The Gaia data give us an unprecedented view to the 3-dimensional (3D) structure of molecular clouds in the Solar neighbourhood. We study how the projected areas and masses of clouds, and consequently the Kennicutt-Schmidt relation (KS-relation), depend on the viewing angle. We derive the probability distributions of the projected areas and masses for nine clouds within 400 pc from the Sun using 3D dust distribution data from the literature. We find that the viewing angle can have a dramatic effect on the observed areas and masses of individual clouds. The joint probability distributions of the areas and masses are strongly correlated, relatively flat, and can show multiple peaks. The typical ranges and 50% quartiles of the distributions are roughly 100-200% and 20-80% of the median value, respectively, making viewing angle effects important for all individual clouds. The threshold value used to define the cloud areas is also important; our analysis suggests that the clouds become more anisotropic for smaller thresholds (larger scales). On average, the areas and masses of the plane-of-the-sky and face-on projections agree, albeit with a large scatter. This suggests that sample averages of areas and masses are relatively free of viewing angle effects, which is important to facilitate comparisons of extragalactic and galactic data. Ultimately, our results demonstrate that a cloud's location in the KS-relation is affected by viewing angle in a non-trivial manner. However, the KS-relation of our sample as a whole is not strongly affected by these effects, because the co-variance of the areas and masses causes the observed mean column density to remain relatively constant.
We use simulations of isolated galaxies with a few parsec resolution to explore the connection between the small-scale star formation rate - gas density relation and the induced large-scale correlation between the star formation rate surface density and the surface density of the molecular gas (the Kennicutt-Schmidt relation). We find that, in the simulations, a power-law small-scale "star formation law" directly translates into an identical power-law Kennicutt-Schmidt relation. If this conclusion holds in the reality as well, it implies that the observed approximately linear Kennicutt-Schmidt…
We study properties of the interstellar medium, an ingredient of stars, and star formation activity, in four nearby galaxy pairs in the early and mid stages of interaction for both a galaxy scale and a kpc scale. The galaxy-scale Kennicutt-Schmidt law shows that seven of eight interacting galaxies have a star formation rate within a factor of three compared with the best-fit of the isolated galaxies, although we have shown that molecular hydrogen gas is efficiently produced from atomic hydrogen during the interaction in the previous paper. The galaxy-scale specific star formation rate (sSFR) a…
We study the Kennicutt-Schmidt relation between average star formation rate and average cold gas surface density in the Hi dominated ISM of nearby spiral and dwarf irregular galaxies. We divide the galaxies into grid cells varying from sub-kpc to tens of kpc in size. Grid-cell measurements of low SFRs using H-alpha emission can be biased and scatter may be introduced because of non-uniform sampling of the IMF or because of stochastically varying star formation. In order to alleviate these issues, we use far-ultraviolet emission to trace SFR, and we sum up the fluxes from different bins with th…
The observationally derived Kennicutt-Schmidt (KS) relation slopes differ from study to study, ranging from sub-linear to super-linear. We investigate the KS-relation variety (slope and normalization) as a function of integrated intensity ratio, R31=CO(J=3-2)/CO(J=1-0) using spatially resolved CO(J=1-0), CO(J=3-2), HI, Ha and 24um data of three nearby spiral galaxies (NGC3627, NGC5055 and M83). We find that (1) the slopes for each subsample with a fixed R31 are shallower but the slope for all datasets combined becomes steeper, (2) normalizations for high R31 subsamples tend to be high, (3) R31…
Recent statistical analysis of two extragalactic observational surveys strongly indicate a sublinear Kennicutt-Schmidt (KS) relationship between the star formation rate (Sigsfr) and molecular gas surface density (Sigmol). Here, we consider the consequences of these results in the context of common assumptions, as well as observational support for a linear relationship between Sigsfr and the surface density of dense gas. If the CO traced gas depletion time (tau_mol) is constant, and if CO only traces star forming giant molecular clouds (GMCs), then the physical properties of each GMC must vary,…
