A1 22 Active Galaxies

Active Galaxies: Types
LACC: Ch 26

• Seyfert Galaxies
• Radio Galaxies
• Quasars

An attempt to answer the “big questions”: what is
out there? how did we get here?

Thursday, May 13, 2010 1

Active Galaxies

Normal vs active galaxies: Normal ones are basically made of
stars emitting visible light; Active ones are much brighter and
have a different, "nonstellar" spectrum.

http://www.phy.olemiss.edu/~luca/astr/Topics-Extrasolar/Active-N.html

Active Galaxies

http://www.astr.ua.edu/keel/agn/seyferts.html

Active Galaxies:
Seyfert Galaxies

All these galaxies show the characteristic intense,
point-like nucleus originally remarked for this class
by Carl Seyfert. The galaxies' Hubble types are also
representative for Seyfert galaxies as a group,
dominated by ... spirals (Sa and Sb, with both
barred and non-barred representatives) and S0
systems.
These are V-band images.... logarithmic intensity mapping was used
to enhance the visibility of both bright and faint structure.

http://www.astr.ua.edu/keel/agn/seyferts.html


Active Galaxies: Radio Galaxies

http://www.astr.ua.edu/keel/agn/radgal.html

Active Galaxies:
Radio Galaxies
One remarkable finding from HST images, barely anticipated
from the ground, is that dust structures close to the nucleus
are prevalent in radio galaxies. These structure often take the
form of disks or rings, at right angles to the radio jets and
thus fitting with the general picture of jets collimated by the
influence of an accretion disk surrounding the central
objects. These are far too large to be the active, hot accretion
disk itself, which should extend to no more than light-months
in radius, but may represent material which has already settled
into its orbital plane and will eventually migrate inwards into
such an accretion disk.
These are red-light ... images.... A logarithmic intensity scale is used to make detail
visible over a wide brightness range. The scale bars indicate one arc-second.

http://www.astr.ua.edu/keel/agn/radgal.html


Quasars

http://chandra.harvard.edu/xray_sources/quasars.html

Quasars
Quasars are peculiar objects that radiate as
much energy per second as a thousand or
more galaxies, from a region that has a
diameter about one millionth that of the host
galaxy. It is as if a powerhouse the size of a
small ﬂashlight produced as much light as all the
houses and businesses in the entire L.A. basin!

Quasars are intense sources of X-rays as well
as visible light. They are the most powerful
type of X-ray source yet discovered. Some
quasars are so bright that they can be seen at a
distance of 12 billion light years.

http://chandra.harvard.edu/xray_sources/quasars.html


Quasar

http://www.astr.ua.edu/keel/agn/pks1117r.html


Quasars

With ground-based telescopes, quasars are typically
boring until you measure their spectrum. As a pretty
typical example, this is the radio-loud quasar PKS
1117-248 at redshift z=0.466 [~1.5 billion parsecs]. I
marked it to reduce puzzlement - this image shows why
various subterfuges involving radio emission, X-rays,
colors, or spectra are needed to pick out quasars
wholesale from foreground stars. Even at this modest
redshift, there's not much of a host galaxy or surrounding
group visible to make it stand out.
This is a red-light CCD image.... The image covers an area
2.9 by 2.9 arcminutes.

http://www.astr.ua.edu/keel/agn/pks1117r.html


Active Galactic Nuclei, AGN

The uniﬁcation scheme explains the connection between different types of radio-
loud AGNs. It is based on the orientation of the AGNs disk to the observer. When
the radio-loud AGN is observed disks edge-on, i.e the central area is blocked
from the direct view, a radio galaxy is seen. If the radiation from central torus is
observed without it being blocked by the central torus, the quasar is seen.

http://www.mpa-garching.mpg.de/HIGHLIGHT/2003/highlight0301_e.html

Active Galaxies vs. Quasars

Seyfert galaxies, radio galaxies, and
quasars are similar objects -- accretion
powered active nuclei. They may differ
in total luminosity (quasars vs active
galaxies) or in radio power (seyfert 1’s
vs radio galaxies/seyfert 2’s) or in host
galaxies (seyferts vs radio galaxies).

http://abyss.uoregon.edu/~js/ast123/lectures/lec12.html

Active Galaxies: Types
LACC: Ch 26

• Seyfert Galaxies: Active Spiral Galaxies, non-
stellar spectrum
• Radio Galaxies: Active Elliptical Galaxies, non-
stellar spectrum
• Quasars: Super Active Galaxies, non-stellar
spectrum
An attempt to answer the “big questions”: what is
out there? how did we get here?


