分类： 天文学 >> 天文学 提交时间： 2023-02-19
Yunjing Wu
Zheng Cai
Fengwu Sun
Fuyan Bian
Xiaojing Lin
Zihao Li
Mingyu Li
Franz E. Bauer
Eiichi Egami
Xiaohui Fan
Jorge González-López
Jianan Li
Feige Wang
Jinyi Yang
Shiwu Zhang
Siwei Zou
摘要： Spiral arms serve crucial purposes in star formation and galaxy evolution. In this paper, we report the identification of A2744-DSG-$z3$, a dusty, multiarm spiral galaxy at $z=3.059$ using the James Webb Space Telescope (JWST) NIRISS imaging and grism spectroscopy. A2744-DSG-$z3$ was discovered as a gravitationally lensed sub-millimeter galaxy with ALMA. This is the most distant stellar spiral structure seen thus far, consistent with cosmological simulations which suggest $z\approx3$ as the epoch when spirals emerge. Thanks to the gravitational lensing and excellent spatial resolution of JWST, the spiral arms are resolved with a spatial resolution of $\approx290$\,pc. Based on SED fitting, the spiral galaxy has a de-lensed star formation rate of $85\pm30 \ M_{\odot}$ yr$^{-1}$, and a stellar mass of $\approx10^{10.6}M_{\odot}$, indicating that A2744-DSG-$z3$ is a main-sequence galaxy. After fitting the spiral arms, we find a stellar effective radius ($R_{e, \rm{star}}$) of $5.0\pm1.5$ kpc. Combing with ALMA measurements, we find that the effective radii ratio between dust and stars is $\approx0.4$, similar to {those} of massive SFGs at $z\sim2$, indicating a compact dusty core in A2744-DSG-$z3$. Moreover, this galaxy appears to be living in a group environment: including A2744-DSG-$z3$, at least three galaxies at $z=3.05 - 3.06$ {are} spectroscopically confirmed by JWST/NIRISS and ALMA, residing within a lensing-corrected projected scale of $\approx 70$ kpc. This, along with the asymmetric brightness profile, further suggests that the spiral arms may be triggered by minor merger events at $z\gtrsim3$.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： We present a study of seven spectroscopically confirmed (Ly$\alpha$ emitting) galaxies at redshift $z\simeq6$ using the $JWST$/NIRCam imaging data. These galaxies, with a wide range of Ly$\alpha$ luminosities, were recently observed in a series of NIRCam broad- and medium-bands. We constrain the rest-frame UV/optical continua and measure the H$\alpha$ line emission of the galaxies using the combination of the $JWST$/NIRCam and archival $HST$/WFC3 infrared photometry. We further estimate their escape fractions of Ly$\alpha$ photons ($f_{\rm esc}^{\rm Ly\alpha}$) and the production efficiency of ionizing photons ($\xi_{\rm ion}$). Among the sample, 6/7 galaxies have Ly$\alpha$ escape fractions of ${\lesssim}10\%$, which might be the status for most of star-forming galaxies at $z\simeq6$. One UV-faint Ly$\alpha$ galaxy with an extremely blue UV slope owns a large value of $f_{\rm esc}^{\rm Ly\alpha}$ reaching ${\simeq}50\%$. These galaxies spread a broad range of $\xi_{\rm ion}$ over log$_{10}$ $\xi_{\rm ion, 0}$ (Hz erg$^{-1}$) $\sim25.0-26.5$. We find that UV-fainter galaxies with bluer UV continuum slopes likely have higher escape fractions of Ly$\alpha$ photons. We also find that galaxies with higher Ly$\alpha$ line emission tend to produce ionizing photons more efficiently. The most Ly$\alpha$-luminous galaxy in the sample has a very high $\xi_{\rm ion, 0}$ of log$_{10}$ $\xi_{\rm ion, 0}$ (Hz erg$^{-1}$) $>26$. Our results support that Ly$\alpha$ galaxies may have served as an important contributor to the cosmic reionization. Blue and bright Ly$\alpha$ galaxies are excellent targets for $JWST$ follow-up spectroscopic observations.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Mingyu Li
Zheng Cai
Fuyan Bian
Xiaojing Lin
