scholarly journals Molecular ISM and Star Formation Efficiency in the Central Kpc

2001 ◽  
Vol 205 ◽  
pp. 228-231 ◽  
Author(s):  
Shardha Jogee
Keyword(s):  
Star Formation ◽  
Star Formation Rate ◽  
Formation Rate ◽  
Radio Continuum ◽  
Gas Content ◽  
Molecular Gas ◽  
Owens Valley ◽  
Radio Observatory ◽  
And Control ◽  
Formation Efficiency

Why do the circumnuclear (inner 1-2 kpc) regions of some spirals develop starbursts, which are intense short-lived (t ≪ 1 Gyr) episodes of star formation characterized by a high star formation rate per unit mass of molecular gas (SFR/MH2), which I refer to as the star formation efficiency (SFE), while others with comparable gas content become non-starbursts? I address this question and other issues on circumnuclear evolution using high resolution (2” or 100-200 pc) CO (J=1>0) observations from the Owens Valley Radio Observatory, optical and NIR images, along with radio continuum (RC) and Brγ data. The sample galaxies are all nearby, moderately inclined, and include the brightest nearby starbursts comparable to M82 and control non-starbursts. Detailed results are in Jogee (1999) and Jogee, Kenney, & Scoville 2000 (in prep.)

scholarly journals Star formation rates, laws, thresholds

2015 ◽  
Vol 11 (S315) ◽  
pp. 167-174
Author(s):  
Stefanie Walch
Keyword(s):  
Star Formation ◽  
Star Formation Rate ◽  
Formation Rate ◽  
Gas Content ◽  
Molecular Gas ◽  
Feedback Mechanisms ◽  
Stellar Feedback ◽  
Short Summary ◽  
Multi Phase ◽  
Formation Efficiency

AbstractOn scales of ≳ several hundred parsec, there are relatively well defined observed relations between the star formation rate surface density of a galaxy and its gas content. I present a short summary of the so-called ‘star formation laws’ and discuss the most established models to explain their origin. Nevertheless, none of the models can explain the offset of these relations, which requires a low star formation efficiency within the total and/or molecular gas. Stellar feedback is proposed to limit the star formation efficiency locally. I discuss the available feedback mechanisms and show recent simulation results on the evolution of the multi-phase interstellar medium under the influence of gravity, cooling, feedback-driven outflows and heating.

scholarly journals Evolution of the star formation efficiency in galaxies

2012 ◽  
Vol 10 (H16) ◽  
pp. 341-341
Author(s):  
Jonathan Braine
Keyword(s):  
Star Formation ◽  
Chemical Evolution ◽  
Conversion Factor ◽  
Star Formation Rate ◽  
Formation Rate ◽  
Molecular Gas ◽  
Present Evidence ◽  
Ngc 6822 ◽  
Physical And Chemical ◽  
Formation Efficiency

AbstractThe physical and chemical evolution of galaxies is intimately linked to star formation, We present evidence that molecular gas (H2) is transformed into stars more quickly in smaller and/or subsolar metallicity galaxies than in large spirals – which we consider to be equivalent to a star formation efficiency (SFE). In particular, we show that this is not due to uncertainties in the N(H2)/Ico conversion factor. Several possible reasons for the high SFE in galaxies like the nearby M33 or NGC 6822 are proposed which, separately or together, are the likely cause of the high SFE in this environment. We then try to estimate how much this could contribute to the increase in cosmic star formation rate density from z = 0 to z = 1.

scholarly journals Explaining the enhanced star formation rate of Jellyfish galaxies in galaxy clusters

2019 ◽  
Vol 486 (1) ◽  
pp. L26-L30 ◽  
Author(s):  
Mohammadtaher Safarzadeh ◽  
Abraham Loeb
Keyword(s):  
Star Formation ◽  
Galaxy Clusters ◽  
Star Formation Rate ◽  
Formation Rate ◽  
Control Sample ◽  
External Pressure ◽  
Gas Content ◽  
Ram Pressure ◽  
Inclination Angles ◽  
Formation Efficiency

