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Title: IMF–METALLICITY: A TIGHT LOCAL RELATION REVEALED BY THE CALIFA SURVEY

Abstract

Variations in the stellar initial mass function (IMF) have been invoked to explain the spectroscopic and dynamical properties of early-type galaxies (ETGs). However, no observations have yet been able to disentangle the physical driver. We analyze here a sample of 24 ETGs drawn from the CALIFA survey, deriving in a homogeneous way their stellar population and kinematic properties. We find that the local IMF is tightly related to the local metallicity, becoming more bottom-heavy toward metal-rich populations. Our result, combined with the galaxy mass–metallicity relation, naturally explains previous claims of a galaxy mass–IMF relation, derived from non-IFU spectra. If we assume that—within the star formation environment of ETGs—metallicity is the main driver of IMF variations, a significant revision of the interpretation of galaxy evolution observables is necessary.

Authors:
; ;  [1];  [2]; ;  [3];  [4];  [5];  [6]; ;  [7];  [8];  [9]; ;
  1. Instituto de Astrofísica de Canarias, c/Vía Láctea s/n, E-38205—La Laguna, Tenerife (Spain)
  2. INAF—Osservatorio Astronomico di Capodimonte, Napoli (Italy)
  3. Kapteyn Astronomical Institute, University of Groningen, Postbus 800, 9700 AV Groningen (Netherlands)
  4. Max Planck Institute for Astronomy, Königstuhl 17, D-69117 Heidelberg (Germany)
  5. Mullard Space Science Laboratory, University College London, Holmbury St Mary, Dorking, Surrey RH5 6NT (United Kingdom)
  6. Instituto de Astronomía, Universidad Nacional Autonóma de México, A.P. 70-264, 04510 México, D.F., México (Mexico)
  7. Instituto de Astrofísica de Andalucía (CSIC), Glorieta de la Astronomía s/n, Aptdo. 3004, E-18080 Granada (Spain)
  8. Instituto de Cosmologia, Relatividade e Astrofísica—ICRA, Centro Brasileiro de Pesquisas Físicas, Rua Dr.Xavier Sigaud 150, CEP 22290-180, Rio de Janeiro, RJ (Brazil)
  9. Departamento de Física Teórica, Universidad Autónoma de Madrid, Cantoblanco, E-28049 Spain (Spain)
Publication Date:
OSTI Identifier:
22518951
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal Letters; Journal Volume: 806; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; GALACTIC EVOLUTION; GALAXIES; MARINE SURVEYS; MASS; METALLICITY; STAR EVOLUTION; STARS; VARIATIONS

