SImulator of GAlaxy Millimetre/submillimetre Emission (SIGAME): CO emission from massive z=2 main-sequence galaxies

Abstract

We present SIGAME (SImulator of GAlaxy Millimetre/submillimetre Emission), a new numerical code designed to simulate the 12CO rotational line emission spectrum of galaxies. Using sub-grid physics recipes to post-process the outputs of smoothed particle hydrodynamics (SPH) simulations, a molecular gas phase is condensed out of the hot and partly ionized SPH gas. The gas is subjected to far-UV radiation fields and cosmic ray ionization rates which are set to scale with the local star formation rate volume density. Level populations and radiative transport of the CO lines are solved with the 3-D radiative transfer code LIME. We have applied SIGAME to cosmological SPH simulations of three disc galaxies at z=2 with stellar masses in the range ~(0.5-2)x10^11 Msun and star formation rates ~40-140 Msun/yr. Global CO luminosities and line ratios are in agreement with observations of disc galaxies at z~2 up to and including J=3-2 but falling short of the few existing J=5-4 observations. The central 5 kpc regions of our galaxies have CO 3-2/1-0 and 7-6/1-0 brightness temperature ratios of ~0.55-0.65 and ~0.02-0.08, respectively, while further out in the disc the ratios drop to more quiescent values of ~0.5 and <0.01. Global CO-to-H2 conversion (alpha_CO) factors are ~=1.5 Msun*pc^2/(K km s/1), i.e. ~2-3 times below typically adopted values for disc galaxies, and alpha_CO increases with radius, in agreement with observations of nearby galaxies. Adopting a top-heavy Giant Molecular Cloud (GMC) mass spectrum does not significantly change the results. Steepening the GMC density profile leads to higher global line ratios for J_up>=3 and CO-to-H2 conversion factors [~=3.6 Msun*pc^2/(K km/s)].

28 pages, 20 figures. Accepted for Publication in MNRAS. Substantial revisions from the previous version, including tests with model galaxies similar to the Milky Way. Improved figures and added tables

References in corpus (29)

• A Highly Consistent Framework for the Evolution of the Star-Forming "Main Sequence" from z~0-6
• The effect of photo-ionization on the cooling rates of enriched, astrophysical plasmas
• Detection of the Characteristic Pion-Decay Signature in Supernova Remnants
• SPLASH: An interactive visualisation tool for Smoothed Particle Hydrodynamics simulations
• Star Formation and Feedback in Smoothed Particle Hydrodynamic Simulations--I. Isolated Galaxies
• The Role of Pressure in GMC Formation II: The H_2 - Pressure Relation
• The Resolved Properties of Extragalactic Giant Molecular Clouds
• COLD GASS, an IRAM legacy survey of molecular gas in massive galaxies: I. Relations between H2, HI, stellar content and structural properties
• Time-Dependent Ionization in Radiatively Cooling Gas
• CO Isotopologues in the Perseus Molecular Cloud Complex: the X-Factor and Regional Variations
• CO excitation of normal star forming galaxies out to z=1.5 as regulated by the properties of their interstellar medium
• Highly-excited CO emission in APM08279+5255 at z=3.9
• ALMA Reveals the Molecular Medium Fueling the Nearest Nuclear Starburst
• CO-dark gas and molecular filaments in Milky Way type galaxies
• [CII] 158$\mu$m Emission and Metallicity in PDRs
• Effective destruction of CO by cosmic rays: implications for tracing H${}_2$ gas in the Universe
• A complete 12CO 2-1 map of M51 with HERA: I. Radial averages of CO, HI, and radio continuum
• A Theory for the Excitation of CO in Star Forming Galaxies
• Metal Cooling in Simulations of Cosmic Structure Formation
• Molecular Star Formation Rate Indicators in Galaxies
• The photoheating of the intergalactic medium in synthesis models of the UV background
• The Role of Galactic Winds on Molecular Gas Emission from Galaxy Mergers
• Incorporating the molecular gas phase in galaxy-size numerical simulations: first applications in dwarf galaxies
• Molecular gas heating mechanisms, and star formation feedback in merger/s tarbursts: NGC 6240 and Arp 193 as case studies
• CO(1-0) line imaging of massive star-forming disc galaxies at z=1.5-2.2
• Early Science with the Large Millimeter Telescope: CO and [C II] Emission in the z=4.3 AzTEC J095942.9+022938 (COSMOS AzTEC-1)
• The Nature of CO Emission From z~6 Quasars
• Spatially resolved physical conditions of molecular gas and potential star formation tracers in M83, revealed by the Herschel SPIRE FTS
• CO line emission from Lyman Break Galaxies. Cosmological simulations and predictions for ALMA

Cited by in corpus (16)

• The [C II] emission as a molecular gas mass tracer in galaxies at low and high redshift
• The art of modeling CO, [CI], and [CII] in cosmological galaxy formation models
• Sub-mm Emission Line Deep Fields: CO and [CII] Luminosity Functions out to z = 6
• VERTICO: The Virgo Environment Traced In CO Survey
• Submillimeter flux as a probe of molecular ISM mass in high-$z$ galaxies
• Radiative transfer meets Bayesian statistics: where does a galaxy's [CII] emission come from?
• Numerical Simulations of Turbulent Molecular Clouds Regulated by Radiation Feedback Forces II: Radiation-Gas Interactions and Outflows
• Warm and Cold Molecular Gas Conditions Modeled in 87 Galaxies Observed by the Herschel SPIRE Fourier Transform Spectrometer
• Reproducing the CO-to-H${}_2$ conversion factor in cosmological simulations of Milky Way-mass galaxies
• Revisiting the [C II]${}_{158\mu \text{m}}$ line-intensity mapping power spectrum from the EoR using non-uniform line-luminosity scatter
• $\text{slick}$: Modeling a Universe of Molecular Line Luminosities in Hydrodynamical Simulations
• The [C II] line emission as an interstellar medium probe in the MARIGOLD galaxies
• Probing the Epoch of Reionization using synergies of line intensity mapping
• Modelling Mechanical Heating in Star-Forming Galaxies: CO and 13CO Line Ratios as Sensitive Probes
• SIGAME v3: Gas Fragmentation in Post-processing of Cosmological Simulations for More Accurate Infrared Line Emission Modeling
• Predicting the resolved CO emission of $z=1-3$ star-forming galaxies