Radiation-pressure Waves and Multiphase Quasar Outflows

We report on quasar outflow properties revealed by analyzing more than 60 composite outflow spectra built from $\sim 60\,000$ CIV absorption troughs in the SDSS-III/BOSS DR12QBAL catalog. We assess the dependences of the equivalent widths of many outflow metal absorption features on outflow velocity, trough width and position, and quasar magnitude and redshift. The evolution of the equivalent widths of the OVI and NV lines with outflow velocity correlates with that of the mean absorption-line width, the outflow electron density, and the strength of lines arising from collisionally-excited meta-stable states. None of these correlations is found for the other high- or low-ionization species, and different behaviors with trough width are also suggested. We find no dependence on quasar magnitude or redshift in any case. All the observed trends can be reconciled by considering a multiphase stratified outflow structure, where inner regions are colder, denser and host lower-ionization species. Given the prevalence of radiative acceleration in quasar outflows found by Mas-Ribas & Mauland (2019), we suggest that radiation pressure sweeps up and compresses the outflowing gas outwards, creating waves or filaments where the multiphase stratified structure could take form. This scenario is supported by the suggested correlation between electron density and outflow velocity, and the similar behavior observed for the line and line-locking components of the absorption features. We show that this outflow structure is also consistent with other X-ray, radiative transfer, and polarization results, and discuss the implications of our findings for future observational and numerical quasar outflow studies.Comment: Main results Figs. 3 and 7. ApJ accepte

Radiation-pressure Waves and Multiphase Quasar Outflows

We report on quasar outflow properties revealed by analyzing more than 60 composite outflow spectra built from ~60,000 C iv absorption troughs in the SDSS-III/BOSS DR12QBAL catalog. We assess the dependences of the equivalent widths of many outflow metal absorption features on outflow velocity, trough width and position, and quasar magnitude and redshift. The evolution of the equivalent widths of the O vi and N v lines with outflow velocity correlates with that of the mean absorption-line width, the outflow electron density, and the strength of lines arising from collisionally excited metastable states. None of these correlations are found for the other high- or low-ionization species, and different behaviors with trough width are also suggested. We find no dependence on quasar magnitude or redshift in any case. All the observed trends can be reconciled by considering a multiphase stratified outflow structure, where inner regions are colder, denser, and host lower-ionization species. Given the prevalence of radiative acceleration in quasar outflows found by Mas-Ribas & Mauland, we suggest that radiation pressure sweeps up and compresses the outflowing gas outward, creating waves or filaments where the multiphase stratified structure could take form. This scenario is supported by the suggested correlation between electron density and outflow velocity, as well as by the similar behavior observed for the line and line-locking components of the absorption features. We show that this outflow structure is also consistent with other X-ray, radiative transfer, and polarization results, and discuss the implications of our findings for future observational and numerical quasar outflow studies

The Ubiquitous Imprint of Radiative Acceleration in the Mean Absorption Spectrum of Quasar Outflows

Observational evidence revealing the main mechanisms that accelerate quasar outflows has proven difficult to obtain due to the complexity of the absorption features that this gas produces in the spectra of the emission sources. We build 36 composite outflow spectra, covering a large range of outflow and quasar parameters, by stacking broad (> 450 km s⁻¹) absorption line systems in the spectra of SDSS-III/BOSS DR12 quasars. The two lines of the atomic doublet of C IV, with a separation of ≈497 km s⁻¹, as well as those of other species, appear well resolved in most of our composites. This agrees with broad outflow troughs consisting of the superposition of narrow absorbers. We also report on the ubiquitous detection of the radiative-acceleration signature known as line-locking in all our composite outflow spectra, including one spectrum that was strictly built from broad absorption line (BAL) systems. This is the first line-locking detection in BAL composite spectra. Line-locking is driven by the C IV atomic doublet and is visible on the blue side of most strong absorption transitions. Similar effects from the doublets of O VI, Si IV, or N V, however, seem to not be present. Our results confirm that radiation pressure is a prevalent mechanism for accelerating outflows in quasars

The Ubiquitous Imprint of Radiative Acceleration in the Mean Absorption Spectrum of Quasar Outflows

Observational evidence revealing the main mechanisms that accelerate quasar outflows has proven difficult to obtain, due to the complexity of the absorption features that this gas produces in the spectra of the emission sources. We build 36 composite outflow spectra, covering a large range of outflow and quasar parameters, by stacking broad ($>450\,{\rm km\,s^{-1}}$) absorption line systems in the spectra of SDSS-III/BOSS DR12 quasars. The two lines of the atomic doublet of CIV, with a separation of $\approx 497\,{\rm km\,s^{-1}}$, as well as those of other species appear well resolved in most of our composites. This agrees with broad outflow troughs consisting in the superposition of narrow absorbers. We also report on the ubiquitous detection of the radiative-acceleration signature known as line locking in all our composite outflow spectra, including one spectrum strictly built from broad absorption line (BAL) systems. This is the first line-locking detection in BAL composite spectra. Line locking is driven by the CIV atomic doublet, and is visible on the blue side of most strong absorption transitions. Similar effects from the doublets of OVI, SiIV, or NV, however, seem to not be present. Our results confirm that radiation pressure is a prevalent mechanism for accelerating outflows in quasars.Comment: Accepted for publication at ApJ. Data at https://github.com/lluism/BAL

