ABSTRACT
ALMA observations have revealed the presence of dust in the first generations of galaxies in the Universe. However, the dust temperature Td remains mostly unconstrained due to the few ...available FIR continuum data at redshift $z$ > 5. This introduces large uncertainties in several properties of high-$z$ galaxies, namely their dust masses, infrared luminosities, and obscured fraction of star formation. Using a new method based on simultaneous C $\scriptstyle \rm II$ 158-μm line and underlying dust continuum measurements, we derive Td in the continuum and C $\scriptstyle \rm II$ detected $z$ ≈ 7 galaxies in the ALMA Large Project REBELS sample. We find 39 < Td < 58 K, and dust masses in the narrow range Md = (0.9−3.6) × 107 M⊙. These results allow us to extend for the first time the reported Td($z$) relation into the Epoch of Reionization. We produce a new physical model that explains the increasing Td($z$) trend with the decrease of gas depletion time, tdep = Mg/SFR, induced by the higher cosmological accretion rate at early times; this hypothesis yields Td ∝ (1 + $z$)0.4. The model also explains the observed Td scatter at a fixed redshift. We find that dust is warmer in obscured sources, as a larger obscuration results in more efficient dust heating. For UV-transparent (obscured) galaxies, Td only depends on the gas column density (metallicity), $T_{\rm d} \propto N_{\rm H}^{1/6}$ (Td ∝ Z−1/6). REBELS galaxies are on average relatively transparent, with effective gas column densities around NH ≃ (0.03−1) × 1021 cm−2. We predict that other high-$z$ galaxies (e.g. MACS0416-Y1, A2744-YD4), with estimated Td ≫ 60 K, are significantly obscured, low-metallicity systems. In fact, Td is higher in metal-poor systems due to their smaller dust content, which for fixed LIR results in warmer temperatures.
ABSTRACT
We study the structure of spatially resolved, line-of-sight velocity dispersion for galaxies in the Epoch of Reionization (EoR) traced by C $\scriptstyle \rm II$ $158\, \mu \rm {m}$ line ...emission. Our laboratory is a simulated prototypical Lyman-break galaxy, ‘Freesia, part of the serra suite’. The analysis encompasses the redshift range 6 < z < 8, when Freesia is in a very active assembling phase. We build velocity dispersion maps for three dynamically distinct evolutionary stages (Spiral Disc at z = 7.4, Merger at z = 8.0, and Disturbed Disc at z = 6.5) using C $\scriptstyle \rm II$ hyperspectral data cubes. We find that, at a high spatial resolution of 0.005 arcsec (≃30 pc), the luminosity-weighted average velocity dispersion is $\sigma _{\rm {CII}}\simeq 23{\text {--}}38\, {\rm km\, s^{-1}}$ with the highest value belonging to the highly structured Disturbed Disc stage. Low-resolution observations tend to overestimate σC ii values due to beam smearing effects that depend on the specific galaxy structure. For an angular resolution of 0.02 arcsec (0.1 arcsec), the average velocity dispersion is $16{\!-\!}34{{\ \rm per\ cent}}$ ($52{\!-\!}115{{\ \rm per\ cent}}$) larger than the actual one. The C $\scriptstyle \rm II$ emitting gas in Freesia has a Toomre parameter $\mathcal {Q}\simeq 0.2$ and rotational-to-dispersion ratio of vc/σ ≃ 7 similar to that observed in z = 2−3 galaxies. The primary energy source for the velocity dispersion is due to gravitational processes, such as merging/accretion events; energy input from stellar feedback is generally sub-dominant ($\lt 10{{\ \rm per\ cent}}$). Finally, we find that the resolved σC ii−ΣSFR relation is relatively flat for $0.02\lt {\Sigma }_{\rm SFR}/{\rm M}_{\odot }\rm {yr}^{-1} {\rm kpc}^{-2} \lt 30$, with the majority of data lying on the derived analytical relation $\sigma \propto \Sigma _{\rm SFR}^{5/7}$. At high SFR, the increased contribution from stellar feedback steepens the relation, and σC ii rises slightly.
