Testing the Stellar Feedback-driven Breathing Mode in Low-mass Galaxies with Gas Kinematics

TL;DR

The study tests the breathing-mode hypothesis from stellar feedback in low-mass galaxies by comparing ionized-gas kinematics (σ_{gas}) from a 103-galaxy Keck/DEIMOS sample (0.02 < z < 0.19; 7.9 < log M_*/M_⊙ < 9.6) to mock observations from eight FIRE-2 simulations. They derive sSFRs from SED fitting and Hα measurements, and compute Δσ_{gas} using the FIRE-2 mass–σ_{gas} relation $\log\sigma_{gas} = 0.198 \log(M_*/M_⊙) - 0.235$, analyzing correlations with sSFR on 10 Myr and 100 Myr timescales. Both data and simulations show a positive Δσ_{gas}–sSFR relation, though FIRE-2 exhibits tighter trends and the observed sample has broader scatter and fewer low-sSFR systems; deeper photometric data (COSMOS2015) indicate observed dwarfs can span the full sSFR range predicted by FIRE-2. The results support short-timescale breathing-mode dynamical effects in low-mass galaxies while highlighting uncertainties in long-term cumulative feedback effects and the need for non-parametric SFHs and deeper, higher-resolution observations to fully constrain the phenomenon.

Abstract

Hydrodynamic simulations have proposed that stellar feedback and bursty star-formation can produce dark matter cores in low-mass galaxies. A key prediction is that feedback-driven gas outflow and inflow cycles can lead to ``breathing modes'' (rapid fluctuations in the global gravitational potential) which drive correlated variations in galaxy size, kinematics, and star-formation rate. In this paper, we test the dynamical effects of feedback-driven breathing modes using a sample of 103 star-forming low-mass galaxies with stellar masses between $7.9<\rm \log M_*/M_\odot<9.6$ and $0.02<z<0.19$. We measure ionized gas velocity dispersions from H$α$ emission lines and compare them to mock observations from the FIRE-2 simulations. We compare gas velocity dispersions ($\rm σ_{gas}$), stellar masses, and specific star-formation rates (sSFR). We find a positive correlation between gas velocity dispersion residuals at fixed stellar masses ($\rm Δσ_{gas}$) and sSFR in both data and simulations. However, the relation is tighter in FIRE-2 compared to the data. FIRE-2 produces more low-sSFR galaxies compared to our observational sample, however, the sSFR distributions agree after limiting both samples to a minimum sSFR. A deeper and more complete photometric sample further indicates that observed low-mass galaxies could span the full range of sSFR predicted in the FIRE-2 simulations. Our results support the existence of short-timescale dynamical effects driven by gas outflow and inflow cycles in low-mass galaxies and motivate additional tests of the breathing mode.

Figures (12)

• Figure 1: Top: $u-r$ color vs. $i$-band magnitude for all the observed low-mass galaxies with Keck/DEIMOS ($7.9<\rm \log M_*/M_\odot<9.6$ at $0.02<z<0.19$, selected from COSMOS2015 catalog). Red points show galaxies that have H$\alpha$ emission lines detected from our Keck/DEIMOS observations. Orange crosses show galaxies confirmed with other spectroscopic observations but without H$\alpha$ measurements from our Keck/DEIMOS observations. Gray squares are galaxies that don't have any successful spectroscopic confirmation. Middle: star-formation rates vs. stellar masses. Bottom: specific star-formation rates vs. stellar masses. Our H$\alpha$ detected sample is highly complete for star-forming galaxies with $\rm log(sSFR)>-10.5\ yr^{-1}$.
• Figure 2: Completeness as a function of stellar masses (top), SFR (middle), and sSFR (bottom) for our H$\alpha$ detected sample. Error bars represent binomial uncertainties based on the number of galaxies in each bin. Overall, our H$\alpha$ detected sample is 81.6% complete compared to the much deeper photometric sample. The completeness generally increases with stellar masses, star-formation rates, and specific star-formation rates.
• Figure 3: Top: spectral energy distribution of an example dwarf galaxy (COSMOS2015 ID: 312605) in our sample. Blue circles are the multi-band photometry obtained from the COSMOS2015 catalog and used for SED fitting with Prospector. The black spectrum and gray boxes show the best-fit model spectrum and mock photometry from the SED fitting. Gray curves on the bottom show the filter transmission curves for each flux measurement. The lower two panels show the zoom-in regions around [OIII] (left panel) and H$\alpha$ (right panel). The red curves are the observed Keck/DEIMOS spectrum for this object. The lower left panel includes the HSC color image of this galaxy. The red rectangle on the galaxy image indicates the slit used for the Keck/DEIMOS observation. These data allow us to derive key properties relevant for this study, including stellar masses, star-formation rates, velocity dispersions.
• Figure 4: Feedback-driven fluctuations in the FIRE-2 simulated galaxy $\rm m11d$ ($\rm \log M_*/M_\odot\sim9.6$). Top: sSFR averaged over 10 Myr (blue solid line, corresponding to sSFR derived from H$\alpha$) and 100 Myr (red dashed line, corresponding to sSFR derived from SED fitting). Bottom: Velocity dispersion measured with ionized HII gas around young stars (blue solid line, corresponding to $\rm \sigma_{gas}$ derived from H$\alpha$) and all gas (red dashed line). The breathing mode scenario suggests that gas responds directly to bursty star-formation, driving fluctuations in the gravitational potential and subsequently transferring the energy to stars and dark matter.
• Figure 5: Ionized gas velocity dispersions vs. specific star-formation rates averaged over 10 Myr for the low-mass galaxies in FIRE-2 simulations. We include 88 snapshots within $0.02<z<0.19$ for each FIRE-2 simulated galaxy. The upper 8 panels show $\rm \sigma_{gas}$ vs. $\rm sSFR_{10Myr}$ for $\rm m11a, m11c, m11d, m11e, m11h, m11i, m11q, m11v$ in FIRE-2, respectively. A positive relation between $\rm \sigma_{gas}$ and $\rm sSFR$, as explained by the feedback-driven breathing mode, can be found in all FIRE-2 simulated galaxies. Though this is weak for $\rm m11h$, which has a relatively less bursty SFH. This might be because that $\rm m11h$ is the diskiest galaxy among our sample, which acts to tamp down the burstiness of the SFH. The bottom panel show all the snapshots from the 8 simulated galaxies together, color-coded by the stellar mass. A clear mass dependence of $\rm \sigma_{gas}$ at a given sSFR can be seen.