SDSS-IV MaNGA: Stellar M/L gradients and the M/L-colour relation in galaxies

Journal article

The stellar mass-to-light ratio gradient in SDSS r-band ∇(M_*/L_r) of a galaxy depends on its mass assembly history, which is imprinted in its morphology and gradients of age, metallicity, and stellar initial mass function (IMF). Taking a MaNGA sample of 2051 galaxies with stellar masses ranging from 10⁹ to 10¹²M_⊙ released in SDSS DR15, we focus on face-on galaxies, without merger and bar signatures, and investigate the dependence of the 2D ∇(M_*/L_r) on other galaxy properties, including M_*/L_r-colour relationships by assuming a fixed Salpeter IMF as the mass normalization reference. The median gradient is ∇M_*/L_r ∼ −0.1 (i.e. the M_*/L_r is larger at the centre) for massive galaxies, becomes flat around M_* ∼ 10¹⁰M_⊙ and change sign to ∇M_*/L_r ∼ 0.1 at the lowest masses. The M_*/L_r inside a half-light radius increases with increasing galaxy stellar mass; in each mass bin, early-type galaxies have the highest value, while pure-disc late-type galaxies have the smallest. Correlation analyses suggest that the mass-weighted stellar age is the dominant parameter influencing the M_*/L_r profile, since a luminosity-weighted age is easily affected by star formation when the specific star formation rate (sSFR) inside the half-light radius is higher than 10⁻³ Gyr⁻¹. With increased sSFR gradient, one can obtain a steeper negative ∇(M_*/L_r). The scatter in the slopes of M_*/L-colour relations increases with increasing sSFR, for example, the slope for post-starburst galaxies can be flattened to 0.45 from the global value 0.87 in the M_*/L versus g − r diagram. Hence converting galaxy colours to M_*/L should be done carefully, especially for those galaxies with young luminosity-weighted stellar ages, which can have quite different star formation histories.

Authors: Ge, J; Mao, S; Lu, Y; Cappellari, M; Long, RJ

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: Oxford University Press
• Journal: Monthly Notices of the Royal Astronomical Society
• Volume: 507
• Issue: 2
• Pages: 2488-2499
• Publication date: 2021-08-13
• Acceptance date: 2021-08-10
• DOI: 10.1093/mnras/stab2341
• EISSN: 1365-2966
• ISSN: 0035-8711
• Language: English
• Keywords: galaxies: star formation; galaxies: fundamental parameters; galaxies: elliptical and lenticular, cD; galaxies: spiral; galaxies: evolution; galaxies: formation; FFR