We have mapped the northern area (30' times 20') of a local group spiral galaxy M33 in 12CO(J=1-0) line with the 45-m telescope at the Nobeyama Radio Observatory. Along with Halpha and Spitzer 24-micron data, we have investigated the relationship between the surface density of molecular gas mass and that of star formation rate (SFR) in an external galaxy (Kennicutt-Schmidt law) with the highest spatial resolution (~80pc) to date, which is comparable to scales of giant molecular clouds (GMCs). At positions where CO is significantly detected, the SFR surface density exhibits a wide range of over…
We have mapped the northern area (30'\times 20') of a local group spiral galaxy M33 in 12CO(1-0) line with the 45-m telescope at the Nobeyama Radio Observatory. Along with Halpha and Spitzer 24-micron data, we have investigated the relationship between the surface density of molecular gas mass and that of star formation rate (SFR) in an external galaxy (Kennicutt-Schmidt law) with the highest spatial resolution (~80pc) to date, which is comparable to scales of giant molecular clouds (GMCs). At positions where CO is significantly detected, the SFR surface density exhibits a wide range of over f…
The Kennicutt-Schmidt law is an empirical relation between the star formation rate surface density ($Σ_{SFR}$) and the gas surface density ($Σ_{gas}$) in disc galaxies. The relation has a power-law form $Σ_{SFR} \propto Σ_{gas}^n$. Assuming that star formation results from gravitational collapse of the interstellar medium, $Σ_{SFR}$ can be determined by dividing $Σ_{gas}$ by the local free-fall time $t_{ff}$. The formulation of $t_{ff}$ yields the relation between $Σ_{SFR}$ and $Σ_{gas}$, assuming that a constant fraction ($\varepsilon_{SFE}$) of gas is converted into stars every $t_{ff}$. Thi…
Studying star formation beyond the optical radius of galaxies allows us to test empirical relations in extreme conditions with low average gas density and low molecular fraction. Previous studies discovered galaxies with extended ultraviolet (XUV) disks, which often contain star forming regions with lower Halpha-to-far-UV (FUV) flux ratios compared to inner disk star forming regions. However, most previous studies lack measurements of molecular gas, which is presumably the component of the interstellar medium out of which stars form. We analyzed published CO measurements and upper limits for f…
We argue that most strong intervening metal absorption line systems, where the rest equivalent width of the MgII 2796A line is >0.5A, are interstellar material in, and outflowing from, star-forming disks. We show that a version of the Kennicutt-Schmidt law is readily obtained if the MgII equivalent widths are interpreted as kinematic broadening from absorbing gas in outflowing winds originating from star-forming galaxies. Taking a phenomenological approach and using a set of observational constraints available for star-forming galaxies, we are able to account for the density distribution of st…
We present results of self-consistent, high-resolution cosmological simulations of galaxy formation at z~3. The simulations employ recently developed recipe for star formation based on the local abundance of molecular hydrogen, which is tracked self-consistently during the course of simulation. The phenomenological H2 formation model accounts for the effects of dissociating UV radiation of stars in each galaxy, as well as self-shielding and shielding of H2 by dust, and therefore allows us to explore effects of lower metallicities and higher UV fluxes prevalent in high redshift galaxies on thei…
In order to test a recent hypothesis that the dispersion in the Schmidt-Kennicutt law arises from variations in the evolutionary stage of star forming molecular clouds, we compared molecular gas and recent star formation in an early-phase merger galaxy pair, Taffy I (UGC\ 12915/UGC\ 12914, VV\ 254) which went through a direct collision 20 Myr ago and whose star forming regions are expected to have similar ages. Narrow-band Pa-alpha image is obtained using the ANIR near-infrared camera on the mini-TAO 1m telescope. The image enables us to derive accurate star formation rates within the galaxy d…
Gravity or turbulence? VII. The Schmidt-Kennicutt law, the star formation efficiency, and the mass density of clusters from gravitational collapse rather than turbulent support
