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Register a new userA Narrowband Imaging Search for [OIII] Emission from Galaxies at z>3
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Harry I. Teplitz
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We present the results of a narrow-band survey of QSO fields at redshifts that place the [OIII](5007) emission line in the 1% 2.16micron filter. We have observed 3 square arcminutes and detected one emission line candidate object in the field around PC 1109+4642. We discuss the possibilities that this object is a star-forming galaxy at the QSO redshift, z_em=3.313 or a Seyfert galaxy. In the former case, we infer a star formation rate of 170 Msun/yr for this Kprime=21.3 object. The galaxy has a compact but resolved morphology, with a FWHM=0.6arcs, or 4.2kpc at z=3.313 (H_0=50 km/s/Mpc and q_0=0.5). The comoving density of such objects in QSO environments appears to be 0.0033Mpc^3, marginally lower (<= 3sigma) than the density observed for Halpha-emitters in absorption-line fields at z~2.5, but similar to the density of Lyman Break Galaxies at z~3. If on the other hand, most of the line emission is [OIII] from a Seyfert 2 nucleus at z=3.31, then the high inferred volume density could imply a large evolution in the Seyfert 2 luminosity function from the current epoch. We find the field containing the object to also contain many faint extended objects in the Kprime image, but little significant excess over the expected number-magnitude relation. We discuss the implication of the emission line being a longer wavelength line at a lower redshift.
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We perform a Very Large Telescope FOcal Reducer and low dispersion Spectrograph 2 (VLT/FORS2) narrowband imaging search around 5 star-forming galaxies at redshift z=0.67-0.69 in the Great Observatories Origins Deep Survey South (GOODS-S) field to constrain the radial extent of large-scale outflows traced by resonantly scattered MgII emission. The sample galaxies span star formation rates in the range 4 $M_{odot}/yr$ < SFR < $40 M_{odot}/yr$ and have stellar masses $9.9 lesssim log M_{*}/M_{odot} lesssim 11.0$, and exhibit outflows traced by MgII absorption with velocities ~150-420 km s$^{-1}$ . These observations are uniquely sensitive, reaching surface brightness limits of 5.81 $times$ $10^{-19}$ ergs sec $^{-1}$ cm$^{-2}$ arcsec$^2$ per 1 arcsec$^2$ aperture (at 5$sigma$ significance). We do not detect any extended emission around any of the sample galaxies, thus placing 5$sigma$ upper limits on the brightness of extended MgII emission of $<6.51 times 10^{-19}$ ergs sec $^{-1}$ cm$^{-2}$ arcsec$^2$ at projected distances $R_{perp} > 8-21$ kpc. The imaging also resolves the MgII absorption observed toward each galaxy spatially, revealing approximately constant absorption strengths across the galaxy disks. In concert with radiative transfer models predicting the surface brightness of MgII emission for a variety of simple wind morphologies, our detection limits suggest that either (1) the extent of the MgII-emitting material in the outflows from these galaxies is limited to $lesssim 20$ kpc; or (2) the outflows are anisotropic and/or dusty.