LACC HW: Franknoi, Morrison, and
Wolff, Voyages Through the Universe,
3rd ed.

• Ch. 26, pp. 601: 3.

Due at the beginning of next week’s ﬁrst class
period (unless there is a test that week, in which
case it’s due the same period as the test).
Be working on your Distance Ladders.


Active Galaxies: Cause
LACC: Ch 26

• Active Galaxies Power Source
• Active Galaxies Causes
• Observations
An attempt to answer the “big questions”: what is out
there? how did we get here?



http://www.astronomynotes.com/galaxy/s12.htm


Active galactic nuclei (hereafter abbreviated AGNs) are
among the most spectacular objects in the Universe. They
produce prodigious luminosities (in some cases as much
as 10,000 times the luminosity of a typical galaxy) in
tiny volumes (much less than one cubic parsec). Most
astronomers now believe that the power for AGNs comes
from accretion onto the supermassive black holes
located at the centre of every galaxy with a bulge.



The dark, dusty
disk represents a
cold outer region,
which moves
inward to within a
few hundred
million miles of the
suspected black
hole. This disk
feeds matter into
the black hole,
where gravity
compresses and
heats the material.
Some hot gas
squirts out from
the black hole's
near-vicinity to
create the radio
jets.

http://teacherlink.ed.usu.edu/tlnasa/pictures/litho/NGC4261/ncg4261.html

A torus of dusty
material is thought to
surround the
accreting black holes
in most AGN.
Radiation which
escapes
perpendicular to the
torus is able to ionize
gas clouds in the
surrounding galaxy,
which leads to
characteristic
emisson line
signatures in the
galaxy spectrum.



Active galaxies are also noteworthy in that they display
very strong cosmological evolution. The most luminous
active galaxies were a thousand times more numerous at
redshift 2.5 than they are today. This strong evolution
with redshift suggests that galaxy formation and the
creation of active nuclei may have gone hand-in-hand
in the early Universe.

The main conclusion reached by the MPA/JHU team is
that strong AGN activity is often associated with strong
bursts of recent star formation in the host galaxy.


Quasars: a normal stage?

It has long been clear that the quasars we can observe evolve strongly with cosmic
time, having gone through a peak about 12 billion years ago when a large fraction of
bright galaxies must have hosted quasars, and with their number falling dramatically
down to the present day. Going outward in redshift and farther back in time, the
number of quasars (at least the very powerful ones that we could ﬁnd so far away)
declines above redshift z=4, with progressively fewer and fewer up to the current
record at z=6.4. Either we are watching the population of quasars "turn on", or for
some reason we can't ﬁnd most of the high-redshift quasars that were there.
http://universe-review.ca/I05-22-CentaurusA.jpg

Quasars -> Active -> Normal

A possible evolutionary sequence for galaxies, beginning with the highly luminous
quasars, decreasing in violence through the radio and Seyfert galaxies, and ending
with normal spirals and ellipticals. The central black holes that powered the early
activity are still there at later times; they simply run out of fuel as time goes on.

http://lifeng.lamost.org/courses/astrotoday/CHAISSON/AT325/HTML/AT32506.HTM


The core of the
Seyfert 2 galaxy
NGC 7742. The
lumpy thick
ring around
the core is an
area of active
star formation.
The ring is
about 3000
light-years from
the core.

http://www.mpa-garching.mpg.de/
HIGHLIGHT/2003/highlight0301_e.html


Active
Galaxies:
mergers?

http://www.whatsnextnetwork.com/
technology/index.php/2007/


Centaurus A
This galaxy is situated in It is of intermediate type
the M83 group of galaxies. between elliptical and
It is one of the most disk (spiral) galaxies:
interesting and peculiar The main body
galaxies in the sky, and is a has all
strong source of radio characteristics
radiation (therefore the of a large
designation Centaurus A); elliptical, but a
it is actually the nearest pronounced
radio galaxy. dust belt is
superimposed
well over the
center, forming
a disk plane
around this
galaxy.