We present an analysis of the global and spatially-resolved Kennicutt-Schmidt (KS) star formation relation in the FIRE (Feedback In Realistic Environments) suite of cosmological simulations, including halos with $z = 0$ masses ranging from $10^{10}$ -- $10^{13}$ M$_{\odot}$. We show that the KS relation emerges and is robustly maintained due to the effects of feedback on local scales regulating star-forming gas, independent of the particular small-scale star formation prescriptions employed. We demonstrate that the time-averaged KS relation is relatively independent of redshift and spatial ave…
The Kennicutt-Schmidt (KS) relation between the gas mass and star formation rate (SFR) describes the star formation regulation in disk galaxies. It is a function of gas metallicity, but the low metallicity regime of the KS diagram is poorly sampled. We have analyzed data for a representative set of extremely metal-poor galaxies (XMPs), as well as auxiliary data, and compared these to empirical and theoretical predictions. The majority of the XMPs possess high specific SFRs, similar to high redshift star-forming galaxies. On the KS plot, the XMP HI data occupy the same region as dwarfs, and ext…
The surface densities of molecular gas, $Σ_{\rm H_2}$, and the star formation rate (SFR), $\dotΣ_\star$, correlate almost linearly on kiloparsec scales in observed star-forming (non-starburst) galaxies. We explore the origin of the linear slope of this correlation using a suite of isolated $L_\star$ galaxy simulations. We show that in simulations with efficient feedback, the slope of the $\dotΣ_\star$-$Σ_{\rm H_2}$ relation on kiloparsec scales is insensitive to the slope of the $\dotρ_\star$-$ρ$ relation assumed at the resolution scale. We also find that the slope on kiloparsec scales depends…
We derive a metallicity dependent relation between the surface density of the star formation rate (Sigma_{SFR}) and the gas surface density (Sigma_{g}) in a feedback regulated model of star formation in galactic disks. In this model, star formation occurs in gravitationally bound protocluster clumps embedded in larger giant molecular clouds with the protocluster clump mass function following a power law function with a slope of -2. Metallicity dependent feedback is generated by the winds of OB stars (M > 5 Msol) that form in the clumps. The quenching of star formation in clumps of decreasing m…
A new analysis of high-resolution data from the Atacama Large Millimeter/submillimeter Array (ALMA) for 5 luminous or ultra-luminous infrared galaxies gives a slope for the Kennicutt-Schmidt (KS) relation equal to $1.74^{+0.09}_{\rm -0.07}$ for gas surface densities $Σ_{\rm mol}>10^3\;M_\odot$ pc$^{-2}$ and an assumed constant CO-to-H$_2$ conversion factor. The velocity dispersion of the CO line, $σ_v$, scales approximately as the inverse square root of $Σ_{\rm mol}$, making the empirical gas scale height determined from $H\sim0.5σ^2/(πGΣ_{\rm mol})$ nearly constant, 150-190 pc, over 1.5 order…
Using N-body/gasdynamic simulations of a Milky Way-like galaxy we analyse a Kennicutt-Schmidt relation, $Σ_{SFR} \propto Σ_{gas}^N$, at different spatial scales. We simulate synthetic observations in CO lines and UV band. We adopt the star formation rate defined in two ways: based on free fall collapse of a molecular cloud - $Σ_{SFR, cl}$, and calculated by using a UV flux calibration - $Σ_{SFR, UV}$. We study a KS relation for spatially smoothed maps with effective spatial resolution from molecular cloud scales to several hundred parsecs. We find that for spatially and kinematically resolved …
We present a detailed description of a phenomenological H2 formation model and local star formation prescription based on the density of molecular (rather than total) gas. Such approach allows us to avoid the arbitrary density and temperature thresholds typically used in star formation recipes. We present results of the model based on realistic cosmological simulations of high-z galaxy formation for a grid of numerical models with varied dust-to-gas ratios and interstellar far UV (FUV) fluxes. Our results show that both the atomic-to-molecular transition on small, ~10 pc scales and the Kennicu…
Hyperluminous infrared galaxies (HyLIRGs) provide crucial "long lever arm" constraints on galaxy evolution. H-ATLAS $J084933.4+021443$, a $z=2.41$ binary HyLIRG with at least two additional luminous companion galaxies, is thus an optimal test-ground for studies of star formation and galaxy evolution during "cosmic noon". We have used ALMA to obtain resolved imaging and kinematics of atomic and molecular emission lines, and rest-frame $340$ to $1160$GHz continuum emission, for the known luminous component galaxies in H-ATLAS $J084933.4+021443$: W, T, M, C. All four component galaxies are spatia…