ABSTRACT We study the recently observed JellyFish galaxies (JFGs), which are found to have their gas content ram pressure stripped away in galaxy clusters. These galaxies are observed to have an enhanced star formation rate of about 0.2 dex compared with a control sample of the same stellar mass in their discs. We model the increase in the star formation efficiency as a function of intracluster medium pressure and parametrize the cold gas content of the galaxies as a function of cluster-centric distance. We show that regarding the external pressure as a positive feedback results in agreement with the observed distribution of enhanced star formation in the JFGs if clouds are shielded from evaporation by magnetic fields. Our results predict that satellites with halo mass $\lt 10^{11}{\rm \, M_\odot }$ moving with Mach numbers $\mathcal {M}\approx 2$, and inclination angles below 60 deg, are more likely to be detected as JFGs.

scholarly journals Dense gas is not enough: environmental variations in the star formation efficiency of dense molecular gas at 100 pc scales in M 51

2019 ◽  
Vol 625 ◽  
pp. A19 ◽  
Author(s):  
M. Querejeta ◽  
E. Schinnerer ◽  
A. Schruba ◽  
E. Murphy ◽  
S. Meidt ◽  
...  
Keyword(s):  
Star Formation ◽  
Surface Density ◽  
Formation Rate ◽  
Radio Continuum ◽  
Molecular Gas ◽  
Dense Gas ◽  
Environmental Variations ◽  
Formation Efficiency ◽  
Density Threshold ◽  
Spiral Arm

It remains unclear what sets the efficiency with which molecular gas transforms into stars. Here we present a new VLA map of the spiral galaxy M 51 in 33 GHz radio continuum, an extinction-free tracer of star formation, at 3″ scales (∼100 pc). We combined this map with interferometric PdBI/NOEMA observations of CO(1–0) and HCN(1–0) at matched resolution for three regions in M 51 (central molecular ring, northern and southern spiral arm segments). While our measurements roughly fall on the well-known correlation between total infrared and HCN luminosity, bridging the gap between Galactic and extragalactic observations, we find systematic offsets from that relation for different dynamical environments probed in M 51; for example, the southern arm segment is more quiescent due to low star formation efficiency (SFE) of the dense gas, despite its high dense gas fraction. Combining our results with measurements from the literature at 100 pc scales, we find that the SFE of the dense gas and the dense gas fraction anti-correlate and correlate, respectively, with the local stellar mass surface density. This is consistent with previous kpc-scale studies. In addition, we find a significant anti-correlation between the SFE and velocity dispersion of the dense gas. Finally, we confirm that a correlation also holds between star formation rate surface density and the dense gas fraction, but it is not stronger than the correlation with dense gas surface density. Our results are hard to reconcile with models relying on a universal gas density threshold for star formation and suggest that turbulence and galactic dynamics play a major role in setting how efficiently dense gas converts into stars.

scholarly journals Star formation laws in extreme starbursts

2012 ◽  
Vol 8 (S292) ◽  
pp. 319-322
Author(s):  
S. García-Burillo ◽  
A. Usero ◽  
A. Alonso-Herrero
Keyword(s):  
Star Formation ◽  
Star Formation Rate ◽  
Formation Rate ◽  
Free Fall ◽  
Quality Data ◽  
Molecular Gas ◽  
Physical Processes ◽  
High Quality Data ◽  
Normal Galaxies ◽  
Formation Efficiency

AbstractThe observational study of star formation laws is paramount to disentangling the physical processes at work on local and global scales in galaxies. To this aim we have expanded the sample of extreme starbursts, represented by local LIRGs and ULIRGs, with high-quality data obtained in the 1-0 line of HCN. The analysis of the new data shows that the star formation efficiency of the dense molecular gas, derived from the FIR/HCN luminosity ratio, is a factor 3-4 higher in extreme starbursts compared to normal galaxies. We find a duality in the Kennicutt-Schmidt laws that is enhanced if we account for the different conversion factor for HCN (αHCN) in extreme starbursts and correct for the unobscured star formation rate in normal galaxies. We find that it is possible to fit the observed differences in the FIR/HCN ratios between normal galaxies and LIRGs/ULIRGs with a common constant star formation rate per free-fall time (SFRff) if we assume that HCN densities are ∼1–2 orders of magnitude higher in LIRGs/ULIRGs, and provided that SFRff∼0.005-0.01 and/or if αHCN is a factor of a few lower than our favored values.

