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Euclid: Quick Data Release (Q1)- The connection between galaxy close encounters and radio activity

M. Magliocchetti, A. La Marca, L. Bisigello, M. Bondi, F. Ricci, S. Fotopoulou, L. Wang, R. Scaramella, L. Pentericci, I. Prandoni, J. G. Sorce, H. J. A. Rottgering, M. J. Hardcastle, J. Petley, F. La Franca, K. Rubinur, Y. Toba, Y. Zhong, M. Mezcua, G. Zamorani, F. Shankar, B. Altieri, S. Andreon, N. Auricchio, C. Baccigalupi, M. Baldi, S. Bardelli, A. Biviano, E. Branchini, M. Brescia, J. Brinchmann, S. Camera, G. Canas-Herrera, V. Capobianco, C. Carbone, J. Carretero, M. Castellano, G. Castignani, S. Cavuoti, K. C. Chambers, A. Cimatti, C. Colodro-Conde, G. Congedo, C. J. Conselice, L. Conversi, Y. Copin, A. Costille, F. Courbin, H. M. Courtois, M. Cropper, A. Da Silva, H. Degaudenzi, G. De Lucia, A. M. Di Giorgio, H. Dole, F. Dubath, C. A. J. Duncan, X. Dupac, S. Dusini, S. Escoffier, M. Farina, R. Farinelli, F. Faustini, S. Ferriol, F. Finelli, M. Frailis, E. Franceschi, P. Franzetti, M. Fumana, S. Galeotta, K. George, B. Gillis, C. Giocoli, J. Gracia-Carpio, A. Grazian, F. Grupp, S. V. H. Haugan, J. Hoar, W. Holmes, I. M. Hook, F. Hormuth, A. Hornstrup, K. Jahnke, M. Jhabvala, B. Joachimi, E. Keihanen, S. Kermiche, A. Kiessling, B. Kubik, M. Kummel, H. Kurki-Suonio, A. M. C. Le Brun, S. Ligori, P. B. Lilje, V. Lindholm, I. Lloro, G. Mainetti, D. Maino, E. Maiorano, O. Mansutti, O. Marggraf, M. Martinelli, N. Martinet, F. Marulli, R. J. Massey, E. Medinaceli, S. Mei, Y. Mellier, M. Meneghetti, E. Merlin, G. Meylan, A. Mora, M. Moresco, L. Moscardini, R. Nakajima, C. Neissner, R. C. Nichol, S. -M. Niemi, C. Padilla, S. Paltani, F. Pasian, K. Pedersen, W. J. Percival, V. Pettorino, S. Pires, G. Polenta, M. Poncet, L. A. Popa, L. Pozzetti, F. Raison, A. Renzi, J. Rhodes, G. Riccio, E. Romelli, M. Roncarelli, R. Saglia, Z. Sakr, D. Sapone, B. Sartoris, M. Schirmer, P. Schneider, T. Schrabback, A. Secroun, G. Seidel, S. Serrano, P. Simon, C. Sirignano, G. Sirri, L. Stanco, J. Steinwagner, P. Tallada-Crespi, A. N. Taylor, I. Tereno, N. Tessore, S. Toft, R. Toledo-Moreo, F. Torradeflot, I. Tutusaus, L. Valenziano, J. Valiviita, T. Vassallo, G. Verdoes Kleijn, A. Veropalumbo, Y. Wang, J. Weller, E. Zucca, M. Huertas-Company, V. Scottez

TL;DR

This study leverages Euclid VIS morphologies and LOFAR 144 MHz data to probe how galaxy mergers relate to radio activity in AGN and star-forming galaxies up to $z\approx2$. By classifying radio sources as AGN or SFG via a redshift-dependent crossover luminosity and matching to Euclid-based merger classifications, the authors uncover a striking dichotomy: radio-selected AGN, particularly those with extended morphologies, preferentially reside in merging systems, driven mostly by $0.5<z<1$ and high-luminosity objects, while radio-emitting SFG favor isolated hosts across redshift and luminosity. The results suggest that external gas from interactions fuels AGN activity and extended radio emission in the local universe, whereas internal gas reservoirs primarily power star formation. Robust against several systematics, these findings shed light on the co-evolution of galaxies and their central black holes and demonstrate the power of combining Euclid and LOFAR data for studying AGN fueling and galaxy interactions.

Abstract

Using the large statistics provided by both Euclid and the LOFAR surveys, we present the first large-scale study of the connection between radio emission, its morphology, and the merging properties of the hosts of radio sources up to z=2. By dividing the radio sample into active galactic nuclei (AGN) and star-forming galaxies, we find that radio-emitting AGN show a clear preference to reside within galaxies undergoing a merging event. This is more significant for AGN that present extended and/or complex radio emission: indeed, about half of them are associated with merging systems, while only 15% are hosted by an isolated galaxy. The observed trend is primarily driven by AGN residing at z < 1, especially in the case of high - P144MHz > 10^24 W Hz-1 sr-1 - radio luminosities (60% in mergers versus 10% isolated regardless of radio appearance). The situation is reversed in the case of radio-emitting star-forming galaxies, which are preferentially associated with isolated systems. This is more significant as we move towards low radio-luminosity/star-formation objects (P144MHz < 10^23 W Hz-1 sr-1) for which we find 40% in isolated systems versus 20% in mergers. These values hold regardless of redshift. We interpret the above result for AGN with their need to accrete outer gas from local encounters in order to trigger (radio) activity, especially in the case of extended radio emission such as hot-spots and lobes. This is mostly observed at z < 1, since in the local Universe galaxies are more gas deprived than their higher-redshift counterparts. Internal gas reservoirs instead seem sufficient to trigger star formation within the majority of galaxies, which indeed prefer to be associated with isolated systems at all redshifts probed. (abridged)

