Modelling the M*-SFR relation at high redshift: untangling factors driving biases in the intrinsic scatter measurement. (arXiv:2001.08560v2 [astro-ph.GA] UPDATED)

Modelling the M*-SFR relation at high redshift: untangling factors driving biases in the intrinsic scatter measurement. (arXiv:2001.08560v2 [astro-ph.GA] UPDATED)
<a href="http://arxiv.org/find/astro-ph/1/au:+Curtis_Lake_E/0/1/0/all/0/1">E. Curtis-Lake</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Chevallard_J/0/1/0/all/0/1">J. Chevallard</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Charlot_S/0/1/0/all/0/1">S. Charlot</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Sandles_L/0/1/0/all/0/1">L. Sandles</a>

We present a method to self-consistently propagate M$_{*}$ and SFR ($Psi$)
uncertainties onto intercept, slope and intrinsic scatter estimates for a
simple model of the main sequence of star forming galaxies where $Psi = alpha
+ beta$M$_{*} + mathcal{N}(0,sigma)$. From simple idealised models set up
with broad-band photometry from NIRCam filters at $zsim5$, we test the method
and compare to methods in the literature. Simplifying the $Psi$ estimate by
basing it on dust-corrected MUV can help to reduce the impact of template set
degeneracies on slope and intercept estimates, but act to bias the intrinsic
scatter estimate. We find that broad-band fluxes alone cannot constrain the
contribution from emission lines, implying that strong priors on the
emission-line contribution are required if no medium-band constraints are
available. Therefore at high redshifts, where emission lines contribute a
higher fraction of the broad-band flux, photometric fitting is sensitive to
$Psi$ variations on short ($sim$ 10 Myr) timescales. Priors on age imposed
with a constant (or rising) star formation history (SFH) do not allow one to
investigate a possible dependence of $sigma$ on M$_{*}$ at high redshifts.
Delayed exponential SFHs have less constrained priors, but do not account for
$Psi$ variations on short timescales, a problem if $sigma$ increases due to
stochasticity of star formation. A simple SFH with current star formation
decoupled from the previous history is appropriate. We show that, for simple
exposure-time calculations assuming point sources, with low levels of dust, we
should be able to obtain unbiased estimates of the main sequence down to
log(M/M$_{odot}$) $sim$ 8 at $zsim5$ with the James Webb Space Telescope
while allowing for stochasticity of star formation.

We present a method to self-consistently propagate M$_{*}$ and SFR ($Psi$)
uncertainties onto intercept, slope and intrinsic scatter estimates for a
simple model of the main sequence of star forming galaxies where $Psi = alpha
+ beta$M$_{*} + mathcal{N}(0,sigma)$. From simple idealised models set up
with broad-band photometry from NIRCam filters at $zsim5$, we test the method
and compare to methods in the literature. Simplifying the $Psi$ estimate by
basing it on dust-corrected MUV can help to reduce the impact of template set
degeneracies on slope and intercept estimates, but act to bias the intrinsic
scatter estimate. We find that broad-band fluxes alone cannot constrain the
contribution from emission lines, implying that strong priors on the
emission-line contribution are required if no medium-band constraints are
available. Therefore at high redshifts, where emission lines contribute a
higher fraction of the broad-band flux, photometric fitting is sensitive to
$Psi$ variations on short ($sim$ 10 Myr) timescales. Priors on age imposed
with a constant (or rising) star formation history (SFH) do not allow one to
investigate a possible dependence of $sigma$ on M$_{*}$ at high redshifts.
Delayed exponential SFHs have less constrained priors, but do not account for
$Psi$ variations on short timescales, a problem if $sigma$ increases due to
stochasticity of star formation. A simple SFH with current star formation
decoupled from the previous history is appropriate. We show that, for simple
exposure-time calculations assuming point sources, with low levels of dust, we
should be able to obtain unbiased estimates of the main sequence down to
log(M/M$_{odot}$) $sim$ 8 at $zsim5$ with the James Webb Space Telescope
while allowing for stochasticity of star formation.

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