We report spectroscopic confirmation and high-resolution infrared imaging of a z = 2.79 triply imaged galaxy behind the Bullet Cluster. This source, a Spitzer-selected luminous infrared galaxy, is ...confirmed via polycyclic aromatic hydrocarbon (PAH) features using the Spitzer Infrared Spectrograph (IRS) and resolved with Hubble Space Telescope Wide Field Camera 3 imaging. In this galaxy, which with a stellar mass M{sub *} {approx} 4 x 10{sup 9} M{sub sun} is one of the two least massive ones studied with IRS at z>2, we also detect H{sub 2} S(4) and H{sub 2} S(5) pure rotational lines (at 3.1{sigma} and 2.1{sigma})-the first detection of these molecular hydrogen lines in a high-redshift galaxy. From the molecular hydrogen lines we infer an excitation temperature T = 377{sup +68}{sub -84} K. The detection of these lines indicates that the warm molecular gas mass is 6{sup +36}{sub -4}% of the stellar mass and implies the likely existence of a substantial reservoir of cold molecular gas in the galaxy. Future spectral observations at longer wavelengths with facilities such as the Herschel Space Observatory, the Large Millimeter Telescope, and the Atacama Pathfinder Experiment thus hold the promise of precisely determining the total molecular gas mass. Given the redshift, and using refined astrometric positions from the high-resolution imaging, we also update the magnification estimate and derived fundamental physical properties of this system. The previously published values for L{sub IR}, star formation rate, and dust temperature are confirmed modulo the revised magnification; however, we find that PAH emission is roughly a factor of 5 stronger than would be predicted by the relations between L{sub IR} and L{sub PAH} reported for SMGs and starbursts in Pope et al.
Abstract
Star cluster formation in the early universe and its contribution to reionization remains largely unconstrained to date. Here we present JWST/NIRCam imaging of the most highly magnified ...galaxy known at
z
∼ 6, the
Sunrise
arc. We identify six young massive star clusters (YMCs) with measured radii spanning from ∼20 down to ∼1 pc (corrected for lensing magnification), estimated stellar masses of ∼10
6–7
M
⊙
, and ages of 1–30 Myr based on SED fitting to photometry measured in eight filters extending to rest frame 7000 Å. The resulting stellar mass surface densities are higher than 1000
M
⊙
pc
−2
(up to a few 10
5
M
⊙
pc
−2
), and their inferred dynamical ages qualify the majority of these systems as gravitationally bound stellar clusters. The star cluster ages map the progression of star formation along the arc, with two evolved systems (≳10 Myr old) followed by very young clusters. The youngest stellar clusters (<5 Myr) show evidence of prominent H
β
+O
iii
emission based on photometry with equivalent widths larger than >1000 Å rest frame and are hosted in a 200 pc sized star-forming complex. Such a region dominates the ionizing photon production with a high efficiency
log
(
ξ
ion
Hz
erg
−
1
)
∼
25.7
. A significant fraction of the recently formed stellar mass of the galaxy (10%–30%) occurred in these YMCs. We speculate that such sources of ionizing radiation boost the ionizing photon production efficiency, which eventually carves ionized channels that might favor the escape of Lyman continuum radiation. The survival of some of the clusters would make them the progenitors of massive and relatively metal-poor globular clusters in the local universe.
