25 research outputs found

    Extremely Red Galaxies at z = 5-9 with MIRI and NIRSpec:Dusty Galaxies or Obscured Active Galactic Nuclei?

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    We study a new population of extremely red objects (EROs) recently discovered by the James Webb Space Telescope (JWST) based on their NIRCam colors F277W − F444W &gt; 1.5 mag. We find 37 EROs in the Cosmic Evolution Early Release Science Survey (CEERS) field with F444W &lt; 28 mag and photometric redshifts between 5 &lt; z &lt; 7, with median z = 6.9 − 1.6 + 1.0 . Surprisingly, despite their red long-wavelength colors, these EROs have blue short-wavelength colors (F150W − F200W ∌ 0 mag) indicative of bimodal spectral energy distributions (SEDs) with a red, steep slope in the rest-frame optical, and a blue, flat slope in the rest-frame UV. Moreover, all these EROs are unresolved, point-like sources in all NIRCam bands. We analyze the SEDs of eight of them with MIRI and NIRSpec observations using stellar population models and active galactic nucleus (AGN) templates. We find that dusty galaxies or obscured AGNs provide similarly good SED fits but different stellar properties: massive and dusty, log M ⋆ / M ⊙ ∌ 10 and A V ≳ 3 mag, or low mass and obscured, log M ⋆ / M ⊙ ∌ 7.5 and A V ∌ 0 mag, hosting an obscured quasi-stellar object (QSO). SED modeling does not favor either scenario, but their unresolved sizes are more suggestive of AGNs. If any EROs are confirmed to have log M ⋆ / M ⊙ ≳ 10.5, it would increase the pre-JWST number density at z &gt; 7 by up to a factor ∌60. Similarly, if they are QSOs with luminosities in the L bol &gt; 1045-46 erg s−1 range, their number would exceed that of bright blue QSOs by more than three orders of magnitude. Additional photometry at mid-infrared wavelengths will reveal the true nature of the red continuum emission in these EROs and will place this puzzling population in the right context of galaxy evolution.</p

    A Milky Way-like barred spiral galaxy at a redshift of 3

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    International audienceThe majority of massive disk galaxies in the local Universe show a stellar barred structure in their central regions, including our Milky Way. Bars are supposed to develop in dynamically cold stellar disks at low redshift, as the strong gas turbulence typical of disk galaxies at high redshift suppresses or delays bar formation. Moreover, simulations predict bars to be almost absent beyond z=1.5z = 1.5 in the progenitors of Milky Way-like galaxies. Here we report observations of ceers-2112, a barred spiral galaxy at redshift zphot∌3z_{\rm phot} \sim 3, which was already mature when the Universe was only 2 Gyr old. The stellar mass (M⋆=3.9×109M⊙M_{\star} = 3.9 \times 10^9 M_{\odot}) and barred morphology mean that ceers-2112 can be considered a progenitor of the Milky Way, in terms of both structure and mass-assembly history in the first 2 Gyr of the Universe, and was the closest in mass in the first 4 Gyr. We infer that baryons in galaxies could have already dominated over dark matter at z∌3z \sim 3, that high-redshift bars could form in approximately 400 Myr and that dynamically cold stellar disks could have been in place by redshift z=4−5z = 4-5 (more than 12 Gyrs ago)

    Spectroscopic verification of very luminous galaxy candidates in the early universe

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    During the first 500 million years of cosmic history, the first stars and galaxies formed and seeded the cosmos with heavy elements. These early galaxies illuminated the transition from the cosmic "dark ages" to the reionization of the intergalactic medium. This transitional period has been largely inaccessible to direct observation until the recent commissioning of JWST, which has extended our observational reach into that epoch. Excitingly, the first JWST science observations uncovered a surprisingly high abundance of early star-forming galaxies. However, the distances (redshifts) of these galaxies were, by necessity, estimated from multi-band photometry. Photometric redshifts, while generally robust, can suffer from uncertainties and/or degeneracies. Spectroscopic measurements of the precise redshifts are required to validate these sources and to reliably quantify their space densities, stellar masses, and star formation rates, which provide powerful constraints on galaxy formation models and cosmology. Here we present the results of JWST follow-up spectroscopy of a small sample of galaxies suspected to be amongst the most distant yet observed. We confirm redshifts z > 10 for two galaxies, including one of the first bright JWST-discovered candidates with z = 11.4, and show that another galaxy with suggested z ~ 16 instead has z = 4.9, with strong emission lines that mimic the expected colors of more distant objects. These results reinforce the evidence for the rapid production of luminous galaxies in the very young Universe, while also highlighting the necessity of spectroscopic verification for remarkable candidates.Comment: Submitted to Natur

