arXiv subjects

Cristian Vignali

Publications and source records attributed to Cristian Vignali.

At least 73 records · Page 4Linked to original sources

arXiv2022

Detection of a radio-filled X-ray cavity within the interstellar medium of NGC 5141

We present the first Chandra detection of a single X-ray cavity within the interstellar medium of the small Fanaroff-Riley type I (FRI) radio galaxy NGC 5141. The X-ray surface brightness depression, located $\approx 4$ kpc away from the galaxy center, is projected on the northern radio lobe, which is completely contained within the galaxy. The thermal gas surrounding the cavity, which extends to $\approx$ 20 kpc, has a bolometric X-ray luminosity (0.1 - 100 keV) of L${_X}\approx2\times10^{40}$ erg s$^{-1}$ and a temperature of $kT\approx0.8$ keV. We calculated the total energy (E$_{cav} = 4PV \approx 10^{55}$ erg) required to inflate the cavity and its age ($t_{cav}\approx 9$ Myrs), assuming that it is filled with relativistic particles and rises buoyantly. The inferred total cavity power is as low as P$_{cav}=E_{cav}/t_{cav}\approx6\times10^{40}$ erg s$^{-1}$, which is the lowest one among the radio-filled systems. Comparing $P_{cav}$ to the bolometric X-ray luminosity (i.e., the cooling luminosity), we conclude that NGC 5141's central active galactic nucleus can heat the interstellar medium and balance its cooling luminosity, confirming that the $P_{cav}-L_{cool}$ relation, mainly tested on groups and clusters, also works for such a low-power system.

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arXiv2022

AGN impact on the molecular gas in galactic centers as probed by CO lines

We present a detailed analysis of the X-ray, infrared, and carbon monoxide (CO) emission for a sample of 35 local ($z \leq 0.15$), active ($L_X \geq 10^{42}$ erg s$^{-1}$) galaxies. Our goal is to infer the contribution of far-ultraviolet (FUV) radiation from star formation (SF), and X-ray radiation from the active galactic nuclei (AGN), respectively producing photodissociation regions (PDRs) and X-ray dominated regions (XDRs), to the molecular gas heating. To this aim, we exploit the CO spectral line energy distribution (CO SLED) as traced by Herschel, complemented with data from single-dish telescopes for the low-J lines, and high-resolution ALMA images of the mid-J CO emitting region. By comparing our results to the Schmidt-Kennicutt relation, we find no evidence for AGN influence on the cold and low-density gas on kpc-scales. On nuclear (r = 250 pc) scales, we find weak correlations between the CO line ratios and either the FUV or X-ray fluxes: this may indicate that neither SF nor AGN radiation dominates the gas excitation, at least at r = 250 pc. From a comparison of the CO line ratios with PDR and XDR models, we find that PDRs can reproduce observations only in presence of extremely high gas densities ($n > 10^5$ cm$^{-3}$). In the XDR case, instead, the models suggest moderate densities ($n \approx 10^{2-4}$ cm$^{-3}$). We conclude that a mix of the two mechanisms (PDR for the mid-J, XDR or possibly shocks for the high-J) is necessary to explain the observed CO excitation in active galaxies.

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arXiv2021

Exploratory X-Ray Monitoring of Luminous Radio-Quiet Quasars at High Redshift: Extended Time-Series Analyses and Stacked Imaging Spectroscopy

