Investigating Quasar Outflows at High Redshift

In this thesis, I present my work on the characterization of quasar outflows which I carried out using the statistics and the ionization properties of Narrow Absorption Lines (NALs). The study is based on a new sample of intermediate resolution spectra of 100 high-redshift quasars (z_em = 3.5 12 4.5), obtained with X-shooter at the European Southern Observatory Very Large Telescope, in the context of the XQ-100 Legacy Survey (Lopez et al., 2016). The combination of high signal-to-noise ratio (S/N), wide wavelength coverage and moderate spectral resolution of this survey have allowed me to look for empirical signatures to distinguish between two classes of absorbers: intrinsic (produced in gas that is physically associated with the quasar) and intervening, without taking into account any a priori definition or velocity cut-off. Previous studies have shown that NALs tend to cluster near the quasar emission redshift, at z_abs = z_em. I detect a significant excess of absorbers over what is expected from randomly distributed intervening structures. This excess does not show a dependence on the quasar bolometric luminosity and it is not due to the redshift evolution of NALs. Most interestingly, it extends far beyond the standard 5000 km/s cut-off traditionally defined for associated absorption lines. I take advantage of the large spectral coverage of the XQ-100 spectra to study the relative numbers of NALs in different transitions, indicative of the ionization structure of the absorbers and their locations relative to the continuum source. Among the ions examined in this work, NV is the ion that best traces the effects of the quasar ionization field, offering an excellent statistical tool to identify intrinsic systems and derive the fraction of quasar driving outflows. I also test the robustness of the use of NV as additional criterium to select intrinsic NALs, performing a stack analysis of the Lya forest of the XQ-100 sample, to search for NV signal at large velocity offsets. Lastly, I compare the properties of the material along the quasar line of sight, derived from my sample, with results based on close quasar pairs investigating the transverse direction. I find a deficiency of cool gas (traced by CII) along the line of sight connected to the quasar host galaxy, in contrast with what is observed in the transverse direction in agreement with the predictions of the AGN unification models

Winds as the origin of radio emission in z=2.5z=2.5 radio-quiet extremely red quasars

Most active galactic nuclei (AGNs) are radio-quiet, and the origin of their radio emission is not well-understood. One hypothesis is that this radio emission is a by-product of quasar-driven winds. In this paper, we present the radio properties of 108 extremely red quasars (ERQs) at $z=2-4$. ERQs are among the most luminous quasars ($L_{bol} \sim 10^{47-48}$ erg/s) in the Universe, with signatures of extreme ($\gg 1000$ km/s) outflows in their [OIII]$\lambda$5007 \AA\ emission, making them the best subjects to seek the connection between radio and outflow activity. All ERQs but one are unresolved in the radio on $\sim 10$ kpc scales, and the median radio luminosity of ERQs is $\nu L_\nu [{\rm 6\,GHz}] = 10^{41.0}$ erg/s, in the radio-quiet regime, but one to two orders of magnitude higher than that of other quasar samples. The radio spectra are steep, with a mean spectral index $\langle \alpha \rangle = -1.0$. In addition, ERQs neatly follow the extrapolation of the low-redshift correlation between radio luminosity and the velocity dispersion of [OIII]-emitting ionized gas. Uncollimated winds, with a power of one per cent of the bolometric luminosity, can account for all these observations. Such winds would interact with and shock the gas around the quasar and in the host galaxy, resulting in acceleration of relativistic particles and the consequent synchrotron emission observed in the radio. Our observations support the picture in which ERQs are signposts of extremely powerful episodes of quasar feedback, and quasar-driven winds as a contributor of the radio emission in the intermediate regime of radio luminosity $\nu L_\nu = 10^{39}-10^{42}$ erg/s.Comment: accepted by MNRA

Probing the Inner Circumgalactic Medium and Quasar Illumination around the Reddest `Extremely Red Quasar' (ERQ)

