Simulating cosmic metal enrichment by the first galaxies

We study cosmic metal enrichment via AMR hydrodynamical simulations in a (10 Mpc/h)$^3$ volume following the Pop III-Pop II transition and for different Pop III IMFs. We have analyzed the joint evolution of metal enrichment on galactic and intergalactic scales at z=6 and z=4. Galaxies account for <9% of the baryonic mass; the remaining gas resides in the diffuse phases: (a) voids, i.e. regions with extremely low density ($\Delta$<1), (b) the true intergalactic medium (IGM, 1<$\Delta$<10) and (c) the circumgalactic medium (CGM, 10<$\Delta<10^{2.5}$), the interface between the IGM and galaxies. By z=6 a galactic mass-metallicity relation is established. At z=4, galaxies with a stellar mass $M_*=10^{8.5}M_\odot$ show log(O/H)+12=8.19, consistent with observations. The total amount of heavy elements rises from $\Omega^{SFH}_Z=1.52\, 10^{-6}$ at z=6 to 8.05 $10^{-6}$ at z=4. Metals in galaxies make up to ~0.89 of such budget at z=6; this fraction increases to ~0.95 at z=4. At z=6 (z=4) the remaining metals are distributed in CGM/IGM/voids with the following mass fractions: 0.06/0.04/0.01 (0.03/0.02/0.01). Analogously to galaxies, at z=4 a density-metallicity ($\Delta$-Z) relation is in place for the diffuse phases: the IGM/voids have a spatially uniform metallicity, Z~$10^{-3.5}$Zsun; in the CGM Z steeply rises with density up to ~$10^{-2}$Zsun. In all diffuse phases a considerable fraction of metals is in a warm/hot (T>$10^{4.5}$K) state. Due to these physical conditions, CIV absorption line experiments can probe only ~2% of the total carbon present in the IGM/CGM; however, metal absorption line spectra are very effective tools to study reionization. Finally, the Pop III star formation history is almost insensitive to the chosen Pop III IMF. Pop III stars are preferentially formed in truly pristine (Z=0) gas pockets, well outside polluted regions created by previous star formation episodes.Comment: 23 pages, 18 figures, 3 tables, Accepted for publication in MNRA

The stellar populations of high-redshift dwarf galaxies

We use high-resolution ($\approx 10$ pc), zoom-in simulations of a typical (stellar mass $M_\star\simeq10^{10}M_\odot$) Lyman Break Galaxy (LBG) at $z\simeq 6$ to investigate the stellar populations of its six dwarf galaxy satellites, whose stellar [gas] masses are in the range $\log (M_\star/M_\odot) \simeq 6-9$ [$\log (M_{gas}/M_\odot) \simeq4.3-7.75$]. The properties and evolution of satellites show no dependence on the distance from the central massive LBG ($< 11.5$ kpc). Instead, their star formation and chemical enrichment histories are tightly connected their stellar (and sub-halo) mass. High-mass dwarf galaxies ($\rm M_\star \gtrsim 5\times 10^8 M_\odot$) experience a long history of star formation, characterised by many merger events. Lower-mass systems go through a series of short star formation episodes, with no signs of mergers; their star formation activity starts relatively late ($z\approx 7$), and it is rapidly quenched by internal stellar feedback. In spite of the different evolutionary patterns, all satellites show a spherical morphology, with ancient and more metal-poor stars located towards the inner regions. All six dwarf satellites experienced high star formation rate ($\rm >5\,M_\odot yr ^{-1}$) bursts, which can be detected by JWST while targeting high-$z$ LBGs.Comment: 17 pages, 14 figures. To be published in MNRA

The dense molecular gas in the z∼6\rm z\sim6 QSO SDSS J231038.88+185519.7 resolved by ALMA

