Recent Topics on Dust in Galaxies：
A Critical Review of Herschel First Results
Tsutomu T. TAKEUCHIA
C
Institute for Advanced Research, Nagoya University,
JAPAN
Special thanks to
Véronique BUAT & Denis BURGARELLALaboratoire d’Astrophysique de Marseille, OAMP, FRANCE

28th Grain Formation WS/Dust in Galaxies, Kobe, 01 Sep. 2010

1. The Star Formation History in the Universe
1.1 The global history of the Universe

http://map.gsfc.nasa.gov/m_mm.html

1. The Star Formation History in the Universe
1.1 The global history of the Universe

CMB
Almost homogeneous and isotropic
No heavy elements
http://map.gsfc.nasa.gov/m_mm.html

1. The Star Formation History in the Universe
1.1 The global history of the Universe
The present-day Universe
Rich in structures of various scales
Heavy elements

http://map.gsfc.nasa.gov/m_mm.html

1. The Star Formation History in the Universe
1.1 The global history of the Universe

Formation andevolution of galaxies:
gBirth and death of stars

http://map.gsfc.nasa.gov/m_mm.html

1.2 Formation and evolution of galaxies
The hiTh
hierarchicalhi l structuret tformationfti
The mass in the Universe is known to be dominated by invisible
matter detected only by gravity (dark matter: DM)
DM). The initial
fluctuations of DM start to grow by gravitational interactions.
Resultingg virialized structures are called dark halos.
Dark halo

The hierarchical structure formation
The dark halos approach each other and finally merge to form
larger halos. The formation proceeds from smaller to larger
structures.
t t
This
Thi isi theth so-calledll d hierarchicalhi
hi l structuret tformation,fticurrently the most reliable scenario of the structure formation in
the Universe.
Dark halo

The hierarchical structure formation
During the merging of dark halos, the baryonic gas falls into
the gravitational potential wells of DM and is compressed there.
Then the gas turns into stars,
Then,stars and galaxies form as large
agglomerations of stars and remaining gas in dark halos.

Dark halo

Galaxyy

The hierarchical structure formation
Dark halos continue merging and form larger and larger halos.
Consequently, galaxies in these halos start to cohabit in thesame newly formed halos
halos. Baryonic structures cannot merge aseasily as dark halos because of gas pressure.

Dark halo

Galaxyy

The hierarchical structure formation
Then, sometimes dark halos are occupied by one or moregalaxies and sometimes no galaxies. The occupation number isstochastic
t h ti (but(b t lloosely
l a functionfti off theth haloh l mass).
) Merging
M igoes on with the cosmic time.

Dark halo

Galaxyy

The hierarchical structure formation
Finally, some galaxies merge and form larger galaxies. Presentday large galaxies (up to Mbaryon ~ 1012 Msun) are thought tohhavefformedd iin ththe merger process. St
Strong merging
i process iis
often accompanied by an effective compression of gas, inducing
star formation.
Dark halo

Galaxyy

The hierarchical structure formation

Important issues:
When, where, and how stars formed?
How large/small were the first galaxies?
H doesHowdtheth siteit off start fformation
ti dependdd on ththe surrounding?
di ?

Chemical evolution of galaxies
After the first star formation in galaxies, all galaxies gradually
accumulate heavy elements produced by their own stars.

The chemical composition of the interstellar medium (ISM) ineach galaxy evolves with time as star formation proceeds:
chemical evolution.
The efficiency of star formation is affected by the chemicalcompositioni i off theh ISM,ISM ii.e., theh star fformationi in
i galaxiesl i isi
regulated by the chemical evolution.

Chemical evolution of galaxies
Star formation
Heavy element production

ISM

Mass ejection

Stellar evolution

Stellar winds
PNe
Heavy element production
Supply of heavy
elements

Mass ejection
SNRs

Stellar death
Heavy element production

Chemical evolution of galaxies
Star formation
Heavy element production

ISM

Mass ejection

SNRs

Protoplanetary
p
y
disk

Dust production
Stellar evolution
Dust

Stellar winds
PNe
Heavy element production
Supply of heavy
elements

Mass ejection

Dust production

Stellar death
Heavy element production

Cool star atmosphere
PNe

Dust production
SNRs

y SNe
Blast wave by

Dust destruction

Chemical evolution of galaxies

Important issues:
production p
proceeded?
How the heavyy element and dust p
How much, what kind of, and when dust formed?