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We conduct a deep narrow-band imaging survey of 13 Ly$alpha$ blobs (LABs) located in the SSA22 proto-cluster at z~3.1 in the CIV and HeII emission lines in an effort to constrain the physical process powering the Ly$alpha$ emission in LABs. Our observations probe down to unprecedented surface brightness limits of 2.1 $-$ 3.4 $times$ 10$^{-18}$ erg s$^{-1}$ cm$^{-2}$ arcsec$^{-2}$ per 1 arcsec$^2$ aperture (5$sigma$) for the HeII$lambda$1640 and CIV$lambda$1549 lines, respectively. We do not detect extended HeII and CIV emission in any of the LABs, placing strong upper limits on the HeII/Ly$alpha$ and CIV/Ly$alpha$ line ratios, of 0.11 and 0.16, for the brightest two LABs in the field. We conduct detailed photoionization modeling of the expected line ratios and find that, although our data constitute the deepest ever observations of these lines, they are still not deep enough to rule out a scenario where the Ly$alpha$ emission is powered by the ionizing luminosity of an obscured AGN. Our models can accommodate HeII/Ly$alpha$ and CIV/Ly$alpha$ ratios as low as $simeq$0.05 and $simeq$0.07 respectively, implying that one needs to reach surface brightness as low as 1 $-$ 1.5 $times$ 10$^{-18}$ erg s$^{-1}$ cm$^{-2}$ arcsec$^{-2}$ (at 5$sigma$) in order to rule out a photoionization scenario. These depths will be achievable with the new generation of image-slicing integral field units such as VLT/MUSE or Keck/KCWI. We also model the expected HeII/Ly$alpha$ and CIV/Ly$alpha$ in a different scenario, where Ly$alpha$ emission is powered by shocks generated in a large-scale superwind, but find that our observational constraints can only be met for shock velocities $v_{rm s} gtrsim$ 250 km s$^{-1}$, which appear to be in conflict with recent observations of quiescent kinematics in LABs.
To understand how strong emission line galaxies (ELGs) contribute to the overall growth of galaxies and star formation history of the universe, we target Strong ELGs (SELGs) from the ZFOURGE imaging survey that have blended (Hb+[OIII]) rest-frame equivalent widths of >230A and 2.5<zphot<4.0. Using Keck/MOSFIRE, we measure 49 redshifts for galaxies brighter than Ks=25 mag as part of our Multi-Object Spectroscopic Emission Line (MOSEL) survey. Our spectroscopic success rate is ~53% and zphot uncertainty is sigma_z= [Delta(z)/(1+z)]=0.0135. We confirm 31 ELGs at 3<zspec<3.8 and show that Strong ELGs have spectroscopic rest-frame [OIII]5007A equivalent widths of 100-500A and tend to be lower mass systems [log(Mstar/Msun)~8.2-9.6] compared to more typical star-forming galaxies. The Strong ELGs lie ~0.9 dex above the star-forming main-sequence at z~3.5 and have high inferred gas fractions of fgas~>60%, i.e. the inferred gas masses can easily fuel a starburst to double stellar masses within ~10-100 Myr. Combined with recent results using ZFOURGE, our analysis indicates that 1) strong [OIII]5007A emission signals an early episode of intense stellar growth in low mass (Mstar<0.1M*) galaxies and 2) many, if not most, galaxies at z>3 go through this starburst phase. If true, low-mass galaxies with strong [OIII]5007A emission (EW_rest>200A) may be an increasingly important source of ionizing UV radiation at z>3.
We present the first spectroscopic measurements of the [OIII] 5007 A line in two z ~ 3.1 Lyman-alpha emitting galaxies (LAEs) using the new near-infrared instrument LUCIFER1 on the 8.4m Large Binocular Telescope (LBT). We also describe the optical imaging and spectroscopic observations used to identify these Lya emitting galaxies. Using the [OIII] line we have measured accurate systemic redshifts for these two galaxies, and discovered a velocity offset between the [OIII] and Ly-alpha lines in both, with the Lya line peaking 342 and 125 km/s redward of the systemic velocity. These velocity offsets imply that there are powerful outflows in high-redshift LAEs. They also ease the transmission of Lya photons through the interstellar medium and intergalactic medium around the galaxies. By measuring these offsets directly, we can refine both Lya-based tests for reionization, and Lya luminosity function measurements where the Lya forest affects the blue wing of the line. Our work also provides the first direct constraints on the strength of the [OIII] line in high-redshift LAEs. We find [OIII] fluxes of 7 and 36 x 10^-17 erg s^-1 cm^-2 in two z ~ 3.1 LAEs. These lines are strong enough to dominate broad-band flux measurements that include the line (in thiscase, K_s band photometry). Spectral energy distribution fits that do not account for the lines would therefore overestimate the 4000 A (and/or Balmer) break strength in such galaxies, and hence also the ages and stellar masses of such high-z galaxies.
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