Evidence for a Nonuniversal Stellar Initial Mass Function from the Integrated Properties of SDSS Galaxies

By E. Hoversten, Karl Glazebrook. 2007

138 citations recorded by the source corpus.

This paper revisits the classical Kennicutt method for inferring the stellar IMF from the integrated light properties of galaxies. The large-size, uniform high-quality data set from the SDSS DR4 is combined with more in-depth modeling and quantitative statistical analysis to search for systematic IMF variations as a function of galaxy luminosity. Galaxy Hα equivalent widths are compared to a broadband color index to constrain the IMF. This parameter space is useful for breaking degeneracies that are traditionally problematic. Age and dust corrections are largely orthogonal to IMF variations. In addition, the effects of metallicity and smooth SFH e-folding times are small compared to IMF variations. We find that for the sample as a whole the best-fitting IMF slope above 0.5 M☉ is Γ = 1.4535, with a negligible random error of ±0.0004 and a systematic error of ±0.1. Galaxies brighter than around Mr,0.1 = − 20 (including galaxies like the Milky Way, which has Mr,0.1 ∼ − 21) are well fitted by a universal Γ ∼ 1.4 IMF, similar to Salpeter, and smooth, exponential SFHs. Fainter galaxies prefer steeper IMFs, and the quality of the fits reveals that for these galaxies a universal IMF with smooth SFHs is actually a poor assumption. Several sources of sample bias are ruled out as the cause of these luminosity-dependent IMF variations. Analysis of bursting SFH models shows that an implausible coordination of burst times is required to fit a universal IMF to the Mr,0.1 = − 17 galaxies. This leads to the conclusions that the IMF in low-luminosity galaxies has fewer massive stars, by either steeper slope or lower upper mass cutoff, and is not universal.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/15a6d7772285f6358ebe5a798557eabe1a5863d4

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In Astronomy and Astrophysics

1. M. Cappellari
2. P. Hopkins
3. L. Hernquist
4. C. Conroy
5. T. Naab
6. R. Somerville
7. R. Dav'e
8. Simon D. M. White

In Instrumentation

1. M. Cappellari
2. P. Hopkins
3. T. Naab
4. L. Hernquist
5. C. Conroy
6. M. Sarzi
7. Simon D. M. White
8. Eric Emsellem

Citations in the corpus

• Galaxies as simple dynamical systems: observational data disfavor dark matter and stochastic star formation (2014, background): “Test VII: Multiphotometric-band surveys of thousands of late-type galaxies by independently working teams have uncovered strong evidence of a systematic change of the galaxy-wide IMF with increasing galaxy mass and increasing SFR [297–299, 307].”
• MODELING THE EXTRAGALACTIC BACKGROUND LIGHT FROM STARS AND DUST (2009, background): “…radiative feedback could lead to a universal IMF in the local universe (Bate 2009), a detailed modeling of a large amount of Sloan Digital Sky Survey data indicates that fainter galaxies generally have an IMF which produces fewer massive stars than brighter galaxies (Hoversten & Glazebrook 2008).”
• A Universal Stellar Initial Mass Function? A critical look at variations in extreme environments (2010, methodology): “Hoversten & Glazebrook (2008) estimated the index of the stellar mass function for ∼ 105 galaxies with SDSS photometry and spectroscopy, by comparing each galaxy’s broadband SDSS colors with its Hα equivalent width6.”
• A CATALOG OF BULGE, DISK, AND TOTAL STELLAR MASS ESTIMATES FOR THE SLOAN DIGITAL SKY SURVEY (2013, background): “…IMF locally (Kroupa 2001), over the past several years there has been mounting evidence for systematic variation of the stellar IMF as a function of galaxy properties (e.g., Cenarro et al. 2003; Hoversten & Glazebrook 2008; van Dokkum & Conroy 2010; Gunawardhana et al. 2011; Dutton et al. 2012).”
• The stellar and sub-stellar IMF of simple and composite populations (2011, background): “Additionally, Hoversten & Glazebrook (2008) found, in the integrated properties of over 50000 SDSS galaxies, that galaxies of lower mass seem to have steeper IMFs than more massive ones, as would be expected from the IGIMF.”
• The role of cold gas and environment on the stellar mass-metallicity relation of nearby galaxies (2012, background): “…has been the focus of recent debate; a few studies have found indirect observational evidence that the IMF may not be universal and instead vary as a function of stellar mass, star formation activity or gas column density (e.g. Lee et al. 2004; Hoversten & Glazebrook 2008; Meurer et al. 2009).”
• The big problems in star formation: The star formation rate, stellar clustering, and the initial mass function (2014, background): “…rates show systematic deficiencies in the amount of Hα they produce per unit far ultraviolet (FUV) emission (Boissier et al. 2007; Lee et al. 2009; Boselli et al. 2009; Meurer et al. 2009), and systematically low Hα equivalent widths (Hoversten & Glazebrook 2008; Gunawardhana et al. 2011).”
• On the galaxy stellar mass function, the mass-metallicity relation, and the implied baryonic mass function (2008, background): “…derived stellar masses relative to the Kroupa IMF at SSP colours evaluated over the range of 0.2–0.85 in g − r. [If the IMF varied with galaxy luminosity (Hoversten & Glazebrook 2008), over time (Davé 2008; van Dokkum 2008) and/or in star bursts (Fardal et al. 2007), this would clearly…”
• Galaxy and Mass Assembly (GAMA): the star formation rate dependence of the stellar initial mass function (2011, methodology): “A number of recent studies now suggest an evolving or spatially varying IMF as a ‘last resort’ explanation to reconcile the observed differences (Hoversten & Glazebrook 2008; Wilkins, Trentham & Hopkins 2008b; Wilkins et al. 2008a; van Dokkum 2008; Meurer et al. 2009).”
• THE MASS–METALLICITY AND LUMINOSITY–METALLICITY RELATIONS FROM DEEP2 AT z ∼ 0.8 (2010, methodology): “Indirect evidences for variations in the local IMF have been provided by the comparison of Hα emission to the far-ultraviolet flux (Meurer et al. 2009) and the Hα flux to broadband color index (Hoversten & Glazebrook 2008).”
• The ATLAS3D project – XX. Mass–size and mass–σ distributions of early-type galaxies: bulge fraction drives kinematics, mass-to-light ratio, molecular gas fraction and stellar initial mass function (2012, result): “Using this technique, Hoversten & Glazebrook (2008) inferred a variation of the IMF with more massive galaxies having a more top-heavy IMF than Salpeter, a result confirmed under the same assumptions (Gunawardhana et al. 2011) by the Galaxy and Mass Assembly (GAMA) survey (Driver et al. 2011).”