分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: We present the JWST Resolved Stellar Populations Early Release Science (ERS) science program. We obtained 27.5 hours of NIRCam and NIRISS imaging of three targets in the Local Group (Milky Way globular cluster M92, ultra-faint dwarf galaxy Draco II, star-forming dwarf galaxy WLM), which span factors of $\sim10^5$ in luminosity, $\sim10^4$ in distance, and $\sim10^5$ in surface brightness. We describe the survey strategy, scientific and technical goals, implementation details, present select NIRCam color-magnitude diagrams (CMDs), and validate the NIRCam exposure time calculator (ETC). Our CMDs are among the deepest in existence for each class of target. They touch the theoretical hydrogen burning limit in M92 ($<0.08$ $M_{\odot}$; SNR $\sim5$ at $m_{F090W}\sim28.2$; $M_{F090W}\sim+13.6$), include the lowest-mass stars observed outside the Milky Way in Draco II (0.09 $M_{\odot}$; SNR $=10$ at $m_{F090W}\sim29$; $M_{F090W}\sim+12.1$), and reach $\sim1.5$ magnitudes below the oldest main sequence turnoff in WLM (SNR $=10$ at $m_{F090W}\sim29.5$; $M_{F090W}\sim+4.6$). The PARSEC stellar models provide a good qualitative match to the NIRCam CMDs, though are $\sim0.05$ mag too blue compared to M92 F090W$-$F150W data. The NIRCam ETC (v2.0) matches the SNRs based on photon noise from DOLPHOT stellar photometry in uncrowded fields, but the ETC may not be accurate in more crowded fields, similar to what is known for HST. We release beta versions of DOLPHOT NIRCam and NIRISS modules to the community. Results from this ERS program will establish JWST as the premier instrument for resolved stellar populations studies for decades to come.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: We report on the discovery of two low-luminosity, broad-line AGN at $z>5$ identified using JWST NIRSpec spectroscopy from the CEERS Survey. We detect broad H$\alpha$ emission from both sources, with FWHM of $2038\pm286$ and $1807\pm207$ km s$^{-1}$, resulting in black hole (BH) masses that are 1-2 dex below that of existing samples of luminous quasars at $z>5$. The first source, CEERS 1670 at $z=5.242$, is 2-3 dex fainter than known quasars at similar redshifts and was previously identified as a candidate low-luminosity AGN based on its rest-frame optical SED. We measure a BH mass of $M_{\rm BH}=1.3\pm0.4\times 10^{7}~M_{\odot}$, confirming that this AGN is powered by the least-massive BH known in the universe at the end of cosmic reionization. The second source, CEERS 3210 at $z=5.624$, is inferred to be a heavily obscured, broad-line AGN caught in a transition phase between a dust-obscured starburst and an unobscured quasar. We estimate its BH mass to be $M_{\rm BH}\simeq 0.9-4.7 \times 10^{7}~M_{\odot}$, depending on the level of dust obscuration assumed. We derive host stellar masses, $M_\star$, allowing us to place constraints on the BH-galaxy mass relationship in the lowest mass range yet probed in the early universe. The $M_{\rm BH}/M_\star$ ratio for CEERS 1670, in particular, is consistent with or higher than the empirical relationship seen in massive galaxies at $z=0$. We examine the emission-line ratios of both sources and find that their location on the BPT and OHNO diagrams is consistent with model predictions for low-metallicity AGN with $Z/Z_\odot \simeq 0.2-0.4$. The spectroscopic identification of low-luminosity, broad-line AGN at $z>5$ with $M_{\rm BH}\simeq 10^{7}~M_{\odot}$ demonstrates the capability of JWST to push BH masses closer to the range predicted for the BH seed population and provides a unique opportunity to study the early stages of BH-galaxy assembly.
