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Middle Res. (200 dpi,
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High Res. (300
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Object
Name: Dwarf Irregular Galaxy Sextans A
Telescope: Subaru Telescope / Prime Focus
Instrument: Suprime-Cam
Filter: V (0.55 microns), R (0.65 microns), I (0.80
microns)
Color: Blue (V), Green (R), Red (I)
Date: UT 2002 November 11
Exposure: 35 min (V), 14 min (R), 24 min (I)
Field of View: approx. 13.3 arcmin x 13.3 arcmin
Orientation: North up, East left
Position: RA (J2000.0) = 10h 11m 1.3s, Dec (J2000.0)
= - 4d 42m 48s (Sextans) |
Young blue stars and older yellow and
red stars shine against a dark sky like jewels in a treasure
chest in this image of Sextans A from Subaru Telescope’s
prime focus camera Suprime-Cam. Sextans A is a dwarf irregular
galaxy belonging to a group of galaxies called the Antlia-Sextans
group 5 million light years from Earth. Even though five
million light years is quite distant (50 billion billion
kilometers or 30 billion billion miles), only about 40
galaxies are closer to our own Milky Way galaxy than Sextans
A. The Antlia-Sextans group is the closest neighbor of
the Local Group, which includes both our own Milky Way
the Andromeda Galaxy.
Irregular galaxies do not have a regular symmetric shape
like spiral or elliptical galaxies. Dwarf irregular galaxies
containing only 100 million to a billion stars are the
most common type of irregular galaxy. One main characteristic
of dwarf irregular galaxies, other than their shape, is
vigorous ongoing star formation. Sextans A has a mass comparable
to only 100 million stars, one thousandth of the Milky
Way, but contains a comparatively large amount of gas and
dust, the raw ingredients for stars and planets. In the
center of Sextans A is a high concentration of neutral
hydrogen gas that serves as a reservoir for the formation
of new stars. The Suprime-Cam image shows both young stars
(blue) old stars (red) near the center of Sextans A where
there is a large reservoir of neutral hydrogen gas and
star formation is most vigorous. The green color highlights
hydrogen gas ionized by radiation (HII regions) from the
blue-hot young stars.
Many dwarf irregular galaxies are surrounded by neutral
hydrogen gas that extends far beyond where the galaxy’s
starlight fades away. Observations with radio telescopes
have confirmed that Sextans A is no exception. The origin
of this hydrogen gas and its effect on star formation are
still unsolved puzzles. Yutaka Komiyama from Subaru Telescope,
the observer of Sextans A, is now working on a solution
using the Suprime-Cam data.
