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Register a new userThe mass-metallicity relation at z~1-2 and its dependence on star formation rate
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We present a new measurement of the gas-phase mass-metallicity relation (MZR), and its dependence on star formation rates (SFRs) at 1.3 < z < 2.3. Our sample comprises 1056 galaxies with a mean redshift of z = 1.9, identified from the Hubble Space Telescope Wide Field Camera 3 (WFC3) grism spectroscopy in the Cosmic Assembly Near-Infrared Deep Extragalactic Survey (CANDELS) and the WFC3 Infrared Spectroscopic Parallel Survey (WISP). This sample is four times larger than previous metallicity surveys at z ~ 2, and reaches an order of magnitude lower in stellar mass (10^8 M_sun). Using stacked spectra, we find that the MZR evolves by 0.3 dex relative to z ~ 0.1. Additionally, we identify a subset of 49 galaxies with high signal-to-noise (SNR) spectra and redshifts between 1.3 < z < 1.5, where H-alpha emission is observed along with [OIII] and [OII]. With accurate measurements of SFR in these objects, we confirm the existence of a mass-metallicity-SFR (M-Z-SFR) relation at high redshifts. These galaxies show systematic differences from the local M-Z-SFR relation, which vary depending on the adopted measurement of the local relation. However, it remains difficult to ascertain whether these differences could be due to redshift evolution, as the local M-Z-SFR relation is poorly constrained at the masses and SFRs of our sample. Lastly, we reproduced our sample selection in the IllustrisTNG hydrodynamical simulation, demonstrating that our line flux limit lowers the normalization of the simulated MZR by 0.2 dex. We show that the M-Z-SFR relation in IllustrisTNG has an SFR dependence that is too steep by a factor of around three.
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Using a sample of dwarf galaxies observed using the VIMOS IFU on the VLT, we investigate the mass-metallicity relation (MZR) as a function of star formation rate (FMR$_{text{SFR}}$) as well as HI-gas mass (FMR$_{text{HI}}$). We combine our IFU data with a subsample of galaxies from the ALFALFA HI survey crossmatched to the Sloan Digital Sky Survey to study the FMR$_{text{SFR}}$ and FMR$_{text{HI}}$ across the stellar mass range 10$^{6.6}$ to 10$^{8.8}$ M$_odot$, with metallicities as low as 12+log(O/H) = 7.67. We find the 1$sigma$ mean scatter in the MZR to be 0.05 dex. The 1$sigma$ mean scatter in the FMR$_{text{SFR}}$ (0.02 dex) is significantly lower than that of the MZR. The FMR$_{text{SFR}}$ is not consistent between the IFU observed galaxies and the ALFALFA/SDSS galaxies for SFRs lower than 10$^{-2.4}$ M$_odot$ yr$^{-1}$, however this could be the result of limitations of our measurements in that regime. The lowest mean scatter (0.01 dex) is found in the FMR$_{text{HI}}$. We also find that the FMR$_{text{HI}}$ is consistent between the IFU observed dwarf galaxies and the ALFALFA/SDSS crossmatched sample. We introduce the fundamental metallicity luminosity counterpart to the FMR, again characterized in terms of SFR (FML$_{text{SFR}}$) and HI-gas mass (FML$_{text{HI}}$). We find that the FML$_{text{HI}}$ relation is consistent between the IFU observed dwarf galaxy sample and the larger ALFALFA/SDSS sample. However the 1$sigma$ scatter for the FML$_{text{HI}}$ relation is not improved over the FMR$_{text{HI}}$ scenario. This leads us to conclude that the FMR$_{text{HI}}$ is the best candidate for a physically motivated fundamental metallicity relation.
We investigate the relationships between stellar mass, gas-phase oxygen abundance (metallicity), star formation rate, and dust content of star-forming galaxies at z$sim$1.6 using Subaru/FMOS spectroscopy in the COSMOS field. The mass-metallicity relation at $zsim1.6$ is steeper than the relation observed in the local Universe. The steeper MZ relation at $zsim1.6$ 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 $zsim1.6$. The most massive galaxies at $zsim1.6$ ($sim 10^{11}M_odot$) are enriched to the level observed in massive galaxies in the local Universe. The mass-metallicity relation we measure at $zsim1.6$ supports the suggestion of an empirical upper metallicity limit that does not significantly evolve with redshift. We find an anti-correlation between metallicity and star formation rate for galaxies at a fixed stellar mass at $zsim1.6$ which is similar to trends observed in the local Universe. We do not find a relation between stellar mass, metallicity and star formation rate that is independent of redshift; our data suggest that there is redshift evolution in this relation. We examine the relation between stellar mass, metallicity and dust extinction. We 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.
