Predicting the number counts of line emitters probed by the EUCLID mission

EUCLID is an ESA space mission that will launch in July 2023 on a SpaceX Falcon 9 vehicle from Cape Canaveral. Using a suite of instruments in the visible and NIR in the telescope for its photometric and spectroscopic observations, EUCLID aims to study the shapes and accurate redshifts of galaxies up to redshift z ∼ 2, which is a lookback time of around 10Gyr. The main goal of these observations will be to constrain the nature of Dark Energy, the mysterious component of the Universe that causes its accelerated expansion. At the same time, these observations will be very helpful to understand the evolution of structures in the universe since the dark energy era. As a part of EUCLID project, we studied various spectroscopic lines covered by EUCLID spectral range (900-1850nm) and made a forecast for their observability, separately for the Wide and Deep survey, together with a review of the physical parameters that can be derived with them. We used the mock catalogs MAMBO and SPRITZ, which are created to accurately reproduce the observable sky, to study and predict the number counts of galaxies emitting a specific line or a group of lines. This is a very important preparatory work to identify scientific analysis that can be performed with EUCLID data, once they will be available. We use 3 different cases to present the number counts. The ’order 0’ number counts where we assume that all the galaxies above the flux limits of 6 × 10−17 ergs/s/cm2 (DEEP survey) and 2 × 10−16 ergs/s/cm2 (WIDE survey) will be observed by the telescope. The second set are the number counts where instead of using the ’order 0’ flux limit, we use a more realistic prediction built exploiting the PILOT simulations (Gabarra et al. (in prep) which gives us the probabilty that a line with a given flux is observed with a good enough S/N to be included in the catalogs, and therefore in the number counts were calculated by applying proper weights to these galaxies. In the final case, the number counts are based on a different and more sophisticated simulations (the EL-COSMOS simulations) that should give more robust results than the previous 2 cases. However, these simulations are not yet fully validated and understood, therefore the predictions made according to this case are to be taken with great care. We use a very large sample of 400, 000 galaxies spread around an area of 3.14deg2 from the mock catalogues. An interesting prediction that come out of our work is that in the regions covered by the DEEP survey, we expect EUCLID to gather a sample of around 60,000 galaxies (1500 galaxies/deg2) at 1.41 ≤ z ≤ 1.81 for which it will be possible to measure the metallicity using R23 method. The sample of galaxies for which we can measure the dust corrected SFR is , but only around – would be observed with the EUCLID telescope in the redshift interval 0.85 to 1.81. We expect 451 gal/deg2 for which all the Paschen lines from Paβ to Paδ will be observed. There are no galaxies for which Paα can be observed as its wavelength is much larger than the maximum possible observable limits of EUCLID’s detectors. We compare the number counts for the three cases and present the number of galaxies for which Hβλ4861 is observed in the redshift interval of 0.85 to 1.41. We get 1000 galaxies/deg2 in case 1, 700 galaxies/deg2 for the PILOT simulations and only 300 galaxies using the EL-COSMOS simulations.