ABSTRACT Spatially resolved studies are key to understanding when, where, and how stars form within galaxies. Using slitless grism spectra and broad-band imaging from the CAnadian NIRISS Unbiased ...Cluster Survey (CANUCS), we study the spatially resolved properties of a strongly lensed (μ = 5.4$\pm$1.8) z = 0.8718 galaxy pair consisting of a blue face-on galaxy (10.2 $\pm$ 0.2 log($M/M_\odot$)) with multiple star-forming clumps and a dusty red edge-on galaxy (9.9 $\pm$ 0.3 log($M/M_\odot$)). We produce accurate H $\alpha$ maps from JWST/NIRISS grism data using a new methodology that accurately models spatially varying continuum and emission line strengths. With spatially resolved indicators, we probe star formation on time-scales of $\sim$10 Myr (NIRISS H $\alpha$ emission line maps) and $\sim$100 Myr (UV imaging and broad-band SED fits). Taking the ratio of the H $\alpha$ to UV flux ($\eta$), we measure spatially resolved star formation burstiness. We find that in the face-on galaxy both H $\alpha$ and broad-band star formation rates (SFRs) drop at large galactocentric radii by a factor of $\sim$4.7 and 3.8, respectively, while SFR over the last $\sim$100 Myrs has increased by a factor of 1.6. Additionally, of the 20 clumps identified in the galaxy pair we find that 7 are experiencing bursty star formation, while 10 clumps are quenching, and 3 are in equilibrium (either being in a state of steady star formation or post-burst). Our analysis reveals that the blue face-on galaxy disc is predominantly in a quenching or equilibrium phase. However, the most intense quenching within the galaxy is seen in the quenching clumps. This pilot study demonstrates what JWST/NIRISS data can reveal about spatially varying star formation in galaxies at Cosmic Noon.
ABSTRACT The epoch of reionization (EoR) progressed through the emission of ionizing photons from galaxies to their local intergalactic medium. In this work, we characterize the dwarf star-forming ...galaxies as candidates for the source of ionizing photons that drove EoR. We investigate the ionizing properties and star formation histories of star-forming dwarf galaxies at the last stages of EoR at $4.8\lt z \lt 7$ using observations from the CAnadian NIRISS Unbiased Cluster Survey (CANUCS). The magnification due to gravitational lensing allows us to probe large dynamic ranges in stellar mass ($2\times 10^{6}\le {M}_*/{\rm M}_\odot \le 5\times 10^{9}$) and ultraviolet (UV) magnitudes ($-22.68\le M_{\rm UV}\le =-15.95$). We find a median UV slope $\beta _{1500}\,$ of $-2. 56\pm 0.23$ and the production efficiency of ionizing photons $\log$$\xi _{\rm {ion}}\,$$=25.39\pm 0.6$ for the full sample ($4.8\lt z \lt 7$) with a median stellar mass of $6.3\pm 0.5\times 10^{7} \, {\rm M}_\odot$. We find both $\beta _{1500}\,$ and $\xi _{\rm {ion}}\,$ are marginally correlated with the stellar mass of the galaxy, indicating a possible greater contribution of dwarf galaxies to the reionization of the Universe. We find that on average, galaxies in our sample are experiencing a recent rise/burst of star formation which translates to a higher scatter in $\xi _{\rm {ion}}\,$ and a large scatter in H$\alpha$ equivalent widths (EWs). Finally, we investigate the trends of H$\alpha$ and O iii + H$\beta$ EWs with UV magnitude and find $M_{\rm UV}$ is correlated between H$\alpha$ but not with O iii + H$\beta$ EWs indicating low metallicities and recent burst in the UV faint galaxies.
Abstract
We report the first gas-phase metallicity map of a distant galaxy measured with the James Webb Space Telescope (JWST). We use the NIRISS slitless spectroscopy acquired by the GLASS Early ...Release Science program to spatially resolve the rest-frame optical nebular emission lines in a gravitationally lensed galaxy at
z
= 3.06 behind the A2744 galaxy cluster. This galaxy (dubbed GLASS-Zgrad1) has stellar mass ∼10
8.6
M
⊙
, instantaneous star formation rate ∼8.6
M
⊙
yr
−1
(both corrected for lensing magnification), and global metallicity one-fourth solar. From its emission-line maps (O
iii
, H
β
, H
γ
, Ne
iii
, and O
ii
), we derive its spatial distribution of gas-phase metallicity using a well-established forward-modeling Bayesian inference method. The exquisite resolution and sensitivity of JWST/NIRISS, combined with lensing magnification, enable us to resolve this
z
∼ 3 dwarf galaxy in ≳50 resolution elements with sufficient signal, an analysis hitherto not possible. We find that the radial metallicity gradient of GLASS-Zgrad1 is strongly inverted (i.e., positive):
Δ
log
(
O
/
H
)
/
Δ
r
= 0.165 ± 0.023 dex kpc
−1
. This measurement is robust at
≳
4
−
σ
confidence level against known systematics. This positive gradient may be due to tidal torques induced by a massive nearby (∼15 kpc projected) galaxy, which can cause inflows of metal-poor gas into the central regions of GLASS-Zgrad1. These first results showcase the power of JWST wide-field slitless spectroscopic modes to resolve the mass assembly and chemical enrichment of low-mass galaxies in and beyond the peak epoch of cosmic star formation (
z
≳ 2). Reaching masses ≲ 10
9
M
⊙
at these redshifts is especially valuable to constrain the effects of galactic feedback and environment and is possible only with JWST’s new capabilities.
