Sky & Telescope - July 2020 - 57

Going Deep by Dave Tosteson

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Astronomers recently identified
a new category of spiral
galaxy. Read on to find out
how to observe them.

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Super Spiral
Galaxies

PATRICK OG LE E T A L. / THE ASTR OPHYSICAL JOUR NAL 2016

he volume of published information is staggering. In my ﬁeld of
medicine alone more than 900,000
articles were published in 2018. Millions of studies in diverse ﬁelds are
reported annually in many thousands
of journals, recording the painstaking
procedures whereby research progresses. It's a rarity when a revolutionary breakthrough - such as the detection of the Higgs boson - occurs in
an established discipline, and it's even
more rare for a whole new category of
object to emerge.
So when I came across a paper in
2016 by Patrick Ogle of Caltech and
his colleagues describing a new class
of spiral galaxy, it was a big surprise.
Surely, by now, astronomers had
sorted out all the subtypes of galaxies.
How could anything have escaped the
myriad surveys and intense scrutiny
of the Hubble Space Telescope and tenmeter-class reﬂectors? But there they
were, hiding in plain sight.

p A MENAGERIE OF SUPER SPIRALS The photomontage shows all 53 superluminous spiral
galaxies in the paper by Ogle and colleagues. The four discussed here are labeled in red.

Discovery of Super Spirals
Ogle and his team trawled through the
NASA/IPAC Extragalactic Database
as part of an ongoing research project
to determine its completeness. They
selected galaxies with redshifts less
than 0.3 (i.e., light left them less than
3.5 billion years ago) and luminosities more than eight times that of the
Milky Way. These criteria, intended
to "capture the rarest, most luminous

galaxies," yielded 1,616 objects. Further
culling based on quantity and quality
of data resulted in a sample of a couple
hundred bright and massive galaxies.
Most of the galaxies were ellipticals, but
to the team's surprise, 53 were spirals.
They dubbed the latter superluminous
spiral galaxies, or super spirals.
The super spirals range from 30
to 340 billion solar masses and from
180,000 to 437,000 light-years in diam-

Superluminous Spirals
Ogle
Number

Object

Redshift (z)

Light-travel
time (Gl-y)

Diameter
(kl-y)

Mag(v)

RA

Dec.

10

2MASX J15430777+1937522

0.23

2.8

214

16.9

15h

17

2MASX J11535621+4923562

0.17

2.1

294

16.1

11h 53.9m

49° 24′

16.3

16h

01.7m

27° 18′

15.9

13h

43.9m

24° 41′

37
48

2MASX J16014061+2718161
2MASX J13435549+2440484

0.16
0.14

2.1
1.8

268
198

43.1m

19° 38′

Magnitudes are calculated from SDSS g and r values. Sizes are from recent catalogs. Visually, an object's size is often smaller than the cataloged value and varies
according to the aperture and magnification of the viewing instrument. Right ascension and declination are for equinox 2000.0. Light-travel times are computed
from redshifts according to current cosmological models. Galaxy names incorporate full coordinates.

s k y a n d t e l e s c o p e . o r g * J U LY 2 0 2 0

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Sky & Telescope - July 2020

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