Physical Properties of a Pilot Sample of Spectroscopic Close Pair Galaxies at z ~ 2

We use Hubble Space Telescope Wide-Field Camera 3 (HST/WFC3) rest-frame optical imaging to select a pilot sample of star-forming galaxies in the redshift range z = 2.00-2.65 whose multi-component morphologies are consistent with expectations for major mergers. We follow up this sample of major merger candidates with Keck/NIRSPEC longslit spectroscopy obtained in excellent seeing conditions (FWHM ~ 0.5 arcsec) to obtain Halpha-based redshifts of each of the morphological components in order to distinguish spectroscopic pairs from false pairs created by projection along the line of sight. Of six pair candidates observed, companions (estimated mass ratios 5:1 and 7:1) are detected for two galaxies down to a 3sigma limiting emission-line flux of ~ 10^{-17} erg/s/cm2. This detection rate is consistent with a ~ 50% false pair fraction at such angular separations (1-2 arcsec), and with recent claims that the star-formation rate (SFR) can differ by an order of magnitude between the components in such mergers. The two spectroscopic pairs identified have total SFR, SFR surface densities, and stellar masses consistent on average with the overall z ~ 2 star forming galaxy population.Comment: 11 pages, 5 figures. Accepted for publication in Ap

ZAP's stress granule localization is correlated with its antiviral activity and induced by virus replication.

Cellular antiviral programs encode molecules capable of targeting multiple steps in the virus lifecycle. Zinc-finger antiviral protein (ZAP) is a central and general regulator of antiviral activity that targets pathogen mRNA stability and translation. ZAP is diffusely cytoplasmic, but upon infection ZAP is targeted to particular cytoplasmic structures, termed stress granules (SGs). However, it remains unclear if ZAP's antiviral activity correlates with SG localization, and what molecular cues are required to induce this localization event. Here, we use Sindbis virus (SINV) as a model infection and find that ZAP's localization to SGs can be transient. Sometimes no apparent viral infection follows ZAP SG localization but ZAP SG localization always precedes accumulation of SINV non-structural protein, suggesting virus replication processes trigger SG formation and ZAP recruitment. Data from single-molecule RNA FISH corroborates this finding as the majority of cells with ZAP localization in SGs contain low levels of viral RNA. Furthermore, ZAP recruitment to SGs occurred in ZAP-expressing cells when co-cultured with cells replicating full-length SINV, but not when co-cultured with cells replicating a SINV replicon. ZAP recruitment to SGs is functionally important as a panel of alanine ZAP mutants indicate that the anti-SINV activity is correlated with ZAP's ability to localize to SGs. As ZAP is a central component of the cellular antiviral programs, these data provide further evidence that SGs are an important cytoplasmic antiviral hub. These findings provide insight into how antiviral components are regulated upon virus infection to inhibit virus spread

The Physical Nature of Rest-UV Galaxy Morphology During the Peak Epoch of Galaxy Formation

Motivated by the irregular and little-understood morphologies of z ~ 2 - 3 galaxies, we use non-parametric coefficents to quantify the morphologies of 216 galaxies which have been spectroscopically confirmed to lie at redshifts z = 1.8 - 3.4 in the GOODS-N field. Using measurements of ultraviolet (UV) and optical spectral lines, multi-band photometric data, and stellar population models we statistically assess possible correlations between galaxy morphology and physical observables such as stellar mass, star formation rate, and the strength of galaxy-scale outflows. We find evidence that dustier galaxies have more nebulous UV morphologies and that larger, more luminous galaxies may drive stronger outflows, but otherwise conclude that UV morphology is either statistically decoupled from the majority of physical observables or determined by too complex a combination of physical processes to provide characterizations with predictive power. Given the absence of strong correlations between UV morphology and physical parameters such as star formation rates, we are therefore unable to support the hypothesis that morphologically irregular galaxies predominantly represent major galaxy mergers. Comparing galaxy samples, we find that IR-selected BzK galaxies and radio-selected submillimeter galaxies (SMGs) have UV morphologies similar to the optically selected sample, while distant red galaxies (DRGs) are more nebulous.Comment: 26 pages. Accepted for publication in the ApJ. Version with full resolution figures is available at http://www.astro.caltech.edu/~drlaw/Papers/UVmorph.pd

