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Euclid: Quick Data Release (Q1) -- A photometric search for ultracool dwarfs in the Euclid Deep Fields

M. Žerjal, C. Dominguez-Tagle, N. Vitas, N. Sedighi, E. L. Martín, M. R. Zapatero Osorio, J. Olivares, S. Muñoz Torres, S. Tsilia, J. -Y. Zhang, D. Barrado, V. J. S. Béjar, H. Bouy, A. Burgasser, P. Cruz, N. Lodieu, P. Mas Buitrago, N. Phan-Bao, E. Solano, R. Tata, B. Goldman, A. Mohandasan, C. Reylé, R. L. Smart, N. Aghanim, B. Altieri, A. Amara, S. Andreon, N. Auricchio, C. Baccigalupi, M. Baldi, A. Balestra, S. Bardelli, P. Battaglia, A. Biviano, A. Bonchi, E. Branchini, M. Brescia, J. Brinchmann, S. Camera, G. Cañas-Herrera, V. Capobianco, C. Carbone, J. Carretero, S. Casas, M. Castellano, G. Castignani, S. Cavuoti, K. C. Chambers, A. Cimatti, C. Colodro-Conde, G. Congedo, C. J. Conselice, L. Conversi, Y. Copin, F. Courbin, H. M. Courtois, M. Cropper, J. -G. Cuby, A. Da Silva, H. Degaudenzi, G. De Lucia, C. Dolding, H. Dole, M. Douspis, F. Dubath, X. Dupac, S. Dusini, S. Escoffier, M. Farina, F. Faustini, S. Ferriol, S. Fotopoulou, M. Frailis, E. Franceschi, S. Galeotta, K. George, B. Gillis, C. Giocoli, P. Gómez-Alvarez, J. Gracia-Carpio, B. R. Granett, A. Grazian, F. Grupp, S. V. H. Haugan, J. Hoar, W. Holmes, F. Hormuth, A. Hornstrup, K. Jahnke, M. Jhabvala, E. Keihänen, S. Kermiche, A. Kiessling, B. Kubik, K. Kuijken, M. Kümmel, M. Kunz, H. Kurki-Suonio, Q. Le Boulc'h, 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. Massey, E. Medinaceli, S. Mei, Y. Mellier, M. Meneghetti, E. Merlin, G. Meylan, A. Mora, M. Moresco, L. Moscardini, R. Nakajima, C. Neissner, 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, R. Rebolo, A. Renzi, J. Rhodes, G. Riccio, E. Romelli, M. Roncarelli, R. Saglia, Z. Sakr, D. Sapone, B. Sartoris, J. A. Schewtschenko, M. Schirmer, P. Schneider, A. Secroun, G. Seidel, M. Seiffert, S. Serrano, P. Simon, C. Sirignano, G. Sirri, L. Stanco, J. Steinwagner, P. Tallada-Crespí, A. N. Taylor, I. Tereno, S. Toft, R. Toledo-Moreo, F. Torradeflot, A. Tsyganov, I. Tutusaus, L. Valenziano, J. Valiviita, T. Vassallo, G. Verdoes Kleijn, A. Veropalumbo, Y. Wang, J. Weller, A. Zacchei, G. Zamorani, F. M. Zerbi, E. Zucca, J. Martín-Fleitas, V. Scottez

Abstract

We present a catalogue of 5306 new ultracool dwarf (UCD) candidates in the three Euclid Deep Fields in the Q1 data release. They range from late M to late T dwarfs, and include 1200 L and T dwarfs. A total of 546 objects have been spectroscopically confirmed, including 329 L dwarfs and 26 T dwarfs. We also provide empirical Euclid colours as a function of spectral type. Our UCD selection criteria are based only on colour ($I_\mathrm{E}-Y_\mathrm{E}>2.5$). The combined requirement for optical detection and stringent signal-to-noise ratio threshold ensure a high purity of the sample, but at the expense of completeness, especially for T dwarfs. The detections range from magnitudes 19 and 24 in the near-infrared bands, and extend down to 26 in the optical band. We discuss Euclid's capability to identify UCD candidates based on its photometric passbands. The average surface density of detected UCDs on the sky is approximately 100 objects per $\mathrm{deg}^2$, including 20 L and T dwarfs per $\mathrm{deg}^2$. This leads to an expectation of at least 1.4 million ultracool dwarfs in the final data release of the Euclid Wide Survey, including at least $300\,000$ L dwarfs, and more than 2600 T dwarfs, using the strict selection criteria from this work.

