Ph.D. Student: Alessandro Ignesti Ph.D. Cycle: XXXIII Supervisors: Prof.ssa M. Gitti (DIFA), Dr. G. Brunetti (IRA INAF)

Interaction between radio plasma and hot gas in clusters

The presence of diffuse radio emission at the center of relaxed galaxy clusters, in the form of the so-called radio mini-halos, reveals that the intra-cluster medium (ICM) is permeated by relativistic particles and magnetic field. However, it is still unclear how relativistic electrons are diffused in the ICM. Another open question is if the central AGN plays a role in the origin of mini halos. In the first two years, we focused on the study of the spatial correlation between radio and X-ray surface brightness for a sample of relaxed clusters. Studying how the radio emission, which traces the ICM non-thermal components, is distributed with respect to the X- ray emission, which is instead a proxy of the thermal ICM density, can give us important insights into the origin of these radio sources. We observed that the distribution of the radio emission is more peaked than the one of the thermal plasma, which suggests that the relativistic particles are generated at the center of the cluster. This is also different from what is observed for giant radio halos in disturbed clusters, thus suggesting that these diffuse radio sources may be intrinsically different. Based on our results, we explored a scenario where the relativistic, radio-emitting electrons are produced by collisions between thermal ICM protons and relativistic protons injected by the central AGN. We found that the AGN cosmic ray luminosity required to power the radio emission (1044-46 erg s-1) is in agreement with the observations and, contrary to the case of giant radio halos, the expected γ-ray emission produced by the particle collisions does not violate the upper limits provided by the Fermi-LAT observatory. Therefore our results confirm that central AGNs can play a crucial role in the origin of diffuse radio emission in relaxed clusters. These results have been published during this last year (Ignesti et al., 2020). During this work, I developed a numerical algorithm to generate grids for point-to-point comparison of surface brightness at different wavelengths and for their statistical analysis. The code has been also applied to the case of the Phoenix cluster (by R. Timmerman, a Ph.D. student in Leiden) and to the MACS J1149.5+2223 cluster (by L. Bruno, a Ph.D. student in Bologna) to investigate the spatial correlation between radio and X-ray emission in these clusters hosting a mini-halo and a giant halo, respectively. I am co-author of the two related papers (Timmerman et al., to be submitted , Bruno et al., in preparation) and I am now working on a final, public release of the code that performs the analysis of the spatial correlation (Ignesti, in preparation). This year I also worked on the observations of two relaxed clusters, 2A0335+096 and Abell 2626, obtained with the Low-Frequency Array (LOFAR) at 144 MHz. Low-frequency observations are crucial to study diffuse radio sources because, by probing the low-energy relativistic particles, they are the only that can reveal the role played by low-efficiency astrophysical phenomena (i.e. ICM turbulence) in the origin the radio emission. I learned and applied the LOFAR data processing during my period in Leiden and I focused on the scientific interpretation of the results after I returned to Bologna. For Abell 2626, we combined the new data, which discovered large plumes of steep-spectrum emission connected to the central source, with archival radio and X-ray observations to carry out a multi-wavelength and multi- frequency study of the cluster. We found that the central radio source, which was previously classified as a radio mini-halo, is more likely the result of a very complex and unique interplay between a relic X-shaped and the motions of the ICM (Ignesti et al., submitted to A&A). Concerning 2A0335+096, LOFAR revealed that the central mini-halo is close to a head- tail radio galaxy with a 700 kpc-long, steep-spectrum, and previously unknown, radio tail. We are currently studying if a physical interplay occurred between these two objects and its implications for the radio mini-halo. Finally, as a side project, we carried on the collaboration with Dr. B. M. Poggianti and the GASP team in Padova started last year with the multi-wavelength study of the jellyfish galaxy JW100 (Poggianti et al., 2019). During this year we studied two other of their sample, JO206 and JO201. For JO206, we cured the X-ray analysis to provide the physical boundaries for the numerical simulations set to study the high degree of polarization observed in this source (Müller et al., submitted to Nature Astronomy). For JO201, we carried out a detailed analysis of its X-ray emission, finding indications that the star formation in the tail could have been partly fueled by the cooling of the ICM onto the stripped, cold filaments (Master thesis of M. Campitiello, paper in preparation).

WORKSHOPS, CONFERENCES & MEETINGS 1st year: • 13-18 May 2018 Noto – IAUS 342: Perseus in Sicily: from Black hole to cluster outskirt (international) Talk : ”Thermal – non-thermal connection in radio mini-halos”; • 10-13 September 2018 Napoli – CLUSTER II (national) Talk : ”Thermal and non-thermal connection in radio mini-halos”. 2nd year: • 13-17 May 2019 Padova – GASP meeting(international) Talk: “X-ray properties of the jellyfish galaxy JW100”; • 8-12 July 2019 Sexten -Tracing cosmic structures with cluster of galaxies (international) Poster: “Radio and X-ray connection in radio mini-halos: implications for hadronic models” ; • 8-13 September 2019 Bologna – X-ray astronomy 2019 (international, member of LOC); Poster: “Multi-phase interplay in the jellyfish galaxy JW100”. 3rd year: • 14 October 2019 Leiden – Cluster meeting Talk: “Radio and X-ray connection in radio mini-halos: implications for hadronic models”; • 16-18 December 2019 Torino – LOFAR SKP Meeting (international) Talks: “The great Kite in the sky”, “The LoTSS-Planck project”; • 16 July 2020 – LOFAR SKP Cluster symposium (international, online meeting) Talk: “The great Kite in the sky: a LOFAR observation of the radio source in Abell 2626”.

