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تسجيل مستخدم جديدPredictions for the CO emission of galaxies from a coupled simulation of galaxy formation and photon dominated regions
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Claudia del P. Lagos
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We combine the galaxy formation model GALFORM with the Photon Dominated Region code UCL_PDR to study the emission from the rotational transitions of 12CO (CO) in galaxies from z=0 to z=6 in the Lambda CDM framework. GALFORM is used to predict the molecular (H2) and atomic hydrogen (HI) gas contents of galaxies using the pressure-based empirical star formation relation of Blitz & Rosolowsky. From the predicted H2 mass and the conditions in the interstellar medium, we estimate the CO emission in the rotational transitions 1-0 to 10-9 by applying the UCL_PDR model to each galaxy. We find that deviations from the Milky-Way CO-H2 conversion factor come mainly from variations in metallicity, and in the average gas and star formation rate surface densities. In the local universe, the model predicts a CO(1-0) luminosity function (LF), CO-to-total infrared (IR) luminosity ratios for multiple CO lines and a CO spectral line energy distribution (SLED) which are in good agreement with observations of luminous and ultra-luminous IR galaxies. At high redshifts, the predicted CO SLED of the brightest IR galaxies reproduces the shape and normalization of the observed CO SLED. The model predicts little evolution in the CO-to-IR luminosity ratio for different CO transitions, in good agreement with observations up to z~5. We use this new hybrid model to explore the potential of using colour selected samples of high-redshift star-forming galaxies to characterise the evolution of the cold gas mass in galaxies through observations with the Atacama Large Millimeter Array.
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Optical emission is detected from filaments around the central galaxies of clusters of galaxies. These filaments have lengths of tens of kiloparsecs. The emission is possibly due to heating caused by the dissipation of mechanical energy and by cosmic
ray induced ionisation. CO millimeter and submillimeter line emissions as well as H$_{2}$ infrared emission originating in such filaments surrounding NGC~1275, the central galaxy of the Perseus cluster, have been detected. Our aim is to identify those molecular species, other than CO, that may emit detectable millimeter and submillimeter line features arising in these filaments, and to determine which of those species will produce emissions that might serve as diagnostics of the dissipation and cosmic ray induced ionisation. The time-dependent UCL photon-dominated region modelling code was used in the construction of steady-state models of molecular filamentary emission regions at appropriate pressures, for a range of dissipation and cosmic ray induced ionisation rates and incident radiation fields.HCO$^+$ and C$_2$H emissions will potentially provide information about the cosmic ray induced ionisation rates in the filaments. HCN and, in particular, CN are species with millimeter and submillimeter lines that remain abundant in the warmest regions containing molecules. Detections of the galaxy cluster filaments in HCO$^{+}$, C$_{2}$H, and CN emissions and further detections of them in HCN emissions would provide significant constraints on the dissipation and cosmic ray induced ionisation rates.
[Abridged] The detection of the rotational lines of CO in proto-galaxies in the early Universe provides one of the most promising ways of probing the fundamental physical properties of a galaxy, such as its size, dynamical mass, gas density, and temp
erature. While such observations are currently limited to the most luminous galaxies, the advent of ALMA will change the situation dramatically, resulting in the detection of numerous normal galaxies at high redshifts. Maps and spectra of rotational CO line emission were calculated from a cosmological N-body/hydrodynamical TreeSPH simulation of a z ~ 3 Lyman break galaxy of UV luminosity about one order of magnitude below L*. To simulate a typical observation of our system with ALMA, we imposed characteristic noise, angular, and spectral resolution constraints. The CO line properties predicted by our simulation are in good agreement with the two Lyman break systems detected in CO to date. We find that while supernovae explosions from the ongoing star formation carve out large cavities in the molecular ISM, they do not generate large enough gas outflows to make a substantial imprint on the CO line profile. This implies that for most proto-galaxies - except possibly the most extreme cases - stellar feedback effects do not affect CO as a dynamical mass tracer. Detecting CO in sub-L* galaxies at z ~3 will push ALMA to the limits of its cababilities, and whether a source is detected or not may depend critically on its inclination angle. Both these effects (sensitivity and inclination) will severely impair the ability of ALMA to infer the gas kinematics and dynamical masses using line observations.
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