Euclid: Quick Data Release (Q1) -- A photometric search for ultracool dwarfs in the Euclid Deep Fields

Abstract

We present a catalogue of 5306 new ultracool dwarf (UCD) candidates in the three Euclid Deep Fields in the Q1 data release. They range from late M to late T dwarfs, and include 1200 L and T dwarfs. A total of 546 objects have been spectroscopically confirmed, including 329 L dwarfs and 26 T dwarfs. We also provide empirical Euclid colours as a function of spectral type. Our UCD selection criteria are based only on colour (). The combined requirement for optical detection and stringent signal-to-noise ratio threshold ensure a high purity of the sample, but at the expense of completeness, especially for T dwarfs. The detections range from magnitudes 19 and 24 in the near-infrared bands, and extend down to 26 in the optical band. We discuss Euclid's capability to identify UCD candidates based on its photometric passbands. The average surface density of detected UCDs on the sky is approximately 100 objects per , including 20 L and T dwarfs per . This leads to an expectation of at least 1.4 million ultracool dwarfs in the final data release of the Euclid Wide Survey, including at least L dwarfs, and more than 2600 T dwarfs, using the strict selection criteria from this work.

Paper Structure

This paper contains 16 sections, 1 equation, 18 figures, 2 tables.

Table of Contents

  1. Introduction
  2. Data
  3. Reference UCDs in fields
  4. Selection of point sources
  5. Extinction estimation
  6. A catalogue of photometric UCD candidates
  7. A catalogue of spectroscopically confirmed UCDs
  8. Spectral typing
  9. Discussion
  10. Empirical photometric sequence
  11. Limitations and contamination of the catalogue
  12. Metal-poor ultracool dwarfs
  13. Comparison with the Dark Energy Survey
  14. Expected detections of UCDs in the forthcoming data releases
  15. Conclusions
  16. ...and 1 more sections

Figures (18)

  • Figure 1: Morphological filters differentiate between extended sources and point sources. The filtering criteria (red lines for ELLIPTICITY and MUMAX_MINUS_MAG) are based on the benchmark ultracool dwarfs 2024AA...686A.171Z. Grey dots are sources from the entire catalogue. The right panel shows that while KRON_RADIUS is not used in the procedure, it correlates well with luminosity for the point sources.
  • Figure 2: Left: Magnitude distributions for each point-source selection filter (we do not plot the FWHM filter). The most limiting is the S/N requirement that raises the completeness and detection limits to ensure a high quality of the point-source catalogue. Right: Signal-to-noise ratio is correlated with luminosity.
  • Figure 3: Magnitude distributions in the point-source catalogue. Completeness limits are approximately 23.5 for the NISP bands and 24.5 for VIS. The filtering procedure was not applied to the band, since it was not used in the candidate selection from the colour-colour diagram.
  • Figure 4: colour-colour diagram. The offset between EDF-N and EDF-S is most prominent in the solar-like region at $0.1<\IE-\YE<0.4$.
  • Figure 5: The 'bluebottle' diagram of point sources. The central sequence starts with white dwarfs below $\IE-\YE<0$, continues with stars, and ends in the cool tip with ultracool dwarfs at $\IE-\YE \gtrsim 2.5$. Their nature is confirmed with the benchmark UCDs from 2024AA...686A.171Z. We overplotted both the new photometric candidate T dwarfs from this work (symbols with error bars), and those that were spectroscopically confirmed (open circles), as listed in Table \ref{['tab.tdwarfs']}. ATMO models 2020Phillips indicate the UCD parameter space, while the PARSEC model traces main sequence and evolved stars with redder $\YE-\HE$.
  • ...and 13 more figures