Caption: A Hubble Space Telescope (HST) image of galaxy Arp 220 in constellation Serpens. The radio lobes are a false color artist's conception.
Features:
- Arp 220 is an
ultraluminous infrared galaxy (ULIRG)
whose heightened luminosity
is probably due to a starburst
(a period of intense
star formation)
triggered by a galaxy merger
that started ∼ 0.7 Gyr ago
(see Wikipedia: Arp 220: Features).
Arp 220 is drawn from the Atlas of Peculiar Galaxies (1966) created by Halton Arp (1927--2013) who yours truly once walked right by in 1989 at the Max Planck Institute for Astrophysics in Garching, Germany.
- The galaxy merger caused
interstellar medium (ISM)
from both progenitor galaxies
to clump in dense regions which became intense
star formation regions
which give rise to the
starburst.
- The galaxy merger also
disrupted the
galaxy disks
and randomized the orientation of the
orbits of the
stars.
- A new galaxy disk
with spiral arms
might form, unless the
active galaxy nucleus (AGN)
activity converts Arp 220 into
quenched galaxy
(see explication below)
on the time scale of
gigayear.
- To explicate
active galaxy nuclei (AGNs):
Large
galaxies
(like
Arp 220) are all thought to
a supermassive black hole (SMBH)
near their
center of mass.
If there is a large
accretion disk surrounding the
SMBH,
then intense
electromagnetic radiation (EMR)
(dominantly in the
ultraviolet band (fiducial range 0.01--0.4 μm)
and visible band (fiducial range 0.4--0.7 μm
= 4000--7000 Å))
will be emitted
from the accretion disk
and
relativistic jets
of matter
(of
interstellar medium (ISM) composition)
will be launched perpendicular
to the
accretion disk
(which for disk galaxies is usually
aligned with the
galaxy disk).
The relativistic jets
slow and expand to become giant
radio lobes
(radio
nebulae) extending
outside of the
luminous part of the
galaxy.
The SMBH and its accretion disk constitute an active galaxy nucleus (AGN). A galaxy with AGN is called an active galaxy.
- It turns out that if the total
mass of a
galaxy
(including dark matter)
exceeds ∼ 10**12 M_☉, then
the galaxy
is or is becoming a
quenched galaxy.
The
quenching
is due to the heating of the
galaxy
ISM
by EMR
from the
accretion disk
around the
SMBH
whether or NOT the
galaxy is recognized
as an
active galaxy.
The heating causes all the gas in the galaxy to be too hot to lose pressure support and and collapse into star formation regions
So star formation turns off and the galaxy becomes a quenched galaxy.
- The ∼ 10**12 M_☉ amount has been called the
golden mass
(see Dekel et al. (2019)).
The time scale for
quenching
after reaching the
golden mass 10**12 M_☉
is of order 1 to 2 to 3 Gyr.
- In fact, typically a
galaxy reaches the
golden mass 10**12 M_☉
following a galaxy merger
as is happening to
Arp 220.
The merged galaxy
of the golden mass 10**12 M_☉
or greater typically turns into a
giant elliptical galaxy.
The time scale for
galaxy merging and
galaxy quenching
is of again of order 1 to 2 to 3 Gyr.
The upshot is that most, maybe nearly all, quenched galaxy by golden mass quenching are giant elliptical galaxies.
-
EOF
- There are, in fact, may possible galaxy quenching processes all of which may act to one degree or another. See file galaxy_quenching.html and references therein.
- There are, in fact, may possible galaxy quenching processes all of which may act to one degree or another. See file galaxy_quenching.html and references therein.
Image link: Wikimedia Commons: File:Active Black Hole Squashes Star Formation.jpg.
Local file: local link: galaxy_quenching_golden_mass.html.
File: Galaxies file: galaxy_quenching_golden_mass.html.