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| 2. |
- Dayal, Pratika, et al.
(författare)
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Warm dark matter constraints from the JWST
- 2024
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press. - 0035-8711 .- 1365-2966. ; 528:2, s. 2784-2789
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Tidskriftsartikel (refereegranskat)abstract
- Warm dark matter (WDM) particles with masses (∼ kilo electronvolt) offer an attractive solution to the small-scale issues faced by the cold dark matter (CDM) paradigm. The delay of structure formation in WDM models and the associated dearth of low-mass systems at high redshifts makes this an ideal time to revisit WDM constraints in light of the unprecedented datasets from the JWST. Developing a phenomenological model based on the halo mass functions in CDM and WDM models, we calculate high redshift (z ∼> 6), the stellar mass functions (SMF) and the associated stellar mass density (SMD) and the maximum stellar mass allowed in a given volume. We find that: (i) WDM as light as 1.5 keV is already disfavoured by the low-mass end of the SMF (stellar mass M∗ ∼ 107 M⨀) although caution must be exerted given the impact of lensing uncertainties; (ii) 1.5 keV WDM models predict SMD values that show a steep decrease from 108.8 to 102 M⨀cMpc−3 from z ∼ 4 to 17 for M∗ ∼> 108 M⨀; and (iii) the 1.5 keV WDM model predicts a sharp and earlier cut-off in the maximum stellar masses for a given number density (or volume) as compared to CDM or heavier WDM models. For example, with a number density of 10−3 cMpc−3, 1.5 (3) KeV WDM models do not predict bound objects at z ∼> 12 (18). Forthcoming JWST observations of multiple blank fields can therefore be used as a strong probe of WDM at an epoch inaccessible by other means.
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| 3. |
- Hsiao, Tiger Yu-Yang, et al.
(författare)
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JWST Reveals a Possible z similar to 11 Galaxy Merger in Triply Lensed MACS0647-JD
- 2023
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Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8205 .- 2041-8213. ; 949:2
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Tidskriftsartikel (refereegranskat)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.
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| 4. |
- Meena, Ashish Kumar, et al.
(författare)
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Two Lensed Star Candidates at z similar or equal to 4.8 behind the Galaxy Cluster MACS J0647.7+7015
- 2023
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Ingår i: Astrophysical Journal Letters. - : Institute of Physics (IOP). - 2041-8205 .- 2041-8213. ; 944:1
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Tidskriftsartikel (refereegranskat)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.
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| 5. |
- Meena, Ashish Kumar, et al.
(författare)
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Two Lensed Star Candidates at z ≃ 4.8 behind the Galaxy Cluster MACS J0647.7+7015
- 2023
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Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8205 .- 2041-8213. ; 944:1
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Tidskriftsartikel (refereegranskat)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.
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| 6. |
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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
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 945:2
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Tidskriftsartikel (refereegranskat)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.
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| 7. |
- Vanzella, Eros, et al.
(författare)
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JWST/NIRCam Probes Young Star Clusters in the Reionization Era Sunrise Arc
- 2023
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 945:1
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Tidskriftsartikel (refereegranskat)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.
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| 8. |
- Vikaeus, Anton, et al.
(författare)
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To be, or not to be : Balmer breaks in high-z galaxies with JWST
- 2024
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press. - 0035-8711 .- 1365-2966. ; 529:2, s. 1299-1307
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Tidskriftsartikel (refereegranskat)abstract
- Standard models of structure formation allow us to predict the cosmic timescales relevant for the onset of star formation and the assembly history of galaxies at high redshifts (z > 10). The strength of the Balmer break represents a well-known diagnostic of the age and star formation history of galaxies, which enables us to compare observations with contemporary simulations – thus shedding light on the predictive power of our current models of star formation in the early Universe. Here, we measure the Balmer break strength for 23 spectroscopically confirmed galaxies at redshifts 6 ≲ z ≲ 12 using public JWST NIRSpec data from the cycle 1 GO 1433 and GO 2282 programmes (PI Coe), as well as public spectroscopic data from the JWST Deep Extragalactic Survey (JADES). We find that the range of observed Balmer break strengths agree well with that of current simulations given our measurement uncertainties. No cases of anomalously strong Balmer breaks are detected, and therefore no severe departures from the predictions of contemporary models of star formation. However, there are indications of a number of outliers in the observed distribution which have weaker Balmer breaks than predicted by simulations.
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| 9. |
- Zackrisson, Erik, et al.
(författare)
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Bubble mapping with the Square Kilometre Array - I. Detecting galaxies with Euclid, JWST, WFIRST, and ELT within ionized bubbles in the intergalactic medium at z > 6
- 2020
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 493:1, s. 855-870
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Tidskriftsartikel (refereegranskat)abstract
- The Square Kilometre Array (SKA) is expected to provide the first tomographic observations of the neutral intergalactic medium at redshifts z > 6 and pinpoint the locations of individual ionized bubbles during early stages of cosmic reionization. In scenarios where star-forming galaxies provide most of the ionizing photons required for cosmic reionization, one expects the first ionized bubbles to be centred on overdensities of such galaxies. Here, we model the properties of galaxy populations within isolated, ionized bubbles that SKA-1 should be able to resolve at z approximate to 7-10, and explore the prospects for galaxy counts within such structures with various upcoming near-infrared telescopes. We find that, for the bubbles that are within reach of SKA-1 tomography, the bubble volume is closely tied to the number of ionizing photons that have escaped from the galaxies within. In the case of galaxy-dominated reionization, galaxies are expected to turn up above the spectroscopic detection threshold of JWST and ELT in even the smallest resolvable bubbles at z <= 10. The prospects of detecting galaxies within these structures in purely photometric surveys with Euclid, WFIRST, JWST, or ELT are also discussed. While spectroscopy is preferable towards the end of reionization to provide a robust sample of bubble members, multiband imaging may be a competitive option for bubbles at z approximate to 10, due to the very small number of line-of-sight interlopers expected at these redshifts.
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