Also discussed by the next talk (Asano et al.).

Dust extinction and hidden star formation

FIR

FUV
Dust

Short-wavelength photons like UV are scattered and absorbed
byy small solid ggrains,, i.e.,, dust ((referred to as “extinction”),),
and re-emitted from dust at far-infrared (FIR).
Hence, to obtain an unbiased view of the cosmic star formation,
it is crucial to treat the information of both FUV and FIR.

Dust extinction and hidden star formation

Hidden SF

Di
Directly
l observedbd SF

The local fraction of the hidden SF is 50-60%, while theffraction
i at z = 1 reaches
h around
d 90% (T(Takeuchi
k hi et al.
l2005a).

Dust extinction and hidden star formationz = 1 (a half of the cosmic age)

(Bouwens et al. 2006)

Dust extinction and hidden star formation

Dust extinction “corrected”???

Directly measuredz = 1 (a half of the cosmic age)

(Bouwens et al. 2006)

Dust extinction and hidden star formation

Important issues:
How strongg is the dust extinction?
How has the extinction evolved in the cosmic history?
H large
How
l
is
i the
th fraction
f ti off hidden
hidd start formation?
fti ?

Also discussed by the third talk (Ikeyama et al
al. and two posters
Fujiwara et al. and Nagaya et al.).

1.3 Issues to be investigated by dust in galaxies
1. When, where, and how stars formed?
2 How large/small were the first galaxies?
2.
3. How does the site of star formation depend on thes rro nding?
surrounding?
4. How the heavy element and dust production proceeded?
5. How much, what kind of, and when dust formed?
6 How strong is the dust extinction?
6.
7. How has the extinction evolved in the cosmic history?
8. How large is the fraction of hidden star formation?
IIssues 11-33 are nott perfectly
f tl traced
t
d by
b d
dustt (IR)(IR), ththoughh weexpect to obtain some information even if partially.

2. Herschel Early Extragalactic Results
2.1 Herschel Space Observatory
Launch: 14 May, 2009
Wavelength: 55 – 671 μm
Main mirror φ: 3.5 m
Direct imaging instruments:
PACS (Poglitsch et al. 2010)
SPIRE (Griffin et al.
al 2010)Heterodyne spectrometer:
HIFI (de Graauw et al. 2010)(Pilbratt et al. 2010)
Special Issues for Herschel early results:
Astronomy & Astrophysics: vol. 518 (2010)
Monthly Notices of the RAS: in press (2010)

2.1 Herschel Space Observatory

PACS and SPIRE bands(Magdis et al. 2010a)
PACS images (Pilbratt et al. 2010)

2.2 Extragalactic key programs
Herschel observation time:
Guaranteed time 1/3
Open time 2/3 (key programs + normal call)
Guaranteed time keyy p
programs:g
HerMES (SPIRE GT, 900h)
PEP (PACS GT, 654.9h)
Open time key programs:
H ATLAS (600h): very wide (550 deg2) shallow survey
H-ATLASGOODS-Herschel (362.6h): ultradeep pencil-beam survey
Key project consortia must make data products and tools
public at the proprietary period (1 year for the 1st year, and 6
months after).

The Herschel ATLAS (H-ATLAS)
Astrophysical Terahertz Large Area Survey• Coveringg 5 bands with PACS and SPIRE (110(- 500 μμm)) infast parallel mode (5-σ limits: 132, 126, 33, 36 and 45
mJy/beam from 110 - 500 μm)• Detect ~ 105 sources up to z ~ 3• Science demonstration phase (SD) datadata, maps and catalogs
will be made public around mid-June 2010 through the URL:
www.h-atlas.orggThe Herschel ATLAS (H-ATLAS)NGP and Equatorial

The widest area survey with Herschel (~ 550 deg2).

SGP

The HerMES
Herschel Multi-tiered Extragalactic Survey
Clusters
Level 1 0.11 ☐°Level 2 0.36 ☐°Level 3 1.25 ☐°Level 4 ~ 4 ☐°Level 5 ~ 30 ☐°Level 6 ~ 40 ☐°LockmanNorth

COSMOSCDFSFLSELAIS S1

In red: SDP fields

GOODS-S

ELAIS N2GOODS-N

ECDFS

Lockman
East

EGS

EGS

UDS

Lockman

ADF-S

UDS

VVDS

BootesBootesELAIS N1

ELAIS N1

XMM-LSSThe HerMES

Thee largest
a gest projectp oject oof Herschele sc e (850 h).
).
Data will be available via HeDaM.

