Abstract
Using an ultra-deep blind survey with the MUSE integral field spectrograph on the European Southern Observatory Very Large Telescope, we obtain spectroscopic redshifts to a depth never ...before explored: galaxies with observed magnitudes
m
AB
≳ 30–32. Specifically, we detect objects via Ly
α
emission at 2.9 <
z
< 6.7 without individual continuum counterparts in areas covered by the deepest optical/near-infrared imaging taken by the
Hubble Space Telescope
, the Hubble Ultra Deep Field. In total, we find 102 such objects in 9 square arcminutes at these redshifts. Detailed stacking analyses confirm the Ly
α
emission as well as the 1216 Å breaks and faint ultraviolet continua (
M
UV
∼ −15). This makes them the faintest spectroscopically confirmed objects at these redshifts, similar to the sources believed to reionize the universe. A simple model for the expected fraction of detected/undetected Ly
α
emitters as a function of luminosity is consistent with these objects being the high-equivalent width tail of the normal Ly
α
-emitter population at these redshifts.
We use the ultra-deep HUDF09 and the deep Early Release Science data from the HST WFC3/IR camera, along with the wide-area Spitzer/IRAC data from GOODS-S to derive spectral energy distributions ...(SEDs) of star-forming galaxies from the rest-frame UV to the optical over a wide luminosity range (M sub(1500) ~ -21 to M sub(1500) ~ -18) from z ~ 7 to z ~ 4. The sample contains ~400 z ~ 4, ~120 z ~ 5, ~60 z ~ 6, and 36 z ~ 7 galaxies. Median stacking enables the first comprehensive SED study of very faint high-z galaxies at multiple redshifts (e.g., 3.6 = 27.4 + or - 0.1 AB mag for the M sub(1500) ~ -18 sources at z ~ 4). At z ~ 4, we study the stacked SEDs over a range of 5 mag reaching down to ~0.06L*z = 4. We use all available SEDs and template fits to derive rest-frame UV-to-optical colors (U - V) at all redshifts and luminosities. We find that this color does not vary significantly with redshift at a fixed luminosity. The UV-to-optical color does show a weak trend with luminosity, becoming redder at higher luminosities. This is most likely due to dust. At z > ~5, we find blue 3.6-4.5 colors ~ -0.3 mag that are most likely due to rest-frame optical emission lines contributing to the flux in the IRAC filter bandpasses. Such contributions would lower both ages and masses by ~2 x. The scatter in our derived SEDs remains large, but the results are most consistent with a lack of any evolution in the SEDs with redshift at a given luminosity. The uniformity of the SEDs suggests a self-similar mode of evolution over a timespan from 0.7 Gyr to 1.5 Gyr after the big bang that encompasses very substantial growth in the stellar mass density in the universe (from ~4 x 10 super(6) to ~2 x 10 super(7) M sub(middot in circle) Mpc super(-3)).
For the first time, we study the evolution of the stellar mass-size relation for star-forming galaxies from z ~ 4 to z ~ 7 from Hubble-WFC3/IR camera observations of the HUDF and Early Release ...Science field. The sizes are measured by determining the best-fit model to galaxy images in the rest-frame 2100 Angstrom with the stellar masses estimated from spectral energy distribution fitting to rest-frame optical (from Spitzer/IRAC) and UV fluxes. We show that the stellar mass-size relation of Lyman break galaxies (LBGs) persists, at least to z ~ 5, and the median size of LBGs at a given stellar mass increases toward lower redshifts. For galaxies with stellar masses of 9.5 < log(Mlow */M sub(middot in circle)) < 10.4, sizes evolve as (1 + z) super(-1.20+ or -0.11). This evolution is very similar for galaxies with lower stellar masses of 8.6 < log(Mlow */M sub(middot in circle)) < 9.5 which is r sub(e) proportional, variant (1 + z) super(-18+ or -0.10), in agreement with simple theoretical galaxy formation models at high z. Our results are consistent with previous measurements of the LBGs mass-size relation at lower redshifts (z ~ 1-3).
We present results from deep X-ray stacking of >4000 high-redshift galaxies from z approximately 1 to 8 using the 4 Ms Chandra Deep Field-South data, the deepest X-ray survey of the extragalactic sky ...to date. The galaxy samples were selected using the Lyman break technique based primarily on recent Hubble Space Telescope ACS and WFC3 observations. Based on such high specific star formation rates (sSFRs): log SFR/M sub(*) > -8.7, we expect that the observed properties of these Lyman break galaxies (LBGs) are dominated by young stellar populations. The X-ray emission in LBGs, eliminating individually detected X-ray sources (potential active galactic nucleus), is expected to be powered by X-ray binaries and hot gas. We find, for the first time, evidence of evolution in the X-ray/SFR relation. Based on X-ray stacking analyses for z < 4 LBGs (covering ~90% of the universe's history), we find that the 2-10 keV X-ray luminosity evolves weakly with redshift (z) and SFR as log L sub(X) = 0.93 log(1 + z) + 0.65 log SFR + 39.80. By comparing our observations with sophisticated X-ray binary population synthesis models, we interpret that the redshift evolution of L sub(X)/SFR is driven by metallicity evolution in high mass X-ray binaries, likely the dominant population in these high sSFR galaxies. We also compare these models with our observations of X-ray luminosity density (total 2-10 keV luminosity per Mpc super(3)) and find excellent agreement. While there are no significant stacked detections at z gap 5, we use our upper limits from 5 lap z lap 8 LBGs to constrain the supermassive black hole accretion history of the universe around the epoch of reionization.
