ABSTRACT
We thoroughly explore the properties of (sub)-millimetre (mm) selected galaxies (SMGs) in the shark semi-analytic model of galaxy formation. Compared to observations, the predicted number ...counts at wavelengths (λ) 0.6–2 mm and redshift distributions at 0.1–2 mm, agree well. At the bright end (≳1 mJy), shark galaxies are a mix of mergers and disc instabilities. These galaxies display a stacked far-ultraviolet (FUV)-to-far-infrared (FIR) spectrum that agrees well with observations. We predict that current optical/NIR surveys are deep enough to detect bright (>1 mJy) λ = 0.85–2 mm-selected galaxies at z ≲ 5, but too shallow to detect counterparts at higher redshift. A James Webb Space Telescope 10 000s survey should detect all counterparts for galaxies with S0.85mm ≳ 0.01 mJy. We predict SMG’s disks contribute significantly (negligibly) to the rest-frame UV (IR). We investigate the 0 ≤ z ≤ 6 evolution of the intrinsic properties of >1 mJy λ = 0.85–2 mm-selected galaxies finding their: (i) stellar masses are $\gt 10^{10.2}\rm \, M_{\odot }$, with the 2 mm ones tracing the most massive galaxies ($\gt 10^{11}\rm \, M_{\odot }$); (ii) specific star formation rates (SFR) are mildly (≈3–10 times) above the main sequence (MS); (iii) host halo masses are $\gtrsim 10^{12.3}\, \rm M_{\odot }$, with 2 mm galaxies tracing the most massive haloes (protoclusters); (iv) SMGs have lower dust masses ($\approx 10^{8}\, \rm M_{\odot }$), higher dust temperatures (≈40–45 K) and higher rest-frame V-band attenuation (>1.5) than MS galaxies; (v) sizes decrease with redshift, from 4 kpc at z = 1 to ≲1 kpc at z = 4; and (vi) the carbon monoxide line spectra of S0.85mm ≳ 1 mJy sources peak at 4 → 3. Finally, we study the contribution of SMGs to the molecular gas and cosmic SFR density at 0 ≤ z ≤ 10, finding that >1 mJy sources make a negligible contribution at z ≳ 3 and 5, respectively, suggesting current observations have unveiled the majority of the SF at 0 ≤ z ≤ 10.
Abstract
We present optical photometry of Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS)/Wide Field Camera (WFC) data of the resolved stellar populations in the outer disc of the ...dwarf irregular galaxy DDO 154. The photometry reveals that young main sequence (MS) stars are almost absent from the outermost H i disc. Instead, most are clustered near the main stellar component of the galaxy. We constrain the stellar initial mass function (IMF) by comparing the luminosity function of the MS stars to simulated stellar populations, assuming a constant star formation rate over the dynamical time-scale. The best-fitting IMF is deficient in high-mass stars compared to a canonical Kroupa IMF, with a best-fitting slope α = −2.45 and upper mass limit MU = 16 M⊙. This top-light IMF is consistent with predictions of the integrated galactic IMF theory. Combining the HST images with H i data from The H i Nearby Galaxy Survey (THINGS), we determine the star formation law (SFL) in the outer disc. The fit has a power-law exponent N = 2.92 ± 0.22 and zero-point A = 4.47 ± 0.65 × 10−7 M⊙ yr−1 kpc−2. This is depressed compared to the Kennicutt–Schmidt SFL, but consistent with weak star formation observed in diffuse H i environments. Extrapolating the SFL over the outer disc implies that there could be significant star formation occurring that is not detectable in H α. Last, we determine the Toomre stability parameter Q of the outer disc of DDO 154 using the THINGS H i rotation curve and velocity dispersion map. 72 per cent of the H i in our field has Q ≤ 4 and this incorporates 96 per cent of the observed MS stars. Hence, 28 per cent of the H i in the field is largely dormant.
ABSTRACT
We explore the properties of central galaxies living in voids using the eagle cosmological hydrodynamic simulations. Based on the minimum void-centric distance, we define four galaxy ...samples: inner void, outer void, wall, and skeleton. We find that inner void galaxies with host halo masses $\lt 10^{12}\,\rm M_{\odot }$ have lower stellar mass and stellar mass fractions than those in denser environments, and the fraction of galaxies with star formation (SF) activity and atomic hydrogen (H i) gas decreases with increasing void-centric distance, in agreement with observations. To mitigate the influence of stellar (halo) mass, we compare inner void galaxies to subsamples of fixed stellar (halo) mass. Compared to denser environments, inner void galaxies with $M_{*}= 10^{9.0-9.5}\,\rm M_{\odot }$ have comparable SF activity and H i gas fractions, but the lowest quenched galaxy fraction. Inner void galaxies with $M_{*}= 10^{9.5-10.5}\,\rm M_{\odot }$ have the lowest H i gas fraction, the highest quenched fraction and the lowest gas metallicities. On the other hand, inner void galaxies with $M_{*}\gt 10^{10.5}\,\rm M_{\odot }$ have comparable SF activity and H i gas fractions to their analogues in denser environments. They retain the highest metallicity gas that might be linked to physical processes that act with lower efficiency in underdense regions such as AGN (active galaxy nucleus) feedback. Furthermore, inner void galaxies have the lowest fraction of positive gas-phase metallicity gradients, which are typically associated with external processes or feedback events, suggesting they have more quiet merger histories than galaxies in denser environments. Our findings shed light on how galaxies are influenced by their large-scale environment.
