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ABSTRACT Galactic outflows strongly influence galactic evolution and have been detected in a range of observations. Hydrodynamic simulations can help interpret these by connecting direct observables to the physical conditions of the outflowing gas. Here we use simulations of isolated disc galaxies ranging from dwarf mass ($$M_{200} = 10^{10}\, \mathrm{M}_{\odot }$$) to Milky Way mass ($$M_{200} = 10^{12}\, \mathrm{M}_{\odot }$$), based on the FIRE-2 subgrid models to investigate multiphase galactic outflows. We use the chimes non-equilibrium chemistry module to create synthetic spectra of common outflow tracers ([C ii]$$_{158\, \mu\rm m}$$, $$\mathrm{CO}_{J(1-0)}$$, H$$\alpha$$ and $$[\mathrm{O}{\small III}]_{5007\, \rm{\mathring{\rm A}}}$$). Using our synthetic spectra we measure the mass outflow rate, kinetic power and momentum flux using observational techniques. In [C ii]$$_{158\, \mu\rm m}$$ we measure outflow rates of $$10^{-4}$$ to 1 $$\mathrm{\, {\rm M}_{\odot }\, \rm yr^{-1}}$$ across an SFR range of $$10^{-3}$$ to 1 $$\text{M}_{\odot }\text{yr}^{-1}$$, which is in reasonable agreement with observations. The significant discrepancy is in $$\mathrm{CO}_{J(1-0)}$$, with the simulations lying $$\approx 1$$ dex below the observational sample. We test observational assumptions used to derive outflow properties from synthetic spectra. We find the greatest uncertainty lies in measurements of electron density, as estimates using the SII doublet can overestimate the actual electron density by up to 2 dex, which changes mass outflow rates by up to 4 dex. We also find that molecular outflows are especially sensitive to the conversion factor between CO luminosity and H2 mass, with outflow rates changing by up to 4 dex in our least massive galaxy. Comparing the outflow properties derived from the synthetic spectra to those derived directly from the simulation, we find that [C ii]$$_{158\, \mu\rm m}$$ probes outflows at greater distances from the disc, whilst we find that molecular gas does not survive at large distances within outflows within our modestly star-forming disc galaxies simulated in this work.
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Dissecting a 30 kpc galactic outflow at z ~ 1.7
ABSTRACT We present the spatially resolved measurements of a cool galactic outflow in the gravitationally lensed galaxy RCS0327 at z ≈ 1.703 using VLT/MUSE IFU observations. We probe the cool outflowing gas, traced by blueshifted Mg ii and Fe ii absorption lines, in 15 distinct regions of the same galaxy in its image-plane. Different physical regions, 5 – 7 kpc apart within the galaxy, drive the outflows at different velocities (Vout ∼ −161 to −240 km s−1), and mass outflow rates ($$\dot{M}_{out} \sim 183$$ – 527 $${\rm M}_{\odot }\, \mathrm{yr}^{-1}$$). The outflow velocities from different regions of the same galaxy vary by 80 km s−1, which is comparable to the variation seen in a large sample of star-burst galaxies in the local universe. Using multiply lensed images of RCS0327, we probe the same star-forming region at different spatial scales (0.5–25 kpc2), we find that outflow velocities vary between ∼ −120 and −242 km s−1, and the mass outflow rates vary between ∼37 and 254 $${\rm M}_{\odot }\, \mathrm{yr}^{-1}$$. The outflow momentum flux in this galaxy is ≥ 100% of the momentum flux provided by star formation in individual regions, and outflow energy flux is ≈ 10% of the total energy flux provided by star formation. These estimates suggest that the outflow in RCS0327 is energy driven. This work shows the importance of small scale variations of outflow properties due to the variations of local stellar properties of the host galaxy in the context of galaxy evolution.
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- Award ID(s):
- 2206853
- PAR ID:
- 10471318
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- Monthly Notices of the Royal Astronomical Society
- Volume:
- 526
- Issue:
- 4
- ISSN:
- 0035-8711
- Format(s):
- Medium: X Size: p. 6297-6320
- Size(s):
- p. 6297-6320
- Sponsoring Org:
- National Science Foundation
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