We present UV luminosity functions of dropout galaxies at with the complete Hubble Frontier Fields data. We obtain a catalog of ∼450 dropout-galaxy candidates (350, 66, and 40 at , 8, and 9, ...respectively), with UV absolute magnitudes that reach mag, ∼2 mag deeper than the Hubble Ultra Deep Field detection limits. We carefully evaluate number densities of the dropout galaxies by Monte Carlo simulations, including all lensing effects such as magnification, distortion, and multiplication of images as well as detection completeness and contamination effects in a self-consistent manner. We find that UV luminosity functions at have steep faint-end slopes, , and likely steeper slopes, at . We also find that the evolution of UV luminosity densities shows a non-accelerated decline beyond in the case of , but an accelerated one in the case of . We examine whether our results are consistent with the Thomson scattering optical depth from the Planck satellite and the ionized hydrogen fraction QH ii at based on the standard analytic reionization model. We find that reionization scenarios exist that consistently explain all of the observational measurements with the allowed parameters of and for , where is the escape fraction, Mtrunc is the faint limit of the UV luminosity function, and is the conversion factor of the UV luminosity to the ionizing photon emission rate. The length of the reionization period is estimated to be (for ), consistent with the recent estimate from Planck.
Abstract
We conduct a comprehensive study on dropout galaxy candidates at
z
∼ 9–16 using the first 90 arcmin
2
James Webb Space Telescope (JWST) Near Infrared Camera images taken by the early release ...observations (ERO) and early release science programs. With the JWST simulation images, we find that a number of foreground interlopers are selected with a weak photo-
z
determination (Δ
χ
2
> 4). We thus carefully apply a secure photo
-z
selection criterion (Δ
χ
2
> 9) and conventional color criteria with confirmations of the ERO Near Infrared Spectrograph spectroscopic redshifts, and obtain a total of 23 dropout galaxies at
z
∼ 9–16, including two candidates at
z
phot
=
16.25
−
0.46
+
0.24
and
16.41
−
0.55
+
0.66
. We perform thorough comparisons of dropout galaxies found in our work with recent JWST studies, and conclude that our galaxy sample is reliable enough for statistical analyses. We derive the UV luminosity functions at
z
∼ 9–16, and confirm that our UV luminosity functions at
z
∼ 9 and 12 agree with those determined by other Hubble Space Telescope and JWST studies. The cosmic star formation rate (SFR) density decreases from
z
∼ 9 to 12, and perhaps to 16, but the densities at
z
∼ 12–16 are higher than the constant star formation efficiency model. Interestingly, there are six bright galaxy candidates at
z
∼ 10–16 with
M
UV
< −19.5 mag and
M
*
∼ 10
8−9
M
⊙
. Because a majority (∼80%) of these galaxies show no signatures of active galactic nuclei in their morphologies, the high cosmic SFR densities and the existence of these UV-luminous galaxies are explained by the lack of suppression of star formation by the UV background radiation at the pre-reionization epoch and/or an efficient UV radiation production by a top-heavy initial mass function with Population III–like star formation.
We present the first statistical sample of faint type 1 AGNs at z > 4 identified by JWST/NIRSpec deep spectroscopy. Among the 185 galaxies at z _spec = 3.8–8.9 confirmed with NIRSpec, our systematic ...search for broad-line emission reveals 10 type 1 AGNs at z = 4.015–6.936 whose broad component is only seen in the permitted H α line and not in the forbidden O iii λ 5007 line that is detected with greater significance than H α . The broad H α line widths of FWHM ≃ 1000–6000 km s ^−1 suggest that the AGNs have low-mass black holes with M _BH ∼ 10 ^6 –10 ^8 M _⊙ , remarkably lower than those of low-luminosity quasars previously identified at z > 4 with ground-based telescopes. JWST and Hubble Space Telescope high-resolution images reveal that the majority of them show extended morphologies indicating significant contribution to the total lights from their host galaxies, except for three compact objects two of which show red spectral energy distributions, probably in a transition phase from faint AGNs to low luminosity quasars. Careful AGN-host decomposition analyses show that their host’s stellar masses are systematically lower than the local relation between the black hole mass and the stellar mass, implying a fast black hole growth consistent with predictions from theoretical simulations. A high fraction of the broad-line AGNs (∼5%), higher than z ∼ 0, indicates that the number density of such faint AGNs is higher than an extrapolation of the quasar luminosity function, implying a large population of AGNs in the early universe. Such faint AGNs contribute to cosmic reionization, while the total contribution is not large, up to ∼50% at z ∼ 6, because of their faint nature.
