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Register a new userDetection of a Lensed z$approx$11 Galaxy in the Rest-Optical with Spitzer/IRAC and the Inferred SFR, Stellar Mass, and Physical Size
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We take advantage of new 100-hour Spitzer/IRAC observations available for MACS0647-JD, a strongly lensed $zapprox11$ galaxy candidate, to provide improved constraints on its physical properties. Probing the physical properties of galaxies at $z>8$ is challenging due to the inherent faintness of such sources and the limited wavelength coverage available. Thanks to the high $approx$2-6$times$ lensing magnification of the multiple images of MACS0647-JD, we can use the sensitive Spitzer/IRAC data to probe the rest-frame optical fluxes of MACS0647-JD and investigate its physical properties including the age and the stellar mass. In deriving Spitzer/IRAC fluxes for MACS0647-JD, great care is taken in coping with the impact of three bright ($approx$8-16 mag) stars in our field to ensure robust results. Assuming a constant star formation rate, the age, stellar mass, and rest-frame UV slope we estimate for MACS0647-JD based on a stack of the photometry are log$_{10}$(age/yr) = 8.6$^{+0.1}_{-2.1}$, log$_{10}$(M$_{*}$/M$_{odot}$) = 9.1$^{+0.2}_{-1.4}$, and $beta = -$1.3$pm$0.6, respectively. We compare our results with expectations from the EAGLE simulation and find that MACS0647-JD has properties consistent with corresponding to the most massive and rapidly star-forming galaxies in the simulation. We also find that its radius, 105$pm$28 pc, is a factor of $approx$2 smaller than the mean size in a separate simulation project DRAGONS. Interestingly enough, the observed size is similar to the small sizes seen in very low-luminosity $zapprox$6-10 galaxies behind lensing clusters.
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We explore deep rest-frame UV to FIR data in the COSMOS field to measure the individual spectral energy distributions (SED) of the ~4000 SC4K (Sobral et al. 2018) Lyman-alpha (Lya) emitters (LAEs) at z~2-6. We find typical stellar masses of 10$^{9.3pm0.6}$ M$_{odot}$ and star formation rates (SFR) of SFR$_{SED}=4.4^{+10.5}_{-2.4}$ M$_{odot}$/yr and SFR$_{Lya}=5.9^{+6.3}_{-2.6}$ M$_{odot}$/yr, combined with very blue UV slopes of beta=-2.1$^{+0.5}_{-0.4}$, but with significant variations within the population. M$_{UV}$ and beta are correlated in a similar way to UV-selected sources, but LAEs are consistently bluer. This suggests that LAEs are the youngest and/or most dust-poor subset of the UV-selected population. We also study the Lya rest-frame equivalent width (EW$_0$) and find 45 extreme LAEs with EW$_0>240$ A (3 $sigma$), implying a low number density of $(7pm1)times10^{-7}$ Mpc$^{-3}$. Overall, we measure little to no evolution of the Lya EW$_0$ and scale length parameter ($w_0$) which are consistently high (EW$_0=140^{+280}_{-70}$ A, $w_0=129^{+11}_{-11}$ A) from z~6 to z~2 and below. However, $w_0$ is anti-correlated with M$_{UV}$ and stellar mass. Our results imply that sources selected as LAEs have a high Lya escape fraction (f$_{esc, Lya}$) irrespective of cosmic time, but f$_{esc, Lya}$ is still higher for UV-fainter and lower mass LAEs. The least massive LAEs ($<10^{9.5}$ M$_{odot}$) are typically located above the star formation Main Sequence (MS), but the offset from the MS decreases towards z~6 and towards $10^{10}$ M$_{odot}$. Our results imply a lack of evolution in the properties of LAEs across time and reveals the increasing overlap in properties of LAEs and UV-continuum selected galaxies as typical star-forming galaxies at high redshift effectively become LAEs.
For the extremely bright lensed galaxy SDSS J1723+3411 at z=1.3293 , we analyze spatially integrated MMT, Keck, and Hubble Space Telescope spectra that fully cover the rest-frame wavelength range of 1400 to 7200 Angstroms. We also analyze near-IR spectra from Gemini that cover H alpha for a portion of the lensed arc. We report fluxes for 42 detected emission lines, and upper limits for an additional 22. This galaxy has extreme emission line ratios and high equivalent widths that are characteristic of extreme emission-line galaxies. We compute strong emission line diagnostics from both the rest-frame optical and rest-frame ultraviolet (UV), to constrain physical conditions and test the spectral diagnostics themselves. We tightly determine the nebular physical conditions using the most reliable diagnostics, and then compare to results from other diagnostics. We find disappointing performance from the UV--only diagnostics: they either are unable to measure the metallicity or dramatically under-estimate it; they over-estimate the pressure; and the UV diagnostic of ionization parameter has a strong metallicity dependence in this regime. Based on these results, we suggest that upcoming James Webb Space Telescope spectroscopic surveys of galaxies in the reionization epoch should invest the additional integration time to capture the optical [O II] and [O III] emission lines, and not rely solely on the rest-frame UV emission lines. We make available the spectra; they represent one of the highest-quality emission line spectral atlases of star-forming galaxy available beyond the local universe, and will aid planning observations with JWST.