Zihao Li
Yunjing Wu
Fengwu Sun
Shiwu Zhang
Siwei Zou
Xiaohui Fan
Eiichi Egami
Stephane Charlot
Gustavo Bruzual
Jacopo Chevallard
摘要： We present the mass-metallicity relation (MZR) at $z=2-3$ in the stellar mass range of $M_\star\approx 10^{6.5}-10^{9.5}M_\odot$ using 55 dwarf galaxies in the Abell 2744 and SMACS J0723-3732 galaxy cluster fields. These dwarf galaxies are identified and confirmed by deep JWST/NIRISS imaging and slitless grism spectroscopic observations. Taking advantage of the gravitational lensing effect, we extend the previous MZR relation at $z=2-3$ to a much lower mass regime by more than 2.5 orders of magnitude compared with previous studies. We find that the MZR has a shallower slope at the low-mass end ($M_\star10^{9}M_\odot$), with a slope turnover point at around the stellar mass of $10^9 M_\odot$. This implies that dominating feedback processes in dwarf galaxies may be different from that in galaxies with higher mass. From $z=3$ to $z=2$, the metallicity of the dwarf galaxies is enhanced by $\approx0.1$ dex for a given stellar mass, consistent with the mild evolution found in galaxies with higher mass. Further, we confirm the existence of a 3D relation between the gas-phase metallicity, stellar mass, and star formation rate, i.e., fundamental metallicity relation (FMR), in dwarf galaxies at $z=2-3$. Our derived FMR, which has no significant redshift evolution, can be used as a benchmark to understand the origin of the anti-correlation between SFR and metallicity of dwarf galaxies in the high-redshift Universe.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： We present a study of seven spectroscopically confirmed (Ly$\alpha$ emitting) galaxies at redshift $z\simeq6$ using the $JWST$/NIRCam imaging data. These galaxies, with a wide range of Ly$\alpha$ luminosities, were recently observed in a series of NIRCam broad- and medium-bands. We constrain the rest-frame UV/optical continua and measure the H$\alpha$ line emission of the galaxies using the combination of the $JWST$/NIRCam and archival $HST$/WFC3 infrared photometry. We further estimate their escape fractions of Ly$\alpha$ photons ($f_{\rm esc}^{\rm Ly\alpha}$) and the production efficiency of ionizing photons ($\xi_{\rm ion}$). Among the sample, 6/7 galaxies have Ly$\alpha$ escape fractions of ${\lesssim}10\%$, which might be the status for most of star-forming galaxies at $z\simeq6$. One UV-faint Ly$\alpha$ galaxy with an extremely blue UV slope owns a large value of $f_{\rm esc}^{\rm Ly\alpha}$ reaching ${\simeq}50\%$. These galaxies spread a broad range of $\xi_{\rm ion}$ over log$_{10}$ $\xi_{\rm ion, 0}$ (Hz erg$^{-1}$) $\sim25.0-26.5$. We find that UV-fainter galaxies with bluer UV continuum slopes likely have higher escape fractions of Ly$\alpha$ photons. We also find that galaxies with higher Ly$\alpha$ line emission tend to produce ionizing photons more efficiently. The most Ly$\alpha$-luminous galaxy in the sample has a very high $\xi_{\rm ion, 0}$ of log$_{10}$ $\xi_{\rm ion, 0}$ (Hz erg$^{-1}$) $>26$. Our results support that Ly$\alpha$ galaxies may have served as an important contributor to the cosmic reionization. Blue and bright Ly$\alpha$ galaxies are excellent targets for $JWST$ follow-up spectroscopic observations.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Yunjing Wu
Zheng Cai
Fengwu Sun
Fuyan Bian
Xiaojing Lin
Zihao Li
Mingyu Li
Franz E. Bauer
Eiichi Egami
Xiaohui Fan
Jorge González-López
Jianan Li
Feige Wang
Jinyi Yang
Shiwu Zhang
Siwei Zou