The first 900 million years (Myr) to redshift z 6 (the first seven per cent of the age of the Universe) remains largely unexplored for the formation of galaxies. Large samples of galaxies have been ...found at z 6 (refs 1-4) but detections at earlier times are uncertain and unreliable. It is not at all clear how galaxies built up from the first stars when the Universe was about 300 Myr old (z 12-15) to z 6, just 600 Myr later. Here we report the results of a search for galaxies at z 7-8, about 700 Myr after the Big Bang, using the deepest near-infrared and optical images ever taken. Under conservative selection criteria we find only one candidate galaxy at z 7-8, where ten would be expected if there were no evolution in the galaxy population between z 7-8 and z 6. Using less conservative criteria, there are four candidates, where 17 would be expected with no evolution. This demonstrates that very luminous galaxies are quite rare 700 Myr after the Big Bang. The simplest explanation is that the Universe is just too young to have built up many luminous galaxies at z 7-8 by the hierarchical merging of small galaxies.
ABSTRACT
Recent observations of lensed sources have shown that the faintest ($M_{\mathrm{UV}} \approx -15\, \mathrm{mag}$) galaxies observed at $z$ = 6−8 appear to be extremely compact. Some of them ...have inferred sizes of less than 40 pc for stellar masses between 106 and $10^7\, {\mathrm{M}}_{\odot }$, comparable to individual super star clusters or star cluster complexes at low redshift. High-redshift, low-mass galaxies are expected to show a clumpy, irregular morphology and if star clusters form in each of these well-separated clumps, the observed galaxy size would be much larger than the size of an individual star-forming region. As supernova explosions impact the galaxy with a minimum delay time that exceeds the time required to form a massive star cluster, other processes are required to explain the absence of additional massive star-forming regions. In this work, we investigate whether the radiation of a young massive star cluster can suppress the formation of other detectable clusters within the same galaxy already before supernova feedback can affect the galaxy. We find that in low-mass ($M_{200} \lesssim 10^{10}\, {\mathrm{M}}_{\odot }$) haloes, the radiation from a compact star-forming region with an initial mass of $10^{7}\, {\mathrm{M}}_{\odot }$ can keep gas clumps with Jeans masses larger than ${\approx } 10^{7}\, {\mathrm{M}}_{\odot }$ warm and ionized throughout the galaxy. In this picture, the small intrinsic sizes measured in the faintest $z$ = 6−8 galaxies are a natural consequence of the strong radiation field that stabilizes massive gas clumps. A prediction of this mechanism is that the escape fraction for ionizing radiation is high for the extremely compact, high-$z$ sources.
We present the first determination of the galaxy luminosity function (LF) at z ∼ 4, 5, 6, and 7, in the rest-frame optical at (z′ band). The rest-frame optical light traces the content in low-mass ...evolved stars (∼stellar mass-M*), minimizing potential measurement biases for M*. Moreover, it is less affected by nebular line emission contamination and dust attenuation, is independent of stellar population models, and can be probed up to z ∼ 8 through Spitzer/IRAC. Our analysis leverages the unique full-depth Spitzer/IRAC 3.6-8.0 m data over the CANDELS/GOODS-N, CANDELS/GOODS-S, and COSMOS/UltraVISTA fields. We find that, at absolute magnitudes where is fainter than mag, linearly correlates with . At brighter , presents a turnover, suggesting that the stellar mass-to-light ratio could be characterized by a very broad range of values at high stellar masses. Median-stacking analyses recover an roughly independent on for mag, but exponentially increasing at brighter magnitudes. We find that the evolution of the LF marginally prefers a pure luminosity evolution over a pure density evolution, with the characteristic luminosity decreasing by a factor of between z ∼ 4 and z ∼ 7. Direct application of the recovered generates stellar mass functions consistent with average measurements from the literature. Measurements of the stellar-to-halo mass ratio at fixed cumulative number density show that it is roughly constant with redshift for . This is also supported by the fact that the evolution of the LF at can be accounted for by a rigid displacement in luminosity, corresponding to the evolution of the halo mass from abundance matching.
In order to clarify the dust production in the early Universe, we constrain the dust mass in high-redshift (z ≳ 5) galaxies using the upper limits obtained by ALMA. We perform fitting to the ...rest-frame UV–far-infrared spectral energy distribution (SED) of a giant Lyα emitter, Himiko, at z = 6.6 and a composite SED of z > 5 Lyman break galaxies (LBGs). For Himiko, we obtain a high dust temperature > 70 K. This high dust temperature puts a strong upper limit on the total dust mass Md ≲ 2 × 106 M⊙, and the dust mass produced per supernova (SN) md,SN ≲ 0.1 M⊙. Such a low md,SN suggests significant loss of dust by reverse shock destruction or outflow. For the LBG sample, we only obtain an upper limit for md,SN as ∼2 M⊙. This clarifies the importance of observing UV-bright objects (like Himiko) to constrain the dust production by SNe.
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