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Register a new userQSO MUSEUM I: A sample of 61 extended Ly$alpha$-emission nebulae surrounding $zsim3$ quasars
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Added by
Fabrizio Arrigoni Battaia
Publication date
2018
fields
Physics
and research's language is
English
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Motivated by the recent discovery of rare Enormous Lyman-Alpha Nebulae (ELAN) around z~2 quasars, we have initiated a long-term observational campaign with the MUSE instrument to directly uncover the astrophysics of the gas around quasars. We present here the first 61 targets of our effort under the acronym QSO MUSEUM (Quasar Snapshot Observations with MUse: Search for Extended Ultraviolet eMission). These quasars have a median redshfit of z=3.17, absolute $i$ magnitude in the range $-29.67leq M_i(z=2)leq-27.03$, and different levels of radio-loudness. This sample unveils diverse specimens of Ly$alpha$ nebulosities extending for tens of kiloparsecs around these quasars (on average out to a maximum projected distance of 80 kpc) above a surface brightness SB$>8.8times10^{-19}$ erg s$^{-1}$ cm$^{-2}$ arcsec$^{-2}$ ($2sigma$). The bulk of the extended Ly$alpha$ emission is within R<50 kpc, and is characterized by relatively quiescent kinematics, with average velocity dispersions of $langle sigma_{rm Lyalpha}rangle < 400$~km~s$^{-1}$. Therefore, the motions within all these Ly$alpha$ nebulosities have amplitudes consistent with gravitational motions expected in dark matter halos hosting quasars at these redshifts, possibly reflecting the complexity in propagating a fast wind on large scales. Our current data suggest a combination of photoionization and resonant scattering as powering mechanisms of the Ly$alpha$ emission. We discover the first $zsim3$ ELAN, which confirms a very low probability ($sim1%$) of occurrence of such extreme systems at these cosmic epochs. Finally, we discuss the redshift evolution currently seen in extended Ly$alpha$ emission around radio-quiet quasars from $zsim3$ to $zsim2$, concluding that it is possibly linked to a decrease of cool gas mass within the quasars CGM from $zsim3$ to $zsim2$, and thus to the balance of cool vs hot media.
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We present spectroscopic observations of six high redshift ($z_{rm em}$ $>$ 2) quasars, which have been selected for their Lyman $alpha$ (Ly$alpha$) emission region being only partially covered by a strong proximate ($z_{rm abs}$ $sim$ $z_{rm em}$) coronagraphic damped Ly$alpha$ system (DLA). We detected spatially extended Ly$alpha$ emission envelopes surrounding these six quasars, with projected spatial extent in the range 26 $le$ $d_{rm Lyalpha}$ $le$ 51 kpc. No correlation is found between the quasar ionizing luminosity and the Ly$alpha$ luminosity of their extended envelopes. This could be related to the limited covering factor of the extended gas and/or due to the AGN being obscured in other directions than towards the observer. Indeed, we find a strong correlation between the luminosity of the envelope and its spatial extent, which suggests that the envelopes are probably ionized by the AGN. The metallicity of the coronagraphic DLAs is low and varies in the range $-$1.75 $<$ [Si/H] $<$ $-$0.63. Highly ionized gas is observed to be associated with most of these DLAs, probably indicating ionization by the central AGN. One of these DLAs has the highest AlIII/SiII ratio ever reported for any intervening and/or proximate DLA. Most of these DLAs are redshifted with respect to the quasar, implying that they might represent infalling gas probably accreted onto the quasar host galaxies through filaments.
We investigate the potential for the emission lines OV] $lambdalambda$1213.8,1218.3 and HeII $lambda$1215.1 to contaminate flux measurements of Ly$alpha$ $lambda$1215.7 in the extended nebulae of quasars. We have computed a grid of photoionization models with a substantial range in the slope of the ionizing powerlaw (-1.5 $<$ $alpha$ $<$ -0.5), gas metallicity (0.01 $<$ $Z/Z_{odot}$ $<$ 3.0), gas density (1 $<$ $n_H$ $<$ 10$^4$ cm$^{-3}$), and ionization parameter (10$^{-5}$ $<$ U $<$ 1.0). We find the contribution from HeII $lambda$1215.1 to be negligible, i.e., $<$ 0.1 of Ly$alpha$ flux, across our entire model grid. The contribution from OV] $lambdalambda$1213.8,1218.3 is generally negligible when U is low (<10$^{-3}$) and/or when the gas metallicity is low ($Z/Z_{odot}$ < 0.1). However, at higher values of U and Z we find that OV] can significantly contaminate Ly$alpha$, in some circumstances accounting for more than half the total flux of the Ly$alpha$+HeII+OV] blend. We also provide means to estimate the fluxes of OV] $lambdalambda$1213.8,1218.3 and HeII $lambda$1215.1 by extrapolating from other lines. We estimate the fluxes of OV] and HeII for a sample of 107 Type 2 active galaxies at z$>$2, and find evidence for significant (>10%) contamination of Ly$alpha$ fluxes in the majority of cases (84%). We also discuss prospects for using OV] $lambdalambda$1213.8,1218.3 as a diagnostic for the presence of AGN activity in high-z Ly$alpha$ emitters, and caution that the presence of significant OV] emission could impact the apparent kinematics of Ly$alpha$, potentially mimicking the presence of high-velocity gas outflows.
