Notes 21

today :
our galactic nucelus
Ultra-Luminous IR Galaxies (ULIRGs)
high-z submillimeter galaxies and QSO’s
starbursts and AGN fueling
Galactic center circumnuclear disk - CND
Paschen α
(stars removed)
Pα
==>
ionized mini-spiral
1 pc
BH (Sgr A* ) : 4x106 M¤
L < 106 L¤
ionized spiral
(Paschen α)
dense H2 clumps
(HCN)
CND : 1 – 3 pc radius MH2 ~ 5x105 (~ GMC)
n ~ 107 – 8 cm-3 (tidally stable)
τorbit = 105 yr , τdyn = 104 yr
no evidence of SF ? !! Christopher etal 2005
1 pc
luminous IR Galaxies (Sanders & Mirabel 96, ARAA)
Annual Reviews
ULIRGS
HyperLIRGS
9:20
12-13
SANDER2
AR12-18
10
L¤
Arp220, Mrk 231, NGC6240
>1013 L¤ IR1520+32
1988ApJ...325...74S
1998
z = 0 Galaxy Luminosity functions
756
SANDERS & MIRABEL
optical
–2
IRAS BGS
IRAS 1Jy ULIGs
Mrk Seyferts
Mrk Starburst
!
cDs
Normal galaxies
–4
–3
–1
log " (Mpc Mbol )
PG QSOs
!
!
–6
IR
–8
–10
9
10
11
log L bol
12
13
(L . )
Figure 1 The luminosity function for infrared galaxies compared with other extragalactic objects.
References: IRAS RBGS (Sanders et al 1996a), IRAS 1-Jy Survey of ULIGs (Kim 1995), PalomarGreen QSOs (Schmidt & Green 1983), Markarian starbursts and Seyfert galaxies (Huchra 1977),
and normal galaxies (Schechter 1976). Determination of the bolometric luminosity for the optically
IR
optical
LFIR high luminosity tail:
Φ ∝ L-2.35
ρ (z) ∝ (1+z)5 ± 2.5
HST ACS Bi imaging – Evans etal 2008
LIR
Observed SEDs Low-z ULIRGs Sanders etal 88
LIR / MH2
LUMINOUS INFRARED GALAXIES
773
Table 3 IRAS galaxy properties versus L ir
10.5–10.99
No. of objectsa
Morphology
echnology on 03/04/12. For personal use only.
Separationb
Opt Spectra
L ir /L B c
L ir /L �CO c
merger
close pair
single (?)
[kpc]
Seyfert 1 or 2
LINER
H II
[L ⊙ (K km s−1 pc2 )−1 ]
50
12%
21%
67%
36.
7%
28%
65%
1
37
11.0–11.49 11.5–11.99
log(L ir /L ⊙ )
50
32%
36%
32%
27.
10%
32%
58%
5
78
30
66%
14%
20%
6.4
17%
34%
49%
13
122
12.0–12.50
40
95%
0%
5%
1.2
34%
38%
28%
25
230
a
Objects in the IRAS BGS plus additional ULIGs from Kim & Sanders (1996).
Mean projected separation of nuclei for mergers and close pairs only.
c
Mean values.
b
higher L è
merging
doubleappears
nuclei
in molecularincreasing
gas; at the lowfreq.
end ofofthis
range the &
luminosity
to be domincreasing
fraction
with AGN-like
emission
lines
inated by starbursts
with Seyferts
becoming
increasinglyopt.
important
at higher
luminosities. Those objects that reach the highest infrared luminosities, L ir >
1012 L ⊙ , contain exceptionally large central concentrations of molecular gas;
because of heavy dust obscuration it is hard to distinguish the relative roles of
starburst and AGN activity, although the conditions are clearly optimal for fuel-
Low-z ULIRGs :
LIR / MH2 èSF efficiency
NGC 6240: merger of 2 massive disk galaxies
w/ xray sources (AGN) in each nucleus HST B and I bands (F450W, F814W) with Hα
Near-infrared
K band image, Keck adaptive optics
XRAY (CXO)
0.5 – 1.5 kev
5.4 arcsec
1.5 – 5 kev
5 – 8 kev
Arp 220
distance 77 Mpc
LIR ~ 2x1012 L¤
(HST/ACS)
(Subaru/Suprime-cam)
Arp 220 (@77 Mpc) -- L = 2x1012 L¤
double nuclei – 300 pc apart
3x109 M¤ H2 on each, counter-rot. HST :
1.1, 1.6, 2.2μm
1 arcsec = 300pc
inclined , opaque disk obscuring nuclear star cluster Arp 220 -- mm-wave imaging : CO and dust
counter-rotating nuclear disks
Sakamoto etal
1999
Arp 220 HCN (4-3) from ALMA
project with Swarnima total HCN flux east : 91 Jy km/s
west : 199 Jy km/s
mean velocity è counter-rotating nuclei Arp 220 properties Arp 220 E
Arp 220 W
size
< 100 pc
120 x 70 pc
TB(CO)
38 K
37 K
ΔV
540 km/s
480 km/s
Mdyn
4x109 M¤
3x109 M¤
Mgas
~2x109 M¤
~2x109 M¤
total Mgas
5x109 M¤
high gas mass fraction
high area filling – not cloudy
filled gas disks AV ~ 2000 !! mag perp. to disk
maximal rate of SF : gasè* on a dynamical timescale
MISM / τorbit è 104 Msun yr-1 -- Arp 220
if SF efficiency high or rapid AGN accretion
L would be higher
what’s wrong ??
something is limiting SF ...
nuclear starburst structure
•  ISM dissipative => disk •  uniform (not cloudy) distribution
observed ! V ~ 70 km / s " thickness,h ~ 20 # 50 pc
(assuming hydrostatic equil.)
rad. press.
gravity
self-regulating:
SFR $" Prad. $" h$" density %" SFR %
M
L
L
& ' 2 and Prad ' 2 " max ~ 200 # 500 L(
M
R
R
dust radiation pressure limited SB :
Frad.
"L / c
=!
g
4#G"M
L$
"L
> 1 for
> 500
(w/ dust abs. ! for 5µm)
"M
M$
Arp 220 -- ΣL / ΣM ~ 1012 / 2x109 ~ 500 L¤ / M¤
==> radiatively self-regulated starburst
can only avoid how ? moving out to high redshift ...
molecular gas and dust at high z cumulative
# per yr
submillimeter galaxies – SMGs
detected in dust continuum several classes of objects – most interesting high-z ULIRGs
negative k-correction è easy to see higher z
sliding up the RJ tail
flux 2000ASPC..200...81H
z=2
observed fluxes (arp 220) vs redshift
1
0
submillimeter galaxies –
apparent dust temp. & IR luminosity
easy to recognize lensed objects wide range of excitation in high z galaxies
unlensed sources CO spatial maps w/ velocity field
CO Maps
Velocities
some w/ rotation gradients some w/ high dispersion
H2 contents at z ~2
Tacconi etal 2010 – sample of 23 massive spirals @ z = 1-3 (not IR or SF selected)
34%
44%
fgas = MH2 / (MH2 + M* )
how to pick out starbursts ?
timescales and concentration
must be physically motivated !
e.g. specific SF rate , sSFR = SFR/M* = 1/τ*
meaningless unless τ* compared w/ something
e.g. τcosmic , τgalaxy
prefer τISM = MISM/SFR
if short compared to τ* or τgal, then bursting
ISM –
fundamental to rejuvenation and activity in galaxies
SF, SN , AGN outstanding ?’s
replenishment relationship of phases – mechanism of transformation
star / planetary formation interesting astrophysics – shock front , turbulence , magnetic effects