We investigate the relationship between the star formation rate (SFR), stellar mass ($M_*$) and molecular gas mass ($M_{H_2}$) for local star-forming galaxies. We further investigate these relationships for high-z (z=1-3) galaxies and for the hosts of a local sample of Active Galactic Nuclei (AGN). We explore which of these dependencies are intrinsic and which are an indirect by-product by employing partial correlation coefficients and random forest regression. We find that for local star-forming galaxies, high-z galaxies, and AGN host galaxies, the Schmidt-Kennicutt relation (SK, between $M_{…
The star formation rate per unit area correlates well with the gas surface density for different types of galaxies. However, this Kennicutt-Schmidt law has not yet been examined for a large, homogeneously selected sample of SMGs, which could provide useful SF implementation information for models of massive galaxy formation and evolution. We aim at determining the K-S law parameters for the first time for a well-selected, statistical sample of SMGs. We used ALMA to conduct a 0.2" resolution, 870 $μ$m imaging survey of 40 SMGs in COSMOS, which were initially selected at 1.1 mm. We analysed a sa…
In this VERTICO science paper we aim to study how the star formation process depends on galactic environment and gravitational interactions in the context of galaxy evolution. We explore the scaling relation between the star formation rate (SFR) surface density and the molecular gas surface density, also known as the Kennicutt-Schmidt (KS) relation, in a subsample of Virgo cluster spiral galaxies. We use new ACA and TP observations from the VERTICO-ALMA Large Program at 720pc resolution to resolve the molecular gas content, as traced by the 12CO(2-1) transition, across the disks of 37 spiral g…
Results from the UV satellite GALEX revealed large extensions of disks in some nearby spiral galaxies, extending out to 3 to 4 times the isophotal radius, r25. M63 is a remarkable example of a spiral galaxy with one of the most extended UV disks, so it offers the opportunity to search for the molecular gas and characterize the star formation in outer disk regions as revealed by the UV emission. We obtained deep CO(1-0) and CO(2-1) observations on the IRAM 30 m telescope along the major axis of the M63 disk from the center out to the galactocentric radius rgal = 1.6 r25 and over a bright UV reg…
Recent studies have shown that star formation in mergers does not seem to follow the same Schmidt-Kennicutt (KS) relation as in spiral disks, presenting a higher star formation rate (SFR) for a given gas column density. In this paper we study why and how different models of star formation arise. To do so we examine the process of star formation in the interacting system Arp 158 and its tidal debris. We perform an analysis of the properties of specific regions of interest in Arp 158 using observations tracing the atomic and the molecular gas, star formation, the stellar populations as well as o…
Kennicutt-Schmidt relation of galaxies over 13 billion years in the COLIBRE hydrodynamical simulations
Cosmic Dawn Center (DAWN)（宇宙黎明中心）；Leiden Observatory, Leiden University（莱顿天文台，莱顿大学）；School of Physics and Astronomy, University of Nottingham（诺丁汉大学物理与天文学学院）；Dipartimento di Fisica G. Occhialini, Università degli Studi di Milano Bicocca（米兰比可卡大学G. Occhialini物理系）；Cardiff Hub for Astrophysics Research & Technology, School of Physics & Astronomy, Cardiff University（卡迪夫大学物理与天文学院，卡迪夫天体物理学研究与技术枢纽）；Research School of Astronomy and Astrophysics, Australian National University（澳大利亚国立大学天体物理学研究学院）；Department of Astrophysics, University of Vienna（维也纳大学天体物理学系）
Sub-kiloparsec Test of the Kennicutt-Schmidt Relation in a Strongly Lensed Dusty Star-Forming Galaxy at z~2.78
Universidad de Valparaíso（瓦尔帕莱索大学）；Millenium Nucleus for Galaxies (MINGAL)（星系千年核（MINGAL））；STAR Institute（STAR研究所）；Université Côte d’Azur（蔚蓝海岸大学）；University of Florida（佛罗里达大学）；Universidad Nacional Autónoma de México（墨西哥国立自治大学）；Instituto Nacional de Astrofísica Óptica y Electrónica (INAOE)（国家天体物理学、光学和电子学研究所）；Universidad Central de Chile（智利中央大学）
We compile observations of molecular gas contents and infrared-based star formation rates (SFRs) for 112 circumnuclear star forming regions, in order to re-investigate the form of the disk-averaged Schmidt surface density star formation law in starbursts. We then combine these results with total gas and SFR surface densities for 153 nearby non-starbursting disk galaxies from de los Reyes \& Kennicutt (2019), to investigate the properties of the combined star formation law, following Kennicutt (1998; K98). We confirm that the combined Schmidt law can be fitted with a single power law with slope…