The HerMES
250µm

350µm

500µm
µ

GOODS-N, the deepest SDP field2.3 Early extragalactic results from HerschelTh
The number
b counts
t off IR galaxies
l i

Euclideaninormalization:
i i
flat
f
counts represent no evolution
in a static Euclidean universe.
universe
HerMES

Very strong evolution of dusty
galaxies is indicated.
indicated(Oliver et al. 2010)

The number counts of IR galaxies

H-ATLAS

Same as the previousSistudy,
but from H-ATLAS. Thanks
to the large area,
area the brightcounts are well determined.
(Clements et al. 2010)

The number counts of IR galaxies(Berta et al. 2010)(Altieri et al. 2010)

The cosmic IR background and its origin

115%% off the CIRBC
iis resolved
from direct counts at 250 mm.
At longer wavelengths
wavelengths, thefraction is higher.
(Oliver et al. 2010)

λ [μm]

45-50%
45
50% of CIRB (100(100-160mm)
160mm)
is resolved into galaxies. Mostof them are at z < 1.0.
(Berta et al. 2010)

Luminosity function of dusty galaxies
Local (z = 0) LF
SDSS, 2MASS, IRAC,
MIPS, and SPIRE dataover 15 deg
d 2 ini a portionti
of HerMES fields.
N.B. The 1/Vmax estimator(the same for all the rest)
is not appropriate to
discuss the shape of the
LF.
ρIR = 1.31 ×108 L☉ yr-1
(Vaccari et al. 2010)

Luminosity function of dusty galaxies
LF at 0 < z < 0.5250 μm selected in H
H-ATLASATLAS.
They claim luminosity density
evolution ∝(1+z)7 up to z = 0.5,05
stronger than in HerMES (cf.
Spitzer:p∝(1( + z)3.9 at z < 1).
)
N. B. Since only 876 have spec-z
out of 2276, photo-z
photo z uncertainty
exists. Also, the faint end
uncertainty hampers theestimation of integrated IR
luminosity.
(Dye et al. 2010)

Luminosity function of dusty galaxies
LF at 0 < z < 2.0
Selection at 250 µm in the
HerMES field.
0 < z < 0.2
0 2 < z < 0.4
0.2
04
0.4 < z < 0.8
0.8 < z < 1.2
1.2 < z < 1.6
1.6 < z < 2.0(Eales et al. 2010)

Strong evolution at 0 < z < 1,
1
but at most weak evolution atz > 1.
N. B. We should note possible
redshift incompleteness athigh z and uncertainty inphoto-z. Also, again the faintend uncertainty hampers theestimation of integrated IR
luminosity.
luminosity

Luminosity function of dusty galaxies
LF at 0 < z < 4.0
Selection at 100 µm and 160µm in the PEP fields.
Note that there are only afew (sometimes one!)point(s)p( ) at highergredshifts.

(Gruppioni et al. 2010)

Spectral energy distribution of dusty galaxies(Boselli et al. 2010)

Spectral energy distribution of dusty galaxies
FIR-Submm color and its
dependence on physicalproperties
S60/S100 positively correlats
with the birthrate parameterb (ratio between current toaverage star formation rates),
rates)
while the S350/S500 correlates
negatively. They also correlatewith metallicity. This time theformer correlates negatively,
while the latter positively.
(B lli ett al.
(Boselli
l 2010)N. B. M82 seems to be an
outlier on the S60/S100-Z plot.

Spectral energy distribution of dusty galaxies
Type 2Type 1

FIR/submm ratio works well to distinguish starburst/AGN,
while submm color does not. Herschel fluxes are always
dominated by starburst.
(Hatziminaoglou et al. 2010)

Dust temperature
Tdust is “significantly”
significantly cooler
than the local dusty galaxies
if LIR is the same ((Tdust is
defined simply by fitting ofgraybody νβBν(T) with afixed β).

(Elbaz et al. 2010)

N.B. The error bars arelarge
g and the claimed
difference would not be
statistically justified. Also, inthe same paper, they claimithat the SED templates
should be modified.
modifiedDust temperature
Tdust of z ~ 2 IRAC peakers have a large dispersion, bridging
submillimeter galaxies (SMGs), and spanning Local
ultraluminous IR galaxies (ULIRGs).
N B Again
A i ini allll thesethkN.B.
works,
Tdust is defined merely bygraybody fitting
fitting.
Another caveat is that sample
selection is not carefully
discussed.

