We present MIRI/JWST medium-resolution spectroscopy (MRS) and imaging (MIRIM) of the lensed galaxy MACS1149-JD1 at a redshift of z = 9.1092 ± 0.0002, when the Universe was about 530 Myr old. We ...detect, for the first time, spatially resolved H α emission in a galaxy at a redshift above nine. The structure of the H α emitting gas consists of two clumps, S and N, carrying about 60% and 40% of the total flux, respectively. The total H α luminosity implies an instantaneous star-formation rate in the range of 3.2 ± 0.3 and 5.3 ± 0.4 M ⊙ yr −1 for sub-solar and solar metallicities. The ionizing photon production efficiency, log( ζ ion ), shows a spatially resolved structure with values of 25.55 ± 0.03; 25.47 ± 0.03; and 25.91 ± 0.09 Hz erg −1 for the integrated galaxy and clumps S and N, respectively. The H α rest-frame equivalent width, EW 0 (H α ), is 726 −182 +660 Å for the integrated galaxy, but it presents extreme values of 531 −96 +300 Å and ≥1951 Å for clumps S and N, respectively. The spatially resolved ionizing photon production efficiency is within the range of values measured in galaxies at a redshift above six and well above the canonical value (25.2 ± 0.1 Hz erg −1 ). The EW 0 (H α ) is a factor of two lower than the predicted value at z = 9.11 based on the extrapolation of the evolution of the EW 0 (H α ) with redshifts, ∝(1 + z ) 2.1 , including galaxies detected with JWST. The extreme difference of the EW 0 (H α ) for clumps S and N indicates the presence of a recent (< 5 Myr) stellar burst in clump N and a star formation over a larger period of time (e.g., ∼50 Myr) in clump S. The different ages of the stellar population place MACS1149-JD1 and clumps N and S at different locations in the log( ζ ion ) to EW 0 (H α ) plane and above the main relation defined from intermediate- and high-redshift ( z = 3 − 7) galaxies detected with JWST. Finally, clump S and N show very different H α kinematics, with velocity dispersions of 56 ± 4 km s −1 and 113 ± 33 km s −1 , likely indicating the presence of outflows or increased turbulence in clump N. The dynamical mass M dyn = (2.4 ± 0.5) × 10 9 M ⊙ , obtained from the size of the integrated H α ionized nebulae and its velocity dispersion, is within the range previously measured with the spatially resolved OIII88 μm line.
Luminous infrared starbursts in the early Universe are thought to be the progenitors of massive quiescent galaxies identified at redshifts 2–4. Using the Mid-IRfrared Instrument (MIRI) on board the
...James Webb
Space Telescope (JWST), we present mid-infrared sub-arcsec imaging and spectroscopy of such a starburst: the slightly lensed hyper-luminous infrared system SPT0311-58 at
z
= 6.9. The MIRI IMager (MIRIM) and Medium Resolution Spectrometer (MRS) observations target the stellar (rest-frame 1.26 μm emission) structure and ionised (Pa
α
and H
α
) medium on kpc scales in the system. The MIRI observations are compared with existing ALMA far-infrared continuum and C
II
158μm imaging at a similar angular resolution. Even though the ALMA observations imply very high star formation rates (SFRs) in the eastern (E) and western (W) galaxies of the system, the H
α
line is, strikingly, not detected in our MRS observations. This fact, together with the detection of the ionised gas phase in Pa
α
, implies very high internal nebular extinction with lower limits (
A
V
) of 4.2 (E) and 3.9 mag (W) as well as even larger values (5.6 (E) and 10.0 (W)) by spectral energy distribution (SED) fitting analysis. The extinction-corrected Pa
α
lower limits of the SFRs are 383 and 230
M
⊙
yr
−1
for the E and W galaxies, respectively. This represents 50% of the SFRs derived from the C
II
158 μm line and infrared light for the E galaxy and as low as 6% for the W galaxy. The MIRIM observations reveal a clumpy stellar structure, with each clump having 3–5×10
9
M
⊙
mass in stars, leading to a total stellar mass of 2.0 and 1.5×10
