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 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