Evidence for a nonuniform initial mass function in the local universe

Gerhardt R. Meurer; O. I. Wong; J. H. Kim; D. J. Hanish; T. M. Heckman; J. Werk; J. Bland-Hawthorn; M. A. Dopita; M. A. Zwaan; B. Koribalski; M. Seibert; D. A. Thilker; H. C. Ferguson; R. L. Webster; M. E. Putman; P. M. Knezek; M. T. Doyle; M. J. Drinkwater; C. G. Hoopes; V. A. Kilborn; M. Meyer; E. V. Ryan-Weber; R. C. Smith; L. Staveley-Smith

doi:10.1088/0004-637X/695/1/765

Evidence for a nonuniform initial mass function in the local universe

Gerhardt R. Meurer^*, O. I. Wong, J. H. Kim, D. J. Hanish, T. M. Heckman, J. Werk, J. Bland-Hawthorn, M. A. Dopita, M. A. Zwaan, B. Koribalski, M. Seibert, D. A. Thilker, H. C. Ferguson, R. L. Webster, M. E. Putman, P. M. Knezek, M. T. Doyle, M. J. Drinkwater, C. G. Hoopes, V. A. KilbornM. Meyer, E. V. Ryan-Weber, R. C. Smith, L. Staveley-Smith

^*Corresponding author for this work

Research output: Contribution to journal › Article › peer-review

228 Citations (Scopus)

Abstract

Many of the results in modern astrophysics rest on the notion that the initial mass function (IMF) is universal. Our observations of a sample of H i selected galaxies in the light of Hα and the far-ultraviolet (FUV) challenge this result. The extinction-corrected flux ratio F_Hα/ f_FUV from these two tracers of star formation shows strong correlations with the surface brightness in Hα and the R band: low surface brightness (LSB) galaxies have lower F_Hα/f_FUV ratios compared to high surface brightness galaxies as well as compared to expectations from equilibrium models of constant star formation rate (SFR) using commonly favored IMF parameters. Weaker but significant correlations of F _Hα/f_FUV with luminosity, rotational velocity, and dynamical mass as well as a systematic trend with morphology, are found. The correlated variations of F_Hα/f_FUV with other global parameters are thus part of the larger family of galaxy scaling relations. The F_Hα/f_FUV correlations cannot be due to residual extinction correction errors, while systematic variations in the star formation history (SFH) cannot explain the trends with both Hα and R surface brightness nor with other global properties. The possibility that LSB galaxies have a higher escape fraction of ionizing photons seems inconsistent with their high gas fraction, and observations of color-magnitude diagrams (CMDs) of a few systems which indicate a real deficit of O stars. The most plausible explanation for the correlations is the systematic variations of the upper mass limit M_u and/or the slope γ which define the upper end of the IMF. We outline a scenario of pressure driving the correlations by setting the efficiency of the formation of the dense star clusters where the highest mass stars preferentially form. Our results imply that the SFR measured in a galaxy is highly sensitive to the tracer used in the measurement. A nonuniversal IMF would also call into question the interpretation of metal abundance patterns in dwarf galaxies as well as SFHs derived from CMDs.

Original language	English
Pages (from-to)	765-780
Number of pages	16
Journal	Astrophysical Journal
Volume	695
Issue number	1
DOIs	https://doi.org/10.1088/0004-637X/695/1/765
Publication status	Published - 10 Apr 2009

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Meurer, G. R., Wong, O. I., Kim, J. H., Hanish, D. J., Heckman, T. M., Werk, J., Bland-Hawthorn, J., Dopita, M. A., Zwaan, M. A., Koribalski, B., Seibert, M., Thilker, D. A., Ferguson, H. C., Webster, R. L., Putman, M. E., Knezek, P. M., Doyle, M. T., Drinkwater, M. J., Hoopes, C. G., ... Staveley-Smith, L. (2009). Evidence for a nonuniform initial mass function in the local universe. Astrophysical Journal, 695(1), 765-780. https://doi.org/10.1088/0004-637X/695/1/765