10
M
⊙
for the E and W galaxies, respectively. The specific star formation (sSFR) in the stellar clumps ranges from 25 to 59 Gyr
−1
, assuming a star formation with a 50–100 Myr constant rate. This sSFR is three to ten times larger than the values measured in galaxies of similar stellar mass at redshifts 6–8. Thus, SPT0311-58 clearly stands out as a starburst system when compared with typical massive star-forming galaxies at similar high redshifts. The overall gas mass fraction is
M
gas
/
M
*
∼ 3, similar to that of
z
∼ 4.5–6 star-forming galaxies, suggesting a flattening of the gas mass fraction in massive starbursts up to redshift 7. The kinematics of the ionised gas in the E galaxy agrees with the known C
II
gas kinematics, indicating a physical association between the ionised gas and the cold ionised or neutral gas clumps. The situation in the W galaxy is more complex, as it appears to be a velocity offset by about +700 km s
−1
in the Pa
α
relative to the C
II
emitting gas. The nature of this offset and its reality are not fully established and require further investigation. The observed properties of SPT0311-58, such as the clumpy distribution at sub(kpc) scales and the very high average extinction, are similar to those observed in low- and intermediate-
z
luminous (E galaxy) and ultra-luminous (W galaxy) infrared galaxies, even though SPT0311-58 is observed only ∼800 Myr after the Big Bang. Such massive, heavily obscured clumpy starburst systems as SPT0311-58 likely represent the early phases in the formation of a massive high-redshift bulge, spheroids and/or luminous quasars. This study demonstrates that MIRI and JWST are, for the first time, able to explore the rest-frame near-infrared stellar and ionised gas structure of these galaxies, even during the Epoch of Reionization.
Luminous infrared galaxies at high redshifts (
z
> 4) include extreme starbursts that build their stellar mass over short periods of time, that is, of 100 Myr or less. These galaxies are considered ...to be the progenitors of massive quiescent galaxies at intermediate redshifts (
z
∼ 2) but their stellar structure and buildup is unknown. Here, we present the first spatially resolved near-infrared (rest-frame 1.1 μm) imaging of GN20, one of the most luminous dusty star-forming galaxies known to date, observed at an epoch when the Universe was only 1.5 Gyr old. The 5.6 μm image taken with the JWST Mid-Infrared Instrument (MIRI/JWST) shows that GN20 is a very luminous galaxy (
M
1.1 μm, AB
= −25.01, uncorrected for internal extinction), with a stellar structure composed of a conspicuous central source and an extended envelope. The central source is an unresolved nucleus that carries 9% of the total flux. The nucleus is co-aligned with the peak of the cold dust emission, and offset by 3.9 kpc from the ultraviolet stellar emission. The diffuse stellar envelope is similar in size (3.6 kpc effective radius) to the clumpy CO molecular gas distribution. The centroid of the stellar envelope is offset by 1 kpc from the unresolved nucleus, suggesting GN20 is involved in an interaction or merger event supported by its location as the brightest galaxy in a proto-cluster. Additional faint stellar clumps appear to be associated with some of the UV- and CO-clumps. The stellar size of GN20 is larger by a factor of about 3 to 5 than known spheroids, disks, and irregulars at
z
∼ 4, while its size and low Sérsic index are similar to those measured in dusty, infrared luminous galaxies at redshift 2 of the same mass (∼10
11
M
⊙
). GN20 has all the ingredients necessary for evolving into a massive spheroidal quiescent galaxy at intermediate redshift: it is a large, luminous galaxy at
z
= 4.05 involved in a short and massive starburst centred in the stellar nucleus and extended over the entire galaxy, out to radii of 4 kpc, and likely induced by the interaction or merger with a member of the proto-cluster.
