J/A+A/642/A55 Lyman α blob LAB 1 MUSE data (Herenz+, 2020)
Deciphering the Lyman alpha blob 1 with with deep MUSE observations.
Herenz E.C., Hayes M., Scarlata C.
<Astron. Astrophys. 642, A55 (2020)>
=2020A&A...642A..55H 2020A&A...642A..55H (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies ; Optical ; Spectroscopy
Keywords: cosmology: observations - galaxies: high-redshift - galaxies: halos -
techniques: imaging spectroscopy
Abstract:
Lyman α blobs (LABs) are large-scale radio-quiet Lyman α
(Lyα) nebula at high-z that occur predominantly in overdense
proto-cluster regions. In particular, there is the prototypical
SSA22a-LAB1 at z=3.1 which has become an observational reference.
We want to understand the powering mechanisms that drive the LAB so
that we may gain empirical insights into the galaxy-formation
processes within a rare dense environment at high-z. Thus, we need to
infer the distribution, the dynamics, and the ionisation state of
LAB 1's Lyα emitting gas.
LAB 1 was observed for 17.2h with the VLT/MUSE integral-field
spectrograph. We produced optimally extracted narrow band images, in
Lyα λ1216, HeII λ1640, and we tried to detect CIV
λ1549 emission. By utilising a moment-based analysis, we mapped
the kinematics and the line profile characteristics of the blob. We
also linked the inferences from the line profile analysis to previous
results from imaging polarimetry.
We map Lyα emission from the blob down to surface-brightness
limits of ∼6x10-19erg/s/cm2/arcsec2. At this depth, we reveal a
bridge between LAB 1 and its northern neighbour LAB 8, as well as a
shell-like filament towards the south of LAB 1. The complexity and
morphology of the Lyα profile vary strongly throughout the blob.
Despite the complexity, we find a coherent large-scale east-west
velocity gradient of ∼1000km/s that is aligned perpendicular to the
major axis of the blob. Moreover, we observe a negative correlation of
Lyα polarisation fraction with Lyα line width and a
positive correlation with absolute line-of-sight velocity. Finally, we
reveal HeII emission in three distinct regions within the blob,
however, we can only provide upper limits for CIV.
Various gas excitation mechanisms are at play in LAB 1: ionising
radiation and feedback effects dominate near the embedded galaxies,
while Lyα scattering contributes at larger distances. However,
HeII/Lyα ratios combined with upper limits on CIV/Lyα are
not able to discriminate between active galactic nucleus (AGN)
ionisation and feedback-driven shocks. The alignment of the angular
momentum vector parallel to the morphological principal axis appears
to be at odds with the predicted norm for high-mass halos, but this
most likely reflects that LAB 1 resides at a node of multiple
intersecting filaments of the cosmic web. LAB 1 can thus be thought of
as a progenitor of a present-day massive elliptical within a galaxy
cluster.
Description:
We here provide the fully reduced MUSE data for LAB 1, optimally
extracted NB images for Lyα and HeII, and maps of the moment
based analysis on the Lyα line profile. The data reduction
methods to produce the datacube are described in Sect. 4 of our paper.
The methods used to create the optimally extracted Lyα and HeII
images are detailed in Sect. 5.2 and 5.5, respectively. Moreover,
Sect. 5.3 details the creation of the moment based maps provided in
this data release. The astronomy given by WCS header of all released
data products is derived from the 2MASS reference frame as described
in Sect. 3.2.
Objects:
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RA (2000) DE Designation(s)
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22 17 25.97 +00 12 38.9 LAB 1 = [TSK2001] LAB 1
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 149 8 List of fits files
fits/* . 8 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 F3.1 arcsec/pix scale Scale of the image
24- 26 I3 --- Nx Number of pixels along X-axis
28- 30 I3 --- Ny Number of pixels along Y-axis
32- 35 I4 --- Nz ? Number of slices for the datacube
37- 43 F7.2 0.1nm blambda ? Lower value of wavelength interval,
for the datacube
45- 51 F7.2 0.1nm Blambda ? Upper value of wavelength interval,
for the datacube
53- 56 F4.2 0.1nm dlambda ? Wavelength resolution, for the datacube
58- 64 I7 Kibyte size Size of FITS file
66- 88 A23 --- FileName Name of FITS file, in subdirectory fits
90 I1 --- n_Title Note on Tile (1)
92-149 A58 --- Title Title of the FITS file
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Note (1): Notes as follows:
1 = The MUSE datacube FITS file contains 5 header-data units (HDUs):
HDU 1: Header summarising basic observational parameters.
HDU 2: Flux density datacube in 10-20erg/s/cm2/Angstroem
HDU 3: Variance datacube in 10-40(erg/s/cm2/Angstroem)2
HDU 4: Running median continuum subtracted flux datacube (see Sect. 4.1)
2 = The FITS file with the Lyα adaptive narrow-band contains 2 HDUs:
HDU 1: Lyα flux in 10-20erg/s/cm2
HDU 2: Variance on the flux in 10^-406 (erg/s/cm2)2
A few foreground galaxies show residuals in the adaptive NB images.
As described in the paper, these galaxies have been masked out in
Figure 4 and Figure 5.
3 = The FITS file with the HeII adaptive narrow-band contains 2 HDUs:
HDU 1: HeII flux in 10-20erg/s/cm2
HDU 2: Variance on the flux in 10-40(erg/s/cm2)2
A few foreground galaxies show residuals in the adaptive NB images.
As described in the paper, these galaxies have been masked out in
Figure 4 and Figure 5.
5 = In km/s and calculated via Eq. (7) in the paper.
6 = In km/s and calculated via Eq. (8) in the paper.
7 = Calculated via Eq. (10) in the paper.
8 = Calculated via Eq. (11) in the paper.
9 = Calculated via Eq. (12) in the paper.
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Acknowledgements:
Edmund Christian Herenz, eherenz(at)eso.org
(End) Patricia Vannier [CDS] 23-Aug-2020