scholarly journals The CO universe: modelling CO emission and H2 abundance in cosmological galaxy formation simulations

2020 ◽  
Vol 498 (4) ◽  
pp. 5960-5971
Author(s):  
Shigeki Inoue ◽  
Naoki Yoshida ◽  
Hidenobu Yajima

ABSTRACT We devise a physical model of formation and distribution of molecular gas clouds (MGCs) in galaxies. We use the model to predict the intensities of rotational transition lines of carbon monoxide (CO) and the molecular hydrogen (H2) abundance. Using the outputs of IllustrisTNG cosmological simulations, we populate MGCs of unresolved sizes in individual simulated galaxies, where the effect of the interstellar radiation field with dust attenuation is also taken into account. We then use the publicly available code despotic (Derive the Energetics and SPectra of Optically Thick Interstellar Clouds) to compute the CO line luminosities and H2 densities without assuming the CO-to-H2 conversion factor (αCO). Our method allows us to study the spatial and kinematic structures traced by CO(1–0) and higher transition lines. We compare the CO luminosities and H2 masses with recent observations of galaxies at low and high redshifts. Our model reproduces well the observed CO–luminosity function and the estimated H2 mass in the local UniverseAbout 10 per cent of molecules in the Universe reside in dwarf galaxies with stellar masses lower than 109 M⊙, but the galaxies are generally ‘CO-dark’ and have typically high αCO. Our model predicts generally lower CO line luminosities than observations at redshifts z ≳ 1–2. We argue that the difference can be explained by the highly turbulent structure suggested for the high-redshift star-forming galaxies.

2020 ◽  
Vol 497 (4) ◽  
pp. 4773-4794 ◽  
Author(s):  
Sebastian Schulz ◽  
Gergö Popping ◽  
Annalisa Pillepich ◽  
Dylan Nelson ◽  
Mark Vogelsberger ◽  
...  

ABSTRACT We study the relation between the UV slope, β, and the ratio between the infrared- and UV luminosities (IRX) of galaxies from TNG50, the latest installment of the IllustrisTNG galaxy formation simulations. We select 7280 star-forming main-sequence (SFMS) galaxies with stellar mass ≥109 M⊙ at redshifts 0 ≤ z ≤ 4 and perform radiative transfer with skirt to model effects of interstellar medium dust on the emitted stellar light. Assuming a Milky Way dust type and a dust-to-metal ratio of 0.3, we find that TNG50 SFMS galaxies generally agree with observationally derived IRX–β relations at z ≲ 1. However, we find a redshift-dependent systematic offset with respect to empirically derived local relations, with the TNG50 IRX–β relation shifting towards lower β and steepening at higher redshifts. This is partially driven by variations in the dust-uncorrected UV slope of galaxies, due to different star formation histories of galaxies selected at different cosmic epochs; we suggest the remainder of the effect is caused by differences in the effective dust attenuation curves of galaxies as a function of redshift. We find a typical galaxy-to-galaxy variation of 0.3 dex in infrared excess (IRX) at fixed β, correlated with intrinsic galaxy properties: galaxies with higher star formation rates, star formation efficiencies, gas metallicities and stellar masses exhibit larger IRX values. We demonstrate a degeneracy between stellar age, dust geometry, and dust composition: z = 4 galaxies with a Small Magellanic Cloud dust type follow the same IRX–β relation as low-redshift galaxies with MW dust. We provide a redshift-dependent fitting function for the IRX–β relation for MW dust based on our models.


2012 ◽  
Vol 8 (S292) ◽  
pp. 289-289 ◽  
Author(s):  
M. Pannella ◽  
D. Elbaz ◽  
E. Daddi