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title = "Evidence for a nonuniform initial mass function in the local universe",

abstract = "Many of the results in modern astrophysics rest on the notion that the initial mass function (IMF) is universal. Our observations of a sample of H i selected galaxies in the light of Hα and the far-ultraviolet (FUV) challenge this result. The extinction-corrected flux ratio FHα/ fFUV from these two tracers of star formation shows strong correlations with the surface brightness in Hα and the R band: low surface brightness (LSB) galaxies have lower FHα/fFUV ratios compared to high surface brightness galaxies as well as compared to expectations from equilibrium models of constant star formation rate (SFR) using commonly favored IMF parameters. Weaker but significant correlations of F Hα/fFUV with luminosity, rotational velocity, and dynamical mass as well as a systematic trend with morphology, are found. The correlated variations of FHα/fFUV with other global parameters are thus part of the larger family of galaxy scaling relations. The FHα/fFUV correlations cannot be due to residual extinction correction errors, while systematic variations in the star formation history (SFH) cannot explain the trends with both Hα and R surface brightness nor with other global properties. The possibility that LSB galaxies have a higher escape fraction of ionizing photons seems inconsistent with their high gas fraction, and observations of color-magnitude diagrams (CMDs) of a few systems which indicate a real deficit of O stars. The most plausible explanation for the correlations is the systematic variations of the upper mass limit Mu and/or the slope γ which define the upper end of the IMF. We outline a scenario of pressure driving the correlations by setting the efficiency of the formation of the dense star clusters where the highest mass stars preferentially form. Our results imply that the SFR measured in a galaxy is highly sensitive to the tracer used in the measurement. A nonuniversal IMF would also call into question the interpretation of metal abundance patterns in dwarf galaxies as well as SFHs derived from CMDs.",

keywords = "Galaxies: ISM, Galaxies: stellar content, Stars: formation, Stars: luminosity function, mass function",

author = "Meurer, {Gerhardt R.} and Wong, {O. I.} and Kim, {J. H.} and Hanish, {D. J.} and Heckman, {T. M.} and J. Werk and J. Bland-Hawthorn and Dopita, {M. A.} and Zwaan, {M. A.} and B. Koribalski and M. Seibert and Thilker, {D. A.} and Ferguson, {H. C.} and Webster, {R. L.} and Putman, {M. E.} and Knezek, {P. M.} and Doyle, {M. T.} and Drinkwater, {M. J.} and Hoopes, {C. G.} and Kilborn, {V. A.} and M. Meyer and Ryan-Weber, {E. V.} and Smith, {R. C.} and L. Staveley-Smith",

year = "2009",

month = apr,

day = "10",

doi = "10.1088/0004-637X/695/1/765",

language = "English",

volume = "695",

pages = "765--780",

journal = "Astrophysical Journal",

issn = "0004-637X",

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Meurer, GR, Wong, OI, Kim, JH, Hanish, DJ, Heckman, TM, Werk, J, Bland-Hawthorn, J, Dopita, MA, Zwaan, MA, Koribalski, B, Seibert, M, Thilker, DA, Ferguson, HC, Webster, RL, Putman, ME, Knezek, PM, Doyle, MT, Drinkwater, MJ, Hoopes, CG, Kilborn, VA, Meyer, M, Ryan-Weber, EV, Smith, RC & Staveley-Smith, L 2009, 'Evidence for a nonuniform initial mass function in the local universe', Astrophysical Journal, vol. 695, no. 1, pp. 765-780. https://doi.org/10.1088/0004-637X/695/1/765

TY - JOUR

T1 - Evidence for a nonuniform initial mass function in the local universe

AU - Meurer, Gerhardt R.

AU - Wong, O. I.

AU - Kim, J. H.

AU - Hanish, D. J.

AU - Heckman, T. M.

AU - Werk, J.

AU - Bland-Hawthorn, J.

AU - Dopita, M. A.

AU - Zwaan, M. A.

AU - Koribalski, B.

AU - Seibert, M.

AU - Thilker, D. A.

AU - Ferguson, H. C.

AU - Webster, R. L.

AU - Putman, M. E.

AU - Knezek, P. M.

AU - Doyle, M. T.

AU - Drinkwater, M. J.

AU - Hoopes, C. G.

AU - Kilborn, V. A.

