Download Can we account for the dust

Origin and evolution of dust in galaxies
Can we account for the dust in galaxies
by stellar sources?
Mikako Matsuura
Origin’s fellow, Institute of Origins, University College London
M.J. Barlow, G.C. Sloan, A.A. Zijlstra, D. Stock, P.A. Whitelock, P. R. Wood,
M.-R.L. Cioni, M.A.T. Groenewegen, K.Volk, J. Bernard-Salas, F. Kemper, T. Kodama, E.
Lagadec, M. Meixner, S. Srinivasan, C. Szyszka, J.Th. van Loon
Introduction

Mid- and far-IR emission of galaxies
◦ Thermal emission from dust grains

Questions to answer
◦ Can we account for dust mass in the
interstellar medium (ISM) by stellar
sources?
 C.f. Main source of the dust in our Galaxy
 Asymptotic giant branch stars (AGB) stars – low and
intermediate stars (Gerz 1989)
 SNe – high mass stars ?
◦ Can we apply for that to all galaxies?
 Testing based on observations
Dust mass in the ISM of galaxies
Drain et al. (2007)
Case 1: Large Magellanic Cloud (LMC)

One of the nearest galaxy
◦ 50 kpc

Spitzer Space Telescope
observations
3.6 micron: blue
8.0 micron: green
24 micron: red
◦ Spectroscopic survey of selected
objects
◦ Photometric survey 3.6-160
mcron
 Entire census of AGB stars
 Measuring dust mass formed in AGB
stars
Optical image
SAGE
Dust mass in the ISM of galaxies
Analysis (1) : selection of dust
forming AGB stars
AGB stars are
the brightest
population in
mid-infrared
Foreground stars
HII regions / YSOs
Distant galaxies
Emission line objects
(WR stars)
Mid-infrared color magnitude
diagramme [8.0] vs [3.6]-[8.0]
Matsuura et al. (2009, MNRAS 396, 918)
Dust mass in the ISM of galaxies
Analysis (2) estimate of gas and dust lost
from individual AGB stars

Detailed analysis of 40 AGB
stars provides dust/gas massloss rate rate (M yr-1)
 JHKL photometry
 Spitzer spectra (5-35 micron)
◦ Spectral energy distributions are
fitted, using radiative transfer code,
including dust
Log dM/dt=
-6.2/[([3.6]-[8.0])+0.83]-3.39
Dust mass-loss rate: 3.1x10-8 M yr-1
Groenewegen et al. (2007, MNRAS 376, 313)
Dust mass in the ISM of galaxies
Identified AGB stars + measured their
mass-loss rate (gas and dust mass)
Detecting dust-embedded AGB stars using Spitzer
Matsuura et al. (2009, MNRAS, 396, 918)
Global dust budget in the Large
Magellanic Cloud

Missing dust mass problem in the LMC!

Current LMC dust mass: 2x106 M
◦ HI+H2 gas mass (8x108 M) x dust-to-gas ratio (0.0025)

Dust injection rate from AGB stars: 4.3x10-5 M yr-1 (up to 8x10-5 M yr-1)
◦ requires>20 Gyrs
Lifetime of the LMC (~15 Gyrs)
◦ Dust lifetime was estimated to be 4-8x108 yrs (Jones et al. 1994)

Dust deficit is short by a factor of 30
SNe
Dust formation?
Shock destruction?
AGB dust
(2-6)x104 M
over (4-8)x108 years
ISM dust
2x106 M
Dust mass in the ISM of galaxies
Other dust sources are
needed
Solutions for the dust deficit?

Lower SN dust destruction rate

Dust from high mass stars
◦ Higher SNII dust production rate

0.5 M from Cas A and 1.2 M from Kepler
◦ Dust from red supergiants (RSG)

High number of RSG population in the LMC

Unaccounted dust mass in AGB stars?

Dust may be formed in starforming regions
Herschel/SPIRE 240
micron image
N49: Supernova
Remnant
Dust mass in the ISM of galaxies
Case 2:
Dust in different environment: low-metallicity galaxies
- Bridging local group galaxies to high-z galaxies
Dust mass in the ISM of galaxies
Can dust be formed at low metallicities?
Dust needs (astronomical) metals!


Oxides
◦ Olivines : Mg2xFe(2-2x)SiO4
◦ Pyroxenes : MgxFe1-xSiO3
Carbonaceous dust
◦ Graphite : C
◦ Amorphous : C
◦ Polycyclic aromatic hydrocarbons
(PAHs)
Dust mass : as a function of metallicity of galaxies
It has been suggested that it is difficult to form dust grains in stars
in low metallicity (Z<0.1 Z) galaxies
But … we found unexpected results
Dust mass in the ISM of galaxies
The Galaxies of the Local Group
Some galaxies have low metallicities
Sculptor dwarf spheroidal (dSph) galaxy
[Z/H]~-1.33
Fornax dwarf spheroidal galaxy
[Z/H]~-1.0
Dust mass in the ISM of galaxies
Spitzer spectra
SiC
Amorphous Carbon
Sculptor dSph galaxy [Z/H]~-1.33
Sloan, Matsuura et al.
(2009, Science 323, 353)
Fornax dSph galaxy [Z/H]~-1.0
Matsuura et al. (2007, MNRAS 382, 1889)
Contrary to expectation, we detected dust at low metallicities
Dust mass in the ISM of galaxies
Dust at low metallicity
AGB stars

 We detected amorphous (+SiC) dust
 Carbon atoms synthesized in AGB stars
Dust formation process
around stars is affected
◦ not only by the metallicity of
the parent galaxies
◦ but also by elements formed
inside stars, in particular,
carbon
◦ Amorphous carbon, PAHs
Matsuura et al. (2005 A&A 434, 691)
(Our Galaxy)
(Fornax and Sculptor dSph galaxies)
Dust mass in the ISM of galaxies
Implications for high-z galaxies with dust
(Before our study)
Our Galaxy
High-z galaxies
Dust sources:
SNe (>8 Msun)
Assumed to be low
metallicity initially
Dust sources:
AGB stars +
SNe?
AGB + SNe
Metallicity
About solar metallicity
Dust can be formed in AGB stars and SNe
even at low metallicity
z~6.4; 0.84 Gyrs
(e.g. Bertoldi et al. 2003)
AGE
10-15 Gyrs
Age of AGB stars is much younger than
previously thought (starting 50 Myrs)
Sloan, Matsuura et al. (2009, Science, 323, 353)
Conclusions

AGB stars are important dust sources
◦ But still found deficit in dust budget in the LMC
 Solutions will be tested using Herschel observations
◦ Dust from AGB stars are more carbon-rich, and contain
more PAHs at lower metallicity <-> ISM: weak PAHs
 High UV radiation in the ISM at low metallicity destroy PAHs

High-z galaxies
◦ Lower metallicities do not hamper dust formation in AGB
stars
◦ Dust mass in high-z galaxies may be explained, if both
SNe and AGB stars contribute dust formation
Dust mass in the ISM of galaxies
Extragalactic Star Formation
5-8th July 2010
Windsor Great Park, suburb of London, England
http://zuserver2.star.ucl.ac.uk/~cl2010/
[email protected]