scholarly journals Molecular gas content in typical L* galaxies at z ∼ 1.5 − 3

2014 ◽  
Vol 10 (S309) ◽  
pp. 285-286
Author(s):  
Miroslava Dessauges-Zavadsky ◽  
Michel Zamojski ◽  
Daniel Schaerer ◽  
Françoise Combes ◽  
Eiichi Egami ◽  
...  
Keyword(s):  
Star Formation ◽  
Formation Rate ◽  
Stellar Mass ◽  
Gas Content ◽  
Physical Parameters ◽  
Molecular Gas ◽  
Star Forming ◽  
Large Spread ◽  
Gas Measurements ◽  
Formation Efficiency

AbstractTo extend the molecular gas measurements to typical L* star-forming galaxies (SFGs) at z ∼ 1.5 − 3, we have observed CO emission for five strongly-lensed galaxies selected from the Herschel Lensing Survey. The combined sample of our L* SFGs with CO-detected SFGs at z >1 from the literature shows a large spread in star formation efficiency (SFE). We find that this spread in SFE is due to variations of several physical parameters, primarily the specific star formation rate, but also stellar mass and redshift. An increase of the molecular gas fraction (fgas) is observed from z ∼ 0.2 to z ∼ 1.2, followed by a quasi non-evolution toward higher redshifts, as found in earlier studies. We provide the first measure of fgas of z >1 SFGs at the low-stellar mass end between 109.4 < M∗/M⊙ < 109.9, which shows a clear fgas upturn.

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 What drives galaxy quenching? Resolving molecular gas and star formation in the green valley

2020 ◽  
Vol 498 (1) ◽  
pp. L66-L71 ◽  
Author(s):  
Simcha Brownson ◽  
Francesco Belfiore ◽  
Roberto Maiolino ◽  
Lihwai Lin ◽  
Stefano Carniani
Keyword(s):  
Star Formation ◽  
Star Formation Rate ◽  
Formation Rate ◽  
Gas Content ◽  
Molecular Gas ◽  
Data Sets ◽  
Star Forming ◽  
Spatially Resolved ◽  
Star Forming Regions ◽  
Central Regions

ABSTRACT We study quenching in seven green valley galaxies on kpc scales by resolving their molecular gas content using 12CO(1–0) observations obtained with NOrthern Extended Millimeter Array and Atacama Large Millimeter Array, and their star formation rate using spatially resolved optical spectroscopy from the Mapping Nearby Galaxies at Apache Point Observatory survey. We perform radial stacking of both data sets to increase the sensitivity to molecular gas and star formation, thereby avoiding biases against strongly quenched regions. We find that both spatially resolved gas fraction (fgas) and star formation efficiency ($\rm {SFE}$) are responsible for quenching green valley galaxies at all radii: both quantities are suppressed with respect to typical star-forming regions. fgas and $\rm {SFE}$ have roughly equal influence in quenching the outer disc. We are, however, unable to identify the dominant mechanism in the strongly quenched central regions. We find that fgas is reduced by $\rm \sim\! 1~dex$ in the central regions, but the star formation rate is too low to be measured, leading to upper limits for the $\rm {SFE}$. Moving from the outer disc to central regions, the reduction in fgas is driven by an increasing $\rm \Sigma _{\star }$ profile rather than a decreasing $\rm \Sigma _{H_{2}}$ profile. The reduced fgas may therefore be caused by a decrease in the gas supply rather than molecular gas ejection mechanisms, such as winds driven by active galactic nuclei. We warn more generally that studies investigating fgas may be deceiving in inferring the cause of quenching, particularly in the central (bulge-dominated) regions of galaxies.