Euclid: Quick Data Release (Q1)- The connection between galaxy close encounters and radio activity

TL;DR

This study leverages Euclid VIS morphologies and LOFAR 144 MHz data to probe how galaxy mergers relate to radio activity in AGN and star-forming galaxies up to . By classifying radio sources as AGN or SFG via a redshift-dependent crossover luminosity and matching to Euclid-based merger classifications, the authors uncover a striking dichotomy: radio-selected AGN, particularly those with extended morphologies, preferentially reside in merging systems, driven mostly by and high-luminosity objects, while radio-emitting SFG favor isolated hosts across redshift and luminosity. The results suggest that external gas from interactions fuels AGN activity and extended radio emission in the local universe, whereas internal gas reservoirs primarily power star formation. Robust against several systematics, these findings shed light on the co-evolution of galaxies and their central black holes and demonstrate the power of combining Euclid and LOFAR data for studying AGN fueling and galaxy interactions.

Abstract

Using the large statistics provided by both Euclid and the LOFAR surveys, we present the first large-scale study of the connection between radio emission, its morphology, and the merging properties of the hosts of radio sources up to z=2. By dividing the radio sample into active galactic nuclei (AGN) and star-forming galaxies, we find that radio-emitting AGN show a clear preference to reside within galaxies undergoing a merging event. This is more significant for AGN that present extended and/or complex radio emission: indeed, about half of them are associated with merging systems, while only 15% are hosted by an isolated galaxy. The observed trend is primarily driven by AGN residing at z < 1, especially in the case of high - P144MHz > 10^24 W Hz-1 sr-1 - radio luminosities (60% in mergers versus 10% isolated regardless of radio appearance). The situation is reversed in the case of radio-emitting star-forming galaxies, which are preferentially associated with isolated systems. This is more significant as we move towards low radio-luminosity/star-formation objects (P144MHz < 10^23 W Hz-1 sr-1) for which we find 40% in isolated systems versus 20% in mergers. These values hold regardless of redshift. We interpret the above result for AGN with their need to accrete outer gas from local encounters in order to trigger (radio) activity, especially in the case of extended radio emission such as hot-spots and lobes. This is mostly observed at z < 1, since in the local Universe galaxies are more gas deprived than their higher-redshift counterparts. Internal gas reservoirs instead seem sufficient to trigger star formation within the majority of galaxies, which indeed prefer to be associated with isolated systems at all redshifts probed. (abridged)

Paper Structure

This paper contains 13 sections, 1 equation, 16 figures, 2 tables.

Table of Contents

  1. Introduction
  2. Radio Selection
  3. Radio data
  4. AGN or star-forming galaxy?
  5. The combined catalogue
  6. Results for radio AGN and star-forming galaxies
  7. AGN
  8. Star-forming galaxies
  9. Possible systematics
  10. Discussion
  11. Radio Luminosity Distributions
  12. Properties of the optical catalogue
  13. Radio and optical images for AGN with extended radio morphology

Figures (16)

  • Figure 1: Redshift distribution of LOFAR sources in the EDF-N region in the redshift interval $0.5< z < 2$. The left-hand panel refers to the whole sample, the middle panel to the sub-class of radio AGN, and the right-hand panel to star-forming galaxies. In each panel the solid line refers to the parent radio sample from the work of bisigello, while the dashed histograms correspond to those sources with optical counterparts from the work of Q1-SP013. The bottom panels show the percentages obtained from the ratios between the above quantities, together with the associated (Poissonian) errors. The middle panel additionally presents the trends for AGN with complex radio morphology, short-long dashed lines for the parent sample and dotted lines for the matched sample.
  • Figure 2: Similar to Fig. \ref{['fig:hist_z']}, but for the 144 MHz luminosity distribution of LOFAR sources in the EDF-N belonging to the redshift interval $0.5<z<2$.
  • Figure 3: Percentage of radio-selected AGN (left-hand panel) and SFG (right-hand panel) in the range $0.5<z<2$ associated with either isolated galaxies (' Isolated Systems' -- blue triangles) or galaxy-galaxy mergers (' Merging Systems' -- red squares). Each panel is subdivided into three sections, where the leftmost one shows the case for the whole sample of radio-selected AGN or SFG with a counterpart from the work of Q1-SP013, the middle one is for radio sources with a compact radio structure, while the rightmost one is for objects presenting complex or extended radio morphologies. Error-bars represent Poissonian uncertainties.
  • Figure 4: Percentage of radio-selected AGN associated with either isolated galaxies or galaxy-galaxy mergers. The subdivision of each panel and the colour/marker styles are as in Fig. 3. The left-hand panel presents the two cases for sources in the $0.5<z<1$ (top) and $1<z<2$ (bottom) range, while the right-hand panel considers objects of different radio luminosities, respectively $P_{144\, \rm MHz}<$ (top) and $>$ (bottom) $10^{24}$ W Hz$^{-1}$ sr$^{-1}$. In this case error-bars represent Poissonian uncertainties derived according to gehrels.
  • Figure 5: Similar to Fig. 4, except that now different panels present different redshift/radio-luminosity (expressed in W Hz$^{-1}$ sr$^{-1}$ units) combinations as shown (see text for details). The point in the top-right part of the top-right panel is off the scale and refers to one single object hosted by a merging system.
  • ...and 11 more figures