scholarly journals Swirls of FIRE: spatially resolved gas velocity dispersions and star formation rates in FIRE-2 disc environments

2020 ◽  
Vol 496 (2) ◽  
pp. 1620-1637 ◽  
Author(s):  
Matthew E Orr ◽  
Christopher C Hayward ◽  
Anne M Medling ◽  
Alexander B Gurvich ◽  
Philip F Hopkins ◽  
...  
Keyword(s):  
Star Formation ◽  
Formation Rate ◽  
Free Fall ◽  
Dense Gas ◽  
Gas Velocity ◽  
Simulation Data ◽  
Spatially Resolved ◽  
Neutral Gas ◽  
Velocity Dispersions ◽  
Gas Fractions

ABSTRACT We study the spatially resolved (sub-kpc) gas velocity dispersion (σ)–star formation rate (SFR) relation in the FIRE-2 (Feedback in Realistic Environments) cosmological simulations. We specifically focus on Milky Way-mass disc galaxies at late times (z ≈ 0). In agreement with observations, we find a relatively flat relationship, with σ ≈ 15–30 km s−1 in neutral gas across 3 dex in SFRs. We show that higher dense gas fractions (ratios of dense gas to neutral gas) and SFRs are correlated at constant σ. Similarly, lower gas fractions (ratios of gas to stellar mass) are correlated with higher σ at constant SFR. The limits of the σ–ΣSFR relation correspond to the onset of strong outflows. We see evidence of ‘on-off’ cycles of star formation in the simulations, corresponding to feedback injection time-scales of 10–100 Myr, where SFRs oscillate about equilibrium SFR predictions. Finally, SFRs and velocity dispersions in the simulations agree well with feedback-regulated and marginally stable gas disc (Toomre’s Q = 1) model predictions, and the simulation data effectively rule out models assuming that gas turns into stars at (low) constant efficiency (i.e. 1 per cent per free-fall time). And although the simulation data do not entirely exclude gas accretion/gravitationally powered turbulence as a driver of σ, it appears to be subdominant to stellar feedback in the simulated galaxy discs at z ≈ 0.

scholarly journals The MALATANG survey: dense gas and star formation from high-transition HCN and HCO+ maps of NGC 253

2020 ◽  
Vol 494 (1) ◽  
pp. 1276-1296
Author(s):  
Xue-Jian Jiang ◽  
Thomas R Greve ◽  
Yu Gao ◽  
Zhi-Yu Zhang ◽  
Qinghua Tan ◽  
...  
Keyword(s):  
Star Formation ◽  
Formation Rate ◽  
Average Density ◽  
Dense Gas ◽  
James Clerk Maxwell ◽  
Physical Conditions ◽  
Spatially Resolved ◽  
Stellar Component ◽  
Integrated Intensity ◽  
High Transition

ABSTRACT To study the high-transition dense-gas tracers and their relationships to the star formation of the inner ∼2 kpc circumnuclear region of NGC 253, we present HCN J = 4−3 and HCO+ J = 4−3 maps obtained with the James Clerk Maxwell Telescope. Using the spatially resolved data, we compute the concentration indices r90/r50 for the different tracers. HCN and HCO+ 4–3 emission features tend to be centrally concentrated, which is in contrast to the shallower distribution of CO 1–0 and the stellar component. The dense-gas fraction (fdense, traced by the velocity-integrated-intensity ratios of HCN/CO and HCO+/CO) and the ratio R31 (CO 3–2/1–0) decline towards larger galactocentric distances, but increase with higher star formation rate surface density. The radial variation and the large scatter of fdense and R31 imply distinct physical conditions in different regions of the galactic disc. The relationships of fdense versus Σstellar, and SFEdense versus Σstellar are explored. SFEdense increases with higher Σstellar in this galaxy, which is inconsistent with previous work that used HCN 1–0 data. This implies that existing stellar components might have different effects on the high-J HCN and HCO+ than their low-J emission. We also find that SFEdense seems to be decreasing with higher fdense which is consistent with previous works, and it suggests that the ability of the dense gas to form stars diminishes when the average density of the gas increases. This is expected in a scenario where only the regions with high-density contrast collapse and form stars.

