分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: We examine the HI gas kinematics of galaxy pairs in two clusters and a group using Australian Square Kilometre Array Pathfinder (ASKAP) WALLABY pilot survey observations. We compare the HI properties of galaxy pair candidates in the Hydra I and Norma clusters, and the NGC 4636 group, with those of non-paired control galaxies selected in the same fields. We perform HI profile decomposition of the sample galaxies using a tool, {\sc baygaud} which allows us to de-blend a line-of-sight velocity profile with an optimal number of Gaussian components. We construct HI super-profiles of the sample galaxies via stacking of their line profiles after aligning the central velocities. We fit a double Gaussian model to the super-profiles and classify them as kinematically narrow and broad components with respect to their velocity dispersions. Additionally, we investigate the gravitational instability of HI gas disks of the sample galaxies using Toomre Q parameters and HI morphological disturbances. We investigate the effect of the cluster environment on the HI properties of galaxy pairs by dividing the cluster environment into three subcluster regions (i.e., outskirts, infalling and central regions). We find that the denser cluster environment (i.e., infalling and central regions) is likely to impact the HI gas properties of galaxies in a way of decreasing the amplitude of the kinematically narrow HI gas ($M_{\rm{narrow}}^{\rm{HI}}$/$M_{\rm{total}}^{\rm{HI}}$), and increasing the Toomre Q values of the infalling and central galaxies. This tendency is likely to be more enhanced for galaxy pairs in the cluster environment.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: We present the first JWST observations of the $z=4.11$ luminous radio galaxy TN J1338$-$1942, obtained as part of the "Prime Extragalactic Areas for Reionization and Lensing Science" (PEARLS) project. Our NIRCam observations, designed to probe the key rest-frame optical continuum and emission line features at this redshift, enable resolved spectral energy distribution modelling that incorporates both a range of stellar population assumptions and radiative shock models. With an estimated stellar mass of $\log_{10}(M/\text{M}_{\odot}) \sim 10.9$, TN J1338$-$1942 is confirmed to be one of the most massive galaxies known at this epoch. Our observations also reveal extremely high equivalent-width nebular emission coincident with the luminous AGN jets that is consistent with radiative shocks surrounded by extensive recent star-formation. We estimate the total star-formation rate (SFR) could be as high as $\sim1800\,\text{M}_{\odot}\,\text{yr}^{-1}$, with the SFR that we attribute to the jet induced burst conservatively $\gtrsim500\,\text{M}_{\odot}\,\text{yr}^{-1}$. The mass-weighted age of the star-formation, $t_{\text{mass}} <4$ Myr, is consistent with the likely age of the jets responsible for the triggered activity and significantly younger than that measured in the core of the host galaxy. The extreme scale of the potential jet-triggered star-formation activity indicates the potential importance of positive AGN feedback in the earliest stages of massive galaxy formation, with our observations also illustrating the extraordinary prospects for detailed studies of high-redshift galaxies with JWST.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: We give an overview and describe the rationale, methods, and first results from NIRCam images of the JWST "Prime Extragalactic Areas for Reionization and Lensing Science" ("PEARLS") project. PEARLS uses up to eight NIRCam filters to survey several prime extragalactic survey areas: two fields at the North Ecliptic Pole (NEP); seven gravitationally lensing clusters; two high redshift proto-clusters; and the iconic backlit VV 191 galaxy system to map its dust attenuation. PEARLS also includes NIRISS spectra for one of the NEP fields and NIRSpec spectra of two high-redshift quasars. The main goal of PEARLS is to study the epoch of galaxy assembly, AGN growth, and First Light. Five fields, the JWST NEP Time-Domain Field (TDF), IRAC Dark Field (IDF), and three lensing clusters, will be observed in up to four epochs over a year. The cadence and sensitivity of the imaging data are ideally suited to find faint variable objects such as weak AGN, high-redshift supernovae, and cluster caustic transits. Both NEP fields have sightlines through our Galaxy, providing significant numbers of very faint brown dwarfs whose proper motions can be studied. Observations from the first spoke in the NEP TDF are public. This paper presents our first PEARLS observations, their NIRCam data reduction and analysis, our first object catalogs, the 0.9-4.5 $\mu$m galaxy counts and Integrated Galaxy Light. We assess the JWST sky brightness in 13 NIRCam filters, yielding our first constraints to diffuse light at 0.9-4.5 {\mu}m. PEARLS is designed to be of lasting benefit to the community.