J/MNRAS/504/3662 Lya-UV Offsets in Galaxies at z∼6 (Lemaux+, 2021)
The size and pervasiveness of Lyα-UV spatial offsets in star-forming
galaxies at z∼6.
Lemaux B.C., Fuller S., Bradac M., Pentericci L., Hoag A., Strait V.,
Treu T., Alvarez C., Bolan P., Gandhi P.J., Jones T., Mason C.,
Pelliccia D., Ribeiro B., Ryan R.E., Schmidt K.B., Vanzella E.,
Khusanova Y., Le Fevre O., Guaita L., Hathi N.P., Koekemoer A., Pforr J.
<Mon. Not. R. Astron. Soc. 504, 3662-3681 (2021)>
=2021MNRAS.504.3662L 2021MNRAS.504.3662L (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies, optical ; Gravitational lensing ; Redshifts ;
Equivalent widths
Keywords: gravitational lensing: strong - techniques: photometric -
techniques: spectroscopic - galaxies: evolution -
galaxies: high-redshift - reionization
Abstract:
We study the projected spatial offset between the ultraviolet
continuum and Lya emission for 65 lensed and unlensed galaxies in the
Epoch of Reionization 5≤z≤7, the first such study at these
redshifts, in order to understand the potential for these offsets to
confuse estimates of the Lya properties of galaxies observed in slit
spectroscopy. While we find that ∼40% of galaxies in our sample show
significant projected spatial offsets, |DeltaLya-UV|, we find a
relatively modest average (median) projected offset of
|DeltaLya-UV|=0.61±0.08 proper kpc for the entire sample. A small
fraction of our sample, ∼10%, exhibit offsets in excess of 2 proper
kpc, with offsets seen up to ∼4 proper kpc, sizes that are
considerably larger than the effective radii of typical galaxies at
these redshifts. An internal comparison and a comparison to studies at
lower redshift yielded no significant evidence of evolution of
Delta_Lya-UV with redshift. In our sample, UV-bright galaxies (with a
median LUV/L*UV=0.67) showed offsets a factor of three greater
than their fainter counterparts (median LUV/L*UV=0.10), 0.89
±0.18 vs. 0.27±0.05 proper kpc, respectively. The presence of
companion galaxies and early-stage merging activity appeared to be
unlikely causes of these offsets. Rather, these offsets appear
consistent with a scenario in which internal anisotropic processes
resulting from stellar feedback, which is stronger in UV-brighter
galaxies, facilitate Lya fluorescence and/or backscattering from
nearby or outflowing gas. The reduction in the Lya flux due to offsets
was quantified. It was found that the differential loss of Lya photons
for galaxies with average offsets is not, if corrected for, a limiting
factor for all but the narrowest slit widths (<0.4"). However, for the
largest offsets, if they are mostly perpendicular to the slit major
axis, slit losses were found to be extremely severe in cases where
slit widths of ≤1" were employed, such as those planned for James
Webb Space Telescope/NIRSpec observations.
Description:
Parameters for the unlensed and lensed galaxies in our sample. The
given parameters for each galaxy are galaxy ID, equitorial
coordinates, the spectroscopic redshift, the projected offset between
the spatial location of the Lya and ultraviolet (UV) continuum
emission, effective radius (when possible), the UV luminosity
normalized by the characteristic UV luminosity at that redshift, the
Lyman alpha line luminosity, and the rest-frame equivalent width of
the Lyman alpha line. For the 36 lensed galaxies in the best-fit
magnification evaluated at the spectroscopic redshift is also
included. For the magnified samples, Lya-UV projected spatial offset,
the effective radius, normalized UV luminosity, and Lya line
luminosity are all corrected by the best-fit magnification. Formal
errors are included for the Lya-UV projected spatial offsets and
effective radii.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 76 28 Sample of unlensed galaxies
table2.dat 82 36 Sample of lensed galaxies
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Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 12 A12 --- ID Name
14- 24 F11.7 deg RAdeg Right ascension (J2000.0)
26- 36 F11.7 deg DEdeg Declination (J2000.0)
38- 42 F5.3 --- zspec Spectral redshift
44- 46 F3.1 --- |deltaLya-UV| Absolute value of the projected spatial
offset between the Lya and UV continuum
emission, in proper_kpc unit
48- 50 F3.1 --- e_|deltaLya-UV| 1sigma error on |deltaLya-UV|,
in proper_kpc unit
52- 54 F3.1 --- re ?=9.9 Intrinsic measured F160W effective
radius, in proper_kpc unit (G1)
56- 58 F3.1 --- E_re ?=9.9 1sigma positive error on re,
in proper_kpc unit (G1)
60- 62 F3.1 --- e_re ?=9.9 1sigma negative error on re,
in proper_kpc unit (G1)
64- 67 F4.2 --- LUVnorm Intrinsic UV luminosity normalized by the
characteristic UV luminosity at the
galaxy's redshift
69- 72 F4.1 [10-7W] logLyalum Log10 of the intrinsic Lya line
luminosity in cgs units
74- 76 I3 0.1nm EWLya Measured rest-frame equivalent width of
the Lyman alpha feature
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 8 A8 --- ID Internal ID, NNNN.NN
10- 20 F11.7 deg RAdeg Right ascension (J2000.0)
22- 32 F11.7 deg DEdeg Declination (J2000.0)
34- 38 F5.3 --- zspec Spectral redshift
40- 42 F3.1 --- |deltaLya-UV| Absolute value of the projected spatial
offset between the Lya and UV continuum
emission, in proper_kpc unit (1)
44- 46 F3.1 --- e_|deltaLya-UV| 1sigma error on |delta_Lya-UV|,
in proper_kpc unit (1)
48- 51 F4.2 --- re ?=9.9 Intrinsic measured F160W effective
radius, in proper_kpc unit (G1) (1)
53- 56 F4.2 --- E_re ?=9.9 1sigma positive error on re,
in proper_kpc unit (G1) (1)
57- 61 F5.2 --- e_re []?=9.9 1sigma negative error on re,
in proper_kpc unit (G1) (1)
63- 67 F5.3 --- LUVnorm Intrinsic UV luminosity normalized by the
characteristic UV luminosity at the
galaxy's redshift (1)
69- 72 F4.1 [10-7W] logLyalum Log10 of the intrinsic Lya line
luminosity in cgs units (1)
74- 76 I3 0.1nm EWLya Measured rest-frame equivalent width of
the Lyman alpha feature
78- 82 F5.1 --- Magni Magnification from best-fit lensing map
evaluated at the spectral redshift
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Note (1): corrected to intrinsic by the magnification.
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Global notes:
Note (G1): A value of 9.9 indicates that the quantity was not measured (only for
re in cases where there was no HST/WFC3 imaging or the S/N was too low)
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Acknowledgements:
Brian C. Lemaux, bclemaux(at)ucdavis.edu
(End) Brian Lemaux [California Univ., Davis], Patricia Vannier [CDS] 28-Apr-2021