Radial gradients in initial mass function sensitive absorption features in the Coma brightest cluster galaxies

Abstract

Using the Oxford Short Wavelength Integral Field specTrograph (SWIFT), we trace radial variations of initial mass function (IMF) sensitive absorption features of three galaxies in the Coma cluster. We obtain resolved spectroscopy of the central 5kpc for the two central brightest-cluster galaxies (BCGs) NGC4889, NGC4874, and the BCG in the south-west group NGC4839, as well as unresolved data for NGC4873 as a low-${\sigma }_{\ast }$ control. We present radial measurements of the IMF-sensitive features sodium NaI${}_{\mathrm{SDSS}}$, calcium triplet CaT and iron-hydride FeH0.99, along with the magnesium MgI0.88 and titanium oxide TiO0.89 features. We employ two separate methods for both telluric correction and sky-subtraction around the faint FeH feature to verify our analysis. Within NGC4889 we find strong gradients of NaI${}_{\mathrm{SDSS}}$ and CaT but a flat FeH profile, which from comparing to stellar population synthesis models, suggests an old, $\alpha$-enhanced population with a Chabrier, or even bottom-light IMF. The age and abundance is in line with previous studies but the normal IMF is in contrast to recent results suggesting an increased IMF slope with increased velocity dispersion. We measure flat NaI${}_{\mathrm{SDSS}}$ and FeH profiles within NGC4874 and determine an old, possibly slightly $\alpha$-enhanced and Chabrier IMF population. We find an $\alpha$-enhanced, Chabrier IMF population in NGC4873. Within NGC4839 we measure both strong NaI${}_{\mathrm{SDSS}}$ and strong FeH, although with a large systematic uncertainty, suggesting a possible heavier IMF. The IMFs we infer for these galaxies are supported by published dynamical modelling. We stress that IMF constraints should be corroborated by further spectral coverage and independent methods on a galaxy-by-galaxy basis.

24 pages, 17 figures, accepted for publication in MNRAS

References in corpus (15)

• Overview of the SDSS-IV MaNGA Survey: Mapping Nearby Galaxies at Apache Point Observatory
• A systematic variation of the stellar initial mass function in early-type galaxies
• Evolutionary stellar population synthesis with MILES - II. Scaled-solar and α-enhanced models
• A method to remove residual OH emission from near infrared spectra
• Stellar populations of early-type galaxies in different environments II. Ages and metallicities
• Submillimetre galaxies in a hierarchical universe: number counts, redshift distribution, and implications for the IMF
• Radial variations in the stellar initial mass function of early-type galaxies
• Dynamical modelling of luminous and dark matter in 17 Coma early-type galaxies
• Variations of the stellar initial mass function in the progenitors of massive early-type galaxies and in extreme starburst environments
• The stellar population histories of early-type galaxies. III. The Coma Cluster
• The SINFONI Nearby Elliptical Lens Locator Survey: Discovery of two new low-redshift strong lenses and implications for the initial mass function in giant early-type galaxies
• The initial mass function of a massive relic galaxy
• Radial kinematics of brightest cluster galaxies
• The accretion histories of brightest cluster galaxies from their stellar population gradients
• The initial mass functions of M31 and M32 through far red stellar absorption features

Cited by in corpus (2)

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