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Lya nebulae, or "Lya blobs", are extended (up to ~100 kpc), bright (L[Lya] > 10^43 erg/s) clouds of Lya emitting gas that tend to lie in overdense regions at z ~ 2--5. The origin of the Lya emission remains unknown, but recent theoretical work suggests that measuring the polarization might discriminate among powering mechanisms. Here we present the first narrowband, imaging polarimetry of a radio-loud Lya nebula, B3 J2330+3927 at z=3.09, with an embedded active galactic nucleus (AGN). The AGN lies near the blob's Lya emission peak and its radio lobes align roughly with the blob's major axis. With the SPOL polarimeter on the 6.5m MMT telescope, we map the total (Lya + continuum) polarization in a grid of circular apertures of radius 0.6" (4.4kpc), detecting a significant (>2sigma) polarization fraction P in nine apertures and achieving strong upper-limits (as low as 2%) elsewhere. P increases from, Comment: 9 pages, 7 figures, accepted for publication in ApJ

We report the detection of diffuse Ly$\alpha$ emission, or Ly$\alpha$ halos (LAHs), around star-forming galaxies at $z\approx3.78$ and $2.66$ in the NOAO Deep Wide-Field Survey Bo\"otes field. Our samples consist of a total of $\sim$1400 galaxies, within two separate regions containing spectroscopically confirmed galaxy overdensities. They provide a unique opportunity to investigate how the LAH characteristics vary with host galaxy large-scale environment and physical properties. We stack Ly$\alpha$ images of different samples defined by these properties and measure their median LAH sizes by decomposing the stacked Ly$\alpha$ radial profile into a compact galaxy-like and an extended halo-like component. We find that the exponential scale-length of LAHs depends on UV continuum and Ly$\alpha$ luminosities, but not on Ly$\alpha$ equivalent widths or galaxy overdensity parameters. The full samples, which are dominated by low UV-continuum luminosity Ly$\alpha$ emitters ($M_{\rm UV} \gtrsim -21$), exhibit LAH sizes of 5$\,-\,6\,$kpc. However, the most UV- or Ly$\alpha$-luminous galaxies have more extended halos with scale-lengths of 7$\,-\,9\,$kpc. The stacked Ly$\alpha$ radial profiles decline more steeply than recent theoretical predictions that include the contributions from gravitational cooling of infalling gas and from low-level star formation in satellites. On the other hand, the LAH extent matches what one would expect for photons produced in the galaxy and then resonantly scattered by gas in an outflowing envelope. The observed trends of LAH sizes with host galaxy properties suggest that the physical conditions of the circumgalactic medium (covering fraction, HI column density, and outflow velocity) change with halo mass and/or star-formation rates., Comment: published in ApJ, minor proof corrections applied

We use spatially extended measurements of Ly$\alpha$ as well as less optically thick emission lines from an $\approx$80 kpc Ly$\alpha$ nebula at $z\approx1.67$ to assess the role of resonant scattering and to disentangle kinematic signatures from Ly$\alpha$ radiative transfer effects. We find that the Ly$\alpha$, CIV, HeII, and CIII] emission lines all tell a similar story in this system, and that the kinematics are broadly consistent with large-scale rotation. First, the observed surface brightness profiles are similar in extent in all four lines, strongly favoring a picture in which the Ly$\alpha$ photons are produced in situ instead of being resonantly scattered from a central source. Second, we see low kinematic offsets between Ly$\alpha$ and the less optically thick HeII line ($\sim$100-200 km s$^{-1}$), providing further support for the argument that the Ly$\alpha$ and other emission lines are all being produced within the spatially extended gas. Finally, the full velocity field of the system shows coherent velocity shear in all emission lines: $\approx$500 km s$^{-1}$ over the central $\approx$50 kpc of the nebula. The kinematic profiles are broadly consistent with large-scale rotation in a gas disk that is at least partially stable against collapse. These observations suggest that the Ly$\alpha$ nebula represents accreting material that is illuminated by an offset, hidden AGN or distributed star formation, and that is undergoing rotation in a clumpy and turbulent gas disk. With an implied mass of M(, Comment: Accepted to ApJ; 25 pages in emulateapj format; 15 figures, 4 tables