    JWST CEERS probes the role of stellar mass and morphology in obscuring galaxies

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    A population of massive galaxies invisible or very faint in deep optical/near-infrared surveys, but brighter at longer wavelengths has been uncovered in the past years. However, the nature of these optically dark/faint galaxies (OFGs, among other nomenclatures) is highly uncertain. In this work, we investigate the drivers of dust attenuation in the JWST era. Particularly, we study the role of stellar mass, size, and orientation in obscuring star-forming galaxies (SFGs) at 3<z<7.53 < z < 7.5, focusing on understanding why galaxies like OFGs are so faint at optical/near-infrared wavelengths. We find that stellar mass is the primary proxy of dust attenuation among those studied. Effective radius and axis ratio do not show a clear link with dust attenuation, with the effect of orientation close to random. However, there is a subset of highly dust attenuated (AV>1A_V > 1, typically) SFGs, of which OFGs are a specific case. For this subset, we find that the key distinctive feature is their compact size (for massive systems with log⁡(M∗/M⊙)>10\log (M_{*}/M_{\odot}) > 10), exhibiting 30% smaller effective radius than the average SFGs at the same stellar mass and redshift. On the contrary, they do not exhibit a preference for low axis ratios (i.e., edge-on disks). The results in this work show stellar mass as a primary proxy of dust attenuation and compact stellar light profiles behind thick dust columns obscuring typical massive SFGs.Comment: Submitted to A&A. 13 pages, 9 figure

    CEERS Key Paper IV: Galaxies at 4<z<94 < z < 9 are Bluer than They Appear -- Characterizing Galaxy Stellar Populations from Rest-Frame ∌1\sim 1 micron Imaging

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    We present results from the Cosmic Evolution Early Release Survey (CEERS) on the stellar-population parameters for 28 galaxies with redshifts 4<z<94<z<9 using imaging data from the James Webb Space Telescope (JWST) Mid-Infrared Instrument (MIRI) combined with data from the Hubble Space Telescope and the Spitzer Space Telescope. The JWST/MIRI 5.6 and 7.7 ÎŒ\mum data extend the coverage of the rest-frame spectral-energy distribution (SED) to nearly 1 micron for galaxies in this redshift range. By modeling the galaxies' SEDs the MIRI data show that the galaxies have, on average, rest-frame UV (1600 \r{A}) −- II-band colors 0.4 mag bluer than derived when using photometry that lacks MIRI. Therefore, the galaxies have lower (stellar)-mass-to-light ratios. The MIRI data reduce the stellar masses by ⟹Δlog⁥M∗⟩=0.25\langle \Delta\log M_\ast\rangle=0.25 dex at 4<z<64<z<6 (a factor of 1.8) and 0.37 dex at 6<z<96<z<9 (a factor of 2.3). This also reduces the star-formation rates (SFRs) by ⟹Δlog⁥SFR⟩=0.14\langle \Delta\log\mathrm{SFR} \rangle=0.14 dex at 4<z<64<z<6 and 0.27 dex at 6<z<96<z<9. The MIRI data also improve constraints on the allowable stellar mass formed in early star-formation. We model this using a star-formation history that includes both a "burst' at zf=100z_f=100 and a slowly varying ("delayed-τ\tau") model. The MIRI data reduce the allowable stellar mass by 0.6 dex at 4<z<64<z< 6 and by ≈\approx1 dex at 6<z<96<z<9. Applying these results globally, this reduces the cosmic stellar-mass density by an order of magnitude in the early universe (z≈9z\approx9). Therefore, observations of rest-frame ≳\gtrsim1 ÎŒ\mum are paramount for constraining the stellar-mass build-up in galaxies at very high-redshifts.Comment: Updated with accepted ApJ version. Part of the CEERS Focus Issue. 27 pages, many figures (4 Figure Sets, available upon reasonable request