The cosmic infrared background (CIB) contains emissions accumulated over the entire history of the Universe, including from objects inaccessible to individual telescopic studies. The near-infrared ...(~1–10 μm) part of the CIB, and its fluctuations, reflects emissions from nucleosynthetic sources and gravitationally accreting black holes. If known galaxies are removed to sufficient depths the source-subtracted CIB fluctuations at near-infrared can reveal sources present in the first stars era and possibly new stellar populations at more recent times. This review discusses the recent progress in this newly emerging field which identified, with new data and methodology, significant source-subtracted CIB fluctuations substantially in excess of what can be produced by remaining known galaxies. The CIB fluctuations further appear coherent with unresolved cosmic x-ray background indicating a very high fraction of black holes among the new sources producing the CIB fluctuations. These observations have led to intensive theoretical efforts to explain the measurements and their properties. While current experimental configurations have limitations in decisively probing these theories, their potentially remarkable implications will be tested in the upcoming CIB measurements with the European Space Agency’s Euclid dark energy mission. The goals and methodologies of LIBRAE (Looking at Infrared Background Radiation with Euclid), a National Aeronautics and Space Administration (NASA) selected project for CIB science with Euclid, which has the potential for transforming the field into a new area of precision cosmology, are described.
We study the redshift evolution of the quasar (QSO) UV luminosity function (LF) for 0.5 < z < 6.5, by collecting the most up to date observational data and, in particular, the recently discovered ...population of faint active galactic nuclei (AGNs). We fit the QSO LF using either a double power-law function or a Schechter function, finding that both forms provide good fits to the data. We derive empirical relations for the LF parameters as a function of redshift and, based on these results, predict the QSO UV LF at z = 8. From the inferred LF evolution, we compute the redshift evolution of the QSO/AGN comoving ionizing emissivity and hydrogen photoionization rate. If faint AGNs are included, the contribution of QSOs to reionization increases substantially. However, their level of contribution critically depends on the detailed shape of the QSO LF, which can be constrained by efficient searches of high-z QSOs. To this aim, we predict the expected (i) number of z > 6 QSOs detectable by ongoing and future near-infrared surveys (as EUCLID and Wide-Field Infrared Survey Telescope), and (ii) number counts for a single radio-recombination line observation with Square Kilometre Array-MID (FoV = 0.49 deg2) as a function of the Hnα flux density, at 0 < z < 8. These surveys (even at z < 6) will be fundamental to better constrain the role of QSOs as reionization sources.
ABSTRACT
We analyse FIR dust continuum measurements for 14 galaxies (redshift z ≈ 7) in the ALMA Reionization Era Bright Emission Line Survey (REBELS) Large Program to derive their physical ...properties. Our model uses three input data, i.e. (a) the UV spectral slope, β, (b) the observed UV continuum flux at 1500 Å, F1500, (c) the observed continuum flux at $\approx 158\, \mu$m, F158, and considers Milky Way (MW) and SMC extinction curves, along with different dust geometries. We find that REBELS galaxies have 28−90.5 per cent of their star formation obscured; the total (UV+IR) star formation rates are in the range $31.5 \lt {\rm SFR}/({\rm M}_\odot \, {\rm yr}^{-1}) \lt 129.5$. The sample-averaged dust mass and temperature are $(1.3\pm 1.1)\times 10^7 \, \mathrm{M}_\odot$ and 52 ± 11 K, respectively. However, in some galaxies dust is particularly abundant (REBELS-14, $M^{\prime }_{\rm d} \approx 3.4 \times 10^7 \, \mathrm{M}_\odot$), or hot (REBELS-18, $T^{\prime }_{\rm d} \approx 67$ K). The dust distribution is compact (<0.3 kpc for 70 per cent of the galaxies). The inferred dust yield per supernova is $0.1 \le y_{\rm d}/\, \mathrm{M}_\odot \le 3.3$, with 70 per cent of the galaxies requiring $y_{\rm d} \lt 0.25 \, \mathrm{M}_\odot$. Three galaxies (REBELS-12, 14, 39) require $y_{\rm d} \gt 1 \, \mathrm{M}_\odot$, which is likely inconsistent with pure SN production, and might require dust growth via accretion of heavy elements from the interstellar medium. With the SFR predicted by the model and a MW extinction curve, REBELS galaxies detected in C ii nicely follow the local LCII−SFR relation, and are approximately located on the Kennicutt–Schmidt relation. The sample-averaged gas depletion time is $0.11\, y_{\rm P}^{-2}$ Gyr, where yP is the ratio of the gas-to-stellar distribution radius. For some systems, a solution simultaneously matching the observed (β, F1500, F158) values cannot be found. This occurs when the index Im = (F158/F1500)/(β − βint), where βint is the intrinsic UV slope, exceeds $I_m^{*}\approx 1120$ for an MW curve. For these objects, we argue that the FIR and UV emitting regions are not co-spatial, questioning the use of the IRX–β relation.