Large-scale cosmological simulations of galaxy formation currently do not resolve the densities at which molecular hydrogen forms, implying that the atomic-to-molecular transition must be modeled ...either on the fly or in postprocessing. We present an improved postprocessing framework to estimate the abundance of atomic and molecular hydrogen and apply it to the IllustrisTNG simulations. We compare five different models for the atomic-to-molecular transition, including empirical, simulation-based, and theoretical prescriptions. Most of these models rely on the surface density of neutral hydrogen and the ultraviolet (UV) flux in the Lyman-Werner band as input parameters. Computing these quantities on the kiloparsec scale resolved by the simulations emerges as the main challenge. We show that the commonly used Jeans length approximation to the column density of a system can be biased and exhibits large cell-to-cell scatter. Instead, we propose to compute all surface quantities in face-on projections and perform the modeling in two dimensions. In general, the two methods agree on average, but their predictions diverge for individual galaxies and for models based on the observed midplane pressure of galaxies. We model the UV radiation from young stars by assuming a constant escape fraction and optically thin propagation throughout the galaxy. With these improvements, we find that the five models for the atomic-to-molecular transition roughly agree on average but that the details of the modeling matter for individual galaxies and the spatial distribution of molecular hydrogen. We emphasize that the estimated molecular fractions are approximate due to the significant systematic uncertainties.
We study the atomic (H i) and molecular hydrogen (H2) contents of early-type galaxies (ETGs) and their gas sources using the galform model of galaxy formation. This model uses a self-consistent ...calculation of the star formation rate, which depends on the H2 content of galaxies. We first present a new analysis of H i Parkes All-Sky Survey and ATLAS3D surveys, with special emphasis on ETGs. The model predicts H i and H2 contents of ETGs in agreement with the observations from these surveys only if partial ram pressure stripping of the hot gas is included, showing that observations of neutral gas in ‘quenched’ galaxies place stringent constraints on the treatment of the hot gas in satellites. We find that ≈90 per cent of ETGs at z = 0 have neutral gas contents supplied by radiative cooling from their hot haloes, 8 per cent were supplied by gas accretion from minor mergers that took place in the last 1 Gyr, while 2 per cent were supplied by mass-loss from old stars. The model predicts neutral gas fractions strongly decreasing with increasing bulge fraction. This is due to the impeded disc regeneration in ETGs, resulting from both active galactic nuclei feedback and environmental quenching by partial ram pressure stripping of the hot gas.
ABSTRACT
Large galaxy samples from multiobject integral field spectroscopic (IFS) surveys now allow for a statistical analysis of the z ∼ 0 galaxy population using resolved kinematic measurements. ...However, the improvement in number statistics comes at a cost, with multiobject IFS survey more severely impacted by the effect of seeing and lower signal-to-noise ratio. We present an analysis of ∼1800 galaxies from the SAMI Galaxy Survey taking into account these effects. We investigate the spread and overlap in the kinematic distributions of the spin parameter proxy $\lambda _{R_{\rm {e}}}$ as a function of stellar mass and ellipticity εe. For SAMI data, the distributions of galaxies identified as regular and non-regular rotators with kinemetry show considerable overlap in the $\lambda _{R_{\rm {e}}}$–εe diagram. In contrast, visually classified galaxies (obvious and non-obvious rotators) are better separated in $\lambda _{R_{\rm {e}}}$ space, with less overlap of both distributions. Then, we use a Bayesian mixture model to analyse the observed $\lambda _{R_{\rm {e}}}$–log (M⋆/M⊙) distribution. By allowing the mixture probability to vary as a function of mass, we investigate whether the data are best fit with a single kinematic distribution or with two. Below log (M⋆/M⊙) ∼ 10.5, a single beta distribution is sufficient to fit the complete $\lambda _{R_{\rm {e}}}$ distribution, whereas a second beta distribution is required above log (M⋆/M⊙) ∼ 10.5 to account for a population of low-$\lambda _{R_{\rm {e}}}$ galaxies. While the Bayesian mixture model presents the cleanest separation of the two kinematic populations, we find the unique information provided by visual classification of galaxy kinematic maps should not be disregarded in future studies. Applied to mock-observations from different cosmological simulations, the mixture model also predicts bimodal $\lambda _{R_{\rm {e}}}$ distributions, albeit with different positions of the $\lambda _{R_{\rm {e}}}$ peaks. Our analysis validates the conclusions from previous, smaller IFS surveys, but also demonstrates the importance of using selection criteria for identifying different kinematic classes that are dictated by the quality and resolution of the observed or simulated data.
