J/A+A/667/A9 Unveiling the warm dense ISM phase in z>6 QSOs (Pensabene+, 2022)
Unveiling the warm and dense ISM in z>6 quasar host galaxies
via water wapor emission.
Pensabene A., van der Werf P., Decarli R., Banados E., Meyer R.A.,
Riechers D., Venemans B., Walter F., Weiss A., Brusa M., Fan X., Wang F.,
Yang J.
<Astron. Astrophys. 667, A9 (2022)>
=2022A&A...667A...9P 2022A&A...667A...9P (SIMBAD/NED BibCode)
ADC_Keywords: QSOs ; Interstellar medium ; Spectra, millimetric/submm
Keywords: galaxies: high-redshift - galaxies: ISM - quasars: emission lines -
quasars: supermassive black holes
Abstract:
Water vapor (H2O) is one of the brightest molecular emitters after
carbon monoxide (CO) in galaxies with high infrared (IR) luminosity,
allowing us to investigate the warm and dense phase of the
interstellar medium (ISM) where star formation occurs. However, due to
the complexity of its radiative spectrum, H2O is not frequently
exploited as an ISM tracer in distant galaxies. Therefore, H2O
studies of the warm and dense gas at high-z remain largely unexplored.
In this work, we present observations conducted with the Northern
Extended Millimeter Array (NOEMA) toward three z>6 IR-bright quasars
J2310+1855, J1148+5251, and J0439+1634 targeted in their multiple
para- and ortho- H2O transitions (312-303, 111-000, 220-211, and
422-413), as well as their far-IR (FIR) dust continuum. By combining
our data with previous measurements from the literature, we estimated
the dust masses and temperatures, continuum optical depths, IR
luminosities, and star formation rates (SFR) from the FIR continuum.
We modeled the H2O lines using the MOLPOP-CEP radiative transfer
code, finding that water vapor lines in our quasar host galaxies are
primarily excited in the warm, dense (with a gas kinetic temperature
and density of Tkin=50K, nH2∼104.5-105cm-3) molecular medium
with a water vapor column density of NH2O∼2x1017-3x1018cm-3.
High-J H2O lines are mainly radiatively pumped by the intense
optically-thin far-IR radiation field associated with a warm dust
component at temperatures of Tdust∼80-190K that account for <5-10%
of the total dust mass. In the case of J2310+1855, our analysis points
to a relatively high value of the continuum optical depth at 100µm
(τ100∼1). Our results are in agreement with expectations based
on the H2O spectral line energy distribution of local and high-z
ultra-luminous IR galaxies and active galactic nuclei (AGN). The
analysis of the Boltzmann diagrams highlights the interplay between
collisions and IR pumping in populating the high H2O energy levels
and it allows us to directly compare the excitation conditions in the
targeted quasar host galaxies. In addition, the observations enable us
to sample the high-luminosity part of the H2O-total-IR (TIR)
luminosity relations (LH2O-LTIR). Overall, our results point to
supralinear trends that suggest H2O-TIR relations are likely driven
by IR pumping, rather than the mere co-spatiality between the FIR
continuum- and line-emitting regions. The observed LH2O/LTIR_ ratios
in our z>6 quasars do not show any strong deviations with respect to
those measured in star-forming galaxies and AGN at lower redshifts.
This supports the notion that H2O can be likely used to trace the
star formation activity buried deep within the dense molecular clouds.
Description:
NOEMA reduced spectra and images at mm wavelengths of three z>6 quasar
host galaxies targeted in multiple H2O lines as well as the
underlying dust continuum emission. Details about calibration and
imaging procedures are provided in the dedicated sections of the
paper.
Objects:
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RA (2000) DE Designation(s)
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23 10 38.882 +18 55 19.700 J2310+1855 = SDSS J231038.88+185519.7
11 48 16.652 +52 51 50.440 J1148+5251 = SDSS J114816.64+525150.3
04 39 47.110 +16 34 15.820 J0439+1634 = 2MASS J04394708+1634160
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
listsp.dat 85 6 List of spectra
listimg.dat 95 12 list of fits images
img/* . 12 Individual fits images
sp/* . 6 Individual fits spectra
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Byte-by-byte Description of file: listsp.dat
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Bytes Format Units Label Explanations
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1- 9 F9.5 deg RAdeg Right Ascension of center (J2000)
10- 18 F9.5 deg DEdeg Declination of center (J2000)
20- 22 I3 --- Nx Number of pixels along X-axis
24 I1 Kibyte size Size of FITS file
26- 38 A13 --- FileName Name of FITS file, in subdirectory sp
40- 85 A46 --- Title Title of the FITS file
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Byte-by-byte Description of file: listimg.dat
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Bytes Format Units Label Explanations
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1- 9 F9.5 deg RAdeg Right Ascension of center (J2000)
10- 18 F9.5 deg DEdeg Declination of center (J2000)
20- 22 I3 --- Nx Number of pixels along X-axis
24- 26 I3 --- Ny Number of pixels along Y-axis
28- 38 E11.5 m/s VRAD Radial velocity
40- 43 I4 Kibyte size Size of FITS file
45- 62 A18 --- FileName Name of FITS file, in subdirectory img
64- 95 A32 --- Title Title of the FITS file
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Acknowledgements:
Antonio Pensabene, antonio.pensabene(at)unimib.it
(End) A. Pensabene [Univ. Milano-Bicocca, Italy], P. Vannier [CDS] 06-Sep-2022