We present our new Atacama Large Millimeter/Submillimeter Array (ALMA) observations targeting O iii88 m, C ii158 m, N ii122 m, and dust-continuum emission for three Lyman break galaxies at z = ...6.0293-6.2037, identified in the Subaru/Hyper Suprime-Cam survey. We clearly detect O iii and C ii lines from all of the galaxies at 4.3-11.8 levels, and identify multi-band dust-continuum emission in two of the three galaxies, allowing us to estimate infrared luminosities and dust temperatures simultaneously. In conjunction with previous ALMA observations for six galaxies at z > 6, we confirm that all the nine z = 6-9 galaxies have high O iii/C ii ratios of , ∼10 times higher than z ∼ 0 galaxies. We also find a positive correlation between the O iii/C ii ratio and the Ly equivalent width (EW) at the ∼90% significance level. We carefully investigate physical origins of the high O iii/C ii ratios at z = 6-9 using Cloudy, and find that high density of the interstellar medium, low C/O abundance ratio, and the cosmic microwave background attenuation are responsible to only a part of the z = 6-9 galaxies. Instead, the observed high O iii/C ii ratios are explained by 10-100 times higher ionization parameters or low photodissociation region (PDR) covering fractions of 0%-10%, both of which are consistent with our N ii observations. The latter scenario can be reproduced with a density-bounded nebula with PDR deficit, which would enhance the Ly , Lyman continuum, and ionizing photons escape from galaxies, consistent with the O iii/C ii-Ly EW correlation we find.
We present the results of ALMA spectroscopic follow-up of a z= 6.766 Lyalpha emitting galaxy behind the cluster RX J1347.1?1145. We report the detection of Cii 158 mu m line fully consistent with the ...Lyalpha redshift and with the peak of the optical emission. Given the magnification of mu= 5.0 + or - 0.3, the intrinsic (corrected for lensing) luminosity of the CII line is L sub(CII)= (ProQuest: Formulae and/or non-USASCII text omitted), roughlt ~5 times fainter than other detections of z~ 7 galaxies. The result indicates that low L sub(CII) in z~ 7 galaxies compared to the local counterparts might be caused by their low metallicities and/or feedback. The small velocity offset (Delta sub(nu)= (ProQuest: Formulae and/or non-USASCII text omitted)) between the Lyalpha and CII line is unusual, and may be indicative of ionizing photons escaping.
We present the results of ALMA spectroscopic follow-up of a z = 6.766 Ly emitting galaxy behind the cluster RX J1347.1−1145. We report the detection of C ii 158 m line fully consistent with the Ly ...redshift and with the peak of the optical emission. Given the magnification of = 5.0 0.3, the intrinsic (corrected for lensing) luminosity of the C ii line is LC ii , roughly ∼5 times fainter than other detections of z ∼ 7 galaxies. The result indicates that low LC ii in z ∼ 7 galaxies compared to the local counterparts might be caused by their low metallicities and/or feedback. The small velocity offset ( ) between the Ly and C ii line is unusual, and may be indicative of ionizing photons escaping.
The radiation from stars and active galactic nuclei (AGN) creates photodissociation regions (PDRs) and X-ray dominated regions (XDRs), where the chemistry or heating are dominated by far-ultraviolet ...(FUV) radiation or X-ray radiation, respectively. PDRs include a wide range of environments from the diffuse interstellar medium to dense star-forming regions. XDRs are found in the center of galaxies hosting AGN, in protostellar disks, and in the vicinity of X-ray binaries. In this review, we describe the dominant thermal, chemical, and radiation transfer processes in PDRs and XDRs, as well as a brief description of models and their use to analyze observations. We then present recent results from Milky Way, nearby extragalactic, and high-redshift observations. Several important results are: \(\bullet\) Velocity resolved PDR lines reveal the kinematics of the neutral atomic gas and provide constraints on the stellar feedback process. Their interpretation is, however, in dispute as observations suggest a prominent role for stellar winds while they are much less important in theoretical models. \(\bullet\) A significant fraction of molecular mass resides in CO-dark gas especially in low-metallicity/highly irradiated environments. \(\bullet\) The CO ladder and CI/CII ratios can determine if FUV or X-rays dominate the ISM heating of extragalactic sources. \(\bullet\) With ALMA, PDR and XDR tracers are now routinely detected on galactic scales over cosmic time. This makes it possible to link the star formation history of the Universe to the evolution of the physical and chemical properties of the gas.
