Interstellar Medium in Extremely High Star-Formation Regions: A Prospect of Observations on the Millimetron Space Observatory

TL;DR

This paper assesses how the Millimetron space observatory can probe the interstellar medium in extremely high star-formation environments, such as ULIRGs, across $z\sim0-3$ by observing far-IR lines and dust continuum. Using local analogs Arp 220 and UGC 5101, the authors forecast detectability and fluxes of ionized-gas lines, high-J CO transitions, water and OH-related lines, and dust emission with Millimetron's bands M1–M7, under realistic integration times. They discuss diagnostics for UV hardness, metallicity, density, and radiation fields, as well as the influence of X-rays and cosmic rays on ISM chemistry, and the potential to study molecular outflows and magnetic fields via absorption and polarization measurements. The work argues that Millimetron will advance our understanding of ISM conditions that enable extreme star formation and SMBH growth, linking local ULIRGs to dusty high-redshift galaxies and refining models of dust production, processing, and gas-phase chemistry in extreme environments.

Abstract

High star-formation rate and active galactic nucleus' emission can significantly transform the interstellar medium. In ultra-luminous infrared galaxies, in which the star-formation rate reaches thousands of solar masses per year, the gas and dust are considerably affected by the ionizing radiation, cosmic rays and shock waves, that can be about a factor of 100--1000 larger than typical values in quiet star-forming galaxies. In these conditions, the emissivity of the gas and dust changes: in dense gas, high ionic and molecular transitions become excited, while dust grains are heated to high temperatures. In this paper, we analyze the possibilities for studying the interstellar medium in extreme conditions of ultra-luminous infrared galaxies at redshifts of $\sim 0-3$, utilizing the atomic and molecular lines, and dust continuum in far infrared range of $100-500μ$m. We discuss the prospect of observations using the instruments of the Millimetron Space Observatory.

Figures (7)

• Figure 1: Expected fluxes in the lines of metal ions from a galaxy similar to Arp 220 at redshift $z$. The symbols from top to bottom correspond to the redshift of the galaxy Arp 220 $z=0.018$ and further $z=0.1$, 0.5, 1, 2 and 3 (for reference these values are indicated near the symbols along one of the curves). The fluxes for $z=0.018$ correspond to those observed in the galaxy Arp 220 and are scaled to the total luminosity in the IR range $10^{12}L_\odot$Rangwala2011. Gray vertical bands show the wavelength ranges of operation of the high-resolution spectrometer of the Millimetron observatory. Thick black lines correspond to the $5\sigma$ receiver sensitivity for an integration time of 1 h and spectral resolution $R = 10^3$. Thick gray lines correspond to 24 h of integration. Thick green lines show the sensitivity for the ALMA interferometric array observations in the 50-antenna mode at $R=10^3$ and 1 h integration, with significance of $5\sigma$. The thick yellow line corresponds to the Herschel/SPIRE sensitivity at 1 h integration with resolution $R=10^3$.
• Figure 2: Expected fluxes in the lines of metal ions from a galaxy similar to UGC 5101 at redshift $z$. The symbols from top to bottom correspond to the redshift of the galaxy UGC 5101 $z=0.038$ and further $z=0.1$, 0.5, 1, 2 and 3 (for reference these values are indicated near the symbols along one of the curves). The fluxes for $z=0.038$ correspond to those observed in the galaxy UGC 5101 and are scaled to the total luminosity in the IR range $10^{12}L_\odot$Armus2004Spinoglio2015. Other notations are the same as in Fig. \ref{['fig-arp220-ions']}.
• Figure 3: Observational capabilities for several lines of metal ions from an object at redshift $z$ in bands M1--M7 of the high-resolution spectrometer of the Millimetron space observatory. The color scale shows the ratio of the expected flux from a galaxy similar to UGC 5101 at redshift $z$ (Fig. \ref{['fig-ugc5101-ions']}) to the receiver sensitivity limit for an integration time of 1 h and spectral resolution $R = 10^3$ (Fig. \ref{['fig-ugc5101-ions']}).
• Figure 4: Expected fluxes in the CO and HCN molecular lines from a galaxy similar to Arp 220 at redshift $z$. The symbols from top to bottom correspond to the redshift of the galaxy Arp 220 $z=0.018$ and further $z=0.1$, 0.5, 1, 2 and 3 (for reference these values are indicated near the symbols along one of the curves). The fluxes are normalized to the total luminosity in the IR range $10^{12}L_\odot$. Other notations are the same as in Fig. \ref{['fig-arp220-ions']}.
• Figure 5: Expected fluxes in the H$_2$O from a galaxy similar to Arp 220, molecular lines from a galaxy similar to Arp 220 at redshift $z$. The symbols from top to bottom correspond to the redshift of the galaxy Arp 220 $z=0.018$ and further $z=0.1$, 0.5, 1, 2 and 3 (for reference these values are indicated near the symbols along one of the curves). The fluxes are scaled to the total IR luminosity $10^{12}L_\odot$. Other notations are the same as in Fig. \ref{['fig-arp220-ions']}.