arXiv subjects

Tiago Costa

Publications and source records attributed to Tiago Costa.

49 records · Page 3Linked to original sources

arXiv2022

AGN-driven outflows and the formation of Ly$α$ nebulae around high-z quasars

The detection of Ly$α$ nebulae around $z\gtrsim 6$ quasars provides evidence for extended gas reservoirs around the first rapidly growing supermassive black holes. Observations of $z > 6$ quasars can be explained by cosmological models provided that the black holes by which they are powered evolve in rare, massive dark matter haloes. Whether these theoretical models also explain the observed extended Ly$α$ emission remains an open question. We post-process a suite of cosmological, radiation-hydrodynamic simulations targeting a quasar host halo at $z>6$ with the Ly$α$ radiative transfer code RASCAS. A combination of recombination radiation from photo-ionised hydrogen and emission from collisionally excited gas powers Ly$α$ nebulae with a surface brightness profile in close agreement with observations. We also find that, even on its own, resonant scattering of the Ly$α$ line associated to the quasar's broad line region can also generate Ly$α$ emission on $\sim 100 \, \rm kpc$ scales, resulting in comparable agreement with observed surface brightness profiles. Even if powered by a broad quasar Ly$α$ line, Ly$α$ nebulae can have narrow line-widths $\lesssim 1000 \, \rm km \, s^{-1}$, consistent with observational constraints. Even if there is no quasar, we find that halo gas cooling produces a faint, extended Ly$α$ glow. However, to light-up extended Ly$α$ nebulae with properties in line with observations, our simulations unambiguously require quasar-powered outflows to clear out the galactic nucleus and allow the Ly$α$ flux to escape and still remain resonant with halo gas. The close match between observations and simulations with quasar outflows suggests that AGN feedback already operates before $z \, = \, 6$ and confirms that high-$z$ quasars reside in massive haloes tracing overdensities.

astro-ph.GA↗

arXiv2021

Resolved Neutral Outflow from a Lensed Dusty Star Forming Galaxy at z=2.09

We report the detection of a massive neutral gas outflow in the z=2.09 gravitationally lensed Dusty Star-Forming Galaxy HATLASJ085358.9+015537 (G09v1.40), seen in absorption with the OH+(1_1-1_0) transition using spatially resolved (0.5"x0.4") Atacama Large Millimeter/submillimeter Array (ALMA) observations. The blueshifted OH+ line is observed simultaneously with the CO(9-8) emission line and underlying dust continuum. These data are complemented by high angular resolution (0.17"x0.13") ALMA observations of CH+(1-0) and underlying dust continuum, and Keck 2.2 micron imaging tracing the stellar emission. The neutral outflow, dust, dense molecular gas and stars all show spatial offsets from each other. The total atomic gas mass of the observed outflow is 6.7x10^9 M_sun, >25% as massive as the gas mass of the galaxy. We find that a conical outflow geometry best describes the OH+ kinematics and morphology and derive deprojected outflow properties as functions of possible inclination (0.38 deg-64 deg). The neutral gas mass outflow rate is between 83-25400 M_sun/yr, exceeding the star formation rate (788+/-300 M_sun/yr) if the inclination is >3.6 deg (mass-loading factor = 0.3-4.7). Kinetic energy and momentum fluxes span 4.4-290x10^9 L_sun and 0.1-3.7x10^37 dyne, respectively (energy-loading factor = 0.013-16), indicating that the feedback mechanisms required to drive the outflow depend on the inclination assumed. We derive a gas depletion time between 29 and 1 Myr, but find that the neutral outflow is likely to remain bound to the galaxy, unless the inclination is small, and may be re-accreted if additional feedback processes do not occur.

astro-ph.GA↗

arXiv2020

Powering galactic super-winds with small-scale AGN winds

We present a new implementation for active galactic nucleus (AGN) feedback through small-scale, ultra-fast winds in the moving-mesh hydrodynamic code AREPO. The wind is injected by prescribing mass, momentum and energy fluxes across a spherical boundary centred on a supermassive black hole according to available constraints for accretion disc winds. After sweeping-up a mass equal to their own, small-scale winds thermalise, powering energy-driven outflows with dynamics, structure and cooling properties in excellent agreement with those of analytic wind solutions. Momentum-driven solutions do not easily occur, because the Compton cooling radius is usually much smaller than the free-expansion radius of the small-scale winds. Through various convergence tests, we demonstrate that our implementation yields wind solutions which are well converged down to the typical resolution achieved in cosmological simulations. We test our model in hydrodynamic simulations of isolated Milky Way - mass galaxies. Above a critical AGN luminosity, initially spherical, small-scale winds power bipolar, energy-driven super-winds that break out of the galactic nucleus, flowing at speeds $> 1000 \rm \, km \, s^{-1}$ out to $\sim 10 \, \rm kpc$. These energy-driven outflows result in moderate, but long-term, reduction in star formation, which becomes more pronounced for higher AGN luminosities and faster small-scale winds. Suppression of star formation proceeds through a rapid mode that involves the removal of the highest-density, nuclear gas and through a slower mode that effectively halts halo gas accretion. Our new implementation makes it possible to model AGN-driven winds in a physically meaningful and validated way in simulations of galaxy evolution, the interstellar medium and black hole accretion flows.

