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

Journal Article · Fri Aug 13 00:00:00 EDT 2021 · Monthly Notices of the Royal Astronomical Society

DOI:https://doi.org/10.1093/mnras/stab2341· OSTI ID:1982525

Ge, Junqiang ^[1]; Mao, Shude ^[2]; Lu, Youjun ^[3]; Cappellari, Michele ^[4]; Long, Richard J. ^[5]; Yan, Renbin ^[6]

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1. Chinese Academy of Sciences (CAS), Beijing (China). National Astronomical Observatories
2. Tsinghua Univ., Beijing (China); Chinese Academy of Sciences (CAS), Beijing (China). National Astronomical Observatories
3. Chinese Academy of Sciences (CAS), Beijing (China). National Astronomical Observatories; University of Chinese Academy of Sciences, Beijing (China)
4. Univ. of Oxford (United Kingdom)
5. Tsinghua Univ., Beijing (China); Univ. of Manchester (United Kingdom)
6. Univ. of Kentucky, Lexington, KY (United States)

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.

• Research Organization: US Department of Energy (USDOE), Washington, DC (United States). Office of Science, Sloan Digital Sky Survey (SDSS)
• Sponsoring Organization: Beijing Municipal Natural Science Foundation; National Key Program for Science and Technology Research and Development; National Key Research and Development Program of China; National Natural Science Foundation of China (NSFC); National Science Foundation (NSF); USDOE Office of Science (SC)
• OSTI ID: 1982525
• Journal Information: Monthly Notices of the Royal Astronomical Society, Journal Name: Monthly Notices of the Royal Astronomical Society Journal Issue: 2 Vol. 507; ISSN 0035-8711
• Publisher: Oxford University Press
• Country of Publication: United States
• Language: English

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