We present three new Chandra X-ray epochs along with new ground-based optical-UV observations as the third installment in a time-series analysis of four high-redshift ($z\sim4.1-4.4$) radio-quiet quasars (RQQs). In total, we present nine epochs for these sources with rest-frame temporal baselines of $\sim1300-2000$ days. We utilize the X-ray data to determine basic variability properties, as well as produce mean spectra and stacked images based on effective exposure times of $\sim40-70$ ks per source. We perform time-series analyses in the soft and hard bands, separately, and compare variability properties to those of sources at lower redshifts and luminosities. The magnitude of X-ray variability of our sources remains consistent with or lower than that of similar sources at lower redshifts, in agreement with the variability-luminosity anti-correlation. The mean power-law photon indices in the stacked Chandra spectra of our sources are consistent with the values measured from their archival XMM-Newton spectra separated by about three years in the rest frame. Along with the X-ray observations we provide near-simultaneous optical monitoring of the sources in the optical-UV regime. The overall variability in the optical-to-X-ray spectral slope is consistent with sources at lower redshifts and the optical-UV observations display mild variability on monthly timescales.

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arXiv2021

Redshift identification of X-ray selected active galactic nuclei in the J1030 field: searching for large-scale structures and high-redshift sources

We publicly release the spectroscopic and photometric redshift catalog of the sources detected with Chandra in the field of the $z$=6.3 quasar SDSS J1030+0525. This is currently the fifth deepest X-ray field, and reaches a 0.5-2 keV flux limit $f_{\rm 0.5-2}$=6$\times$10$^{-17}$ erg s$^{-1}$ cm$^{-2}$. By using two independent methods, we measure a photometric redshift for 243 objects, while 123 (51%) sources also have a spectroscopic redshift, 110 of which coming from an INAF-Large Binocular Telescope (LBT) Strategic Program. We use the spectroscopic redshifts to determine the quality of the photometric ones, and find it in agreement with that of other X-ray surveys which used a similar number of photometric data-points. In particular, we measure a sample normalized median absolute deviation $σ_{NMAD}$=1.48||$z_{phot}$-$z_{spec}$||/(1+$z_{spec}$)=0.065. We use these new spectroscopic and photometric redshifts to study the properties of the Chandra J1030 field. We observe several peaks in our spectroscopic redshift distribution between $z$=0.15 and $z$=1.5, and find that the sources in each peak are often distributed across the whole Chandra field of view. This evidence confirms that X-ray selected AGN can efficiently track large-scale structures over physical scales of several Mpc. Finally, we computed the Chandra J1030 $z>$3 number counts: while the spectroscopic completeness at high-redshift of our sample is limited, our results point towards a potential source excess at $z\geq$4, which we plan to either confirm or reject in the near future with dedicated spectroscopic campaigns.

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arXiv2021

Compton-Thick AGN in the NuSTAR era VII. A joint NuSTAR, Chandra and XMM-Newton analysis of two nearby, heavily obscured sources

We present the joint Chandra, XMM-Newton and NuSTAR analysis of two nearby Seyfert galaxies, NGC 3081 and ESO 565-G019. These are the only two having Chandra data in a larger sample of ten low redshift ($z \le 0.05$), candidates Compton-thick Active Galactic Nuclei (AGN) selected in the 15-150 keV band with Swift-BAT that were still lacking NuSTAR data. Our spectral analysis, performed using physically-motivated models, provides an estimate of both the line-of-sight (l.o.s.) and average (N$_{H,S}$) column densities of the two torii. NGC 3081 has a Compton-thin l.o.s. column density N$_{H,z}$=[0.58-0.62] $\times 10^{24}$cm$^{-2}$, but the N$_{H,S}$, beyond the Compton-thick threshold (N$_{H,S}$=[1.41-1.78] $\times 10^{24}$cm$^{-2}$), suggests a "patchy" scenario for the distribution of the circumnuclear matter. ESO 565-G019 has both Compton-thick l.o.s. and N$_{H,S}$ column densities (N$_{H,z}>$2.31 $\times 10^{24}$cm$^{-2}$ and N$_{H,S} >$2.57 $\times 10^{24}$cm$^{-2}$, respectively). The use of physically-motivated models, coupled with the broad energy range covered by the data (0.6-70 keV and 0.6-40 keV, for NGC 3081 and ESO 565-G019, respectively) allows us to constrain the covering factor of the obscuring material, which is C$_{TOR}$=[0.63-0.82] for NGC 3081, and C$_{TOR}$=[0.39-0.65] for ESO 565-G019.

