| 1. |
- Flury, Sophia R., et al.
(author)
-
The Low-redshift Lyman Continuum Survey. I. New, Diverse Local Lyman Continuum Emitters
- 2022
-
In: Astrophysical Journal Supplement Series. - : American Astronomical Society. - 0067-0049 .- 1538-4365. ; 260:1
-
Journal article (peer-reviewed)abstract
- The origins of Lyman continuum (LyC) photons responsible for the reionization of the universe are as of yet unknown and highly contested. Detecting LyC photons from the Epoch of Reionization is not possible due to absorption by the intergalactic medium, which has prompted the development of several indirect diagnostics to infer the rate at which galaxies contribute LyC photons to reionize the universe by studying lower-redshift analogs. We present the Low-redshift Lyman Continuum Survey (LzLCS) comprising measurements made with the Hubble Space Telescope Cosmic Origins Spectrograph for a z = 0.2-0.4 sample of 66 galaxies. After careful processing of the far-UV spectra, we obtain a total of 35 Lyman continuum emitters (LCEs) detected with 97.725% confidence, nearly tripling the number of known local LCEs. We estimate escape fractions from the detected LyC flux and upper limits on the undetected LyC flux, finding a range of LyC escape fractions up to 50%. Of the 35 LzLCS LCEs, 12 have LyC escape fractions greater than 5%, more than doubling the number of known local LCEs with cosmologically relevant LyC escape.
|
|
| 2. |
- Flury, Sophia R., et al.
(author)
-
The Low-redshift Lyman Continuum Survey. II. New Insights into LyC Diagnostics
- 2022
-
In: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 930:2
-
Journal article (peer-reviewed)abstract
- The Lyman continuum (LyC) cannot be observed at the epoch of reionization (z greater than or similar to 6) owing to intergalactic H i absorption. To identify LyC emitters (LCEs) and infer the fraction of escaping LyC, astronomers have developed various indirect diagnostics of LyC escape. Using measurements of the LyC from the Low-redshift Lyman Continuum Survey (LzLCS), we present the first statistical test of these diagnostics. While optical depth indicators based on Ly alpha, such as peak velocity separation and equivalent width, perform well, we also find that other diagnostics, such as the [O iii]/[O ii] flux ratio and star formation rate surface density, predict whether a galaxy is an LCE. The relationship between these galaxy properties and the fraction of escaping LyC flux suggests that LyC escape depends strongly on H i column density, ionization parameter, and stellar feedback. We find that LCEs occupy a range of stellar masses, metallicities, star formation histories, and ionization parameters, which may indicate episodic and/or different physical causes of LyC escape.
|
|
| 3. |
- Fudamoto, Yoshinobu, et al.
(author)
-
The Extended [C II] under Construction? : Observation of the Brightest High-z Lensed Star-forming Galaxy at z=6.2
- 2024
-
In: Astrophysical Journal. - : Institute of Physics Publishing (IOPP). - 0004-637X .- 1538-4357. ; 961:1
-
Journal article (peer-reviewed)abstract
- We present results of [C ii] 158 μm emission line observations, and report the spectroscopic redshift confirmation of a strongly lensed (μ ∼ 20) star-forming galaxy, MACS0308-zD1 at z = 6.2078 ± 0.0002. The [C ii] emission line is detected with a signal-to-noise ratio >6 within the rest-frame UV-bright clump of the lensed galaxy (zD1.1) and exhibits multiple velocity components; the narrow [C ii] has a velocity full width half maximum (FWHM) of 110 ± 20 km s−1, while broader [C ii] is seen with an FWHM of 230 ± 50 km s−1. The broader [C ii] component is blueshifted (−80 ± 20 km s−1) with respect to the narrow [C ii] component, and has a morphology that extends beyond the UV-bright clump. We find that, while the narrow [C ii] emission is most likely associated with zD1.1, the broader component is possibly associated with a physically distinct gas component from zD1.1 (e.g., outflowing or inflowing gas). Based on the nondetection of λ158μm dust continuum, we find that MACS0308-zD1's star formation activity occurs in a dust-free environment indicated by a strong upper limit of infrared luminosity ≲9 × 108L⊙. Targeting this strongly lensed faint galaxy for follow-up Atacama Large Millimeter/submillimeter Array and JWST observations will be crucial to characterize the details of typical galaxy growth in the early Universe.
|
|
| 4. |
- Hsiao, Tiger Yu-Yang, et al.
