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Marcella Brusa

Publications and source records attributed to Marcella Brusa.

At least 55 records · Page 3Linked to original sources
arXiv2021

A titanic interstellar medium ejection from a massive starburst galaxy at redshift 1.4

Feedback-driven winds from star formation or active galactic nuclei might be a relevant channel for the abrupt quenching star formation in massive galaxies. However, both observations and simulations support the idea that these processes are non-conflictingly co-evolving and self-regulating. Furthermore, evidence of disruptive events that are capable of fast quenching is rare, and constraints on their statistical prevalence are lacking. Here we present a massive starburst galaxy at z=1.4 which is ejecting $46 \pm 13$\% of its molecular gas mass at a startling rate of $\gtrsim 10,000$ M$_{\odot}{\rm yr}^{-1}$. A broad component that is red-shifted from the galaxy emission is detected in four (low- and high-J) CO and [CI] transitions and in the ionized phase, which ensures a robust estimate of the expelled gas mass. The implied statistics suggest that similar events are potentially a major star-formation quenching channel. However, our observations provide compelling evidence that this is not a feedback-driven wind, but rather material from a merger that has been probably tidally ejected. This finding challenges some literature studies in which the role of feedback-driven winds might be overstated.

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arXiv2020

X-ray redshifts for obscured AGN: a case study in the J1030 deep field

We present a procedure to constrain the redshifts of obscured ($N_H > 10^{22}$ cm$^{-2}$) Active Galactic Nuclei (AGN) based on low-count statistics X-ray spectra, which can be adopted when photometric and/or spectroscopic redshifts are unavailable or difficult to obtain. We selected a sample of 54 obscured AGN candidates on the basis of their X-ray hardness ratio, $HR>-0.1$, in the Chandra deep field ($\sim$479 ks, 335 arcmin$^2$) around the $z=6.3$ QSO SDSS J1030+0524. The sample has a median value of $\approx80$ net counts in the 0.5-7 keV energy band. We estimate reliable X-ray redshift solutions taking advantage of the main features in obscured AGN spectra, like the Fe 6.4 keV K$\mathrmα$ emission line, the 7.1 keV Fe absorption edge and the photoelectric absorption cut-off. The significance of such features is investigated through spectral simulations, and the derived X-ray redshift solutions are then compared with photometric redshifts. Both photometric and X-ray redshifts are derived for 33 sources. When multiple solutions are derived by any method, we find that combining the redshift solutions of the two techniques improves the rms by a factor of two. Using our redshift estimates ($0.1\lesssim z \lesssim 4$), we derived absorbing column densities in the range $\sim 10^{22}-10^{24}$ cm$^{-2}$ and absorption-corrected, 2-10 keV rest-frame luminosities between $\sim 10^{42}$ and $10^{45}$ erg s$^{-1}$, with median values of $N_H = 1.7 \times 10^{23}$ cm$^{-2}$ and $L_{\mathrm{2-10\, keV}} = 8.3\times10^{43}$ erg s$^{-1}$, respectively. Our results suggest that the adopted procedure can be applied to current and future X-ray surveys, for sources detected only in the X-rays or that have uncertain photometric or single-line spectroscopic redshifts.

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arXiv2020

Linking the small scale relativistic winds and the large scale molecular outflows in the z = 1.51 lensed quasar HS 0810+2554

We present Atacama Large Millimeter/submillimeter Array (ALMA) observations of the quadruply lensed z=1.51 quasar HS 0810+2554 which provide useful insight on the kinematics and morphology of the CO molecular gas and the ~2 mm continuum emission in the quasar host galaxy. Lens modeling of the mm-continuum and the spectrally integrated CO(3-2) images indicates that the source of the mm-continuum has an eccentricity of e~0.9 with a size of ~1.6 kpc and the source of line emission has an eccentricity of e~0.7 with a size of ~1 kpc. The spatially integrated emission of the CO(2-1) and CO(3-2) lines shows a triple peak structure with the outer peaks separated by Dv_21 = 220 +\- 19 km s^-1 and Dv_32 = 245 +/- 28 km s^-1, respectively, suggesting the presence of rotating molecular CO line emitting gas. Lensing inversion of the high spatial resolution images confirms the presence of rotation of the line emitting gas. Assuming a conversion factor of alpha_CO = 0.8 M_solar (K km s^-1 pc^2)^-1 we find the molecular gas mass of HS 0810+2554 to be M _ Mol = [(5.2 +/- 1.5)/mu_32] x10^10 M_solar, where mu_32 is the magnification of the CO(3-2) emission. We report the possible detection, at the 3.0 - 4.7 sigma confidence level, of shifted CO(3-2) emission lines of high-velocity clumps of CO emission with velocities up to 1702 km s^-1. We find that the momentum boost of the large scale molecular wind is below the value predicted for an energy-conserving outflow given the momentum flux observed in the small scale ultrafast outflow.