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arXiv2021

The most luminous blue quasars at 3.0<z<3.3. II. CIV/X-ray emission and accretion disc physics

We analyse the properties of the CIV broad emission line in connection with the X-ray emission of 30 bright SDSS quasars at z~3.0-3.3 with pointed XMM-Newton observations, which were selected to test the suitability of AGN as cosmological tools. In our previous work, we found that a large fraction (~25%) of the quasars in this sample are X-ray underluminous by factors of >3-10. As absorbing columns of >10$^{23}$ cm$^{-2}$ can be safely ruled out, their weakness is most likely intrinsic. Here we explore possible correlations between the UV and X-ray features of these sources to investigate the origin of X-ray weakness. We fit their UV SDSS spectra and analyse their CIV properties (e.g., equivalent width, EW; line peak velocity, $\upsilon_{\rm peak}$) as a function of the X-ray photon index and 2-10 keV flux. We confirm the trends of CIV $\upsilon_{\rm peak}$ and EW with UV luminosity at 2500 angstrom for both X-ray weak and X-ray normal quasars, as well as the correlation between X-ray weakness and CIV EW. In contrast to some recent work, we do not observe any clear relation between the 2-10 keV luminosity and $\upsilon_{\rm peak}$. We find a correlation between the hard X-ray flux and the integrated CIV flux for X-ray normal quasars, whilst X-ray weak quasars deviate from the main trend by more than 0.5 dex. We argue that X-ray weakness might be interpreted in a starved X-ray corona picture associated with an ongoing disc-wind phase. If the wind is ejected in the vicinity of the black hole, the extreme-UV radiation that reaches the corona will be depleted, depriving the corona of seeds photons and generating an X-ray weak quasar. Yet, at the largest UV luminosities (>10$^{47}$ erg s$^{-1}$), there will still be an ample reservoir of ionising photons that can explain the excess CIV emission observed in the X-ray weak quasars with respect to normal sources of similar X-ray luminosities.

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arXiv2021

Multiphase Powerful Outflows Detected in High-z Quasars

We present results from a comprehensive study of ultrafast outflows (UFOs) detected in a sample of fourteen quasars, twelve of which are gravitationally lensed, in a redshift range of 1.41-3.91, near the peak of the AGN and star formation activity. New XMM-Newton observations are presented for six of them which were selected to be lensed and contain a narrow absorption line (NAL) in their UV spectra. Another lensed quasar was added to the sample, albeit already studied, because it was not searched for UFOs. The remaining seven quasars of our sample are known to contain UFOs. The main goals of our study are to infer the outflow properties of high-z quasars, constrain their outflow induced feedback, study the relationship between the outflow properties and the properties of the ionizing source, and compare these results to those of nearby AGN. Our study adds six new detections ( > 99% confidence) of UFOs at z > 1.4, almost doubling the current number of cases. Based on our survey of six quasars selected to contain a NAL and observed with XMM-Newton, the coexistence of intrinsic UV NALs and UFOs is found to be significant in > 83% of these quasars suggesting a link between multiphase AGN feedback properties of the meso- and micro-scale. The kinematic luminosities of the UFOs of our high-z sample are large compared to their bolometric luminosities (median of L_K/L_Bol ~ 50%). This suggests they provide efficient feedback to influence the evolution of their host galaxies and that magnetic driving may be a significant contributor to their acceleration.