AbstractWe quantitatively explore in a unbiased way the evolution of dust attenuation up to z ≈ 4 as a function of galaxy properties. We have used one of the deepest datasets available at present, in the GOODS-N field, to select a star forming galaxy sample and robustly measure galaxy redshifts, star formation rates, stellar masses and UV restframe properties. Our main results can be summarized as follows: i) we confirm that galaxy stellar mass is a main driver of UV dust attenuation in star forming galaxies: more massive galaxies are more dust attenuated than less massive ones; ii) strikingly, we find that the correlation does not evolve with redshift: the amount of dust attenuation is the same at all cosmic epochs for a fixed stellar mass; iii) this finding explains why and how the SFR–AUV relation evolves with redshift: the same amount of star formation is less attenuated at higher redshift because it is hosted in less massive galaxies; iv) combining our finding with results from line emission surveys, we confirm that line reddening is larger than continuum reddening, at least up to z ≈ 1.5; v) given the redshift evolution of the mass-metallicity relation, we predict that star forming galaxies at a fixed metal content are more attenuated at high redshift. Finally, we explored the correlation between UV dust attenuation and the spectral slope: vi) the correlation is evolving with redshift with star forming galaxies at lower redshift having redder spectra than higher redshift ones for the same amount of dust attenuation.


2019 ◽  
Vol 490 (3) ◽  
pp. 3196-3233 ◽  
Author(s):  
Annalisa Pillepich ◽  
Dylan Nelson ◽  
Volker Springel ◽  
Rüdiger Pakmor ◽  
Paul Torrey ◽  
...  

Abstract We present a new cosmological, magnetohydrodynamical simulation for galaxy formation: TNG50, the third and final instalment of the IllustrisTNG project. TNG50 evolves 2 × 21603 dark matter particles and gas cells in a volume 50 comoving Mpc across. It hence reaches a numerical resolution typical of zoom-in simulations, with a baryonic element mass of $8.5\times 10^4\, {\rm M}_{\odot }$ and an average cell size of 70–140 pc in the star-forming regions of galaxies. Simultaneously, TNG50 samples ∼700 (6500) galaxies with stellar masses above $10^{10} \, (10^8)\, {\rm M}_{\odot }$ at $z$ = 1. Here we investigate the structural and kinematical evolution of star-forming galaxies across cosmic time (0 ≲ $z$ ≲ 6). We quantify their sizes, disc heights, 3D shapes, and degree of rotational versus dispersion-supported motions as traced by rest-frame V-band light (i.e. roughly stellar mass) and by $\rm H\,\alpha$ light (i.e. star-forming and dense gas). The unprecedented resolution of TNG50 enables us to model galaxies with sub-kpc half-light radii and with ≲300-pc disc heights. Coupled with the large-volume statistics, we characterize a diverse, redshift- and mass-dependent structural and kinematical morphological mix of galaxies all the way to early epochs. Our model predicts that for star-forming galaxies the fraction of disc-like morphologies, based on 3D stellar shapes, increases with both cosmic time and galaxy stellar mass. Gas kinematics reveal that the vast majority of $10^{9-11.5}\, {\rm M}_{\odot }$ star-forming galaxies are rotationally supported discs for most cosmic epochs (Vrot/σ > 2–3, $z$ ≲ 5), being dynamically hotter at earlier epochs ($z$ ≳ 1.5). Despite large velocity dispersion at high redshift, cold and dense gas in galaxies predominantly arranges in disky or elongated shapes at all times and masses; these gaseous components exhibit rotationally dominated motions far exceeding the collisionless stellar bodies.


2019 ◽  
Vol 489 (1) ◽  
pp. 1357-1372 ◽  
Author(s):  
Yisheng Qiu ◽  
Simon J Mutch ◽  
Elisabete da Cunha ◽  
Gregory B Poole ◽  
J Stuart B Wyithe

ABSTRACT We present a new analysis of high-redshift UV observations using a semi-analytic galaxy formation model, and provide self-consistent predictions of the infrared excess (IRX)–β relations and cosmic star formation rate density. We combine the Charlot & Fall dust attenuation model with the meraxes semi-analytic model, and explore three different parametrizations for the dust optical depths, linked to star formation rate, dust-to-gas ratio, and gas column density, respectively. A Bayesian approach is employed to statistically calibrate model-free parameters including star formation efficiency, mass loading factor, dust optical depths, and reddening slope directly against UV luminosity functions and colour–magnitude relations at $z$ ∼ 4–7. The best-fitting models show excellent agreement with the observations. We calculate IRX using energy balance arguments and find that the large intrinsic scatter in the IRX–β plane correlates with specific star formation rate. Additionally, the difference among the three dust models suggests at least a factor of 2 systematic uncertainty in the dust-corrected star formation rate when using the Meurer IRX–β relation at $z$ ≳ 4.