scholarly journals Atomic and molecular gas in IllustrisTNG galaxies at low redshift

2019 ◽  
Vol 487 (2) ◽  
pp. 1529-1550 ◽  
Author(s):  
Benedikt Diemer ◽  
Adam R H Stevens ◽  
Claudia del P Lagos ◽  
A R Calette ◽  
Sandro Tacchella ◽  
...  
Keyword(s):  
Star Formation ◽  
Star Formation Rate ◽  
Formation Rate ◽  
Gas Content ◽  
Neutral Gas ◽  
Mass Size ◽  
Mass Functions ◽  
Gas Fractions ◽  
Size Relation ◽  
Good Agreement

ABSTRACT We have recently developed a post-processing framework to estimate the abundance of atomic and molecular hydrogen (H i and H2, respectively) in galaxies in large-volume cosmological simulations. Here we compare the H i and H2 content of IllustrisTNG galaxies to observations. We mostly restrict this comparison to z ≈ 0 and consider six observational metrics: the overall abundance of H i and H2, their mass functions, gas fractions as a function of stellar mass, the correlation between H2 and star formation rate, the spatial distribution of gas, and the correlation between gas content and morphology. We find generally good agreement between simulations and observations, particularly for the gas fractions and the H i mass–size relation. The H2 mass correlates with star formation rate as expected, revealing an almost constant depletion time that evolves up to z = 2 as observed. However, we also discover a number of tensions with varying degrees of significance, including an overestimate of the total neutral gas abundance at z = 0 by about a factor of 2 and a possible excess of satellites with no or very little neutral gas. These conclusions are robust to the modelling of the H i/H2 transition. In terms of their neutral gas properties, the IllustrisTNG simulations represent an enormous improvement over the original Illustris run. All data used in this paper are publicly available as part of the IllustrisTNG data release.

scholarly journals The [C ii]–SFR correlation in dwarf galaxies across cosmic time

2020 ◽  
Vol 492 (2) ◽  
pp. 2818-2827 ◽  
Author(s):  
Alessandro Lupi ◽  
Stefano Bovino
Keyword(s):  
Star Formation ◽  
Dwarf Galaxy ◽  
Formation Rate ◽  
Cosmic Time ◽  
Theoretical Models ◽  
Large Scatter ◽  
Star Forming ◽  
Spatially Resolved ◽  
Star Forming Regions ◽  
Neutral Gas

ABSTRACT Current galaxy observations suggest that a roughly linear correlation exists between the [C ii] emission and the star formation rate, either as spatially resolved or integrated quantities. Observationally, this correlation seems to be independent of metallicity, but the very large scatter does not allow to properly assess whether this is true. On the other hand, theoretical models tend to suggest a metallicity dependence of the correlation. In this study, we investigate the metallicity evolution of the correlation via a high-resolution zoom-in cosmological simulation of a dwarf galaxy employing state-of-the-art sub-grid modelling for gas cooling, star formation, and stellar feedback, and that self-consistently evolves the abundances of metal elements out of equilibrium. Our results suggest that the correlation should evolve with metallicity, in agreement with theoretical predictions, but also that this evolution can be hardly detected in observations, because of the large scatter. We also find that most of the [C ii] emission is associated with neutral gas at low-intermediate densities, whereas the highest emissivity is produced by the densest regions around star-forming regions.

scholarly journals Spatially resolved star formation and fuelling in galaxy interactions

2020 ◽  
Author(s):  
Jorge Moreno ◽  
Paul Torrey ◽  
Sara L Ellison ◽  
David R Patton ◽  
Connor Bottrell ◽  
...  
Keyword(s):  
Star Formation ◽  
Formation Rate ◽  
Dense Gas ◽  
Galaxy Interactions ◽  
Galaxy Surveys ◽  
Spatially Resolved ◽  
Numerical Predictions ◽  
Orbital Geometry ◽  
The Galaxy ◽  
Multi Wavelength