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arXiv2021

The connection between star formation and supermassive Black Hole activity in the local Universe

We present a study of the active galactic nucleus (AGN) activity in the local Universe (z < 0.33) and its correlation with the host galaxy properties, derived from a Sloan Digital Sky Survey (SDSS DR8) sample with spectroscopic star-formation rate (SFR) and stellar mass ($\mathcal{M}_{\ast}$) determination. To quantify the level of AGN activity we used X-ray information from the XMM-Newton Serendipitous Source Catalogue (3XMM DR8). Applying multiwavelength AGN selection criteria (optical BPT-diagrams, X-ray/optical ratio etc) we found that 24% of the detected sources are efficiently-accreting AGN with moderate-to-high X-ray luminosity, which are twice as likely to be hosted by star-forming galaxies than by quiescent ones. The distribution of the specific Black Hole accretion rate (sBHAR, $λ_{\mathrm{sBHAR}}$) shows that nuclear activity in local, non-AGN dominated galaxies peaks at very low accretion rates ($-4 \lesssim \logλ_{\mathrm{sBHAR}} \lesssim -3$) in all stellar mass ranges. However, we observe systematically larger values of sBHAR for galaxies with active star-formation than for quiescent ones, as well as an increase of the mean $λ_{\mathrm{sBHAR}}$ with SFR for both star-forming and quiescent galaxies. These findings confirm the decreased level of AGN activity with cosmic time and are consistent with a scenario where both star-formation and AGN activity are fuelled by a common gas reservoir.

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arXiv2021

An XMM-Newton study of active-inactive galaxy pairs

While theory and simulations indicate that galaxy mergers play an important role in the cosmological evolution of accreting black holes and their host galaxies, samples of Active Galactic Nuclei (AGN) in galaxies at close separations are still small. In order to increase the sample of AGN pairs, we undertook an archival project to investigate the X-ray properties of a SDSS-selected sample of 32 galaxy pairs with separations $\le$150 kpc containing one optically-identified AGN, that were serendipitously observed by XMM-Newton. We discovered only one X-ray counterpart among the optically classified non-active galaxies, with a weak X-ray luminosity ($\simeq$5$\times$10$^{41}$ erg s$^{-1}$). 59% (19 out of 32) of the AGN in our galaxy pair sample exhibit an X-ray counterpart, covering a wide range in absorption corrected X-ray luminosity (5$\times$10$^{41}$-2$\times$10$^{44}$ erg s$^{-1}$). More than 79% of these AGN are obscured (column density $N_H>$10$^{22}$ cm$^{-2}$), with more than half thereof ({\it i.e.}, about 47% of the total AGN sample) being Compton-thick. AGN/no-AGN pairs are therefore more frequently X-ray obscured (by a factor $\simeq$1.5) than isolated AGN. When compared to a luminosity and redshift-matched sample of {\it bona fide} dual AGN, AGN/no-AGN pairs exhibit one order-of-magnitude lower X-ray column density in the same separation range ($>$10 kpc). A small sample (4 objects) of AGN/no-AGN pairs with sub-pc separation are all heavily obscured, driving a formal anti-correlation between the X-ray column density and the galaxy pair separation in these systems. These findings suggest that the galactic environment has a key influence on the triggering of nuclear activity in merging galaxies.

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arXiv2021

Chandra and Magellan/FIRE follow-up observations of PSO167-13: an X-ray weak QSO at $z=6.515$