Citation Formats

Martín-Navarro, Ignacio, Vazdekis, Alexandre, Falcón-Barroso, Jesús, La Barbera, Francesco, Lyubenova, Mariya, Trager, S. C., Ven, Glenn van de, Ferreras, Ignacio, Sánchez, S. F., García-Benito, R., Mendoza, M. A., Mast, D., Sánchez-Blázquez, P., E-mail: imartin@iac.es, Collaboration: CALIFA Team, and and others. IMF–METALLICITY: A TIGHT LOCAL RELATION REVEALED BY THE CALIFA SURVEY. United States: N. p., 2015. Web. doi:10.1088/2041-8205/806/2/L31.
Martín-Navarro, Ignacio, Vazdekis, Alexandre, Falcón-Barroso, Jesús, La Barbera, Francesco, Lyubenova, Mariya, Trager, S. C., Ven, Glenn van de, Ferreras, Ignacio, Sánchez, S. F., García-Benito, R., Mendoza, M. A., Mast, D., Sánchez-Blázquez, P., E-mail: imartin@iac.es, Collaboration: CALIFA Team, & and others. IMF–METALLICITY: A TIGHT LOCAL RELATION REVEALED BY THE CALIFA SURVEY. United States. doi:10.1088/2041-8205/806/2/L31.
Martín-Navarro, Ignacio, Vazdekis, Alexandre, Falcón-Barroso, Jesús, La Barbera, Francesco, Lyubenova, Mariya, Trager, S. C., Ven, Glenn van de, Ferreras, Ignacio, Sánchez, S. F., García-Benito, R., Mendoza, M. A., Mast, D., Sánchez-Blázquez, P., E-mail: imartin@iac.es, Collaboration: CALIFA Team, and and others. Sat . "IMF–METALLICITY: A TIGHT LOCAL RELATION REVEALED BY THE CALIFA SURVEY". United States. doi:10.1088/2041-8205/806/2/L31.
@article{osti_22518951,
title = {IMF–METALLICITY: A TIGHT LOCAL RELATION REVEALED BY THE CALIFA SURVEY},
author = {Martín-Navarro, Ignacio and Vazdekis, Alexandre and Falcón-Barroso, Jesús and La Barbera, Francesco and Lyubenova, Mariya and Trager, S. C. and Ven, Glenn van de and Ferreras, Ignacio and Sánchez, S. F. and García-Benito, R. and Mendoza, M. A. and Mast, D. and Sánchez-Blázquez, P., E-mail: imartin@iac.es and Collaboration: CALIFA Team and and others},
abstractNote = {Variations in the stellar initial mass function (IMF) have been invoked to explain the spectroscopic and dynamical properties of early-type galaxies (ETGs). However, no observations have yet been able to disentangle the physical driver. We analyze here a sample of 24 ETGs drawn from the CALIFA survey, deriving in a homogeneous way their stellar population and kinematic properties. We find that the local IMF is tightly related to the local metallicity, becoming more bottom-heavy toward metal-rich populations. Our result, combined with the galaxy mass–metallicity relation, naturally explains previous claims of a galaxy mass–IMF relation, derived from non-IFU spectra. If we assume that—within the star formation environment of ETGs—metallicity is the main driver of IMF variations, a significant revision of the interpretation of galaxy evolution observables is necessary.},
doi = {10.1088/2041-8205/806/2/L31},
journal = {Astrophysical Journal Letters},
number = 2,
volume = 806,
place = {United States},
year = {Sat Jun 20 00:00:00 EDT 2015},
month = {Sat Jun 20 00:00:00 EDT 2015}
}
  • We use spatially and temporally resolved maps of stellar population properties of 300 galaxies from the CALIFA integral field survey to investigate how the stellar metallicity (Z {sub *}) relates to the total stellar mass (M {sub *}) and the local mass surface density (μ{sub *}) in both spheroidal- and disk-dominated galaxies. The galaxies are shown to follow a clear stellar mass-metallicity relation (MZR) over the whole 10{sup 9}-10{sup 12} M {sub ☉} range. This relation is steeper than the one derived from nebular abundances, which is similar to the flatter stellar MZR derived when we consider only young stars.more » We also find a strong relation between the local values of μ{sub *} and Z {sub *} (the μZR), betraying the influence of local factors in determining Z {sub *}. This shows that both local (μ{sub *}-driven) and global (M {sub *}-driven) processes are important in determining metallicity in galaxies. We find that the overall balance between local and global effects varies with the location within a galaxy. In disks, μ{sub *} regulates Z {sub *}, producing a strong μZR whose amplitude is modulated by M {sub *}. In spheroids it is M {sub *} that dominates the physics of star formation and chemical enrichment, with μ{sub *} playing a minor, secondary role. These findings agree with our previous analysis of the star formation histories of CALIFA galaxies, which showed that mean stellar ages are mainly governed by surface density in galaxy disks and by total mass in spheroids.« less
  • It has been proposed that the (stellar) mass-(gas) metallicity relation of galaxies exhibits a secondary dependence on star formation rate (SFR), and that the resulting M {sub *}-Z-SFR relation may be redshift-invariant, i.e., ''fundamental''. However, conflicting results on the character of the SFR dependence, and whether it exists, have been reported. To gain insight into the origins of the conflicting results, we (1) devise a non-parametric, astrophysically motivated analysis framework based on the offset from the star-forming ({sup m}ain{sup )} sequence at a given M {sub *} (relative specific SFR); (2) apply this methodology and perform a comprehensive re-analysis ofmore » the local M {sub *}-Z-SFR relation, based on SDSS, GALEX, and WISE data; and (3) study the impact of sample selection and of using different metallicity and SFR indicators. We show that metallicity is anti-correlated with specific SFR regardless of the indicators used. We do not find that the relation is spurious due to correlations arising from biased metallicity measurements or fiber aperture effects. We emphasize that the dependence is weak/absent for massive galaxies (log M {sub *} > 10.5), and that the overall scatter in the M {sub *}-Z-SFR relation does not greatly decrease from the M {sub *}-Z relation. We find that the dependence is stronger for the highest SSFR galaxies above the star-forming sequence. This two-mode behavior can be described with a broken linear fit in 12+log(O/H) versus log (SFR/M {sub *}), at a given M {sub *}. Previous parameterizations used for comparative analysis with higher redshift samples that do not account for the more detailed behavior of the local M {sub *}-Z-SFR relation may incorrectly lead to the conclusion that those samples follow a different relationship.« less