The discovery of quasars few hundred megayears after the Big Bang represents a major challenge to our understanding of black holes and galaxy formation and evolution. Their luminosity is produced by extreme gas accretion onto black holes, which already reached masses of 10$^9$ M$_odot$ by z ~ 6. Simultaneously, their host galaxies form hundreds of stars per year, using up gas in the process. To understand which environments are able to sustain the rapid formation of these extreme sources we started a VLT/MUSE effort aimed at characterizing the surroundings of a sample of 5.7 < z < 6.6 quasars dubbed: the Reionization Epoch QUasar InvEstigation with MUSE (REQUIEM) survey. We here present results of our searches for extended Ly-Alpha halos around the first 31 targets observed as part of this program. Reaching 5-sigma surface brightness limits of 0.1-1.1 x 10$^{-17}$ erg/s/cm$^2$/arcsec$^2$ over a 1 arcsec$^2$ aperture, we were able to unveil the presence of 12 Ly-Alpha nebulae, 8 of which are newly discovered. The detected nebulae show a variety of emission properties and morphologies with luminosities ranging from 8 x 10$^{42}$ to 2 x 10$^{44}$ erg/s, FWHMs between 300 and 1700 km/s, sizes < 30 pkpc, and redshifts consistent with those of the quasar host galaxies. As the first statistical and homogeneous investigation of the circum-galactic medium of massive galaxies at the end of the reionization epoch, the REQUIEM survey enables the study of the evolution of the cool gas surrounding quasars in the first 3 Gyr of the Universe. A comparison with the extended Ly-Alpha emission observed around bright (M$_{1450}$ < -25 mag) quasars at intermediate redshift indicates little variations on the properties of the cool gas from z ~ 6 to z ~ 3 followed by a decline in the average surface brightness down to z ~ 2.
Direct Ly $alpha$ imaging of intergalactic gas at $zsim2$ has recently revealed giant cosmological structures around quasars, e.g. the Slug Nebula (Cantalupo et al. 2014). Despite their high luminosity, the detection rate of such systems in narrow-band and spectroscopic surveys is less than 10%, possibly encoding crucial information on the distribution of gas around quasars and the quasar emission properties. In this study, we use the MUSE integral-field instrument to perform a blind survey for giant Ly $alpha$ nebulae around 17 bright radio-quiet quasars at $3<z<4$ that does not suffer from most of the limitations of previous surveys. After data reduction and analysis performed with specifically developed tools, we found that each quasar is surrounded by giant Ly $alpha$ nebulae with projected sizes larger than 100 physical kpc and, in some cases, extending up to 320 kpc. The circularly averaged surface brightness profiles of the nebulae appear very similar to each other despite their different morphologies and are consistent with power laws with slopes $approx-1.8$. The similarity between the properties of all these nebulae and the Slug Nebula suggests a similar origin for all systems and that a large fraction of gas around bright quasars could be in a relatively cold (T$sim$10$^4$K) and dense phase. In addition, our results imply that such gas is ubiquitous within at least 50 kpc from bright quasars at $3<z<4$ independently of the quasar emission opening angle, or extending up to 200 kpc for quasar isotropic emission.
We present deep MUSE observations of five quasars within the first Gyr of the Universe ($zgtrsim6$), four of which display extended Ly$alpha$ halos. After PSF-subtraction, we reveal halos surrounding two quasars for the first time, as well as confirming the presence of two more halos for which tentative detections exist in long-slit spectroscopic observations and narrow-band imaging. The four Ly$alpha$ halos presented here are diverse in morphology and size, they each display spatial asymmetry, and none are centred on the position of the quasar. Spectra of the diffuse halos demonstrate that none are dramatically offset in velocity from the systemic redshift of the quasars ($Delta$ v $< 200$ kms$^{-1}$), however each halo shows a broad Ly$alpha$ line, with a velocity width of order $sim1000$ kms$^{-1}$. Total Ly$alpha$ luminosities range between $sim$ $2 times 10^{43}$ erg s$^{-1}$ and $sim$ $2 times 10^{44}$ erg s$^{-1}$, reaching maximum radial extents of $13 - 30$ pkpc from the quasar positions. We find larger sizes and higher Ly$alpha$ luminosities than previous literature results at this redshift, but find no correlation between the quasar properties and the Ly$alpha$ halo, suggesting that the detected emission is most closely related to the physical properties of the circum-galactic medium
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