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Register a new userSeparate ways: The Mass-Metallicity Relation does not strongly correlate with Star Formation Rate in SDSS-IV MaNGA galaxies
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Jorge Karolt Barrera-Ballesteros
Publication date
2017
fields
Physics
and research's language is
English
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We present the integrated stellar mass-metallicity relation (MZR) for more than 1700 galaxies included in the integral field area SDSS-IV MaNGA survey. The spatially resolved data allow us to determine the metallicity at the same physical scale (effective radius in arcsecs, $mathrm{R_{eff}}$ ) using a heterogeneous set of ten abundance calibrators. Besides scale factors, the shape of the MZR is similar for all calibrators, consistent with those reported previously using single-fiber and integral field spectroscopy. We compare the residuals of this relation against the star formation rate (SFR) and specific SFR (sSFR). We do not find a strong secondary relation of the MZR with either SFR or the sSFR for any of the calibrators, in contrast with previous single-fiber spectroscopic studies. Our results agree with an scenario in which metal enrichment happens at local scales, with global outflows playing a secondary role in shaping the chemistry of galaxies and cold-gas inflows regulating the stellar formation.
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Star formation rate density, $Sigma_{rm SFR}$, has shown a remarkable correlation with both components of the baryonic mass at kpc scales (i.e., the stellar mass density, and the molecular gas mass density; $Sigma_{ast}$, and $Sigma_{rm mol}$, respectively) for galaxies in the nearby Universe. In this study we propose an empirical relation between $Sigma_{rm SFR}$ and the baryonic mass surface density ($Sigma_{rm b}$ =$Sigma_{rm mol,Av}$ + $Sigma_{ast}$; where $Sigma_{rm mol,Av}$ is the molecular gas density derived from the optical extinction, Av) at kpc scales using the spatially-resolved properties of the MaNGA survey - the largest sample of galaxies observed via Integral Field Spectroscopy (IFS, $sim$ 8400 objects). We find that $Sigma_{rm SFR}$ tightly correlates with $Sigma_{rm b}$. Furthermore, we derive an empirical relation between the $Sigma_{rm SFR}$ and a second degree polynomial of $Sigma_{rm b}$ yielding a one-to-one relation between these two observables. Both, $Sigma_{rm b}$ and its polynomial form show a stronger correlation and smaller scatter with respect to $Sigma_{rm SFR}$ than the relations derived using the individual components of $Sigma_{rm b}$. Our results suggest that indeed these three parameters are physically correlated, suggesting a scenario in which the two components of the baryonic mass regulate the star-formation activity at kpc scales.
We study the link between the kinematic-morphology of galaxies, as inferred from integral-field stellar kinematics, and their relation between mass and star formation rate (SFR). Our sample consists of $sim 3200$ galaxies with integral-field spectroscopic data from the MaNGA survey with available determinations of their effective stellar angular momentum within the half-light radius $lambda_{R_e}$. We find that for star-forming galaxies, namely along the star formation main sequence (SFMS), the $lambda_{R_e}$ values remain large and almost unchanged over about two orders of magnitude in stellar mass, with the exception of the lowest masses $mathcal{M}_{star}lesssim2times10^{9} mathcal{M}_{odot}$, where $lambda_{R_e}$ slightly decreases. The SFMS is dominated by spiral galaxies with small bulges. Below the SFMS, but above the characteristic stellar mass $mathcal{M}_{rm crit}approx2times10^{11} mathcal{M}_{odot}$, there is a sharp decrease in $lambda_{R_e}$ with decreasing star formation rate: massive galaxies well below the SFMS are mainly slow-rotator early-type galaxies, namely genuinely spheroidal galaxies without disks. Below the SFMS and below $mathcal{M}_{rm crit}$ the decrease of $lambda_{R_e}$ with decreasing SFR becomes modest or nearly absent: low-mass galaxies well below the SFMS, are fast-rotator early-type galaxies, and contain fast-rotating stellar disks like their star-forming counterparts. We also find a small but clear environmental dependence for the massive galaxies: in the mass range $10^{10.9}-10^{11.5} mathcal{M}_{odot}$, galaxies in rich groups or denser regions or classified as central galaxies have lower values of $lambda_{R_e}$. While no environmental dependence is found for galaxies of lower mass. We discuss how our results can be understood as due to the different star formation and mass assembly histories of galaxies with varying mass.