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arXiv2019

Testing the paradigm: First spectroscopic evidence of a quasar-galaxy Mpc-scale association at cosmic dawn

State-of-the-art models of massive black hole formation postulate that quasars at $z>6$ reside in extreme peaks of the cosmic density structure in the early universe. Even so, direct observational evidence of these overdensities is elusive, especially on large scales ($\gg$1 Mpc) as the spectroscopic follow-up of $z>6$ galaxies is observationally expensive. Here we present Keck / DEIMOS optical and IRAM / NOEMA millimeter spectroscopy of a $z\sim6$ Lyman-break galaxy candidate originally discovered via broadband selection, at a projected separation of 4.65 physical Mpc (13.94 arcmin) from the luminous $z$=6.308 quasar J1030+0524. This well-studied field presents the strongest indication to date of a large-scale overdensity around a $z>6$ quasar. The Keck observations suggest a $z\sim6.3$ dropout identification of the galaxy. The NOEMA 1.2mm spectrum shows a 3.5$σ$ line that, if interpreted as [CII], would place the galaxy at $z$=6.318 (i.e., at a line-of-sight separation of 3.9 comoving Mpc assuming that relative proper motion is negligible). The measured [CII] luminosity is $3\times10^8$ L$_\odot$, in line with expectations for a galaxy with a star formation rate $\sim15$ M$_\odot$ yr$^{-1}$, as inferred from the rest-frame UV photometry. Our combined observations place the galaxy at the same redshift as the quasar, thus strengthening the overdensity scenario for this $z>6$ quasar. This pilot experiment demonstrates the power of millimeter-wavelength observations in the characterization of the environment of early quasars.

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arXiv2019

The X-ray properties of $z>6$ quasars: no evident evolution of accretion physics in the first Gyr of the Universe

X-ray emission from QSOs has been used to assess SMBH accretion properties up to $z$~6. However, at $z>6$ only ~15 QSOs are covered by sensitive X-ray observations, preventing a statistically significant investigation of the X-ray properties of QSOs in the first Gyr of the Universe. We present new Chandra observations of 10 $z>6$ QSOs, selected to have virial black-hole mass estimates from Mg II line spectroscopy. Adding archival X-ray data for an additional 15 $z>6$ QSOs, we investigate the X-ray properties of the QSO population in the first Gyr of the Universe, focusing in particular on the $L_{UV}-L_{X}$ relation, which is traced by the $α_{ox}$ parameter, and the shape of their X-ray spectra. We performed photometric analyses to derive estimates of the X-ray luminosities, and thus the $α_{ox}$ values and bolometric corrections ($K_{bol}=L_{bol}/L_{X}$). We compared the resulting $α_{ox}$ and $K_{bol}$ distributions with the results found for QSO samples at lower redshift. Finally, we performed a basic X-ray spectral analysis of the brightest $z>6$ QSOs to derive their individual photon indices, and joint spectral analysis of the whole sample to estimate the average photon index. We confirm a lack of significant evolution of $α_{ox}$ with redshift, extending the results from previous works up to $z>6$, and the trend of an increasing bolometric correction with increasing luminosity found for QSOs at lower redshifts. The average power-law photon index of our sample ($Γ=2.20_{-0.34}^{+0.39}$ and $Γ=2.13_{-0.13}^{+0.13}$ for sources with $<30$ and $>30$ net counts, respectively) is slightly steeper than, but still consistent with, typical QSOs at $z=1-6$. All these results point toward a lack of substantial evolution of the inner accretion-disk/hot-corona structure in QSOs from low redshift to $z>6$. Our data hint at generally high Eddington ratios at $z>6$.

