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J/AJ/132/271        SFR of M31 from resolved stars in near-IR    (Olsen+, 2006)

The star formation histories of the bulge and disk of M31 from resolved stars in the near-infrared. Olsen K.A.G., Blum R.D., Stephens A.W., Davidge T.J., Massey P., Strom S.E., Rigaut F. <Astron. J., 132, 271-289 (2006)> =2006AJ....132..271O
ADC_Keywords: Galaxies, nearby ; Models, evolutionary Keywords: galaxies: individual (M31) - galaxies: stellar content - instrumentation: adaptive optics - Local Group - techniques: photometric Abstract: We discuss H and K observations of three fields in the bulge and disk of M31 obtained with the ALTAIR adaptive optics system and NIRI instrument on Gemini North. These are the highest resolution and deepest near-infrared observations obtained to date of the inner regions of M31 and demonstrate the promise of ground-based adaptive optics for studying the crowded regions of nearby galaxies. We have combined our observations with previously published Hubble Space Telescope Near-Infrared Camera and Multi-Object Spectrometer observations of nine M31 fields and have derived the coarse star formation histories of M31's bulge and inner disk. From fits to the MK luminosity functions, we find the stellar population mix to be dominated by old, nearly solar-metallicity stars. The old populations, which we define as having age ≥6Gyr, indeed dominate the star formation histories at all radii independent of the relative contributions of bulge and disk stars. Although all of our fields contain some bulge contribution, our results suggest that there is no age difference between the bulge and disk to the limit of our precision. File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table3.dat 115 480 Summary of Luminosity Function Fits
Byte-by-byte Description of file: table3.dat
Bytes Format Units Label Explanations
1- 9 A9 --- ID Solution identifier 11- 13 F3.1 --- AK The K band dust extinction used in model 15- 16 I2 Gyr Age Model age 18- 23 F6.2 solMass/yr Z1e-4 ? Best fit star formation rate for Z=0.0001 25- 28 F4.2 solMass/yr e_Z1e-4 ? Error in Z1e-4 31- 36 F6.2 solMass/yr Z4e-4 ? Best fit star formation rate for Z=0.0004 38- 41 F4.2 solMass/yr e_Z4e-4 ? Error in Z4e-4 44- 49 F6.2 solMass/yr Z1e-3 ? Best fit star formation rate for Z=0.001 51- 54 F4.2 solMass/yr e_Z1e-3 ? Error in Z1e-3 57- 61 F5.2 solMass/yr Z8e-3 ? Best fit star formation rate for Z=0.008 63- 66 F4.2 solMass/yr e_Z8e-3 ? Error in Z8e-3 69- 73 F5.2 solMass/yr Z1.9e-2 ? Best fit star formation rate for Z=0.019 75- 79 F5.2 solMass/yr e_Z1.9e-2 ? Error in Z1.9e-2 82- 86 F5.2 solMass/yr Z3e-2 ? Best fit star formation rate for Z=0.03 88- 92 F5.2 solMass/yr e_Z3e-2 ? Error in Z3e-2 95-101 F7.2 --- chi2 ? Best fit model χ2 value (1) 103-108 F6.2 --- sigma ? Extent that chi2 deviates from model expectation (2) 110-115 F6.3 % Prob ? Probability that chi2 arose by chance (3)
Note (1): Where χ2=2*Sumi(mi-ni+ni*ln(ni/mi)), see text. Note (2): Calculated as (χ2-<χ2>)/σ, where the bracketed quantities are the expected mean and variance of χ2 for each model. Note (3): If the LFs were truly drawn from the given models, then we expect Prob∼50%; low values of Prob are indicative that the models are not good fits.
History: From electronic version of the journal
(End) Greg Schwarz [AAS], Patricia Vannier [CDS] 07-Sep-2007
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