The discovery of hundreds of QSOs in the first Gyr of the Universe powered by already grown SMBHs challenges our knowledge of SMBH formation. In particular, investigations of $z>6$ QSOs presenting notable properties can provide unique information on the physics of fast SMBH growth in the early universe. We present the results of follow-up observations of the $z=6.515$ radio-quiet QSO PSO167-13, which is interacting with a close companion galaxy. The PSO167-13 system has been recently proposed to host the first heavily obscured X-ray source at high redshift. We observed PSO167-13 with Chandra/ACIS-S (177 ks), and obtained new spectroscopic observations (7.2 h) with Magellan/FIRE. No significant X-ray emission is detected from the PSO167-13 system, suggesting that the obscured X-ray source previously tentatively detected was either due to a strong background fluctuation or is highly variable. The upper limit (90% confidence level) on the X-ray emission of PSO167-13 ($L_{2-10\,\mathrm{keV}}<8.3\times10^{43}\,\mathrm{erg s^{-1}}$) is the lowest available for a $z>6$ QSO. The ratio between the X-ray and UV luminosity of $α_{ox}<-1.95$ makes PSO167-13 a strong outlier from the $α_{ox}-L_{UV}$ and $L_X-L_{\mathrm{bol}}$ relations. In particular, its X-ray emission is $>6$ times weaker than the expectation based on its UV luminosity. The new Magellan/FIRE spectrum of PSO167-13 is strongly affected by the unfavorable sky conditions, but the tentatively detected C IV and Mg II emission lines appear strongly blueshifted. The most plausible explanations for the X-ray weakness of PSO167-13 are intrinsic weakness or small-scale absorption by Compton-thick material. The possible strong blueshift of its emission lines hints at the presence of nuclear winds, which could be related to its X-ray weakness.

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arXiv2021

Mid-IR cosmological spectrophotometric surveys from space: Measuring AGN and star formation at the Cosmic Noon with a SPICA-like mission

We use the SPace Infrared telescope for Cosmology and Astrophysics (SPICA) project as a template to demonstrate how deep spectrophotometric surveys covering large cosmological volumes over extended fields (1-15 square degrees) with a mid-IR imaging spectrometer (17-36 micron) in conjunction with deep 70 micron photometry with a far-IR camera, at wavelengths which are not affected by dust extinction can answer the most crucial questions in current galaxy evolution studies. A SPICA-like mission will be able for the first time to provide an unobscured three dimensional (3-D, i.e. x, y and redshift z) view of galaxy evolution back to an age of the Universe of less than ~2 Gyrs, in the mid-IR rest-frame. This survey strategy will produce a full census of the Star formation Rate (SFR) in the Universe, using Polycyclic Aromatic Hydrocarbons (PAH) bands and fine-structure ionic lines, reaching the characteristic knee of the galaxy luminosity function, where the bulk of the population is distributed, at any redshift up to z ~3.5. Deep follow-up pointed spectroscopic observations with grating spectrometers { onboard the satellite}, across the full IR spectral range (17-210 micron), would simultaneously measure Black Hole Accretion Rate (BHAR), from high-ionization fine-structure lines, and SFR, from PAH and low- to mid-ionization lines in thousands of galaxies from solar to low metallicities, down to the knee of their luminosity functions. The analysis of the resulting atlas of IR spectra will reveal the physical processes at play in evolving galaxies across cosmic time, especially its heavily dust-embedded phase during the activity peak at the cosmic noon (z ~1-3), through IR emission lines and features that are insensitive to the dust obscuration.

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arXiv2021

Old and New Major Mergers in the SOSIMPLE galaxy, NGC 7135

The simultaneous advancement of high resolution integral field unit spectroscopy and robust full-spectral fitting codes now make it possible to examine spatially-resolved kinematic, chemical composition, and star-formation history from nearby galaxies. We take new MUSE data from the Snapshot Optical Spectroscopic Imaging of Mergers and Pairs for Legacy Exploration (SOSIMPLE) survey to examine NGC 7135. With counter-rotation of gas, disrupted kinematics and asymmetric chemical distribution, NGC 7135 is consistent with an ongoing merger. Though well hidden by the current merger, we are able to distinguish stars originating from an older merger, occurring 6-10 Gyr ago. We further find a gradient in ex-situ material with galactocentric radius, with the accreted fraction rising from 0% in the galaxy centre, to ~7% within 0.6 effective radii.