astro-ph.GA↗

arXiv2019

The REQUIEM Survey I: A Search for Extended Ly-Alpha Nebular Emission Around 31 z>5.7 Quasars

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.

astro-ph.GA↗

arXiv2019

Reading thin film permanent magnet irregular patterns using magnetoresistive sensors

Magnetic encoders currently provide accurate positioning information by reading periodic patterns with equally spaced structures or bits. As this technology evolves to fulfill industrial demands for cheaper and more accurate systems, variations of this concept with non-periodic and non-predetermined patterns emerge. In this work, we take the first step towards the development of such devices using equally sized bits with different separations. We show magnetic scans of 1000 μm wide and 2000 Å thick CoCrPt structures with separations between 63 and 3000 μm, obtained with tunnel magnetoresisistive sensors. A theoretical model to describe the magnetic field created by these structures is also proposed, which matches the trend of the experimental signals. We also show that there is a spatial resolution loss for reading distances higher than a threshold that depends on the minimum feature size of the sample.

physics.app-ph↗

arXiv2019

How AGN feedback drives the size growth of the first quasars

Quasars at $z \,=\, 6$ are powered by accretion onto supermassive black holes with masses $M_{\rm BH} \sim 10^9 \rm \, M_{\odot}$. Their rapid assembly requires efficient gas inflow into the galactic nucleus, sustaining black hole accretion at a rate close to the Eddington limit, but also high central star formation rates. Using a set of cosmological 'zoom-in' hydrodynamic simulations performed with the moving mesh code Arepo, we show that $z \,=\, 6$ quasar host galaxies develop extremely tightly bound stellar bulges with peak circular velocities $300$ - $500$ km s$^{-1}$ and half-mass radii $\approx 0.5 \, \rm kpc$. Despite their high binding energy, we find that these compact bulges expand at $z \, < \, 6$, with their half-mass radii reaching $ \approx 5$ kpc by $z \, = \, 3$. The circular velocity drops by factors $\approx 2$ from their initial values to $200$ - $300$ km s$^{-1}$ at $z \, \approx \, 3$ and the stellar profile undergoes a cusp-core transformation. By tracking individual stellar populations, we find that the gradual expansion of the stellar component is mainly driven by fluctuations in the gravitational potential induced by bursty AGN feedback. We also find that galaxy size growth and the development of a cored stellar profile does not occur if AGN feedback is ineffective. Our findings suggest that AGN-driven outflows may have profound implications for the internal structure of massive galaxies, possibly accounting for their size growth, the formation of cored ellipticals as well as for the saturation of the $M_{\rm BH}$ - $σ_{\star}$ seen at high velocity dispersions $σ_{\star}$.

astro-ph.GA↗

arXiv2019

The hidden satellites of massive galaxies and quasars at high-redshift

Using cosmological, radiation-hydrodynamic simulations targeting a rare $\approx \, 2 \times 10^{12} \, \rm M_\odot$ halo at $z \, = \, 6$, we show that the number counts and internal properties of satellite galaxies within the massive halo are sensitively regulated by a combination of local stellar radiative feedback and strong tidal forces. Radiative feedback operates before the first supernova explosions erupt and results in less tightly-bound galaxies. Satellites are therefore more vulnerable to tidal stripping when they accrete onto the main progenitor and are tidally disrupted on a significantly shorter timescale. Consequently, the number of satellites with $M_{\rm \star} > 10^{7} \, \rm M_\odot$ within the parent system's virial radius drops by up to $60 \%$ with respect to an identical simulation performed without stellar radiative feedback. Radiative feedback also impacts the central galaxy, whose effective radius increases by a factor $\lesssim 3$ due to the presence of a more extended and diffuse stellar component. We suggest that the number of satellites in the vicinity of massive high-redshift galaxies is an indication of the strength of stellar radiative feedback and and can be anomalously low in the extreme cosmic environments of high-redshift quasars.

