The MASSIVE Survey. XVI. The Stellar Initial Mass Function in the Center of MASSIVE Early-type Galaxies

Journal Article · Mon Jun 20 00:00:00 EDT 2022 · The Astrophysical Journal

DOI:https://doi.org/10.3847/1538-4357/ac69ea· OSTI ID:1983263

Gu, Meng  ^[1]; Greene, Jenny E.  ^[1]; Newman, Andrew B.  ^[2]; Kreisch, Christina  ^[1]; Quenneville, Matthew E.  ^[3]; Ma, Chung-Pei  ^[3]; Blakeslee, John P.  ^[4]

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1. Princeton Univ., NJ (United States)
2. Observatories of the Carnegie Institution for Science, Pasadena, CA (United States)
3. Univ. of California, Berkeley, CA (United States)
4. National Optical-Infrared Astronomy Research (NOIR) Laboratory, Tucson, AZ (United States)

The stellar initial mass function (IMF) is a fundamental property in the measurement of stellar masses and galaxy star formation histories. In this work, we focus on the most massive galaxies in the nearby universe $$\mathrm{log}({M}_{\star }/\,{M}_{\odot })\gt 11.2$$. We obtain high-quality Magellan/LDSS-3 long-slit spectroscopy with a wide wavelength coverage of 0.4–1.01 μm for 41 early-type galaxies (ETGs) in the MASSIVE survey and derive high signal-to-noise spectra within an aperture of R_e/8. Using detailed stellar synthesis models, we constrain the elemental abundances and stellar IMF of each galaxy through full spectral modeling. All the ETGs in our sample have an IMF that is steeper than a Milky Way (Kroupa) IMF. The best-fit IMF mismatch parameter, α_IMF = (M/L)/(M/L)_MW, ranges from 1.1 to 3.1, with an average of $$\langle$$α_IMF$$\rangle$$ = 1.84, suggesting that on average, the IMF is more bottom heavy than Salpeter. Comparing the estimated stellar masses with the dynamical masses, we find that most galaxies have stellar masses that are smaller than their dynamical masses within the 1σ uncertainty. We complement our sample with lower-mass galaxies from the literature and confirm that $$\mathrm{log}({\alpha }_{\mathrm{IMF}})$$ is positively correlated with $$\mathrm{log}(\sigma )$$, $$\mathrm{log}({M}_{\star })$$, and $$\mathrm{log}({M}_{\mathrm{dyn}})$$. From the combined sample, we show that the IMF in the centers of more massive ETGs is more bottom heavy. In addition, we find that $$\mathrm{log}({\alpha }_{\mathrm{IMF}})$$ is positively correlated with both [Mg/Fe] and the estimated total metallicity [Z/H]. We find suggestive evidence that the effective stellar surface density Σ_Kroupa might be responsible for the variation of α_IMF. We conclude that σ, [Mg/Fe], and [Z/H] are the primary drivers of the global stellar IMF variation.

• Research Organization: Oak Ridge Institute for Science and Education (ORISE), Oak Ridge, TN (United States)
• Sponsoring Organization: USDOE Office of Science (SC); National Science Foundation (NSF)
• Contributing Organization: Argonne National Laboratory (ANL); Fermi National Accelerator Laboratory (FNAL); Lawrence Berkeley National Laboratory (LBNL)
• Grant/Contract Number: SC0014664; AST-1815417; AST-1817100
• OSTI ID: 1983263
• Journal Information: The Astrophysical Journal, Vol. 932, Issue 2; ISSN 0004-637X
• Publisher: IOP Publishing
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
Initial mass function
Galaxy evolution
Galaxy formation
Galaxy properties
Galaxy stellar content