Browsing by Author "Mazzucchelli, C."

Now showing 1 - 5 of 5
  • No Thumbnail Available
    Item
    A lack of Lyman α emitters within 5 Mpc of a luminous quasar in an overdensity at z=6.9: Potential evidence of negative quasar feedback at protocluster scales
    (2024) Lambert, Trystan S.; Assef, R. J.; Mazzucchelli, C.; Banados, E.; Aravena, M.; Barrientos, F.; Gonzalez-Lopez, J.; Hu, W.; Infante, L.; Malhotra, S.; Moya-Sierralta, C.; Rhoads, J.; Valdes, F.; Wang, J.; Wold, I. G. B.; Zheng, Z.
    High-redshift quasars are thought to live in the densest regions of space, which should be made evident by an overdensity of galaxies around them. However, campaigns to identify these overdensities by searching for Lyman-break galaxies (LBGs) and Lyman alpha emitters (LAEs) have had mixed results. These may be explained by either the small field of view of some of the experiments, the broad redshift ranges targeted by LBG searches, and the inherently high uncertainty of quasar redshifts estimated from ultraviolet emission lines, which makes it difficult to place the Ly-alpha emission line within a narrowband filter. Here, we present a 3 square degree search (similar to 1000 pMpc(2)) for LAEs around the z = 6.9 quasar VIK J2348-3054 using the Dark Energy CAMera (DECam) housed on the 4m Blanco telescope, finding 38 LAEs. The systemic redshift of VIK J2348-3054 is known from ALMA [CII] observations and places the Ly-alpha emission line of companions within the NB964 narrowband of DECam. This is the largest field-of-view LAE search around a z > 6 quasar conducted to date. We find that this field is similar to ten times more overdense than Chandra Deep-Field South, observed previously with the same instrumental setup as well as several combined blank fields. This is strong evidence that VIK J2348-3054 resides in an overdensity of LAEs over several Mpc. Surprisingly, we find a lack of LAEs within 5 physical Mpc of the quasar and take this to most likely be evidence of quasar-suppressing star formation in its immediate vicinity. This result highlights the importance of performing overdensity searches over large areas to properly assess the density of those regions of the Universe.
  • No Thumbnail Available
    Item
    Discovery of the first heavily obscured QSO candidate at z > 6 in a close galaxy pair
    (2019) Vito, F.; Brandt, W. N.; Bauer, F. E.; Gilli, R.; Luo, B.; Zamorani, G.; Calura, F.; Comastri, A.; Mazzucchelli, C.; Mignoli, M.; Nanni, R.; Shemmer, O.; Vignali, C.; Brusa, M.; Cappelluti, N.; Civano, F.; Volonteri, M.
    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 gigayear 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 (approximate to 5 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 Atacama large millimeter array (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 x 10(24) cm(-2) and N-H > 6 x 10(23) 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.
  • No Thumbnail Available
    Item
    Chandra and Magellan/FIRE follow-up observations of PSO167-13: An X-ray weak QSO at z=6.515
    (2021) Vito, F.; Brandt, W. N.; Ricci, F.; Congiu, E.; Connor, T.; Banados, E.; Bauer, F. E.; Gilli, R.; Luo, B.; Mazzucchelli, C.; Mignoli, M.; Shemmer, O.; Vignali, C.; Calura, F.; Comastri, A.; Decarli, R.; Gallerani, S.; Nanni, R.; Brusa, M.; Cappelluti, N.; Civano, F.; Zamorani, G.
    Context. The discovery of hundreds of quasi-stellar objects (QSOs) in the first gigayear of the Universe powered by already grown supermassive black holes (SMBHs) challenges our knowledge of SMBH formation. In particular, investigations of z>6 QSOs that present notable properties can provide unique information on the physics of fast SMBH growth in the early Universe.Aims. 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 recently been proposed to host the first heavily obscured X-ray source at high redshift. The goals of these new observations are to confirm the existence of the X-ray source and to investigate the rest-frame UV properties of the QSO.Methods. We observed the PSO167-13 system with Chandra/ACIS-S (177 ks) and obtained new spectroscopic observations (7.2 h) with Magellan/FIRE.Results. 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 (L2-10 keV<8.3x10(43) erg s(-1)) is the lowest available for a z>6 QSO. The ratio between the X-ray and UV luminosity of alpha (ox)<-1.95 makes PSO167-13 a strong outlier from the (ox)-L-UV and L-X-L-bol relations. In particular, its X-ray emission is more than six times weaker than the expectation based on its UV luminosity. The new Magellan/FIRE spectrum of PSO167-13 is strongly affected by unfavorable sky conditions, but the tentatively detected C IV and Mg II emission lines appear strongly blueshifted.Conclusions. 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.