Recurring meetings: • Thermal and Non-Thermal cluster meetings1; • Internal Weekly PhD Seminars and Journal Club1; • Monthly General and HI GASP telecons.

Ph.D. SCHOOL 1st year: • 11-13 December 2017 Bologna, Italy -Workshop on self-calibration and advanced imaging (national) ; • 17-21 September 2018 Dwingellow, Netherlands - 5th LOFAR data processing school (international). 2nd year: • 11-14 June 2019 Bologna, Italy - The first Italian LOFAR school (national);

1 The activity was suspended in March 2020 due to the COVID-19 emergency. INTERNAL COURSES 1st year: • 6 -17 November 2017 Bologna, Italy – Corso di PYTHON: Everything you always wanted to know abut PYTHON; • 21-25 May 2018 Bologna, Italy - Spectral energy distribution of galaxies. 2nd year: • 17-21 June 2019 Bologna, Italy - Statistics for Astrophysics. 3rd year: • 27 May – 22 July 2020 - Virtual Seminars on Multi-messenger Astronomy; • 17-22 September 2020 Bologna, Italy - Gaia: Great advances in Astrophysics.

ISA LECTURES

• 13 November 2018 “A heart attack: can re-wire the heart?”; • 8 January 2019 “Sbagliando si impara: the power of errors for learning and teaching”; • 3 December 2019 “The physics of the vacuum”; • 11 February 2020 “Beyond perturbation theory: integrability from fundamentals to applications”.

RESEARCH PERIOD ABROAD

25 August-1 December 2019, Leiden, Netherlands, project: “Detecting diffuse emission at the center of relaxed cluster with LOFAR”, supervised by Dr. H. J. A. Röttgering at the Leiden Observatory.

PUBLICATIONS

Refereed journals: • “The mystery of the ‘Kite’ radio source in Abell 2626: insights from new Chandra observations” A. Ignesti, M. Gitti, G. Brunetti, E. O’sullivan, C.L. Sarazin, K.W. Wong 2018, Astronomy & Astrophysics 610, A89;

• “GASP XXIII: A jellyfish galaxy as an astrophysical laboratory of the baryonic cycle” B. M. Poggianti, A. Ignesti, M. Gitti, A. Wolter, F. Brighenti, A. Biviano, K. George, B. Vulcani, M. Gullieuszik, A. Moretti, R. Paladino, D. Bettoni, A. Franchetto, J. Fritz, Y. Jaffé, M. Radovich, N. Tomicic, 2019, The Astrophysical Journal, Volume 887, Issue 2, article id. 155, pp. ;

• “Radio and X-ray connection in radio mini-halos: implications for hadronic models” A. Ignesti, G. Brunetti, M. Gitti and S. Giacintucci, 2020, A&A, 640, A3;

• “Diffuse Radio Sources in a Statistically Complete Sample of High Galaxy Clusters ” G. Giovannini, M. Cau, A. Bonafede, H. Ebeling, L. Feretti, M. Girardi, M. Gitti, F. Govoni, A. Ignesti, M. Murgia, G. B. Taylor, V. Vacca (Accepted of publication in A&A on 15/06/2020, arXiv:2006.08494);

• “Highly ordered magnetic fields in the tail of the jellyfish galaxy JO206” A. Müller, B. Poggianti , C. Pfrommer , B. Adebahr , P. Serra , A. Ignesti , M. Sparre , M. Gitti , R. Dettmar , B. Vulcani , A. Moretti (submitted to Nature Astronomy, second referee report arrived, only minor comments);

• “The great Kite in the sky: a LOFAR observation of the radio source in Abell 2626” A. Ignesti, T. Shimwell, G. Brunetti, M. Gitti, H. Intema, R. J. van Weeren, M. J. Hardcastle, A. O. Clarke, A. Botteon, G. Di Gennaro, M. Brüggen, I. Browne, S. Mandal, H. J. A. Röttgering, V. Cuciti, F. de Gasperin, R. Cassano, A. M. M. Scaife (submitted to A&A on 29/07/2020);

• “Very Large Array observations of the mini-halo and AGN feedback in the Phoenix cluster” R. Timmerman, R. J. van Weeren, M. McDonald, A. Ignesti, B. R. McNamara, J.Hlavacek- Larrondo, and H. J. A. Röttgering (to be submitted to A&A);

• “Introducing PT-REX, the Point-to-point Trend Extractor” A. Ignesti (to be submitted to New Astronomy).

Proceedings: • “Thermal and non-thermal connection in radio mini-halos” A. Ignesti, G. Brunetti, M. Gitti, S. Giacintucci, 2018, Perseus in Sicily: From Black Hole to Cluster Outskirts. Proceedings of the International Astronomical Union, Volume 342, pp. 137-140.

ACCEPTED OBSERVATION PROPOSALS

• LOFAR LC11_014, PI A. Ignesti “Revealing the origin of the diffuse radio emission in 2A0335+096” Approved time: 8 hrs; • Chandra Cycle 21 ID 21800206, PI M. Gitti “Studyng AGN feeding and feedback in the most quenched cool core cluster” Approved time: 420 ks; • GMRT 38_025, PI V. Cuciti “A systematic spectral study of diffuse radio emission in galaxy clusters with the uGMRT and LOFAR” Approved time: 125 hrs.