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This paper uses an alternative way to measure the star formation rate SFR vs stellar mass M* (star-forming sequence - SFS) at cosmic noon by using nearly dust-insensitive Pa-alpha emission line measurements (for SFR) and rest-frame H-band imaging (for stellar mass). They use a sample of 609 galaxies using the NIRCam/grism from the FRESCO survey. The main finding is that above log M* ~ 9.5 M_\odot their recovered SFS are consistent with previous studies but with better agreement with the estimates of SFR using the PROSPECTOR code. They point out the critical need to properly distinguish between quiescent and star-forming galaxies when putting constraints on the scaling relation and the various limitations of current work in the field such as the dust attenuation laws and the SFH in the SED fitting methods.

The paper presents JWST/NIRSpec IFU observations of the sub-millimeter galaxy GN20, targeting rest-frame optical emission. Combined spectral analysis and dynamical modelling reveal an asymmetric and clumpy morphology of Hα line emission, whose large-scale kinematics is compatible with a turbulent (σ~90 km/s), rotating disk (vrot ~ 500 km/s), consistently with previous studies on molecular and ionised gas kinematics. Also, the authors find clear evidence for non-circular motions in Hα kinematics, possibly due to external perturbations, accretion or radial flows. In the central region, broad line emission (FWHM~1000-2000 km/s) in Hα+[NII] line multiple points to either fast AGN-driven winds or AGN broad-line region emission. The presence of an AGN in GN20 is also supported by the high values of [NII]/ Hα > 0.4 and EW(H) > 6 Å largely observed across the galaxy.

This paper presents the study on the evolution of galaxy SFR and ΣSFR from redshift z ∼ 4 to z ∼ 10, using a statistical sample of 230 galaxies observed with JWST in the GLASS and CEERS surveys.

They derive the ΣSFR 'Main Sequence' for the first time at z > 4. They also find:

• ΣSFR mildly increases in the redshift range studied (see fig below), consistent with predictions from various semi-analytic models of galaxy evolution

• The star-forming 'Main Sequence' relation persists up to redshift ∼ 10, with a consistent best-fit slope compared to lower redshifts.

• The ΣSFR 'Main Sequence' at z > 4 show a very mild increase with stellar mass, with normalisation about ∼ 2.5 dex higher compared to the local Universe.

• ΣSFR is tightly related to ionising source properties, as indicated by the O32 index

• Correlations of ΣSFR and sSFR with the escape fraction are found, with slopes in agreement with low-redshift observations and models

• Outflow signatures in Hα and [O III] λ5007Å lines are detected in ∼ 20% of galaxies at z < 6

• Positive correlations between A_v and ΣSFR, and flat trends with sSFR, suggest no evidence of a drop in AV in extremely star-forming galaxies

This paper:

• Introduces a method to estimate stellar half-mass radii for galaxies at 0.5 < z < 2.5, utilising integrated UV-to-midIR photometric data.
• Validates the method by comparing their estimates with measurements from JWST/NIRCam imaging for a subset of CEERS galaxies, showing excellent agreement with small systematic offsets and scatter within the error budget.
• Examines the effect of projection using a deprojection technique that considers the shape distribution of galaxies, their dependencies on stellar mass and redshift, and concludes that deprojection has little impact on the size-mass distribution.
• Reveals that the size-mass distribution of galaxies at 0.5 < z < 1.5 is less steep in the rest-frame optical than previously believed, primarily due to the influence of massive star-forming galaxies.
• Offers a straightforward conversion from light-to-stellar mass weighted sizes, making it valuable for galaxies lacking spatially resolved near-IR imaging or at high z.
• Acknowledges uncertainties in small galaxies, challenging due to limited understanding of the near-IR PSF of NIRCam.

