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Register a new userDiscovery of a very Lyman-$alpha$-luminous quasar at z=6.62
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Added by
Ekaterina Koptelova
Publication date
2017
fields
Physics
and research's language is
English
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Distant luminous quasars provide important information on the growth of the first supermassive black holes, their host galaxies and the epoch of reionization. The identification of quasars is usually performed through detection of their Lyman-$alpha$ line redshifted to $sim$ 0.9 microns at z>6.5. Here, we report the discovery of a very Lyman-$alpha$ luminous quasar, PSO J006.1240+39.2219 at redshift z=6.618, selected based on its red colour and multi-epoch detection of the Lyman-$alpha$ emission in a single near-infrared band. The Lyman-$alpha$-line luminosity of PSO J006.1240+39.2219 is unusually high and estimated to be 0.8$times$10$^{12}$ Solar luminosities (about 3% of the total quasar luminosity). The Lyman-$alpha$ emission of PSO J006.1240+39.2219 shows fast variability on timescales of days in the quasar rest frame, which has never been detected in any of the known high-redshift quasars. The high luminosity of the Lyman-$alpha$ line, its narrow width and fast variability resemble properties of local Narrow-Line Seyfert 1 galaxies which suggests that the quasar is likely at the active phase of the black hole growth accreting close or even beyond the Eddington limit.
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We study six luminous Lyman-alpha emitters (LAEs) with very blue rest-frame UV continua at $5.7le z le 6.6$. These LAEs have previous HST and Spitzer IRAC observations. Combining our newly acquired HST images, we find that their UV-continuum slopes $beta$ are in a range of $-3.4le beta le -2.6$. Unlike previous, tentative detections of $beta simeq -3$ in photometrically selected, low-luminosity galaxies, our LAEs are spectroscopically confirmed and luminous ($M_{rm UV}<-20$ mag). We model their broadband spectral energy distributions (SEDs), and find that two $betasimeq-2.6pm0.2$ galaxies can be well fitted with young and dust-free stellar populations. However, it becomes increasingly difficult to fit bluer galaxies. We explore further interpretations by including non-zero LyC escape fraction $f_{rm esc}$, very low metallicities, and/or AGN contributions. Assuming $f_{rm esc}simeq0.2$, we achieve the bluest slopes $betasimeq-2.7$ when nebular emission is considered. This can nearly explain the SEDs of two galaxies with $betasimeq-2.8$ and --2.9 ($sigma_{beta}=0.15$). Larger $f_{rm esc}$ values and very low metallicities are not favored by the strong nebular line emission (evidenced by the IRAC flux) or the observed (IRAC 1 - IRAC 2) color. Finally, we find that the $betasimeq-2.9$ galaxy can potentially be well explained by the combination of a very young population with a high $f_{rm esc}$ ($ge0.5$) and an old, dusty population. We are not able to produce two $beta simeq -3.4 pm0.4$ galaxies. Future deep spectroscopic observations are needed to fully understand these galaxies.
Bright quasars, observed when the Universe was less than one billion years old (z>5.5), are known to host massive black holes (~10$^{9}$ M$_{odot}$), and are thought to reside in the center of massive dark matter overdensities. In this picture, overdensities of galaxies are expected around high redshift quasars. However, observations based on the detection of Lyman Break Galaxies (LBGs) around these quasars do not offer a clear picture: this may be due to the uncertain redshift constraints of LBGs, which are selected through broad-band filters only. To circumvent such uncertainties, we here perform a search for Lyman Alpha Emitting galaxies (LAEs) in the field of the quasar PSO J215.1512-16.0417 at z~5.73, through narrow band, deep imaging with FORS2 at the VLT. We study an area of 37 arcmin$^{2}$, i.e. ~206 comoving Mpc$^{2}$ at the redshift of the quasar. We find no evidence for an overdensity of LAEs in the quasar field with respect to blank field studies. Possible explanations for these findings include that our survey volume is too small, or that the strong ionizing radiation from the quasar hinders galaxy formation in its immediate proximity. Another possibility is that these quasars are not situated in the dense environments predicted by some simulations.
