Tides or dark matter sub-halos: Which ones are more attractive?

Young tidal dwarf galaxies (TDGs) are observed in the tidal debris of gas-rich interacting galaxies. In contrast to what is generally assumed to be the case for isolated dwarf galaxies, TDGs are not embedded in their own dark matter (DM) sub-halo. Hence, they are more sensitive to stellar feedback and could be disrupted on a short time-scale. Detailed numerical and observational studies demonstrate that isolated DM-dominated dwarf galaxies can have lifetimes of more than 10 Gyr. For TDGs that evolve in a tidal field with compressing accelerations equal to the gravitational acceleration within a DM sub-halo typical of an isolated dwarf galaxy, a similar survival time is expected. The tidal acceleration profile depends on the virial mass of the host galaxy and the distance between the TDG and its host. We analytically compare the tidal compression to the gravitational acceleration due to either cuspy or cored DM sub-halos of various virial masses. For example, the tidal field at a distance of 100 kpc to a host halo of 10^13 Msol can be as stabilizing as a 10^9 Msol DM sub-halo. By linking the tidal field to the equivalent gravitational field of a DM sub-halo, we can use existing models of isolated dwarfs to estimate the survivability of TDGs. We show that part of the unexpectedly high dynamical masses inferred from observations of some TDGs can be explained by tidal compression and hence TDGs require to contain less unobservable matter to understand their rotation curves.Comment: 11 pages, 7 figures, accepted for publication in MNRA

The mass-metallicity relation of tidal dwarf galaxies

Dwarf galaxies generally follow a mass-metallicity (MZ) relation, where more massive objects retain a larger fraction of heavy elements. Young tidal dwarf galaxies (TDGs), born in the tidal tails produced by interacting gas-rich galaxies, have been thought to not follow the MZ relation, because they inherit the metallicity of the more massive parent galaxies. We present chemical evolution models to investigate if TDGs that formed at very high redshifts, where the metallicity of their parent galaxy was very low, can produce the observed MZ relation. Assuming that galaxy interactions were more frequent in the denser high-redshift universe, TDGs could constitute an important contribution to the dwarf galaxy population. The survey of chemical evolution models of TDGs presented here captures for the first time an initial mass function (IMF) of stars that is dependent on both the star formation rate and the gas metallicity via the integrated galactic IMF (IGIMF) theory. As TDGs form in the tidal debris of interacting galaxies, the pre-enrichment of the gas, an underlying pre-existing stellar population, infall, and mass dependent outflows are considered. The models of young TDGs that are created in strongly pre-enriched tidal arms with a pre-existing stellar population can explain the measured abundance ratios of observed TDGs. The same chemical evolution models for TDGs, that form out of gas with initially very low metallicity, naturally build up the observed MZ relation. The modelled chemical composition of ancient TDGs is therefore consistent with the observed MZ relation of satellite galaxies.Comment: 7 pages, 3 figures, MNRAS accepte

Radiative cooling rates, ion fractions, molecule abundances and line emissivities including self-shielding and both local and metagalactic radiation fields

We use the spectral synthesis code Cloudy to tabulate the properties of gas for an extensive range in redshift (z=0 to 9), temperature (log T [K] = 1 to 9.5), metallicity (log Z/$\mathrm{Z}_{\odot}$ = -4 to +0.5, Z=0), and density (log $n_{\mathrm{H}}$ [$\mathrm{cm}^{-3}$] = -8 to +6). This therefore includes gas with properties characteristic of the interstellar, circumgalactic and intergalactic media. The gas is exposed to a redshift-dependent UV/X-ray background, while for the self-shielded lower-temperature gas (i.e. ISM gas) an interstellar radiation field and cosmic rays are added. The radiation field is attenuated by a density- and temperature-dependent column of gas and dust. Motivated by the observed star formation law, this gas column density also determines the intensity of the interstellar radiation field and the cosmic ray density. The ionization balance, molecule fractions, cooling rates, line emissivities, and equilibrium temperatures are calculated self-consistently. We include dust, cosmic rays, and the interstellar radiation field step-by-step to study their relative impact. These publicly available tables are ideal for hydrodynamical simulations. They can be used stand alone or coupled to a non-equilibrium network for a subset of elements. The release includes a C routine to read in and interpolate the tables, as well as an easy to use python graphical user interface to explore the tables.Comment: Accepted for publication in MNRAS; 29 pages, 24 figures; for data files and more info see: https://www.sylviaploeckinger.com/radcool; minor changes to match published versio

TangoSIDM Project: Is the Stellar Mass Tully-Fisher relation consistent with SIDM?

Self-interacting dark matter (SIDM) has the potential to significantly influence galaxy formation in comparison to the cold, collisionless dark matter paradigm (CDM), resulting in observable effects. This study aims to elucidate this influence and to demonstrate that the stellar mass Tully-Fisher relation imposes robust constraints on the parameter space of velocity-dependent SIDM models. We present a new set of cosmological hydrodynamical simulations that include the SIDM scheme from the TangoSIDM project and the SWIFT-EAGLE galaxy formation model. Two cosmological simulations suites were generated: one (Reference model) which yields good agreement with the observed $z=0$ galaxy stellar mass function, galaxy mass-size relation, and stellar-to-halo mass relation; and another (WeakStellarFB model) in which the stellar feedback is less efficient, particularly for Milky Way-like systems. Both galaxy formation models were simulated under four dark matter cosmologies: CDM, SIDM with two different velocity-dependent cross sections, and SIDM with a constant cross section. While SIDM does not modify global galaxy properties such as stellar masses and star formation rates, it does make the galaxies more extended. In Milky Way-like galaxies, where baryons dominate the central gravitational potential, SIDM thermalises, causing dark matter to accumulate in the central regions. This accumulation results in density profiles that are steeper than those produced in CDM from adiabatic contraction. The enhanced dark matter density in the central regions of galaxies causes a deviation in the slope of the Tully-Fisher relation, which significantly diverges from the observational data. In contrast, the Tully-Fisher relation derived from CDM models aligns well with observations.Comment: 17 pages, 10 figures and 3 tables. Submitted to MNRAS. Comments welcom