分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The recent searches for z>11 galaxies using the James Webb Space Telescope have resulted in an unexpectedly high number of candidate objects, which imply at least an order of magnitude higher number density of $z>11$ galaxies than the previously favored predictions. A question has risen whether there are some new types of contaminants among these candidates. The candidate sample of Yan et al. (2023a), totalling 87 dropouts, is the largest one, and we notice that a number of these candidates are point-like. We hypothesize that the point-source dropouts could be supernovae at high redshifts. Further investigation shows that most of their spectral energy distributions indeed can be explained by supernovae at various redshifts from z ~ 1--15, which lends support to this hypothesis. Attributing such point-source dropouts to supernova contamination cannot eliminate the tension, however, because they only account for ~10% of the Yan et al.'s sample. On the other hand, the discovery of "contaminant" supernovae at $z>3$ will have a series of important implications. Ironically, the existence of supernovae at $z>10$ would still imply that the previously favored picture of early galaxy formation severely underestimates the global star formation rate density such redshifts. Multiple-epoch JWST imaging will be the simplest and yet the most efficient way to further test this hypothesis.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Haojing Yan
Seth H. Cohen
Rogier A. Windhorst
Rolf A. Jansen
Zhiyuan Ma
John F. Beacom
Cheng Cheng
Jia-Sheng Huang
Norman A. Grogin
S. P. Willner
Min Yun
Heidi B. Hammel
Stefanie N. Milam
Christopher J. Conselice
Simon P. Driver
Brenda Frye
Madeline A. Marshall
Anton Koekemoer
Christopher N. A. Willmer
Aaron Robotham
摘要： Using the first epoch of four-band NIRCam observations obtained by the James Webb Space Telescope (JWST) Prime Extragalactic Areas for Reionization and Lensing Science Program in the Spitzer IRAC Dark Field, we search for F150W and F200W dropouts. In 14.2 arcmin^2, we have found eight F150W dropouts and eight F200W dropouts, all brighter than 27.5 mag (the brightest being ~24 mag) in the band to the red side of the break. As they are detected in multiple bands, these must be real objects. Their nature, however, is unclear, and characterizing their properties is important for realizing the full potential of JWST. If the observed color decrements are due to the Lyman break, these objects should be at z >~ 11.7 and z >~ 15.4, respectively. The color diagnostics show that at least four F150W dropouts are far away from the usual contaminators encountered in dropout searches (red galaxies at much lower redshifts or brown dwarf stars). While the diagnostics of the F200W dropouts are less certain due to the limited number of passbands, at least one of them is likely not a known type of contaminant, and the rest are consistent with either high-redshift galaxies with evolved stellar populations or old galaxies at z ~ 3 to 8. If a significant fraction of our dropouts are indeed at z ~ 12, we have to face the severe problem of explaining their high luminosities and number densities. Spectroscopic identifications of such objects are urgently needed.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Cheng Cheng
Haojing Yan
Jia-Sheng Huang
Christopher N. A. Willmer
Zhiyuan Ma
Gustavo Orellana-González
摘要： Using the 0.9--4.4~$\mu$m imaging data from the James Webb Space Telescope (JWST) Early Release Observation in the SMACS J0723.3-7327 galaxy cluster field, we discuss the properties of three submillimeter galaxies (SMGs) detected by the Atacama Large Millimeter Array. These sources are magnified by 1.4--2.1$\times$due to gravitational lensing. This is the first time that SMG host galaxies are resolved in the rest-frame near-infrared (NIR). One source was previous undetected by HST, while the remaining two are disk galaxies with S\'ersic indices of $\sim 0.9$ and star formation rates on or just below the star formation "main sequence". Their submillimeter emission originates from the inner parts of the hosts, suggesting that their dust contents are concentrated towards the center. The host half-light radii measured in the rest-frame NIR are $\sim$1.5$\times$ smaller than those measured in the rest-frame optical, consistent with a concentrated dust distribution. The more severe extinction that optical light suffers towards the center makes it seemingly less concentrated. Therefore, we expect that the optically-based determination of the stellar mass distribution within host galaxies could still be severely biased by dust. Interestingly, these two disk galaxies are dramatically different in their outer regions, with one being star forming and the other being quiescent. Upcoming JWST observations of statistically significant samples of SMGs will allow us to understand the correlation between the dusty star forming regions and their hosts.