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J/A+A/509/A61    Long slit spectroscopy in M31             (Saglia+, 2010)

The old and heavy bulge of M31. I. Kinematics and stellar populations. Saglia R.P., Fabricius M., Bender R., Montalto M., Lee C.-H., Riffeser A., Seitz S., Morganti L., Gerhard O., Hopp U. <Astron. Astrophys. 509, A61 (2010)> =2010A&A...509A..61S
ADC_Keywords: Galaxies, nearby ; Radial velocities ; Equivalent widths Keywords: galaxies: kinematics and dynamics - galaxies: individual: M31 - galaxies: stellar content Abstract: We present new optical long-slit data along six position angles of the bulge region of M31. We derive accurate stellar and gas kinematics reaching 5-arcmin from the center, where the disk light contribution is always less than 30%, and out to 8-arcmin along the major axis, where the disk provides 55% of the total light. We show that the velocity dispersions of McElroy (1983ApJ...270..485M) are severely underestimated (by up to 50km/s). As a consequence, previous dynamical models have underestimated the stellar mass of M31's bulge by a factor of 2. As a further consequence, the light-weighted velocity dispersion of the galaxy grows to 166km/s and to 170km/s if rotation is also taken into account, thus reducing the discrepancy between the predicted and measured mass of the black hole at the center of M31 from a factor of 3 to a factor of 2. The kinematic position angle varies with distance, pointing to triaxiality, but a quantitative conclusion can be reached only after simultaneous proper dynamical modeling of the bulge and disk components is performed. We detect gas counter-rotation near the bulge minor axis. We measure eight emission-corrected Lick indices. They are approximately constant on circles. Using simple stellar population models we derive the age, metallicity and α-element overabundance profiles. Except for the region in the inner arcsecs of the galaxy, the bulge of M31 is uniformly old (≥12Gyr, with many best-fit ages at the model grid limit of 15Gyr), slightly α-elements overabundant ([α/Fe]∼0.2) and of solar metallicity, in agreement with studies of the resolved stellar components. The predicted u-g, g-r and r-i Sloan color profiles match the dust-corrected observations reasonably well, within the known limitations of current simple stellar population models. The stellar populations have approximately radially constant mass-to-light ratios (M/LR∼4-4.5M/L☉_ for a Kroupa IMF), which is in agreement with the stellar dynamical estimates based on our new velocity dispersions. In the inner arcsecs the luminosity-weighted age drops to 4-8Gyr, while the metallicity increases to above three times the solar value. Starting from 6-arcmin from the center along the major axis, the mean age drops to ≥8Gyr with slight supersolar metallicity (~+0.1dex) and α-element overabundance (~+0.2dex) for a mass-to-light ratio M/LR<=3M/L☉_. Diagnostic diagrams based on the [OIII]/Hβ and [NI]Hβ emission line equivalent widths (EWs) ratios indicate that the gas is ionized by shocks outside 10-arcsec, but an AGN-like ionizing source could be present near the center. We speculate that a gas-rich minor merger happened some 100Myr ago, causing the observed minor axis gas counter-rotation, the recent star formation event and possibly some nuclear activity. Description: The stellar and gas kinematics (Table 2), the equivalent widths of the Hβ gas emission line, plus the EW ratios [OIII]/Hβ and [NI]/NI (Table 3), and the Lick absorption line strength indices (Table 4) of the bulge of M31 presented here have been measured from spectra taken with the Hobby-Eberly Telescope and the Low Resolution Spectrograph. We observed at six position angles, with a slit width of 1.5-arcsec, a spectral resolution of sigma=57km/s and covering the spectral range 4787-5857Å, with seeing values between 1.4 and 2.5-arcsec. Objects: ---------------------------------------------------------- RA (2000) DE Designation(s) ---------------------------------------------------------- 00 42 44.3 +41 16 09 M31 = Andromeda galaxy ---------------------------------------------------------- File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table1.dat 55 24 Log of the observations table2.dat 53 478 Stellar kinematics along 6 position angles table3.dat 70 478 Gas kinematics and emission equivalent width and ratios along 6 position angles table4.dat 128 478 Lick indices along 6 position angles