Zhang et al look at 61 galaxies between z=5.4 and 8.9, both using NIRSpec spectroscopy and NIRCam imaging, to study the outflow properties in their sample. They make a study of both spatially extended [OIII] emission in the imaging (5/61) and broad component in the emission line, indicating the presence of fast winds (5/30); including one galaxy that has both spatially extended emission and a broad component in the spectra. They compute the ratio of the wind velocity over the escape velocity of the galaxies' halo, and find that none of the detected outflows have velocities high enough to eject gas outside the gravitational well of the halo. They conjecture that they are witnessing the different phases of a star forming outflow event (as shown in the figure, where in the beginning outflows can only be seen in the spectra, then an extended emission is observed, and finally it falls back into the galaxy). They also compare their outflow incidence in the extended emission at high redshift to local studies, and find an increase in the incidence broadly consistent with the increase in major merger rate; but fail to observe a similar increase in incidence with the "spectral" outflows (Figure 11).

spatially resolved SED fitting in five 5<z<9 galaxies with spectroscopic redshift from NIRSpec and photometric coverage from NIRCam. Clear gradients in color maps and most physical params. Bursty SF happens in on small scales which dominate the integrated light. Integrated measurement give young ages, lower stellar masses (0.5 - 1 dex). implications in the shape and evolution of stellar mass function. Extrended process of galaxy formation hidden behind the light of most recently formed stars.

Metallicity based on strong emission lines measurements

66 low stellar mass (log M/M ~ 8.5) galaxies at 3 < z < 10, observed with JWST/NIRSpec as part of the JADES programme in its deep GOODS-S tier” MSA

“shallower slope at the lowmass-end of the mass-metallicity relation (MZR), with 12 + log(O/H) = (7.88±0.03) + (0.17±0.04) log(M?/108M ), in good agreement with the MZR probed by local analogues of high-redshift systems like ‘green pea’ and ‘blueberry’ galaxies.”

lower normalisation compared to low z galaxies, and less marked compared to mosdef z~3 galaxies.

“indications of a flattening of the slope of the lowmass end of the MZR with redshift,”

“Interestingly, the slope inferred at z = 6 − 10 is consistent with zero within ∼ 1σ, suggesting that the mass-metallicity relation might be in its initial build-up phase and not yet fully in place at these epochs.” but z bin is sparsely populated and might be selection biases.

Comparison with simulations

“most simulations appear to reasonably reproduce the normalisation of the relation at M?≈ 108−9, though underpredicting the abundances observed at log(M*/M )<8, with the theoretical MZRs characterised by steeper slopes than inferred from our sample”

“inferred MZR slopes with those predicted by (semi-)analytical chemical evolution models”: slope matched by models including SN-driven wind feedback, momentum driven winds at low masses, energy driven at high masses

“scenario in which the dominant feedback mechanism in galaxies changes in different mass regimes, producing a shallower MZR slope at low M*

Larger scatter at high  z indicative of the stocasticity in SF and ISM enrichment process in these early phases of the galaxy formation.

FMR = fundamental metallicity relation

“On average, the JWST galaxy sample is characterised by a reasonable agreement (within the measurement uncertainites) with the predictions of the local FMR up to z∼ 6, despite a non negligible number of galaxies significantly offset below the relation at ≥ 2 − 3σ. However, we identify a trend with increasing redshift in which galaxies are seen to sit preferentially below the FMR predictions, with in particular sources at z > 6 that are significantly less enriched than their M?and SFR would predict were they local galaxies.”

1)“it might reveal prominent accretion of pristine gas at high-redshift, happening on timescales shorter than the gas depletion, star-formation, ISM enrichment and mixing timescales compared to lower redshift galaxies, increasing the gas reservoir and diluting the galaxy metal content at fixed M? and SFR”

2) “the efficiency of metal removals could also be enhanced, such that the metal loading factor of outflows is higher at fixed SFR than the one required to reproduce the observed FMR at lower redshifts”

spectroscopic study of a rare bright galaxy at z=9.3 with Mstar = 2.5x10^9 forming 25Msun/yr and with metallicity 1/10 solar

“The system has a morphology typically associated to two interacting galaxies, with a two-component main clump of very young stars (age less than 10 million years) surrounded by an extended stellar population (130 ± 20 million years old,”

[OII] reveals high density of ISM and high ionisation.

Evidence of absorption features indicating that Lyalpha emission is samped by interstellar and circumgalactic medium.
Efficient build up of metals after the big bang in mergers.

“the 4.4μm sizes of ∼1000 galaxies with log M∗/M ≥ 9 and 1.0 ≤ z ≤ 2.5 from public CEERS imaging in the EGS deep field.” = 1.6um rest, compared to sizes measured at 1.5um (5500 AA rest)

“We find that, on average, galaxy half-light radii are ∼ 9% smaller at 4.4μm than 1.5μm in this sample.” difference is stronger at higher stellar masses and redder colors. Meaning that galaxy structures were already complex 8-10 Gyr ago. Similar results from HST using M/L from stellar pop models but this is model independent.