Using a spectral decomposition technique (Soto & Martin 2012, hereafter Paper I), we investigate the physical origin of the high-velocity emission line gas in a sample of 39 gas-rich, ultraluminous infrared galaxy (ULIRG) mergers. Regions with shock-like excitation were identified in two kinematically distinct regimes, characterized by broad ($��>$ 150 \kms) and narrow linewidths. Here we investigate the physical origin of the high-velocity (broad) emission with shock-like line ratios. Considering the large amount of extinction in these galaxies, the blueshift of the broad emission suggests an origin on the near side of the galaxy and therefore an interpretation as a galactic outflow. The large spatial extent of the broad, shocked emission component is generally inconsistent with an origin in the narrow-line region of a AGN, so we conclude that energy and momentum supplied by the starburst drives these outflows. The new data are used to examine the fraction of the supernova energy radiated by shocks and the mass loss rate in the warm-ionized phase of the wind. We show that the shocks produced by galactic outflows can be recognized in moderately high-resolution, integrated spectra of these nearby, ultraluminous starbursts. The spectral fitting technique introduced in Paper I may therefore be used to improve the accuracy of the physical properties measured for high-redshift galaxies from their (observed frame) infrared spectra., Submitted to ApJ. 12 Pages, 7 Figures, 1 Table. This is a companion paper to "Gas Excitation in ULIRGS: Maps of Diagnostic Emission-Line Ratios in Space and Velocity" by Soto & Martin 2012

Giant Lya nebulae (or Lya "blobs") are likely sites of ongoing massive galaxy formation, but the rarity of these powerful sources has made it difficult to form a coherent picture of their properties, ionization mechanisms, and space density. Systematic narrow-band Lya nebula surveys are ongoing, but the small redshift range covered and the observational expense limit the comoving volume that can be probed by even the largest of these surveys and pose a significant problem when searching for such rare sources. We have developed a systematic search technique designed to find large Lya nebulae at 2, Comment: Accepted to ApJ after minor revision; 25 pages in emulateapj format; 18 figures, 3 tables

Detailed analysis of the substructure of Lya nebulae can put important constraints on the physical mechanisms at work and the properties of galaxies forming within them. Using high resolution HST imaging of a Lya nebula at z~2.656, we have taken a census of the compact galaxies in the vicinity, used optical/near-infrared colors to select system members, and put constraints on the morphology of the spatially-extended emission. The system is characterized by (a) a population of compact, low luminosity (~0.1 L*) sources --- 17 primarily young, small (Re~1-2 kpc), disky galaxies including an obscured AGN --- that are all substantially offset (>20 kpc) from the line-emitting nebula; (b) the lack of a central galaxy at or near the peak of the Lya emission; and (c) several nearly coincident, spatially extended emission components --- Lya, HeII, and UV continuum --- that are extremely smooth. These morphological findings are difficult to reconcile with theoretical models that invoke outflows, cold flows, or resonant scattering, suggesting that while all of these physical phenomena may be occurring, they are not sufficient to explain the powering and large extent of Lya nebulae. In addition, although the compact galaxies within the system are irrelevant as power sources, the region is significantly overdense relative to the field galaxy population (by at least a factor of 4). These observations provide the first estimate of the luminosity function of galaxies within an individual Lya nebula system, and suggest that large Lya nebulae may be the seeds of galaxy groups or low-mass clusters., Accepted to ApJ after minor revision; 33 pages in emulateapj format, 21 figures, 4 tables

We have discovered a ~45 kpc Lya nebula (or Lya ``blob'') at z~1.67 which exhibits strong, spatially-extended HeII emission and very weak CIV and CIII] emission. This is the first spatially-extended Lya+HeII emitter observed and the lowest redshift Lya blob yet found. Strong Lya and HeII-1640 emission in the absence of metal lines has been proposed as a unique observational signature of primordial galaxy formation (e.g., from gravitational cooling radiation or Population III star formation), but no convincing examples of spatially-extended Lya+HeII emitters have surfaced either in Lya-emitting galaxy surveys at high redshifts (z > 4) or in studies of Lya nebulae at lower redshifts. From comparisons with photoionization models, we find that the observed line ratios in this nebula are consistent with low metallicity gas (Z < 10^-2 - 10^-3 Z_sun), but that this conclusion depends on the unknown ionization parameter of the system. The large HeII equivalent width (~37+/-10A) and the large HeII/Lya ratio (0.12+/-0.04) suggest that the cloud is being illuminated by a hard ionizing continuum, either an AGN or very low metallicity stars, or perhaps powered by gravitational cooling radiation. Thus far there is no obvious sign of a powerful AGN in or near the system, so in order to power the nebula while remaining hidden from view even in the mid-infrared, the AGN would need to be heavily obscured. Despite the strong Lya+HeII emission, it is not yet clear what is the dominant power source for this nebula. The system therefore serves as an instructive example of how the complexities of true astrophysical sources will complicate matters when attempting to use a strong Lya+HeII signature as a unique tracer of primordial galaxy formation., Accepted for publication in ApJ; emulateapj format, 17 pages, 7 figures, 3 tables; updated coordinates

