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Abstract:

Symbolic Regression (SR) algorithms attempt to learn analytic expressions which fit data accurately and in a highly interpretable manner. Conventional SR suffers from two fundamental issues which we address here. First, these methods search the space stochastically (typically using genetic programming) and hence do not necessarily find the best function. Second, the criteria used to select the equation optimally balancing accuracy with simplicity have been variable and subjective. To address these issues we introduce Exhaustive Symbolic Regression (ESR), which systematically and efficiently considers all possible equations—made with a given basis set of operators and up to a specified maximum complexity— and is therefore guaranteed to find the true optimum (if parameters are perfectly optimised) and a complete function ranking subject to these constraints. We implement the minimum description length principle as a rigorous method for combining these preferences into a single objective. To illustrate the power of ESR we apply it to a catalogue of cosmic chronometers and the Pantheon+ sample of supernovae to learn the Hubble rate as a function of redshift, finding 40 functions (out of 5.2 million trial functions) that fit the data more economically than the Friedmann equation. These low-redshift data therefore do not uniquely prefer the expansion history of the standard model of cosmology. We make our code and full equation sets publicly available.

Abstract:

We present new ALMA observations of the CO(3-2) transition and 854micron continuum at 0.06-0.3" resolution, together with new VLT/SINFONI observations of NGC7172. This is a luminous (bolometric luminosity of ~10^44 erg/s) Seyfert galaxy that belongs to the Galaxy Activity, Torus, and Outflow Survey (GATOS). The CO(3-2) observations reveal the presence of a highly inclined cold molecular gas ring with an approximate radius of 3-4"~540-720 pc, which is likely associated with an inner Lindblad resonance of a putative stellar bar. There are noncircular motions in the VLT/SINFONI [SiVI]1.96micron and H2 at 2.12micron, and ALMA CO(3-2) velocity fields. After subtracting the stellar velocity field, we detected [SiVI] blueshifted velocities of a few hundred km/s to the south of the AGN. They trace outflowing ionized gas outside the plane of the galaxy and out to projected distances of ~200 pc. The CO(3-2) position-velocity diagram along the kinematic minor axis displays noncircular motions with observed velocities of up to ~150 km/s. Assuming that these are taking place in the disk of the galaxy, the observed velocity signs imply that the molecular gas ring is not only rotating but also outflowing. We derived an integrated cold molecular gas mass outflow rate of ~40 Msun/yr for the ring. Using the 854micron map, we resolved a 32 pc radius torus with a gas mass of 8x10^5 Msun. These torus properties are similar to other Seyfert galaxies in the GATOS sample. We measured a decreased cold molecular gas concentration in the nuclear-torus region relative to the circumnuclear region when compared to other less luminous Seyfert galaxies. We conclude that the effects of AGN feedback in NGC7172, which are likely caused by the AGN wind and/or the moderate luminosity radio jet, are seen as a large-scale outflowing molecular gas ring and accompanying redistribution of molecular gas in the nuclear regions.Comment: Accepted for publication to A&

Abstract:

We present new CO (J = 5-4 and 7-6) and [C I] (3P2-3P1 and 3P1-3P0) emission line observations of the star-forming galaxy D49 at the massive end of the main sequence at z = 3. We incorporate previous CO (J = 3-2) and optical-to-millimetre continuum observations to fit its spectral energy distribution. Our results hint at high-J CO luminosities exceeding the expected location on the empirical correlations with the infrared luminosity. [CI] emission fully consistent with the literature trends is found. We do not retrieve any signatures of a bright active galactic nucleus that could boost the J = 5-4, 7-6 lines in either the infrared or X-ray bands, but warm photon-dominated regions, shocks, or turbulence could in principle do so. We suggest that mechanical heating could be a favourable mechanism able to enhance the gas emission at fixed infrared luminosity in D49 and other main-sequence star-forming galaxies at high redshift, but further investigation is necessary to confirm this explanation. We derive molecular gas masses from dust, CO, and [C I] that all agree within the uncertainties. Given its high star formation rate ~500 Mo yr-1 and stellar mass > 1011.5 Mo, the short depletion timescale of < 0.3 Gyr might indicate that D49 is experiencing its last growth spurt and will soon transit to quiescence.