Byte-by-byte Description of file: table1.dat
Bytes Format Units Label Explanations
1- 10 A10 "YYYY/MM/DD" Date Observation date 12- 18 A7 --- PAc Position angle code 20- 22 I3 deg PA Corresponding position angle 24- 27 F4.2 arcsec Seeing ? FWHM of seeing 29- 55 A27 --- Com Comments
Byte-by-byte Description of file: table2.dat
Bytes Format Units Label Explanations
1- 6 F6.1 arcsec R Distance from the center, positive East (G1) 8- 10 A3 --- PAc Position angle code (see Table 1) (G2) 12- 17 F6.1 km/s RV Stellar radial velocity, positive receiding (G3) 19- 21 F3.1 km/s e_RV Error on stellar radial velocity 23- 27 F5.1 km/s sigma Stellar velocity dispersion 29- 31 F3.1 km/s e_sigma Error on stellar velocity dispersion 33- 37 F5.2 --- h3 3rd order Hermite coefficient 39- 42 F4.2 --- e_h3 Error on 3rd order Hermite coefficient 44- 48 F5.2 --- h4 4th order Hermite coefficient 50- 53 F4.2 --- e_h4 Error on 4th order Hermite coefficient
Byte-by-byte Description of file: table3.dat
Bytes Format Units Label Explanations
1- 6 F6.1 arcsec R Distance from the center, positive East (G1) 8- 10 A3 --- PAc Position angle (see Table 1) (G2) 12- 17 F6.1 km/s Vgas Gas radial velocity, positive receiding (G3) 19- 23 F5.1 km/s e_Vgas ?=999.9 Error on gas radial velocity (1) 25- 29 F5.1 km/s sgas Gas velocity dispersion 31- 35 F5.1 km/s e_sgas ?=999.9 Error on gas velocity dispersion (1) 38- 41 F4.2 0.1nm Hbe Equivalent width (EW) of Hβ gas emission 43- 46 F4.2 0.1nm e_Hbe Error on EW of the Hβ gas emission 48- 52 F5.1 --- O/H ?=999.9 Ratio [OIII]/Hbeta of the gas emission equivalent widths (2) 54- 58 F5.1 --- e_O/H ?=999.9 Error on O/H (1) 60- 64 F5.1 --- N/H ?=999.9 Ratio [NI]/Hbeta of the gas emission equivalent widths (2) 66- 70 F5.1 --- e_N/H ?=999.9 Error on N/H (1)
Note (1): data with errors 999.9 are not reliable Note (2): ratios larger than 999.9 are given the value 999.9
Byte-by-byte Description of file: table4.dat
Bytes Format Units Label Explanations
1- 6 F6.1 arcsec R Distance from the center, positive East (G1) 8- 10 A3 --- PAc Position angle (see Table 1) (G2) 12- 15 F4.2 0.1nm Hbeta Hβ line strength 18- 21 F4.2 0.1nm e_Hbeta Error on the Hβ line strength 26- 29 F4.2 0.1nm Mgb Mgb line strength 32- 35 F4.2 0.1nm e_Mgb Error on the Mgb line strength 38- 41 F4.2 0.1nm Fe5015 Fe5015 line strength 45- 48 F4.2 0.1nm e_Fe5015 Error on the Fe5015 line strength 54- 57 F4.2 0.1nm Fe5270 Fe5270 line strength 61- 64 F4.2 0.1nm e_Fe5270 Error on the Fe5270 line strength 70- 73 F4.2 0.1nm Fe5335 Fe5335 line strength 77- 80 F4.2 0.1nm e_Fe5335 Error on the Fe5335 line strength 86- 89 F4.2 0.1nm Fe5406 Fe5406 line strength 93- 96 F4.2 0.1nm e_Fe5406 Error on the Fe5406 line strength 102-105 F4.2 0.1nm Fe5709 Fe5709 line strength 109-112 F4.2 0.1nm e_Fe5709 Error on the Fe5709 line strength 118-121 F4.2 0.1nm Fe5782 Fe5782 line strength 125-128 F4.2 0.1nm e_Fe5782 Error on the Fe5782 line strength
Global notes: Note (G1): the MN slit data (PA=138) with |R|>100arcsec are not aligned with the center (see paper), but R is given as if no shift was present. Note (G2): Position angles codes are given in table1; these orientations are also illustrated in Fig.1 of the paper Note (G3): relative to the center and with symmetrization shifts applied (see paper).
Acknowledgements: Roberto Saglia, saglia(at)mpe.mpg.de History: * 12-Nov-2009: Original version * 28-Mar-2010: 'R' parameter could vary of ±0.1arcsec in table3 and table4 compared to table2; R values were homogenized.
(End) Roberto Saglia [MPE, Germany], Patricia Vannier [CDS] 12-Nov-2009
The document above follows the rules of the Standard Description for Astronomical Catalogues.From this documentation it is possible to generate f77 program to load files into arrays or line by line

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