scholarly journals CHANG-ES

2018 ◽  
Vol 611 ◽  
pp. A72 ◽  
Author(s):  
Marita Krause ◽  
Judith Irwin ◽  
Theresa Wiegert ◽  
Arpad Miskolczi ◽  
Ancor Damas-Segovia ◽  
...  
Keyword(s):  
Star Formation ◽  
Wind Velocity ◽  
Surface Density ◽  
Spiral Galaxies ◽  
Star Formation Rate ◽  
Formation Rate ◽  
Cosmic Ray ◽  
Scale Height ◽  
Radio Continuum ◽  
Frequency Bands

Aim. The vertical halo scale height is a crucial parameter to understand the transport of cosmic-ray electrons (CRE) and their energy loss mechanisms in spiral galaxies. Until now, the radio scale height could only be determined for a few edge-on galaxies because of missing sensitivity at high resolution.Methods. We developed a sophisticated method for the scale height determination of edge-on galaxies. With this we determined the scale heights and radial scale lengths for a sample of 13 galaxies from the CHANG-ES radio continuum survey in two frequency bands.Results. The sample average values for the radio scale heights of the halo are 1.1 ± 0.3 kpc in C-band and 1.4 ± 0.7 kpc in L-band. From the frequency dependence analysis of the halo scale heights we found that the wind velocities (estimated using the adiabatic loss time) are above the escape velocity. We found that the halo scale heights increase linearly with the radio diameters. In order to exclude the diameter dependence, we defined a normalized scale height h˜ which is quite similar for all sample galaxies at both frequency bands and does not depend on the star formation rate or the magnetic field strength. However, h˜ shows a tight anticorrelation with the mass surface density.Conclusions. The sample galaxies with smaller scale lengths are more spherical in the radio emission, while those with larger scale lengths are flatter. The radio scale height depends mainly on the radio diameter of the galaxy. The sample galaxies are consistent with an escape-dominated radio halo with convective cosmic ray propagation, indicating that galactic winds are a widespread phenomenon in spiral galaxies. While a higher star formation rate or star formation surface density does not lead to a higher wind velocity, we found for the first time observational evidence of a gravitational deceleration of CRE outflow, e.g. a lowering of the wind velocity from the galactic disk.

scholarly journals xGASS: cold gas content and quenching in galaxies below the star-forming main sequence

2020 ◽  
Vol 493 (2) ◽  
pp. 1982-1995 ◽  
Author(s):  
Steven Janowiecki ◽  
Barbara Catinella ◽  
Luca Cortese ◽  
Amelie Saintonge ◽  
Jing Wang
Keyword(s):  
Star Formation ◽  
Main Sequence ◽  
Star Formation Rate ◽  
Formation Rate ◽  
Gas Content ◽  
Gas Reservoirs ◽  
Star Forming ◽  
Correct Model ◽  
Gas Measurements ◽  
Cold Gas

ABSTRACT We use H i and H2 global gas measurements of galaxies from xGASS and xCOLD GASS to investigate quenching paths of galaxies below the Star forming main sequence (SFMS). We show that the population of galaxies below the SFMS is not a 1:1 match with the population of galaxies below the H i and H2 gas fraction scaling relations. Some galaxies in the transition zone (TZ) 1σ below the SFMS can be as H i-rich as those in the SFMS, and have on average longer gas depletion time-scales. We find evidence for environmental quenching of satellites, but central galaxies in the TZ defy simple quenching pathways. Some of these so-called ‘quenched’ galaxies may still have significant gas reservoirs and be unlikely to deplete them any time soon. As such, a correct model of galaxy quenching cannot be inferred with star formation rate (or other optical observables) alone, but must include observations of the cold gas. We also find that internal structure (particularly, the spatial distribution of old and young stellar populations) plays a significant role in regulating the star formation of gas-rich isolated TZ galaxies, suggesting the importance of bulges in their evolution.

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