We present the local HII region metallicity near the site of the recently discovered multiply lensed supernova (SN; SN Refsdal) at redshift 1.49. SN Refsdal is located at the outer spiral arm ($sim$7 kpc) of the lensed host galaxy, which we have prev
iously reported to exhibit a steep negative galactocentric metallicity gradient. Based on our updated near-infrared integral field spectroscopic data, the gas-phase metallicity averaged in an intrinsic radius of $sim$ 550 pc surrounding an HII region $sim$ 200 pc away from the SN site is 12 + log(O/H)$_{rm PP04N2}$ $le$ 8.67. The metallicity averaged over nine HII regions at similar galactocentric distances ($sim$5-7 kpc) as SN Refsdal is constrained to be 12 + log(O/H)$_{rm PP04N2}$ $le$ 8.11. Given the fortuitous discovery of SN Refsdal in an advantageously lensed face-on spiral, this is the first observational constraint on the local metallicity environment of an SN site at redshift $z>1$.
We present the spectroscopic confirmation of a galaxy cluster at $z=2.095$ in the COSMOS field. This galaxy cluster was first reported in the ZFOURGE survey as harboring evolved massive galaxies using photometric redshifts derived with deep near-infr
ared (NIR) medium-band filters. We obtain medium resolution ($R sim$ 3600) NIR spectroscopy with MOSFIRE on the Keck 1 telescope and secure 180 redshifts in a $12times12$ region. We find a prominent spike of 57 galaxies at $z=2.095$ corresponding to the galaxy cluster. The cluster velocity dispersion is measured to be $sigma_{rm v1D}$ = 552 $pm$ 52 km/s. This is the first study of a galaxy cluster in this redshift range ($z gt 2.0$) with the combination of spectral resolution ($sim$26 km/s) and the number of confirmed members (${>}50$) needed to impose a meaningful constraint on the cluster velocity dispersion and map its members over a large field of view. Our $Lambda$CDM cosmological simulation suggests that this cluster will most likely evolve into a Virgo-like cluster with ${rm M_{vir}}{=}10^{14.4pm0.3} {rm M_odot}$ ($68%$ confidence) at $zsim$ 0. The theoretical expectation of finding such a cluster is $sim$ $4%$. Our results demonstrate the feasibility of studying galaxy clusters at $z > 2$ in the same detailed manner using multi-object NIR spectrographs as has been done in the optical in lower redshift clusters.
With the rapid progress in metallicity gradient studies at high-redshift, it is imperative that we thoroughly understand the systematics in these measurements. This work investigates how the [NII]/Halpha ratio based metallicity gradients change with
angular resolution, signal-to-noise (S/N), and annular binning parameters. Two approaches are used: 1. We downgrade the high angular resolution integral-field data of a gravitationally lensed galaxy and re-derive the metallicity gradients at different angular resolution; 2. We simulate high-redshift integral field spectroscopy (IFS) observations under different angular resolution and S/N conditions using a local galaxy with a known gradient. We find that the measured metallicity gradient changes systematically with angular resolution and annular binning. Seeing-limited observations produce significantly flatter gradients than higher angular resolution observations. There is a critical angular resolution limit beyond which the measured metallicity gradient is substantially different to the intrinsic gradient. This critical angular resolution depends on the intrinsic gradient of the galaxy and is < 0.02 arcsec for our simulated galaxy. We show that seeing-limited high-redshift metallicity gradients are likely to be strongly affected by resolution-driven gradient flattening. Annular binning with a small number of annuli produces a more flattened gradient than the intrinsic gradient due to weak line smearing. For 3-annuli bins, a minimum S/N of ~ 5 on the [NII] line is required for the faintest annulus to constrain the gradients with meaningful errors.
