J/A+A/611/A22 Jekyll & Hyde galaxies ALMA cube & spectrum (Schreiber+, 2018)
Jekyll & Hyde: quiescence and extreme obscuration in a pair of massive galaxies
1.5 Gyr after the Big Bang.
Schreiber C., Labbe I., Glazebrook K., Bekiaris G., Papovich C., Costa T.,
Elbaz D., Kacprzak G.G., Nanayakkara T., Oesch P., Pannella M., Spitler L.,
Straatman C., Tran K.-V., Wang T.
<Astron. Astrophys. 611, A22 (2018)>
=2018A&A...611A..22S 2018A&A...611A..22S (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies, spectra ; Spectra, millimetric/submm
Keywords: galaxies: evolution - galaxies: high-redshift -
galaxies: kinematics and dynamics -
galaxies: star formation - galaxies: stellar content -
submillimeter: galaxies
Abstract:
We obtained ALMA spectroscopy and deep imaging to investigate the
origin of the unexpected sub-millimeter emission toward the most
distant quiescent galaxy known to date, ZF-COSMOS-20115 at z=3.717. We
show here that this sub-millimeter emission is produced by another
massive (M*∼1011M☉), compact (r1/2=0.67±0.14kpc) and
extremely obscured galaxy (AV∼3.5), located only 0.4300 (3.1kpc)
away from the quiescent galaxy. We dub the quiescent and dusty
galaxies Jekyll and Hyde, respectively. No dust emission is detected
at the location of the quiescent galaxy, implying SFR<13M☉/yr
which is the most stringent upper limit ever obtained for a quiescent
galaxy at these redshifts. The two sources are spectroscopically
confirmed to lie at the same redshift thanks to the detection of
[CII]158 in Hyde (z=3.709), which provides one the few robust
redshifts for a highly-obscured "H-dropout" galax
(H-[4.5]=5.1±0.8). The [CII] line shows a clear rotating-disk
velocity profile which is blueshifted compared to the Balmer lines of
Jekyll by 549±60km/s, demonstrating that it is produced by another
galaxy. Careful de-blending of the Spitzer imaging confirms the
existence of this new massive galaxy, and its non-detection in the
Hubble images requires extremely red colors and strong attenuation by
dust. Full modeling of the UV-to-far-IR emission of both galaxies
shows that Jekyll has fully quenched at least 200Myr prior to
observation and still presents a challenge for models, while Hyde only
harbors moderate star-formation with SFR≲120M_☉/yr, and is
located at least a factor 1.4 below the z∼4 main sequence. Hyde could
also have stopped forming stars less than 200Myr before being
observed; this interpretation is also suggested by its compactness
comparable to that of z∼4 quiescent galaxies and its low [CII]/FIR
ratio, but significant on-going star-formation cannot be ruled out.
Lastly, we find that despite its moderate SFR, Hyde hosts a dense
reservoir of gas comparable to that of the most extreme starbursts.
This suggests that whatever mechanism has stopped or reduced its
star-formation must have done so without expelling the gas outside of
the galaxy. Because of their surprisingly similar mass, compactness,
environment and star-formation history, we argue that Jekyll and Hyde
can be seen as two stages of the same quenching process, and provide a
unique laboratory to study this poorly understood phenomenon.
Description:
These files consist of the full ALMA data cube for the galaxies Jekyll
and Hyde, together with the extracted continuum image and the spectrum
of Hyde. The data cube was produced by CASA (v4.7.0), the continuum
image was constructed as the weighted average in line-free channels,
and the spectrum was extracted at the peak flux position of Hyde. The
data cube and spectrum files contain two extensions, one for the flux,
and another for the uncertainty. This uncertainty was determined from
the RMS of the cube data between 2 and 8" away from the center. All
fluxes are in units of Jansky, and the spectral axis is given in
observed frequency (GHz). The images were not CLEANed, therefore the
dirty beam (which is also provided here) is the correct point-spread
function to use when analyzing these images.
Objects:
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RA (2000) DE Designation(s)
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10 00 14.7620 +02 22 43.270 Jekyll & Hyde = [SLS2014] ZF-COSMOS-13172
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 109 4 List of fits files
fits/* . 4 Individual fits files
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Byte-by-byte Description of file: list.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- 30 I3 --- Nz ? Number of slices (for the data cude)
32- 53 A22 --- Obs.Date Observation date (YYYY-MM-DDThh:mm:ss.ss)
55- 57 I3 GHz bFreq ? Lower value of frequency interval
59- 65 F7.3 GHz BFreq ? Upper value of frequency interval
67- 75 F9.7 GHz dFreq ? Frequency resolution
77- 80 I4 Kibyte size Size of FITS file
82- 90 A9 --- FileName Name of FITS file, in subdirectory fits
92-109 A18 --- Title Title of the FITS file
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Acknowledgements:
Corentin Schreiber, cschreib(at)strw.leidenuniv.nl
(End) Patricia Vannier [CDS] 14-Dec-2017