This galaxy seems to have "eaten" at least
one larger spiral in the last few billion years.
http://www.seds.org/
messier/xtra/ngc/n5128.html

Centaurus A
A fantastic jumble of young blue star clusters, gigantic glowing
gas clouds, and imposing dark dust lanes surrounds the central
region of the active galaxy Centaurus A.
This mosaic of Hubble Space Telescope
images taken in blue, green, and red light has
been processed to present a natural color
picture of this cosmic maelstrom.
Infrared images from the Hubble
have also shown that hidden at the
center of this activity are what seem
to be disks of matter spiraling into a
black hole with a billion times the
mass of the Sun!

Centaurus A itself is
apparently the
result of a collision
of two galaxies
and the left over
debris is steadily
being consumed
by the black hole.
Astronomers believe that such black hole
central engines generate the radio, X-ray,
and gamma-ray energy radiated by
Centaurus A and other active galaxies.
But for an active galaxy Centaurus A is close, a mere 10
million light-years away, and is a relatively convenient
http://apod.nasa.gov/ laboratory for exploring these powerful sources of energy.
apod/ap070729.html

Centaurus A
Peering deep inside Centaurus A, the closest active galaxy to Earth, the Spitzer
Space Telescope's penetrating infrared cameras recorded this startling vista. About
1,000 light-years across, the twisted cosmic dust cloud apparently shaped like a
parallelogram is likely the result of a smaller spiral galaxy falling into the giant
Centaurus A.

The parallelogram lies along the active galaxy's central band of dust and stars
visible in more familiar optical images. Astronomers believe that the striking
geometric shape represents an approximately edge-on view of the infalling spiral
galaxy's disk in the process of being twisted and warped by the interaction.
Ultimately, debris from the ill-fated spiral galaxy should provide fuel for the
supermassive black hole lurking at the center of Centaurus A.

http://apod.nasa.gov/apod/ap040624.html

Centaurus A
Its core hidden from optical view by a thick lane of dust,
the giant elliptical galaxy Centaurus A was among the
ﬁrst objects observed by the orbiting Chandra X-ray
Observatory. Astronomers were not disappointed, as
Centaurus A's appearance in x-rays
makes its classiﬁcation as an active
galaxy easy to appreciate.

Perhaps the most striking
feature of this Chandra
false-color x-ray view is
the jet, 30,000 light-
years long. Blasting
toward the upper left
corner of the picture, the
jet seems to arise from
the galaxy's bright
central x-ray source --
suspected of harboring
a black hole with a
million or so times the
mass of the Sun.
Centaurus A is also seen to be teeming with other individual x-ray sources and a pervasive, diffuse x-ray
glow. Most of these individual sources are likely to be neutron stars or solar mass black holes accreting
material from their less exotic binary companion stars. The diffuse high-energy glow represents gas
throughout the galaxy heated to temperatures of millions of degrees C. At 11 million light-years distant in
the constellation Centaurus, Centaurus A (NGC 5128) is the closest active galaxy.

http://apod.nasa.gov/apod/ap030705.html

Centaurus A

A radio image of the
same galaxy reveals a
dramatically different
view: giant radio
lobes are emerging
perpendicular to the
dust lane.

http://archive.ncsa.uiuc.edu/Cyberia/NumRel/RelUniverse2.html

Centaurus A

http://universe-review.ca/I05-22-CentaurusA.jpg


Active Galaxies: Cause
LACC: Ch 26
• Active Galaxies Power Source: an Active Galactic
Nucleus [AGN]--matter in an accretion disc
spiraling in to a supermassive black hole
• Active Galaxies Causes: a normal part of early
galaxy development and/or galaxy mergers
• Observations: X-rays (from accretion disc and
jets), visible (bright galaxy nucleus), infrared (dust
waiting to be eaten), radio (lobes larger than the
galaxy itself)
An attempt to answer the “big questions”: what is out
there? how did we get here?


LACC HW: Franknoi, Morrison, and
Wolff, Voyages Through the Universe,
3rd ed.

• Ch 27: Tutorial Quizzes accessible from: http://
www.brookscole.com/cgi-brookscole/course_products_bc.pl?
ﬁd=M20b&product_isbn_issn=9780495017899&discipline_number=19

Due at the beginning of next week’s ﬁrst class
period (unless there is a test that week, in which
case it’s due the same period as the test).
Be working on your Distance Ladders.


A1 22 Active Galaxies

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A1 22 Active Galaxies