(author)
-
JWST Reveals a Possible z similar to 11 Galaxy Merger in Triply Lensed MACS0647-JD
- 2023
-
In: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8205 .- 2041-8213. ; 949:2
-
Journal article (peer-reviewed)abstract
- MACS0647-JD is a triply lensed z similar to 11 galaxy originally discovered with the Hubble Space Telescope. The three lensed images are magnified by factors of similar to 8, 5, and 2 to AB mag 25.1, 25.6, and 26.6 at 3.5 mu m. The brightest is over a magnitude brighter than other galaxies recently discovered at similar redshifts z > 10 with JWST. Here, we report new JWST imaging that clearly resolves MACS0647-JD as having two components that are either merging galaxies or stellar complexes within a single galaxy. The brighter larger component "A" is intrinsically very blue (ss similar to-2.6 +/- 0.1), likely due to very recent star formation and no dust, and is spatially extended with an effective radius similar to 70 +/- 24 pc. The smaller component "B" (r similar to 20-+ 58 pc) appears redder (ss similar to-2 +/- 0.2), likely because it is older (100-200 Myr) with mild dust extinction (AV similar to 0.1 mag). With an estimated stellar mass ratio of roughly 2:1 and physical projected separation similar to 400 pc, we may be witnessing a galaxy merger 430 million years after the Big Bang. We identify galaxies with similar colors in a high-redshift simulation, finding their star formation histories to be dissimilar, which is also suggested by the spectral energy distribution fitting, suggesting they formed further apart. We also identify a candidate companion galaxy "C" similar to 3 kpc away, likely destined to merge with A and B. Upcoming JWST Near Infrared Spectrograph observations planned for 2023 January will deliver spectroscopic redshifts and more physical properties for these tiny magnified distant galaxies observed in the early universe.
|
|
| 5. |
- Meena, Ashish Kumar, et al.
(author)
-
Two Lensed Star Candidates at z similar or equal to 4.8 behind the Galaxy Cluster MACS J0647.7+7015
- 2023
-
In: Astrophysical Journal Letters. - : Institute of Physics (IOP). - 2041-8205 .- 2041-8213. ; 944:1
-
Journal article (peer-reviewed)abstract
- We report the discovery of two extremely magnified lensed star candidates behind the galaxy cluster MACS J0647.7+015 using recent multiband James Webb Space Telescope (JWST) NIRCam observations. The star candidates are seen in a previously known, z (phot) similar or equal to 4.8 dropout giant arc that straddles the critical curve. The candidates lie near the expected critical curve position, but lack clear counter-images on the other side of it, suggesting these are possibly stars undergoing caustic crossings. We present revised lensing models for the cluster, including multiply imaged galaxies newly identified in the JWST data, and use them to estimate background macro-magnifications of at least greater than or similar to 90 and greater than or similar to 50 at the positions of the two candidates, respectively. With these values, we expect effective, caustic-crossing magnifications of similar to[10(3)-10(5)] for the two star candidates. The spectral energy distributions of the two candidates match well the spectra of B-type stars with best-fit surface temperatures of similar to 10,000 K, and similar to 12,000 K, respectively, and we show that such stars with masses greater than or similar to 20 M (circle dot) and greater than or similar to 50 M (circle dot), respectively, can become sufficiently magnified to be observable. We briefly discuss other alternative explanations and conclude that these objects are likely lensed stars, but also acknowledge that the less-magnified candidate may alternatively reside in a star cluster. These star candidates constitute the second highest-redshift examples to date after Earendel at z (phot) similar or equal to 6.2, establishing further the potential of studying extremely magnified stars at high redshifts with JWST. Planned future observations, including with NIRSpec, will enable a more detailed view of these candidates in the near future.
|
|
| 6. |
- Meena, Ashish Kumar, et al.
