Deep Spitzer/IRAC Data for z~10 galaxies Reveal Blue Balmer Break Colors: Young Stellar Populations at ~500 Myr of Cosmic Time

Abstract

We present the deepest constraints yet on the median rest-UV+optical SED of $z\sim 10$ galaxies, prior to JWST science operations. We constructed stacks based on four robust $J_{125}$-dropouts, previously identified across the GOODS fields. We used archival HST/WFC3 data and the full depth Spitzer/IRAC mosaics from the GREATS program, the deepest coverage at $\sim 3-5\mu$m to date. The most remarkable feature of the SED is a blue IRAC $[3.6]-[4.5]=-0.18\pm 0.25$ mag color. We also find a nearly flat $H_{160}-[3.6]=0.07\pm 0.22$ mag color, corresponding to a UV slope $\beta =-1.92\pm 0.25$. This is consistent with previous studies, and indicative of minimal dust absorption. The observed blue IRAC color and SED fitting suggest that $z\sim 10$ galaxies have very young (few $\times 10$ Myr) stellar populations, with $80\%$ of stars being formed in the last $\lesssim 160$ Myr ($2\sigma$). While an exciting result, the uncertainties on the SED are too large to allow us to place strong constraints on the presence of a nebular continuum in $z\sim 10$ galaxies (as might be suggested by the blue $[3.6]-[4.5]<0$ mag color). The resulting sSFR is consistent with the specific accretion rate of dark matter halos, indicative of a star-formation efficiency showing quite limited evolution at such early epochs.

Submitted to ApJ. 9 pages, 3 figures. Comments welcome

References in corpus (40)

• Cosmic Star Formation History
• EAZY: A Fast, Public Photometric Redshift Code
• UV Luminosity Functions at redshifts z~4 to z~10: 10000 Galaxies from HST Legacy Fields
• Introducing the Illustris Project: the evolution of galaxy populations across cosmic time
• The Hubble Ultra Deep Field
• Stellar Population Inference with Prospector
• New Determinations of the UV Luminosity Functions from z~9 to z~2 show a remarkable consistency with halo growth and a constant star formation efficiency
• The Relation Between SFR and Stellar Mass for Galaxies at 3.5 $\le z\le$ 6.5 in CANDELS
• The mass evolution of the first galaxies: stellar mass functions and star formation rates at $4<z<7$ in the CANDELS GOODS-South field
• The galaxy stellar mass function at 3.5<z<7.5 in the CANDELS/UDS, GOODS-South, and HUDF fields
• z~7-10 Galaxies in the HUDF and GOODS fields, and their UV Luminosity Functions
• The chemical enrichment in the early Universe as probed by JWST via direct metallicity measurements at z~8
• ALMA Spectroscopic Survey in the Hubble Ultra Deep Field: Survey Description
• A lack of evolution in the very bright-end of the galaxy luminosity function from z = 8-10
• On the Stellar Populations of Galaxies at z=9-11: The Growth of Metals and Stellar Mass at Early Times
• The Star Formation Main Sequence in the Hubble Space Telescope Frontier Fields
• Galaxy Stellar Mass Functions from z~10 to z~6 using the Deepest Spitzer/IRAC Data: No Significant Evolution in the Stellar-to-Halo Mass Ratio of Galaxies in the First Gyr of Cosmic Time
• The ALMA Spectroscopic Survey Large Program: The Infrared Excess of z=1.5-10 UV-selected Galaxies and the Implied High-Redshift Star Formation History
• A New Census of the 0.2< z <3.0 Universe, Part II: The Star-Forming Sequence
• Normal, Dust-Obscured Galaxies in the Epoch of Reionization
• The GREATS H$\beta$+[OIII] Luminosity Function and Galaxy Properties at $\mathbf{z}\sim 8$: Walking the Way of JWST
• Merger Rates of Dark-Matter Haloes
• A Census of the Bright z=8.5-11 Universe with the Hubble and Spitzer Space Telescopes in the CANDELS Fields
• The ALPINE-ALMA [CII] Survey: Obscured Star Formation Rate Density and Main Sequence of star-forming galaxies at z>4
• The ALMA REBELS Survey: Specific Star-Formation Rates in the Reionization Era
• MMT Spectroscopy of Lyman-alpha at z$\simeq$7: Evidence for Accelerated Reionization Around Massive Galaxies
• Evidence for GN-z11 as a luminous galaxy at redshift 10.957
• The Star Formation Burstiness and Ionizing Efficiency of Low-mass Galaxies
• Probing Cosmic Dawn : Ages and Star Formation Histories of Candidate $z\ge$9 Galaxies
• Searching for Islands of Reionization: A Potential Ionized Bubble Powered by a Spectroscopic Overdensity at z = 8.7
• High Equivalent Width of Hα+[N II] Emission in z~8 Lyman-break Galaxies from IRAC 5.8μm Observations: Evidence for Efficient Lyman-continuum Photon production in the Epoch of Re-ionization
• Sizes of Lensed Lower-luminosity z=4-8 Galaxies from the Hubble Frontier Field Program
• Stellar mass functions of galaxies at 4<z<7 from an IRAC-selected sample in COSMOS/UltraVISTA: limits on the abundance of very massive galaxies
• An alternate approach to measure specific star formation rates at 2<z<7
• The Physical Properties of Luminous $z\gtrsim 8$ Galaxies and Implications for the Cosmic Star Formation Rate Density From $\sim$0.35 deg${}^2$ of (Pure-)Parallel HST Observations
• Blue Rest-Frame UV-Optical Colors in z~8 Galaxies from GREATS: Very Young Stellar Populations at ~650 Myr of Cosmic Time
• Young Galaxy Candidates in the Hubble Frontier Fields IV. MACS J1149.5+2223
• Balmer Break Galaxy Candidates at $z\sim 6$: a Potential View on the Star-Formation Activity at $z\gtrsim 14$
• RELICS: Properties of z>5.5 Galaxies Inferred from Spitzer and Hubble Imaging Including A Candidate z~6.8 Strong [OIII] Emitter
• The Spitzer/IRAC Legacy over the GOODS Fields: Full-Depth 3.6, 4.5, 5.8 and 8.0um Mosaics and Photometry for > 9000 Galaxies at z~3.5-10 from the GOODS Re-ionization Era wide-Area Treasury from Spitzer (GREATS)

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