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: We present an investigation into the first 500 Myr of galaxy evolution from the Cosmic Evolution Early Release Science (CEERS) survey. CEERS, one of 13 JWST ERS programs, targets galaxy formation from z~0.5 to z>10 using several imaging and spectroscopic modes. We make use of the first epoch of CEERS NIRCam imaging, spanning 35.5 sq. arcmin, to search for candidate galaxies at z>9. Following a detailed data reduction process implementing several custom steps to produce high-quality reduced images, we perform multi-band photometry across seven NIRCam broad and medium-band (and six Hubble broadband) filters focusing on robust colors and accurate total fluxes. We measure photometric redshifts and devise a robust set of selection criteria to identify a sample of 26 galaxy candidates at z~9-16. These objects are compact with a median half-light radius of ~0.5 kpc. We present an early estimate of the z~11 rest-frame ultraviolet (UV) luminosity function, finding that the number density of galaxies at M_UV ~ -20 appears to evolve very little from z~9 to z~11. We also find that the abundance (surface density [arcmin^-2]) of our candidates exceeds nearly all theoretical predictions. We explore potential implications, including that at z>10 star formation may be dominated by top-heavy initial mass functions, which would result in an increased ratio of UV light per unit halo mass, though a complete lack of dust attenuation and/or changing star-formation physics may also play a role. While spectroscopic confirmation of these sources is urgently required, our results suggest that the deeper views to come with JWST should yield prolific samples of ultra-high-redshift galaxies with which to further explore these conclusions.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: Lyman Break Galaxy (LBG) candidates at z>10 are rapidly being identified in JWST/NIRCam observations. Due to the (redshifted) break produced by neutral hydrogen absorption of rest-frame UV photons, these sources are expected to drop out in the bluer filters while being well detected in redder filters. However, here we show that dust-enshrouded star-forming galaxies at lower redshifts (z10 LBGs, representing potential contaminants in LBG candidate samples. First, we analyze CEERS-DSFG-1, a NIRCam dropout undetected in the F115W and F150W filters but detected at longer wavelengths. Combining the JWST data with (sub)millimeter constraints, including deep NOEMA interferometric observations, we show that this source is a dusty star-forming galaxy (DSFG) at z~5.1. We also present a tentative 2.6sigma SCUBA-2 detection at 850um around a recently identified z~16 LBG candidate in the same field and show that, if the emission is real and associated with this candidate, the available photometry is consistent with a z~5 dusty galaxy with strong nebular emission lines despite its blue near-IR colors. Further observations on this candidate are imperative to mitigate the low confidence of this tentative submillimeter emission and its positional uncertainty. Our analysis shows that robust (sub)millimeter detections of NIRCam dropout galaxies likely imply z=4-6 redshift solutions, where the observed near-IR break would be the result of a strong rest-frame optical Balmer break combined with high dust attenuation and strong nebular line emission, rather than the rest-frame UV Lyman break. This provides evidence that DSFGs may contaminate searches for ultra high-redshift LBG candidates from JWST observations.