Abstract
We present the evolution of the mass–metallicity (MZ) relation at
z
= 4–10 derived with 135 galaxies identified in JWST/NIRSpec data taken from the three major public spectroscopy programs ...of ERO, GLASS, and CEERS. Because there are many discrepancies between the flux measurements reported by the early ERO studies, we first establish our NIRSpec data reduction procedure for reliable emission-line flux measurements and errors, successfully explaining Balmer decrements with no statistical tensions thorough comparisons with the early ERO studies. Applying the reduction procedure to the 135 galaxies, we obtain emission-line fluxes for physical property measurements. We confirm that 10 out of the 135 galaxies with O
iii
λ
4363 lines have electron temperatures of ≃(1.1–2.3) × 10
4
K, similar to lower-
z
star-forming galaxies, which can be explained by heating by young massive stars. We derive the metallicities of the 10 galaxies by a direct method and the rest of the galaxies with strong lines using the metallicity calibrations of Nakajima et al. applicable for these low-mass metal-poor galaxies, anchoring the metallicities with the direct-method measurements. We thus obtain the MZ relation and star formation rate (SFR)–MZ relation over
z
= 4–10. We find that there is a small evolution of the MZ relation from
z
∼ 2–3 to
z
= 4–10, while interestingly the SFR–MZ relation shows no evolution up to
z
∼ 8 but a significant decrease at
z
> 8 beyond the errors This SFR–MZ relation decrease at
z
> 8 may suggest a break of the metallicity equilibrium state via star formation, inflow, and outflow, while further statistical and local-baseline studies are needed for a conclusion.
ABSTRACT We present statistics of 133 faint 1.2 mm continuum sources detected in about 120 deep Atacama Large Millimeter/submillimeter Array (ALMA) pointing data that include all the archival deep ...data available by 2015 June. We derive number counts of 1.2 mm continuum sources down to 0.02 mJy partly with the assistance of gravitational lensing, and find that the total integrated 1.2 mm flux of the securely identified sources is Jy deg−2 which corresponds to of the extragalactic background light (EBL) measured by Cosmic Background Explorer observations. These results suggest that the major 1.2 mm EBL contributors are sources with 0.02 mJy, and that very faint 1.2 mm sources with 0.02 mJy contribute negligibly to the EBL with the possible flattening and/or truncation of number counts in this very faint flux regime. To understand the physical origin of our faint ALMA sources, we measure the galaxy bias bg by the counts-in-cells technique, and place a stringent upper limit of bg < 3.5 that is not similar to bg values of massive distant red galaxies and submillimeter galaxies but comparable to those of UV-bright, star-forming BzK galaxies (sBzKs) and Lyman break galaxies (LBGs). Moreover, in the optical and near-infrared (NIR) deep fields, we identify optical-NIR counterparts for 59% of our faint ALMA sources, the majority of which have luminosities, colors, and the IRX-β relation the same as sBzKs and LBGs. We thus conclude that about a half of our faint ALMA sources are dust-poor, high-z galaxies as known as sBzKs and LBGs in optical studies, and that these faint ALMA sources are not miniature (U)LIRGs simply scaled down with the infrared brightness.
We present very faint dropout galaxies at z ∼ 6−9 with a stellar mass M down to that are found in deep optical/near-infrared (NIR) images of the full data sets of the Hubble Frontier Fields (HFF) ...program in conjunction with deep ground-based and Spitzer images and gravitational-lensing magnification effects. We investigate stellar populations of the HFF dropout galaxies with the optical/NIR photometry and BEAGLE models made of self-consistent stellar population synthesis and photoionization models, carefully including strong nebular emission impacting on the photometry. We identify 453 galaxies with . Our best-estimate function is comparable to a model of star formation duration time of 100 Myr that is assumed in Bouwens et al. We derive the galaxy stellar mass functions (GSMFs) at z ∼ 6-9 that agree with those obtained by previous studies at , and that extend to . Estimating the stellar mass densities with the GSMFs, we find a very slow evolution from z ∼ 9 to z ∼ 6-7, which is consistent with the one estimated from star formation rate density measurements. In conjunction with the estimates of the galaxy effective radii Re on the source plane, we have pinpointed four objects with low stellar masses ( ) and very compact morphologies ( pc) that are comparable with those of globular clusters (GCs) in the Milky Way today. These objects are candidates of star clusters, some of which may be related to GCs today.
Abstract
Strong high-ionization lines such as He
ii
of young galaxies are puzzling at high and low redshift. Although recent studies suggest the existence of nonthermal sources, whether their ...ionizing spectra can consistently explain multiple major emission lines remains a question. Here we derive the general shapes of the ionizing spectra for three local extremely metal-poor galaxies (EMPGs) that show strong He
ii
λ
4686. We parameterize the ionizing spectra composed of a blackbody and power-law radiation mimicking various stellar and nonthermal sources. We use photoionization models for nebulae and determine seven parameters of the ionizing spectra and nebulae by Markov Chain Monte Carlo methods, carefully avoiding systematics of abundance ratios. We obtain the general shapes of ionizing spectra explaining ∼10 major emission lines within observational errors with smooth connections from observed X-ray and optical continua. We find that an ionizing spectrum of one EMPG has a blackbody-dominated shape, while the others have convex downward shapes at >13.6 eV, which indicate a diversity of the ionizing spectrum shapes. We confirm that the convex downward shapes are fundamentally different from ordinary stellar spectrum shapes, and that the spectrum shapes of these galaxies are generally explained by the combination of the stellar and ultraluminous X-ray sources. Comparisons with stellar synthesis models suggest that the diversity of the spectrum shapes arises from differences in the stellar age. If galaxies at
z
≳ 6 are similar to the EMPGs, high-energy (>54.4 eV) photons of the nonstellar sources negligibly contribute to cosmic reionization due to relatively weak radiation.
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