(author)
-
Two Lensed Star Candidates at z ≃ 4.8 behind the Galaxy Cluster MACS J0647.7+7015
- 2023
-
In: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8205 .- 2041-8213. ; 944:1
-
Journal article (peer-reviewed)abstract
- We report the discovery of two extremely magnified lensed star candidates behind the galaxy cluster MACS J0647.7+015 using recent multiband James Webb Space Telescope (JWST) NIRCam observations. The star candidates are seen in a previously known, zphot ≃ 4.8 dropout giant arc that straddles the critical curve. The candidates lie near the expected critical curve position, but lack clear counter-images on the other side of it, suggesting these are possibly stars undergoing caustic crossings. We present revised lensing models for the cluster, including multiply imaged galaxies newly identified in the JWST data, and use them to estimate background macro-magnifications of at least ≳90 and ≳50 at the positions of the two candidates, respectively. With these values, we expect effective, caustic-crossing magnifications of ∼[103–105] for the two star candidates. The spectral energy distributions of the two candidates match well the spectra of B-type stars with best-fit surface temperatures of ∼10,000 K, and ∼12,000 K, respectively, and we show that such stars with masses ≳20 M⊙ and ≳50 M⊙, respectively, can become sufficiently magnified to be observable. We briefly discuss other alternative explanations and conclude that these objects are likely lensed stars, but also acknowledge that the less-magnified candidate may alternatively reside in a star cluster. These star candidates constitute the second highest-redshift examples to date after Earendel at zphot ≃ 6.2, establishing further the potential of studying extremely magnified stars at high redshifts with JWST. Planned future observations, including with NIRSpec, will enable a more detailed view of these candidates in the near future.
|
|
| 7. |
- Saldana-Lopez, Alberto, et al.
(author)
-
The Low-Redshift Lyman Continuum Survey Unveiling the ISM properties of low-z Lyman-continuum emitters
- 2022
-
In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 663
-
Journal article (peer-reviewed)abstract
- Aims. Combining 66 ultraviolet (UV) spectra and ancillary data from the recent Low-Redshift Lyman Continuum Survey (LzLCS) and 23 LyC observations by earlier studies, we form a statistical sample of star-forming galaxies at z similar to 0.2-0.4 with which we study the role of cold interstellar medium (ISM) gas in the leakage of ionizing radiation. We also aim to establish empirical relations between the H I neutral and low-ionization state (LIS) absorption lines with different galaxy properties.Methods. We first constrain the massive star content (stellar ages and metallicities) and UV attenuation by fitting the stellar continuum with a combination of simple stellar population models. The models, together with accurate LyC flux measurements, allow us to determine the absolute LyC photon escape fraction for each galaxy (f(esc)(abs)). We then measure the equivalent widths and residual fluxes of multiple H I and LIS lines, and the geometrical covering fraction of the UV emission, adopting the picket-fence model.Results. The LyC escape fraction spans a wide range, with a median f(esc)(abs) (0.16, 0.84 quantiles) of 0.04 (0.02, 0.20), and 50 out of the 89 galaxies detected in the LyC (1 sigma upper limits of f(esc)(abs) less than or similar to 0.01 for non-detections, typically). The H I and LIS line equivalent widths scale with the UV luminosity and attenuation, and inversely with the residual flux of these lines. Additionally, Ly alpha equivalent widths scale with both the H I and LIS residual fluxes, but anti-correlate with the corresponding H I or LIS equivalent widths. The H I and LIS residual fluxes are correlated, indicating that the neutral gas is spatially traced by the low-ionization transitions. We find that the observed trends of the absorption lines and the UV attenuation are primarily driven by the geometric covering fraction of the gas. The observed nonuniform gas coverage also demonstrates that LyC photons escape through low-column-density channels in the ISM. The equivalent widths and residual fluxes of both the H I and LIS lines strongly correlate with f(esc)(abs): strong LyC leakers (highest f(esc)(abs)) show weak absorption lines, low UV attenuation, and large Ly alpha equivalent widths. We provide several empirical calibrations to estimate f(esc)(abs) from UV absorption lines. Finally, we show that simultaneous UV absorption line and dust attenuation measurements can, in general, predict the escape fraction of galaxies. We apply our method to available measurements of UV LIS lines of 15 star-forming galaxies at z similar to 4 6 (plus 3 high-z galaxy composites), finding that these high-redshift, UV-bright galaxies (M-UV less than or similar to 21) may have low escape fractions, f(esc)(abs) less than or similar to 0.1.Conclusions. UV absorption lines trace the cold ISM gas of galaxies, which governs the physics of the LyC escape. We show that, with some assumptions, the absolute LyC escape can be statistically predicted using UV absorption lines, and the method can be applied to study galaxies across a wide redshift range, including in the epoch of cosmic reionization.
