scholarly journals CO observations as a diagnostic of possible environmental effects

2002 ◽  
Vol 206 ◽  
pp. 248-251
Author(s):  
Marcio A. G. Maia ◽  
Duilia de Mello ◽  
Tommy Wiklind
Keyword(s):  
Star Formation ◽  
Environmental Effects ◽  
Diagnostic Tool ◽  
Molecular Gas ◽  
Low Density ◽  
Physical Processes ◽  
Two Samples ◽  
Formation Efficiency ◽  
Very High ◽  
Co Observations

We have compared two samples of galaxies in very high and low density environments in order to study their physical properties and stablish any possible relation among them. This paper focus on the CO content as a diagnostic tool to examine galaxy properties such as the amount of molecular gas and the star formation efficiency. The similarities in star formation efficiency of the dense environments and the field galaxies suggest that the physical processes controling the formation of stars from the molecular gas are local rather than global.

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 CO observations towards H i-rich Ultradiffuse Galaxies

2020 ◽  
Vol 499 (1) ◽  
pp. L26-L30
Author(s):  
Junzhi Wang ◽  
Kai Yang ◽  
Zhi-Yu Zhang ◽  
Min Fang ◽  
Yong Shi ◽  
...  
Keyword(s):  
Star Formation ◽  
Virgo Cluster ◽  
Molecular Gas ◽  
Upper Limits ◽  
Low Mass ◽  
Co Detection ◽  
Atomic Gas ◽  
Low Efficiency ◽  
Formation Efficiency ◽  
Co Observations

ABSTRACT We present CO observations towards a sample of six H i-rich Ultradiffuse galaxies (UDGs) as well as one UDG (VLSB-A) in the Virgo Cluster with the Institut de RadioAstronomie Millimétrique (IRAM) 30-m telescope. CO J = 1–0 is marginally detected at 4σ level in AGC 122966, as the first detection of CO emission in UDGs. We estimate upper limits of molecular mass in other galaxies from the non-detection of CO lines. These upper limits and the marginal CO detection in AGC 122966 indicate low mass ratios between molecular and atomic gas masses. With the star formation efficiency derived from the molecular gas, we suggest that the inefficiency of star formation in such H i-rich UDGs is likely caused by the low efficiency in converting molecules from atomic gas, instead of low efficiency in forming stars from molecular gas.

scholarly journals Watching the Birth of Super Star Clusters

2004 ◽  
Vol 221 ◽  
pp. 125-130
Author(s):  
Jean L. Turner ◽  
Sara C. Beck
Keyword(s):  
Star Formation ◽  
Dwarf Galaxy ◽  
Star Clusters ◽  
Star Cluster ◽  
Molecular Gas ◽  
Radio Observations ◽  
General Properties ◽  
Super Star Clusters ◽  
Formation Efficiency ◽  
Very High

Subarcsecond infrared and radio observations yield important information about the formation of super star clusters from their surrounding gas. We discuss the general properties of ionized and molecular gas near young, forming SSCs, as illustrated by the prototypical young, forming super star cluster nebula in the dwarf galaxy NGC 5253. This super star cluster appears to have a gravitationally bound nebula, and the lack of molecular gas suggests a very high star formation efficiency, consistent with the formation of a large, bound cluster.

From global to local scales in galaxies

2020 ◽  
Vol 15 (S359) ◽  
pp. 391-395
Author(s):  
Sebastian F. Sánchez ◽  
Carlos Lopez Cobá
Keyword(s):  
Star Formation ◽  
Spatial Scales ◽  
Bimodal Distribution ◽  
Spectroscopic Properties ◽  
Molecular Gas ◽  
Ionized Gas ◽  
Galaxy Surveys ◽  
Quenching Process ◽  
Formation Efficiency ◽  
Integral Field

AbstractWe summarize here some of the results reviewed recently by Sanchez (2020) comprising the advances in the comprehension of galaxies in the nearby universe based on integral field spectroscopic galaxy surveys. In particular we explore the bimodal distribution of galaxies in terms of the properties of their ionized gas, showing the connection between the star-formation (quenching) process with the presence (absence) of molecular gas and the star-formation efficiency. We show two galaxy examples that illustrates the well known fact that ionization in galaxies (and the processes that produce it), does not happen monolitically at galactic scales. This highlight the importance to explore the spectroscopic properties of galaxies and the evolutionary processes unveiled by them at different spatial scales, from sub-kpc to galaxy wide.

scholarly journals A large amount of diffuse molecular gases in the bar of the strongly barred galaxy NGC 1300: cause of the low star formation efficiency

2020 ◽  
Vol 495 (4) ◽  
pp. 3840-3858 ◽  
Author(s):  
Fumiya Maeda ◽  
Kouji Ohta ◽  
Yusuke Fujimoto ◽  
Asao Habe ◽  
Kaito Ushio
Keyword(s):  
Star Formation ◽  
Molecular Gas ◽  
Full Width ◽  
Half Maximum ◽  
Barred Galaxies ◽  
Molecular Gases ◽  
Formation Efficiency

