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Register a new userThe Detection of Intergalactic Halpha Emission from the Slug Nebula at z~2.3
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The Slug Nebula is one of the largest and most luminous Lyman-alpha (LyA) nebulae discovered to date, extending over 450 kiloparsecs (kpc) around the bright quasar UM287 at z=2.283. Characterized by high surface brightnesses over intergalactic scales, its LyA emission may either trace high-density ionized gas (clumps) or large column densities of neutral material. To distinguish between these two possibilities, information from a non-resonant line such as Halpha is crucial. Therefore, we analyzed a deep MOSFIRE observation of one of the brightest LyA emitting regions in the Slug Nebula with the goal of detecting associated Halpha emission. We also obtained a deep, moderate resolution LyA spectrum of the nearby brightest region of the Slug. We detected an Halpha flux of F_(Halpha)= 2.62 +/- 0.47 x 10^-17 erg/cm^2/s (SB_(Halpha)=2.70 +/- 0.48 x 10^-18 erg/cm^2/s/sq) at the expected spatial and spectral location. Combining the Halpha detection with its corresponding LyA flux (determined from the narrow-band imaging) we calculate a flux ratio of F_(LyA_/F_(Halpha)= 5.5 +/- 1.1. The presence of a skyline at the location of the Halpha emission decreases the signal to noise ratio of the detection and our ability to put stringent constraints on the Halpha kinematics. Our measurements argue for the origin of the LyA emission being recombination radiation, suggesting the presence of high-density ionized gas. Finally, our high-resolution spectroscopic study of the LyA emission does not show evidence of a rotating disk pattern and suggest a more complex origin for at least some parts of the Slug Nebula.
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With a projected size of about 450 kpc at z~2.3, the Slug Ly-alpha nebula is a rare laboratory to study, in emission, the properties of the intergalactic gas in the Cosmic Web. Since its discovery, the Slug has been the subject of several spectroscopic follow-ups to constrain the properties of the emitting gas. Here we report the results of a deep MUSE integral-field spectroscopic search for non-resonant, extended HeII1640 and metal emission. Extended HeII radiation is detected on scales of about 100 kpc, but only in some regions associated with the bright Ly-alpha emission and a continuum-detected source, implying large and abrupt variations in the line ratios across adjacent regions in projected space. The recent detection of associated H-alpha emission and similar abrupt variations in the Ly-alpha kinematics, strongly suggest that the HeII/Ly-alpha gradient is due to large variations in the physical distances between the associated quasar and these regions. This implies that the overall length of the emitting structure could extend to physical Mpc scales and be mostly oriented along our line of sight. At the same time, the relatively low HeII/Ly-alpha values suggest that the emitting gas has a broad density distribution that - if expressed in terms of a lognormal - implies dispersions as high as those expected in the interstellar medium of galaxies. These results strengthen the possibility that the density distribution of intergalactic gas at high-redshift is extremely clumpy and multiphase on scales below our current observational spatial resolution of a few physical kpc.
[Abridged] We present a detailed study of the largest sample of intervening O VI systems in the redshift range 1.9 < z < 3.1 detected in high resolution (R ~ 45,000) spectra of 18 bright QSOs observed with VLT/UVES. Based on Voigt profile and apparent optical depth analysis we find that (i) the Doppler parameters of the O VI absorption are usually broader than those of C IV (ii) the column density distribution of O VI is steeper than that of C IV (iii) line spread (delta v) of the O VI and C IV are strongly correlated (at 5.3sigma level) with delta v(O VI) being systematically larger than delta v(C IV) and (iv) delta v(O VI) and delta v(C IV) are also correlated (at > 5sigma level) with their respective column densities and with N(H I) (3 and 4.5 sigma respectively). These findings favor the idea that C IV and O VI absorption originate from different phases of a correlated structure and systems with large velocity spread are probably associated with overdense regions. The velocity offset between optical depth weighted redshifts of C IV and O VI absorption is found to be in the range 0 < |Delta v (O VI - CIV)| < 48 km/s with a median value of 8 km/s. We compare the properties of O VI systems in our sample with that of low redshift (z < 0.5) samples from the literature and find that (i) the O VI components at low-z are systematically wider than at high-z with an enhanced non-thermal contribution to their b-parameter, (ii) the slope of the column density distribution functions for high and low-z are consistent, (iii) range in gas temperature estimated from a subsample of well aligned absorbers are similar at both high and low-z, and (iv) Omega_{O VI} = (1.0 pm 0.2) times10^{-7} for N(O VI) > 10^{13.7} cm^{-2}, estimated in our high-z sample, is very similar to low-z estimations.