(Magdis et al. 2010b,
astro-ph/1007.4900)

Extinction properties and hidden star formation
Possible decrease of dust attenuation in distant (z < 0.5) IR
luminous galaxies was found.
IRAS/GALEX(Buat et al. 2010, astro-ph/1007.1857)

HerMES/GALEXExtinction properties and hidden star formation
The Local starburst law (the so called Meurer’s law)overestimates dust attenuation in most of the cases (cf. talk by
Ikeyama et al.).
Local starburst relation

Local relation for star
forming galaxies(Buat et al. 2010, astro-ph/1007.1857)

Extinction properties and hidden star formation
SFRUV +SFRIR = SFRTOT : total star formation rate
SFR from β-corrected UVSFR from uncorrected UV(Buat et al. 2010,
astro-ph/1007.1857)

If the β-correction of UV would
work well, the SFR calculated
from corrected UV should havebeen the same as the SFRTOT
defined above.
However, it is NOT the case:
SFRUV underestimates SFRTOTO
by a factor of ~ 6, and the SFR
from UV corrected usingg the UV
slope β overestimates SFRTOT bya factor of 2-3.

Hidden star formation and evolution of stellar mass
The growth history of stellar mass in galaxies is one of the mostimportant clues to understand the galaxy growth in the cosmic
history This is reflected in the SFR and specific SFR (SFR/M*).
history.
)

mass completeness limit

The SFR is estimated by adding SFRUV(optical data with model)
and SFRdust (Herschel).
(Herschel)(Rodighiero et al. 2010)

Hidden star formation and evolution of stellar mass

Redshift z

The decreasing trend of SSFR with M* (downsizing) is seen ataanyy redshift
eds t range,a ge, but tthee slope
s ope steepens
steepe s up to z = 2..
N.B. However, still results from different studies do not agreewith each other
other.
(Rodighiero et al. 2010)

Clustering of dusty galaxies and structure formation
Spatial distribution of galaxies
carry crucial information on the
structure formation and galaxy
formation in dark halos.
Low-z dustyL
d t galaxies
l i are biasedbi d
to starbursts and late-type star
forming ones.
ones
In contrast, at higher redshifts,
dusty galaxies are speculated to
be progenitors of present-day
massive ellipticalpggalaxies.

The SDP field (4 deg×4 deg)

H-ATLAS will provide us with ideal data. However, thecurrently available area is still small, and numbers of galaxy
candidates are of 300-6000.
(Maddox et al. 2010)

Clustering of dusty galaxies and structure formation

Signal?

Signal?

Theyy claim that theyy found a clustering
g for brightestgsourcesand possibly high-z objects. However, the minimum number ofclustering analysis would be ~ 2000, i.e., in most of the analysis
with the SDP data, the sample size is insufficient.
(Maddox et al. 2010)

Clustering of dusty galaxies and structure formation
Halo
H
l modeld l isi now a fashonablef h
bl simple
i ltheoretical framework to model the dark
matter and dark halo distribution
distribution.
The basic idea is to divide the matter power
spectrum into two components: clusteringof halos and density profile of each halo.
In principle, angular clustering of dusty
galaxies have information on the dark halos
in which dusty galaxies reside.
HerMES p
provide relatively
y largeg number ((~3000-8000) of dusty galaxies at z ~ 2.
(Cooray et al. 2010)

Clustering of dusty galaxies and structure formation
By th
B
the h
halo
l modeld l andd observedbdclustering, with redshift
distribution the halo occupation
distribution,
distribution can be estimated.
From HerMES,
HerMES they found thatgalaxies detected at 250 mm (> 30y) reside in dark halos withmJy)
Mhalo > (5 ± 4)×1012 M☉, while
14 ± 8 % of them are satellites inmore massive halos.

Redhisft distribution

N.B. this type
yp of analysis
y strongly
g y depends
pon the redshift
distribution of the sources. The z-distribution is indirectly
reconstructed by assuming the SED of galaxies, which are also
very uncertaini andd to beb iinvestigated.
id(Cooray et al. 2010)

Nature of dust in high-z galaxies
Dust content of high-z galaxies is crucial to understand theearly evolution of galaxies. Especially, dust-to-gas (orstellar) mass ratio is a key factor for theoretical modeling(cf. talk by Asano et al.).

