Impact of stochastic star-formation histories and dust on selecting quiescent galaxies with JWST photometry

Abstract

While the James Webb Space Telescope (JWST) now allows identifying quiescent galaxies (QGs) out to early epochs, the photometric selection of quiescent galaxy candidates (QGCs) and the derivation of key physical quantities are highly sensitive to the assumed star-formation histories (SFHs). We aim to quantify how the inclusion of JWST/MIRI data and different SFH models impacts the selection and characterisation of QGCs. We test the robustness of the physical properties inferred from the spectral energy distribution (SED) fitting, such as M*, age, star formation rate (SFR), and AV, and study how they impact the quiescence criteria of the galaxies across cosmic time. We perform SED fitting for ~13000 galaxies at z<6 from the CEERS/MIRI fields with up to 20 optical-mid infrared (MIR) broadband coverage. We implement three SFH prescriptions: flexible delayed, NonParametric, and extended Regulator. For each model, we compare results obtained with and without MIRI photometry and dust emission models. We evaluate the impact of these configurations on the number of candidate QGCs, selected based on rest UVJ colours, sSFR and main-sequence offset, and on their key physical properties such as M*, AV, and stellar ages. The number of QGCs selected varies significantly with the choice of SFH from 171 to 224 out of 13000 galaxies, depending on the model. This number increases to 222-327 when MIRI data are used (up to ~45% more QGCs). This enhancement is driven by improved constraints on dust attenuation and M*. We find a strong correlation between AV and M*, with massive galaxies (M*~10^11 M\odot) being 1.5-4.2 times more attenuated in magnitude than low-mass systems (M*~10^9 M\odot), depending on SFH. Regardless of the SFH assumption, ~13% of QGCs exhibit significant attenuation (AV > 0.5) in support of recent JWST studies challenging the notion that quiescent galaxies are uniformly dust-free.

Figures (11)

• Figure 1: Exemplary QGCs from our final sample: a massive system on the left; a less–massive one on the right. Top: CIGALE SEDs. Black solid and dashed lines show the best–fit SEDs for the same galaxy using the Regulator SFH with and without JWST/MIRI photometry for MIRI and no–MIRI run, respectively. Blue circles are detections; triangles are $3\sigma$ upper limits. JWST cutouts are displayed above each SED. Shaded envelopes indicate the range of $K$–band–normalized SEDs for QGCs binned by median $A_V$; the legend lists the median $A_V$ values and number of objects in each bin. Bottom: Specific star-formation histories (sSFHs) for the same QGC from the MIRI run. The dark–blue solid, violet dashed, and light–blue dash-dotted lines correspond to the Regulator, NonParametric, and DelayedBQ models, respectively. The thick and thin dark-blue lines show the difference between MIRI and no-MIRI runs. The black dotted line marks the quiescent threshold and the black dashed line the star-forming threshold (following Pacifici16). Arrows mark the quantities used in this work for the Regulator model: the quenching time $T_q$, the quenching moment $\tau_q$, the cosmic time at the observation redshift $\tau(z_o)$, and the time since quenching $\Delta T \equiv \tau(z_o)-\tau_q$.
• Figure 2: Top: the distribution of the M$_\star$ in function of redshift of the final sample from Regulator MIRI run. Bottom: distributions of differences in main physical properties (SFR in M$_\odot/$yr and the M$_\star$ in M$_\odot$, A$_V$ in mag, age in Myr) between MIRI and no-MIRI runs. The hatched region shows the 90th percentiles of the distributions (P$_{90}$) in both directions.
• Figure 3: Difference in estimated physical properties of galaxies from the final sample using different SFH models within MIRI run as a function of redshift. Panels from left to right: DelayedBQ-NonParametric, NonParametric-Regulator and Regulator-DelayedBQ. Panels from top to down show distribution of difference for: A$_V$ in mag, age in Myr, SFR in M$_\odot/$yr and the M$_\star$ in M$_\odot$. The blue dashed line presents the median of distribution. The hatched region shows the 90th percentiles of the distributions (P$_{90}$) above and below the median value.
• Figure 4: Top: SFR-M$_\star$ plane for different redshifts with galaxies from the final sample from MIRI run with Regulator SFH. The different lines present quiescence selection from literature: black -- sSFR criterion, dark blue -- Popesso23, violet -- Koprowski24, light blue -- Merida25. The grey crosses represent QGCs selected by sSFR criterion in Regulator, MIRI run, which were not recovered in no-MIRI run. Bottom: Comparison of the QGCs sample size depending on the selection criterion and SFH model for the MIRI and no-MIRI runs. The colours of the points represent the MSs and are the same as at top panel. The markers represent SFH model: triangle -- Regulator, circles -- NonParametric, squares -- DelayedBQ. The dashed line shows one-to-one relation. With the shaded regions we mark 30%, 60% and 100% relative distance from the one-to-one relation.
• Figure 5: Comparison of UVJ diagrams for galaxies with $z<2.5$ (top 6 panels) and $2.5\leq z<6$ (bottom 6 panels) for mass-complete sample (M$_*\geq10^8$M$_\odot$) from different runs. The squares are sized logarithmically according to the number of galaxies in the bin. We colour-code the median attenuation in V-band (A$_V$) as the histogram in the background. The grey crosses represent the QGCs selected with sSFR criterion. The blue dashed line shows the redshift-dependent criterion for quiescence by Antwi-Danso23. We mark the fraction of QGCs (sSFR criterion) caught by UVJ criterion in the lower right corner of each panel. The top panels show the results from the MIRI run and the bottom panels show the results from the no-MIRI run. The columns are related to the SFH model used in the run, from left: DelayedBQ, NonParametric, and Regulator. Additionally, we include galaxies for which we are able to recover as QGs using Koprowski24 MS offset criteria: with cyan crosses QGs from Carnall23b and with magenta stars QGs from Long24. For details check App. \ref{['APP:UVJ']}.