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arXiv2019

Measuring the Obscuring Column of a Disk Megamaser AGN in a Nearby Merger

Active Galactic Nuclei (AGNs) hosting disk water megamasers are well known to be obscured by large amounts of gas, likely due to the presence along the line of sight of an almost edge-on disky structure orbiting the supermassive black hole. Correcting for the high obscuration is crucial to infer parameters intrinsic to the source, like its luminosity. We present a broadband X-ray spectral analysis of a water megamaser AGN in an early merger (NGC 5765B), combining Chandra and NuSTAR data. NGC 5765B is highly Compton-thick and reflection-dominated, following the general trend among disk megamasers. Combining the exquisite black hole mass from masers with our X-ray spectroscopy, the Eddington ratio of the megamaser is estimated to be in the $2-14\%$ range, and its robustness is confirmed through SED fitting.

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arXiv2019

Discovery of the first heavily obscured QSO candidate at $z>6$ in a close galaxy pair

While theoretical arguments predict that most of the early growth of supermassive black holes (SMBHs) happened during heavily obscured phases of accretion, current methods used for selecting $z>6$ quasars (QSOs) are strongly biased against obscured QSOs, thus considerably limiting our understanding of accreting SMBHs during the first Gyr of the Universe from an observational point of view. We report the $Chandra$ discovery of the first heavily obscured QSO candidate in the early universe, hosted by a close ($\approx5$ kpc) galaxy pair at $z=6.515$. One of the members is an optically classified type 1 QSO, PSO167-13. The companion galaxy was first detected as a [C II] emitter by ALMA. An X-ray source is significantly ($P=0.9996$) detected by $Chandra$ in the 2-5 keV band, with $<1.14$ net counts in the 0.5-2 keV band, although the current positional uncertainty does not allow a conclusive association with either PSO167-13 or its companion galaxy. From X-ray photometry and hardness-ratio arguments, we estimated an obscuring column density of $N_H>2\times10^{24}\,\mathrm{cm^{-2}}$ and $N_H>6\times10^{23}\,\mathrm{cm^{-2}}$ at $68\%$ and $90\%$ confidence levels, respectively. Thus, regardless of which of the two galaxies is associated with the X-ray emission, this source is the first heavily obscured QSO candidate at $z>6$.

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arXiv2019

Cosmic evolution of supermassive black holes: A view into the next two decades

The discoveries made over the past 20 years by Chandra and XMM-Newton surveys in conjunction with multiwavelength imaging and spectroscopic data available in the same fields have significantly changed the view of the supermassive black hole (SMBH) and galaxy connection. These discoveries have opened up several exciting questions that are beyond the capabilities of current X-ray telescopes and will need to be addressed by observatories in the next two decades. As new observatories peer into the early Universe, we will begin to understand the physics and demographics of SMBH infancy (at $z>6$) and investigate the influence of their accretion on the formation of the first galaxies ($§$ 2.1). We will also be able to understand the accretion and evolution over the cosmic history (at $z\sim$1-6) of the full population of black holes in galaxies, including low accretion rate, heavily obscured AGNs at luminosities beyond the reach of current X-ray surveys ($§$2.2 and $§$2.3), enabling us to resolve the connection between SMBH growth and their environment.

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arXiv2019

Multi-phase outflows in Mkn 848 observed with SDSS-MaNGA Integral Field Spectroscopy