(Abridged) The knowledge of the number and of the physical nature of low-metallicity massive galaxies is crucial for the determination and interpretation of the mass-metallicity relation (MZR). Using VLT-ISAAC near-infrared (NIR) spectroscopy of 39 zCOSMOS z~0.7 galaxies, we have measured Halpha and [NII] emission line fluxes for galaxies with [OII], Hbeta and [OIII] available from VIMOS optical spectroscopy. The NIR spectroscopy enables us to break the degeneracy of the R23 method to derive unambiguously O/H gas metallicities, and also SFRs from extinction corrected Halpha. Using, as a benchmark, the position in the D4000 vs. [OIII]/Hbeta diagram of galaxies with reliable O/Hs from NIR spectroscopy, we were able to break the lower/upper branch R23 degeneracy of additional 900 zCOSMOS z~0.7 galaxies. Additionally, the Halpha-based SFR measurements were used to find the best SFR calibration based on [OII] for the zCOSMOS z~0.7 galaxies without Halpha measurements. We find a fraction of 19% of lower mass 9.5<logM/Msun<10.3 zCOSMOS galaxies which shows a larger evolution of the MZR relation, compared to higher mass galaxies, being more metal poor at a given mass by a factor of 2-3 compared to SDSS. This indicates that the low-mass MZR slope is getting steeper at z~0.7 compared to local galaxies. The existence of these metal-poor galaxies at z~0.7 can be interpreted as the chemical version of galaxy downsizing. Moreover, the sample of zCOSMOS galaxies shows direct evidence that SFR influences the MZR at these redshifts. The comparison of the measured metallicities for the zCOSMOS sample with the values expected for a non-evolving fundamental metallicity relation (FMR) shows broadly agreement, and reveals that also galaxies with lower metallicities and typically higher (specific) SFRs, as found in our zCOSMOS sample at z~0.7, are in agreement with the predictions of a non-evolving Z(M,SFR).
To investigate the mass dependence of structural transformation and star formation quenching, we construct three galaxy samples using massive ($M_* > 10^{10} M_{odot}$) red, green, and blue galaxy populations at $0.5<z<2.5$ in five 3D--{it HST}/CANDELS fields. The structural parameters, including effective radius ($r_{rm e}$), galaxy compactness ($Sigma_{1.5}$), and second order moment of 20% brightest pixels ($M_{20}$) are found to be correlated with stellar mass. S{e}rsic index ($n$), concentration ($C$), and Gini coefficient ($G$) seem to be insensitive to stellar mass. The morphological distinction between blue and red galaxies is found at a fixed mass bin, suggesting that quenching processes should be accompanied with transformations of galaxy structure and morphology. Except for $r_e$ and $Sigma_{1.5}$ at high mass end, structural parameters of green galaxies are intermediate between red and blue galaxies in each stellar mass bin at $z < 2$, indicating green galaxies are at a transitional phase when blue galaxies are being quenched into quiescent statuses. The similar sizes and compactness for the blue and green galaxies at high-mass end implies that these galaxies will not appear to be significantly shrunk until they are completely quenched into red QGs. For the green galaxies at $0.5<z<1.5$, a morphological transformation sequence of bulge buildup can be seen as they are gradually shut down their star formation activities, while a faster morphological transformation is verified for the green galaxies at $1.5<z<2.5$.
We present the results on the study of the global and local M-Z relation based on the first data available from the CALIFA survey (150 galaxies). This survey provides integral field spectroscopy of the complete optical extent of each galaxy (up to 2-3 effective radii), with enough resolution to separate individual HII regions and/or aggregations. Nearly $sim$3000 individual HII regions have been detected. The spectra cover the wavelength range between [OII]3727 and [SII]6731, with a sufficient signal-to-noise to derive the oxygen abundance and star-formation rate associated with each region. In addition, we have computed the integrated and spatially resolved stellar masses (and surface densities), based on SDSS photometric data. We explore the relations between the stellar mass, oxygen abundance and star-formation rate using this dataset. We derive a tight relation between the integrated stellar mass and the gas-phase abundance, with a dispersion smaller than the one already reported in the literature ($sigma_{Delta{rm log(O/H)}}=$0.07 dex). Indeed, this dispersion is only slightly larger than the typical error derived for our oxygen abundances. However, we do not find any secondary relation with the star-formation rate, other than the one induced due to the primary relation of this quantity with the stellar mass. We confirm the result using the $sim$3000 individual HII regions, for the corresponding local relations. Our results agree with the scenario in which gas recycling in galaxies, both locally and globally, is much faster than other typical timescales, like that of gas accretion by inflow and/or metal loss due to outflows. In essence, late-type/disk dominated galaxies seem to be in a quasi-steady situation, with a behavior similar to the one expected from an instantaneous recycling/closed-box model.
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