Finding the first generation of galaxies in the early Universe is the greatest step forward towards understanding galaxy formation and evolution. For a strategic survey of such galaxies and the ...interpretation of the obtained data, this paper presents an ultraviolet-to-optical spectral model of galaxies with a great care of the nebular emission. In particular, we present a machine-readable table of intensities of 119 nebular emission lines from Lyα to the rest-frame 1
m as a function of metallicity from zero to the solar one. Based on the spectral model, we present criteria of equivalent widths of Lyα, He iiλ1640, Hα, Hβ and O iiiλ5007 to select extremely metal-poor and metal-free galaxies although these criteria have uncertainty caused by the Lyman continuum escape fraction and the star formation duration. We also present criteria of broad-band colours which will be useful to select candidates for spectroscopic follow-up from drop-out galaxies. We propose the line intensity ratio of O iiiλ5007 to Hβ < 0.1 as the most robust criterion for <1/1000 of the solar metallicity. This ratio of a galaxy with a few M⊙ yr−1 at z∼ 8 is detectable by spectroscopy with the James Webb Space Telescope within a reasonable exposure time.
We present an updated version of the so-called Madau model for attenuation of the radiation from distant objects by intergalactic neutral hydrogen. First, we derive the distribution function of ...intergalactic absorbers from the latest observational statistics of the Lyα forest, Lyman-limit systems and damped Lyα systems. The distribution function reproduces the observed redshift evolution of the Lyα depression and the mean-free path of the Lyman continuum excellently and simultaneously. We then derive a set of analytic functions describing the mean intergalactic attenuation curve for objects at z > 0.5. The new model predicts less (or more) Lyα attenuation for z ≃ 3–5 (z > 6) sources through the usual broad-band filters relative to the original Madau model. This may cause a systematic difference in the photometric redshift estimates, which is, however, still small: about 0.05. Finally, we find a more than 0.5 mag overestimation of Lyman-continuum attenuation in the original Madau model at z > 3, which causes a significant overcorrection against direct observations of the Lyman continuum of galaxies.
It has been proposed that supermassive black holes (SMBHs) are originated from direct-collapse black holes (DCBHs) that are formed at z ≳ 10 in the primordial gas in the case where H2 cooling is ...suppressed by strong external radiation. In this work, we study the critical specific intensity J
crit required for DCBH formation for various radiation spectral shapes by a series of one-zone calculations of a collapsing primordial-gas cloud. We calculate the critical specific intensity at the Lyman–Werner (LW) bands
$J_{\rm LW,21}^{\rm crit}$
(in units of 10−21 erg s−1 Hz−1 sr−1 cm−2) for realistic spectra of metal-poor galaxies. We find that J
crit is not sensitive to the age or metallicity for the constant star formation galaxies with
$J_{\rm LW,21}^{\rm crit}=1300-1400$
, while J
crit decreases as galaxies become older or more metal-enriched for the instantaneous starburst galaxies. However, for the young (the age < 100 Myr) and/or extremely metal poor (Z < 5 × 10−4 Z⊙) instantaneous starburst galaxies, such dependence is not strong and
$J_{\rm LW,21}^{\rm crit}= 1000-1400$
. We also find that J
crit is solely determined by the ratio between the H− and H2 photodissociation rate coefficients,
$k_{\rm H^-,pd}/k_{\rm H_2,pd}$
, with which we develop a formula to estimate J
crit for a given spectrum. The higher value of J
crit for the realistic spectra than those expected in the literature significantly reduces the estimated DCBH number density n
DCBH. By extrapolating the result of Dijkstra, Ferrara & Mesinger, we obtain n
DCBH ∼ 10−10 cMpc−3 at z = 10, which is roughly consistent with the observed number density of high-redshift SMBHs n
SMBH ∼ 10−9 cMpc−3 at z ∼ 6, considering large uncertainties in the estimation.
