A Search for dense molecular gas in high redshift infrared-luminous galaxies

Carilli, Chris L.; Solomon, P.; Vanden Bout, P.; Walter, F.; Beelen, Alexandre; Cox, Pierre; Bertoldi, F.; Menten, K.M.; Isaak, Kate G.; Chandler, C.J.

doi:10.1086/426014

A Search for dense molecular gas in high redshift infrared-luminous galaxies

Sep, 2004

6 pages

Published in:

Astrophys.J. 618 (2005) 586-591

e-Print:

astro-ph/0409054 [astro-ph]

DOI:

10.1086/426014

View in:

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Abstract: (arXiv)

We present a search for HCN emission from four high redshift far infrared (IR) luminous galaxies. Current data and models suggest that these high

z

IR luminous galaxies represent a major starburst phase in the formation of spheroidal galaxies, although many of the sources also host luminous active galactic nuclei (AGN), such that a contribution to the dust heating by the AGN cannot be precluded. HCN emission is a star formation indicator, tracing dense molecular hydrogen gas within star-forming molecular clouds (n(H

_2

)

\sim 10^5

cm

^{-3}

). HCN luminosity is linearly correlated with IR luminosity for low redshift galaxies, unlike CO emission which can also trace gas at much lower density. We report a marginal detection of HCN (1-0) emission from the

z=2.5832

QSO J1409+5628, with a velocity integrated line luminosity of

L_{\rm HCN}'=6.7\pm2.2 \times10^{9}

K km s

^{-1}

pc

^2

, while we obtain 3

\sigma

upper limits to the HCN luminosity of the

z=3.200

QSO J0751+2716 of

L_{\rm HCN}'=1.0\times10^{9}

K km s

^{-1}

pc

^2

,

L_{\rm HCN}'=1.6\times10^{9}

K km s

^{-1}

pc

^2

for the

z= 2.565

starburst galaxy J1401+0252, and

L_{\rm HCN}'=1.0\times10^{10}

K km s

^{-1}

pc

^2

for the

z = 6.42

QSO J1148+5251. We compare the HCN data on these sources, plus three other high-

z

IR luminous galaxies, to observations of lower redshift star-forming galaxies. The values of the HCN/far-IR luminosity ratios (or limits) for all the high

z

sources are within the scatter of the relationship between HCN and far-IR emission for low

z

star-forming galaxies (truncated).

galaxies: active
galaxies: formation
galaxies: high-redshift
galaxies: ISM
galaxies: starburst
infrared: galaxies

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