We present deep Keck/MOSFIRE $H$-band spectroscopic observations covering the [CIII],CIII]$lambdalambda1907,1909$ doublet for three $zsim8$ galaxy candidates in the AEGIS field. Along with non-detections in two galaxies, we obtain one of the highest-redshift detections to-date of [CIII]$lambda 1907$ for the galaxy AEGIS-33376, finding $z_{rm spec}=7.945pm0.001$. We measure a [CIII]$lambda$1907 flux of $2.24pm0.71times10^{-18} mbox{ erg}mbox{ s}^{-1} mbox{ cm}^{-2}$, corresponding to a rest-frame equivalent width of $20.3pm6.5 unicode{x212B}$ for the single line. Given the not very constraining upper limit for CIII]$lambda 1909$ based on strong sky-line contamination, we assume a [CIII]$lambda$1907/CIII]$lambda 1909$ doublet ratio of 1.5 and infer a total [CIII],CIII]$lambdalambda1907,1909$ equivalent width of $33.7pm 10.8 unicode{x212B}$. We repeat the same reductions and analysis on multiple subsets of our raw data divided on the basis of time and observing conditions, verifying that the [CIII]$lambda 1907$ emission is present for AEGIS-33376 throughout our observations. We also confirm that the significance of the [CIII]$lambda 1907$ detection in different subsets of our data tracks that of brighter emission features detected on the same multi-slit mask. These multiple tests suggest that the observed emission line is real and associated with the $zsim 8$ target. The strong observed [CIII],CIII]$lambdalambda1907,1909$ in AEGIS-33376 likely indicates ISM conditions of low metallicity, high ionization parameter, and a hard ionizing spectrum, although AGN contributions are possible. This single detection represents a sizable increase in the current sample [CIII],CIII]$lambdalambda1907,1909$ detections at $z>7$, while $textit{JWST}$ will provide the first statistical samples of such measurements at these redshifts.
We present results from an Halpha emission-line survey in a one square degree area centered on the Orion Nebula Cluster, obtained with the Wide Field Grism Spectrograph-2 on the 2.2-meter telescope of the University of Hawaii. We identified 587 stars with Halpha emission, 99 of which, located mainly in the outer regions of the observed area, have not appeared in previous Halpha surveys. We determined the equivalent width (EW) of the line, and based on it classified 372 stars as classical T Tauri stars (CTTS) and 187 as weak line T Tauri stars (WTTS). Simultaneous r, i photometry indicates a limiting magnitude of r ~ 20 mag, but the sample is incomplete at r > 17 mag. The surface distribution of the Halpha emission stars reveals a clustered and a dispersed population, the former consisting of younger and more massive young stars than the latter. Comparison of the derived EWs with those found in the literature indicates variability of the Halpha line. We found that the typical amplitudes of the variability are not greater than a factor 2-3 in the most cases. We identified a subgroup of low-EW stars with infrared signatures indicative of optically thick accretion disks. We studied the correlations between the equivalent width and other properties of the stars. Based on literature data we examined several properties of our CTTS and WTTS subsamples and found significant differences in mid-infrared color indices, average rotational periods, and spectral energy distribution characteristics of the subsamples.
In the hierarchical model of structure formation, giant elliptical galaxies form through merging processes within the highest density peaks known as protoclusters. While high-redshift radio galaxies usually pinpoint the location of these environments, we have recently discovered at z~2-3 three Enormous (>200 kpc) Lyman-Alpha Nebulae (ELANe) that host multiple AGN and that are surrounded by overdensities of Lyman-alpha Emitters (LAE). These regions are prime candidates of massive protoclusters in the early stages of assembly. To characterize the star-forming activity within these rare structures - both on ELAN and protocluster scales - we have initiated an observational campaign with the JCMT and the APEX telescopes. In this paper we report on sensitive SCUBA-2/JCMT 850 and 450 $mu$m observations of a 128 arcmin$^2$ field comprising the ELAN MAMMOTH-1, together with the peak of the hosting BOSS1441 LAE overdensity at z=2.32. These observations unveil $4.0pm1.3$ times higher source counts at 850 $mu$m with respect to blank fields, likely confirming the presence of an overdensity also in obscured tracers. We find a strong detection at 850 $mu$m associated with the continuum source embedded within the ELAN MAMMOTH-1, which - together with the available data from the literature - allow us to constrain the spectral energy distribution of this source to be of an ULIRG with a far-infrared luminosity of $L_{rm FIR}^{rm SF}=2.4^{+7.4}_{-2.1}times10^{12}$ L$_{odot}$, and hosting an obscured AGN. Such a source is thus able to power the hard photoionization plus outflow scenario depicted in Cai et al. (2017b) to explain the extended Lyman-alpha, HeII$lambda1640$ and CIV$lambda1549$ emission, and their kinematics. In addition, the two brightest detections at 850 $mu$m ($f_{850}>18$ mJy) sit at the density peak of the LAEs overdensity, likely pinpointing the core of the protocluster.
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