ABSTRACT
Recent observations have revealed the presence of strong C iii emission (EW$_{\rm {C\,{\small III}}}\gt 20$ Å) in z > 6 galaxies, the origin of which remains unclear. In an effort to ...understand the nature of these line emitters, we have initiated a survey targeting C iii emission in gravitationally lensed reionization-era analogues identified in Hubble Space Telescope imaging of clusters from the Reionization Lensing Cluster Survey. Here, we report initial results on four galaxies selected to have low stellar masses (2–8 × 107 M⊙) and J125-band flux excesses indicative of intense O iii + H β emission (EW$_{\rm {O\,{\small III}+H\,\beta }}$ = 500–2000 Å), similar to what has been observed at z > 6. We detect C iii emission in three of the four sources, with the C iii EW reaching values seen in the reionization era (EW$_{\rm {C\,{\small III}}}\simeq 17\!-\!22$ Å) in the two sources with the strongest optical line emission (EW$_{\rm {O\,{\small III}+H\,\beta }}\simeq 2000$ Å). We have obtained a Magellan/FIRE (Folded-port InfraRed Echellette) near-infrared spectrum of the strongest C iii emitter in our sample, revealing gas that is both metal poor and highly ionized. Using photoionization models, we are able to simultaneously reproduce the intense C iii and optical line emission for extremely young (2–3 Myr) and metal-poor (0.06–0.08 Z⊙) stellar populations, as would be expected after a substantial upturn in the star formation rate of a low-mass galaxy. The sources in this survey are among the first for which C iii has been used as the primary means of redshift confirmation. We suggest that it should be possible to extend this approach to z > 6 with current facilities, using C iii to measure redshifts of objects with IRAC excesses indicating EW$_{\rm {O\,{\small III}+H\,\beta }}\simeq 2000$ Å, providing a method of spectroscopic confirmation independent of Ly α.
Abstract
Detailed observations of star-forming galaxies at high redshift are critical to understanding the formation and evolution of the earliest galaxies. Gravitational lensing provides an ...important boost, allowing observations at physical scales unreachable in unlensed galaxies. We present three lensed galaxies from the RELICS survey at
z
phot
= 6–10, including the most highly magnified galaxy at
z
phot
∼ 6 (WHL 0137–zD1, dubbed the Sunrise Arc), the brightest known lensed galaxy at
z
phot
∼ 6 (MACS 0308–zD1), and the only spatially resolved galaxy currently known at
z
phot
∼ 10 (SPT 0615–JD). The Sunrise Arc contains seven star-forming clumps with delensed radii as small as 3 pc, the smallest spatial scales yet observed in a
z
> 6 galaxy, while SPT 0615–JD contains features measuring a few tens of parsecs. MACS 0308–zD1 contains an
r
∼ 30 pc clump with a star formation rate (SFR) of ∼3
M
⊙
yr
−1
, giving it an SFR surface density of Σ
SFR
∼ 10
3
M
⊙
yr
−1
kpc
−2
. These galaxies provide a unique window into small-scale star formation during the epoch of reionization. They will be excellent targets for future observations with JWST, including one approved program targeting the Sunrise Arc.