Quasar proximity zones at $z>5.5$ correspond to over-dense and over-ionized environments. Galaxies found inside proximity zones can therefore display features which would otherwise be masked by absorption in the IGM. We demonstrate the utility of this quasar-galaxy synergy by reporting the discovery of the first three `proximate Lyman-$alpha$ emitters (LAEs) within the proximity zone of quasar J0836 at $z=5.802$ (textit{Aerith A, B} and textit{C}). textit{Aerith A}, located behind the quasar with an impact parameter $D_perp = 278$ pkpc, provides the first detection of a Lyman-$alpha$ transverse proximity effect. We model the transmission and show it constrains the onset of J0836s quasar phase to $0.2 text{Myr}<t<20text{Myr}$ in the past. The second object, textit{Aerith B} at a distance $D=750$ pkpc from the quasar, displays a bright, broad double-peaked lal emission line. Based on relations calibrated at $zleq3$, the peak separation implies a low ionizing $f_{text{esc}} lesssim 1%$, the most direct such constraint on a reionization-era galaxy. We fit the Ly-$alpha$ line with an outflowing shell model, finding a completely typical central density $text{log N}_{text{HI}}/text{cm}^{-2} = 19.3_{-0.2}^{+0.8}$, outflow velocity $v=16_{-11}^{+4}$ km s$^{-1}$, and gas temperature $text{log} T/text{K} = 3.8_{-0.7}^{+0.8}$ compared to $2<z<3$ analogue LAEs. Finally, we detect an emission line at $lambda=8177$ AA in object textit{Aerith C} which, if it is lal at $z=5.726$, would correspond closely with the end of the quasars proximity zone ($Delta z<0.02$ from the boundary) and suggests the quasar influences the IGM up to $sim85$ cMpc away, making it the largest quasar proximity zone. Via the analyses conducted here, we illustrate how proximate LAEs offer unique insight into the ionizing properties of both quasars and galaxies during the epoch of reionization.
We present IRAM PdBI observations of the CO(3-2) and CO(5-4) line transitions from a Ly-alpha blob at z~2.7 in order to investigate the gas kinematics, determine the location of the dominant energy source, and study the physical conditions of the molecular gas. CO line and dust continuum emission are detected at the location of a strong MIPS source that is offset by ~1.5 from the Ly-alpha peak. Neither of these emission components is resolved with the 1.7 beam, showing that the gas and dust are confined to within ~7kpc from this galaxy. No millimeter source is found at the location of the Ly-alpha peak, ruling out a central compact source of star formation as the power source for the Ly-alpha emission. Combined with a spatially-resolved spectrum of Ly-alpha and HeII, we constrain the kinematics of the extended gas using the CO emission as a tracer of the systemic redshift. Near the MIPS source, the Ly-alpha profile is symmetric and its line center agrees with that of CO line, implying that there are no significant bulk flows and that the photo-ionization from the MIPS source might be the dominant source of the Ly-alpha emission. In the region near the Ly-alpha peak, the gas is slowly receding (~100km/s) with respect to the MIPS source, thus making the hyper-/superwind hypothesis unlikely. We find a sub-thermal line ratio between two CO transitions, I_CO(5-4)/I_CO(3-2)=0.97+/-0.21. This line ratio is lower than the average values found in high-z SMGs and QSOs, but consistent with the value found in the Galactic center, suggesting that there is a large reservoir of low-density molecular gas that is spread over the MIPS source and its vicinity.
We report the detection of the most luminous high-redshift Lyman Alpha Emitting galaxy (LAE) yet seen, with log L(Ly alpha) = 43.9 ergs/s. The galaxy -- COSMOS Lyman alpha 1, or COLA1 -- was detected in a search for ultra-luminous LAEs with Hyper Suprime-Cam on the Subaru telescope. It was confirmed to lie at z = 6.593 based on a Lyman alpha line detection obtained from followup spectroscopy with the DEIMOS spectrograph on Keck2. COLA1 is the first very high-redshift LAE to show a multi-component Lyman alpha line profile with a blue wing, which suggests that it could lie in a highly ionized region of the intergalactic medium and could have significant infall. If this interpretation is correct, then ultra-luminous LAEs like COLA1 offer a unique opportunity to determine the properties of the HII regions around these galaxies which will help in understanding the ionization of the z ~ 7 intergalactic medium.
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