREMES
Even
more exotic are hyper-luminous infrared
galaxies (HyLIRGs), which top 10 trillion times (1013)
the Sun's luminosity. The current titleholder for
the most prodigious output is WISE J224607.55052634.9,
discovered in 2015. It blazed in the very
early universe (light-travel time of 12.5 billion years)
with an infrared luminosity of 220 trillion Suns.
40 JUNE 2022 * SKY & TELESCOPE
ers, we're getting a sneak preview of our own galaxy's future
destiny. The Milky Way is on an inevitable collision course
and eventual merger with the Andromeda Galaxy (M31) in
several billion years.
¢ Contributing Editor STEVE GOTTLIEB chases colliding
LIRGs and other exotic targets from northern California. He
can be reached at astrogottlieb@gmail.com.
EXTRA MATERIAL Go to https://is.gd/merging_spirals for
finder charts for the targets discussed here.
http://www.SHUTTERSTOCK.COM https://www.is.gd/merging_spirals
Sky & Telescope - June 2022

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