Abstract
We report the discovery of a low-mass
z
= 5.200 ± 0.002 galaxy that is in the process of ceasing its star formation. The galaxy, MACS0417-z5BBG, is multiply imaged with magnification factors ...∼40 by the galaxy cluster MACS J0417.5-1154, observed as part of the CAnadian NIRISS Unbiased Cluster Survey (CANUCS). Using observations of MACS0417-z5BBG with a JWST/NIRSpec Prism spectrum and NIRCam imaging, we investigate the mechanism responsible for the cessation of star formation of the galaxy and speculate about possibilities for its future. Using spectrophotometric fitting, we find a remarkably low stellar mass of
M
*
=
4.3
±
0.8
0.9
×
10
7
M
⊙
, less than 1% of the characteristic stellar mass at
z
∼ 5. We measure a delensed rest-UV half-light radius in the source plane of
30
±
5
7
pc and measure a star formation rate from H
α
of
0.14
±
0.12
0.17
M
⊙
yr
−1
. We find that under the assumption of a double power-law star formation history, MACS0417-z5BBG has seen a recent rise in star formation, peaking ∼10–30 Myr ago and declining precipitously since then. Together, these measurements reveal a low-mass, extremely compact galaxy which is in the process of ceasing star formation. We investigate the possibilities of mechanisms that have led to the cessation of star formation in MACS0417-z5BBG, considering stellar and active galactic nuclei (AGN) feedback and environmental processes. We can likely rule out most environmental processes but leave open the possibility of a low-mass AGN that does not leave a broad-line imprint on the spectrum or that MACS0417-z5BBG could be a star-forming galaxy in the lull of a bursty star formation history.
Abstract
The gravitationally lensed star WHL 0137–LS, nicknamed Earendel, was identified with a photometric redshift
z
phot
= 6.2 ± 0.1 based on images taken with the Hubble Space Telescope. Here we ...present James Webb Space Telescope (JWST) Near Infrared Camera images of Earendel in eight filters spanning 0.8–5.0
μ
m. In these higher-resolution images, Earendel remains a single unresolved point source on the lensing critical curve, increasing the lower limit on the lensing magnification to
μ
> 4000 and restricting the source plane radius further to
r
< 0.02 pc, or ∼4000 au. These new observations strengthen the conclusion that Earendel is best explained by an individual star or multiple star system and support the previous photometric redshift estimate. Fitting grids of stellar spectra to our photometry yields a stellar temperature of
T
eff
≃ 13,000–16,000 K, assuming the light is dominated by a single star. The delensed bolometric luminosity in this case ranges from
log
(
L
)
=
5.8
to 6.6
L
⊙
, which is in the range where one expects luminous blue variable stars. Follow-up observations, including JWST NIRSpec scheduled for late 2022, are needed to further unravel the nature of this object, which presents a unique opportunity to study massive stars in the first billion years of the universe.
We present the first results of the K-band Multi-Object Spectrometer (KMOS) Lens-Amplified Spectroscopic Survey, a new ESO Very Large Telescope large program, doing multi-object integral field ...spectroscopy of galaxies gravitationally lensed behind seven galaxy clusters selected from the Hubble Space Telescope (HST) Grism Lens-Amplified Survey from Space. Using the power of the cluster magnification, we are able to reveal the kinematic structure of 25 galaxies at , in four cluster fields, with stellar masses . This sample includes five sources at with lower stellar masses than in any previous kinematic integral field unit (IFU) surveys. Our sample displays a diversity in kinematic structure over this mass and redshift range. The majority of our kinematically resolved sample is rotationally supported, but with a lower ratio of rotational velocity to velocity dispersion than in the local universe, indicating the fraction of dynamically hot disks changes with cosmic time. We find that no galaxies with stellar mass in our sample display regular ordered rotation. Using the enhanced spatial resolution from lensing, we resolve a lower number of dispersion-dominated systems compared to field surveys, competitive with findings from surveys using adaptive optics. We find that the KMOS IFUs recover emission line flux from HST grism-selected objects more faithfully than slit spectrographs. With artificial slits, we estimate that slit spectrographs miss, on average, 60% of the total flux of emission lines, which decreases rapidly if the emission line is spatially offset from the continuum.
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