Constraining the halo-ISM connection through multi-transition carbon monoxide line-intensity mapping

Line-intensity mapping (LIM) surveys will characterise the cosmological large-scale structure of emissivity in a range of atomic and molecular spectral lines, but existing literature rarely considers whether these surveys can recover excitation properties of the tracer gas species, such as the carbon monoxide (CO) molecule. Combining basic empirical and physical assumptions with the off-the-shelf Radex radiative transfer code or a Gaussian process emulator of Radex outputs, we devise a basic dark matter halo model for CO emission by tying bulk CO properties to halo properties, exposing physical variables governing CO excitation as free parameters. The CO Mapping Array Project (COMAP) is working towards a multi-band survey programme to observe both CO(1-0) and CO(2-1) at $z\sim7$. We show that this programme, as well as a further 'Triple Deluxe' extension to higher frequencies covering CO(3-2), is fundamentally capable of successfully recovering the connection between halo mass and CO abundances, and constraining the molecular gas kinetic temperature and density within the star-forming interstellar medium in ways that single-transition CO LIM cannot. Given a fiducial thermal pressure of $\sim10^4$ K cm$^{-3}$ for molecular gas in halos of $\sim10^{10}\,M_\odot$, simulated multi-band COMAP surveys successfully recover the thermal pressure within 68% interval half-widths of 0.5--0.6 dex. Construction of multi-frequency LIM instrumentation to access multiple CO transitions is crucial in harnessing this capability, as part of a cosmic statistical probe of gas metallicity, dust chemistry, and other physical parameters in star-forming regions of the first galaxies and proto-galaxies out of reionisation.Comment: 26 pages + appendices and bibliography (37 pages total including title page); 10 figures, 6 tables; to be submitted to JCA

Characteristic Functions for Cosmological Cross-Correlations

We introduce a novel unbiased, cross-correlation estimator for the one-point statistics of cosmological random fields. One-point statistics are a useful tool for analysis of highly non-Gaussian density fields, while cross-correlations provide a powerful method for combining information from pairs of fields and separating them from noise and systematics. We derive a new Deconvolved Distribution Estimator that combines the useful properties of these two methods into one statistic. Using two example models of a toy Gaussian random field and a line intensity mapping survey, we demonstrate these properties quantitatively and show that the DDE can be used for inference. This new estimator can be applied to any pair of overlapping, non-Gaussian cosmological observations, including large-scale structure, the Sunyaev-Zeldovich effect, weak lensing, and many others.Comment: 13 pages, 13 figures, for submission to MNRA

The Early Universe was Dust-Rich and Extremely Hot

We investigate the dust properties and star-formation signature of galaxies in the early universe by stacking 111,227 objects in the recently released COSMOS catalogue on maps at wavelengths bracketing the peak of warmed dust emission. We find an elevated far-infrared luminosity density to redshift 10, indicating abundant dust in the early universe. We further find an increase of dust temperature with redshift, reaching ~ 119 +- 7 K at z ~ 9, suggesting either the presence of silicate rich dust originating from Population II stars, or sources of heating beyond simply young hot stars. Lastly, we try to understand how these objects have been missed in previous surveys, and how to design observations to target them. All code, links to the data, and instructions to reproduce this research in full is located at https://github.com/marcoviero/simstack3/

Cross-correlating Carbon Monoxide Line-intensity Maps with Spectroscopic and Photometric Galaxy Surveys

Line-intensity mapping (LIM or IM) is an emerging field of observational work, with strong potential to fit into a larger effort to probe large-scale structure and small-scale astrophysical phenomena using multiple complementary tracers. Taking full advantage of such complementarity means, in part, undertaking line-intensity surveys with galaxy surveys in mind. We consider the potential for detection of a cross-correlation signal between COMAP and blind surveys based on photometric redshifts (as in COSMOS) or based on spectroscopic data (as with the HETDEX survey of Lyman-$\alpha$ emitters). We find that obtaining $\sigma_z/(1+z)\lesssim0.003$ accuracy in redshifts and $\gtrsim10^{-4}$ sources per Mpc$^3$ with spectroscopic redshift determination should enable a CO-galaxy cross spectrum detection significance at least twice that of the CO auto spectrum. Either a future targeted spectroscopic survey or a blind survey like HETDEX may be able to meet both of these requirements.Comment: 19 pages + appendix (31 pages total), 16 figures, 6 tables; accepted for publication in Ap

158 μm emission as an indicator of galaxy star formation rate

Observations of local star-forming galaxies (SFGs) show a tight correlation between their singly ionized carbon line luminosity () and star formation rate (SFR), suggesting that may be a useful SFR tracer for galaxies. Some other galaxy populations, however, are found to have lower than local SFGs, including the infrared (IR)-luminous, starburst galaxies at low and high redshifts as well as some moderately SFGs at the epoch of re-ionization (EoR). The origins of this ' deficit' is unclear. In this work, we study the -SFR relation of galaxies using a sample of z = 0-8 galaxies with extracted from cosmological volume and zoom-in simulations from the Feedback in Realistic Environments (fire) project. We find a simple analytic expression for /SFR of galaxies in terms of the following parameters: mass fraction of -emitting gas (Zgas), gas metallicity (Zgas), gas density (ngas), and gas depletion time (). We find two distinct physical regimes: -rich galaxies, where tdep is the main driver of the deficit and -poor galaxies where Zgas is the main driver. The observed deficit of IR-luminous galaxies and early EoR galaxies, corresponding to the two different regimes, is due to short gas depletion time and low gas metallicity, respectively. Our result indicates that the deficit is a common phenomenon of galaxies, and caution needs to be taken when applying a constant -to-SFR conversion factor derived from local SFGs to estimate cosmic SFR density at high redshifts and interpret data from upcoming line intensity mapping experiments