A&A 686, A85 (2024) We present MIRI/JWST medium-resolution spectroscopy (MRS) and imaging (MIRIM)
of the lensed galaxy MACS1149-JD1 at a redshift of $z$=9.1092$\pm$0.0002
(Universe age about 530 ...Myr). We detect, for the first time, spatially resolved
H$\alpha$ emission in a galaxy at a redshift above nine. The structure of the
H$\alpha$ emitting gas consists of two clumps, S and N. The total H$\alpha$
luminosity implies an instantaneous star-formation of 5.3$\pm$0.4 $M_{\odot}$
yr$^{-1}$ for solar metallicities. The ionizing photon production efficiency,
$\log(\zeta_\mathrm{ion})$, shows a spatially resolved structure with values of
25.55$\pm$0.03, 25.47$\pm$0.03, and 25.91$\pm$0.09 Hz erg$^{-1}$ for the
integrated galaxy, and clumps S and N, respectively. The H$\alpha$ rest-frame
equivalent width, EW$_{0}$(H$\alpha$), is 726$^{+660}_{-182}$ \'Angstrom for
the integrated galaxy, but presents extreme values of 531$^{+300}_{-96}$
\'Angstrom and $\geq$1951 \'Angstrom for clumps S and N, respectively. The
spatially resolved ionizing photon production efficiency is within the range of
values measured in galaxies at redshift above six, and well above the canonical
value (25.2$\pm$0.1 Hz erg$^{-1}$). The extreme difference of
EW$_{0}$(H$\alpha$) for Clumps S and N indicates the presence of a recent (<5
Myrs) burst in clump N and a star formation over a larger period of time (e.g.,
$\sim$50 Myr) in clump S. Finally, clump S and N show very different H$\alpha$
kinematics with velocity dispersions of 56$\pm$4 km s$^{-1}$ and 113$\pm$33 km
s$^{-1}$, likely indicating the presence of outflows or increased turbulence in
the clump N. The dynamical mass, $M_\mathrm{dyn}$=
(2.4$\pm$0.5)$\times$10$^{9}$ $M_{\odot}$, is within the range measured with
the spatially resolved OIII88$\mu$m line.
Luminous infrared galaxies at high redshifts (\(z\)>4) include extreme starbursts that build their stellar mass over short periods of time (>100 Myr). These galaxies are considered to be the ...progenitors of massive quiescent galaxies at intermediate redshifts (\(z\sim\)2) but their stellar structure and buildup is unknown. Here, we present the first spatially resolved near-infrared imaging of GN20, one of the most luminous dusty star-forming galaxies known to date, observed at an epoch when the Universe was only 1.5 Gyr old. The 5.6\(\mu\)m image taken with the JWST Mid-Infrared Instrument (MIRI/JWST) shows that GN20 is a very luminous galaxy (M\(_\mathrm{1.1\mu m,AB}\)=\(-\)25.01), with a stellar structure composed of a conspicuous central source and an extended envelope. The central source is an unresolved nucleus that carries 9% of the total flux. The nucleus is co-aligned with the peak of the cold dust emission, and offset by 3.9 kpc from the ultraviolet stellar emission. The diffuse stellar envelope is similar in size to the clumpy CO molecular gas distribution. The centroid of the stellar envelope is offset by 1 kpc from the unresolved nucleus, suggesting GN20 is involved in an interaction or merger event supported by its location as the brightest galaxy in a proto-cluster. The stellar size of GN20 is larger by a factor of about 3-5 than known spheroids, disks, and irregulars at \(z\sim\)4, while its size and low Sérsic index are similar to those measured in dusty, infrared luminous galaxies at \(z\sim\)2 of the same mass. GN20 has all the ingredients necessary for evolving into a massive spheroidal quiescent galaxy at intermediate \(z\): it is a large, luminous galaxy at \(z\)=4.05 involved in a short and massive starburst centred in the stellar nucleus and extended over the entire galaxy, out to radii of 4 kpc, and likely induced by the interaction or merger with a member of the proto-cluster.