Author(s):  
Judit Fogasy ◽  
K K Knudsen ◽  
G Drouart ◽  
B Gullberg

Abstract Both theoretical and observational results suggest that high-redshift radio galaxies (HzRGs) inhabit overdense regions of the universe and might be the progenitors of local, massive galaxies residing in the centre of galaxy clusters. In this paper we present CO(3–2) line observations of the HzRG TXS 0828+193 (z = 2.57) and its environment using the Atacama Large Millimeter/submillimeter Array. In contrast to previous observations, we detect CO emission associated with the HzRG and derive a molecular gas mass of $(0.9\pm 0.3)\times 10^{10}\, \rm M_{\odot }$. Moreover, we confirm the presence of a previously detected off-source CO emitting region (companion #1), and detect three new potential companions. The molecular gas mass of each companion is comparable to that of the HzRG. Companion #1 is aligned with the axis of the radio jet and has stellar emission detected by Spitzer. Thus this source might be a normal star-forming galaxy or alternatively a result of jet-induced star formation. The newly found CO sources do not have counterparts in any other observing band and could be high-density clouds in the halo of TXS 0828+193 and thus potentially linked to the large-scale filamentary structure of the cosmic web.


2020 ◽  
Vol 15 (S359) ◽  
pp. 136-140
Author(s):  
Minju M. Lee ◽  
Ichi Tanaka ◽  
Rohei Kawabe

AbstractWe present studies of a protocluster at z =2.5, an overdense region found close to a radio galaxy, 4C 23.56, using ALMA. We observed 1.1 mm continuum, two CO lines (CO (4–3) and CO (3–2)) and the lower atomic carbon line transition ([CI](3P1-3P0)) at a few kpc (0″.3-0″.9) resolution. The primary targets are 25 star-forming galaxies selected as Hα emitters (HAEs) that are identified with a narrow band filter. These are massive galaxies with stellar masses of > 1010Mʘ that are mostly on the galaxy main sequence at z =2.5. We measure the molecular gas mass from the independent gas tracers of 1.1 mm, CO (3–2) and [CI], and investigate the gas kinematics of galaxies from CO (4–3). Molecular gas masses from the different measurements are consistent with each other for detection, with a gas fraction (fgas = Mgas/(Mgas+ Mstar)) of ≃ 0.5 on average but with a caveat. On the other hand, the CO line widths of the protocluster galaxies are typically broader by ˜50% compared to field galaxies, which can be attributed to more frequent, unresolved gas-rich mergers and/or smaller sizes than field galaxies, supported by our high-resolution images and a kinematic model fit of one of the galaxies. We discuss the expected scenario of galaxy evolution in protoclusters at high redshift but future large surveys are needed to get a more general view.


2020 ◽  
Vol 498 (1) ◽  
pp. 164-180 ◽  
Author(s):  
Harley Katz ◽  
Dominika Ďurovčíková ◽  
Taysun Kimm ◽  
Joki Rosdahl ◽  
Jeremy Blaizot ◽  
...  

ABSTRACT Identifying low-redshift galaxies that emit Lyman continuum radiation (LyC leakers) is one of the primary, indirect methods of studying galaxy formation in the epoch of reionization. However, not only has it proved challenging to identify such systems, it also remains uncertain whether the low-redshift LyC leakers are truly ‘analogues’ of the sources that reionized the Universe. Here, we use high-resolution cosmological radiation hydrodynamics simulations to examine whether simulated galaxies in the epoch of reionization share similar emission line properties to observed LyC leakers at z ∼ 3 and z ∼ 0. We find that the simulated galaxies with high LyC escape fractions (fesc) often exhibit high O32 and populate the same regions of the R23–O32 plane as z ∼ 3 LyC leakers. However, we show that viewing angle, metallicity, and ionization parameter can all impact where a galaxy resides on the O32–fesc plane. Based on emission line diagnostics and how they correlate with fesc, lower metallicity LyC leakers at z ∼ 3 appear to be good analogues of reionization-era galaxies. In contrast, local [S ii]-deficient galaxies do not overlap with the simulated high-redshift LyC leakers on the S ii Baldwin–Phillips–Terlevich (BPT) diagram; however, this diagnostic may still be useful for identifying leakers. We use our simulated galaxies to develop multiple new diagnostics to identify LyC leakers using infrared and nebular emission lines. We show that our model using only [C ii]158 μm and [O iii]88 μm can identify potential leakers from non-leakers from the local Dwarf Galaxy Survey. Finally, we apply this diagnostic to known high-redshift galaxies and find that MACS 1149_JD1 at z = 9.1 is the most likely galaxy to be actively contributing to the reionization of the Universe.


