Mikako Matsuura Origin’s fellow, Institute of Origins, University College London

1. Origin and evolution of dust in galaxiesCan 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

2. 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 Drain et al. (2007) Dust mass in the ISM of galaxies

3. Case 1: Large Magellanic Cloud (LMC) • One of the nearest galaxy • 50 kpc • Spitzer Space Telescope observations • Spectroscopic survey of selected objects • Photometric survey 3.6-160 mcron • Entire census of AGB stars • Measuring dust mass formed in AGB stars 3.6 micron: blue 8.0 micron: green 24 micron: red Optical image SAGE Dust mass in the ISM of galaxies

4. Analysis (1) : selection of dust forming AGB stars Foreground stars AGB stars are the brightest population in mid-infrared 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

5. Analysis (2) estimate of gas and dust lost from individual AGB stars • Detailed analysis of 40 AGB stars provides dust/gas mass-loss rate rate (M yr-1) • JHKL photometry • Spitzer spectra (5-35 micron) • Spectral energy distributions are fitted, using radiative transfer code, including dust Dust mass-loss rate: 3.1x10-8 M yr-1 Log dM/dt= -6.2/[([3.6]-[8.0])+0.83]-3.39 Groenewegen et al. (2007, MNRAS 376, 313) Dust mass in the ISM of galaxies

6. 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)

7. 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 Other dust sources are needed Dust mass in the ISM of galaxies

8. 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

9. Case 2: Dust in different environment: low-metallicity galaxies - Bridging local group galaxies to high-z galaxies Dust mass in the ISM of galaxies

10. 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

11. 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

12. 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

13. 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

14. Implications for high-z galaxies with dust (Before our study) Our Galaxy High-z galaxies Dust sources: SNe (>8 Msun) Dust sources: AGB stars + SNe? AGB + SNe Assumed to be low metallicity initially z~6.4; 0.84 Gyrs (e.g. Bertoldi et al. 2003) About solar metallicity 10-15 Gyrs Metallicity Dust can be formed in AGB stars and SNe even at low metallicity AGE Age of AGB stars is much younger than previously thought (starting 50 Myrs) Sloan, Matsuura et al. (2009, Science, 323, 353)

15. 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

16. Extragalactic Star Formation 5-8th July 2010 Windsor Great Park, suburb of London, England http://zuserver2.star.ucl.ac.uk/~cl2010/ cl2010@star.ucl.ac.uk