2015ApJ...806..198W


C.D.S. - SIMBAD4 rel 1.7 - 2020.01.21CET17:48:33

2015ApJ...806..198W - Astrophys. J., 806, 198 (2015/June-3)

The high-mass stellar initial mass function in M31 clusters.

WEISZ D.R., JOHNSON L.C., FOREMAN-MACKEY D., DOLPHIN A.E., BEERMAN L.C., WILLIAMS B.F., DALCANTON J.J., RIX H.-W., HOGG D.W., FOUESNEAU M., JOHNSON B.D., BELL E.F., BOYER M.L., GOULIERMIS D., GUHATHAKURTA P., KALIRAI J.S., LEWIS A.R., SETH A.C. and SKILLMAN E.D.

Abstract (from CDS):

We have undertaken the largest systematic study of the high-mass stellar initial mass function (IMF) to date using the optical color-magnitude diagrams (CMDs) of 85 resolved, young (4 Myr < t < 25 Myr), intermediate mass star clusters (103-104 M), observed as part of the Panchromatic Hubble Andromeda Treasury program. We fit each cluster's CMD to measure its mass function (MF) slope for stars ≳2 M. By modeling the ensemble of clusters, we find the distribution of MF slopes is best described by Γ = +1.45–0.06+0.03 with a very small intrinsic scatter and no drastic outliers. This model allows the MF slope to depend on cluster mass, size, and age, but the data imply no significant dependencies within this regime of cluster properties. The lack of an age dependence suggests that the MF slope has not significantly evolved over the first ∼25 Myr and provides direct observational evidence that the measured MF represents the IMF. Taken together, this analysis–based on an unprecedented large sample of young clusters, homogeneously constructed CMDs, well-defined selection criteria, and consistent principled modeling–implies that the high-mass IMF slope in M31 clusters is universal. The IMF has a slope (Γ = +1.45–0.06+0.03; statistical uncertainties) that is slightly steeper than the canonical Kroupa (+1.30) and Salpeter (+1.35) values, and our measurement of it represents a factor of ∼20 improvement in precision over the Kroupa IMF (+1.30±0.7). Using our inference model on select Milky Way (MW) and LMC high-mass IMF studies from the literature, we find ΓMW ∼ +1.15 ± 0.1 and ΓLMC ∼ +1.3 ± 0.1, both with intrinsic scatter of ∼0.3-0.4 dex. Thus, while the high-mass IMF in the Local Group may be universal, systematics in the literature of IMF studies preclude any definitive conclusions; homogenous investigations of the high-mass IMF in the local universe are needed to overcome this limitation. Consequently, the present study represents the most robust measurement of the high-mass IMF slope to date. To facilitate practical use over the full stellar mass spectrum, we have grafted the M31 high-mass IMF slope onto widely used sub-solar mass Kroupa and Chabrier IMFs. The increased steepness in the M31 high-mass IMF slope implies that commonly used UV- and Hα-based star formation rates should be increased by a factor of ∼1.3-1.5 and the number of stars with masses > 8 M is ∼25% fewer than expected for a Salpeter/Kroupa IMF.

Abstract Copyright:

Journal keyword(s): galaxies: star clusters: general - galaxies: star formation - Hertzsprung-Russell and C-M diagrams - Local Group - stars: luminosity function, mass function