The characterisation of galaxy-scale outflows in terms of their multi-phase nature, amount, and effects of flowing material is crucial to place constraints on models of galaxy evolution. This study can proceed only with the detailed investigation of individual targets. We present a spatially resolved spectroscopic optical data analysis of Mkn 848, a complex system consisting of two merging galaxies at z~0.04 that are separated 7.5 kpc (projected distance). Motivated by the presence of a multi-phase outflow in the north-west system revealed by the SDSS integrated spectrum, we analysed the publicly available MaNGA data, which cover almost the entire merging system, to study the physical properties of cool and warm gas in detail. Galaxy-wide outflowing gas in multiple phases is revealed for the first time in the two merging galaxies. We also detect spatially resolved resonant NaID emission associated with the outflows. The derived outflow energetics may be consistent with a scenario in which both winds are accelerated by stellar processes and AGN activity, although we favour an AGN origin given the high outflow velocities and the ionisation conditions observed in the outflow regions. Deeper observations are required, however, to better constrain the nature of these multi-phase outflows. Outflow energetics in the north-west system are strongly different between the ionised and atomic gas components, the latter of which is associated with mass outflow rate and kinetic and momentum powers that are 1-2 dex higher; those associated with the south-east galaxy are instead similar. Strong kp-scale outflows are revealed in an ongoing merger system, suggesting that feedback can potentially impact the host galaxy even in the early merger phases. The characterisation of the neutral and ionised gas phases has proved to be crucial for a comprehensive study of the outflow phenomena.

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arXiv2018

X-UDS: The Chandra Legacy Survey of the UKIDSS Ultra Deep Survey Field

We present the X-UDS survey, a set of wide and deep Chandra observations of the Subaru-XMM Deep/UKIDSS Ultra Deep Survey (SXDS/UDS) field. The survey consists of 25 observations that cover a total area of 0.33 deg$^{2}$. The observations are combined to provide a nominal depth of ~600 ksec in the central 100 arcmin$^{2}$ region of the field that has been imaged with Hubble/WFC3 by the CANDELS survey and $\sim$200 ksec in the remainder of the field. In this paper, we outline the survey's scientific goals, describe our observing strategy, and detail our data reduction and point source detection algorithms. Our analysis has resulted in a total of 868 band-merged point sources detected with a false-positive Poisson probability of $<1\times10^{-4}$. In addition, we present the results of an X-ray spectral analysis and provide best-fitting neutral hydrogen column densities, $N_{\rm H}$, as well as a sample of 51 Compton-thick active galactic nucleus candidates. Using this sample, we find the intrinsic Compton-thick fraction to be 30-35% over a wide range in redshift ($z=0.1-3$), suggesting the obscured fraction does not evolve very strongly with epoch. However, if we assume that the Compton-thick fraction is dependent on luminosity, as is seen for Compton-thin sources, then our results are consistent with a rise in the obscured fraction out to $z\sim3$. Finally, an examination of the host morphologies of our Compton-thick candidates shows a high fraction of morphological disturbances, in agreement with our previous results. All data products described in this paper are made available via a public website.

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arXiv2018

Probing AGN Inner Structure with X-ray Obscured Type 1 AGN

Using the X-ray-selected active galactic nuclei (AGN) from the XMM-XXL north survey and the SDSS Baryon Oscillation Spectroscopic Survey (BOSS) spectroscopic follow-up of them, we compare the properties of X-ray unobscured and obscured broad-line AGN (BLAGN1 and BLAGN2; $N_\textrm{H}$below and above $10^{21.5}$ cm$^{-2}$), including their X-ray luminosity $L_X$, black hole mass, Eddington ratio $λ_{\textrm{Edd}}$, optical continuum and line features. We find that BLAGN2 have systematically larger broad line widths and hence apparently higher (lower) $M_{\textrm{BH}}$ ($λ_{\textrm{Edd}}$) than BLAGN1. We also find that the X-ray obscuration in BLAGN tends to coincide with optical dust extinction, which is optically thinner than that in narrow-line AGN (NLAGN) and likely partial-covering to the broad line region. All the results can be explained in the framework of a multi-component, clumpy torus model by interpreting BLAGN2 as an intermediate type between BLAGN1 and NLAGN in terms of an intermediate inclination angle.

