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Published June 3, 2026 | Version v2
Journal article Open

Data products of "Euclid Quick Data Release (Q1): The impact of AGN emission on SED-derived physical properties"

Authors/Creators

  • 1. Osservatorio di Capodimonte
  • 2. ROR icon Max Planck Institute for Extraterrestrial Physics
  • 3. ROR icon Astronomical Observatory of Rome

Description

The following archive corresponds to the data products of the paper "Euclid Quick Data Release (Q1): The impact of AGN emission on SED-derived physical properties" by Laloux et al. 2026 (aa59340-26)

Inside Laloux26.tar.xz, there are 6 files:

  • README.txt: information regarding the content of the archive
  • SED_properties.fits: This catalogue contains the SED properties of all the sources analysed in Laloux+26, combining the three samples (A, B, C) and the three fields (EDFN, EDFS, EDFF). It also provides the flags of the different AGN selections used in this work.
  • column.txt: This file describes the columns of the SED_properties.fits catalogue.
  • zphot_PDF.fits: This catalogue contains the complete photometric Probability Distribution Function (zPDF) computed in this work. 
    The zPDF is computed on the redshift grid numpy.linspace(0, 7, 701) and the "zphot_this_work" value is set as zgrid[numpy.argmax(zPDF)].
  • array_reliabilities.npy: numpy array containing the reliability grid values used to construct the reliability functions.
  • create_relia_fct.py: python script which opens the array_reliabilities.npy and construct the dictionary of reliability functions "dict_relia".

"dict_relia" has 21 keys, corresponding to different combinations of available bands. This key is indicated for each source in the "band_availability" column of SED_properties.fits.
For each band combination, dict_relia[bands] possesses 15 keys, indicating the type of functions:

  • "interp_region" and "interp_region_GAL" are equal to 1 in the interpolation regions of the reliability functions for AGN and inactive galaxies, respectively.
  • "reliability_{property}": indicates the reliability of the measurement of a given property.
  • "needed_sigma_Mstar": multiplicative factor of the Mstar uncertainties to make them more realistic and ensure at least 68% reliability.
  • "needed_sigma_GAL_Mstar": same as above, but for inactive galaxies.
  • "offset_SFR": offset to be added to the SFR measurement to correct for the AGN bias
  • "scatter_offset_SFR": scatter to be quadratically added to the SFR uncertainty after bias-correction

Abstract

Abstract of Laloux et al. (2026):

The Euclid Quick Data Release (Q1) is a powerful dataset to study active galactic nuclei (AGN) and their host galaxies. Deriving their physical properties through multi-component spectral energy distribution (SED) fitting is a challenging task for AGN, but it is greatly aided by the Euclid near-infrared photometry.
Here we present a new method to quantify the reliability of SED-derived parameters, such as AGN bolometric and monochromatic luminosities, host's stellar mass $M_\star$, star-formation rate (SFR) and specific star-formation rate (sSFR), by using mock SEDs of AGN built by combining observed SEDs of QSOs and galaxies. 
We apply this methodology to the ${\sim}1$ million Q1 AGN candidates, constructing a catalogue of AGN and host galaxy properties, alongside their respective reliability values.
With a reliability threshold at 0.5, we find 88\% of sources with robust stellar masses and 76\% with reliable AGN luminosities. 
Moreover, through SED fitting we also measure the AGN fraction $f_{\rm AGN}$ of the total mid-infrared flux and we use its lower-limit to select AGN. A $f_{\rm AGN, \, low} > 0.075$ threshold yields 85\% completeness and purity.
Comparable to colour-colour AGN selections, this method has the advantage of being less affected by redshift evolution and exploring fainter magnitudes.
Additionally, by comparing the AGN and host galaxy parameters across different identification methods, we find that the probed range in stellar mass and AGN luminosity can be quite different. This highlights the importance of combining different approaches and accounting for their selection biases when studying AGN and their role in galaxy evolution. 
Finally, for the X-ray detected sample, we present the X-ray to mid-IR luminosity relation, and the correlation between stellar mass and bolometric luminosity as a function of redshift, in good agreement with previous results.

Files

Files (4.9 GB)

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md5:eadad0bc74c55f9925c077d2d75188e8
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Additional details

Funding

National Institute for Astrophysics
AGN & Euclid: a close entanglement 01.05.23.01.14

Software

Programming language
Python