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: We report the results of James Webb Space Telescope/NIRCam observations of 19 (sub)millimeter (submm/mm) sources detected by the Atacama Large Millimeter Array (ALMA). The accurate ALMA positions allowed unambiguous identifications of their NIRCam counterparts. Taking gravitational lensing into account, these represent 16 distinct galaxies in three fields and constitute the largest sample of its kind to date. The counterparts' spectral energy distributions from rest-frame ultraviolet to near infrared provide photometric redshifts ($110^{10.5}$ Msol), which are similar to sub-millimeter galaxy (SMG) hosts studied previously. However, our sample is fainter in submm/mm than the classic SMG samples are, and our sources exhibit a wider range of properties. They have dust-embedded star-formation rates as low as 10 Msol yr$^{-1}$, and the sources populate both the star-forming main sequence and the quiescent categories. The deep NIRCam data allow us to study the rest-frame near-IR morphologies. Excluding two multiply imaged systems and one quasar, the majority of the remaining sources are disk-like and show either little or no disturbance. This suggests that secular growth is a potential route for the assembly of high-mass disk galaxies. While a few hosts have large disks, the majority have small disks (median half-mass radius of 1.6 kpc). At this time, it is unclear whether this is due to the prevalence of small disks at these redshifts or some unknown selection effects of deep ALMA observations. A larger sample of ALMA sources with NIRCam observations will be able to address this question.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: We perform a ground-based near-infrared spectroscopic survey using the Keck/MOSFIRE spectrograph to target Ly$\alpha$ emission at $7.0$4$\sigma$ level in eight $z>7$ galaxies, which include additional members of the known $z\sim7.7$ Ly$\alpha$-emitter (LAE) cluster (Tilvi et al. 2020). With the addition of these newly-discovered $z\sim7.7$ LAEs, this is currently the largest measured LAE cluster at $z>7$. The unusually-high Ly$\alpha$ detection rate at $z\sim7.7$ in this field suggests significantly stronger Ly$\alpha$ emission from the clustered LAEs than from the rest of our targets. We estimate the ionized bubble sizes around these LAEs and conclude that the LAEs are clustered within an extended ionized structure created by overlapping ionized bubbles which allow the easier escape of Ly$\alpha$ from galaxies. It is remarkable that the brightest object in the cluster has the lowest measured redshift of the Ly$\alpha$ line, being placed in front of the other LAEs in the line-of-sight direction. This suggests that we are witnessing the enhanced IGM transmission of Ly$\alpha$ from galaxies on the rear side of an ionized area. This could be a consequence of Ly$\alpha$ radiative transfer: Ly$\alpha$ close to the central velocity is substantially scattered by the IGM while Ly$\alpha$ from the rear-side galaxies is significantly redshifted to where it has a clear path.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: We present a comprehensive analysis of the evolution of the morphological and structural properties of a large sample of galaxies at z=3-9 using early JWST CEERS NIRCam observations. Our sample consists of 850 galaxies at z>3 detected in both CANDELS HST imaging and JWST CEERS NIRCam images to enable a comparison of HST and JWST morphologies. Our team conducted a set of visual classifications, with each galaxy in the sample classified by three different individuals. We also measure quantitative morphologies using the publicly available codes across all seven NIRCam filters. Using these measurements, we present the fraction of galaxies of each morphological type as a function of redshift. Overall, we find that galaxies at z>3 have a wide diversity of morphologies. Galaxies with disks make up a total of 60\% of galaxies at z=3 and this fraction drops to ~30% at z=6-9, while galaxies with spheroids make up ~30-40% across the whole redshift range and pure spheroids with no evidence for disks or irregular features make up ~20%. The fraction of galaxies with irregular features is roughly constant at all redshifts (~40-50%), while those that are purely irregular increases from ~12% to ~20% at z>4.5. We note that these are apparent fractions as many selection effects impact the visibility of morphological features at high redshift. The distributions of S\'ersic index, size, and axis ratios show significant differences between the morphological groups. Spheroid Only galaxies have a higher S\'ersic index, smaller size, and higher axis ratio than Disk/Irregular galaxies. Across all redshifts, smaller spheroid and disk galaxies tend to be rounder. Overall, these trends suggest that galaxies with established disks and spheroids exist across the full redshift range of this study and further work with large samples at higher redshift is needed to quantify when these features first formed.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: We present results from the Cosmic Evolution Early Release Survey (CEERS) on
the stellar-population parameters for 28 galaxies with redshifts $4