摘要： Spiral arms serve crucial purposes in star formation and galaxy evolution. In this paper, we report the identification of A2744-DSG-$z3$, a dusty, multiarm spiral galaxy at $z=3.059$ using the James Webb Space Telescope (JWST) NIRISS imaging and grism spectroscopy. A2744-DSG-$z3$ was discovered as a gravitationally lensed sub-millimeter galaxy with ALMA. This is the most distant stellar spiral structure seen thus far, consistent with cosmological simulations which suggest $z\approx3$ as the epoch when spirals emerge. Thanks to the gravitational lensing and excellent spatial resolution of JWST, the spiral arms are resolved with a spatial resolution of $\approx290$\,pc. Based on SED fitting, the spiral galaxy has a de-lensed star formation rate of $85\pm30 \ M_{\odot}$ yr$^{-1}$, and a stellar mass of $\approx10^{10.6}M_{\odot}$, indicating that A2744-DSG-$z3$ is a main-sequence galaxy. After fitting the spiral arms, we find a stellar effective radius ($R_{e, \rm{star}}$) of $5.0\pm1.5$ kpc. Combing with ALMA measurements, we find that the effective radii ratio between dust and stars is $\approx0.4$, similar to {those} of massive SFGs at $z\sim2$, indicating a compact dusty core in A2744-DSG-$z3$. Moreover, this galaxy appears to be living in a group environment: including A2744-DSG-$z3$, at least three galaxies at $z=3.05 - 3.06$ {are} spectroscopically confirmed by JWST/NIRISS and ALMA, residing within a lensing-corrected projected scale of $\approx 70$ kpc. This, along with the asymmetric brightness profile, further suggests that the spiral arms may be triggered by minor merger events at $z\gtrsim3$.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Xiaojing Lin
Zheng Cai
Siwei Zou
Zihao Li
Zuyi Chen
Fuyan Bian
Fengwu Sun
Yiping Shu
Yunjing Wu
Mingyu Li
Jianan Li
Xiaohui Fan
J. Xavier Prochaska
Daniel Schaerer
Stephane Charlot
Daniel Espada
Miroslava Dessauges-Zavadsky
Eiichi Egami
Daniel Stark
Kirsten K. Knudsen
摘要： Direct observations of low-mass, low-metallicity galaxies at $z\gtrsim4$ provide an indispensable opportunity for detailed inspection of the ionization radiation, gas flow, and metal enrichment in sources similar to those that reionized the Universe. Combining the James Webb Space Telescope (JWST), VLT/MUSE, and ALMA, we present detailed observations of a strongly lensed, low-mass ($\approx 10^{7.6}$ ${\rm M}_\odot$) galaxy at $z=3.98$ (also see Vanzella et al. 2022). We identify strong narrow nebular emission, including CIV $\lambda\lambda1548,1550$, HeII $\lambda1640$, OIII] $\lambda\lambda1661,1666$, [NeIII] $\lambda3868$, [OII] $\lambda3727$, and Balmer series of Hydrogen from this galaxy, indicating a metal-poor HII region ($\lesssim 0.12\ {\rm Z}_\odot$) powered by massive stars. Further, we detect a metal-enriched damped Ly$\alpha$ system (DLA) associated with the galaxy with the HI column density of $N_{\rm{HI}}\approx 10^{21.8}$ cm$^{-2}$. The metallicity of the associated DLA may reach the super solar metallicity (${\gtrsim Z}_\odot$). Moreover, thanks to JWST and gravitational lensing, we present the resolved UV slope ($\beta$) map at the spatial resolution of $\approx 100$ pc at $z=4$, with steep UV slopes reaching $\beta \approx -2.5$ around three star-forming clumps. Combining with low-redshift analogs, our observations suggest that low-mass, low-metallicity galaxies, which dominate reionization, could be surrounded by a high covering fraction of the metal-enriched, neutral-gaseous clouds. This implies that the metal enrichment of low-mass galaxies is highly efficient, and further support that in low-mass galaxies, only a small fraction of ionizing radiation can escape through the interstellar or circumgalactic channels with low column-density neutral gas.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Xiaojing Lin