Abstract
We present an analysis to disentangle the connection between physical quantities that characterize the conditions of ionized H ii regions – metallicity (Z), ionization parameter (U), and ...electron density (ne) – and the global stellar mass (M*) and specific star formation rate (sSFR = SFR/M*) of the host galaxies. We construct composite spectra of galaxies at 0.027 ≤ z ≤ 0.25 from Sloan Digital Sky Survey, separating the sample into bins of M* and sSFR, and estimate the nebular conditions from the emission-line flux ratios. Specially, metallicity is estimated from the direct method based on the faint auroral lines O iiiλ4363 and O iiλλ7320,7330. The derived metallicities cover a range of 12 + log O/H ∼ 7.6–8.9. It is found that the three nebular parameters, Z, U, and ne, are tightly correlated with the location in the M*–sSFR plane. With simple physically motivated ansätze, we derive scaling relations between these physical quantities by performing multiregression analysis. In particular, we find that U is primarily controlled by sSFR, as U∝sSFR0.43, but also depends significantly on both Z and ne. The derived partial dependence of U∝Z−0.36 is weaker than the apparent correlation (U∝Z−1.52). The partial dependence of U on ne is found to be $U \propto n_\mathrm{e}^{-0.29}$. The scaling relations we derived are in agreement with predictions from theoretical models and observations of each aspect of the link between these quantities. Our results provide a useful set of equations to predict the nebular conditions and emission-line fluxes of galaxies in semi-analytic models.
ABSTRACT
The estimation of the temperature and mass of dust in high-redshift galaxies is essential for discussions of the origin of dust in the early Universe. However, this is made difficult by ...limited sampling of the infrared spectral-energy distribution. Here, we present an algorithm for deriving the temperature and mass of dust in a galaxy, assuming dust to be in radiative equilibrium. We formulate the algorithm for three geometries: a thin spherical shell, a homogeneous sphere and a clumpy sphere. We also discuss the effects of the mass absorption coefficients of dust at ultraviolet and infrared wavelengths, κUV and κIR, respectively. As an example, we apply the algorithm to a normal, dusty star-forming galaxy at z = 7.5, A1689zD1, for which three data points in the dust continuum are available. Using κUV = 5.0 × 104 and $\kappa _{\rm IR}=30(\lambda /100\,\mu{\rm m})^{-\beta }$ cm2 g−1 with β = 2.0, we obtain dust temperatures of 38–70 K and masses of 106.5–7.3 M⊙ for the three geometries considered. We obtain similar temperatures and masses from just a single data point in the dust continuum, suggesting that the algorithm is useful for high-redshift galaxies with limited infrared observations. In the case of the clumpy sphere, the temperature becomes equal to that of the usual modified black-body fit, because an additional parameter describing the clumpiness works as an adjuster. The best-fitting clumpiness parameter is ξcl = 0.1, corresponding to ∼10 per cent of the volume filling factor of the clumps in this high-redshift galaxy if the clump size is ∼10 pc, similar to that of giant molecular clouds in the local Universe.
We present two bright galaxy candidates at z ∼ 12–13 identified in our H-dropout Lyman break selection with 2.3 deg(exp 2) near-infrared deep imaging data. These galaxy candidates, selected after ...careful screening of foreground interlopers, have spectral energy distributions showing a sharp discontinuity around 1.7 μm, a flat continuum at 2–5 μm, and nondetections at <1.2 μm in the available photometric data sets, all of which are consistent with a z > 12 galaxy. An ALMA program targeting one of the candidates shows a tentative 4σ O III 88 μm line at z = 13.27, in agreement with its photometric redshift estimate. The number density of the z ∼ 12–13 candidates is comparable to that of bright z ∼ 10 galaxies and is consistent with a recently proposed double-power-law luminosity function rather than the Schechter function, indicating little evolution in the abundance of bright galaxies from z ∼ 4 to 13. Comparisons with theoretical models show that the models cannot reproduce the bright end of rest-frame ultraviolet luminosity functions at z ∼ 10–13. Combined with recent studies reporting similarly bright galaxies at z ∼ 9–11 and mature stellar populations at z ∼ 6–9, our results indicate the existence of a number of star-forming galaxies at z > 10, which will be detected with upcoming space missions such as the James Webb Space Telescope, Nancy Grace Roman Space Telescope, and GREX-PLUS.
