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Register a new userZFIRE: The Kinematics of Star-Forming Galaxies as a Function of Environment at z~2
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We perform a kinematic analysis of galaxies at $zsim2$ in the COSMOS legacy field using near-infrared (NIR) spectroscopy from Keck/MOSFIRE as part of the ZFIRE survey. Our sample consists of 75 Ks-band selected star-forming galaxies from the ZFOURGE survey with stellar masses ranging from log(M$_{star}$/M$_{odot}$)$=9.0-11.0$, 28 of which are members of a known overdensity at $z=2.095$. We measure H$alpha$ emission-line integrated velocity dispersions ($sigma_{rm int}$) from 50$-$230 km s$^{-1}$, consistent with other emission-line studies of $zsim2$ field galaxies. From these data we estimate virial, stellar, and gas masses and derive correlations between these properties for cluster and field galaxies at $zsim2$. We find evidence that baryons dominate within the central effective radius. However, we find no statistically significant differences between the cluster and the field, and conclude that the kinematics of star-forming galaxies at $zsim2$ are not significantly different between the cluster and field environments.
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The global star formation rates (SFR) of galaxies at fixed stellar masses increase with redshift and are known to vary with environment unto z~2. We explore here whether the changes in the star formation rates can also apply to the electron densities of the inter-stellar medium (ISM) by measuring the [OII] (3727A/3729A) ratio for cluster and field galaxies at z~2. We measure a median electron density of ne = 366+/-84 cm-3 for six galaxies (with 1-sigma scatter = 163 cm-3) in the UDS proton-cluster at z=1.62. We find that the median electron density of galaxies in the UDS photo-cluster environment is three times higher compared to the median electron density of field galaxies (ne = 113+/- 63 cm-3 and 1-sigma scatter = 79 cm-3) at comparable redshifts, stellar mass and SFR. However, we note that a sample of six photo-cluster galaxies is insufficient to reliably measure the electron density in the average porto-cluster environment at z~2. We conclude that the electron density increases with redshift in both cluster and field environments up to z~2 (ne = 30 +/- 1 cm-3 for z ~ 0 to ne =254+/- 76 cm-3 for z~1.5). We find tentative evidence (~2.6 sigma ) for a possible dependence of electron density on environment, but the results require confirmation with larger sample sizes.
We perform a kinematic and morphological analysis of 44 star-forming galaxies at $zsim2$ in the COSMOS legacy field using near-infrared spectroscopy from Keck/MOSFIRE and F160W imaging from CANDELS/3D-HST as part of the ZFIRE survey. Our sample consists of cluster and field galaxies from $2.0 < z < 2.5$ with K band multi-object slit spectroscopic measurements of their H$alpha$ emission lines. H$alpha$ rotational velocities and gas velocity dispersions are measured using the Heidelberg Emission Line Algorithm (HELA), which compares directly to simulated 3D data-cubes. Using a suite of simulated emission lines, we determine that HELA reliably recovers input S$_{0.5}$ and angular momentum at small offsets, but $V_{2.2}/sigma_g$ values are offset and highly scattered. We examine the role of regular and irregular morphology in the stellar mass kinematic scaling relations, deriving the kinematic measurement S$_{0.5}$, and finding $log(S_{0.5}) = (0.38pm0.07)log(M/M_{odot}-10) + (2.04pm0.03)$ with no significant offset between morphological populations and similar levels of scatter ($sim0.16$ dex). Additionally, we identify a correlation between M$_{star}$ and $V_{2.2}/sigma_g$ for the total sample, showing an increasing level of rotation dominance with increasing M$_{star}$, and a high level of scatter for both regular and irregular galaxies. We estimate the specific angular momenta ($j_{disk}$) of these galaxies and find a slope of $0.36pm0.12$, shallower than predicted without mass-dependent disk growth, but this result is possibly due to measurement uncertainty at M$_{star}$ $<$ 9.5. However, through a K-S test we find irregular galaxies to have marginally higher $j_{disk}$ values than regular galaxies, and high scatter at low masses in both populations.