Dusty quasars might be in a young stage of galaxy evolution with prominent quasar feedback. A recently discovered population of luminous, extremely red quasars at $z\sim$~2--4 has extreme spectral properties related to exceptionally powerful quasar-driven outflows. We present Keck/KCWI observations of the reddest known ERQ, at $z=$\,2.3184, with extremely fast [\ion{O}{III}]~$\lambda$5007 outflow at $\sim$6000~km~s$^{-1}$. The Ly$\alpha$ halo spans $\sim$100~kpc. The halo is kinematically quiet, with velocity dispersion $\sim$300~km~s$^{-1}$ and no broadening above the dark matter circular velocity down to the spatial resolution $\sim$6~kpc from the quasar. We detect spatially-resolved \ion{He}{II}~$\lambda$1640 and \ion{C}{IV}~$\lambda$1549 emissions with kinematics similar to the Ly$\alpha$ halo and a narrow component in the [\ion{O}{III}]~$\lambda$5007. Quasar reddening acts as a coronagraph allowing views of the innermost halo. A narrow Ly$\alpha$ spike in the quasar spectrum is inner halo emission, confirming the broad \ion{C}{IV}~$\lambda$1549 in the unresolved quasar is blueshifted by $2240$~km~s$^{-1}$ relative to the halo frame. We propose the inner halo is dominated by moderate-speed outflow driven in the past and the outer halo dominated by inflow. The high central concentration of the halo and the symmetric morphology of the inner region are consistent with the ERQ being in earlier evolutionary stage than blue quasars. The \ion{He}{II}~$\lambda$1640/Ly$\alpha$ ratio of the inner halo and the asymmetry level of the overall halo are dissimilar to Type~II quasars, suggesting unique physical conditions for this ERQ that are beyond orientation differences from other quasar populations. We find no evidence of mechanical quasar feedback in the Ly$\alpha$-emitting halo.Comment: 20 pages, 18 figures, published in MNRA

Possible evidence of the radio AGN quenching of neighbouring galaxies at z ∼ 1

Using 57 radio active galactic nuclei (RAGNs) at 0.55 ≤ z ≤ 1.3 drawn from five fields of the Observations of Redshift Evolution in Large-Scale Environments (ORELSE) survey, we study the effect of injection of energy from outbursts of RAGN on their spectroscopically confirmed neighbouring galaxies (SNGs). We observe an elevated fraction of quenched neighbours (f_q) within 500 kpc projected radius of RAGN in the most dense local environments compared to those of non-RAGN control samples matched to the RAGN population in colour, stellar mass, and local environment at 2σ significance. Further analyses show that there are offsets at similar significance between f_qs of RAGN-SNGs and the appropriate control samples for galaxies specifically in cluster environments and those hosted by most massive cluster galaxies, which tentatively suggests that some negative feedback from the RAGN is occurring in these dense environments. In addition, we find that the median radio power of RAGN increases with increasing local overdensity, an effect which may lend itself to the quenching of neighbouring galaxies. Furthermore, we find that, in the highest local overdensities, the f_q of the sub-sample of lower stellar mass RAGN-SNGs is larger than that of the higher stellar mass RAGN-SNGs sub-sample, which indicates a more pronounced effect from RAGN on lower stellar mass galaxies. We propose a scenario in which RAGN residing within clusters might heat the intracluster medium (ICM) affecting both in situ star formation and any inflowing gas that remains in their neighbouring galaxies

Host galaxies of high-redshift extremely red and obscured quasars

We present Hubble Space Telescope 1.4-1.6 micron images of the hosts of ten extremely red quasars (ERQs) and six type 2 quasar candidates at z=2-3. ERQs, whose bolometric luminosities range between 10^47 and 10^48 erg/sec, show spectroscopic signs of powerful ionized winds, whereas type 2 quasar candidates are less luminous and show only mild outflows. After performing careful subtraction of the quasar light, we clearly detect almost all host galaxies. The median rest-frame B-band luminosity of the ERQ hosts in our sample is 10^11.2 L_Sun, or 4 L* at this redshift. Two of the ten hosts of ERQs are in ongoing mergers. The hosts of the type 2 quasar candidates are 0.6 dex less luminous, with 2/6 in likely ongoing mergers. Intriguingly, despite some signs of interaction and presence of low-mass companions, our objects do not show nearly as much major merger activity as do high-redshift radio-loud galaxies and quasars. In the absence of an overt connection to major ongoing gas-rich merger activity, our observations are consistent with a model in which the near-Eddington accretion and strong feedback of ERQs are associated with relatively late stages of mergers resulting in early-type remnants. These results are in some tension with theoretical expectations of galaxy formation models, in which rapid black hole growth occurs within a short time of a major merger. Type 2 quasar candidates are less luminous, so they may instead be powered by internal galactic processes.Comment: Accepted to MNRAS; 23 pages, including 9 figures and 2 table