“Our results indicate that galaxy mass profiles are significantly more compact than their rest-frame optical light profiles at cosmic noon, and demonstrate that spatial variations in age and attenuation are important, particularly for massive galaxies.” May be due to dust: centers more obscured than outskirts. Or older stellar ages.

“New JWST multi-band infrared imaging, along with a legacy of UV-optical imaging from HST, will allow us to extend spatially-resolved stellar population fitting methodologies to quantify age and dust gradients in galaxies at cosmic noon, and to place strong constraints on their underlying stellar mass distributions”

Halo mass of 3.3x10^11Msun, also progenitor of coma-like cluster.

JWST follow-up observations of an ex- tremely faint, highly magnified Lyα arclet, originally identified at z = 6.639 with HFF and VLT/MUSE deep observations, as a possible region hosting extremely metal-poor stars (Vanzella et al. 2020). 

JWST/NIRSpec IFU observations confirm the redshift of the underlying forming system, z = 6.639. 

No significant stellar counterpart is detected in the stacked JWST/NIRCam, NIRISS, and Hubble images, down to a UV magnitude m2000 ≃ 30.4 at 2σ level, corresponding to an in- trinsic magnitude m2000 > 35.8 (or fainter than M2000 = −11). Such a low luminosity implies a stellar mass ≲ 104 M⊙, assum- ing no dust extinction and an instantaneous burst scenario.

The deficiency of metal lines of LAP1 implies an extremely low metallicity, 12+log(O/H) < 6.3 (Z < 0.004Z⊙), approaching the properties expected for a pristine star-forming region. This is the most metal poor star-forming region currently known in the reionization era and a promising site that may host isolated, pristine stars.

EW to understand the conditions of the ISM and the nature of the underlying stellar pop.  Identify easily galaxies with strong emission lines or weak stellar continua, which is characteristic of galaxies with SF burst with a young stellar pop. O/B type stars power nebular lines.

“observe rest-optical emission lines out to z ∼ 3.4, to a depth and with a spatial resolution higher than ever before (Hα to z < 2.4; [Oiii]+Hβ to z < 3.4)”

“[Oiii]λ5007 equivalent width (EW) distribution for a sample of 76 1 < z < 3.4 SFGs” with zspec from previous studies (then in future expand to other objects). EW independent of lensing magnification.

“abundance fraction of extreme emission line galaxies with EW> 750 ̊A in our sample to be 12%” SF above this threshold produces ionising photons with higher efficiency and potential for igh escape fracts. very young stellar pops.
12% > than 3.8% measured at z~2 with HST, but biases in samples.

“correlation between the measured Hβ and [Oiii]λ5007 EWs, supporting that the high [Oiii]λ5007 EW objects require massive stars in young stellar populations to generate the high energy photons needed to doubly ionise oxygen.”

“objects up to 2 mag fainter in the near-infrared than previous WFSS studies with the Hubble Space Telescope.” higher sensitivity provides higher precision, unlock 2.4<z<3.4 [OIII] observations previously unobtainable with HST.h

“first demonstration of the capabilities of JWST /NIRISS for studying rest-optical emission lines in high-redshift SFGs.”

“electron densities ne in the inter-stellar medium (ISM) of 14 star-forming galaxies at z = 4−9 observed by the JWST/NIRSpec GLASS, ERO, and CEERS programs.” fluxes calibrated from PN data.

“ne & 300 cm−3 significantly higher than those of low-z galaxies at a given stellar mass, star-formation rate (SFR), and specific SFR.”

“ne ∝ (1+z)p with p ∼ 1 − 2. The p ∼ 1 − 2 evolutionary relation can be explained by a combination of the compact morphology and the reduction of ne due to the high electron temperature of the high-z metal poor nebulae.”

“Beyond z & 4, ne values had not been investigated due to the lack of high-sensitivity near-infrared spectrographs before the arrival of James Webb Space Telescope (JWST),”

ne probes the physical state of the ISM. Study evolution for similar ionisation regions (OII and SII), control for M* and SFR.

“These results suggest that ne values are irrespective of M∗, SFR, or sSFR at 0 . z . 3.”

“higher than those of the lower-z galaxies at a given M∗ and SFR. We emphasize that the median ne values of the JWST galaxies are still higher than those of the galaxies with similar sSFRs to the JWST galaxies.”