scholarly journals New Constraints on the 12CO(2 − 1)/(1 − 0) Line Ratio Across Nearby Disc Galaxies

2021 ◽  
Author(s):  
J S den Brok ◽  
D Chatzigiannakis ◽  
F Bigiel ◽  
J Puschnig ◽  
A T Barnes ◽  
...  
Keyword(s):  
Surface Density ◽  
Massive Star ◽  
Formation Rate ◽  
Molecular Gas ◽  
Star Forming ◽  
Large Program ◽  
The Galaxy ◽  
The Mean ◽  
Point To Point ◽  
Disc Galaxies

Abstract Both the CO(2-1) and CO(1-0) lines are used to trace the mass of molecular gas in galaxies. Translating the molecular gas mass estimates between studies using different lines requires a good understanding of the behaviour of the CO(2-1)-to-CO(1-0) ratio, R21. We compare new, high quality CO(1-0) data from the IRAM 30-m EMPIRE survey to the latest available CO(2-1) maps from HERACLES, PHANGS-ALMA, and a new IRAM 30-m M51 Large Program. This allows us to measure R21 across the full star-forming disc of nine nearby, massive, star-forming spiral galaxies at 27″(∼1 − 2 kpc) resolution. We find an average R21 = 0.64 ± 0.09 when we take the luminosity-weighted mean of all individual galaxies. This result is consistent with the mean ratio for disc galaxies that we derive from single-pointing measurements in the literature, $R_{\rm 21, lit}~=~0.59^{+0.18}_{-0.09}$. The ratio shows weak radial variations compared to the point-to-point scatter in the data. In six out of nine targets the central enhancement in R21 with respect to the galaxy-wide mean is of order $\sim 10{-}20\%$. We estimate an azimuthal scatter of ∼20% in R21 at fixed galactocentric radius but this measurement is limited by our comparatively coarse resolution of 1.5 kpc. We find mild correlations between R21 and CO brightness temperature, IR intensity, 70-to-160 μm ratio, and IR-to-CO ratio. All correlations indicate that R21 increases with gas surface density, star formation rate surface density, and the interstellar radiation field.

scholarly journals Less than the sum of its parts: the dust-corrected H α luminosity of star-forming galaxies explored at different spatial resolutions with MaNGA and MUSE

2020 ◽  
Vol 498 (3) ◽  
pp. 4205-4221
Author(s):  
N Vale Asari ◽  
V Wild ◽  
A L de Amorim ◽  
A Werle ◽  
Y Zheng ◽  
...  
Keyword(s):  
Spatial Resolution ◽  
Formation Rate ◽  
Flux Ratio ◽  
Star Forming ◽  
The Galaxy ◽  
Nearby Galaxies ◽  
Point To Point ◽  
Dust Attenuation ◽  
The Impact ◽  
Lower Limits

ABSTRACT The H α and H β emission-line luminosities measured in a single integrated spectrum are affected in non-trivial ways by point-to-point variations in dust attenuation in a galaxy. This work investigates the impact of this variation when estimating global H α luminosities corrected for the presence of dust by a global Balmer decrement. Analytical arguments show that the dust-corrected H α luminosity is always underestimated when using the global H α/H β flux ratio to correct for dust attenuation. We measure this effect on 156 face-on star-forming galaxies from the Mapping Nearby Galaxies at APO (MaNGA) survey. At 1–2 kpc spatial resolution, the effect is small but systematic, with the integrated dust-corrected H α luminosity underestimated by 2–4 per cent (and typically not more than by 10 per cent), and depends on the specific star formation rate of the galaxy. Given the spatial resolution of MaNGA, these are lower limits for the effect. From Multi Unit Spectroscopic Explorer (MUSE) observations of NGC 628 with a resolution of 36 pc, we find the discrepancy between the globally and the point-by-point dust-corrected H α luminosity to be 14 ± 1 per cent, which may still underestimate the true effect. We use toy models and simulations to show that the true difference depends strongly on the spatial variance of the H α/H β flux ratio, and on the slope of the relation between H αluminosity and dust attenuation within a galaxy. Larger samples of higher spatial resolution observations are required to quantify the dependence of this effect as a function of galaxy properties.

scholarly journals Simulations of the star-forming molecular gas in an interacting M51-like galaxy

