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 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$11-17 candidates.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: Selecting the first galaxies at z>7-10 from JWST surveys is complicated by z7-10 Lyman Break Galaxies (LBGs). Dust-obscured 3-1.5$ and z>4. While there are some redshifts (z~3.75) where our stack is more degenerate with the photometry of z>10 LBGs between $\lambda_{rest}\sim0.3-0.8\,\mu$m, redder filter coverage beyond $\lambda_{obs}>3.5\,\mu$m and far-IR/sub-mm follow-up may be useful for breaking the degeneracy and making a crucial separation between two fairly unconstrained populations, dust-obscured galaxies at z~3-6 and LBGs at z>10.