Zheng Cai
Siwei Zou
Zihao Li
Zuyi Chen
Fuyan Bian
Fengwu Sun
Yiping Shu
Yunjing Wu
Mingyu Li
Jianan Li
Xiaohui Fan
J. Xavier Prochaska
Daniel Schaerer
Stephane Charlot
Daniel Espada
Miroslava Dessauges-Zavadsky
Eiichi Egami
Daniel Stark
Kirsten K. Knudsen
摘要： Direct observations of low-mass, low-metallicity galaxies at $z\gtrsim4$ provide an indispensable opportunity for detailed inspection of the ionization radiation, gas flow, and metal enrichment in sources similar to those that reionized the Universe. Combining the James Webb Space Telescope (JWST), VLT/MUSE, and ALMA, we present detailed observations of a strongly lensed, low-mass ($\approx 10^{7.6}$ ${\rm M}_\odot$) galaxy at $z=3.98$ (also see Vanzella et al. 2022). We identify strong narrow nebular emission, including CIV $\lambda\lambda1548,1550$, HeII $\lambda1640$, OIII] $\lambda\lambda1661,1666$, [NeIII] $\lambda3868$, [OII] $\lambda3727$, and Balmer series of Hydrogen from this galaxy, indicating a metal-poor HII region ($\lesssim 0.12\ {\rm Z}_\odot$) powered by massive stars. Further, we detect a metal-enriched damped Ly$\alpha$ system (DLA) associated with the galaxy with the HI column density of $N_{\rm{HI}}\approx 10^{21.8}$ cm$^{-2}$. The metallicity of the associated DLA may reach the super solar metallicity (${\gtrsim Z}_\odot$). Moreover, thanks to JWST and gravitational lensing, we present the resolved UV slope ($\beta$) map at the spatial resolution of $\approx 100$ pc at $z=4$, with steep UV slopes reaching $\beta \approx -2.5$ around three star-forming clumps. Combining with low-redshift analogs, our observations suggest that low-mass, low-metallicity galaxies, which dominate reionization, could be surrounded by a high covering fraction of the metal-enriched, neutral-gaseous clouds. This implies that the metal enrichment of low-mass galaxies is highly efficient, and further support that in low-mass galaxies, only a small fraction of ionizing radiation can escape through the interstellar or circumgalactic channels with low column-density neutral gas.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Ben Wang
Jiaqi Zou
Zheng Cai
J. Xavier Prochaska
Zechang Sun
Jiani Ding
Andreu Font-Ribera
Alma Gonzalez
Hiram K. Herrera-Alcantar
Vid Irsic
Xiaojing Lin
David Brooks
Solène Chabanier
Roger de Belsunce
Nathalie Palanque-Delabrouille
Gregory Tarle
Zhimin Zhou
摘要： We have updated and applied a convolutional neural network (CNN) machine learning model to discover and characterize damped Ly$\alpha$ systems (DLAs) based on Dark Energy Spectroscopic Instrument (DESI) mock spectra. We have optimized the training process and constructed a CNN model that yields a DLA classification accuracy above 99$\%$ for spectra which have signal-to-noise (S/N) above 5 per pixel. Classification accuracy is the rate of correct classifications. This accuracy remains above 97$\%$ for lower signal-to-noise (S/N) $\approx1$ spectra. This CNN model provides estimations for redshift and HI column density with standard deviations of 0.002 and 0.17 dex for spectra with S/N above 3 per pixel. Also, this DLA finder is able to identify overlapping DLAs and sub-DLAs. Further, the impact of different DLA catalogs on the measurement of Baryon Acoustic Oscillation (BAO) is investigated. The cosmological fitting parameter result for BAO has less than $0.61\%$ difference compared to analysis of the mock results with perfect knowledge of DLAs. This difference is lower than the statistical error for the first year estimated from the mock spectra: above $1.7\%$. We also compared the performance of CNN and Gaussian Process (GP) model. Our improved CNN model has moderately 14$\%$ higher purity and 7$\%$ higher completeness than an older version of GP code, for S/N $>$ 3. Both codes provide good DLA redshift estimates, but the GP produces a better column density estimate by $24\%$ less standard deviation. A credible DLA catalog for DESI main survey can be provided by combining these two algorithms.