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Title: The Role of the CMB in Redshift Related Departures from the Gao–Solomon Relation

Abstract

A strong correlation between the far-IR and HCN(1−0) line luminosities, known as the Gao–Solomon relation, has been observed to hold over more than 10 orders of magnitude in the local universe. Departures from this relation at redshifts ≳1.5 have been interpreted as evidence for increased dense gas star formation efficiency in luminous galaxies during the period of peak of star formation in the history of the universe. We examine whether the offsets from the relation can be explained by the hotter Cosmic Microwave Background (CMB) at high redshift, which, due to a loss of contrast against the hotter background, reduces the observable molecular-line flux far more significantly than the far-IR continuum bands. Simple line-of-sight modeling argues for highly significant departures from the Gao–Solomon relation at high redshift for kinetic temperatures ∼15 K, while more complex toy-galaxy models based on NGC 1068 suggest a much weaker effect with the galaxy integrated HCN line flux falling by only 10% at z = 3, within the intrinsic scatter of the relation. We conclude that, while the CMB is unlikely to explain the deviations reported in the literature, it may introduce a second-order effect on the relation by raising the low-luminosity end of themore » Gao–Solomon relation in cooler galaxies. A similar examination of the CO-IR relation finds tantalizing signs of the CMB having a measurable effect on the integrated CO emission in high-redshift galaxies, but these signs cannot be confirmed with the current data.« less

Authors:
;  [1]
  1. Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT (United Kingdom)
Publication Date:
OSTI Identifier:
22679717
Resource Type:
Journal Article
Journal Name:
Astrophysical Journal
Additional Journal Information:
Journal Volume: 849; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0004-637X
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; CARBON MONOXIDE; CORRELATIONS; EMISSION; FAR INFRARED RADIATION; GALAXIES; HEAT EXCHANGERS; HYDROCYANIC ACID; LUMINOSITY; MOLECULES; RADIANT HEAT TRANSFER; RED SHIFT; RELICT RADIATION; SIMULATION; SPECTRA; STARS; UNIVERSE

Citation Formats

Tunnard, R., and Greve, T. R., E-mail: richard.tunnard.13@ucl.ac.uk. The Role of the CMB in Redshift Related Departures from the Gao–Solomon Relation. United States: N. p., 2017. Web. doi:10.3847/1538-4357/AA8E4D.
Tunnard, R., & Greve, T. R., E-mail: richard.tunnard.13@ucl.ac.uk. The Role of the CMB in Redshift Related Departures from the Gao–Solomon Relation. United States. doi:10.3847/1538-4357/AA8E4D.
Tunnard, R., and Greve, T. R., E-mail: richard.tunnard.13@ucl.ac.uk. Wed . "The Role of the CMB in Redshift Related Departures from the Gao–Solomon Relation". United States. doi:10.3847/1538-4357/AA8E4D.
@article{osti_22679717,
title = {The Role of the CMB in Redshift Related Departures from the Gao–Solomon Relation},
author = {Tunnard, R. and Greve, T. R., E-mail: richard.tunnard.13@ucl.ac.uk},
abstractNote = {A strong correlation between the far-IR and HCN(1−0) line luminosities, known as the Gao–Solomon relation, has been observed to hold over more than 10 orders of magnitude in the local universe. Departures from this relation at redshifts ≳1.5 have been interpreted as evidence for increased dense gas star formation efficiency in luminous galaxies during the period of peak of star formation in the history of the universe. We examine whether the offsets from the relation can be explained by the hotter Cosmic Microwave Background (CMB) at high redshift, which, due to a loss of contrast against the hotter background, reduces the observable molecular-line flux far more significantly than the far-IR continuum bands. Simple line-of-sight modeling argues for highly significant departures from the Gao–Solomon relation at high redshift for kinetic temperatures ∼15 K, while more complex toy-galaxy models based on NGC 1068 suggest a much weaker effect with the galaxy integrated HCN line flux falling by only 10% at z = 3, within the intrinsic scatter of the relation. We conclude that, while the CMB is unlikely to explain the deviations reported in the literature, it may introduce a second-order effect on the relation by raising the low-luminosity end of the Gao–Solomon relation in cooler galaxies. A similar examination of the CO-IR relation finds tantalizing signs of the CMB having a measurable effect on the integrated CO emission in high-redshift galaxies, but these signs cannot be confirmed with the current data.},
doi = {10.3847/1538-4357/AA8E4D},
journal = {Astrophysical Journal},
issn = {0004-637X},
number = 1,
volume = 849,
place = {United States},
year = {2017},
month = {11}
}