2020 ◽  
Vol 492 (2) ◽  
pp. 2973-2995 ◽  
Author(s):  
Robin G Tress ◽  
Rowan J Smith ◽  
Mattia C Sormani ◽  
Simon C O Glover ◽  
Ralf S Klessen ◽  
...  
Keyword(s):  
Star Formation ◽  
Large Scale ◽  
Formation Rate ◽  
Three Dimensional ◽  
Molecular Gas ◽  
Secondary Importance ◽  
Star Forming ◽  
The Galaxy ◽  
Cold Star ◽  
Self Gravity

ABSTRACT We present here the first of a series of papers aimed at better understanding the evolution and properties of giant molecular clouds (GMCs) in a galactic context. We perform high-resolution, three-dimensional arepo simulations of an interacting galaxy inspired by the well-observed M51 galaxy. Our fiducial simulations include a non-equilibrium, time-dependent, chemical network that follows the evolution of atomic and molecular hydrogen as well as carbon and oxygen self-consistently. Our calculations also treat gas self-gravity and subsequent star formation (described by sink particles), and coupled supernova feedback. In the densest parts of the simulated interstellar medium (ISM), we reach sub-parsec resolution, granting us the ability to resolve individual GMCs and their formation and destruction self-consistently throughout the galaxy. In this initial work, we focus on the general properties of the ISM with a particular focus on the cold star-forming gas. We discuss the role of the interaction with the companion galaxy in generating cold molecular gas and controlling stellar birth. We find that while the interaction drives large-scale gas flows and induces spiral arms in the galaxy, it is of secondary importance in determining gas fractions in the different ISM phases and the overall star formation rate. The behaviour of the gas on small GMC scales instead is mostly controlled by the self-regulating property of the ISM driven by coupled feedback.

scholarly journals Star formation in CALIFA early-type galaxies: a matter of discs

2019 ◽  
Vol 488 (1) ◽  
pp. L80-L84 ◽  
Author(s):  
J Méndez-Abreu ◽  
S F Sánchez ◽  
A de Lorenzo-Cáceres
Keyword(s):  
Star Formation ◽  
Main Sequence ◽  
Formation Rate ◽  
Molecular Gas ◽  
Early Type ◽  
Star Forming ◽  
Integral Field Spectroscopy ◽  
The Galaxy ◽  
First Time ◽  
Integral Field

ABSTRACT The star formation main sequence (SFMS) is a tight relation between the galaxy star formation rate (SFR) and its total stellar mass (M⋆). Early-type galaxies (ETGs) are often considered as low-SFR outliers of this relation. We study, for the first time, the separated distribution in the SFR versus M⋆ of bulges and discs of 49 ETGs from the CALIFA survey. This is achieved using c2d, a new code to perform spectrophotometric decompositions of integral field spectroscopy data cubes. Our results reflect that: (i) star formation always occurs in the disc component and not in bulges; (ii) star-forming discs in our ETGs are compatible with the SFMS defined by star-forming galaxies at z ∼ 0; (iii) the star formation is not confined to the outskirts of discs, but it is present at all radii (even where the bulge dominates the light); (iv) for a given mass, bulges exhibit lower sSFR than discs at all radii; and (v) we do not find a deficit of molecular gas in bulges with respect to discs for a given mass in our ETGs. We speculate our results favour a morphological quenching scenario for ETGs.

scholarly journals Star Formation Thresholds: The View from Inside the Galaxy

2015 ◽  
Vol 11 (S315) ◽  
pp. 183-190
Author(s):  
James Di Francesco
Keyword(s):  
Star Formation ◽  
Surface Density ◽  
Column Density ◽  
Star Formation Rate ◽  
Formation Rate ◽  
Star Forming ◽  
Gould Belt ◽  
The Galaxy ◽  
Dynamical Properties ◽  
The Relationship

AbstractWe explore the relationship between the total gas surface density and star formation rate surface density, a.k.a., the “Kennicutt-Schmidt relation,” in a Galactic context. Specifically, we probe the origins of thresholds in the behaviour of the K-S relation at 10 M⊙ pc−2 and 100-200 M⊙ pc−2 using images from the Herschel Hi-GAL and Gould Belt surveys. In both cases, pervasive filamentary structures are seen, possibly due to turbulent motions. The Hi-GAL image supports the view that at ~10 M⊙ pc−2 gas becomes molecular, leading to the formation of clouds that harbour star formation. The GBS images suggest the 100-200 M⊙ pc−2 threshold originates from the nature of filaments being stable until a critical column density of ~160 M⊙ pc−2 is reached. Therefore, the transition between non-star-forming and star-forming gas in clouds (and galaxies) may be set universally by the dynamical properties of filaments.