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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

Unveiling sub-parsec supermassive black hole binary candidates in active galactic nuclei

Elusive supermassive black hole binaries (SMBHBs) are thought to be the penultimate stage of galaxy mergers, preceding a final coalescence phase. SMBHBs are sources of continuous gravitational waves, possibly detectable by pulsar timing arrays; the identification of candidates could help in performing targeted gravitational wave searches. Due to their origin in the innermost parts of active galactic nuclei (AGN), X-rays are a promising tool to unveil the presence of SMBHBs, by means of either double Fe K$α$ emission lines or periodicity in their light curve. Here we report on a new method to select SMBHBs by means of the presence of a periodic signal in their Swift-BAT 105-months light curves. Our technique is based on the Fisher's exact g-test and takes into account the possible presence of colored noise. Among the 553 AGN selected for our investigation, only the Seyfert 1.5 Mrk 915 emerged as possible candidate for a SMBHB; from the subsequent analysis of its light curve we find a period $P_0=35\pm2$ months, and the null hypothesis is rejected at the $3.7σ$ confidence level. We also present a detailed analysis of the BAT light curve of the only previously X-ray-selected binary candidate source in the literature, the Seyfert 2 galaxy MCG+11-11-032. We find $P_0=26.3\pm0.6$ months, consistent with the one inferred from previously reported double Fe K$α$ emission lines.

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arXiv2020

The web of the Giant: spectroscopic confirmation of a Large Scale Structure around the z=6.31 quasar SDSS J1030+0524

We report on the spectroscopic confirmation of a large scale structure around the luminous, z=6.31 QSO SDSS~J1030+0524, that is powered by a billion solar mass black hole. The structure is populated by at least six members, four Lyman Break Galaxies (LBGs) and two Lyman Alpha Emitters (LAEs). The four LBGs have been identified among a sample of 21 i-band dropouts with z{AB}<25.5 selected up to projected separations of 5 physical Mpc (15 arcmin) from the QSO. Their redshifts have been determined through up to 8hr-long multi-object spectroscopic observations at 8-10m class telescopes. The two LAEs have been identified in a 6hr VLT/MUSE observation centered on the QSO. The redshifts of the six galaxies cover the range 6.129-6.355. Assuming that peculiar velocities are negligible, this range corresponds to radial separations of +/-5 physical Mpc from the QSO, that is comparable to the projected scale of the observed LBG distribution on the sky. We conservatively estimate that this structure is significant at >3.5 sigma level, and that the level of the galaxy overdensity is at least 1.5-2 within the large volume sampled (~780 physical Mpc^3). The spectral properties of the six member galaxies (Lyalpha strength and UV luminosity) are similar to those of field galaxies at similar redshifts. This is the first spectroscopic identification of a galaxy overdensity around a super-massive black hole in the first billion years of the Universe. Our finding lends support to the idea that the most distant and massive black holes form and grow within massive (>10^{12} Msun) dark matter halos in large scale structures, and that the absence of earlier detections of such systems was likely due to observational limitations.

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arXiv2020

Chandra reveals a luminous Compton-thick QSO powering a $Lyα$ blob in a $z=4$ starbursting protocluster

Galaxy clusters in the local universe descend from high-redshift overdense regions known as protoclusters. The large gas reservoirs and high rate of galaxy interaction in protoclusters are expected to trigger star-formation activity and luminous SMBH accretion in the host galaxies. We investigated the AGN content of a gas-rich and starbursting protocluster at $z=4$, known as the Distant Red Core (DRC). We observed with Chandra (139 ks) the 13 identified members of the structure, and searched for luminous and possibly obscured AGN among them. We also tested whether a hidden AGN can power the $Lyα$ blob (LAB) detected with VLT/MUSE in the DRC. We detected obscured X-ray emission from the two most gas-rich members of the DRC, named DRC-1 and DRC-2. Both of them are resolved into multiple interacting clumps in high-resolution ALMA and HST observations. In particular, DRC-2 is found to host a luminous ($L_{2-10\,\mathrm{keV}}\approx3\times10^{45}\,\mathrm{erg\,s^{-1}}$) Compton-thick ($N_H\gtrsim10^{24}\,\mathrm{cm^{-2}}$) QSO, comparable to the most luminous QSOs known at all cosmic times. The AGN fraction among DRC members is consistent with results found for lower redshift protoclusters. However, X-ray stacking analysis reveals that SMBH accretion is likely also taking place in other DRC galaxies that are not detected individually by Chandra. Our results point toward the presence of a strong link between large gas reservoirs, galaxy interactions, and luminous and obscured nuclear activity in protocluster members. The powerful and obscured QSO detected in DRC-2 is likely powering the nearby LAB detected with VLT/MUSE, possibly through photoionization; however, we propose that the diffuse $Lyα$ emission may be due to gas shocked by a massive outflow launched by DRC-2 over a $\approx10$ kpc scale.

