Galaxy formation and evolution

Abstract:

We present the ALMA-CRISTAL survey, an ALMA Cycle 8 Large Program designed to investigate the physical properties of star-forming galaxies at 4 ≲ z ≲ 6 through spatially resolved, multiwavelength observations. This survey targets 19 star-forming main-sequence galaxies selected from the ALPINE survey, using ALMA Band 7 observations to study [C  II ] 158 μm line emission and dust continuum, complemented by JWST/NIRCam and HST imaging to map stellar and UV emission. The CRISTAL sample expanded to 39 after including newly detected galaxies in the CRISTAL fields, archival data, and pilot study targets. The resulting dataset provides a detailed view of gas, dust, and stellar structures on kiloparsec scales at the end of the era of reionization. The survey reveals diverse morphologies and kinematics, including rotating disks, merging systems, [C  II ] emission tails from potential interactions, and clumpy star formation. Notably, the [C  II ] emission in many cases extends beyond the stellar light seen in HST and JWST imaging. Scientific highlights include CRISTAL-10, exhibiting an extreme [C  II ] deficit similar to Arp 220, and CRISTAL-13, where feedback from young star-forming clumps likely causes an offset between the stellar clumps and the peaks of [C  II ] emission. CRISTAL galaxies exhibit global [C  II ]/FIR ratios that decrease with increasing FIR luminosity, similar to trends seen in local galaxies but shifted to higher luminosities, likely due to their higher molecular gas content. CRISTAL galaxies also span a previously unexplored range of global FIR surface brightness at high-redshift, showing that high-redshift galaxies can have elevated [C  II ]/FIR ratios. These elevated ratios are likely influenced by factors such as lower-metallicity gas, the presence of significant extraplanar gas, and contributions from shock-excited gas.

Abstract:

The ALMA [C II] Resolved Ism in STar-forming gALaxies (CRISTAL) survey is a Cycle 8 ALMA Large Program that studies the cold- gas component of high-redshift galaxies. Its subarcsecond-resolution observations are key to distinguishing physical mechanisms that shaped galaxies during cosmic dawn. In this paper, we explore the morphology and kinematics of the cold gas, star-forming, and stellar components in the star-forming main-sequence galaxy CRISTAL-05/HZ3, at z = 5.54. Our analysis includes ALMA observations at a spatial resolution of 0.3″ (∼2 kpc) of the [C II] line. While CRISTAL-05 was previously classified as a single source, our observations reveal that the system is a close interacting pair that is surrounded by an extended component of carbon-enriched gas. This is imprinted in the disturbed elongated [C II] morphology and in the separation of the two components in the position-velocity diagram (∼100 km s −1 ). The central region is composed of two components, named C05-NW and C05-SE, and the former is the dominant component. A significant fraction of [C II] arises beyond the close pair up to 10 kpc, while the regions forming new massive stars and the stellar component seem compact (r [C II] ∼4 × r UV ), as traced by rest-frame UV and optical imaging obtained with the Hubble Space Telescope and the James Webb Space Telescope. Our kinematic model, constructed using the DYSMALpy software, yields a minor contribution of dark matter of C05-NW within a radius of ∼2 × R eff . Finally, we explore the resolved [C II] /far-IR ratios as a proxy for shock-heating produced by this merger. We argue that the extended [C II] emission is mainly caused by the merger of the galaxies, which could not be discerned with lower-resolution observations. Our work emphasizes the need for high-resolution observations to fully characterize the dynamic stages of infant galaxies and the physical mechanisms that drive the metal enrichment of the circumgalactic medium.

Abstract:

We study the evolution of the bar fraction in disk galaxies between 0.5 < z < 4.0 using multiband colored images from JWST Cosmic Evolution Early Release Science Survey (CEERS). These images were classified by citizen scientists in a new phase of the Galaxy Zoo (GZ) project called GZ CEERS. Citizen scientists were asked whether a strong or weak bar was visible in the host galaxy. After considering multiple corrections for observational biases, we find that the bar fraction decreases with redshift in our volume-limited sample (n = 398); from 25−4+6 % at 0.5 < z < 1.0 to 3−1+6 % at 3.0 < z < 4.0. However, we argue it is appropriate to interpret these fractions as lower limits. Disentangling real changes in the bar fraction from detection biases remains challenging. Nevertheless, we find a significant number of bars up to z = 2.5. This implies that disks are dynamically cool or baryon dominated, enabling them to host bars. This also suggests that bar-driven secular evolution likely plays an important role at higher redshifts. When we distinguish between strong and weak bars, we find that the weak bar fraction decreases with increasing redshift. In contrast, the strong bar fraction is constant between 0.5 < z < 2.5. This implies that the strong bars found in this work are robust long-lived structures, unless the rate of bar destruction is similar to the rate of bar formation. Finally, our results are consistent with disk instabilities being the dominant mode of bar formation at lower redshifts, while bar formation through interactions and mergers is more common at higher redshifts.

Abstract:

Abstract We present the first results of the JWST Emission Line Survey (JELS). Utilising the first NIRCam narrow-band imaging at 4.7μm, over 63 arcmin2 in the PRIMER/COSMOS field, we have identified 609 emission line galaxy candidates. From these, we robustly selected 35 Hα star-forming galaxies at z ∼ 6.1, with Hα star-formation rates ($\rm {SFR_{H\alpha }}$) of $\sim 0.9-15\ \rm {{\rm M}_{\odot } \ yr^{-1}}$. Combining our unique Hα sample with the exquisite panchromatic data in the field, we explored their physical properties and star-formation histories, and compared these to a broad-band selected sample at z ∼ 6 which has offered vital new insights into the nature of high-redshift galaxies. UV-continuum slopes (β) were considerably redder for our Hα sample (〈β〉 ∼ −1.92) compared to the broad-band sample (〈β〉 ∼ −2.35). This was not due to dust attenuation as our Hα sample was relatively dust-poor (median AV = 0.23); instead, we argue that the reddened slopes could be due to nebular continuum. We compared $\rm {SFR_{H\alpha }}$ and the UV-continuum-derived $\rm {SFR_{UV}}$ to SED-fitted measurements averaged over canonical timescales of 10 and 100 Myr ($\rm {SFR_{10}}$ and $\rm {SFR_{100}}$). We found an increase in recent SFR for our sample of Hα emitters, particularly at lower stellar masses ($<10^9 \ \rm {{\rm M}_{\odot }}$). We also found that $\rm {SFR_{H\alpha }}$ strongly traces SFR averaged over 10 Myr timescales, whereas the UV-continuum over-predicts SFR on 100 Myr timescales at low stellar masses. These results point to our Hα sample undergoing ‘bursty’ star formation. Our F356W z ∼ 6 sample showed a larger scatter in $\rm {SFR_{10}/SFR_{100}}$ across all stellar masses, which has highlighted how narrow-band photometric selections of Hα emitters are key to quantifying the burstiness of star-formation activity.