Abstract We investigate the spatial structure and evolution of star formation and the interstellar medium (ISM) in interacting galaxies. We use an extensive suite of parsec-scale galaxy merger simulations (stellar mass ratio = 2.5:1), which employs the ’Feedback In Realistic Environments-2’ model (fire-2). This framework resolves star formation, feedback processes, and the multi-phase structure of the ISM. We focus on the galaxy-pair stages of interaction. We find that close encounters substantially augment cool (HI) and cold-dense (H2) gas budgets, elevating the formation of new stars as a result. This enhancement is centrally-concentrated for the secondary galaxy, and more radially extended for the primary. This behaviour is weakly dependent on orbital geometry. We also find that galaxies with elevated global star formation rate (SFR) experience intense nuclear SFR enhancement, driven by high levels of either star formation efficiency (SFE) or available cold-dense gas fuel. Galaxies with suppressed global SFR also contain a nuclear cold-dense gas reservoir, but low SFE levels diminish SFR in the central region. Concretely, in the majority of cases, SFR-enhancement in the central kiloparsec is fuel-driven (55% for the secondary, 71% for the primary) - whilst central SFR-suppression is efficiency-driven (91% for the secondary, 97% for the primary). Our numerical predictions underscore the need of substantially larger, and/or merger-dedicated, spatially-resolved galaxy surveys - capable of examining vast and diverse samples of interacting systems - coupled with multi-wavelength campaigns aimed to capture their internal ISM structure.

scholarly journals Testing the star formation scaling relations in the clumps of the North American and Pelican nebulae cloud complex

2020 ◽  
Vol 500 (3) ◽  
pp. 3123-3141
Author(s):  
Swagat R Das ◽  
Jessy Jose ◽  
Manash R Samal ◽  
Shaobo Zhang ◽  
Neelam Panwar
Keyword(s):  
Star Formation ◽  
Surface Density ◽  
Star Formation Rate ◽  
Formation Rate ◽  
Free Fall ◽  
Scaling Relations ◽  
Time Model ◽  
Fall Time ◽  
The North ◽  
Crossing Time

ABSTRACT The processes that regulate star formation within molecular clouds are still not well understood. Various star formation scaling relations have been proposed as an explanation, one of which is to formulate a relation between the star formation rate surface density $\rm \Sigma _{SFR}$ and the underlying gas surface density $\rm \Sigma _{gas}$. In this work, we test various star formation scaling relations, such as the Kennicutt–Schmidt relation, the volumetric star formation relation, the orbital time model, the crossing time model and the multi free-fall time-scale model, towards the North American Nebula and Pelican Nebula and in the cold clumps associated with them. Measuring stellar mass from young stellar objects and gaseous mass from CO measurements, we estimate the mean $\rm \Sigma _{SFR}$, the star formation rate per free-fall time and the star formation efficiency for clumps to be 1.5 $\rm M_{\odot}\, yr^{-1}\, kpc^{-2}$, 0.009 and 2.0 per cent, respectively, while for the whole region covered by both nebulae (which we call the ‘NAN’ complex) the values are 0.6 $\rm M_{\odot}\, yr^{-1}\, kpc^{-2}$, 0.0003 and 1.6 per cent, respectively. For the clumps, we notice that the observed properties are in line with the correlation obtained between $\rm \Sigma _{SFR}$ and $\rm \Sigma _{gas}$, and between $\rm \Sigma _{SFR}$ and $\rm \Sigma _{gas}$ per free-fall time and orbital time for Galactic clouds. At the same time, we do not observe any correlation with $\rm \Sigma _{gas}$ per crossing time and multi free-fall time. Even though we see correlations in the former cases, however, all models agree with each other within a factor of 0.5 dex. It is not possible to discriminate between these models because of the current uncertainties in the input observables. We also test the variation of $\rm \Sigma _{SFR}$ with the dense gas but, because of low statistics, a weak correlation is seen in our analysis.