    CEERS Key Paper. V. Galaxies at 4 &lt; z &lt; 9 Are Bluer than They Appear-Characterizing Galaxy Stellar Populations from Rest-frame ∌1 ÎŒm Imaging

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    We present results from the Cosmic Evolution Early Release Survey on the stellar population parameters for 28 galaxies with redshifts 4 &lt; z &lt; 9 using imaging data from the James Webb Space Telescope (JWST) Mid-Infrared Instrument (MIRI) combined with data from the Hubble Space Telescope and the Spitzer Space Telescope. The JWST/MIRI 5.6 and 7.7 ÎŒm data extend the coverage of the rest-frame spectral energy distribution to nearly 1 ÎŒm for galaxies in this redshift range. By modeling the galaxies’ SEDs the MIRI data show that the galaxies have, on average, rest-frame UV (1600 Å)—I-band colors 0.4 mag bluer than derived when using photometry that lacks MIRI. Therefore, the galaxies have lower ratios of stellar mass to light. The MIRI data reduce the stellar masses by 〈 Δ log M * 〉 = 0.25 dex at 4 &lt; z &lt; 6 and 0.37 dex at 6 &lt; z &lt; 9. This also reduces the star formation rates (SFRs) by 〈ΔlogSFR〉 = 0.14 dex at 4 &lt; z &lt; 6 and 0.27 dex at 6 &lt; z &lt; 9. The MIRI data also improve constraints on the allowable stellar mass formed in early star formation. We model this using a star formation history that includes both a “burst” at z f = 100 and a slowly varying (“delayed-τ”) model. The MIRI data reduce the allowable stellar mass by 0.6 dex at 4 &lt; z &lt; 6 and by ≈1 dex at 6 &lt; z &lt; 9. Applying these results globally, this reduces the cosmic stellar-mass density by an order of magnitude in the early Universe (z ≈ 9). Therefore, observations of rest-frame ≳1 ÎŒm are paramount for constraining the stellar-mass buildup in galaxies at very high redshifts.</p

    The Physical Conditions of Emission-Line Galaxies at Cosmic Dawn from JWST/NIRSpec Spectroscopy in the SMACS 0723 Early Release Observations

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    We present rest-frame optical emission-line flux ratio measurements for five z>5z>5 galaxies observed by the JWST Near-Infared Spectrograph (NIRSpec) in the SMACS 0723 Early Release Observations. We add several quality-control and post-processing steps to the NIRSpec pipeline reduction products in order to ensure reliable relative flux calibration of emission lines that are closely separated in wavelength, despite the uncertain \textit{absolute} spectrophotometry of the current version of the reductions. Compared to z∌3z\sim3 galaxies in the literature, the z>5z>5 galaxies have similar [OIII]λ\lambda5008/HÎČ\beta ratios, similar [OIII]λ\lambda4364/HÎł\gamma ratios, and higher (∌\sim0.5 dex) [NeIII]λ\lambda3870/[OII]λ\lambda3728 ratios. We compare the observations to MAPPINGS V photoionization models and find that the measured [NeIII]λ\lambda3870/[OII]λ\lambda3728, [OIII]λ\lambda4364/HÎł\gamma, and [OIII]λ\lambda5008/HÎČ\beta emission-line ratios are consistent with an interstellar medium that has very high ionization (log⁥(Q)≃8−9\log(Q) \simeq 8-9, units of cm~s−1^{-1}), low metallicity (Z/Z⊙â‰Č0.2Z/Z_\odot \lesssim 0.2), and very high pressure (log⁥(P/k)≃8−9\log(P/k) \simeq 8-9, units of cm−3^{-3}). The combination of [OIII]λ\lambda4364/HÎł\gamma and [OIII]λ\lambda(4960+5008)/HÎČ\beta line ratios indicate very high electron temperatures of 4.1<log⁥(Te/K)<4.44.1<\log(T_e/{\rm K})<4.4, further implying metallicities of Z/Z⊙â‰Č0.2Z/Z_\odot \lesssim 0.2 with the application of low-redshift calibrations for ``TeT_e-based'' metallicities. These observations represent a tantalizing new view of the physical conditions of the interstellar medium in galaxies at cosmic dawn.Comment: Accepted for publication in AAS Journals. 14 pages, 6 figures, 3 table
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