  In this work we study how to employ the upcoming Legacy Survey of Space and
Time (LSST) data to constrain physical properties of normal, star forming
galaxies. We use simulated LSST data and existing real observations to test the
estimations of the physical properties of galaxies, such as star formation rate
(SFR), stellar mass ($M_{star}$), and dust luminosity ($L_{dust}$). We focus on
normal star-forming galaxies, as they form the majority of the galaxy
population in the universe and therefore are more likely to be observed by the
LSST. We perform a simulation of LSST observations and uncertainties of 50,385
real galaxies within redshift range $0<z<2.5$. In order to achieve this goal,
we used the unique multi-wavelength data from the Herschel Extragalactic Legacy
Project (HELP) survey. Our analysis focus on two fields: ELAIS-N1 and COSMOS.
To obtain galaxy physical properties we fit their Spectral Energy Distributions
(SEDs) using the Code Investigating GALaxy Emission (CIGALE). We compare the
main galaxy physical properties obtained from the fit of the observed
multi-wavelength photometry of galaxies (from UV to FIR) to the ones obtained
from the simulated LSST optical measurements only. The stellar masses estimated
based on the LSST measurements are in agreement with the full UV-FIR SED
estimations, as they depend mainly on the UV and optical emission, well covered
by LSST in the considered redshift range. We obtain a clear overestimation of
SFR, $L_{dust}$, $M_{dust}$ estimated with LSST only, highly correlated with
redshift. We investigate the cause of this overestimation and we conclude that
it is related to an overestimation of the dust attenuation, both UV and NIR. We
find that it is necessary to employ auxiliary rest-frame mid-infrared
observations, simulated UV observations, or FUV attenuation (AFUV)- Mstar
relation, to correct the overestimation.
