Dissecting Galaxies with Quantitative Spectroscopy of the Brightest Stars in the Universe

Abstract

Measuring distances to galaxies, determining their chemical composition, investigating the nature of their stellar populations and the absorbing properties of their interstellar medium are fundamental activities in modern extragalactic astronomy helping to understand the evolution of galaxies and the expanding universe. The optically brightest stars in the universe, blue supergiants of spectral A and B, are unique tools for these purposes. With absolute visual magnitudes up to M_V = -9.5 they are the ideal to obtain accurate quantitative information about galaxies through the powerful modern methods of quantitative stellar spectroscopy. The spectral analyis of individual blue supergiant targets provides invaluable information about chemical abundances and abundance gradients, which is more comprehensive than the one obtained from HII regions, as it includes additional atomic species, and which is also more accurate, since it avoids the systematic uncertainties inherent in the strong line studies usually applied to the HII regions of spiral galaxies beyond the Local Group. Simultaneously, the spectral analysis yields stellar parameters and interstellar extinction for each individual supergiant target, which provides an alternative very accurate way to determine extragalactic distances through a newly developed method, called the Flux-weighted Gravity - Luminosity Relationship (FGLR). With the present generation of 10m-class telescopes these spectroscopic studies can reach out to distances of 10 Mpc. The new generation of 30m-class will allow to extend this work out to 30 Mpc, a substantial volume of the local universe.

Karl Schwarzschild Lecture 2009. To appear in Astronomische Nachrichten

References in corpus (19)

• Wilkinson Microwave Anisotropy Probe (WMAP) Three Year Results: Implications for Cosmology
• Five-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Cosmological Interpretation
• The Hubble Constant: A Summary of the HST Program for the Luminosity Calibration of Type Ia Supernovae by Means of Cepheids
• A new Cepheid distance to the maser-host galaxy NGC 4258 and its implications for the Hubble Constant
• Extragalactic chemical abundances: do HII regions and young stars tell the same story? The case of the spiral galaxy NGC 300
• A cosmic abundance standard: chemical homogeneity of the solar neighbourhood and the ISM dust-phase composition
• The M33 Metallicity Project: Resolving the Abundance Gradient Discrepancies in M33
• Quantitative Spectroscopy of 24 A supergiants in the Sculptor galaxy NGC 300: Flux weighted gravity luminosity relationship, metallicity and metallicity gradient
• The metallicity gradient of M 33: chemical abundances of HII regions
• Cepheid Calibrations of Modern Type Ia Supernovae:Implications for the Hubble Constant
• The Araucaria Project: the Local Group Galaxy WLM--Distance and metallicity from quantitative spectroscopy of blue Supergiants
• Toward a New Distance to the Active Galaxy NGC 4258: II. Centripetal Accelerations and Investigation of Spiral Structure
• Cepheids in external galaxies. I. The maser-host galaxy NGC 4258 and the metallicity dependence of P-L and P-W relations
• Metallicity-corrected Tip of the Red Giant Branch Distance to NGC 4258
• Quantitative spectroscopy of Deneb
• The Araucaria Project. The Distance to the Sculptor Galaxy NGC 247 from Near-Infrared Photometry of Cepheid Variables
• The Araucaria Project. The Distance to the Local Group Galaxy WLM from Near-Infrared Photometry of Cepheid Variables
• Detection of Beat Cepheids in M33 and Their Use as a Probe of the M33 Metallicity Distribution
• Parameters and Winds of Hot Massive Stars

Cited by in corpus (5)

• Testing a Predictive Theoretical Model for the Mass Loss Rates of Cool Stars
• Red Supergiant Stars as Cosmic Abundance Probes: NLTE Effects in J-band Iron and Titanium Lines
• The potential of Red Supergiants as extra-galactic abundance probes at low spectral resolution
• Quantitative spectroscopy of Galactic BA-type supergiants. I. Atmospheric parameters
• Distance and Reddening of the Isolated Dwarf Irregular Galaxy NGC 1156