J/ApJ/916/50 HST/WFC3 grism sp. of 2 strongly lensed galaxies (Florian+, 2021)
Spatial variation in strong line ratios and physical conditions in two strongly
lensed galaxies at z∼1.4.
Florian M.K., Rigby J.R., Acharyya A., Sharon K., Gladders M.D., Kewley L.,
Khullar G., Gozman K., Brammer G., Momcheva I., Nicholls D., LaMassa S.,
Dahle H., Bayliss M.B., Wuyts E., Johnson T., Whitaker K.
<Astrophys. J., 916, 50 (2021)>
=2021ApJ...916...50F 2021ApJ...916...50F
ADC_Keywords: Gravitational lensing; Galaxies, spectra; Optical; Redshifts;
Infrared sources
Keywords: High-redshift galaxies ; Interstellar medium ;
Strong gravitational lensing ; Galaxy properties
Abstract:
Upcoming space-based integral field spectrographs will enable
spatially resolved spectroscopy of distant galaxies, including at the
scale of individual star-forming regions (i.e., down to just tens of
parsecs) in galaxies that have been strongly gravitationally lensed.
In the meantime, there is only a very small set of lensed galaxies
where such spatial detail is possible at wavelengths containing
important rest-optical emission lines, even with the Hubble Space
Telescope's Wide Field Camera 3 infrared channel grisms. Here, we
examine two of these sources, SDSS J1723+3411 and SDSS J2340+2947,
using HST WFC3/IR grism data and supporting spatially unresolved
spectroscopy from several ground-based instruments to explore the size
of spatial variations in observed strong emission-line ratios like O32
and R23, which are sensitive to ionization parameter and metallicity,
and the Balmer decrement, which is an indicator of reddening. We find
significant spatial variation in the reddening and in the
reddening-corrected O32 and R23 values that correspond to spreads of a
few tenths of a dex in ionization parameter and metallicity. We also
find clear evidence of a negative radial gradient in star formation in
SDSS J2340+2947 and tentative evidence of one in SDSS J1723+3411,
though its star formation is quite asymmetric. Finally, we find that
reddening can vary enough spatially to make spatially resolved
reddening corrections necessary in order to characterize gradients in
line ratios and the physical conditions inferred from them,
necessitating the use of space-based integral field units for future
work on larger, more statistically robust samples.
Description:
SDSS J1723+3411 (SGAS J1723) was observed in six bands with HST WFC3:
F160W, F140W, F110W, and F105W in the IR channel, and F775W and F390W
in the UVIS channel. Imaging in the F160W and F110W bands was
conducted as part of HST GO13003 (PI: Gladders) on 2013 March 14 for
1112s each. Imaging with the UVIS channel in the F775W and F390W bands
was conducted as part of the same program, with total integration
times of 2380 and 2368s, respectively. Imaging in the F140W and F105W
bands was conducted as part of HST GO14230 (PI: Rigby) in 2016 January
and July alongside the grism observations, for a total integration of
923s per band.
SDSS J2340+2947 (SGAS J2340) was observed in four bands with HST WFC3:
F140W and F105W in the IR channel, paired with the grism observations,
and F814W and F390W in the UVIS channel, all from program GO14230
(PI: Rigby). In the IR channel, SGAS J2340 was observed with the F105W
filter for 973s and with F140W for 1635s; in the UVIS channel, it was
observed with the F814W filter for 2504s and with F390W for 2600s.
Data from the IRAC instrument of the Spitzer Space Telescope, acquired
during the post-cryogenic "warm mission," were obtained through
program 90232 (for SGAS J1723; PI J. Rigby) and program 12001 (for
SGAS J2340; PI J. Rigby). See Section 3.2.
Both galaxies were observed with the ESI spectrograph on the Keck II
telescope in echellette mode with a 1" slit on the nights of
2016-August-27 and 28 UT. See Section 3.3.
Gemini GNIRS observations of SGAS J1723 and SGAS J2340 were obtained
through the Gemini Fast Turnaround mode in program GN-2016B-FT-11
(PI Rigby). Observations were conducted on UT 2016 September 7.