Lyman-α polarization intensity mapping

We present a formalism that incorporates hydrogen Lyman-alpha (Lyα) polarization arising from the scattering of radiation in galaxy halos into the intensity mapping approach. Using the halo model, and Lyα emission profiles based on simulations and observations, we calculate auto and cross power spectra at redshifts 3 ≤ z ≤ 13 for the Lyα total intensity, I, polarized intensity, P, degree of polarization, Π=P/I, and two new quantities, the astrophysical E and B modes of Lyα polarization. The one-halo terms of the Π power spectra show a turnover that signals the average extent of the polarization signal, and thus the extent of the scattering medium. The position of this feature depends on redshift, as well as on the specific emission profile shape and extent, in our formalism. Therefore, the comparison of various Lyα polarization quantities and redshifts can break degeneracies between competing effects, and it can reveal the true shape of the emission profiles, which, in turn, are associated to the physical properties of the cool gas in galaxy halos. Furthermore, measurements of Lyα E and B modes may be used as probes of galaxy evolution, because they are related to the average degree of anisotropy in the emission and in the halo gas distribution across redshifts. The detection of the polarization signal at z∼3–5 requires improvements in the sensitivity of current ground-based experiments by a factor of ∼10, and of ∼100 for space-based instruments targeting the redshifts z∼9–10, the exact values depending on the specific redshift and experiment. Interloper contamination in polarization is expected to be small, because the interlopers need to also be polarized. Overall, Lyα polarization boosts the amount of physical information retrievable on galaxies and their surroundings, most of it not achievable with total emission alone

Revealing the Warm and Hot Halo Baryons via Thomson Scattering of Quasar Light

The baryonic content and physical properties of the warm and hot ($10^5\lesssim T\lesssim 10^7$ K) phases of the circumgalactic medium (CGM) are poorly constrained, owing to the lack of observables probing the requisite range of temperature, spatial scale, halo mass, and redshift. The radiation from a luminous quasar produces a spatially extended emission halo resulting from Thomson scattering off of free electrons in the CGM, which can be used to measure the electron density profile, and therefore, the amount of warm and hot baryonic matter present. We predict the resulting surface brightness profiles and show that they are easily detectable in a three hour integration with the James Webb Space Telescope (JWST), out to $\sim 100$ physical kpc from the centers of individual hyper-luminous quasars. This electron scattering surface brightness is redshift independent, and the signal-to-noise ratio depends only very weakly on redshift, in principle allowing measurements of the warm and hot CGM into the Epoch of Reionization at $z\sim 6.5$. We consider a litany of potential contaminants, and find that for fainter quasars at $z\lesssim1$, extended stellar halos might be of comparable surface brightness. At $z>2$, JWST mid-IR observations start to probe rest-frame optical/UV wavelengths implying that scattering by dust grains in the CGM becomes significant, although multi-color observations should be able to distinguish these scenarios given that Thomson scattering is achromatic.Comment: 22 pages, 8 figures. Version accepted for publication at ApJ. Busy reader, see Fig. 6 (quasi-constant detectability of Thomson scattering halos up to Reionization

Small-scale Intensity Mapping: Extended Lyα\alpha, Hα\alpha and Continuum emission as a Probe of Halo Star Formation in High-redshift Galaxies

Lyman alpha halos are observed ubiquitously around star-forming galaxies at high redshift, but their origin is still a matter of debate. We demonstrate that the emission from faint unresolved satellite sources, $M_{\rm UV} \gtrsim -17$, clustered around the central galaxies may play a major role in generating spatially extended Ly$\alpha$, continuum (${\rm UV + VIS}$) and H$\alpha$ halos. We apply the analytic formalism developed in Mas-Ribas & Dijkstra (2016) to model the halos around Lyman Alpha Emitters (LAEs) at $z=3.1$, for several different satellite clustering prescriptions. In general, our UV and Ly$\alpha$ surface brightness profiles match the observations well at $20\lesssim r \lesssim 40$ physical kpc from the centers of LAEs. We discuss how our profiles depend on various model assumptions and how these can be tested and constrained with future H$\alpha$ observations by the James Webb Space Telescope (JWST). Our analysis shows how spatially extended halos constrain (i) the presence of otherwise undetectable satellite sources, (ii) the integrated, volumetric production rates of Ly$\alpha$ and LyC photons, and (iii) their population-averaged escape fractions. These quantities are all directly relevant for understanding galaxy formation and evolution and, for high enough redshifts, cosmic reionization.Comment: 13 pages, 6 figures, edited to match accepted ApJ version. Results unaffected. New descriptive flow-chart figure (Fig.6