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Based on the Sloan Digital Sky Survey Data Release 16, we have detected the large-scale structure of Ly$\alpha$ emission in the Universe at redshifts $z = 2$--3.5 by cross-correlating quasar positions and Ly$\alpha$ emission imprinted in the residual spectra of luminous red galaxies. We apply an analytical model to fit the corresponding Ly$\alpha$ surface brightness profile and multipoles of the redshift-space quasar-Ly$\alpha$ emission cross-correlation function. The model suggests an average cosmic Ly$\alpha$ luminosity density of ${6.6_{-3.1}^{+3.3}}\times 10^{40} {\rm erg\, s^{-1} cMpc^{-3}}$, a $\sim 2\sigma$ detection with a median value about 8--9 times those estimated from deep narrowband surveys of Ly$\alpha$ emitters at similar redshifts. Although the low signal-to-noise ratio prevents us from a significant detection of the Ly$\alpha$ forest-Ly$\alpha$ emission cross-correlation, the measurement is consistent with the prediction of our best-fit model from quasar-Ly$\alpha$ emission cross-correlation within current uncertainties. We rule out the scenario that these Ly$\alpha$ photons mainly originate from quasars. We find that Ly$\alpha$ emission from star-forming galaxies, including contributions from that concentrated around the galaxy centers and that in the diffuse Ly$\alpha$ emitting halos, is able to explain the bulk of the the Ly$\alpha$ luminosity density inferred from our measurements. Ongoing and future surveys can further improve the measurements and advance our understanding of the cosmic Ly$\alpha$ emission field.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Mingyu Li
Zheng Cai
Fuyan Bian
Xiaojing Lin
Zihao Li
Yunjing Wu
Fengwu Sun
Shiwu Zhang
Siwei Zou
Xiaohui Fan
Eiichi Egami
Stephane Charlot
Gustavo Bruzual
Jacopo Chevallard
摘要： We present the mass-metallicity relation (MZR) at $z=2-3$ in the stellar mass range of $M_\star\approx 10^{6.5}-10^{9.5}M_\odot$ using 55 dwarf galaxies in the Abell 2744 and SMACS J0723-3732 galaxy cluster fields. These dwarf galaxies are identified and confirmed by deep JWST/NIRISS imaging and slitless grism spectroscopic observations. Taking advantage of the gravitational lensing effect, we extend the previous MZR relation at $z=2-3$ to a much lower mass regime by more than 2.5 orders of magnitude compared with previous studies. We find that the MZR has a shallower slope at the low-mass end ($M_\star10^{9}M_\odot$), with a slope turnover point at around the stellar mass of $10^9 M_\odot$. This implies that dominating feedback processes in dwarf galaxies may be different from that in galaxies with higher mass. From $z=3$ to $z=2$, the metallicity of the dwarf galaxies is enhanced by $\approx0.1$ dex for a given stellar mass, consistent with the mild evolution found in galaxies with higher mass. Further, we confirm the existence of a 3D relation between the gas-phase metallicity, stellar mass, and star formation rate, i.e., fundamental metallicity relation (FMR), in dwarf galaxies at $z=2-3$. Our derived FMR, which has no significant redshift evolution, can be used as a benchmark to understand the origin of the anti-correlation between SFR and metallicity of dwarf galaxies in the high-redshift Universe.
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