Abstract
With the aim of improving predictions on far-infrared (FIR) line emission from Giant Molecular Clouds (GMCs), we study the effects of photoevaporation (PE) produced by external ...far-ultraviolet (FUV) and ionizing (extreme-ultraviolet) radiation on GMC structure. We consider three different GMCs with mass in the range MGMC = 103-106 M⊙. Our model includes (i) an observationally based inhomogeneous GMC density field, and (ii) its time evolution during the PE process. In the fiducial case (MGMC ≈ 105 M⊙), the PE time (tpe) increases from 1 to 30 Myr for gas metallicity Z = 0.05–1 Z⊙, respectively. Next, we compute the time-dependent luminosity of key FIR lines tracing the neutral and ionized gas layers of the GMCs, (C ii at 158 μm, O iii at 88 μm) as a function of G0, and Z until complete PE at tpe. We find that the specific C ii luminosity is almost independent of the GMC model within the survival time of the cloud. Stronger FUV fluxes produce higher C ii and O iii luminosities, however, lasting for progressively shorter times. At Z = Z⊙, the C ii emission is maximized ($L_{\rm C\,\small {II}} \approx 10^4\,\rm {L_{{\odot }}}$ for the fiducial model) for t < 1 Myr and log G0 ≥ 3. Noticeably, and consistently with the recent detection by Inoue et al. of a galaxy at redshift z ≈ 7.2, for Z ≤ 0.2 Z⊙, the O iii line might outshine C ii emission by up to ≈1000 times. We conclude that the O iii line is a key diagnostic of low-metallicity interstellar medium, especially in galaxies with very young stellar populations.
Past observations of quasar host galaxies at z> 6 have found cold gas and star formation on compact scales of a few kiloparsecs. We present new high sensitivity IRAM Plateau de Bure Interferometer ...follow-up observations of the C ii 158 μm emission line and far-infrared (FIR) continuum in the host galaxy of SDSS J1148+5251, a luminous quasar at redshift 6.4189. We find that a large portion of the gas traced by C ii is at high velocities, up to ~1400 km s-1relative to the systemic velocity, confirming the presence of a major outflow as indicated by previous observations. The outflow has a complex morphology and reaches a maximum projected radius of ≃30 kpc. The extreme spatial extent of the outflow allows us, for the first time in an external galaxy, to estimate mass-loss rate, kinetic power, and momentum rate of the outflow as a function of the projected distance from the nucleus and the dynamical time scale. These trends reveal multiple outflow events during the past 100 Myr, although the bulk of the mass, energy, and momentum appear to have been released more recently within the past ~20 Myr. Surprisingly, we discover that the quiescent gas at systemic velocity is also extremely extended. More specifically, we find that, while 30% of the C ii within v ∈(−200, 200) km s-1 traces a compact component that is not resolved by our observations, 70% of the C ii emission in this velocity range is extended with a projected full width at half maximum (FWHM) size of 17.4 ± 1.4 kpc. We detect FIR continuum emission associated with both the compact and the extended C ii components, although the extended FIR emission has a FWHM of 11 ± 3 kpc, thus smaller than the extended C ii source. Overall, our results indicate that the cold gas traced by C ii is distributed up to r ~ 30 kpc in the host galaxy of SDSS J1148+5251. A large amount of extended C ii is likely to be associated with star formation occurring on large scales, but the C ii source extends well beyond the FIR continuum, and additional multi-wavelength observations are needed in order to clarify the origin of this very extended C ii .