Simbad objects: 45

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Number of rows : 45

N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2020
#notes
1 M 31 G 00 42 44.330 +41 16 07.50 4.86 4.36 3.44     ~ 10670 1
2 Bol D89 GlC 00 43 01.331 +41 26 24.03 19.85   18.90   18.32 ~ 14 1
3 [JSD2015] AP 98 Cl* 00 43 37.190 +41 10 29.22 17.42       16.93 ~ 4 0
4 [JSD2015] AP 390 Cl* 00 43 38.779 +41 22 50.61 16.49       16.76 ~ 3 0
5 [JSD2015] AP 285 Cl* 00 43 47.039 +41 12 37.94 15.40       16.76 ~ 3 0
6 [JSD2015] AP 552 Cl* 00 43 51.152 +41 25 00.93 15.03       16.94 ~ 3 0
7 KHM31 191 Cl* 00 44 01.974 +41 39 03.34 18.73 18.41 18.24   18.75 ~ 6 0
8 [JSD2015] AP 447 Cl* 00 44 18.255 +41 20 05.86 17.64       16.90 ~ 3 0
9 [JSD2015] AP 403 Cl* 00 44 25.14 +41 20 49.8 15.28 15.84 15.56 15.39 15.77 ~ 6 1
10 [JSD2012] PC 1152 Cl* 00 44 29.032 +41 51 31.05 17.81       16.96 ~ 5 0
11 M31GC J004435+415328 GlC 00 44 34.80 +41 53 27.2 17.35 17.74 18.32   17.15 ~ 21 1
12 [JSD2015] AP 431 Cl* 00 44 51.281 +41 29 25.35 16.47       17.41 ~ 4 0
13 [JSD2012] PC 961 Cl* 00 44 52.892 +41 54 06.33 19.04       17.52 ~ 5 0
14 [JSD2015] AP 462 Cl* 00 45 30.309 +41 46 23.91 18.31       17.73 ~ 4 0
15 [JSD2015] AP 522 Cl* 00 46 32.913 +42 12 35.77 15.91       17.23 ~ 4 0
16 [JSD2012] PC 74 Cl* 00 46 34.493 +42 11 24.38 15.73       16.82 ~ 4 0
17 NAME NGC 869/884 OpC 02 20.5 +57 08           ~ 49 0
18 IC 1805 OpC 02 32 42 +61 27.0   7.03 6.5     ~ 468 2
19 NGC 1747 As* 04 55 11 -67 10.7   9.41 9.37     ~ 24 1
20 NGC 1761 As* 04 56 39 -66 29.0     9.94     ~ 96 0
21 NGC 1763 As* 04 56 51.5 -66 24 25     9.40     ~ 153 3
22 NGC 1871 As* 05 13 52.360 -67 27 19.88   10.21 10.09     ~ 35 0
23 NGC 1935 As* 05 21 58 -67 57.3           ~ 101 0
24 NGC 1937 As* 05 22 29 -67 53.7           ~ 42 1
25 NGC 1893 OpC 05 22 44 +33 24.7   7.90 7.5     ~ 227 0
26 NAME LMC G 05 23 34.6 -69 45 22     0.4     ~ 14469 1
27 LH 58 As* 05 26 45 -68 49.9   7.97 7.96     ~ 55 0
28 LH 73 As* 05 32 01 -68 40.9           ~ 16 0
29 LH 83 As* 05 35 34 -66 03.0           ~ 40 1
30 RMC 136 Cl* 05 38 42.396 -69 06 03.36   9.63 9.50     ~ 1689 2
31 LH 114 As* 05 43 18 -67 51.5     11.32     ~ 35 0
32 NGC 2122 As* 05 48 55 -70 04.1     10.43     ~ 90 0
33 LH 118 As* 05 49 33 -70 06.3           ~ 44 0
34 NGC 2244 OpC 06 31 55 +04 56.5   5.26 4.8     ~ 559 4
35 Cl Trumpler 14 OpC 10 43 56 -59 33.0   5.70 5.5     ~ 418 0
36 Cl Trumpler 16 OpC 10 45 10 -59 43.0   5.35 5.0     ~ 417 0
37 M 16 OpC 18 18 48 -13 48.4   6.58 6.0     ~ 923 2
38 NGC 6823 OpC 19 43 09 +23 18.0   7.71 7.1     ~ 247 2
39 NGC 6871 OpC 20 05 59 +35 46.6   5.43 5.2     ~ 193 0
40 Cl Berkeley 86 OpC 20 20 12 +38 41.4   8.66 7.9     ~ 102 0
41 M 29 OpC 20 23 56 +38 31.4   7.30 6.6     ~ 217 0
42 Ass Cyg OB 2 As* 20 33.2 +41 19           ~ 768 0
43 NGC 7280 GiP 22 26 27.5777963451 +16 08 53.429262697   13.6       ~ 145 0
44 Ass Cep OB 5 As* 23 02 16 +57 01.3           ~ 18 1
45 NAME Local Group GrG ~ ~           ~ 6761 0

    Equat.    Gal    SGal    Ecl

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2020.01.21-17:48:33

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