Dawn K. Erb

The resonantly scattered Lyα line illuminates the extended halos of neutral hydrogen in the circumgalactic medium of galaxies. We present integral field Keck Cosmic Web Imager observations of double-peaked, spatially extended Lyα emission in 12 relatively low-mass (M⋆∼ 10 9 M⊙) z∼ 2 galaxies characterized by extreme nebular emission lines. Using individual spaxels and small bins as well as radially binned profiles of larger regions, we find that for most objects in the sample the Lyα blue-to-red peak ratio increases, the peak separation decreases, and the fraction of flux emerging at line center increases with radius. We use new radiative transfer simulations to model each galaxy with a clumpy, multiphase outflow with radially varying outflow velocity, and self-consistently apply the same velocity model to the low-ionization interstellar absorption lines. These models reproduce the trends of peak ratio, peak …

The COS Legacy Archive Spectroscopic SurveY (CLASSY), a Hubble Space Telescope (HST) treasury program, used data from the Cosmic Origins Spectrograph (COS) to create the first catalog of high signal-to-noise, high-resolution, and broad-wavelength spectra of local high-z analog galaxies in the rest-frame UV (1150-2000 Å). Analysis of the far-ultraviolet emission lines of these galaxies helps us understand the properties of the interstellar medium (ISM) of the first generation of galaxies, a focus for observation by the James Webb Space Telescope (JWST). To more robustly understand the conditions that excite these emission lines, we need to constrain the spatial distribution and variation of the UV photons arriving from such analog galaxies within and beyond the COS aperture radius of 2.5". We present methods and preliminary analysis from an HST project taking high-resolution images of three nearby low …

Q0142-BX165 3.69±0.03 43.2 1.57±0.22 8.4 0.19±0.027 22.6 54.1±1.9 84.5±2.7 0.17±0.005 658±10 0.021±0.002 Q0142-BX186 0.36±0.02 42.2 0.31±0.04 8.4 0.04±0.005 16.4 30.9±6.0 49.6±8.0 0.32±0.067 687±31 0.019±0.016 Q0207-BX87 3.72±0.03 43.1 3.88±0.69 9.0 0.43±0.076 25.6 73.3±4.1 130.3±6.9 0.23±0.007 522±13 0.074±0.002 Q0207-BX144 4.61±0.04 43.2 2.06±0.22 8.5 0.24±0.026 27.1 44.1±2.5 110.2±5.1 0.18±0.012 631±7− 0.002±0.003 Q0449-BX110 1.98±0.03 42.9 1.10±0.09 9.0 0.12±0.010 20.9 49.8±4.0 87.6±5.4 0.42±0.021 700±13 0.038±0.004 Q0449-BX115 1.73±0.03 42.9 8.57±2.86a 8.9 0.96±0.320 17.1 98.9±10.6 129.7±12.1 0.21±0.011 518±8 0.029±0.003 Q0821-MD36 2.11±0.03 43.1 1.13±0.20 9.1 0.12±0.022 20.2 86.8±7.9 145.8±12.3 0.15±0.009 352±5 0.091±0.003 Q1549-BX102 1.87±0.03 42.9 2.71±1.13 8.9 0.30±0.127 21.6 44.9±3.8 78.0±5.2 0.43±0.019 649±9 0.016±0.004 …

Our first deep observations of high redshift galaxies revealed exceptionally strong high-ionization nebular emission lines. Characterizing and describing the detailed observations of the earliest galaxies with JWST and future extremely large telescopes will hinge on our understanding of these lines. However, current stellar population synthesis models catastrophically fail to reproduce the observed strengths of these extreme emission lines, often invoking theories of rare phenomena to understand this emission. Fortunately, progress is possible: high-spatial-resolution maps of very-high-ionization emission can help constrain the options for these potentially exotic sources. Here, we propose 25 orbits of high-spatial-resolution HST imaging to map the spatial morphology of HeII 4686 emission in five nearby low-metallicity, highly-ionized galaxies selected for their strong HeII emission. We will compare the spatial …

We provide one of the most comprehensive metallicity studies at z ~ 4 by analyzing the UV/optical HST photometry, and rest-frame VLT-FORS2 ultraviolet and VLT-XSHOOTER optical spectra of J0332-3557, a gravitationally lensed galaxy magnified by a factor of 20. With a 5{\sigma} detection of the auroral O III] {\lambda}1666 line, we are able to derive a direct gas metallicity estimate for our target. We find Zgas = 12 + log(O/H) = 8.26 +/- 0.06, which is compatible with an increasing of both the gas fraction and the outflow metal loading factor from z ~ 0 to z ~ 4. J0332 is the most metal-rich individual galaxy at z > 3.6 for which the C/O ratio has been measured. We derive a low log(C/O)= -1.02 +/- 0.2, which suggests that J0332 is in the early stages of ISM carbon enrichment driven mostly by massive stars. The low C/O also indicates that J0332 is characterized by a low star formation efficiency, higher yields of oxygen and longer burst duration. We find that the EW[C III]1906,9 is as low as ~ 3 {\AA}. The main drivers of the low EW[C III]1906,9 are the higher gas metallicity and the low C/O. J0332 is characterized by one diffuse and two more compact regions ~ 1 kpc in size. We find that the carbon emission mostly originates in the compact knots.

Galactic outflows powered by star formation are a key driver of the baryon cycle, regulating star formation in galaxies and the gaseous content of the circumgalactic medium across cosmic time. We propose to combine high resolution, spatially resolved stellar population measurements from broadband HST imaging with spatially resolved measurements of gas flows from the Keck Cosmic Web Imager (KCWI; all data is already in hand), in order to assess the relationships between star-formation-driven outflows, galactic structure and stellar populations at the peak epoch of star formation. Our sample consists of ten gravitationally lensed galaxies at z~ 2-3, including some of the brightest lensed galaxies known. We have already obtained and analyzed the necessary HST imaging for three objects in the sample, and this combined archival+ GO proposal completes the wavelength coverage with five orbits of new WFC3 …

High-redshift galaxies acquire gas to fuel new star formation by accreting gas from the intergalactic medium (IGM) and the circumgalactic medium (CGM) as well as by merging with other galaxies. Lyα photons produced by star formation within the central HII regions of a galaxy scatter resonantly off of HI gas surrounding the galaxy and thereby illuminate extended halos of HI gas, called Lyα halos, in the CGM of galaxies at both low and high redshifts, which may permit the observation of galaxy growth via IGM accretion or recycled CGM accretion. Here we present new integral field observations from the Keck Cosmic Web Imager (KCWI) of the Lyα halos surrounding a pair of UV continuum-selected galaxies at z= 2.3, Q1700-BX710 and Q1700-BX711 (M∗= 4× 10 8 M⊙), which are separated by 48 proper kpc and reside within the protocluster HS1700+ 643. Our integral field observations reveal that Lyα emission with …

Observations of low-ionization state metal lines provide crucial insights into the interstellar medium (ISM) of galaxies, yet, disentangling the physical processes responsible for the emerging line profiles is difficult. This work investigates how mock spectra generated using a single galaxy in a radiation-hydrodynamical simulation can help us interpret observations of a real galaxy. We create 22,500 C ii and Si ii spectra from the virtual galaxy at different times and through multiple lines of sight and compare them with the 45 observations of low-redshift star-forming galaxies from the COS Legacy Spectroscopic SurveY (classy). We find that the mock profiles provide accurate replicates of the observations of 38 galaxies with a broad range of stellar masses (10 6–10 9 M⊙) and metallicities (0.02–0.55 Z⊙). Additionally, we highlight that aperture losses explain the weakness of the fluorescent emission in several classy …