scholarly journals CO in the Milky Way

1997 ◽  
Vol 170 ◽  
pp. 11-18 ◽  
Author(s):  
Leo Blitz
Keyword(s):  
Angular Momentum ◽  
Milky Way ◽  
Star Formation Rate ◽  
Formation Rate ◽  
Molecular Gas ◽  
Active Star ◽  
Star Forming ◽  
The Galaxy ◽  
Atomic Gas ◽  
Hubble Time

If the CO distribution of the Milky Way is described as a truncated exponential rather than as a molecular ring with some gas at large radii, it becomes easier to understand the evolution of the disk of stars. The star formation rate per unit molecular gas mass is constant as a function of radius, and the H2 depletion time turns out to be only a few percent of the Hubble time. This very short timescale requires that the atomic gas act as a reservoir for the active star forming gas. Because the HI has such a different radial distribution, there must either be infall from outside the Galaxy, an efficient way for the atomic gas in the disk to lose angular momentum, or both, leading to measurable infall or inflow velocities. The truncation radius of CO is probably due to the recently identified stellar bar.

scholarly journals Cosmic rays across the star-forming galaxy sequence. II: Stability limits and the onset of cosmic ray-driven outflows

2021 ◽  
Author(s):  
Roland M Crocker ◽  
Mark R Krumholz ◽  
Todd A Thompson
Keyword(s):  
Star Formation ◽  
Cosmic Rays ◽  
Surface Density ◽  
Star Formation Rate ◽  
Formation Rate ◽  
Cosmic Ray ◽  
Star Forming ◽  
Rate Versus ◽  
The Galaxy ◽  
Plausible Mechanism

Abstract Cosmic rays (CRs) are a plausible mechanism for launching winds of cool material from the discs of star-forming galaxies. However, there is no consensus on what types of galaxies likely host CR-driven winds, or what role these winds might play in regulating galaxies’ star formation rates. Using a detailed treatment of the transport and losses of hadronic CRs developed in the previous paper in this series, here we develop a semi-analytic model that allows us to assess the viability of using CRs to launch cool winds from galactic discs. In particular, we determine the critical CR fluxes – and corresponding star formation rate surface densities – above which hydrostatic equilibrium within a given galaxy is precluded because CRs drive the gas off in a wind or otherwise render it unstable. Our model demonstrates that catastrophic, CR-driven wind loss is a possibility at galactic mean surface densities below $\, {\lesssim}\, 10^2 \ M_{\odot }$ pc−2. In this regime – encompassing the Galaxy and local dwarfs – the locus of the CR stability curve patrols the high side of the observed distribution of galaxies in the Kennicutt-Schmidt parameter space of star formation rate versus gas surface density. However, hadronic losses render CRs unable to drive global winds in galaxies with surface densities above the ∼102 − 103M⊙ pc−2 transition region. Our results show that quiescent, low surface density galaxies like the Milky Way are poised on the cusp of instability, such that small changes to ISM parameters can lead to the launching of CR-driven outflows, and we suggest that, as a result, CR feedback sets an ultimate limit to the star formation efficiency of most modern galaxies.

scholarly journals Using the Milky Way as a template for understanding star formation in extreme environments across cosmological timescales

2012 ◽  
Vol 8 (S292) ◽  
pp. 333-333
Author(s):  
Steven N. Longmore
Keyword(s):  
Star Formation ◽  
Milky Way ◽  
Formation Rate ◽  
Volume Density ◽  
Galactic Centre ◽  
Molecular Gas ◽  
Dense Gas ◽  
Star Forming ◽  
Star Formation Activity ◽  
The Galaxy