scholarly journals Heart of darkness: the influence of galactic dynamics on quenching star formation in galaxy spheroids

2020 ◽  
Vol 495 (1) ◽  
pp. 199-223 ◽  
Author(s):  
Jindra Gensior ◽  
J M Diederik Kruijssen ◽  
Benjamin W Keller
Keyword(s):  
Star Formation ◽  
Main Sequence ◽  
Formation Rate ◽  
Free Fall ◽  
Galactic Centre ◽  
Causal Connection ◽  
Isolated Galaxies ◽  
Stellar Halo ◽  
Hydrodynamical Simulations ◽  
The Impact

ABSTRACT Quenched galaxies are often observed to contain a strong bulge component. The key question is whether this reflects a causal connection – can star formation be quenched dynamically by bulges or the spheroids of early-type galaxies? We systematically investigate the impact of these morphological components on star formation, by performing a suite of hydrodynamical simulations of isolated galaxies containing a spheroid. We vary the bulge mass and scale radius, while the total initial stellar, halo, and gas mass are kept constant, with a gas fraction of 5 per cent. In addition, we consider two different sub-grid star formation prescriptions. The first follows most simulations in the literature by assuming a constant star formation efficiency per free-fall time, whereas in the second model it depends on the gas virial parameter, following high-resolution simulations of turbulent fragmentation. Across all simulations, central spheroids increase the gas velocity dispersion towards the galactic centre. This increases the gravitational stability of the gas disc, suppresses fragmentation and star formation, and results in galaxies hosting extremely smooth and quiescent gas discs that fall below the galaxy main sequence. These effects amplify when using the more sophisticated, dynamics-dependent star formation model. Finally, we discover a pronounced relation between the central stellar surface density and star formation rate (SFR), such that the most bulge-dominated galaxies show the strongest deviation from the main sequence. We conclude that the SFR of galaxies is not only set by the balance between accretion and feedback, but carries a (sometimes dominant) dependence on the gravitational potential.

scholarly journals The effects of population III radiation backgrounds on the cosmological 21-cm signal

2020 ◽  
Vol 493 (1) ◽  
pp. 1217-1226 ◽  
Author(s):  
Richard H Mebane ◽  
Jordan Mirocha ◽  
Steven R Furlanetto
Keyword(s):  
Black Holes ◽  
Star Formation ◽  
Radio Emission ◽  
Formation Rate ◽  
Fine Tuning ◽  
Absorption Feature ◽  
Simulation Code ◽  
X Ray ◽  
Neutral Gas ◽  
Population Iii

ABSTRACT We investigate the effects of Population III (Pop III) stars and their remnants on the cosmological 21-cm global signal. By combining a semi-analytic model of Pop III star formation with a global 21-cm simulation code, we investigate how X-ray and radio emission from accreting Pop III black holes may affect both the timing and depth of the 21-cm absorption feature that follows the initial onset of star formation during the Cosmic Dawn. We compare our results to the findings of the EDGES experiment, which has reported the first detection of a cosmic 21-cm signal. In general, we find that our fiducial Pop III models, which have peak star formation rate densities of ∼10−4 M⊙ yr−1 Mpc−3 between z ∼ 10 and z ∼ 15, are able to match the timing of the EDGES signal quite well, in contrast to models that ignore Pop III stars. To match the unexpectedly large depth of the EDGES signal without recourse to exotic physics, we vary the parameters of emission from accreting black holes (formed as Pop III remnants) including the intrinsic strength of X-ray and radio emission as well as the local column density of neutral gas. We find that models with strong radio emission and relatively weak X-ray emission can self-consistently match the EDGES signal, though this solution requires fine-tuning. We are only able to produce signals with sharp features similar to the EDGES signal if the Pop III IMF is peaked narrowly around $140 \, \mathrm{M}_\odot$.

