Sky and Telescope - March 2018 - 30

Starburst Galaxies

q WHERE STARS COME ALIVE This close-up of the core region of
NGC 1569 in Camelopardalis shows the roiling star-forming regions.
Challenge yourself and see if you can detect the two SSCs separated by
6″ masquerading as a 15th-magnitude "double star." Use a large telescope with high power and point it toward the core of this galaxy.

M A RCH 2 018 * SK Y & TELESCOPE

p TIDAL FORCES Around 450 million years ago, M82 and its massive
companion, M81, swept by each other. The tidal forces from the close
passage triggered star formation and outflows in M82. Even though
these galaxies are morphologically different, they are gravitationally
locked in a cosmic dance. Look for this odd couple in Ursa Major.

Not nearly as striking but still a very interesting galaxy in
a larger telescope is NGC 1569 in Camelopardalis. A member of the IC 342/Maffei Group of galaxies, NGC 1569 is
classiﬁed as a Magellanic irregular galaxy due to its distorted
shape. At 11 million light-years, this galaxy lies somewhat
closer to us than M82 and, like most members of this group,
is heavily obscured (or reddened) by the Milky Way. An
outburst began around 100 million years ago, and following a
ﬁnal surge some 5 to 10 million years ago, the starburst phase
has now ﬁnished, but star formation is still ongoing. Visually,
this is a small, fairly high surface brightness galaxy located
a little less than 3° southwest of Alpha (α) Camelopardalis.
Moderate aperture should reveal the asymmetric disk mottled
with dark rifts and bright knots. Use high power and a large
scope to spot the two largest SSCs visible as a tiny 15th-magnitude "double star" separated by 6″ near the galactic core.
Certainly not all starburst galaxies are irregular in appearance, a case in point being NGC 3310 in Ursa Major. It's
a compact grand design spiral that cannibalized a small
dwarf galaxy around 100 million years ago. This devouring
resulted in a circumnuclear ring of intense star formation.
Deep images of the galaxy reveal extensive shells of dust
and hydrogen gas. As with many other representatives of
this class, NGC 3310 has high surface brightness and takes
magniﬁcation well. It shares the ﬁeld with a bright 5.5-magnitude star and appears as a fairly small, round glow with a
condensed core region.
NGC 4038/NGC 4039 in Corvus, also known as the
Antennae Galaxies or the Ringtail Galaxy, is a striking example of a pair of merging disk galaxies undergoing a massive
outburst of star formation. The galaxies were two separate
entities more than a billion years ago but eventually began a

STA RS CO ME A LIV E: N ASA / ESA / A . A LOISI / HUBBLE HERITAG E TE A M (STSCI / AUR A); TIDA L FORCES: M ASIL IM AGING TE A M

There appear to have been two main episodes of star
formation in M82. The ﬁrst episode, yielding most of the
older stars in the disk, started around 450 million years ago
and lasted for some 350 million years. This would have been
triggered by tidal forces due to a close interaction with its
massive neighbor, M81. More recent starburst activity dating back to less than 10 million years is concentrated in the
nuclear region of the galaxy and is associated with the SSCs
observed by the HST.
Located about 10° northwest of Alpha (α) Ursae Majoris
(Dubhe) and about 2° east of 24 Ursae Majoris, the Cigar
Galaxy is a stunning sight in even the smallest aperture.
In a modest refractor, M82 is a mottled, silvery streak with
unusually high surface brightness for a galaxy. As a result, it
can be observed under moderately light-polluted urban skies
and under much higher magniﬁcations than the typical galaxy. Larger telescopes reveal numerous dark, dusty rifts and
bright knots scattered along the disk that become much more
intricate around the galaxy's core region. Using a 24-inch f/5
at 339×, I could clearly see several of the SSC complex regions,
including a few possible SSCs as very faint "stars" embedded
in the bright nebulosity. However, the southern and northern
superwind plumes, normally so prominent as a bipolar outﬂow in Hα images, weren't visible other than as slight diffuse
glows above and below the equatorial plane of the galaxy.
Photographically, this is an exciting target yielding beautiful images, especially in cameras equipped with Hα ﬁlters, or
those with good red sensitivity for capturing the superwind
plumes that were produced during periods of elevated supernova activity. You can also try narrowband ﬁlters to capture
details missed by more conventional imaging.

Sky and Telescope - March 2018

Table of Contents for the Digital Edition of Sky and Telescope - March 2018