ABSTRACT
We present Atacama Large Millimeter/submillimeter Array (ALMA) observations of eight highly excited CO (${\rm J_{\rm up}}$ > 8) lines and continuum emission in two z ∼ 6 quasars: ...SDSS J231038.88+185519.7 (hereafter J2310), for which CO(8–7), CO(9–8), and CO(17–16) lines have been observed, and ULAS J131911.29+095951.4 (J1319), observed in the CO(14–13), CO(17–16), and CO(19–18) lines. The continuum emission of both quasars arises from a compact region (<0.9 kpc). By assuming a modified blackbody law, we estimate dust masses of log(Mdust/M⊙) = 8.75 ± 0.07 and log(Mdust/M⊙) = 8.8 ± 0.2 and dust temperatures of Tdust = 76 ± 3 K and $T_{\rm dust}=66^{+15}_{-10}\,{\rm K}$, respectively, for J2310 and J1319. Only CO(8–7) and CO(9–8) in J2310 are detected, while 3σ upper limits on luminosities are reported for the other lines of both quasars. The CO line luminosities and upper limits measured in J2310 and J1319 are consistent with those observed in local active galactic nuclei and starburst galaxies, and other z ∼ 6 quasars, except for SDSS J1148+5251 (J1148), the only quasar at z = 6.4 with a previous CO(17–16) line detection. By computing the CO spectral line energy distributions normalized to the CO(6–5) line and far-infrared luminosities for J2310, J1319, and J1148, we conclude that different gas heating mechanisms (X-ray radiation and/or shocks) may explain the different CO luminosities observed in these z ∼ 6 quasar. Future ${\rm J_{\rm up}}$ > 8 CO observations will be crucial to understand the processes responsible for molecular gas excitation in luminous high-z quasars.
ABSTRACT
We investigate the infrared (IR) emission of high-redshift (z ∼ 6), highly star-forming (${{\rm SFR}\gt 100\,{\rm M}_{\odot }\, {\rm yr}^{-1}}$) galaxies, with/without active galactic nuclei ...(AGN), using a suite of cosmological simulations featuring dust radiative transfer. Synthetic spectral energy distributions (SEDs) are used to quantify the relative contribution of stars/AGN to dust heating. In dusty (Md ≳ 3 × 107 M⊙) galaxies, ≳50–90 per cent of the ultraviolet (UV) radiation is obscured by dust inhomogeneities on scales ≳100 pc. In runs with AGN, a clumpy, warm (≈250 K) dust component coexists with a colder (≈60 K) and more diffuse one, heated by stars. Warm dust provides up to ${50 {{\ \rm per\ cent}}}$ of the total infrared (IR) luminosity, but only ${\lesssim}0.1 {{\ \rm per\ cent}}$ of the total mass content. The AGN boosts the MIR flux by 10–100 times with respect to star-forming galaxies, without significantly affecting the far-IR. Our simulations successfully reproduce the observed SED of bright (MUV ∼ −26) z ∼ 6 quasars, and show that these objects are part of complex, dust-rich merging systems, containing multiple sources (accreting black holes and/or star-forming galaxies) in agreement with recent HST and ALMA observations. Our results show that the proposed ORIGINS missions will be able to investigate the mid-IR (MIR) properties of dusty star-forming galaxies and to obtain good-quality spectra of bright quasars at z ∼ 6. Finally, the MIR-to-FIR flux ratio of faint (MUV ∼ −24) AGN is >10 times higher than for normal star-forming galaxies. This implies that combined JWST/ORIGINS/ALMA observations will be crucial to identify faint and/or dust-obscured AGN in the distant Universe.
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