AbstractRecent surface- and volume-density star formation relations have been proposed which potentially unify our understanding of how gas is converted into stars, from the nearest star forming regions to ultra-luminous infrared galaxies. The inner 500 pc of our Galaxy – the Central Molecular Zone – contains the largest concentration of dense, high-surface density molecular gas in the Milky Way, providing an environment where the validity of these star-formation prescriptions can be tested.We have used recently-available data from HOPS, MALT90 and HiGAL at wavelengths where the Galaxy is transparent, to find the dense, star-forming molecular gas across the Milky Way [Longmore et al. (2012a), Longmore et al. (2012b)]. We use water and methanol maser emission to trace star formation activity within the last 105 years and 30 GHz radio continuum emission from the Wilkinson Microwave Anisotropy Satellite (WMAP) to estimate the high-mass star formation rate averaged over the last ∼ 4 × 106 years.We find the dense gas distribution is dominated by the very bright and spatially-extended emission within a few degrees of the Galactic centre [Purcell et al. (2012)]. This region accounts for ∼80% of the NH3(1,1) integrated intensity but only contains 4% of the survey area. However, in stark contrast, the distribution of star formation activity tracers is relatively uniform across the Galaxy.To probe the dense gas vs SFR relationship towards the Galactic centre region more quantitatively, we compared the HiGAL column density maps to the WMAP-derived SFR across the same region. The total mass and SFR derived using these methods agree well with previous values in the literature. The main conclusion from this analysis is that both the column-density threshold and volumetric SF relations over-predict the SFR by an order of magnitude given the reservoir of dense gas available to form stars. The region 1° < l < 3.5°, |b| < 0.5° is particular striking in this regard. It contains ∼107 M⊙ of dense molecular gas — enough to form 1000 Orion-like clusters — but the present-day star formation rate within this gas is only equivalent to that in Orion. This implication of this result is that any universal column/volume density relations must be a necessary but not sufficient condition for SF to occur.Understanding why such large reservoirs of dense gas deviate from commonly assumed SF relations is of fundamental importance and may help in the quest to understand SF in more extreme (dense) environments, like those found in interacting galaxies and at earlier epochs of the Universe.

scholarly journals The ALMaQUEST survey – III. Scatter in the resolved star-forming main sequence is primarily due to variations in star formation efficiency

2020 ◽  
Vol 493 (1) ◽  
pp. L39-L43 ◽  
Author(s):  
Sara L Ellison ◽  
Mallory D Thorp ◽  
Lihwai Lin ◽  
Hsi-An Pan ◽  
Asa F L Bluck ◽  
...  
Keyword(s):  
Star Formation ◽  
Surface Density ◽  
Main Sequence ◽  
Star Formation Rate ◽  
Formation Rate ◽  
Molecular Gas ◽  
Star Forming ◽  
The Absolute ◽  
Correlation Statistics ◽  
Formation Efficiency

ABSTRACT Using a sample of 11 478 spaxels in 34 galaxies with molecular gas, star formation, and stellar maps taken from the ALMA-MaNGA QUEnching and STar formation (ALMaQUEST) survey, we investigate the parameters that correlate with variations in star formation rates on kpc scales. We use a combination of correlation statistics and an artificial neural network to quantify the parameters that drive both the absolute star formation rate surface density (ΣSFR), as well as its scatter around the resolved star-forming main sequence (ΔΣSFR). We find that ΣSFR is primarily regulated by molecular gas surface density ($\Sigma _{\rm H_2}$) with a secondary dependence on stellar mass surface density (Σ⋆), as expected from an ‘extended Kennicutt–Schmidt relation’. However, ΔΣSFR is driven primarily by changes in star formation efficiency (SFE), with variations in gas fraction playing a secondary role. Taken together, our results demonstrate that whilst the absolute rate of star formation is primarily set by the amount of molecular gas, the variation of star formation rate above and below the resolved star-forming main sequence (on kpc scales) is primarily due to changes in SFE.

scholarly journals The ALPINE−ALMA [C ii] Survey: on the nature of an extremely obscured serendipitous galaxy

2020 ◽  
Vol 496 (1) ◽  
pp. 875-887 ◽  
Author(s):  
M Romano ◽  
P Cassata ◽  
L Morselli ◽  
B C Lemaux ◽  
M Béthermin ◽  
...  
Keyword(s):  
Near Infrared ◽  
Spectral Energy Distribution ◽  
Formation Rate ◽  
Spectral Energy ◽  
Physical Parameters ◽  
Star Forming ◽  
Average Value ◽  
First Case ◽  
Large Program ◽  
The Galaxy