Bars inhabit the majority of local-Universe disk galaxies and may be important drivers of galaxy evolution through the redistribution of gas and angular momentum within disks. We investigate the star formation and gas properties of bars in galaxies spanning a wide range of masses, environments, and star formation rates using the MaNGA galaxy survey. Using a robustly-defined sample of 684 barred galaxies, we find that fractional (or scaled) bar length correlates with the hosts offset from the star-formation main sequence. Considering the morphology of the H$alpha$ emission we separate barred galaxies into different categories, including barred, ringed, and central configurations, together with H$alpha$ detected at the ends of a bar. We find that only low-mass galaxies host star formation along their bars, and that this is located predominantly at the leading edge of the bar itself. Our results are supported by recent simulations of massive galaxies, which show that the position of star formation within a bar is regulated by a combination of shear forces, turbulence and gas flows. We conclude that the physical properties of a bar are mostly governed by the existing stellar mass of the host galaxy, but that they also play an important role in the galaxys ongoing star formation.
Gas stripping of spiral galaxies or mergers are thought to be the formation mechanisms of lenticular galaxies. In order to determine the conditions in which each scenario dominates, we derive stellar populations of both the bulge and disk regions of 279 lenticular galaxies in the MaNGA survey. We find a clear bimodality in stellar age and metallicity within the population of S0s and this is strongly correlated with stellar mass. Old and metal-rich bulges and disks belong to massive galaxies, and young and metal-poor bulges and disks are hosted by low-mass galaxies. From this we conclude that the bulges and disks are co-evolving. When the bulge and disk stellar ages are compared, we find that the bulge is almost always older than the disk for massive galaxies ($textrm{M}_{star} > 10^{10}~textrm{M}_{odot}$). The opposite is true for lower mass galaxies. We conclude that we see two separate populations of lenticular galaxies. The old, massive, and metal-rich population possess bulges that are predominantly older than their disks, which we speculate may have been caused by morphological or inside-out quenching. In contrast, the less massive and more metal-poor population have bulges with more recent star formation than their disks. We postulate they may be undergoing bulge rejuvenation (or disk fading), or compaction. Environment doesnt play a distinct role in the properties of either population. Our findings give weight to the notion that while the faded spiral scenario likely formed low-mass S0s, other processes, such as mergers, may be responsible for high-mass S0s.
Within the standard model of hierarchical galaxy formation in a {Lambda}CDM Universe, the environment of galaxies is expected to play a key role in driving galaxy formation and evolution. In this paper we investigate whether and how the gas metallicity and the star formation surface density ({Sigma}_SFR) depend on galaxy environment. To this end we analyse a sample of 1162 local, star-forming galaxies from the galaxy survey Mapping Nearby Galaxies at APO (MaNGA). Generally, both parameters do not show any significant dependence on environment. However, in agreement with previous studies, we find that low-mass satellite galaxies are an exception to this rule. The gas metallicity in these objects increases while their {Sigma}SFR decreases slightly with environmental density. The present analysis of MaNGA data allows us to extend this to spatially resolved properties. Our study reveals that the gas metallicity gradients of low-mass satellites flatten and their {Sigma}SFR gradients steepen with increasing environmental density. By extensively exploring a chemical evolution model, we identify two scenarios that are able to explain this pattern: metal-enriched gas accretion or pristine gas inflow with varying accretion timescales. The latter scenario better matches the observed {Sigma}SFR gradients, and is therefore our preferred solution. In this model, a shorter gas accretion timescale at larger radii is required. This suggests that outside-in quenching governs the star formation processes of low-mass satellite galaxies in dense environments.
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