Ever since the pioneering work of Schmidt a half-century ago there has been great interest in finding an appropriate empirical relation that would directly link some property of interstellar gas with the process of star formation within it. Schmidt conjectured that this might take the form of a power-law relation between the rate of star formation (SFR) and the surface density of interstellar gas. However, recent observations suggest that a linear scaling relation between the total SFR and the amount of dense gas within molecular clouds appears to be the underlying physical relation that most …
We present simulations of the evolution of self-gravitating dense gas on kiloparsec-size scales in a galactic disk, designed to study dense clump formation from giant molecular clouds (GMCs). These dense clumps are expected to be the precursors to star clusters and this process may be the rate limiting step controling star formation rates in galactic systems as described by the Kennicutt-Schmidt relation. The evolution of these simulated GMCs and clumps is determined by self-gravity balanced by turbulent pressure support and the large scale galactic shear. While the cloud structures and densit…
We investigate Schmidt's conjecture (i.e., that the star formation rate scales in a power-law fashion with the gas density) for four well-studied local molecular clouds (GMCs). Using the Bayesian methodology we show that a local Schmidt scaling relation of the form Sigma*(A_K) = kappa x (A_K)^{beta} (protostars pc^{-2}) exists within (but not between) GMCs. Further we find that the Schmidt scaling law, by itself, does not provide an adequate description of star formation activity in GMCs. Because the total number of protostars produced by a cloud is given by the product of Sigma*(A_K) and S'(>…
The extended Schmidt law (ESL) is a variant of the Schmidt law which relates the surface densities of gas and star formation, with the surface density of stellar mass added as an extra parameter. We empirically investigate for the first time whether low metallicity faint dwarf irregular galaxies (dIrrs) follow the ESL. Here we consider the `global' law where surface densities are averaged over the galactic discs. dIrrs are unique not only because they are at the lowest end of mass and star formation scales for galaxies, but also because they are metal-poor compared to the general population of…
Spatially resolved HI studies of dwarf galaxies have provided a wealth of precision data. However these high-quality, resolved observations are only possible for handful of dwarf galaxies in the Local Volume. Future HI surveys are unlikely to improve the current situation. We therefore explore a method for estimating the surface density of the atomic gas from global HI parameters, which are conversely widely available. We perform empirical tests using galaxies with resolved HI maps, and find that our approximation produces values for the surface density of atomic hydrogen within typically 0.5d…
We investigate the relation between star formation rate (SFR) and gas surface densities in Galactic star forming regions using a sample of YSOs and massive clumps. Our YSO sample consists of objects located in 20 molecular clouds from the Spitzer cores to disks and Gould's Belt surveys. We estimate the gas surface density (Sigma_gas) from Av maps and YSO SFR surface densities (Sigma_SFR) from the number of YSOs, assuming a mean mass and lifetime. We also divide the clouds into contour levels of Av, counting only the youngest Class I and Flat SED YSOs. For a sample of massive star forming clump…
There has been much recent work dedicated to exploring secondary correlations in the mass-metallicity relation, with significant dependence on both the star formation rate and HI content being demonstrated. Previously, a paucity of molecular gas data (combined with sample selection bias) hampered the investigation of any such relation with molecular gas content. In this work, we assemble a sample of 221 galaxies from a variety of surveys in the redshift range 0 < z < 2, to explore the connection between molecular gas content and metallicity. We explore the effect of gas mass on the mass-metall…