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The recent searches for z>11 galaxies using the James Webb Space Telescope have resulted in an unexpectedly high number of candidate objects, which imply at least an order of magnitude higher number density of $z>11$ galaxies than the previously favored predictions. A question has risen whether there are some new types of contaminants among these candidates. The candidate sample of Yan et al. (2023a), totalling 87 dropouts, is the largest one, and we notice that a number of these candidates are point-like. We hypothesize that the point-source dropouts could be supernovae at high redshifts. Further investigation shows that most of their spectral energy distributions indeed can be explained by supernovae at various redshifts from z ~ 1--15, which lends support to this hypothesis. Attributing such point-source dropouts to supernova contamination cannot eliminate the tension, however, because they only account for ~10% of the Yan et al.'s sample. On the other hand, the discovery of "contaminant" supernovae at $z>3$ will have a series of important implications. Ironically, the existence of supernovae at $z>10$ would still imply that the previously favored picture of early galaxy formation severely underestimates the global star formation rate density such redshifts. Multiple-epoch JWST imaging will be the simplest and yet the most efficient way to further test this hypothesis.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Rogier A. Windhorst
Seth H. Cohen
Rolf A. Jansen
Jake Summers
Scott Tompkins
Christopher J. Conselice
Simon P. Driver
Haojing Yan
Dan Coe
Brenda Frye
Norman Grogin
Anton Koekemoer
Madeline A. Marshall
Rosalia O'Brien
Nor Pirzkal
Aaron Robotham
Russell E. Ryan,
Christopher N. A. Willmer
Timothy Carleton
Jose M. Diego
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
Cheng Cheng
Jia-Sheng Huang
Ian Smail
Haojing Yan
Seth H. Cohen
Rolf A. Jansen
Rogier A. Windhorst
Zhiyuan Ma
Anton Koekemoer
Christopher N. A. Willmer
S. P. Willner
Jose M. Diego
Brenda Frye
Christopher J. Conselice
Leonardo Ferreira
Andreea Petric
Min Yun
Hansung B. Gim
Maria del Carmen Polletta
Kenneth J. Duncan
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
Cheng Cheng
Jia-Sheng Huang
Ian Smail
Haojing Yan
Seth H. Cohen
Rolf A. Jansen
Rogier A. Windhorst
Zhiyuan Ma
Anton Koekemoer
Christopher N. A. Willmer
S. P. Willner
Jose M. Diego
Brenda Frye
Christopher J. Conselice
Leonardo Ferreira
Andreea Petric
Min Yun
Hansung B. Gim
Maria del Carmen Polletta
Kenneth J. Duncan
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 present an analysis of the optical-to-near-IR counterparts of a sample of candidate dusty starbursts at z > 6. These objects were pre-selected based on the rising trend of their far-infrared-to-sub-millimeter spectral energy distributions and the fact that they are radio-weak. Their precise positions are available through millimeter and/or radio interferometry, which enable us to search for their counterparts in the deep optical-to-near-IR images. The sample include five z > 6 candidates. Three of them have their counterparts identified, one is still invisible in the deepest images, and one is a known galaxy at z = 5.667 that is completely blocked by a foreground galaxy. The three with counterparts identified are analyzed using population systhesis model, and they have photometric redshift solutions ranging from 7.5 to 9.0. Assuming that they are indeed at these redshifts and that they are not gravitationally lensed, their total IR luminosities are 10^{13.8-14.1} L_sun and the inferred star formation rates are 6.3--13 x 10^3 M_sun/yr. The existence of dusty starbursts at such redshifts would imply that the universe must be forming stars intensely very early in time in at least some galaxies, otherwise there would not be enough dust to produce the descendants observed at these redshifts. The inferred host galaxy stellar masses of these three objects, which are at >~ 10^{11} M_sun (if not affected by gravitational lensing), present a difficulty in explanation unless we are willing to accept that their progenitors either kept forming stars at a rate of >~ 10^3 M_sun/yr or were formed through intense instantaneous bursts. Spectroscopic confirmation of such objects will be imperative.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： On July 13, 2022, NASA released to the whole world the data obtained by the James Webb Space Telescope (JWST) Early Release Observations (ERO). These are the first set of science-grade data from this long-awaited facility, marking the beginning of a new era in astronomy. In the study of the early universe, JWST will allow us to push far beyond z ~ 11, the redshift boundary previously imposed by the 1.7 um red cut-off of the Hubble Space Telescope (HST). In contrast, JWST's NIRCam reaches 5 um. Among the JWST ERO targets there is a nearby galaxy cluster SMACS 0723-73, which is a massive cluster and has been long recognized as a potential "cosmic telescope" in amplifying background galaxies. The ERO six-band NIRCam observations on this target have covered an additional flanking field not boosted by gravitational lensing, which also sees far beyond HST. Here we report the result from our search of candidate objects at z > 11 using these ERO data. In total, there are 87 such objects identified by using the standard "dropout" technique. These objects are all detected in multiple bands and therefore cannot be spurious. For most of them, their multi-band colors are inconsistent with known types of contaminants. If the detected dropout signature is interpreted as the expected Lyman-break, it implies that these objects are at z ~ 11--20. The large number of such candidate objects at such high redshifts is not expected from the previously favored predictions and demands further investigations. JWST spectroscopy on such objects will be critical.
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