See Section 3.4.
Spectroscopy for SGAS J1723 and SGAS J2340 was conducted using the HST
WFC3/IR G141 and G102 grisms alongside the direct imaging from program
GO14230. At the redshift of these arcs, z∼1.4, these grism
observations cover the wavelength range from just blueward of
[OII]λλ3727,3729 to just redward of Hα. Each
target was observed twice with each grism, using two different roll
angles. For SGAS J1723, observations in each grism were performed for
5112s at one roll angle and 4812s at the other. SGAS J2340 was
observed with a similar strategy except that the exposure times were
7518s for both roll angles with the G141 grism and 5012 and 5112s for
the two roll angles with the G102 grism.
See Section 3.5 and 5.6.
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 61 2 The positions and redshifts of the targets
spectra.dat 88 20 *Summary of the 1D HST WFC3-IR grism spectra
included in the subdirectory "sp"
sp/* . 20 Individual spectra in ASCII format
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Note on spectra.dat: These spectra are neither continuum-subtracted,
corrected for Milky Way reddening, nor corrected for reddening from
dust within these targets.
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Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 A10 --- ID Shorter identifier as used in the paper
12- 13 I2 h RAh Hour of right ascension (J2000) (1)
15- 16 I2 min RAm Minute of right ascension (J2000)
18- 19 I2 s RAs Second of right ascension (J2000)
21 A1 --- DE- Sign of declination (J2000) (1)
22- 23 I2 deg DEd Degree of declination (J2000) (1)
25- 26 I2 arcmin DEm Arcminute of declination (J2000)
28- 29 I2 arcsec DEs Arcsecond of declination (J2000)
31- 37 F7.5 --- zGal [1.32/1.43] Redshift of the galaxy (2)
39- 45 F7.5 --- e_zGal [2e-05/0.0002] zGal uncertainty (2)
47- 61 A15 --- Name Target name
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Note (1): R.A. and decl. are given in the J2000 coordinates and correspond
to the centers of each lensing system (i.e., the BCG).
Note (2): Redshifts and uncertainties are for the lensed source galaxies and
were determined by the GNIRS spectroscopy reported in this paper
(Section 5.5).
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Byte-by-byte Description of file: spectra.dat
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Bytes Format Units Label Explanations
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1- 40 A40 --- FileName Name of the ASCII file in subdirectory "sp"
42- 48 A7 --- Inst HST instrument (always "WFC3-IR")
50- 53 A4 --- Grism Grism ID
55- 64 A10 --- ID Target name ("SGAS J1723" or "SGAS J2340")
66- 88 A23 --- Comm Observation details (1)
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Note (1): "bothroll" refers to stacks of spectra from both roll angles
while "roll139" denotes spectra using only the 139 degree roll angle
(this only applies to the smaller, complete image 2 of sgas1723). For
the target sgas2340, "4stackednoim3" refers to a stack of spectra of 4
of the complete images, namely images 1,2, and 4 from the 043 degree
roll angle and image 1 from the 327 degree roll angle. For spectra of
regions within sgas2340, strings such as "A1A2A4A1" denote, for
example, that spectra from images A1, A2, and A4 from one roll angle
were used and only the image A1 from the second roll angle was used.
See Figure 1 and Table 2.
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Byte-by-byte Description of file: sp/*
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
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1- 7 F7.1 0.1nm lambda [7475/17613] Wavelength in Angstrom units
9- 26 E18.6 cW/m2/nm Flux [-2.4e-16/1.3e-16]?=0 Flux
in erg/s/cm2/Å units
28- 44 E17.5 cW/m2/nm e_Flux [7.3e-20/1.1e-16]?=0 Uncertainty in Flux
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History:
From electronic version for Table 1.
Spectra downloaded from: http://zenodo.org/record/4747939#.Y71E1KeZNH5
(End) Emmanuelle Perret [CDS] 10-Jan-2023