The early-type galaxies NGC 1407 and NGC 1400 - II: star formation and chemical evolutionary history

Abstract

We present a possible star formation and chemical evolutionary history for two early-type galaxies NGC 1407 and NGC 1400. They are the two brightest galaxies of the NGC 1407 (or Eridanus-A) group, one of the 60 groups studied as part of the Group Evolution Multi-wavelength Study (GEMS). Our analysis is based on new high signal-to-noise spatially resolved integrated spectra obtained at the ESO 3.6m telescope, out to 0.6 (NGC 1407) and 1.3 (NGC 1400) effective radii. Using Lick/IDS indices we estimate luminosity-weighted ages, metallicities and $\alpha$-element abundance ratios. Colour radial distributions from HST/ACS and Subaru Suprime-Cam multi-band wide-field imaging are compared to colours predicted from spectroscopically determinated ages and metallicities using single stellar population models. The galaxies formed over half of their mass in a single short-lived burst of star formation (> 100 M(sun)/year) at redshift z>5. This likely involved an outside-in mechanism with supernova-driven galactic winds, as suggested by the flatness of the alpha-element radial profiles and the strong negative metallicity gradients. Our results support the predictions of the revised version of the monolithic collapse model for galaxy formation and evolution. We speculate that, since formation the galaxies have evolved quiescently and that we are witnessing the first infall of NGC 1400 in the group.

14 pages, 9 tables, 6 figures, Accepted for publication in MNRAS

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• The SLUGGS Survey: stellar masses and effective radii of early-type galaxies from Spitzer Space Telescope 3.6$\mu$m imaging
• The early-type galaxies NGC 1407 and NGC 1400 - I: spatially resolved radial kinematics and surface photometry
• The Optical Colors of Giant Elliptical Galaxies and their Metal-Rich Globular Clusters Indicate a Bottom-Heavy Initial Mass Function
• Stellar population properties of individual massive early-type galaxies at 1.4 < z < 2
• Tracing the Assembly History of NGC 1395 through its Globular Cluster System
• The ALHAMBRA survey: 2-D analysis of the stellar populations in massive early-type galaxies at z < 0.3
• Spatially-resolved stellar populations and kinematics with KCWI: probing the assembly history of the massive early-type galaxy NGC 1407
• Variation in the stellar initial mass function from the chromospheric activity of M dwarfs in early-type galaxies
• Galaxy archaeology for wet mergers: Globular cluster age distributions in the Milky Way and nearby galaxies
• Nonlinear Color-Metallicity Relations of Globular Clusters. IX. Different Radial Number Density Profiles between Blue and Red Clusters