ABSTRACT We report the serendipitous discovery of a dust-obscured galaxy observed as part of the Atacama Large Millimeter Array (ALMA) Large Program to INvestigate [C ii] at Early times (ALPINE). While this galaxy is detected both in line and continuum emissions in ALMA Band 7, it is completely dark in the observed optical/near-infrared bands and only shows a significant detection in the UltraVISTA Ks band. We discuss the nature of the observed ALMA line, that is [C ii] at $z$ ∼ 4.6 or high-J CO transitions at $z$ ∼ 2.2. In the first case, we find a [C ii]/FIR luminosity ratio of $\mathrm{log}{(L_{[\mathrm{ C}\, \rm {\small {II}}]}/L_{\mathrm{ FIR}})} \sim -2.5$, consistent with the average value for local star-forming galaxies (SFGs). In the second case instead, the source would lie at larger CO luminosities than those expected for local SFGs and high-z submillimetre galaxies. At both redshifts, we derive the star formation rate (SFR) from the ALMA continuum and the physical parameters of the galaxy, such as the stellar mass (M*), by fitting its spectral energy distribution. Exploiting the results of this work, we believe that our source is a ‘main-sequence’, dusty SFG at $z$ = 4.6 (i.e. [C ii] emitter) with $\mathrm{log(SFR/M_{\odot }\, yr^{-1})}\sim 1.4$ and log(M*/M⊙) ∼ 9.9. As a support to this scenario our galaxy, if at this redshift, lies in a massive protocluster recently discovered at $z$ ∼ 4.57, at only ∼1 proper Mpc from its centre. This work underlines the crucial role of the ALPINE survey in making a census of this class of objects, in order to unveil their contribution to the global SFR density at the end of the Reionization epoch.

scholarly journals Realistic mock observations of the sizes and stellar mass surface densities of massive galaxies in FIRE-2 zoom-in simulations

2020 ◽  
Vol 501 (2) ◽  
pp. 1591-1602
Author(s):  
T Parsotan ◽  
R K Cochrane ◽  
C C Hayward ◽  
D Anglés-Alcázar ◽  
R Feldmann ◽  
...  
Keyword(s):  
Galaxy Formation ◽  
Surface Density ◽  
Stellar Mass ◽  
Massive Galaxies ◽  
Star Forming ◽  
Stellar Feedback ◽  
Central Surface ◽  
Stellar Ages ◽  
The Galaxy ◽  
Zoom In

ABSTRACT The galaxy size–stellar mass and central surface density–stellar mass relationships are fundamental observational constraints on galaxy formation models. However, inferring the physical size of a galaxy from observed stellar emission is non-trivial due to various observational effects, such as the mass-to-light ratio variations that can be caused by non-uniform stellar ages, metallicities, and dust attenuation. Consequently, forward-modelling light-based sizes from simulations is desirable. In this work, we use the skirt  dust radiative transfer code to generate synthetic observations of massive galaxies ($M_{*}\sim 10^{11}\, \rm {M_{\odot }}$ at z = 2, hosted by haloes of mass $M_{\rm {halo}}\sim 10^{12.5}\, \rm {M_{\odot }}$) from high-resolution cosmological zoom-in simulations that form part of the Feedback In Realistic Environments project. The simulations used in this paper include explicit stellar feedback but no active galactic nucleus (AGN) feedback. From each mock observation, we infer the effective radius (Re), as well as the stellar mass surface density within this radius and within $1\, \rm {kpc}$ (Σe and Σ1, respectively). We first investigate how well the intrinsic half-mass radius and stellar mass surface density can be inferred from observables. The majority of predicted sizes and surface densities are within a factor of 2 of the intrinsic values. We then compare our predictions to the observed size–mass relationship and the Σ1−M⋆ and Σe−M⋆ relationships. At z ≳ 2, the simulated massive galaxies are in general agreement with observational scaling relations. At z ≲ 2, they evolve to become too compact but still star forming, in the stellar mass and redshift regime where many of them should be quenched. Our results suggest that some additional source of feedback, such as AGN-driven outflows, is necessary in order to decrease the central densities of the simulated massive galaxies to bring them into agreement with observations at z ≲ 2.

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