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arXiv2018

NGC 1275: an outlier of the black hole-host scaling relations

The active galaxy NGC 1275 lies at the center of the Perseus cluster of galaxies, being an archetypal BH-galaxy system that is supposed to fit well with the M_BH-host scaling relations obtained for quiescent galaxies. Since it harbours an obscured AGN, only recently our group has been able to estimate its black hole mass. Here our aim is to pinpoint NGC 1275 on the less dispersed scaling relations, namely the M_BH-sigma_star and M_BH-L_bul planes. Starting from our previous work Ricci et al. 2017b, we estimate that NGC 1275 falls well outside the intrinsic dispersion of the M_BH-sigma_star plane being ~1.2 dex (in black hole mass) displaced with respect to the scaling relations. We then perform a 2D morphological decomposition analysis on Spitzer/IRAC images at 3.6 mic and find that, beyond the bright compact nucleus that dominates the central emission, NGC 1275 follows a de Vaucouleurs profile with no sign of significant star formation nor clear merger remnants. Nonetheless, its displacement on the M_BH-L_(3.6,bul) plane with respect to the scaling relation is as high as observed in the M_BH-sigma_star.

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arXiv2017

A census of radio-selected AGN on the COSMOS field and of their FIR properties

We use the new catalogue by Laigle et al. (2016) to provide a full census of VLA-COSMOS radio sources. We identify 90% of such sources and sub-divide them into AGN and star-forming galaxies on the basis of their radio luminosity. The AGN sample is COMPLETE with respect to radio selection at all z<3.5. Out of 704 AGN, 272 have a counterpart in the Herschel maps. By exploiting the better statistics of the new sample, we confirm the results of Magliocchetti et al. (2014): the probability for a radio-selected AGN to be detected at FIR wavelengths is both a function of radio luminosity and redshift, whereby powerful sources are more likely FIR emitters at earlier epochs. Such an emission is due to star-forming processes within the host galaxy. FIR emitters and non-FIR emitters only differentiate in the z<1 universe. At higher redshifts they are indistinguishable from each other, as there is no difference between FIR-emitting AGN and star-forming galaxies. Lastly, we focus on radio AGN which show AGN emission at other wavelengths. We find that MIR emission is mainly associated with ongoing star-formation and with sources which are smaller, younger and more radio luminous than the average parent population. X-ray emitters instead preferentially appear in more massive and older galaxies. We can therefore envisage an evolutionary track whereby the first phase of a radio-active AGN and of its host galaxy is associated with MIR emission, while at later stages the source becomes only active at radio wavelengths and possibly also in the X-ray.

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arXiv2017

The Hunt for Red Quasars: Luminous Obscured Black Hole Growth Unveiled in the Stripe 82 X-ray Survey

We present results of a ground-based near-infrared campaign with Palomar TripleSpec, Keck NIRSPEC, and Gemini GNIRS to target two samples of reddened active galactic nucleus (AGN) candidates from the 31 deg$^2$ Stripe 82 X-ray survey. One sample, which is $\sim$89\% complete to $K<16$ (Vega), consists of eight confirmed AGNs, four of which were identified with our follow-up program, and is selected to have red $R-K$ colors ($>4$, Vega). The fainter sample ($K>17$, Vega) represents a pilot program to follow-up four sources from a parent sample of 34 that are not detected in the single-epoch SDSS catalog and have {\it WISE} quasar colors. All twelve sources are broad-line AGNs (at least one permitted emission line has a FWHM exceeding 1300 km s$^{-1}$) and span a redshift range $0.59 < z < 2.5$. Half the ($R-K$)-selected AGNs have features in their spectra suggestive of outflows. When comparing these sources to a matched sample of blue Type 1 AGNs, we find the reddened AGNs are more distant ($z > 0.5$) and a greater percentage have high X-ray luminosities ($L_{\rm X,full} > 10^{44}$ erg s$^{-1}$). Such outflows and high luminosities may be consistent with the paradigm that reddened broad-line AGNs represent a transitory phase in AGN evolution as described by the major merger model for black hole growth. Results from our pilot program demonstrate proof-of-concept that our selection technique is successful in discovering reddened quasars at $z > 1$ missed by optical surveys.