We use ZFIRE and ZFOURGE observations with the Spectral Energy Distribution (SED) fitting tool Prospector to reconstruct the star formation histories (SFHs) of proto-cluster and field galaxies at $zsim 2 $ and compare our results to the TNG100 run of the IllustrisTNG cosmological simulation suite. In the observations, we find that massive proto-cluster galaxies ($log[{rm M}_{ast}/{rm M}_{odot}]>$10.5) form $45 pm 8 %$ of their total stellar mass in the first $2$ Gyr of the Universe compared to $31 pm 2 %$ formed in the field galaxies. In both observations and simulations, massive proto-cluster galaxies have a flat/declining SFH with decreasing redshift compared to rising SFH in their field counterparts. Using IllustrisTNG, we find that massive galaxies ($log[{rm M}_{ast}/{rm M}_{odot}] geq 10.5$) in both environments are on average $approx190$ Myr older than low mass galaxies ($log[{rm M}_{ast}/{rm M}_{odot}]= 9-9.5$). However, the difference in mean stellar ages of cluster and field galaxies is minimal when considering the full range in stellar mass ($log[{rm M}_{ast}/{rm M}_{odot}] geq 9$). We explore the role of mergers in driving the SFH in IllustrisTNG and find that massive cluster galaxies consistently experience mergers with low gas fraction compared to other galaxies after 1 Gyr from the Big Bang. We hypothesize that the low gas fraction in the progenitors of massive cluster galaxies is responsible for the reduced star formation.
We present an overview and the first data release of ZFIRE, a spectroscopic redshift survey of star-forming galaxies that utilizes the MOSFIRE instrument on Keck-I to study galaxy properties in rich environments at $1.5<z<2.5$. ZFIRE measures accurate spectroscopic redshifts and basic galaxy properties derived from multiple emission lines. The galaxies are selected from a stellar mass limited sample based on deep near infra-red imaging ($mathrm{K_{AB}<25}$) and precise photometric redshifts from the ZFOURGE and UKIDSS surveys as well as grism redshifts from 3DHST. Between 2013--2015 ZFIRE has observed the COSMOS and UDS legacy fields over 13 nights and has obtained 211 galaxy redshifts over $1.57<z<2.66$ from a combination of nebular emission lines (such as Halpha, NII, Hbeta, OII, OIII, SII) observed at 1--2micron. Based on our medium-band NIR photometry, we are able to spectrophotometrically flux calibrate our spectra to around10% accuracy. ZFIRE reaches $5sigma$ emission line flux limits of around$mathrm{3times10^{-18}~erg/s/cm^2}$ with a resolving power of $R=3500$ and reaches masses down to around10$^{9}$msol. We confirm that the primary input survey, ZFOURGE, has produced photometric redshifts for star-forming galaxies (including highly attenuated ones) accurate to $Delta z/(1+zmathrm{_{spec})}=0.015$ with $0.7%$ outliers. We measure a slight redshift bias of $<0.001$, and we note that the redshift bias tends to be larger at higher masses. We also examine the role of redshift on the derivation of rest-frame colours and stellar population parameters from SED fitting techniques. The ZFIRE survey extends spectroscopically-confirmed $zsim 2$ samples across a richer range of environments, here we make available the first public release of the data for use by the community.footnote{url{http://zfire.swinburne.edu.au}}
We present results from IROCKS (Intermediate Redshift OSIRIS Chemo-Kinematic Survey) for sixteen z~1 and one z~1.4 star-forming galaxies. All galaxies were observed with OSIRIS with the laser guide star adaptive optics system at Keck Observatory. We use rest-frame nebular Ha emission lines to trace morphologies and kinematics of ionized gas in star-forming galaxies on sub-kiloparsec physical scales. We observe elevated velocity dispersions (sigma > 50 km/s) seen in z > 1.5 galaxies persist at z~1 in the integrated galaxies. Using an inclined disk model and the ratio of v/sigma, we find that 1/3 of the z~1 sample are disk candidates while the other 2/3 of the sample are dominated by merger-like and irregular sources. We find that including extra attenuation towards HII regions derived from stellar population synthesis modeling brings star formation rates (SFR) using Ha and stellar population fit into a better agreement. We explore properties of compact Ha sub-component, or clump, at z~1 and find that they follow a similar size-luminosity relation as local HII regions but are scaled-up by an order of magnitude with higher luminosities and sizes. Comparing the z~1 clumps to other high-redshift clump studies, we determine that the clump SFR surface density evolves as a function of redshift. This may imply clump formation is directly related to the gas fraction in these systems and support disk fragmentation as their formation mechanism since gas fraction scales with redshift.
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