Using MIRI on-board JWST we present mid-infrared sub-arcsec imaging (MIRIM) and spectroscopy (MRS) of the hyperluminous infrared system SPT0311-58 at z=6.9. MIRI observations are compared with ...existing ALMA far-infrared continuum and CII158\(\mu\)m imaging. Even though the ALMA observations suggests very high star formation rates (SFR) in the eastern (E) and western (W) galaxies of the system, the H\(\alpha\) line is not detected. This, together with the detection of the Pa\(\alpha\) line, implies very high optical nebular extinction with lower limits of 4.2 (E) and 3.9 mag (W), and even larger 5.6 (E) and 10.0 (W) for SED derived values. The extinction-corrected Pa\(\alpha\) SFRs are 383 and 230M\(_{\odot}\)yr\(^{-1}\) for the E and W galaxies, respectively. This represents 50% of the SFRs derived from the CII158\(\mu\)m line and infrared light for the E galaxy and as low as 6% for the W galaxy. The MIRI observations reveal a clumpy stellar structure, with each clump having 3 to 5 \(\times\)10\(^{9}\)M\(_\mathrm{\odot}\), leading to a total stellar mass of 2.0 and 1.5\(\times\)10\(^{10}\)M\(_\mathrm{\odot}\) for the E and W galaxies, respectively. The specific SFR in the stellar clumps ranges from 25 to 59Gyr\(^{-1}\), which are 3 to 10 times larger than the values measured in galaxies of similar mass at redshifts 6 to 8. The overall gas mass fraction is \(M_\mathrm{gas}\)/\(M_*\sim3\), similar to that of z=4.5-6 star-forming galaxies. The observed properties of SPT0311-58 such as the clumpy distribution at sub(kpc) scales and the very high average extinction are similar to those observed in low- and intermediate-z LIRGs and ULIRGs, even though SPT0311-58 is observed only 800 Myr after the Big Bang. Massive, heavily obscured, clumpy starburst systems like SPT0311-58 likely represent the early phases in the formation of massive high-z bulge/spheroids and luminous quasars.
We present MIRI/JWST medium-resolution spectroscopy (MRS) and imaging (MIRIM) of the lensed galaxy MACS1149-JD1 at a redshift of \(z\)=9.1092\(\pm\)0.0002 (Universe age about 530 Myr). We detect, for ...the first time, spatially resolved H\(\alpha\) emission in a galaxy at a redshift above nine. The structure of the H\(\alpha\) emitting gas consists of two clumps, S and N. The total H\(\alpha\) luminosity implies an instantaneous star-formation of 5.3\(\pm\)0.4 \(M_{\odot}\) yr\(^{-1}\) for solar metallicities. The ionizing photon production efficiency, \(\log(\zeta_\mathrm{ion})\), shows a spatially resolved structure with values of 25.55\(\pm\)0.03, 25.47\(\pm\)0.03, and 25.91\(\pm\)0.09 Hz erg\(^{-1}\) for the integrated galaxy, and clumps S and N, respectively. The H\(\alpha\) rest-frame equivalent width, EW\(_{0}\)(H\(\alpha\)), is 726\(^{+660}_{-182}\) Ángstrom for the integrated galaxy, but presents extreme values of 531\(^{+300}_{-96}\) Ángstrom and \(\geq\)1951 Ángstrom for clumps S and N, respectively. The spatially resolved ionizing photon production efficiency is within the range of values measured in galaxies at redshift above six, and well above the canonical value (25.2\(\pm\)0.1 Hz erg\(^{-1}\)). The extreme difference of EW\(_{0}\)(H\(\alpha\)) for Clumps S and N indicates the presence of a recent (<5 Myrs) burst in clump N and a star formation over a larger period of time (e.g., \(\sim\)50 Myr) in clump S. Finally, clump S and N show very different H\(\alpha\) kinematics with velocity dispersions of 56\(\pm\)4 km s\(^{-1}\) and 113\(\pm\)33 km s\(^{-1}\), likely indicating the presence of outflows or increased turbulence in the clump N. The dynamical mass, \(M_\mathrm{dyn}\)= (2.4\(\pm\)0.5)\(\times\)10\(^{9}\) \(M_{\odot}\), is within the range measured with the spatially resolved OIII88\(\mu\)m line.