We analysed the high-resolution (up to $\sim$0.2") ALMA CO (2-1) and 1.3 mm dust continuum data of eight gas-rich post-starburst galaxies (PSBs) in the local Universe, six of which had been studied by Smercina et al. (2022). In contrast to this study reporting the detections of extraordinarily compact (i.e., unresolved) reservoirs of molecular gas in the six PSBs, our visibility-plane analysis resolves the CO (2-1) emission in all eight PSBs with effective radii ($R_\mathrm{e,CO}$) of $0.8_{-0.4}^{+0.9}$ kpc, typically consisting of gaseous components at both circumnuclear and extended disc sc…
We investigate the nature of the scaling relations between the surface density of star formation rate ($Σ_{\rm SFR}$), stellar mass ($Σ_*$), and molecular gas mass ($Σ_{\rm H_2}$), aiming at distinguishing between the relations that are primary, i.e. more fundamental, and those which are instead an indirect by-product of the other relations. We use the ALMaQUEST survey and analyse the data by using both partial correlations and Random Forest regression techniques. We unambiguously find that the strongest intrinsic correlation is between $Σ_{\rm SFR}$ and $Σ_{\rm H_2}$ (i.e. the resolved Schmid…
A tight relation between the [CII]158$μ$m line luminosity and star formation rate is measured in local galaxies. At high redshift ($z>5$), though, a much larger scatter is observed, with a considerable (15-20\%) fraction of the outliers being [CII]-deficient. Moreover, the [CII] surface brightness ($Σ_{\rm CII}$) of these sources is systematically lower than expected from the local relation. To clarify the origin of such [CII]-deficiency we have developed an analytical model that fits local [CII] data, and has been validated against radiative transfer simulations performed with CLOUDY. The mod…
We present P-GADGET3-K, an updated version of GADGET3, that incorporates the chemistry package KROME. P-GADGET3-K follows the hydrodynamical and chemical evolution of cosmic structures, incorporating the chemistry and cooling of H$_2$ and metal cooling in non-equilibrium. We performed different runs of the same ICs to assess the impact of various physical parameters and prescriptions, namely gas metallicity, molecular hydrogen formation on dust, star formation recipes including or not H$_2$ dependence, and the effects of numerical resolution. We find that the characteristics of the simulated s…
I review here the spatially-resolved spectroscopic properties of low-redshift star-forming galaxies (and their retired counter-parts), using results from the most recent Integral Field Spectroscopy galaxy surveys. First, I briefly summarise the global spectroscopic properties of these galaxies, discussing the main ionization processes, and the global relations described between the star-formation rates, oxygen abundances, and average properties of their stellar populations (age and metallicity) with the stellar mass. Second, I present the local distribution of the ionizing processes, down to k…
We analyse the star formation (SF) relations in a sample of 16 nearby luminous infrared galaxies (LIRGs) with more than 2800 regions defined on scales of 90 to 500 pc. We used ALMA to map the distribution of the cold molecular gas traced by the J = 2-1 line of CO and archival PaαHST/NICMOS imaging to trace the recent SF. In four objects, we find two different branches in the Kennicutt-Schmidt relation at 90 pc scales, suggesting the existence of a duality in this relation. The two branches correspond to two different dynamical environments within each galaxy. One branch, which corresponds to t…
By using a novel interface between the modern smoothed particle hydrodynamics code GASOLINE2 and the chemistry package KROME, we follow the hydrodynamical and chemical evolution of an isolated galaxy. In order to assess the relevance of different physical parameters and prescriptions, we constructed a suite of ten simulations, in which we vary the chemical network (primordial and metal species), how metal cooling is modelled (non-equilibrium versus equilibrium; optically thin versus thick approximation), the initial gas metallicity (from ten to hundred per cent solar), and how molecular hydrog…
We report on a multi parameter analysis of giant molecular clouds (GMCs) in the nearby spiral galaxy M33. A catalog of GMCs identifed in 12CO(J=3-2) was used to compile associated 12CO(J=1-0), dust, stellar mass and star formation rate. Each of the 58 GMCs are categorized by their evolutionary stage. Applying the principal component analysis on these parameters, we construct two principal components PC1 and PC2 which retain 75% of the information in the original dataset. PC1 is interpreted as expressing the total interstellar matter content, and PC2 as the total activity of star formation. You…