2006 ◽  
Vol 2 (S235) ◽  
pp. 139-139
Author(s):  
L. Sodré ◽  
A. Mateus ◽  
R. Cid Fernandes ◽  
G. Stasińska ◽  
W. Schoenell ◽  
...  

AbstractWe revisit the bimodality of the galaxy population seen in the local universe. We address this issue in terms of physical properties of galaxies, such as mean stellar ages and stellar masses, derived from the application of a spectral synthesis method to galaxy spectra from the SDSS. We show that the mean light-weighted stellar age of galaxies presents the best description of the bimodality seen in the galaxy population. The stellar mass has an additional role since most of the star-forming galaxies present in the local universe are low-mass galaxies. Our results give support to the existence of a ‘downsizing’ in galaxy formation, where nowadays massive galaxies tend to have stellar populations older than those found in less massive objects.


2015 ◽  
Vol 11 (A29B) ◽  
pp. 197-198
Author(s):  
Andrew J. Bunker

AbstractI discuss stellar populations in galaxies at high redshift (z > 6), in particular the blue rest-frame UV colours which have been detected in recent years through near-IR imaging with HST. These spectral slopes of β < −2 are much more blue than star-forming galaxies at lower redshift, and may suggest less dust obscuration, lower metallicity or perhaps a different initial mass function. I describe current work on the luminosity function of high redshift star- forming galaxies, the evolution of the fraction of strong Lyman-α emitters in this population, and the contribution of the ionizing photon budget from such galaxies towards the reionization of the Universe. I also describe constraints placed by Spitzer/IRAC on stellar populations in galaxies within the first billion years, and look towards future developments in spectroscopy with Extremely Large Telescopes and the James Webb Space Telescope, including the JWST/NIRSpec GTO programme on galaxy evolution at high redshift.


2019 ◽  
Vol 15 (S352) ◽  
pp. 234-238
Author(s):  
Donatella Romano ◽  
Zhi-Yu Zhang ◽  
Francesca Matteucci ◽  
Rob J. Ivison ◽  
Padelis P. Papadopoulos

AbstractDetermining the shape of the stellar initial mass function (IMF) and whether it is constant or varies in space and time is the Holy Grail of modern astrophysics, with profound implications for all theories of star and galaxy formation. On a theoretical ground, the extreme conditions for star formation (SF) encountered in the most powerful starbursts in the Universe are expected to favour the formation of massive stars. Direct methods of IMF determination, however, cannot probe such systems, because of the severe dust obscuration affecting their starlight. The next best option is to observe CNO bearing molecules in the interstellar medium at millimetre/ submillimetre wavelengths, which, in principle, provides the best indirect evidence for IMF variations. In this contribution, we present our recent findings on this issue. First, we reassess the roles of different types of stars in the production of CNO isotopes. Then, we calibrate a proprietary chemical evolution code using Milky Way data from the literature, and extend it to discuss extragalactic data. We show that, though significant uncertainties still hamper our knowledge of the evolution of CNO isotopes in galaxies, compelling evidence for an IMF skewed towards high-mass stars can be found for galaxy-wide starbursts. In particular, we analyse a sample of submillimetre galaxies observed by us with the Atacama Large Millimetre Array at the peak of the SF activity of the Universe, for which we measure 13C/18O⋍1. This isotope ratio is especially sensitive to IMF variations, and is little affected by observational uncertainties. At the end, ongoing developments of our work are briefly outlined.


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