With the goal of investigating the degree to which the mid-infrared emission traces the star formation rate (SFR), we analyze Spitzer 8 um and 24 um data of star-forming regions in a sample of 33 nearby galaxies with available HST/NICMOS images in the Paschen-alpha (1.8756 um) emission line. The galaxies are drawn from the Spitzer Infrared Nearby Galaxies Survey (SINGS) sample, and cover a range of morphologies and a factor ~10 in oxygen abundance. Published data on local low-metallicity starburst galaxies and Luminous Infrared Galaxies are also included in the analysis. Both the stellar-continuum-subtracted 8 um emission and the 24 um emission correlate with the extinction-corrected Pa-alpha line emission, although neither relationship is linear. Simple models of stellar populations and dust extinction and emission are able to reproduce the observed non-linear trend of the 24 um emission versus number of ionizing photons, including the modest deficiency of 24 um emission in the low metallicity regions, which results from a combination of decreasing dust opacity and dust temperature at low luminosities. Conversely, the trend of the 8 um emission as a function of the number of ionizing photons is not well reproduced by the same models. The 8 um emission is contributed, in larger measure than the 24 um emission, by dust heated by non-ionizing stellar populations, in agreement with previous findings. Two SFR calibrations, one using the 24 um emission and the other using a combination of the 24 um and H-alpha luminosities (Kennicutt et al. 2007), are presented. No calibration is presented for the 8 um emission, because of its significant dependence on both metallicity and environment. The calibrations presented here should be directly applicable to systems dominated by on-going star formation., Comment: 67 pages, 15 figures, accepted for publication on the Astrophysical Journal; replacement contains: correction to equation 8; important tweaks to equation 9; various typos corrected

We explore the nature of variations in dust emission within an individual galaxy using 3.6 - 160 micron Spitzer Space Telescope observations and 450 and 850 micron James Clerk Maxwell Telescope observations of the edge-on Sd spiral galaxy NGC 4631 with the goals of understanding the relation between polycyclic aromatic hydrocarbons (PAH) and dust emission, studying the variations in the colors of the dust emission, and searching for possible excess submillimeter emission compared to what is anticipated based on dust models applied to the mid- and far-infrared data. PAH emission at 8 micron is found to correlate best with hot dust emission at 24 micron on kiloparsec scales, although the relation breaks down on scales equal to hundreds of parsecs, possibly because of differences in the mean free paths between the photons that excite the PAHs and heat the dust and possibly because the PAHs are destroyed by the hard radiation fields in the centers of some star formation regions. The ratio of 8 micron PAH emission to 160 micron cool dust emission appears to be a function of radius. The 70/160 and 160/450 micron flux density ratios are remarkably constant even though the surface brightness varies by a factor of 25 in each wave band, which suggests that the emission is from dust heated by a nearly-uniform radiation field. Globally, we find an excess of 850 micron emission relative to what would be predicted by dust models. The 850 micron excess is highest in regions with low 160 micron surface brightness, although the strength and statistical significance of this result depends on the model fit to the data. We rule out variable emissivity functions or ~4 K dust as the possible origins of this 850 micron emission, but we do discuss the other possible mechanisms that could produce the emission.

We obtained medium-resolution spectra of 336 quasar candidates in the COSMOS HST/Treasury field using the MMT 6.5-meter telescope and the Hectospec multi-object spectrograph. Candidates were drawn from the Sloan Digital Sky Survey (SDSS) DR1 catalog using quasar flags set by the SDSS multi-color quasar target selection algorithm. In this paper we present our discovery spectra from 1.39 square degrees (69.5% of the COSMOS field) and a discussion of the selection method and yields. We confirmed 95 quasars, including at least 2 BALs; 80 of these are new quasars that do not appear in previous quasar confirmation follow-up studies. The candidates additionally included 184 compact emission-line galaxies, a third of which are likely Type 2 AGN, and 12 stars. The quasars span a range in magnitude of 18.3, Comment: Accepted for publication in ApJ; emulateapj style; 25 pages, 13 figures, 4 tables