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: Galaxy morphology in atomic hydrogen (HI) and in the ultra-violet (UV) are closely linked. This has motivated their combined use to quantify morphology over the full H i disk for both H i and UV imaging. We apply galaxy morphometrics: Concentration, Asymmetry, Gini, M20 and Multimode-Intensity-Deviation statistics to the first moment-0 maps of the WALLABY survey of galaxies in the Hydra cluster center. Taking advantage of this new HI survey, we apply the same morphometrics over the full HI extent on archival GALEX FUV and NUV data to explore how well HI truncated, extended ultraviolet disk (XUV) and other morphological phenomena can be captured using pipeline WALLABY data products. Extended HI and UV disks can be identified relatively straightforward from their respective concentration. Combined with WALLABY HI, even the shallowest GALEX data is sufficient to identify XUV disks. Our second goal is to isolate galaxies undergoing ram-pressure stripping in the H i morphometric space. We employ four different machine learning techniques, a decision tree, a k-nearest neighbour, a support-vector machine, and a random forest. Up to 80% precision and recall are possible with the Random Forest giving the most robust results.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: Stellar bars are key drivers of secular evolution in galaxies and can be effectively studied using rest-frame near-infrared (NIR) images, which trace the underlying stellar mass and are less impacted by dust and star formation than rest-frame UV or optical images. We leverage the power of {\it{JWST}} CEERS NIRCam images to present the first quantitative identification and characterization of stellar bars at $z>1$ based on rest-frame NIR F444W images of high resolution (~1.3 kpc at z ~ 1-3). We identify stellar bars in these images using quantitative criteria based on ellipse fits. For this pilot study, we present six examples of robustly identified bars at $z>1$ with spectroscopic redshifts, including the two highest redshift bars at ~2.136 and 2.312 quantitatively identified and characterized to date. The stellar bars at $z$ ~ 1.1-2.3 presented in our study have projected semi-major axes of ~2.9-4.3 kpc and projected ellipticities of ~0.41-0.53 in the rest-frame NIR. The barred host galaxies have stellar masses ~ $ 1 \times 10^{10}$ to $2 \times 10^{11}$ $M_{\odot}$, star formation rates of ~ 21-295 $M_{\odot}$ yr$^{-1}$, and several have potential nearby companions. Our finding of bars at $z$ ~1.1-2.3 demonstrates the early onset of such instabilities and supports simulations where bars form early in massive dynamically cold disks. It also suggests that if these bars at lookback times of 8-10 Gyr survive out to present epochs, bar-driven secular processes may operate over a long time and have a significant impact on some galaxies by z ~ 0.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: We report the results of James Webb Space Telescope/NIRCam observations of 19 (sub)millimeter (submm/mm) sources detected by the Atacama Large Millimeter Array (ALMA). The accurate ALMA positions allowed unambiguous identifications of their NIRCam counterparts. Taking gravitational lensing into account, these represent 16 distinct galaxies in three fields and constitute the largest sample of its kind to date. The counterparts' spectral energy distributions from rest-frame ultraviolet to near infrared provide photometric redshifts ($110^{10.5}$ Msol), which are similar to sub-millimeter galaxy (SMG) hosts studied previously. However, our sample is fainter in submm/mm than the classic SMG samples are, and our sources exhibit a wider range of properties. They have dust-embedded star-formation rates as low as 10 Msol yr$^{-1}$, and the sources populate both the star-forming main sequence and the quiescent categories. The deep NIRCam data allow us to study the rest-frame near-IR morphologies. Excluding two multiply imaged systems and one quasar, the majority of the remaining sources are disk-like and show either little or no disturbance. This suggests that secular growth is a potential route for the assembly of high-mass disk galaxies. While a few hosts have large disks, the majority have small disks (median half-mass radius of 1.6 kpc). At this time, it is unclear whether this is due to the prevalence of small disks at these redshifts or some unknown selection effects of deep ALMA observations. A larger sample of ALMA sources with NIRCam observations will be able to address this question.