We present ALMA observations of the CO(6-5) and [CII] emission lines and the sub-millimeter continuum of the $z\sim6$ quasi-stellar object (QSO) SDSS J231038.88+185519.7. Compared to previous studies, we have analyzed a synthetic beam that is ten times smaller in angular size, we have achieved ten times better sensitivity in the CO(6-5) line, and two and half times better sensitivity in the [CII] line, enabling us to resolve the molecular gas emission. We obtain a size of the dense molecular gas of $2.9\pm0.5$ kpc, and of $1.4\pm0.2$ kpc for the 91.5 GHz dust continuum. By assuming that CO(6-5) is thermalized, and by adopting a CO--to--$H_2$ conversion factor $\rm \alpha_{CO} = 0.8~ M_{\odot}~K^{-1}~ (km/s)^{-1} ~pc^{2}$, we infer a molecular gas mass of $\rm M(H_2)=(3.2 \pm0.2) \times 10^{10}\rm M_{\odot}$. Assuming that the observed CO velocity gradient is due to an inclined rotating disk, we derive a dynamical mass of $\rm M_{dyn}~sin^2(i) = (2.4\pm0.5) \times 10^{10}~ M_{\odot}$, which is a factor of approximately two smaller than the previously reported estimate based on [CII]. Regarding the central black hole, we provide a new estimate of the black hole mass based on the C~IV emission line detected in the X-SHOOTER/VLT spectrum: $\rm M_{BH}=(1.8\pm 0.5) \times 10^{9}~ M_{\odot}$. We find a molecular gas fraction of $\rm \mu=M(H_2)/M^*\sim4.4$, where $\rm M^*\approx M_{dyn} - M(H_2)-M(BH)$. We derive a ratio $v_{rot}/\sigma \approx 1-2$ suggesting high gas turbulence, outflows/inflows and/or complex kinematics due to a merger event. We estimate a global Toomre parameter $Q\sim 0.2-0.5$, indicating likely cloud fragmentation. We compare, at the same angular resolution, the CO(6-5) and [CII] distributions, finding that dense molecular gas is more centrally concentrated with respect to [CII]. We find that the current BH growth rate is similar to that of its host galaxy.Comment: A&A in pres

Inhibition of Bromodomain and Extraterminal Domain (BET) Proteins by JQ1 Unravels a Novel Epigenetic Modulation to Control Lipid Homeostasis

The homeostatic control of lipid metabolism is essential for many fundamental physiological processes. A deep understanding of its regulatory mechanisms is pivotal to unravel prospective physiopathological factors and to identify novel molecular targets that could be employed to design promising therapies in the management of lipid disorders. Here, we investigated the role of bromodomain and extraterminal domain (BET) proteins in the regulation of lipid metabolism. To reach this aim, we used a loss-of-function approach by treating HepG2 cells with JQ1, a powerful and selective BET inhibitor. The main results demonstrated that BET inhibition by JQ1 efficiently decreases intracellular lipid content, determining a significant modulation of proteins involved in lipid biosynthesis, uptake and intracellular trafficking. Importantly, the capability of BET inhibition to slow down cell proliferation is dependent on the modulation of cholesterol metabolism. Taken together, these data highlight a novel epigenetic mechanism involved in the regulation of lipid homeostasis

The interstellar medium of high-redshift galaxies: Gathering clues from C III] and [C II] lines

Context. A tight relation between [C II] 158 μm line luminosity and the star formation rate (SFR) has been observed for local galaxies. At high redshift (z &gt; 5), galaxies instead deviate downwards from the local Σ[C II] − ΣSFR relation. This deviation might be caused by different interstellar medium (ISM) properties in galaxies at early epochs. Aims. To test this hypothesis, we combined the [C II] and SFR data with C III] 1909 Å line observations and our physical models. We additionally investigated how ISM properties, such as burstiness, κs, total gas density, n, and metallicity, Z, affect the deviation from the Σ[C II] − ΣSFR relation in these sources. Methods. We present the VLT/X-shooter observations targeting the C III] λ1909 line emission in three galaxies at 5.5 &lt; z &lt; 7.0. We include archival X-shooter data of two other sources at 5.5 &lt; z &lt; 7.0 and the VLT/MUSE archival data of six galaxies at z ∼ 2. We extend our sample of galaxies with eleven star-forming systems at 6 &lt; z &lt; 7.5, with either C III] or [C II] detection reported in the literature. Results. We detected C III] λλ1907, 1909 line emission in HZ10 and we derived the intrinsic, integrated flux of the C III] λ1909 line. We constrained the ISM properties for our sample of galaxies, κs, n, and Z, by applying our physically motivated model based on the MCMC algorithm. For the most part, high-z star-forming galaxies show subsolar metallicities. The majority of the sources have log(κs) ≳ 1, that is, they overshoot the Kennicutt–Schmidt (KS) relation by about one order of magnitude. Conclusions. Our findings suggest that the whole KS relation might be shifted upwards at early times. Furthermore, all the high-z galaxies of our sample lie below the Σ[C II] − ΣSFR local relation. The total gas density, n, shows the strongest correlation with the deviation from the local Σ[C II] − ΣSFR relation, namely, low-density high-z systems have lower [C II] surface brightness, in agreement with theoretical models