(Santini et al. 2010)

Nature of dust in high-z galaxies

Somewhat puzzling feature is that the dust-to-gas mass ratio of
dusty starbursts and submm galaxies are much higher than that
expected from their metallicity, and the Herschel PEP result
confirmed this for high-zgsubmm ggalaxies. The interpretationpisstill under debate.
(Santini et al. 2010)

Other interesting extragalactic topics
1. Photometric observation of a Local metal-poor dwarf NGC
1705 (O’Halloran et al. 2010).
2 FIR-to-radio2.
FIR to radio correlation (Ivison et alal. 2010)
2010).
3. FIR (100 and 160 mm) SFR estimators (Boquien et al. 2010).
4. Thee cos
cosmicc SF
S historys o y ofo QSO hostos galaxiesges (Serjeant(Se jeete al.
2010).
5. Sunyaev-Zel’dovich effect at λ < 650 μm (Zemcov et al.
2010).
6. PACS spectroscopy of high-z dusty galaxies (Strum et al.
2010).
2010)
7. Dust content of Cassiopeia A SNR (Barlow et al. 2010).
etc…

3. Summary
1 Metal1.
M t l andd dustd t isi a keyk factorf t tot understandd t d ththe cosmicihistory of galaxy formation.
2 Herschel is providing data with unprecedented quality at
2.
wavelengths from 100 to 500 μm, as well as spectroscopic
observations. Data from the key projects will be opened to
public.
3. Far-IR to submm number counts are very well determined
i widein
id range off flux,
fl
from
f
1.0
1 0 JyJ to
t 1 mJy.
J Though
Th
h th
the
counts are simple statistics, they are very useful to constrain
cosmological galaxy evolution model. Also, the cosmic IR
background (CIRB) is decomposed into individual sources.
Now 50% of the CIRB is explained by galaxies.
4. Luminosity functions of submm galaxies were estimated.
They can work as a stronger constraint on theoreticalmodels,d l bbutt bbecause off th
the lilimitation
it ti ini estimation
ti ti method,
th dfurther investigation is needed.

3. Summary
5 G
5.
Galaxyl
SEDs
SED are very wellll determinedd t
i d att λ = 100 – 500 μm.
Their metallicity dependence is also clarified. Though AGN
contribution is significant at λ < 100 μm,
μm the SED is
dominated by star formation at λ > 100 μm.
6. Dust temperature is often discussed, but often very unclear
in definition and/or results.
7. Dust extinction is quantified toward higher-z than before.
Hi h dusty
High-zd t galaxies
l i havehstatisticallyt ti ti ll lowerlextinction
ti ti thanththe low-z counterparts. It was also found that the IR excessUV slope (β) relation (Meurer(Meurer’ss law) does not to work wellat any redshifts.
8. Galaxy downsizing is confirmed up to z ~ 2. The slope of
SSFR as a function of stellar mass shows steepening towardhigher-z. However, since still many studies show discrepant
results,
lt further
f th more careful
f l analysis
l i isi needed.
d d

3. Summary
9 G
9.
Galaxylclusteringl t i carries
i cruciali l informationi f
ti on thethstructure formation and galaxy evolution. However, thoughclustering signal of dusty galaxies was found
found, the sample
size is too small to have reliable result.
10. Halo model was adopted to examine the dark halo
environment of dusty galaxies. For this analysis, the sample
size was acceptably large, but the uncertainty of redshift
di t ib ti hampers
distributionhtot haveha firmfi
result.
lt
11. Dust-to-gas/stellar mass ratio of dusty galaxies was
examined for highhigh-zz galaxies. It is known that dusty
starbursts tend to have too much dust with respect to their
metallicity. This weird tendency was confirmed for
Herschel sample. This problem remains to be solved.

The data will be public.
public
It is ourselves who will solvethese problems! Let’s try!

Acknowledgement
TTT has been supportedppbyy Programgfor ImprovementpofResearch Environment for Young Researchers from Special
Coordination Funds for Promoting Science and Technology
commissioned
i iby the Ministryi i
off Education,i
Culture,C
Sports,S
Science and Technology (MEXT) of Japan.
Some slides and figuresgwere ppreparedpbyy Véroniqueq Buat and
Denis Burgarella.