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 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 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 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 Environmental Effects on the ISM and Star Formation Properties of Nearby Spiral Galaxies

2015 ◽  
Vol 11 (S315) ◽  
Author(s):  
Angus Mok ◽  
Christine Wilson
Keyword(s):  
Star Formation ◽  
Environmental Effects ◽  
Spiral Galaxies ◽  
Star Formation Rate ◽  
Formation Rate ◽  
Molecular Gas ◽  
Turbulent Pressure ◽  
Cluster Environment ◽  
Gas Properties

AbstractWe studied molecular gas properties in a sample of 98 Hi - flux selected spiral galaxies within ~ 25 Mpc using the CO J = 3 − 2 line, observed with the JCMT, and subdivided into isolated, group, and Virgo subsamples. We find a larger mean H2 mass in the Virgo galaxies compared to group galaxies, despite their lower mean Hi mass. Combining our data with complementary Hα star formation rate measurements, Virgo galaxies have a longer molecular gas depletion times compared to group galaxies, perhaps due to heating processes in the cluster environment or differences in the turbulent pressure.

scholarly journals The evolution of the spiral galaxy M51a

2015 ◽  
Vol 11 (S319) ◽  
pp. 129-129
Author(s):  
Xiaoyu Kang ◽  
Fenghui Zhang ◽  
Ruixiang Chang
Keyword(s):  
Star Formation ◽  
Surface Density ◽  
Evolutionary History ◽  
Surface Brightness ◽  
Star Formation Rate ◽  
Formation Rate ◽  
Molecular Gas ◽  
Peak Time ◽  
Model Predictions ◽  
Inside Out

AbstractA simple model for M51a is constructed to explore its evolutionary history by assuming its disk grows from continuous gas infall, which is shaped by a free parameter-the infall-peak time tp. By adopting a constant infall-peak time tp = 7.0Gyr, our model predictions can reproduce most of the observed constraints and still show that the disk of M51a forms inside-out. Our results also show that the current molecular gas surface density, the star-formation rate and the UV-band surface brightness are important quantities to trace the effect of recent interactions on galactic star-formation process.

scholarly journals The EDGE-CALIFA survey: exploring the role of molecular gas on galaxy star formation quenching

2020 ◽  
Vol 644 ◽  
pp. A97
Author(s):  
D. Colombo ◽  
S. F. Sanchez ◽  
A. D. Bolatto ◽  
V. Kalinova ◽  
A. Weiß ◽  
...  
Keyword(s):  
Star Formation ◽  
Galaxy Evolution ◽  
Large Scale ◽  
Formation Rate ◽  
Molecular Gas ◽  
Star Forming ◽  
Average Value ◽  
First Results ◽  
Gas Consumption ◽  
Formation Efficiency

Understanding how galaxies cease to form stars represents an outstanding challenge for galaxy evolution theories. This process of “star formation quenching” has been related to various causes, including active galactic nuclei activity, the influence of large-scale dynamics, and the environment in which galaxies live. In this paper, we present the first results from a follow-up of CALIFA survey galaxies with observations of molecular gas obtained with the APEX telescope. Together with the EDGE-CARMA observations, we collected 12CO observations that cover approximately one effective radius in 472 CALIFA galaxies. We observe that the deficit of galaxy star formation with respect to the star formation main sequence (SFMS) increases with the absence of molecular gas and with a reduced efficiency of conversion of molecular gas into stars, which is in line with the results of other integrated studies. However, by dividing the sample into galaxies dominated by star formation and galaxies quenched in their centres (as indicated by the average value of the Hα equivalent width), we find that this deficit increases sharply once a certain level of gas consumption is reached, indicating that different mechanisms drive separation from the SFMS in star-forming and quenched galaxies. Our results indicate that differences in the amount of molecular gas at a fixed stellar mass are the primary drivers for the dispersion in the SFMS, and the most likely explanation for the start of star formation quenching. However, once a galaxy is quenched, changes in star formation efficiency drive how much a retired galaxy differs in its star formation rate from star-forming ones of similar masses. In other words, once a paucity of molecular gas has significantly reduced star formation, changes in the star formation efficiency are what drives a galaxy deeper into the red cloud, hence retiring it.

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 5.5. The detection of a gas-rich bar in the interacting galaxy UGC 2855

1998 ◽  
Vol 184 ◽  
pp. 219-220
Author(s):  
S. Hüttemeister ◽  
S. Aalto ◽  
W. F. Wall
Keyword(s):  
Star Formation ◽  
Central Region ◽  
Star Formation Rate ◽  
Formation Rate ◽  
Starburst Galaxies ◽  
Large Percentage ◽  
Molecular Gas ◽  
Transient Phenomena

Bars fuel the prolific star formation rate in many Starburst galaxies. They provide a mechanism for feeding gas into the nuclei as well as a laboratory for the study of molecular gas that is unbound and diffuse due to tidal strain and cloud collisions. A large percentage of galaxies show a stellar bar which is, however, in most cases almost devoid of (molecular) gas, except in the central region. Thus, long gaseous bars are rare and transient phenomena.

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