Dust attenuation law in JWST galaxies at z = 7-8

Attenuation curves in galaxies depend on dust chemical composition, content, and grain size distribution. Such parameters are related to intrinsic galaxy properties such as metallicity, star formation rate, and stellar age. Due to the lack of observational constraints at high redshift, dust empirical curves measured in the local Universe (e.g. Calzetti and SMC curves) have been employed to describe the dust attenuation at early epochs. We exploit the high sensitivity and spectral resolution of the JWST to constrain the dust attenuation curves in high-z galaxies. Our goals are to check whether dust attenuation curves evolve with redshift and quantify the dependence of the inferred galaxy properties on the assumed dust attenuation law. We develop a modified version of the SED fitting code BAGPIPES by including a detailed dust attenuation curve parametrization. Dust parameters are derived, along with galaxy properties, from the fit to the data from FUV to mm bands. Once applied to three star-forming galaxies at z = 7-8, we find that their attenuation curves differ from local templates. One out of three galaxies shows a characteristic MW bump, typically associated to the presence of small carbonaceous dust grains such as PAHs. This is one of the first evidences suggesting the presence of PAHs in early galaxies. Galaxy properties such as stellar mass and SFR inferred from SED fitting are strongly affected by the assumed attenuation curve, though the adopted star formation history also plays a major role. Our results highlight the importance of accounting for the potential diversity of dust attenuation laws when analyzing the properties of galaxies at the EoR, whose dust properties are still poorly understood. The application of our method to a larger sample of galaxies observed with JWST can provide us important insights into the properties of dust and galaxies in the early universe.Comment: 19 pages, 10 figure

Witnessing Galaxy Assembly at the Edge of the Reionization Epoch

We report the discovery of Serenity-18, a galaxy at z=5.939 for which we could measure the content of molecular gas, M(H_2)~ 5 x10^9 M_sun, traced by the CO(6-5) emission, together with the metal-poor ([Fe/H]=-3.08 +- 0.12, [Si/H]=-2.86 +- 0.14) gas clump/filament which is possibly feeding its growth. The galaxy has an estimated star formation rate of ~100 M_sun yr^{-1}, implying that it is a typical main sequence galaxy at these redshifts. The metal-poor gas is detected through a damped Lyman-alpha absorber (DLA) observed at a spatial separation of 40 kpc and at the same redshift of Serenity-18, along the line of sight to the quasar SDSS J2310+1855 (z_em = 6.0025). The chemical abundances measured for the damped Lyman-alpha system are in very good agreement with those measured for other DLAs discovered at similar redshifts, indicating an enrichment due to massive PopII stars. The galaxy/Damped system we discovered is a direct observational evidence of the assembly of a galaxy at the edge of the reionization epoch.STFC ER

A survey of high-z galaxies: serra simulations

We introduce SERRA, a suite of zoom-in high-resolution (1.2 ×104 M⊙, ≃ 25 pc at z = 7.7) cosmological simulations including non-equilibrium chemistry and on-the-fly radiative transfer. The outputs are post-processed to derive galaxy ultraviolet (UV) + far-infrared (FIR) continuum and emission line properties. Results are compared with available multiwavelength data to constrain the physical properties [e.g. star formation rates (SFRs), stellar/gas/dust mass, metallicity] of high-redshift 6 ≲ z ≲ 15 galaxies. This flagship paper focuses on the z = 7.7 sub-sample, including 202 galaxies with stellar mass 107 M⊙ ≲ M⊙ ≲ 5 ×1010 M⊙, and specific star formation rate ranging from sSFR ∼100 Gyr-1 in young, low-mass galaxies to ∼10 Gyr-1 for older, massive ones. At this redshift, SERRA galaxies are typically bursty, i.e. they are located abo v e the Schmidt-Kennicutt relation by a factor κs = 3.03+4.9-1.8, consistent with recent findings for [O III ] and [C II ] emitters at high z. They also show relatively large InfraRed eXcess (IRX = LFIR/LUV) values as a result of their compact/clumpy morphology effectively blocking the stellar UV luminosity. Note that this conclusion might be affected by insufficient spatial resolution at the molecular cloud level. We confirm that early galaxies lie on the standard [C II ] -SFR relation; their observed L[OIII]/L [CII] ≃ 1-10 ratios can be reproduced by a part of the SERRA galaxies without the need of a top-heavy initial mass function and/or anomalous C/O abundances. [O I] line intensities are similar to local ones, making ALMA high-z detections challenging but feasible ( ∼6 h for an SFR of 50 M⊙yr-1)

The black hole and host galaxy growth in an isolated z∼6z\sim 6 QSO observed with ALMA