  • We analyze the optical continuum of star-forming galaxies in the Sloan Digital Sky Survey by fitting stacked spectra with stellar population synthesis models to investigate the relation between stellar mass, stellar metallicity, dust attenuation, and star formation rate. We fit models calculated with star formation and chemical evolution histories that are derived empirically from multi-epoch observations of the stellar mass–star formation rate and the stellar mass–gas-phase metallicity relations, respectively. We also fit linear combinations of single-burst models with a range of metallicities and ages. Star formation and chemical evolution histories are unconstrained for these models. The stellar mass–stellar metallicity relationsmore » obtained from the two methods agree with the relation measured from individual supergiant stars in nearby galaxies. These relations are also consistent with the relation obtained from emission-line analysis of gas-phase metallicity after accounting for systematic offsets in the gas-phase metallicity. We measure dust attenuation of the stellar continuum and show that its dependence on stellar mass and star formation rate is consistent with previously reported results derived from nebular emission lines. However, stellar continuum attenuation is smaller than nebular emission line attenuation. The continuum-to-nebular attenuation ratio depends on stellar mass and is smaller in more massive galaxies. Our consistent analysis of stellar continuum and nebular emission lines paves the way for a comprehensive investigation of stellar metallicities of star-forming and quiescent galaxies.« less
  • We investigate the relationships between stellar mass, gas-phase oxygen abundance (metallicity), star formation rate (SFR), and dust content of star-forming galaxies at z ∼ 1.6 using Subaru/FMOS spectroscopy in the COSMOS field. The mass-metallicity (MZ) relation at z ∼ 1.6 is steeper than the relation observed in the local universe. The steeper MZ relation at z ∼ 1.6 is mainly due to evolution in the stellar mass where the MZ relation begins to turnover and flatten. This turnover mass is 1.2 dex larger at z ∼ 1.6. The most massive galaxies at z ∼ 1.6 (∼10{sup 11} M {sub ☉})more » are enriched to the level observed in massive galaxies in the local universe. The MZ relation we measure at z ∼ 1.6 supports the suggestion of an empirical upper metallicity limit that does not significantly evolve with redshift. We find an anti-correlation between metallicity and SFR for galaxies at a fixed stellar mass at z ∼ 1.6, which is similar to trends observed in the local universe. We do not find a relation between stellar mass, metallicity, and SFR that is independent of redshift; rather, our data suggest that there is redshift evolution in this relation. We examine the relation between stellar mass, metallicity, and dust extinction, and find that at a fixed stellar mass, dustier galaxies tend to be more metal rich. From examination of the stellar masses, metallicities, SFRs, and dust extinctions, we conclude that stellar mass is most closely related to dust extinction.« less
  • The growth of galaxies is one of the key problems in understanding the structure and evolution of the universe and its constituents. Galaxies can grow their stellar mass by accretion of halo or intergalactic gas clouds, or by merging with smaller or similar mass galaxies. The gas available translates into a rate of star formation, which controls the generation of metals in the universe. The spatially resolved history of their stellar mass assembly has not been obtained so far for any given galaxy beyond the Local Group. Here we demonstrate how massive galaxies grow their stellar mass inside-out. We reportmore » the results from the analysis of the first 105 galaxies of the largest three-dimensional spectroscopic survey to date of galaxies in the local universe (CALIFA). We apply the fossil record method of stellar population spectral synthesis to recover the spatially and time resolved star formation history of each galaxy. We show, for the first time, that the signal of downsizing is spatially preserved, with both inner and outer regions growing faster for more massive galaxies. Further, we show that the relative growth rate of the spheroidal component, nucleus, and inner galaxy, which happened 5-7 Gyr ago, shows a maximum at a critical stellar mass {approx}7 Multiplication-Sign 10{sup 10} M{sub Sun }. We also find that galaxies less massive than {approx}10{sup 10} M{sub Sun} show a transition to outside-in growth, thus connecting with results from resolved studies of the growth of low-mass galaxies.« less