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arXiv2020

Piercing through Highly Obscured and Compton-thick AGNs in the Chandra Deep Fields. II. Are Highly Obscured AGNs the Missing Link in the Merger-Triggered AGN-Galaxy Coevolution Models?

By using a large highly obscured ($N_{\rm H} > 10^{23}\ \rm cm^{-2}$) AGN sample (294 sources at $z \sim 0-5$) selected from detailed X-ray spectral analyses in the deepest Chandra surveys, we explore distributions of these X-ray sources in various optical/IR/X-ray color-color diagrams and their host-galaxy properties, aiming at characterizing the nuclear obscuration environment and the triggering mechanism of highly obscured AGNs. We find that the refined IRAC color-color diagram fails to identify the majority of X-ray selected highly obscured AGNs, even for the most luminous sources with ${\rm log}\,L_{\rm X}\, \rm (erg\ s^{-1}) > 44$. Over 80% of our sources will not be selected as heavily obscured candidates using the flux ratio of $f_{\rm 24 μm}\, /\,f_R > 1000$ and $R - K > 4.5$ criteria, implying complex origins and conditions for the obscuring materials that are responsible for the heavy X-ray obscuration. The average star formation rate of highly obscured AGNs is similar to that of stellar mass- ($M_*$-) and $z$-controlled normal galaxies, while the lack of quiescent hosts is observed for the former. Partial correlation analyses imply that highly obscured AGN activity (traced by $L_{\rm X}$) appears to be more fundamentally related to $M_*$, and no dependence of $N_{\rm H}$ on either $M_*$ or SFR is detected. Morphology analyses reveal that 61% of our sources have a significant disk component, while only 27% of them exhibit irregular morphological signatures. These findings together point toward a scenario where secular processes (e.g., galactic-disk instabilities), instead of mergers, are most probable to be the leading mechanism that triggers accretion activities of X-ray-selected highly obscured AGNs.

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arXiv2020

The molecular gas in the central region of NGC 7213

We present a multi-wavelength study (from X-ray to millimetre) of the nearby low-luminosity active galactic nucleus (LLAGN) NGC 7213. We combine the information from the different bands to characterize the source in terms of contribution from the AGN and the host-galaxy interstellar medium (ISM). This approach allows us to provide a coherent picture of the role of the AGN and its impact, if any, on the star formation and molecular gas properties of the host galaxy. We focused our study on archival ALMA Cycle 1 observations, where the CO(2-1) emission line has been used as a tracer of the molecular gas. Using the 3DBarolo code on ALMA data, we performed the modelling of the molecular gas kinematics traced by the CO(2-1) emission, finding a rotationally dominated pattern. The host-galaxy molecular gas mass was estimated from the integrated CO(2-1) emission line obtained with APEX data, assuming an $α_{CO}$ conversion factor. By using the ALMA data, we would have underestimated the gas masses by a factor $\sim$3, given the filtering out of the large scale emission in interferometric observations. We also performed a complete X-ray spectral analysis on archival observations, revealing a relatively faint and unobscured AGN. The AGN results to be too faint to significantly affect the properties of the host-galaxy, such as star formation activity and molecular gas kinematics and distribution.

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