First detection of the 448 GHz ortho-H2O line at high redshift: probing the structure of a starburst nucleus at z = 3.63. (arXiv:2001.06589v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Yang_C/0/1/0/all/0/1">C. Yang</a> (1), <a href="http://arxiv.org/find/astro-ph/1/au:+Gonzalez_Alfonso_E/0/1/0/all/0/1">E. González-Alfonso</a> (2), <a href="http://arxiv.org/find/astro-ph/1/au:+Omont_A/0/1/0/all/0/1">A. Omont</a> (3), <a href="http://arxiv.org/find/astro-ph/1/au:+Pereira_Santaella_M/0/1/0/all/0/1">M. Pereira-Santaella</a> (4), <a href="http://arxiv.org/find/astro-ph/1/au:+Fischer_J/0/1/0/all/0/1">J. Fischer</a> (5), <a href="http://arxiv.org/find/astro-ph/1/au:+Beelen_A/0/1/0/all/0/1">A. Beelen</a> (6), <a href="http://arxiv.org/find/astro-ph/1/au:+Gavazzi_R/0/1/0/all/0/1">R. Gavazzi</a> (3) ((1) ESO Chile, (2) Universidad de Alcalá, (3) IAP, (4) CSIC-INTA, (5) GMU, (6) IAS-Orsay)
Submillimeter rotational lines of H2O are a powerful probe in warm gas
regions of the ISM, tracing scales and structures ranging from kpc disks to the
most compact and dust-obscured regions of galactic nuclei. The
ortho-H2O(423-330) line at 448 GHz, which was recently detected in a local
luminous infrared galaxy (Pereira-Santaella et al. 2017), offers a unique
constraint on the excitation conditions and ISM properties in deeply buried
galaxy nuclei since the line requires high far-IR optical depths to be excited.
In this letter, we report the first high-redshift detection of the 448 GHz
H2O(423-330) line using ALMA, in a strongly lensed submillimeter galaxy (SMG)
at z=3.63. After correcting for magnification, the luminosity of the 448 GHz
H2O line is ~10^6 L_sun. In combination with three other previously detected
H2O lines, we build a model that “resolves” the dusty ISM structure of the SMG,
and find that it is composed of a ~1 kpc optically thin (optical depth at
100{mu}m {tau}_{100}~0.3) disk component with dust temperature T_{dust}
approx 50 K emitting a total infrared power of 5e12 L_sun with surface density
Sigma_{IR}=4e11 L_sun kpc^{-2}, and a very compact (0.1 kpc) heavily
dust-obscured ({tau}_{100} gtrsim 1) nuclear core with very warm dust (100 K)
and Sigma_{IR}=8e12 L_sun kpc^{-2}. The H2O abundance in the core component,
X_{H2O}~(0.3-5)e{-5}, is at least one order of magnitude higher than in the
disk component. The optically thick core has the characteristic properties of
an Eddington-limited starburst, providing evidence that radiation pressure on
dust is capable of supporting the ISM in buried nuclei at high redshifts. The
multi-component ISM structure revealed by our models illustrates that dust and
molecules such as H2O are present in regions characterized by highly differing
conditions and scales, extending from the nucleus to more extended regions of
SMGs.
Submillimeter rotational lines of H2O are a powerful probe in warm gas
regions of the ISM, tracing scales and structures ranging from kpc disks to the
most compact and dust-obscured regions of galactic nuclei. The
ortho-H2O(423-330) line at 448 GHz, which was recently detected in a local
luminous infrared galaxy (Pereira-Santaella et al. 2017), offers a unique
constraint on the excitation conditions and ISM properties in deeply buried
galaxy nuclei since the line requires high far-IR optical depths to be excited.
In this letter, we report the first high-redshift detection of the 448 GHz
H2O(423-330) line using ALMA, in a strongly lensed submillimeter galaxy (SMG)
at z=3.63. After correcting for magnification, the luminosity of the 448 GHz
H2O line is ~10^6 L_sun. In combination with three other previously detected
H2O lines, we build a model that “resolves” the dusty ISM structure of the SMG,
and find that it is composed of a ~1 kpc optically thin (optical depth at
100{mu}m {tau}_{100}~0.3) disk component with dust temperature T_{dust}
approx 50 K emitting a total infrared power of 5e12 L_sun with surface density
Sigma_{IR}=4e11 L_sun kpc^{-2}, and a very compact (0.1 kpc) heavily
dust-obscured ({tau}_{100} gtrsim 1) nuclear core with very warm dust (100 K)
and Sigma_{IR}=8e12 L_sun kpc^{-2}. The H2O abundance in the core component,
X_{H2O}~(0.3-5)e{-5}, is at least one order of magnitude higher than in the
disk component. The optically thick core has the characteristic properties of
an Eddington-limited starburst, providing evidence that radiation pressure on
dust is capable of supporting the ISM in buried nuclei at high redshifts. The
multi-component ISM structure revealed by our models illustrates that dust and
molecules such as H2O are present in regions characterized by highly differing
conditions and scales, extending from the nucleus to more extended regions of
SMGs.
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