  • No Thumbnail Available
    Item
    Raining in MKW 3 s: A Chandra-MUSE Analysis of X-Ray Cold Filaments around 3CR 318.1
    (2021) Jimenez-Gallardo, A.; Massaro, F.; Balmaverde, B.; Paggi, A.; Capetti, A.; Forman, W. R.; Kraft, R. P.; Baldi, R. D.; Mahatma, V. H.; Mazzucchelli, C.; Missaglia, V.; Ricci, F.; Venturi, G.; Baum, S. A.; Liuzzo, E.; O'Dea, C. P.; Prieto, M. A.; Rottgering, H. J. A.; Sani, E.; Sparks, W. B.; Tremblay, G. R.; van Weeren, R. J.; Wilkes, B. J.; Harwood, J. J.; Mazzotta, P.; Kuraszkiewicz, J.
    We present the analysis of X-ray and optical observations of gas filaments observed in the radio source 3CR 318.1, associated with NGC 5920, the brightest cluster galaxy (BCG) of MKW 3 s, a nearby cool core galaxy cluster. This work is one of the first X-ray and optical analyses of filaments in cool core clusters carried out using MUSE observations. We aim at identifying the main excitation processes responsible for the emission arising from these filaments. We complemented the optical VLT/MUSE observations, tracing the colder gas phase, with X-ray Chandra observations of the hotter highly ionized gas phase. Using the MUSE observations, we studied the emission line intensity ratios along the filaments to constrain the physical processes driving the excitation, and, using the Chandra observations, we carried out a spectral analysis of the gas along these filaments. We found a spatial association between the X-ray and optical morphology of these filaments, which are colder and have lower metal abundance than the surrounding intracluster medium (ICM), as already seen in other BCGs. Comparing with previous results from the literature for other BCGs, we propose that the excitation process that is most likely responsible for these filaments emission is a combination of star formation and shocks, with a likely contribution from self-ionizing, cooling ICM. Additionally, we conclude that the filaments most likely originated from AGN-driven outflows in the direction of the radio jet.
  • No Thumbnail Available
    Item
    The Cavity of 3CR 196.1: Hα Emission Spatially Associated with an X-Ray Cavity
    (2022) Jimenez-Gallardo, A.; Sani, E.; Ricci, F.; Mazzucchelli, C.; Balmaverde, B.; Massaro, F.; Capetti, A.; Forman, W. R.; Kraft, R. P.; Venturi, G.; Gendron-Marsolais, M.; Prieto, M. A.; Marconi, A.; Pena-Herazo, H. A.; Baum, S. A.; O'Dea, C. P.; Lovisari, L.; Gilli, R.; Torresi, E.; Paggi, A.; Missaglia, V.; Tremblay, G. R.; Wilkes, B. J.
    We present a multifrequency analysis of the radio galaxy 3CR 196.1 (z=0.198), associated with the brightest galaxy of the cool-core cluster CIZAJ0815.4-0303. This nearby radio galaxy shows a hybrid radio morphology and an X-ray cavity, all signatures of a turbulent past activity, potentially due to merger events and active galactic nuclei (AGN) outbursts. We present results of the comparison between Chandra and Very Large Telescope Multi-Unit Spectroscopic Explorer data for the inner region of the galaxy cluster, on a scale of tens of kpc. We discovered H alpha + [N ii]lambda 6584 emission spatially associated with the X-ray cavity (at similar to 10 kpc from the galaxy nucleus) instead of with its rim. This result differs from previous discoveries of ionized gas surrounding X-ray cavities in other radio galaxies harbored in galaxy clusters and could represent the first reported case of ionized gas filling an X-ray cavity, either due to different AGN outbursts or to the cooling of warm (10(4) < T <= 10(7) K) AGN outflows. We also found that the H alpha, [N ii]lambda lambda 6548, 6584, and [S ii]lambda lambda 6718, 6733 emission lines show an additional redward component, at similar to 1000 km s(-1) from rest frame, with no detection in H beta or [O iii]lambda lambda 4960, 5008. We believe the most likely explanation for this redward component is the presence of a background gas cloud as there appears to be a discrete difference of velocities between this component and the rest frame.