We exploit moderately resolved OIII, CII and dust continuum ALMA observations to derive the gas density (\(n\)), the gas-phase metallicity (\(Z\)) and the deviation from the Kennicutt-Schmidt (KS) ...relation (\(\kappa_s\)) on ~sub-kpc scales in the interstellar medium (ISM) of five bright Lyman Break Galaxies at the Epoch of Reionization (\(z\approx 7\)). To do so, we use GLAM, a state-of-art, physically motivated Bayesian model that links the CII and OIII surface brightness (\(\Sigma_{\rm CII}\), \(\Sigma_{\rm OIII}\)) and the SFR surface density (\(\Sigma_{\rm SFR}\)) to \(n\), \(\kappa_s\), and \(Z\). All five sources are characterized by a central starbursting region, where the \(\Sigma_{\rm gas}\) vs \(\Sigma_{\rm SFR}\) align ~10x above the KS relation (\(\kappa_s\approx10\)). This translates into gas depletion times in the range \(t_{\rm dep}\approx 80-250\) Myr. The inner starbursting centers are characterized by higher gas density (\(\log (n/{\rm cm^{-3}}) \approx 2.5-3.0\)) and higher metallicity (\(\log (Z/Z_{\odot}) \approx -0.5\)) than the galaxy outskirts. We derive marginally negative radial metallicity gradients (\(\nabla \log Z \approx -0.03 \pm 0.07\)dex/kpc), and a dust temperature (\(T_d\approx\)32-38 K) that anticorrelates with the gas depletion time.
We report on a \(\rm{CII}_{158\mu\rm{m}}\) search using the Atacama Large Millimeter/submillimeter Array (ALMA) on three lensed, confirmed {\lya} emitting galaxies at \(z \sim 7\). Our targets are ...ultra-violet (UV) faint systems with stellar masses on the order of \(M_{*} \sim 10^{9} M_{\odot}\). We detect a single CII line emission (\(4\sigma\)) from the brightest (\(L \sim 2.4 \times 10^{10}L_{\odot}\)) galaxy in our sample, MACS0454-1251. We determine a systemic redshift (\(z_{\rm{CII}} = 6.3151 \pm 0.0005\)) for MACS0454-1251 and measure a {\lya} velocity offset of \(\Delta v \approx 300 \pm 70 \rm{km\,s}^{-1}\). The remaining two galaxies we detect no {\ct} but provide \(3 \sigma\) upper limits on their {\ct} line luminosities which we use to investigate the \(L_{\textrm{CII}} - \rm{SFR}\) relation. Overall our single {\ct} detection shows agreement with the relation for dwarf and local starburst galaxies. Our CII deficient galaxies could potentially be exhibiting low metallicities (\(Z<Z_{\odot}\)). Another possible explanation for weaker CII emission could be strong feedback from star formation disrupting molecular clouds. We do not detect continuum emission in any of the sources, placing upper limits on their dust masses. Assuming a single dust temperature of \(T_{d}=35 \rm{K}\) dust masses (\(M_{\rm{dust}}\)) range from \(< 4.8 \times 10^{7} M_{\odot} \) to \(2.3 \times 10^{8} M_{\odot}\). Collectively, our results suggest faint reionization era sources could be metal poor and/or could have strong feedback suppressing CII emission.