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arXiv2017

An X-ray/SDSS sample (II): outflowing gas plasma properties

Galaxy-scale outflows are nowadays observed in many active galactic nuclei (AGNs); however, their characterisation in terms of (multi-) phase nature, amount of flowing material, effects on the host galaxy, is still unsettled. In particular, ionized gas mass outflow rate and related energetics are still affected by many sources of uncertainties. In this respect, outflowing gas plasma conditions, being largely unknown, play a crucial role. Taking advantage of the spectroscopic analysis results we obtained studying the X-ray/SDSS sample of 563 AGNs at z $<0.8$ presented in our companion paper, we analyse stacked spectra and sub-samples of sources with high signal-to-noise temperature- and density-sensitive emission lines to derive the plasma properties of the outflowing ionized gas component. For these sources, we also study in detail various diagnostic diagrams to infer information about outflowing gas ionization mechanisms. We derive, for the first time, median values for electron temperature and density of outflowing gas from medium-size samples ($\sim 30$ targets) and stacked spectra of AGNs. Evidences of shock excitation are found for outflowing gas. We measure electron temperatures of the order of $\sim 1.7\times10^4$ K and densities of $\sim 1200$ cm$^{-3}$ for faint and moderately luminous AGNs (intrinsic X-ray luminosity $40.5<log(L_X)<44$ in the 2-10 keV band). We caution that the usually assumed electron density ($N_e=100$ cm$^{-3}$) in ejected material might result in relevant overestimates of flow mass rates and energetics and, as a consequence, of the effects of AGN-driven outflows on the host galaxy.

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arXiv2017

The MUSE view of He 2-10: no AGN ionization but a sparkling starburst

We study the physical and dynamical properties of the ionized gas in the prototypical HII galaxy Henize 2-10 using MUSE integral field spectroscopy. The large scale dynamics is dominated by extended outflowing bubbles, probably the results of massive gas ejection from the central star forming regions. We derive a mass outflow rate dMout/dt~0.30 Msun/yr, corresponding to mass loading factor eta~0.4, in range with similar measurements in local LIRGs. Such a massive outflow has a total kinetic energy that is sustainable by the stellar winds and Supernova Remnants expected in the galaxy. We use classical emission line diagnostic to study the dust extinction, electron density and ionization conditions all across the galaxy, confirming the extreme nature of the highly star forming knots in the core of the galaxy, which show high density and high ionization parameter. We measure the gas phase metallicity in the galaxy taking into account the strong variation of the ionization parameter, finding that the external parts of the galaxy have abundances as low as 12 + log(O/H)~8.3, while the central star forming knots are highly enriched with super solar metallicity. We find no sign of AGN ionization in the galaxy, despite the recent claim of the presence of a super massive active Black Hole in the core of He~2-10. We therefore reanalyze the X-ray data that were used to propose the presence of the AGN, but we conclude that the observed X-ray emission can be better explained with sources of a different nature, such as a Supernova Remnant.

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arXiv2017

An X-ray/SDSS sample (I): multi-phase outflow incidence and dependence on AGN luminosity

Multi-phase fast, massive outflows have been postulated to play a crucial role in galaxy evolution. The aim of this work is to constrain the nature and the fraction of outflowing gas in AGNs, as well as the nuclear conditions possibly at the origin of such phenomena. We present a large spectroscopic sample of X-ray detected SDSS AGNs at z <0.8. X-ray and optical flux ratio diagnostics are used to select the sample. Physical and kinematic characterisation are derived re-analysing optical (and X-ray) spectra. We derive the incidence of ionised (~40%) and atomic (< 1%) outflows covering a wide range of AGN bolometric luminosity, from 10^42 to 10^46 erg/s. We also derive bolometric luminosities and X-ray bolometric corrections to test whether the presence of outflows is associated with an X-ray loudness, as suggested by our recent results obtained studying high-z QSOs. We study the relations between the outflow velocity inferred from [O III] kinematic analysis and different AGN power tracers, such as black hole mass (M_BH), [O III] and X-ray luminosity. We show a well defined positive trend between outflow velocity and L_X, for the first time over a range of 5 order of magnitudes. Overall, we find that in the QSO-luminosity regime and at M_BH>10^8 Msun the fraction of AGNs with outflows becomes >50%. Finally, we discuss our results about X-ray bolometric corrections and outflow incidence in cold and ionised phases in the context of an evolutionary sequence allowing two distinct stages for the feedback phase: an initial stage characterized by X-ray/optical obscured AGNs in which the atomic gas is still present in the ISM and the outflow processes involve all the gas components, and a later stage associated with unobscured AGNs, which line of sight has been cleaned and the cold components have been heated or exhausted.

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