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 present the data release and data reduction process for the Epoch 1 NIRCam observations for the Cosmic Evolution Early Release Science Survey (CEERS). These data consist of NIRCam imaging in six broadband filters (F115W, F150W, F200W, F277W, F356W and F444W) and one medium band filter (F410M) over four pointings, obtained in parallel with primary CEERS MIRI observations (Yang et al. in prep). We reduced the NIRCam imaging with the JWST Calibration Pipeline, with custom modifications and reduction steps designed to address additional features and challenges with the data. Here we provide a detailed description of each step in our reduction and a discussion of future expected improvements. Our reduction process includes corrections for known pre-launch issues such as 1/f noise, as well as in-flight issues including snowballs, wisps, and astrometric alignment. Many of our custom reduction processes were first developed with pre-launch simulated NIRCam imaging over the full 10 CEERS NIRCam pointings. We present a description of the creation and reduction of this simulated dataset in the Appendix. We provide mosaics of the real images in a public release, as well as our reduction scripts with detailed explanations to allow users to reproduce our final data products. These represent one of the first official public datasets released from the Directors Discretionary Early Release Science (DD-ERS) program.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: We present ALMA Band 7 observations of a remarkably bright galaxy candidate at $z_{\rm phot}$=$16.7^{+1.9}_{-0.3}$ ($M_{\rm UV}$=$-21.6$), S5-z17-1, identified in JWST Early Release Observation data of Stephen's Quintet. We do not detect the dust continuum at 866 $\mu$m, ruling out the possibility that S5-z17-1 is a low-$z$ dusty starburst with a star-formation rate (SFR) of $\gtrsim 30\,M_{\odot}$ yr$^{-1}$. We detect a 5.1$\sigma$ line feature at $338.726\pm0.007$ GHz exactly coinciding with the JWST source position, with a 2% likelihood of the signal being spurious. The most likely line identification would be [OIII]52$\mu$m at $z=16.01$ or [CII]158$\mu$m at $z=4.61$, whose line luminosities do not violate the non-detection of the dust continuum in both cases. Together with three other $z\gtrsim$ 11-13 candidate galaxies recently observed with ALMA, we conduct a joint ALMA and JWST spectral energy distribution (SED) analysis and find that the high-$z$ solution at $z\sim$11-17 is favored in every candidate as a very blue (UV continuum slope of $\approx-2.3$) and luminous ($M_{\rm UV}$ $\approx$ [$-$24:$-$21]) system. Still, we find in some candidates that reasonable SED fits ($\Delta$ $\chi^{2}\lesssim4$) are reproduced by type-II quasar and/or quiescent galaxy templates with strong emission lines at $z\sim3$-5, where such populations predicted from their luminosity functions and EW([OIII]+H$\beta$) distributions are abundant in survey volumes used for the $z\sim$11-17 candidates. While these recent ALMA observation results have strengthened the likelihood of the high-$z$ solutions, lower-$z$ possibilities are not completely ruled out in some of the $z\sim$11-17 candidates.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: We perform a ground-based near-infrared spectroscopic survey using the Keck/MOSFIRE spectrograph to target Ly$\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: The new capabilities that JWST offers in the near- and mid-infrared (IR) are
used to investigate in unprecedented detail the nature of optical/near-IR
faint, mid-IR bright sources, HST-dark galaxies among them. We gather JWST data
from the CEERS survey in the EGS, jointly with HST data, and analyze spatially
resolved optical-to-mid-IR spectral energy distributions (SEDs) to estimate
both photometric redshifts in 2 dimensions and stellar populations properties
in a pixel-by-pixel basis. We select 138 galaxies with F150W-F356W>1.5 mag,
F356W100 Gyr^-1); (2) 18% are quiescent/dormant (i.e., subject
to reignition and rejuvenation) galaxies at 3
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: 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 present the mid-IR (MIR) morphologies for 70 star-forming galaxies (SFGs) at $0.210^{9}~M_\odot}$ using JWST MIRI observations from the Cosmic Evolution Early Release Science survey (CEERS). The MIRI bands span the MIR (7.7--21 $\mu$m), enabling us to measure the effective radii ($R_{\mathrm{eff}}$) and S\'{e}rsic indexes of these SFGs at rest-frame 6.2 and 7.7 $\mu$m, which contains strong emission from Polycyclic aromatic hydrocarbon (PAH) features, a well-established tracer of star formation in galaxies. We compare the PAH-band morphologies to those in rest-frame Near-UV (NUV) using HST ACS/F435W or ACS/F606W and optical/near-IR using HST WFC3/F160W imaging from UVCANDELS and CANDELS, where the NUV-band and F160W trace the profile of (unobscured) massive stars and the stellar continuum, respectively. The $R_{\mathrm{eff}}$ of galaxies in the PAH-band are slightly smaller ($\sim$10) than those in F160W for more massive galaxies with $\mathrm{M_*\gtrsim10^{9.5}~M_\odot}$ at $z\leq1.2$ and with $\mathrm{M_*\gtrsim10^{10}~M_\odot}$ at $z\geq1.2$, but the PAH-band and F160W have a similar fractions of light within 1 kpc. In contrast, the $R_{\rm{eff}}$ of galaxies in the NUV-band are larger, with lower fractions of light within 1 kpc compared to the F160W for galaxies at $z\leq1.2$. Using the MIRI data to estimate the surface density of the IR-based SFR, we find the correlation between the IR-based SFR surface density and stellar mass has a steeper slope than that of the UV-based surface density and stellar mass, suggesting galaxies with higher stellar masses having increasing amounts of obscured fraction of star formation in their inner regions. This paper demonstrates how the high-angular resolution data from JWST/MIRI can reveal new information about the morphology of obscured-star formation.