Morphologies of Galaxies in and around a Protocluster at z=2.300

We present results from the first robust investigation of galaxy morphology as a function of environment at z>1.5. Our study is motivated by the fact that star-forming galaxies contained within a protocluster at z=2.3 in the HS1700+64 field have significantly older ages and larger stellar masses on average than those at similar redshifts but more typical environmental densities. In the analysis of HST/ACS images, we apply non-parametric statistics to characterize the rest-frame UV morphologies of a sample of 85 UV-selected star-forming galaxies at z=1.7-2.9, 22 of which are contained in the protocluster. The remaining 63 control-sample galaxies are not in the protocluster but have a similar mean redshift of ~2.3. We find no environmental dependence for the distributions of morphological properties. Combining the measured morphologies with the results of population synthesis modeling, we find only weak correlations, if any, between morphological and stellar population properties such as stellar mass, age, extinction and star-formation rate. Given the incomplete census of the protocluster galaxy population, and the lack of correlation between rest-frame UV morphology and star-formation history at z~2 within our sample, the absence of environmental trends in the distribution of morphological properties is not surprising. Additionally, using a larger sample of photometric candidates, we compare morphological distributions for 282 UV-selected and 43 near-IR-selected galaxies. While the difference in the degree of nebulosity between the two samples appears to be a byproduct of the fainter average rest-frame UV surface brightness of the near-IR-selected galaxies, we find that, among the lowest surface brightness galaxies, the near-IR-selected objects have significantly smaller angular sizes (abridged).Comment: 25 pages including 16 figures. Accepted for publication in ApJ. Version with full resolution figures available at http://www.astro.princeton.edu/~apeter/LBG/papers/peter2007_fullres.ps.g

Integral Field Spectroscopy of High-Redshift Star Forming Galaxies with Laser Guided Adaptive Optics: Evidence for Dispersion-Dominated Kinematics

We present early results from an ongoing study of the kinematic structure of star-forming galaxies at redshift z ~ 2 - 3 using integral-field spectroscopy of rest-frame optical nebular emission lines in combination with Keck laser guide star adaptive optics (LGSAO). We show kinematic maps of 3 target galaxies Q1623-BX453, Q0449-BX93, and DSF2237a-C2 located at redshifts z = 2.1820, 2.0067, and 3.3172 respectively, each of which is well-resolved with a PSF measuring approximately 0.11 - 0.15 arcsec (~ 900 - 1200 pc at z ~ 2-3) after cosmetic smoothing. Neither galaxy at z ~ 2 exhibits substantial kinematic structure on scales >~ 30 km/s; both are instead consistent with largely dispersion-dominated velocity fields with sigma ~ 80 km/s along any given line of sight into the galaxy. In contrast, DSF2237a-C2 presents a well-resolved gradient in velocity over a distance of ~ 4 kpc with peak-to-peak amplitude of 140 km/s. It is unlikely that DSF2237a-C2 represents a dynamically cold rotating disk of ionized gas as the local velocity dispersion of the galaxy (sigma = 79 km/s) is comparable to the observed shear. Using extant multi-wavelength spectroscopy and photometry we relate these kinematic data to physical properties such as stellar mass, gas fraction, star formation rate, and outflow kinematics and consider the applicability of current galaxy formation models.[Abridged]Comment: 19 pages, 10 figures (5 color); accepted for publication in ApJ. Version with full-resolution figures is available at http://www.astro.caltech.edu/~drlaw/Papers/OSIRIS_data1.pd