A tight relation between C II line luminosity and the star formation rate (SFR) has been observed for local galaxies. At high redshift (z > 5), galaxies instead deviate downwards from the local ...\(\Sigma\)_C II - \(\Sigma\)_SFR relation. This deviation might be caused by different interstellar medium (ISM) properties in galaxies at early epochs. To test this hypothesis, we combined the C II and SFR data with C III line observations and our physical models. We additionally investigated how ISM properties, such as burstiness, \(\kappa_s\), total gas density, \(n\), and metallicity, \(Z\), affect the deviation from the \(\Sigma\)_C II - \(\Sigma\)_SFR relation in these sources. We present the VLT/X-SHOOTER observations targeting the C III \({\lambda}1909\) line emission in three galaxies at 5.5 < z < 7. We include X-SHOOTER and VLT/MUSE archival data of eight galaxies at 2 < z < 7, and eleven star-forming systems at 6 < z < 7.5, with either C III or C II detection reported in the literature. We detected C III \({\lambda}{\lambda}1907, 1909\) line emission in HZ10 and we derived the intrinsic, integrated flux of the C III \({\lambda}1909\) line. We constrained the ISM properties for our sample of galaxies, \(\kappa_s\) , \(n\), 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 \(log(\kappa_s) > 1\), that is, they overshoot the Kennicutt-Schmidt (KS) relation by about one order of magnitude, implying that the whole KS relation might be shifted upwards at early times. Furthermore, all the high-z galaxies of our sample lie below the \(\Sigma\)_C II - \(\Sigma\)_SFR local relation. The total gas density, \(n\), shows the strongest correlation with the deviation from the local \(\Sigma\)_C II - \(\Sigma\)_SFR relation.
We present a new physically-motivated model for estimating the molecular line emission in active galaxies. The model takes into account (i) the internal density structure of giant molecular clouds ...(GMCs), (ii) the heating associated both to stars and to the active galactic nuclei (AGN), respectively producing photodissociation regions (PDRs) and X-ray dominated regions (XDRs) within the GMCs, and (iii) the mass distribution of GMCs within the galaxy volume. The model needs, as input parameters, the radial profiles of molecular mass, far-UV flux and X-ray flux for a given galaxy, and it has two free parameters: the CO-to-H2 conversion factor \(\alpha_{CO}\), and the X-ray attenuation column density \(N_H\). We test this model on a sample of 24 local (\(z \leq 0.06\)) AGN-host galaxies, simulating their carbon monoxide spectral line energy distribution (CO SLED). We compare the results with the available observations and calculate, for each galaxy, the best (\(\alpha_{CO}\), \(N_H\)) with a Markov chain Monte Carlo algorithm, finding values consistent with those present in the literature. We find a median \(\alpha_{CO} = 4.8\) M\(_{\odot}\) (K km s\(^{-1}\) pc\(^{2}\))\(^{-1}\) for our sample. In all the modelled galaxies, we find the XDR component of the CO SLED to dominate the CO luminosity from \(J_{\text{upp}} \geq 4\). We conclude that, once a detailed distribution of molecular gas density is taken into account, PDR emission at mid-/high-\(J\) becomes negligible with respect to XDR.
We present a detailed analysis of the X-ray, infrared, and carbon monoxide (CO) emission for a sample of 35 local (\(z \leq 0.15\)), active (\(L_X \geq 10^{42}\) erg s\(^{-1}\)) galaxies. Our goal is ...to infer the contribution of far-ultraviolet (FUV) radiation from star formation (SF), and X-ray radiation from the active galactic nuclei (AGN), respectively producing photodissociation regions (PDRs) and X-ray dominated regions (XDRs), to the molecular gas heating. To this aim, we exploit the CO spectral line energy distribution (CO SLED) as traced by Herschel, complemented with data from single-dish telescopes for the low-J lines, and high-resolution ALMA images of the mid-J CO emitting region. By comparing our results to the Schmidt-Kennicutt relation, we find no evidence for AGN influence on the cold and low-density gas on kpc-scales. On nuclear (r = 250 pc) scales, we find weak correlations between the CO line ratios and either the FUV or X-ray fluxes: this may indicate that neither SF nor AGN radiation dominates the gas excitation, at least at r = 250 pc. From a comparison of the CO line ratios with PDR and XDR models, we find that PDRs can reproduce observations only in presence of extremely high gas densities (\(n > 10^5\) cm\(^{-3}\)). In the XDR case, instead, the models suggest moderate densities (\(n \approx 10^{2-4}\) cm\(^{-3}\)). We conclude that a mix of the two mechanisms (PDR for the mid-J, XDR or possibly shocks for the high-J) is necessary to explain the observed CO excitation in active galaxies.
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