|
|
| 8. |
-
Spatially Resolved Stellar Populations of 0.3 < z < 6.0 Galaxies in WHL 0137–08 and MACS 0647+70 Clusters as Revealed by JWST : How Do Galaxies Grow and Quench over Cosmic Time?
- 2023
-
In: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 945:2
-
Journal article (peer-reviewed)abstract
- We study the spatially resolved stellar populations of 444 galaxies at 0.3 < z < 6.0 in two clusters (WHL 0137–08 and MACS 0647+70) and a blank field, combining imaging data from the Hubble Space Telescope and JWST to perform spatially resolved spectral energy distribution (SED) modeling using ᴘɪXᴇᴅꜰɪᴛ. The high spatial resolution of the imaging data combined with magnification from gravitational lensing in the cluster fields allows us to resolve a large fraction of our galaxies (109) to subkiloparsec scales. At redshifts around cosmic noon and higher (2.5 ≲ z ≲ 6.0), we find mass-doubling times to be independent of radius, inferred from flat specific star formation rate (sSFR) radial profiles and similarities between the half-mass and half-SFR radii. At lower redshifts (1.5 ≲ z ≲ 2.5), a significant fraction of our star-forming galaxies shows evidence for nuclear starbursts, inferred from a centrally elevated sSFR and a much smaller half-SFR radius compared to the half-mass radius. At later epochs, we find more galaxies suppress star formation in their centers but are still actively forming stars in the disk. Overall, these trends point toward a picture of inside-out galaxy growth consistent with theoretical models and simulations. We also observe a tight relationship between the central mass surface density and global stellar mass with ∼0.38 dex scatter. Our analysis demonstrates the potential of spatially resolved SED analysis with JWST data. Future analysis with larger samples will be able to further explore the assembly of galaxy mass and the growth of their structures.
|
|
| 9. |
- Vanzella, Eros, et al.
(author)
-
JWST/NIRCam Probes Young Star Clusters in the Reionization Era Sunrise Arc
- 2023
-
In: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 945:1
-
Journal article (peer-reviewed)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 ∼106–7 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 105 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 Hβ+[O ııı] 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(ξion [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.
|
|
| 10. |
- Welch, Brian, et al.
(author)
-
JWST Imaging of Earendel, the Extremely Magnified Star at Redshift z=6.2
- 2022
-
In: Astrophysical Journal Letters. - : Institute of Physics (IOP). - 2041-8205 .- 2041-8213. ; 940
-
Journal article (peer-reviewed)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 mu 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 mu > 4000 and restricting the source plane radius further to r < 0.02 pc, or similar to 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) similar to 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 L-theta, 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.
|
|
| 11. |
- Welch, Brian, et al.
(author)
-
RELICS : Small-scale Star Formation in Lensed Galaxies at z=6-10
- 2023
-
In: Astrophysical Journal. - : Institute of Physics (IOP). - 0004-637X .- 1538-4357. ; 943:1
-
Journal article (peer-reviewed)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) similar to 6 (WHL 0137-zD1, dubbed the Sunrise Arc), the brightest known lensed galaxy at z (phot) similar to 6 (MACS 0308-zD1), and the only spatially resolved galaxy currently known at z (phot) similar to 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 similar to 30 pc clump with a star formation rate (SFR) of similar to 3 M (circle dot) yr(-1), giving it an SFR surface density of sigma(SFR) similar to 10(3) M (circle dot) 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.
|
|