scholarly journals SDSS-IV MaNGA: effects of morphology in the global and local star formation main sequences

2019 ◽  
Vol 488 (3) ◽  
pp. 3929-3948 ◽  
Author(s):  
M Cano-Díaz ◽  
V Ávila-Reese ◽  
S F Sánchez ◽  
H M Hernández-Toledo ◽  
A Rodríguez-Puebla ◽  
...  
Keyword(s):  
Star Formation ◽  
Surface Density ◽  
Main Sequence ◽  
Formation Rate ◽  
Stellar Mass ◽  
Star Forming ◽  
Spatially Resolved ◽  
Star Formation Activity ◽  
Global And Local ◽  
Universal Mechanism

ABSTRACT We study the global star formation rate (SFR) versus stellar mass (M*) correlation, and the spatially resolved SFR surface density (ΣSFR) versus stellar mass surface density (Σ*) correlation, in a sample of ∼2000 galaxies from the MaNGA MPL-5 survey. We classify galaxies and spatially resolved areas into star forming and retired according to their ionization processes. We confirm the existence of a star-forming main sequence (SFMS) for galaxies and spatially resolved areas, and show that they have the same nature, with the global as a consequence of the local one. The latter presents a bend below a limit Σ* value, ≈3 × 107 M$\odot$ kpc−2, which is not physical. Using only star-forming areas (SFAs) above this limit, a slope and a scatter of ≈1 and ≈0.27 dex are determined. The retired galaxies/areas strongly segregate from their respective SFMSs, by ∼−1.5 dex on average. We explore how the global/local SFMSs depend on galaxy morphology, finding that for star-forming galaxies and SFAs, there is a trend to lower values of star formation activity with earlier morphological types, which is more pronounced for the local SFMS. The morphology not only affects the global SFR due to the diminish of SFAs with earlier types, but also affects the local SF process. Our results suggest that the local SF at all radii is established by some universal mechanism partially modulated by morphology. Morphology seems to be connected to the slow aging and sharp decline of the SF process, and on its own it may depend on other properties as the environment.

scholarly journals The Cosmic Baryon and Metal Cycles

2020 ◽  
Vol 58 (1) ◽  
pp. 363-406 ◽  
Author(s):  
Céline Péroux ◽  
J. Christopher Howk
Keyword(s):  
Star Formation ◽  
Mass Density ◽  
Formation Rate ◽  
Cosmic Time ◽  
Dust Content ◽  
Star Formation History ◽  
Molecular Gas ◽  
Neutral Gas ◽  
Formation History ◽  
The Universe

Characterizing the relationship between stars, gas, and metals in galaxies is a critical component of understanding the cosmic baryon cycle. We compile contemporary censuses of the baryons in collapsed structures and their chemical makeup and dust content. We show the following: ▪  The [Formula: see text] mass density of the Universe is well determined to redshifts [Formula: see text] and shows minor evolution with time. New observations of molecular hydrogen reveal its evolution mirrors that of the global star-formation rate density, implying a universal cosmic molecular gas depletion timescale. The low-redshift decline of the star-formation history is thus driven by the lack of molecular gas supply due to a drop in net accretion rate related to the decreased growth of dark matter halos. ▪  The metal mass density in cold gas ([Formula: see text] K) contains virtually all the metals produced by stars for [Formula: see text]. At lower redshifts, the contributors to the total amount of metals are more diverse; at [Formula: see text], most of the observed metals are bound in stars. Overall, there is little evidence for a “missing metals problem” in modern censuses. ▪  We characterize the dust content of neutral gas over cosmic time, finding the dust-to-gas and dust-to-metals ratios fall with decreasing metallicity. We calculate the cosmological dust mass density in the neutral gas up to [Formula: see text]. There is good agreement between multiple tracers of the dust content of the Universe.

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