astro-ph.GA↗

arXiv2018

Quenching star formation with quasar outflows launched by trapped IR radiation

We present cosmological radiation-hydrodynamic simulations, performed with the code Ramses-RT, of radiatively-driven outflows in a massive quasar host halo at $z = 6$. Our simulations include both single- and multi-scattered radiation pressure on dust from a quasar and are compared against simulations performed with thermal feedback. For radiation pressure-driving, we show that there is a critical quasar luminosity above which a galactic outflow is launched, set by the equilibrium of gravitational and radiation forces. While this critical luminosity is unrealistically high in the single-scattering limit for plausible black hole masses, it is in line with a $\approx 3 \times 10^9 \, \rm M_\odot$ black hole accreting at its Eddington limit, if infrared (IR) multi-scattering radiation pressure is included. The outflows are fast ($v \, \gtrsim \, 1000 \, \rm km \, s^{-1}$) and strongly mass-loaded with peak mass outflow rates $\approx 10^3 - 10^4 \, \rm M_\odot \, yr^{-1}$, but short-lived ($< 10 \, \rm Myr$). Outflowing material is multi-phase, though predominantly composed of cool gas, forming via a thermal instability in the shocked swept-up component. Radiation pressure- and thermally-driven outflows both affect their host galaxies significantly, but in different, complementary ways. Thermally-driven outflows couple more efficiently to diffuse halo gas, generating more powerful, hotter and more volume-filling outflows. IR radiation, through its ability to penetrate dense gas via diffusion, is more efficient at ejecting gas from the bulge. The combination of gas ejection through outflows with internal pressurisation by trapped IR radiation leads to a complete shut down of star formation in the bulge. We hence argue that radiation pressure-driven feedback may be an important ingredient in regulating star formation in compact starbursts, especially during the quasar's `obscured' phase.

astro-ph.GA↗

arXiv2018

Driving gas shells with radiation pressure on dust in radiation-hydrodynamic simulations

We present radiation-hydrodynamic simulations of radiatively-driven gas shells launched by bright active galactic nuclei (AGN) in isolated dark matter haloes. Our goals are (1) to investigate the ability of AGN radiation pressure on dust to launch galactic outflows and (2) to constrain the efficiency of infrared (IR) multi-scattering in boosting outflow acceleration. Our simulations are performed with the radiation-hydrodynamic code RAMSES-RT and include both single- and multi-scattered radiation pressure from an AGN, radiative cooling and self-gravity. Since outflowing shells always eventually become transparent to the incident radiation field, outflows that sweep up all intervening gas are likely to remain gravitationally bound to their halo even at high AGN luminosities. The expansion of outflowing shells is well described by simple analytic models as long as the shells are mildly optically thick to IR radiation. In this case, an enhancement in the acceleration of shells through IR multi-scattering occurs as predicted, i.e. a force dP/dt = tau_IR L/c is exerted on the gas. For high optical depths tau_IR > 50, however, momentum transfer between outflowing optically thick gas and IR radiation is rapidly suppressed, even if the radiation is efficiently confined. At high tau_IR, the characteristic flow time becomes shorter than the required trapping time of IR radiation such that the momentum flux dP/dt << tau_IR L/c. We argue that while unlikely to unbind massive galactic gaseous haloes, AGN radiation pressure on dust could play an important role in regulating star formation and black hole accretion in the nuclei of massive compact galaxies at high redshift.

astro-ph.GA↗

arXiv2017

Jekyll & Hyde: quiescence and extreme obscuration in a pair of massive galaxies 1.5 Gyr after the Big Bang

We obtained ALMA spectroscopy and imaging to investigate the origin of the unexpected sub-mm emission toward the most distant quiescent galaxy known to date, ZF-COSMOS-20115 at z=3.717. We show here that this sub-mm emission is produced by another massive, compact and extremely obscured galaxy, located only 3.1 kpc away from the quiescent galaxy. We dub the quiescent and dusty galaxies Jekyll and Hyde, respectively. No dust emission is detected at the location of Jekyll, implying SFR < 13 Msun/yr, which is the most stringent upper limit ever obtained for a quiescent galaxy at these redshifts. The two sources are confirmed to lie at the same redshift thanks to the detection of [CII]158 in Hyde, which provides one the few robust redshifts for an "H-dropout" galaxy. The line has a rotating-disk velocity profile blueshifted from Jekyll by 549+/-60 km/s, demonstrating that it is produced by another galaxy. Careful de-blending of the Spitzer imaging confirms the existence of Hyde, and its non-detection with Hubble requires extreme attenuation by dust. Modeling the photometry of both galaxies shows that Jekyll has fully quenched >200 Myr prior to observation and still presents a challenge for models, while Hyde only harbors moderate star-formation (SFR<120 Msun/yr) and is located at least a factor 1.4 below the z~4 main sequence. Hyde could also have stopped forming stars <200 Myr before being observed, which would be consistent with its hight compactness similar to z~4 quiescent galaxies and its low [CII]/FIR ratio, but significant SF cannot be ruled out. Finally, we show that Hyde hosts a dense reservoir of gas comparable to that of extreme starbursts, suggesting that its SFR was reduced without expelling the gas outside of the galaxy. We argue that Jekyll and Hyde can be seen as two stages of quenching, and provide a unique laboratory to study this poorly understood phenomenon. [abridged]

astro-ph.GA↗

arXiv2015

The environment of bright QSOs at z ~ 6: Star forming galaxies and X-ray emission