Powerful winds in high-redshift obscured and red quasars

Quasar-driven outflows must have made their most significant impact on galaxy formation during the epoch when massive galaxies were forming most rapidly. To study the impact of quasar feedback, we conducted rest-frame optical integral field spectrograph (IFS) observations of three extremely red quasars (ERQs) and one type-2 quasar at z = 2–3, obtained with the NIFS and OSIRIS instruments at the Gemini North and W. M. Keck Observatory with the assistance of laser-guided adaptive optics. We use the kinematics and morphologies of the [O III] 5007 Å and H α 6563 Å emission lines redshifted into the near-infrared to gauge the extents, kinetic energies and momentum fluxes of the ionized outflows in the quasars host galaxies. For the ERQs, the galactic-scale outflows are likely driven by radiation pressure in a high column density environment or due to an adiabatic shock. The outflows in the ERQs carry a significant amount of energy ranging from 0.05 to 5  per cent of the quasar’s bolometric luminosity, powerful enough to have a significant impact on the quasar host galaxies. The outflows are resolved on kpc scales, the observed outflow sizes are generally smaller than other ionized outflows observed at high redshift. The high ratio between the momentum flux of the ionized outflow and the photon momentum flux from the quasar accretion disc and high nuclear obscuration makes these ERQs great candidates for transitional objects where the outflows are likely responsible for clearing material in the inner regions of each galaxy, unveiling the quasar accretion disc at optical wavelengths

Ionized Gas Extended Over 40 kpc in an Odd Radio Circle Host Galaxy

A new class of extragalactic astronomical sources discovered in 2021, named Odd Radio Circles (ORCs, Norris et al. 2021), are large rings of faint, diffuse radio continuum emission spanning ~1 arcminute on the sky. Galaxies at the centers of several ORCs have photometric redshifts of z~0.3-0.6, implying physical scales of several 100 kiloparsecs in diameter for the radio emission, the origin of which is unknown. Here we report spectroscopic data on an ORC including strong [OII] emission tracing ionized gas in the central galaxy of ORC4 at z=0.4512. The physical extent of the [OII] emission is ~40 kpc in diameter, larger than expected for a typical early-type galaxy (Pandya et al, 2017) but an order of magnitude smaller than the large-scale radio continuum emission. We detect a ~200 km/s velocity gradient across the [OII] nebula, as well as a high velocity dispersion of ~180 km/s. The [OII] equivalent width (EW, ~50 Ang) is extremely high for a quiescent galaxy. The morphology, kinematics, and strength of the [OII] emission are consistent with the infall of shock ionized gas near the galaxy, following a larger-scale, outward moving shock driven by a galactic wind. Both the extended optical and radio emission, while observed on very different scales, may therefore result from the same dramatic event.Comment: 7 figures, accepted to Natur

Kinematics, Structure, and Mass Outflow Rates of Extreme Starburst Galactic Outflows

We present results on the properties of extreme gas outflows in massive ($\rm M_* \sim$10$^{11} \ \rm M_{\odot}$), compact, starburst ($\rm SFR \sim$$200 \, \rm M_{\odot} \ yr^{-1}$) galaxies at z = $0.4-0.7$ with very high star formation surface densities ($\rm \Sigma_{SFR} \sim$$2000 \,\rm M_{\odot} \ yr^{-1} \ kpc^{-2}$). Using optical Keck/HIRES spectroscopy of 14 HizEA starburst galaxies we identify outflows with maximum velocities of$820 - 2860 \kmps. High-resolution spectroscopy allows us to measure precise column densities and covering fractions as a function of outflow velocity and characterize the kinematics and structure of the cool gas outflow phase (T \sim$10$^4 K). We find substantial variation in the absorption profiles, which likely reflects the complex morphology of inhomogeneously-distributed, clumpy gas and the intricacy of the turbulent mixing layers between the cold and hot outflow phases. There is not a straightforward correlation between the bursts in the galaxies' star formation histories and their wind absorption line profiles, as might naively be expected for starburst-driven winds. The lack of strong \mgii \ absorption at the systemic velocity is likely an orientation effect, where the observations are down the axis of a blowout. We infer high mass outflow rates of \rm \sim$50$-$2200$\rm M_{\odot} \, yr^{-1}$, assuming a fiducial outflow size of 5 kpc, and mass loading factors of$\eta\sim$5 for most of the sample.$\eta\sim$20 for two galaxies. While these values have high uncertainties, they suggest that starburst galaxies are capable of ejecting very large amounts of cool gas that will substantially impact their future evolution.Comment: Accepted for publication in The Astrophysical Journa