STARBURST GALAXIES – course 3
* SEDs
* Starbursts & Co.
* Spectral features
* Radio-infrared correlation
* ULIRGs & HyLIRGs
* Fuel & efficiency
* Starburst – AGN symbiosis
NGC7742
Note:
1. νFν measures energy per decade frequency
2. QSR (excessive radio emitter) is missing
RADIO – FIR correlation
UV from hot stars, plus dust heating, ionizing flux (f-f)
and synchrotron (SNR)
Their (logaritmic) ratio is u-, or q-parameter:
departure usually indicates radio-excess
IRAS COLOR-COLOR DIAGRAM:
COLD, COOL, AND WARM DUST
THE RADIO-FIR CORRELATION,
FOR WELL-KNOWN NEARBY
OBJECTS
Recall the infrared
diagnostic tools:
emission lines as
well as spectral
features !
SPECTROSCOPY
M104 is LINER*, as
are M81 and M87
*Low Ionization Nuclear Emission line Region
LINERs display
relatively strong [OI]
and [OII], and weak
[OIII]
Ionization source is
AGN plus shocks plus
hot stars. Substantial
fraction display radio
cores (i.e., AGN)
Seyfert’s (at least the
Type-1 being AGN)
have ~hard ionizing
source
LINERs, Seyfert’s, and star-forming galaxies were
recently found to display continuous distributions
of emission line properties:
DIFFERENCES
ARE SUBTLE AND
GRADUAL
Note:
H, L, S, T(C) (and N) types
Galaxies in our back yard
Ho, Filippenko & Sargent (1993, HFS93):
spectroscopy of 486 northern galaxies having
BT < 12.5, including 94 LINERs
GALAXIES IN THE NEARBY UNIVERSE
Normal/starburst
galaxies
Transition objects (T)
LINERs (L)
Seyfert galaxies (S)
(Kauffmann et al. 2003:
55.757 SDSS emission
line galaxies)
SDSS Seyfert’s
generally display
signatures of a
young (0.2 – 2
Gyr) stellar
population: AGN
post-starburst
phenomenon?
Line emitters: median
Hα luminosity is 2×1039
erg/sec, which is factor
50 less than typical
Markarian Seyfert’s.
In other words: many
LLAGN included.
Speculation
The relative
contribution of AGN
vs. shock vs. hot
star ionization
determines the
migration off the
normal SF locus
Star-forming
galaxies with
increasing
mass/
metallicity
T
AGN massive
post-starburst
galaxies?!
!! Episodic
phenomenon.
Line spectroscopy – what have we learned
Preferably in the infrared (less extinction)
Stellar features, like CO-bands, from (super)giants
Pa, Br recombination lines; Brγ right in K-window –
its EW is extinction-independent age indicator, as
continuum originates in red (super)giants, and line
flux measures Ly-continuum ionizing flux
Shock-excited fine-structure lines like [FeII]; [FeII]
1.64μm and 1.26μm arise from same upper level,
hence extinction tool!
Photoionization lines of ions give opportunity to
address ionization potential (starburst or AGN)
Cooling lines in photodissociation regions, like
[OI]63μm and [CII]158μm, occur at the boundary of
ionized and neutral gas
SF efficiency
L(FIR)/L(CO) indicates the SFR per unit fuel. Its value ranges from
a few or some tens in star-forming spirals to several hundreds in
ULIRGs and >103 in high z starburst objects (course 4).
Stars form in dusty molecular clouds (cooling and
adsorption), spontaneously or induced by
radiation/wind pressure from pre-existing star clusters,
or cloud-cloud collisions (mergers).
IR galaxies are rich in molecular
gas; the mass in H2 is generally
obtained from the CO-luminosity
(taking the ~MW conversion factor):
~109 – 1010 M, which is ~ 1 – 10 x
MW gas, BUT from small volume!
L(FIR) traces the (non-)ionizing radiation from young
OB-stars, being absorbed by dust and re-emitted at
~60μm. Leitherer et al. (1999) show that for an α=2.35
IMF and mass range 1-100M : SFR ~ 1 x 10-10 L(FIR)
LIRGs, ULIRGs, and
HyLIRGs contain huge
dust and gas masses:
besides molecular gas
also neutral hydrogen
SFR correlates with L(FIR):
Antennae, N7252=Arp226, SuperAntennae, and Arp220: HI contours
on R-band, with K-band inserts
Local galaxies with logL(FIR)<11.8
ULIRGs
HyLIRGs
ONGOING STAR-FORMATION IN QSO HOSTS
1990s: UV
and visual
imaging,
often
indicative
of peculiar
galaxies
A fair fraction of radioquiet QSOs has
substantial FIR emission,
with FIR/radio ratio’s
indicative of 50:50
contributions of AGN and
star-formation
Their FIR-colors are
consistent with that
picture
‘COOL’ vs. ‘WARM’
DUST EMITTERS:
INDICATING THE
RELATIVE
CONTRIBUTIONS
OF COLD AND
WARM DUST
COLD SF DUST
+
WARM AGN DUST
Also (PG = Palomar Green) QSOs follow the SFE
behaviour as found in infrared selected galaxies
AGN detections in the Hubble Deep Field, using VLBI
VLA J123716+621733
Garrett et al. 2000
VLA J123642+621545
VLA J123716+621512
With sufficient FIR SED coverage, one can decompose
the multi-temperature dust: here radio galaxy Cyg A,
having cold ISM dust, cool SF dust and hot AGN dust
VLA J123721+621129
VLA J123623+621642
VLA J123714+620823
VLA J123700+620909
VLA J123608+621035
Radio / IR flux ratio (q24), for the HDF objects
PDB: Given the increasing evidence that
nearby low luminosity AGN are post-starburst
systems (some post-ULIRGs) and the
increasing evidence that QSO and radio
galaxy hosts contain dust, gas and young stars,
and recalling that galaxy merging and
interaction triggers star-formation, it is
conceivable that – under certain conditions –
circumnuclear star clusters may fuel the MBH
in a mass-loss phase.