We employ cosmological hydrodynamical simulations to investigate models in which the supermassive black holes (BHs) powering luminous z ~ 6 QSOs grow from massive seeds. We simulate at high resolution 18 fields sampling regions with densities ranging from the mean cosmic density all the way to the highest sigma peaks in the Millennium simulation volume. Only in the most massive halos, BHs can grow to masses up to ~ 10^9 Msun by z ~ 6 without invoking super-Eddington accretion. Accretion onto the most massive BHs becomes limited by thermal AGN feedback by z ~ 9-8 with further BH growth proceeding in short Eddington limited bursts. Our modelling suggests that current flux-limited surveys of QSOs at high redshift preferentially detect objects at their peak luminosity and therefore miss a substantial population of QSOs powered by similarly massive BHs but with low accretion rates. To test whether the required host halo masses are consistent with the observed galaxy environment of z ~ 6 QSOs, we produce realistic rest-frame UV images of our simulated galaxies. Without strong stellar feedback, our simulations predict numbers of bright galaxies larger than observed by a factor ten or more. Supernova-driven galactic winds reduce the predicted numbers to a level consistent with observations indicating that stellar feedback was already very efficient at high redshifts. We have further investigated the effect of thermal AGN feedback on the surrounding gas. Our adopted AGN feedback prescription drives mostly energy-driven highly anisotropic outflows with gas speeds of >= 1000 km/s to distances of >= 10 kpc consistent with observations. The spatially extended thermal X-ray emission around bright QSOs powered by these outflows can exceed by large factors the emission expected without AGN feedback and is an important diagnostic of the mechanism whereby AGN feedback energy couples to surrounding gas.

astro-ph.CO↗

arXiv2015

Feedback from Active Galactic Nuclei: Energy- versus momentum-driving

We employ hydrodynamical simulations using the moving-mesh code AREPO to investigate the role of energy and momentum input from Active Galactic Nuclei (AGN) in driving large-scale galactic outflows. We start by reproducing analytic solutions for both energy- and momentum-driven outflowing shells in simulations of a spherical isolated dark matter potential with gas in hydrostatic equilibrium and with no radiative cooling. We confirm that for this simplified setup, galactic outflows driven by a momentum input rate of order L_Edd/c can establish an M_BH - sigma relation with slope and normalisation similar to that observed. We show that momentum input at a rate of L_Edd/c is however insufficient to drive efficient outflows once cooling and gas inflows as predicted by cosmological simulations at resolved scales are taken into account. We argue that observed large-scale AGN-driven outflows are instead likely to be energy-driven and show that such outflows can reach momentum fluxes exceeding 10 L_Edd/c within the innermost 10 kpc of the galaxy. The outflows are highly anisotropic, with outflow rates and a velocity structure found to be inadequately described by spherical outflow models. We verify that the hot energy-driven outflowing gas is expected to be strongly affected by metal-line cooling, leading to significant amounts (>10^9 M_sun) of entrained cold gas.

astro-ph.GA↗

arXiv2015

Fast cold gas in hot AGN outflows

Observations of the emission from spatially extended cold gas around bright high-redshift QSOs reveal surprisingly large velocity widths exceeding 2000 km s^(-1), out to projected distances as large as 30 kpc. The high velocity widths have been interpreted as the signature of powerful AGN-driven outflows. Naively, these findings appear in tension with hydrodynamic models in which AGN-driven outflows are energy-driven and thus very hot with typical temperatures T = 10^6-7 K. Using the moving-mesh code Arepo, we perform 'zoom-in' cosmological simulations of a z = 6 QSO and its environment, following black hole growth and feedback via energy-driven outflows. In the simulations, the QSO host galaxy is surrounded by a clumpy circum-galactic medium pre-enriched with metals due to supernovae-driven galactic outflows. As a result, part of the AGN-driven hot outflowing gas can cool radiatively, leading to large amounts (> 10^9 M_sun) of cold gas comoving with the hot bipolar outflow. This results in velocity widths of spatially extended cold gas similar to those observed. We caution, however, that gas inflows, random motions in the deep potential well of the QSO host galaxy and cooling of supernovae-driven winds contribute significantly to the large velocity width of the cold gas in the simulations, complicating the interpretation of observational data.

astro-ph.GA↗