* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Aging nearby spiral galaxies using H
Space Interferometry Mission wikipedia , lookup
Modified Newtonian dynamics wikipedia , lookup
Nebular hypothesis wikipedia , lookup
Cygnus (constellation) wikipedia , lookup
Observational astronomy wikipedia , lookup
Theoretical astronomy wikipedia , lookup
Dyson sphere wikipedia , lookup
Perseus (constellation) wikipedia , lookup
Aquarius (constellation) wikipedia , lookup
Timeline of astronomy wikipedia , lookup
Star catalogue wikipedia , lookup
Stellar classification wikipedia , lookup
International Ultraviolet Explorer wikipedia , lookup
High-velocity cloud wikipedia , lookup
Type II supernova wikipedia , lookup
Corvus (constellation) wikipedia , lookup
Stellar kinematics wikipedia , lookup
Hayashi track wikipedia , lookup
Aging nearby spiral galaxies using H-alpha to UV flux ratios: Effect of model parameters Francesca von Braun-Bates Star formation in spiral galaxies Formation occurs in spiral arms: » Pressure waves change density of gas clouds: · Compression triggers protostar formation · Meanwhile spiral density wave keeps moving » Young blue stars evolve fastest: · Go supernova in very short time · So pressure wave hasn't moved far if star still shining Therefore blue stars trace starforming regions The H-alpha and UV fluxes UV emitted by all stars » Planck curve: blackbody radiates at all wavelengths » Flux = total radiation integrated over area Hydrogen-alpha wavelength caused by ionisation: » Interstellar medium 10% He, 90% H (by no. of particles) » HI region + Lyman photon = HII region » Free e- recombine & fall through energy transitions » 3→2 transition emits 6563Å = H-α line Importance of the flux ratio Hα : UV output decreases over Myr » UV relatively constant » Hα caused by stars M > 10M: · High temperature = UV photons · large mass = short lifetime Red: UV (1500Ǻ) Blue: Optical H-α (6563Ǻ) image of M51 (GALEX) Taking ratio of individual “pixels” of galaxy images indicates age of star-forming region » ...but this depends on how the ratio decreases... » So run lots of possible scenarios and compare Modelling star forming regions Evolutionary synthesis models: » Combine theories of physical stellar proerties: mass loss, spectral output, plasma/gas dynamics &c. » Different options to cover most types of conditions: user-chosen » Outputs projected observable data Leitherer et al. “Starburst99” program: » Simulates evolution of single GMC » Input plausible parameters for nearby spirals » Outputs photometry & spectral data Metallicity Proportion of star made from “metals” »Big Bang cosmology forms H, He in early universe »All heavier elements formed in starsmetals Negligible change over model lifetime (Leitherer 97) »Metals returned to ISM by supernovae · Few SNe within 50Myr · Only returned to local region Initial Mass Function IMF: total number of stars of a certain mass range initially created per unit volume » “Determines the evolution, surface brightness, chemical enrichment, and baryonic content of galaxies” (Chabrier) Simple power law: dN/dm m-α » Different indices depending on mass » High mass stars hottest → most luminous → easiest to observe → distribution best understood Salpeter (1955): canonical IMF: α = 2.35 Kroupa (1997): accounts for underabundance of low-mass stars in Salpeter α= Evolutionary Mass-Loss Tracks “Stellar thermostat” : pressure vs gravity » Large star = weak surface gravity → outer layers loosely held → puff off as star ages Path on H-R diagram forms “mass loss track”: » Mass, luminosity, temperature changes over star's lifetime 2 main models about precise behaviour of star: » Geneva track » Padova track Converting data to flux ratio SB99 does not directly output flux ratio » Must be inferred from simulated observable data... » ...converted to a standard set of units » ...then normalised to match directly-measured real data Results Conclusions Model results consistent = insensitive to parameters Ages reliable Zero-age flux ratio: » Discriminator between models » Eliminate extreme models? Flux ratio calibration: » Very sensitive to zero-age flux: currently assume youngest stars <2Myr Further discrimination requires independent age data Further Research Age maps » Narrow escape fraction uncertainty: currently 0-50% (!) » Use truncated IMF: reduces stars >30M Acknowledgements and References Supervisor: Dr. John O'Byrne Based on Hons. Thesis by and advice from Madhura Killedar References (except where cited): » Flux ratio, SB99, converting to flux: Killedar, M. 2006; Mapping ages by » » » determining the H-alpha to UV flux ratio; Sydney University Metallicity: Murphy, T. 2007; Galactic Recycling lecture for PHYS1500 17/09/2007 Initial mass function: Chabrier G. 2003; Galactic Stellar and Substellar Initial Mass Function; Publications of the Astronomical Society of the Pacific, vol. 115 pp.763-795 Evolutionary track: various citation of Maeder & Maynet