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Register a new userDeep submillimeter and radio observations in the SSA22 field. I. Powering sources and Ly{alpha} escape fraction of Ly{alpha} blobs
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We study the heating mechanisms and Ly{alpha} escape fractions of 35 Ly{alpha} blobs (LABs) at z = 3.1 in the SSA22 field. Dust continuum sources have been identified in 11 of the 35 LABs, all with star formation rates (SFRs) above 100 Msun/yr. Likely radio counterparts are detected in 9 out of 29 investigated LABs. The detection of submm dust emission is more linked to the physical size of the Ly{alpha} emission than to the Ly{alpha} luminosities of the LABs. A radio excess in the submm/radio detected LABs is common, hinting at the presence of active galactic nuclei. Most radio sources without X-ray counterparts are located at the centers of the LABs. However, all X-ray counterparts avoid the central regions. This may be explained by absorption due to exceptionally large column densities along the line-of-sight or by LAB morphologies, which are highly orientation dependent. The median Ly{alpha} escape fraction is about 3% among the submm-detected LABs, which is lower than a lower limit of 11% for the submm-undetected LABs. We suspect that the large difference is due to the high dust attenuation supported by the large SFRs, the dense large-scale environment as well as large uncertainties in the extinction corrections required to apply when interpreting optical data.
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In this work we model the observed evolution in comoving number density of Lyman-alpha blobs (LABs) as a function of redshift, and try to find which mechanism of emission is dominant in LAB. Our model calculates LAB emission both from cooling radiation from the intergalactic gas accreting onto galaxies and from star formation (SF). We have used dark matter (DM) cosmological simulation to which we applied empirical recipes for Ly$alpha$ emission produced by cooling radiation and SF in every halo. In difference to the previous work, the simulated volume in the DM simulation is large enough to produce an average LABs number density. At a range of redshifts $zsim 1-7$ we compare our results with the observed luminosity functions of LABs and LAEs. Our cooling radiation luminosities appeared to be too small to explain LAB luminosities at all redshifts. In contrast, for SF we obtained a good agreement with observed LFs at all redshifts studied. We also discuss uncertainties which could influence the obtained results, and how LAB LFs could be related to each other in fields with different density.
We exploit wide-field Ly$alpha$ imaging with Subaru to probe the environment around TN J1338-1942, a powerful radio galaxy with a >100 kpc Ly$alpha$ halo at z=4.11. We used a sample of Ly$alpha$ emitters (LAEs) down to $log(L_{rm Lyalpha} [erg, s^{-1}])sim 42.8$ to measure the galaxy density around TNJ1338, compared to a control sample from a blank field taken with the same instrument. We found that TNJ1338 resides in a region with a peak overdensity of $delta_{rm LAE}=2.8pm 0.5$ on scales of $8, h^{-1}rm Mpc$ (on the sky) and $112, h^{-1}rm Mpc$ (line of sight) in comoving coordinates. Adjacent to this overdensity, we found a strong underdensity where virtually no LAEs are detected. We used a semi-analytical model of LAEs derived from the Millennium Simulation to compare our results with theoretical predictions. While the theoretical density distribution is consistent with the blank field, overdense regions such as that around TNJ1338 are very rare, with a number density of $6.4times 10^{-8}rm Mpc^{-3}$ (comoving), corresponding to the densest < 0.4 percentile at $zsimeq 4.1$. We also found that the Ly$alpha$ luminosity function in the TNJ1338 field differs from that in the blank field: the number of bright LAEs ($log(L_{rm Lyalpha}[erg,s^{-1}]) gtrsim 43.3$) is enhanced, while the number of fainter LAEs is relatively suppressed. These results suggest that some powerful radio galaxies associated with Ly$alpha$ nebulae reside in extreme overdensities on $sim 3$--$6, rm Mpc$ scales, where star-formation and AGN activity may be enhanced via frequent galaxy mergers or high rates of gas accretion from the surroundings.
The Ly$alpha$ escape fraction is a key measure to constrain the neutral state of the intergalactic medium and then to understand how the universe was fully reionized. We combine deep narrowband imaging data from the custom-made filter NB393 and the $H_{2}S$1 filter centered at 2.14 $mu$m to examine the Ly$alpha$ emitters and H$alpha$ emitters at the same redshift $z=2.24$. The combination of these two populations allows us to determine the Ly$alpha$ escape fraction at $z=2.24$. Over an area of 383 arcmin$^{2}$ in the Extended Chandra Deep Field South (ECDFS), 124 Ly$alpha$ emitters are detected down to NB393 = 26.4 mag at the 5$sigma$ level, and 56 H$alpha$ emitters come from An14. Of these, four have both Ly$alpha$ and H$alpha$ emissions (LAHAEs). We measure the individual/volumetric Ly$alpha$ escape fraction by comparing the observed Ly$alpha$ luminosity/luminosity density to the extinction-corrected H$alpha$ luminosity/luminosity density. We revisit the extinction correction for H$alpha$ emitters using the Galactic extinction law with the color excess for nebular emission. We also adopt the Calzetti extinction law together with an identical color excess for stellar and nebular regions to explore how the uncertainties in extinction correction affect our results. In both cases, an anti-correlation between the Ly$alpha$ escape fraction and dust attenuation is found among the LAHAEs, suggesting that dust absorption is responsible for the suppression of the escaping Ly$alpha$ photons. However, the estimated Ly$alpha$ escape fraction of individual LAHAEs varies up to ~3 percentage points between the two methods of extinction correction. We find the global Ly$alpha$ escape fraction at $z=2.24$ to be ($3.7pm1.4$)% in the ECDFS. The variation in the color excess of the extinction causes a discrepancy of ~1 percentage point in the global Ly$alpha$ escape fraction.
We present results of a survey for giant Ly-alpha nebulae (LABs) at z=3 with Subaru/Suprime-Cam. We obtained Ly-alpha imaging at z=3.09+-0.03 around the SSA22 protocluster and in several blank fields. The total survey area is 2.1 square degrees, corresponding to a comoving volume of 1.6 x 10^6 Mpc^3. Using a uniform detection threshold of 1.4 x 10^{-18} erg s^{-1} cm^{-2} arcsec^{-2} for the Ly-alpha images, we construct a sample of 14 LAB candidates with major-axis diameters larger than 100 kpc, including five previously known blobs and two known quasars. This survey triples the number of known LABs over 100 kpc. The giant LAB sample shows a possible morphology-density relation: filamentary LABs reside in average density environments as derived from compact Ly-alpha emitters, while circular LABs reside in both average density and overdense environments. Although it is hard to examine the formation mechanisms of LABs only from the Ly-alpha morphologies, more filamentary LABs may relate to cold gas accretion from the surrounding inter-galactic medium (IGM) and more circular LABs may relate to large-scale gas outflows, which are driven by intense starbursts and/or by AGN activities. Our survey highlights the potential usefulness of giant LABs to investigate the interactions between galaxies and the surrounding IGM from the field to overdense environments at high-redshift.
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.
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