High Velocity Dispersion in A Rare Grand Design Spiral Galaxy at Redshift z=2.18

Although relatively common in the local Universe, only one grand-design spiral galaxy has been spectroscopically confirmed to lie at z>2 (HDFX 28; z=2.011), and may prove to be a major merger that simply resembles a spiral in projection. The rarity of spirals has been explained as a result of disks being dynamically 'hot' at z>2 which may instead favor the formation of commonly-observed clumpy structures. Alternatively, current instrumentation may simply not be sensitive enough to detect spiral structures comparable to those in the modern Universe. At redshifts <2, the velocity dispersion of disks decreases, and spiral galaxies are more numerous by z~1. Here we report observations of the grand design spiral galaxy Q2343-BX442 at z=2.18. Spectroscopy of ionized gas shows that the disk is dynamically hot, implying an uncertain origin for the spiral structure. The kinematics of the galaxy are consistent with a thick disk undergoing a minor merger, which can drive the formation of short-lived spiral structure. A duty cycle of < 100 Myr for such tidally-induced spiral structure in a hot massive disk is consistent with their rarity.Comment: Accepted for publication in Nature (July 19 2012). Includes 15-page supplemen

An HST/WFC3-IR Morphological Survey of Galaxies at z = 1.5-3.6: II. The Relation between Morphology and Gas-Phase Kinematics

We analyze rest-frame optical morphologies and gas-phase kinematics as traced by rest-frame far-UV and optical spectra for a sample of 204 star forming galaxies in the redshift range z ~ 2-3 drawn from the Keck Baryonic Structure Survey (KBSS). We find that spectroscopic properties and gas-phase kinematics are closely linked to morphology: compact galaxies with semi-major axis radii r <~ 2 kpc are substantially more likely than their larger counterparts to exhibit LyA in emission. Although LyA emission strength varies widely within galaxies of a given morphological type, all but one of 19 galaxies with LyA equivalent width W_LyA > 20 Angstroms have compact and/or multiple-component morphologies with r <= 2.5 kpc. The velocity structure of absorption lines in the galactic continuum spectra also varies as a function of morphology. Galaxies of all morphological types drive similarly strong outflows (as traced by the blue wing of interstellar absorption line features), but the outflows of larger galaxies are less highly ionized and exhibit larger optical depth at the systemic redshift that may correspond to a decreasing efficiency of feedback in evacuating gas from the galaxy. This v ~ 0 km/s gas is responsible both for shifting the mean absorption line redshift and attenuating W_LyA (via a longer resonant scattering path) in galaxies with larger rest-optical half light radii. In contrast to galaxies at lower redshifts, there is no evidence for a correlation between outflow velocity and inclination, suggesting that outflows from these puffy and irregular systems may be poorly collimated. (Abbrev.)Comment: 18 pages, 11 figures. Revised version accepted for publication in ApJ. Version with full-resolution figures is available at http://di.utoronto.ca/~drlaw/Papers/wfc3_uvspec.pd

Imaging Spectroscopy of Ionized Gaseous Nebulae around Optically Faint AGNs at Redshift z ∼ 2

We present Keck/OSIRIS laser guide-star assisted adaptive optics (LGSAO) integral-field spectroscopy of [O III] λ5007 nebular emission from 12 galaxies hosting optically faint (R = 20–25; ν L_ν ~ 10^(44) – 10^(46) erg s^(−1)) active galactic nuclei (AGNs) at redshift z ~ 2–3. In combination with deep Hubble Space Telescope Wide Field Camera 3 (HST/WFC3) rest-frame optical imaging, Keck/MOSFIRE rest-optical spectroscopy, and Keck/KCWI rest-UV integral-field spectroscopy, we demonstrate that both the continuum and emission-line structures of these sources exhibit a wide range of morphologies, from compact, isolated point sources to double-AGN merging systems with extensive ~50 kpc tidal tails. One of the 12 galaxies previously known to exhibit a proximate damped Lyα system coincident in redshift with the galaxy shows evidence for both an extended [O III] narrow-line emission region and spatially offset Lyα emission (with morphologically distinct blueshifted and redshifted components) indicative of large-scale gas flows photoionized by the central AGN. We do not find widespread evidence of star formation in the host galaxies surrounding these AGNs; the [O III] velocity dispersions tend to be high (σ = 100–500 km s^(-1)), the continuum morphologies are much more compact than a mass-matched star-forming comparison sample, and the diagnostic nebular emission-line ratios are dominated by an AGN-like ionizing spectrum. The sample is most consistent with a population of AGNs that radiate at approximately their Eddington limit and photoionize extended [O III] nebulae whose characteristic sizes scale approximately as the square root of the AGN luminosity