Lyman continuum leaking AGN in the SSA22 field Micheva, Genoveva; Iwata, Ikuru; Inoue, Akio K
Monthly notices of the Royal Astronomical Society,
02/2017, Letnik:
465, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Subaru/SuprimeCam narrow-band photometry of the SSA22 field reveals the presence of four Lyman continuum (LyC) candidates among a sample of 14 active galactic nuclei (AGNs). Two show offsets and ...likely have stellar LyCin nature or are foreground contaminants. The remaining two LyC candidates are type I AGN. We argue that the average LyC escape fraction of high-redshift, low-luminosity AGN is not likely to be unity, as often assumed in the literature. From direct measurement we obtain the average LyC-to-UV flux density ratio and ionizing emissivity for a number of AGN classes and find it at least a factor of 2 lower than values obtained assuming f sub( esc) = 1. Comparing to recent Ly a forest measurements, AGNs at redshift z ~ 3 make up at most ~12 per cent and as little as ~5 per cent of the total ionizing budget. Our results suggest that AGNs are unlikely to dominate the ionization budget of the Universe at high redshifts.
The fraction of ionizing photons that escape (f sub(esc)) from z gap 6 galaxies is an important parameter for assessing the role of these objects in the reionization of the universe, but the opacity ...of the intergalactic medium precludes a direct measurement of f sub(esc) for individual galaxies at these epochs. We argue that since f sub(esc) regulates the impact of nebular emission on the spectra of galaxies, it should nonetheless be possible to indirectly probe f sub(esc) well into the reionization epoch. As a first step, we demonstrate that by combining measurements of the rest-frame UV slope beta with the equivalent width of the H beta emission line, galaxies with very high Lyman continuum escape fractions (f sub(esc) > or =, slanted 0.5) should be identifiable up to z approximately 9 through spectroscopy with the upcoming James Webb Space Telescope (JWST). By targeting strongly lensed galaxies behind low-redshift galaxy clusters, JWST spectra of sufficiently good quality can be obtained for M sub(1500) lap -16.0 galaxies at z approximately 7 and for M sub(1500) gap -17.5 galaxies at z approximately 9. Dust-obscured star formation may complicate the analysis, but supporting observations with ALMA or the planned SPICA mission may provide useful constraints on this effect.
Abstract
In the first image of the James Webb Space Telescope (JWST) of SMACS J0723.3-7327, one of the most outstanding features is the emergence of a large number of red spiral galaxies, because ...such red spiral galaxies are only a few percent in the number fraction among nearby spiral galaxies. While these apparently red galaxies were already detected with the Spitzer Space Telescope at ∼3–4
μ
m, the revolutionized view from the JWST’s unprecedented spatial resolution has unveiled their hidden spiral morphology for the first time. Within the red spiral galaxies, we focus on the two reddest galaxies that are very faint in the <0.9
μ
m
bands and show red colors in the 2–4
μ
m bands. Our study finds that the two extremely red spiral galaxies are likely to be in the cosmic noon (1 <
z
< 3). One of the extremely red spiral galaxies is more likely to be a passive galaxy having moderate dust reddening (i.e., ∼zero star formation rate with A
V
~ 1 mag). The other is consistent with both passive and dusty starburst solutions (i.e., star formation rate > 100 M
⊙
yr−1 with A
V
∼ 3 mag). These “red spiral” galaxies would be an interesting, potentially new population of galaxies, as we start to see their detailed morphology using the JWST, for the first time.
A fundamental quest of modern astronomy is to locate the earliest galaxies and study how they influenced the intergalactic medium a few hundred million years after the Big Bang
. The abundance of ...star-forming galaxies is known to decline
from redshifts of about 6 to 10, but a key question is the extent of star formation at even earlier times, corresponding to the period when the first galaxies might have emerged. Here we report spectroscopic observations of MACS1149-JD1
, a gravitationally lensed galaxy observed when the Universe was less than four per cent of its present age. We detect an emission line of doubly ionized oxygen at a redshift of 9.1096 ± 0.0006, with an uncertainty of one standard deviation. This precisely determined redshift indicates that the red rest-frame optical colour arises from a dominant stellar component that formed about 250 million years after the Big Bang, corresponding to a redshift of about 15. Our results indicate that it may be possible to detect such early episodes of star formation in similar galaxies with future telescopes.
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