We present a comprehensive observational study of the gas phase metallicity of star-forming galaxies from z ~ 0 -> 3. We combine our new sample of gravitationally lensed galaxies with existing lensed and non-lensed samples to conduct a large investig
ation into the mass-metallicity (MZ) relation at z > 1. We apply a self-consistent metallicity calibration scheme to investigate the metallicity evolution of star-forming galaxies as a function of redshift. The lensing magnification ensures that our sample spans an unprecedented range of stellar mass (3*10^{7}-6*10^{10} M_sun). We find that at the median redshift of z=2.07, the median metallicity of the lensed sample is 0.35 dex lower than the local SDSS star-forming galaxies and 0.18 dex lower than the z ~ 0.8 DEEP2 galaxies. We also present the z ~ 2 MZ relation using 19 lensed galaxies. A more rapid evolution is seen between z ~ 1->3 than z ~ 0 -> 1 for the high-mass galaxies (10^{9.5-11} M_sun), with almost twice as much enrichment between z ~ 1 -> 3 than between z ~ 1 -> 0. We compare this evolution with the most recent cosmological hydrodynamic simulations with momentum driven winds. We find that the model metallicity is consistent with the observed metallicity within the observational error for the low mass bins. However, for higher masses, the model over-predicts the metallicity at all redshifts. The over-prediction is most significant in the highest mass bin of 10^{10-11} M_sun.
We present the spatially resolved emission line ratio properties of a ~10^10 M_sun star-forming galaxy at redshift z=1.03. This galaxy is gravitationally lensed as a triple-image giant arc behind the massive lensing cluster Abell 2667. The main image
of the galaxy has magnification factors of 14+/-2.1 in flux and ~ 2 by 7 in area, yielding an intrinsic spatial resolution of 115-405 pc after AO correction with OSIRIS at KECK II. The HST morphology shows a clumpy structure and the Halpha kinematics indicates a large velocity dispersion with V_{max} sin(i)/sigma ~ 0.73, consistent with high redshift disk galaxies of similar masses. From the [NII]/Halpha line ratios, we find that the central 350 parsec of the galaxy is dominated by star formation. The [NII]/Halpha line ratios are higher in the outer-disk than in the central regions. Most noticeably, we find a blue-shifted region of strong [NII]/Halpha emission in the outer disk. Applying our recent HII region and slow-shock models, we propose that this elevated [NII]/Halpha ratio region is contaminated by a significant fraction of shock excitation due to galactic outflows. Our analysis suggests that shocked regions may mimic flat or inverted metallicity gradients at high redshift.
We present the first metallicity gradient measurement for a grand-design face-on spiral galaxy at z~1.5. This galaxy has been magnified by a factor of 22$times$ by a massive, X-ray luminous galaxy cluster MACS,J1149.5+2223 at z=0.544. Using the Laser
Guide Star Adaptive Optics aided integral field spectrograph OSIRIS on KECK II, we target the Halpha emission and achieve a spatial resolution of 0.1, corresponding to a source plane resolution of 170 pc. The galaxy has well-developed spiral arms and the nebular emission line dynamics clearly indicate a rotationally supported disk with V_{rot}/sigma~4. The best-fit disk velocity field model yields a maximum rotation of V_{rot} sin{i}=150$pm$15 km s^{-1}, and a dynamical mass of M_{dyn}=1.3$pm0.2times10^{10}csc^2(i) M_{odot} (within 2.5,kpc), where the inclination angle i=45$pm10^{circ}$. Based on the [NII] and Halpha ratios, we measured the radial chemical abundance gradient from the inner hundreds of parsecs out to ~5 kpc. The slope of the gradient is -0.16$pm$0.02 dex kpc$^{-1}$, significantly steeper than the gradient of late-type or early-type galaxies in the local universe. If representative of disk galaxies at z~1.5, our results support an inside-out disk formation scenario in which early infall/collapse in the galaxy center builds a chemically enriched nucleus, followed by slow enrichment of the disk over the next 9 Gyr.
We present the rest-frame optical spectrum of a strongly lensed galaxy at redshift z =1.7 behind the cluster Abell 1689. We detect the temperature sensitive auroral line [O III] 4363, which allows the first direct metallicity measurement for galaxies
at z > 1. Our high signal-to-noise spectrum indicates that the target is an extremely low metallicity star-forming galaxy.We estimate an intrinsic absolute B band magnitude of M_{B}=-18.3 pm 0.1$, with a stellar mass of 4.4$pm1.2times10^{8}$ M$_{odot}$. This galaxy extends the luminosity-metallicity relation of star-forming galaxies at z > 2 by more than an order of magnitude. Given the double-nuclei like morphology and velocity profile of ha, we tentatively suggest that it could be a merger or a proto-rotating disk galaxy.