The outstanding mass growth of supermassive black holes (SMBHs) at the Reionisation Epoch and how it is related to the concurrent growth of their host galaxies, poses challenges to theoretical models aimed at explaining how these systems formed in short timescales (<1 Gyr). To trace the average evolutionary paths of quasi-stellar objects (QSOs) and their host galaxies in the BH mass-host mass ($M_{\rm dyn}$) plane, we compare the star formation rate (SFR), derived from the accurate estimate of the dust temperature and the dust mass ($T_{\rm dust}, M_{\rm dust}$), with the BH accretion rate. To this aim, we analysed a deep, $900$ pc resolution ALMA observation of the sub-mm continuum, [CII] and H$_2$O of the $z\sim 6$ QSO J2310+1855, enabling a detailed study of dust properties and cold gas kinematics. We performed an accurate SED analysis obtaining a dust temperature of $T_{\rm dust} = 71$ K and a dust mass of $M_{\rm dust}= 4.4 \times 10^8\ \rm M_{\odot}$. The implied AGN-corrected SFR is $1240 \ \rm M_{\odot}yr^{-1}$, a factor of 2 smaller than previously reported for this QSO. We derived the best estimate of the dynamical mass $M_{\rm dyn} = 5.2\times 10^{10}\ \rm M_{\odot}$ within $r = 1.7$ kpc, based on a dynamical model of the system. We found that ${\rm SFR}/M_{\rm dyn}>\dot M_{\rm BH}/M_{\rm BH}$, suggesting that AGN feedback might be efficiently acting to slow down the SMBH accretion, while the stellar mass assembly is still vigorously taking place in the host galaxy. In addition, we were also able to detect high-velocity emission on the red and blue sides of the [CII] emission line, that traces a gaseous outflow, and for the first time, we mapped a spatially-resolved water vapour disk through the H$_2$O v=0 $3_{(2,2)}-3_{(1,3)}$ emission line detected at $\nu_{\rm obs} = 274.074$ GHz, whose kinematic properties and size are broadly consistent with those of the [CII] disk.Comment: 15 pages, 10 figures, 4 tables. Accepted in A&

Black hole and host galaxy growth in an isolated z 6 QSO observed with ALMA

The outstanding mass growth of supermassive black holes (SMBHs) at the epoch of reionisation and its relation to the concurrent growth of their host galaxies poses challenges to theoretical models aimed at explaining how these systems formed on short timescales (&lt; 1 Gyr). To trace the average evolutionary paths of quasi-stellar objects (QSOs) and their host galaxies in the plane of BH mass to host mass (Mdyn), we compare the star formation rate (SFR), derived from the accurate estimate of the dust temperature and the dust mass (Tdust, Mdust) based on infrared and sub-millimeter (sub-mm) spectral energy distribution (SED), with the BH accretion rate, derived from Lbol based on X-ray and optical and ultraviolet SED. To this aim, we analysed a deep ALMA observation of the sub-mm continuum, [CII], and H2O of the z ∼ 6 QSO J2310+1855 with a resolution of 900 pc, which enabled a detailed study of dust properties and cold gas kinematics. We performed an accurate SED analysis obtaining a dust temperature of Tdust = 71 ± 4 K, dust mass Mdust = (4.4 ± 0.7)×108 M⊙, and total far-infrared luminosity of LTIR = 2.5−0.5+0.6 × 1013 L⊙. The implied active galactic nuclei (AGN) – corrected SFR = 1240−260+310 M⊙ yr−1 is a factor of 2 lower than previously reported for this QSO. We measured a gas-to-dust ratio of GDR = 101 ± 20. The dust continuum and [CII] surface brightness profiles are spatially extended out to r ∼ 6.7 kpc and r ∼ 5 kpc, respectively, with half-light radii of 0.9 and 1.1 kpc for the dust and gas, respectively. The derived gas surface density, Σgas, and star formation rate density, ΣSFR, place the J2310+1855 host galaxy above the Kennicutt-Schmidt relation. We derived a best estimate of the dynamical mass Mdyn = 5.2 × 1010 M⊙ within r = 1.7 kpc based on a dynamical model of the system with a rotating disk inclined at i = 25 deg. The Toomre parameter profile across the disk is Qgas ∼ 3 and implies that the disk is unstable. We found that SFR/Mdyn &gt; ṀBH/MBH, suggesting that AGN feedback might be efficiently acting to slow down the SMBH accretion, while stellar mass assembly is still vigorously taking place in the host galaxy. In addition, we were also able to detect high-velocity emission on the red and blue sides of the [CII] emission line that is not consistent with disk rotation and traces a gaseous outflow. We derived an outflow mass Mout = 3.5 × 108 M⊙, and a mass outflow rate in the range Ṁout = 1800 − 4500 M⊙ yr−1. The implied Ėout ∼ 0.0005 − 0.001 Lbol is in agreement with the values observed for ionised winds. For the first time, we mapped a spatially resolved water vapour disk through the H2O v = 0 3(2, 2) − 3(1, 3) emission line detected at νobs = 274.074 GHz, whose kinematic properties and size are broadly consistent with those of the [CII] disk. The luminosity ratio LH2O/LTIR = 1.4 × 10−5 is consistent with line excitation by dust-reprocessed star formation in the interstellar medium of the host galaxy