ABSTRACT
In the protogalactic density field, diffuse gas and collision-less cold dark matter (DM) are often assumed sufficiently mixed that both components experience identical tidal torques. ...However, haloes in cosmological simulations consistently end up with a higher specific angular momentum (sAM) in gas, even in simulations without radiative cooling and galaxy formation physics. We refine this result by analysing the spin distributions of gas and DM in ∼50 000 well-resolved haloes in a non-radiative cosmological simulation from the SURFS suite. The sAM of the halo gas on average ends up ∼40 per cent above that of the DM. This can be pinned down to an excess AM in the inner halo (<50 per cent virial radius), paralleled by a more coherent rotation pattern in the gas. We uncover the leading driver for this AM difference through a series of control simulations of a collapsing ellipsoidal top-hat, where gas and DM are initially well mixed. These runs reveal that the pressurized inner gas shells collapse more slowly, causing the DM ellipsoid to spin ahead of the gas ellipsoid. The arising torque generally transfers AM from the DM to the gas. The amount of AM transferred via this mode depends on the initial spin, the initial axes ratios, and the collapse factor. These quantities can be combined in a single dimensionless parameter, which robustly predicts the AM transfer of the ellipsoidal collapse. This simplistic model can quantitatively explain the average AM excess of the gas found in the more complex non-radiative cosmological simulation.
ABSTRACT
We use the eagle cosmological simulations to study the evolution of the vertical velocity dispersion of cold gas, σz, in central disc galaxies and its connection to stellar feedback, ...gravitational instabilities, cosmological gas accretion, and galaxy mergers. To isolate the impact of feedback, we analyse runs that turn off stellar and (or) active galactic nuclei feedback in addition to a run that includes both. The evolution of σz and its dependence on stellar mass and star formation rate in eagle are in good agreement with observations. Galaxies hosted by haloes of similar virial mass, $\rm M_{200}$, have similar σz values even in runs where feedback is absent. The prevalence of local instabilities in discs is uncorrelated with σz at low redshift and becomes only weakly correlated at high redshifts and in galaxies hosted by massive haloes. σz correlates most strongly with the specific gas accretion rate onto the disc as well as with the degree of misalignment between the inflowing gas and the disc’s rotation axis. These correlations are significant across all redshifts and halo masses, with misaligned accretion being the primary driver of high gas turbulence at redshifts z ≲ 1 and for halo masses $\rm M_{200} \lesssim 10^{11.5} {\rm M}_{\odot }$. Galaxy mergers increase σz, but because they are rare in our sample, they play only a minor role in its evolution. Our results suggest that the turbulence of cold gas in eagle discs results from a complex interplay of different physical processes whose relative importance depends on halo mass and redshift.
Abstract
Due to their extremely dust-obscured nature, much uncertainty still exists surrounding the stellar mass growth and content in dusty, star-forming galaxies (DSFGs) at
z
> 1. In this work, we ...present a numerical model built using empirical data on DSFGs to estimate their stellar mass contributions across the first ∼10 Gyr of cosmic time. We generate a dust-obscured stellar mass function that extends beyond the mass limit of star-forming stellar mass functions in the literature, and predict that massive DSFGs constitute as much as 50%–100% of all star-forming galaxies with
M
≥10
11
M
⊙
at
z
> 1. We predict the number density of massive DSFGs and find general agreement with observations, although more data is needed to narrow wide observational uncertainties. We forward-model mock massive DSFGs to their quiescent descendants and find remarkable agreement with observations from the literature demonstrating that, to first order, massive DSFGs are a sufficient ancestral population to describe the prevalence of massive quiescent galaxies at
z
> 1. We predict that massive DSFGs and their descendants contribute as much as 25%–60% to the cosmic stellar mass density during the peak of cosmic star formation, and predict an intense epoch of population growth during the ∼1 Gyr from
z
= 6 to 3 during which the majority of the most massive galaxies at high-
z
grow and then quench. Future studies seeking to understand massive galaxy growth and evolution in the early universe should strategize synergies with data from the latest observatories (e.g., JWST and the Atacama Large Millimeter/submillimeter Array) to better include the heavily dust-obscured galaxy population.
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