AU - Meyer, M.

AU - Ryan-Weber, E. V.

AU - Smith, R. C.

AU - Staveley-Smith, L.

PY - 2009/4/10

Y1 - 2009/4/10

N2 - Many of the results in modern astrophysics rest on the notion that the initial mass function (IMF) is universal. Our observations of a sample of H i selected galaxies in the light of Hα and the far-ultraviolet (FUV) challenge this result. The extinction-corrected flux ratio FHα/ fFUV from these two tracers of star formation shows strong correlations with the surface brightness in Hα and the R band: low surface brightness (LSB) galaxies have lower FHα/fFUV ratios compared to high surface brightness galaxies as well as compared to expectations from equilibrium models of constant star formation rate (SFR) using commonly favored IMF parameters. Weaker but significant correlations of F Hα/fFUV with luminosity, rotational velocity, and dynamical mass as well as a systematic trend with morphology, are found. The correlated variations of FHα/fFUV with other global parameters are thus part of the larger family of galaxy scaling relations. The FHα/fFUV correlations cannot be due to residual extinction correction errors, while systematic variations in the star formation history (SFH) cannot explain the trends with both Hα and R surface brightness nor with other global properties. The possibility that LSB galaxies have a higher escape fraction of ionizing photons seems inconsistent with their high gas fraction, and observations of color-magnitude diagrams (CMDs) of a few systems which indicate a real deficit of O stars. The most plausible explanation for the correlations is the systematic variations of the upper mass limit Mu and/or the slope γ which define the upper end of the IMF. We outline a scenario of pressure driving the correlations by setting the efficiency of the formation of the dense star clusters where the highest mass stars preferentially form. Our results imply that the SFR measured in a galaxy is highly sensitive to the tracer used in the measurement. A nonuniversal IMF would also call into question the interpretation of metal abundance patterns in dwarf galaxies as well as SFHs derived from CMDs.

AB - Many of the results in modern astrophysics rest on the notion that the initial mass function (IMF) is universal. Our observations of a sample of H i selected galaxies in the light of Hα and the far-ultraviolet (FUV) challenge this result. The extinction-corrected flux ratio FHα/ fFUV from these two tracers of star formation shows strong correlations with the surface brightness in Hα and the R band: low surface brightness (LSB) galaxies have lower FHα/fFUV ratios compared to high surface brightness galaxies as well as compared to expectations from equilibrium models of constant star formation rate (SFR) using commonly favored IMF parameters. Weaker but significant correlations of F Hα/fFUV with luminosity, rotational velocity, and dynamical mass as well as a systematic trend with morphology, are found. The correlated variations of FHα/fFUV with other global parameters are thus part of the larger family of galaxy scaling relations. The FHα/fFUV correlations cannot be due to residual extinction correction errors, while systematic variations in the star formation history (SFH) cannot explain the trends with both Hα and R surface brightness nor with other global properties. The possibility that LSB galaxies have a higher escape fraction of ionizing photons seems inconsistent with their high gas fraction, and observations of color-magnitude diagrams (CMDs) of a few systems which indicate a real deficit of O stars. The most plausible explanation for the correlations is the systematic variations of the upper mass limit Mu and/or the slope γ which define the upper end of the IMF. We outline a scenario of pressure driving the correlations by setting the efficiency of the formation of the dense star clusters where the highest mass stars preferentially form. Our results imply that the SFR measured in a galaxy is highly sensitive to the tracer used in the measurement. A nonuniversal IMF would also call into question the interpretation of metal abundance patterns in dwarf galaxies as well as SFHs derived from CMDs.

KW - Galaxies: ISM

KW - Galaxies: stellar content

KW - Stars: formation

KW - Stars: luminosity function, mass function

UR - http://www.scopus.com/inward/record.url?scp=70349339504&partnerID=8YFLogxK

U2 - 10.1088/0004-637X/695/1/765

DO - 10.1088/0004-637X/695/1/765

M3 - Article

SN - 0004-637X

VL - 695

SP - 765

EP - 780

JO - Astrophysical Journal

JF - Astrophysical Journal

IS - 1

ER -

Evidence for a nonuniform initial mass function in the local universe

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