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Register a new userNIR Spectroscopy of Star-Forming Galaxies at z~1.4 with Subaru/FMOS: The Mass-Metallicity Relation
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We present near-infrared spectroscopic observations of star-forming galaxies at z~1.4 with FMOS on the Subaru Telescope. We observed K-band selected galaxies in the SXDS/UDS fields with K<23.9 mag, 1.2<z_ph<1.6, M*>10^{9.5} Msun, and expected F(Halpha)>10^{-16} erg s^{-1} cm^{-2}. 71 objects in the sample have significant detections of Halpha. For these objects, excluding possible AGNs identified from the BPT diagram, gas-phase metallicities are obtained from [NII]/Halpha line ratio. The sample is split into three stellar mass bins, and the spectra are stacked in each stellar mass bin. The mass-metallicity relation obtained at z~1.4 is located between those at z~0.8 and z~2.2. We constrain an intrinsic scatter to be ~0.1 dex or larger in the mass-metallicity relation at z~1.4; the scatter may be larger at higher redshifts. We found trends that the deviation from the mass-metallicity relation depends on the SFR and the half light radius: Galaxies with higher SFR and larger half light radii show lower metallicities at a given stellar mass. One possible scenario for the trends is the infall of pristine gas accreted from IGM or through merger events. Our data points show larger scatter than the fundamental metallicity relation (FMR) at z~0.1 and the average metallicities slightly deviate from the FMR. The compilation of the mass-metallicity relations at z~3 to z~0.1 shows that they evolve smoothly from z~3 to z~0 without changing the shape so much except for the massive part at z~0.
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We present a stellar mass-metallicity relation at z~1.4 with an unprecedentedly large sample of ~340 star-forming galaxies obtained with FMOS on the Subaru Telescope. We observed K-band selected galaxies at 1.2 < z_{ph} < 1.6 in the SXDS/UDS fields with M_{*} > 10^{9.5} M_{sun}, and expected F(Halpha) > 5 times 10^{-17} erg s^{-1} cm^{-2}. Among the observed ~1200 targets, 343 objects show significant Halpha emission lines. The gas-phase metallicity is obtained from [NII]lambda 6584/Halpha line ratio, after excluding possible active galactic nuclei (AGNs). Due to the faintness of the [NII]lambda 6584 lines, we apply the stacking analysis and derive the mass-metallicity relation at z~1.4. Our results are compared to past results at different redshifts in the literature. The mass-metallicity relation at z~1.4 is located between those at z~0.8 and z~2.2; it is found that the metallicity increases with decreasing redshift from z~3 to z~0 at fixed stellar mass. Thanks to the large size of the sample, we can study the dependence of the mass-metallicity relation on various galaxy physical properties. The average metallicity from the stacked spectra is close to the local FMR in the higher metallicity part but >0.1 dex higher in metallicity than the FMR in the lower metallicity part. We find that galaxies with larger E(B-V), B-R, and R-H colours tend to show higher metallicity by ~0.05 dex at fixed stellar mass. We also find relatively clearer size dependence that objects with smaller half light radius tend to show higher metallicity by ~0.1 dex at fixed stellar mass, especially in the low mass part.
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.
Intrinsic alignments (IA), the coherent alignment of intrinsic galaxy orientations, can be a source of a systematic error of weak lensing surveys. The redshift evolution of IA also contains information about the physics of galaxy formation and evolution. This paper presents the first measurement of IA at high redshift, $zsim 1.4$, using the spectroscopic catalog of blue star-forming galaxies of the FastSound redshift survey, with the galaxy shape information from the Canada-Hawaii-France telescope lensing survey. The IA signal is consistent with zero with power-law amplitudes fitted to the projected correlation functions for density-shape and shape-shape correlation components, $A_{delta+}=-0.0071pm 0.1340$ and $A_{++}=-0.0505pm 0.0848$, respectively. These results are consistent with those obtained from blue galaxies at lower redshifts (e.g., $A_{delta+}=0.0035_{-0.0389}^{+0.0387}$ and $A_{++}=0.0045_{-0.0168}^{+0.0166}$ at $z=0.51$ from the WiggleZ survey). The upper limit of the constrained IA amplitude corresponds to a few percent contamination to the weak-lensing shear power spectrum, resulting in systematic uncertainties on the cosmological parameter estimations by $-0.052<Delta sigma_8<0.039$ and $-0.039<Delta Omega_m<0.030$.
We present new accurate measurements of the physical properties of a statistically significant sample of 103 galaxies at z~2 using near-infrared spectroscopy taken as part of the 3D-HST survey. We derive redshifts, metallicities and star formation rates (SFRs) from the [OII], [OIII] and Hbeta nebular emission lines and exploit the multi-wavelength photometry available in CANDELS to measure stellar masses. We find the mass-metallicity relation (MZR) derived from our data to have the same trend as previous determinations in the range 0<z<3, with lower mass galaxies having lower metallicities. However we find an offset in the relation compared to the previous determination of the z~2 MZR by Erb et al. 2006b, who measure metallicities using the [NII]/Halpha ratio, with metallicities lower at a given mass. Incorporating our SFR information we find that our galaxies are offset from the Fundamental Metallicity Relation (FMR) by ~0.3 dex. We investigate the photoionization conditions and find that our galaxies are consistent with the elevated ionization parameter previously reported in high-redshift galaxies. Using the BPT diagram we argue that, if this is the case, metallicity indicators based on [NII] and Halpha may not be consistent with the ones obtained via oxygen lines and Hbeta. Using a recent determination of the theoretical evolution of the star forming sequence in the BPT diagram we convert our measured [OIII]/Hbeta line ratios to [NII]/Halpha ratios. From the [NII]/Halpha ratio we infer systematically higher metallicities in better agreement with the FMR. Our results thus suggest the evolution of the FMR previously reported at z~2-3 may be an artifact of the differential evolution in metallicity indicators, and caution against using locally calibrated metallicity relations at high redshift which do not account for evolution in the physical conditions of star-forming regions.
FastSound is a galaxy redshift survey using the near-infrared Fiber Multi-Object Spectrograph (FMOS) mounted on the Subaru Telescope, targeting H$alpha$ emitters at $z sim 1.18$--$1.54$ down to the sensitivity limit of H$alpha$ flux $sim 2 times 10^{-16} rm erg cm^{-2} s^{-1}$. The primary goal of the survey is to detect redshift space distortions (RSD), to test General Relativity by measuring the growth rate of large scale structure and to constrain modified gravity models for the origin of the accelerated expansion of the universe. The target galaxies were selected based on photometric redshifts and H$alpha$ flux estimates calculated by fitting spectral energy distribution (SED) models to the five optical magnitudes of the Canada France Hawaii Telescope Legacy Survey (CFHTLS) Wide catalog. The survey started in March 2012, and all the observations were completed in July 2014. In total, we achieved $121$ pointings of FMOS (each pointing has a $30$ arcmin diameter circular footprint) covering $20.6$ deg$^2$ by tiling the four fields of the CFHTLS Wide in a hexagonal pattern. Emission lines were detected from $sim 4,000$ star forming galaxies by an automatic line detection algorithm applied to 2D spectral images. This is the first in a series of papers based on FastSound data, and we describe the details of the survey design, target selection, observations, data reduction, and emission line detections.
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