We present new stellar mass functions at $zsim6$, $zsim7$, $zsim8$, $zsim9$ and, for the first time, $zsim10$, constructed from $sim800$ Lyman-Break galaxies previously identified over the XDF/UDF, parallels and the five CANDELS fields. Our study is distinctive due to (1) the much deeper ($sim200$ hour) wide-area Spitzer/IRAC imaging at $3.6mu$m and $4.5mu$m from the GOODS Re-ionization Era wide Area Treasury from Spitzer (GREATS) program and (2) consideration of $zsim6-10$ sources over a $3times$ larger area than previous HST+Spitzer studies. The Spitzer/IRAC data enable $ge2sigma$ rest-frame optical detections for an unprecedented $50%$ of galaxies down to a stellar mass limit of $sim10^{8}mathcal{M}_odot$ across all redshifts. Schechter fits to our volume densities suggest a combined evolution in characteristic mass $mathcal{M}^*$ and normalization factor $phi^*$ between $zsim6$ and $zsim8$. The stellar mass density (SMD) increases by $sim1000times$ in the $sim500$ Myr between $zsim10$ and $zsim6$, with indications of a steeper evolution between $zsim10$ and $zsim8$, similar to the previously-reported trend of the star-formation rate density. Strikingly, abundance matching to the Bolshoi-Planck simulation indicates halo mass densities evolving at approximately the same rate as the SMD between $zsim10$ and $zsim4$. Our results show that the stellar-to-halo mass ratios, a proxy for the star-formation efficiency, do not change significantly over the huge stellar mass build-up occurred from $zsim10$ to $zsim6$, indicating that the assembly of stellar mass closely mirrors the build-up in halo mass in the first $sim1$ Gyr of cosmic history. JWST is poised to extend these results into the first galaxy epoch at $zgtrsim10$.
Characterizing the galaxy population in the early Universe holds the key to understanding the evolution of these objects and the role they played in cosmic reionization. However, the number of observations at the very highest redshifts are to date, few. In order to shed light on the properties of galaxies in the high-redshift Universe and their interstellar media, we observe the Lyman-$alpha$ emitting galaxy z7_GSD_3811 at $z=7.664$ with band 6 and 8 at the Atacama Large Millimeter/submillimeter Array (ALMA). We target the far-infrared [O III] 88 $mu m$, [C II] 158 $mu m$ emission lines and dust continuum in the star-forming galaxy z7_GSD_3811 with ALMA. We combine these measurements with earlier observations in the rest-frame ultraviolet (UV) in order to characterize the object, and compare results to those of earlier studies observing [O III] and [C II] emission in high-redshift galaxies. The [O III] 88 $mu m$ and [C II] 158 $mu m$ emission lines are undetected at the position of z7_GSD_3811, with $3sigma$ upper limits of $1.6 times 10^{8} L_{odot}$ and $4.0 times 10^{7} L_{odot}$, respectively. We do not detect any dust continuum in band 6 nor band 8. The measured rms in the band 8 and band 6 continuum is 26 and 9.9 $mu Jy beam^{-1}$, respectively. Similar to several other high-redshift galaxies, z7_GSD_3811 exhibits low [C II] emission for its star formation rate compared to local galaxies. Furthermore, our upper limit on the [O III] line luminosity is lower than all the previously observed [O III] lines in high-redshift galaxies with similar ultraviolet luminosities. Our ALMA band 6 and 8 dust continuum observations imply that z7_GSD_3811 likely has a low dust content, and our non-detections of the [O III] and [C II] lines could indicate that z7_GSD_3811 has a low metallicity ($Z lesssim 0.1 Z_{odot}$).
We present results from deep Spitzer/Infrared Array Camera (IRAC) observations of 28 metal-poor, strongly star-forming galaxies selected from the DEEP2 Galaxy Survey. By modelling infrared and optical photometry, we derive stellar masses and other stellar properties. We determine that these metal-poor galaxies have low stellar masses, $M_{star}$ $approx10^{8.1}$-$10^{9.5}$ $M_{odot}$. Combined with the Balmer-derived star formation rates (SFRs), these galaxies have average inverse SFR/$M_{star}$ of $approx$100 Myr. The evolution of stellar mass-gas metallicity relation to $zapprox0.8$ is measured by combining the modelled masses with previously obtained spectroscopic measurements of metallicity from [O III] $lambda$4363 detections. Here, we include measurements for 79 galaxies from the Metal Abundances across Cosmic Time Survey. Our mass-metallicity relation is lower at a given stellar mass than at $z=0.1$ by 0.27 dex. This demonstrates a strong evolution in the mass-metallicity relation, $(1+z)^{-1.45^{+0.61}_{-0.76}}$. We find that the shape of the $zapprox0.8$ mass-metallicity relation, a steep rise in metallicity at low stellar masses, transitioning to a plateau at higher masses, is consistent with $zsim0.1$ studies. We also compare the evolution in metallicity between $zapprox0.8$ and $zsim0.1$ against recent strong-line diagnostic studies at intermediate redshifts and find good agreement. Specifically, we find that lower mass galaxies ($4times10^8$ $M_{odot}$) built up their metal content 1.6 times more rapidly than higher mass galaxies ($10^{10}$ $M_{odot}$). Finally, we examine whether the mass-metallicity relation has a secondary dependence on SFR, and statistically concluded that there is no strong secondary dependence for $zapprox0.8$ low-mass galaxies.
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