PRUSSIC II -- ALMA imaging of dense-gas tracers in SDP.81: Evidence for low mechanical heating and a sub-solar metallicity in a z=3.04 dusty galaxy

M. Rybak; J. van Marrewijk; J. A. Hodge; P. Andreani; G. Calistro Rivera; L. Graziani; J. P. McKean; S. Viti; P. P. van der Werf

doi:10.1051/0004-6361/202347315

arXiv · 2308.02886

PRUSSIC II -- ALMA imaging of dense-gas tracers in SDP.81: Evidence for low mechanical heating and a sub-solar metallicity in a z=3.04 dusty galaxy

M. Rybak·J. van Marrewijk·J. A. Hodge·P. Andreani·G. Calistro Rivera·L. Graziani·J. P. McKean·S. Viti·P. P. van der Werf

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Abstract

We present deep ALMA Band 3 observations of the HCN, HCO+, and HNC (4-3) emission in SDP.81, a well-studied z = 3.042 strongly lensed galaxy. These lines trace the high-density gas, which remains almost entirely unexplored in z$\geq$1 galaxies. Additionally, these dense-gas tracers are potentially powerful diagnostics of the mechanical heating of the interstellar medium. While the HCN(4-3) and HNC(4-3) lines are not detected, the HCO+(4-3) emission is clearly detected and resolved. This is the third detection of this line in a high-redshift star-forming galaxy. We find an unusually high HCO+/HCN intensity ratio of $\geq$2.2. Based on the photodissociation region modelling, the most likely explanation for the elevated HCO+/HCN ratio is that SDP.81 has low mechanical heating - less than 10% of the total energy budget - and a sub-solar metallicity, Z=0.5 Z$_\odot$. While such conditions might not be representative of the general population of high-redshift dusty galaxies, lower-than-solar metallicity might have a significant impact on gas masses inferred from CO observations. In addition, we report the detection of CO(0-1) absorption from the foreground lensing galaxy and CO(1-0) emission from a massive companion to the lensing galaxy, approximately 50 kpc to the southeast.

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M. Rybak, J. van Marrewijk, J. A. Hodge, P. Andreani, G. Calistro Rivera, L. Graziani, J. P. McKean, S. Viti, P. P. van der Werf. 2023-08-05. PRUSSIC II -- ALMA imaging of dense-gas tracers in SDP.81: Evidence for low mechanical heating and a sub-solar metallicity in a z=3.04 dusty galaxy. https://doi.org/10.1051/0004-6361/202347315

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