ABSTRACT In many barred galaxies, star formation efficiency (SFE) in the bar is lower than those in the arm and bar-end, and its cause has still not been clear. Focusing on the strongly barred galaxy NGC 1300, we investigate the possibility that the presence of a large amount of diffuse molecular gas, which would not contribute to the SF, makes the SFE low in appearance. We examine the relation between the SFE and the diffuse molecular gas fraction (fdif), which is derived using the 12CO(1–0) flux obtained from the interferometer of ALMA 12-m array, which has no sensitivity on diffuse (extended; full width at half-maximum ⪆700 pc) molecular gases due to the lack of ACA, and the total 12CO(1–0) flux obtained from Nobeyama 45-m single-dish telescope. We find that the SFE decreases with increasing fdif. The fdif and SFE are 0.74−0.91 and $0.06\!-\!0.16 ~\rm Gyr^{-1}$ in the bar regions, and 0.28−0.65 and $0.23\!-\!0.96 ~\rm Gyr^{-1}$ in the arm and bar-end regions, respectively. This result supports the idea that the presence of a large amount of diffuse molecular gas makes the SFE low. The suppression of the SFE in the bar has also been seen even when we exclude the diffuse molecular gas components. This suggests that the low SFE appears to be caused not only by a large amount of diffuse molecular gases but also by other mechanisms such as fast cloud–cloud collisions.

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 Galaxies hosting an active galactic nucleus: a view from the CALIFA survey

2020 ◽  
Vol 492 (3) ◽  
pp. 3073-3090 ◽  
Author(s):  
Eduardo A D Lacerda ◽  
Sebastián F Sánchez ◽  
R Cid Fernandes ◽  
Carlos López-Cobá ◽  
Carlos Espinosa-Ponce ◽  
...  
Keyword(s):  
Star Formation ◽  
Morphological Type ◽  
Molecular Gas ◽  
Main Role ◽  
Type I ◽  
Massive Galaxies ◽  
Star Forming ◽  
Integral Field Spectroscopy ◽  
Almost All ◽  
Formation Efficiency

ABSTRACT We study the presence of optically-selected active galactic nuclei (AGNs) within a sample of 867 galaxies extracted from the extended Calar-Alto Legacy Integral Field spectroscopy Area (eCALIFA) spanning all morphological classes. We identify 10 Type-I and 24 Type-II AGNs, amounting to ∼4 per cent of our sample, similar to the fraction reported by previous explorations in the same redshift range. We compare the integrated properties of the ionized and molecular gas, and stellar population of AGN hosts and their non-active counterparts, combining them with morphological information. The AGN hosts are found in transitory parts (i.e. green-valley) in almost all analysed properties which present bimodal distributions (i.e. a region where reside star-forming galaxies and another with quiescent/retired ones). Regarding morphology, we find AGN hosts among the most massive galaxies, with enhanced central stellar-mass surface density in comparison to the average population at each morphological type. Moreover, their distribution peaks at the Sab-Sb classes and none are found among very late-type galaxies (>Scd). Finally, we inspect how the AGN could act in their hosts regarding the quenching of star-formation. The main role of the AGN in the quenching process appears to be the removal (or heating) of molecular gas, rather than an additional suppression of the already observed decrease of the star-formation efficiency from late-to-early type galaxies.

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 Head-on collisions: how to bring large quantities of gas out of inner disks

2004 ◽  
Vol 217 ◽  
pp. 420-421
Author(s):  
Jonathan Braine ◽  
U. Lisenfeld ◽  
P.-A. Duc
Keyword(s):  
Star Formation ◽  
Molecular Clouds ◽  
Intergalactic Medium ◽  
Spiral Galaxies ◽  
Molecular Gas ◽  
Hii Region ◽  
Neutral Gas ◽  
Dense Cores ◽  
Clear Cases ◽  
Formation Efficiency

Head-on collisions of spiral galaxies can bring large quantities of gas out of spiral disks and into the intergalactic medium. Only two clear cases (UGC 12914/5 and UGC 813/6) of such collisions are known (Condon et al. 1993, 2002) and in both cases several 109 M⊙ of neutral gas is found in the bridge between the two galaxies which are now separating. About half of the gas is molecular. The gas, atomic or molecular, is brought out by collisions between clouds, which then acquire an intermediate velocity and end up between the galaxies. The bridges contain no old stars and in each case only one HII region despite the large masses of molecular gas, such that the star formation efficiency is very low in the bridges. The collisions occurred 20 – 50 million years ago, much greater than the collapse time for dense cores. We (Braine et al. 2003, 2004) show that collisions between molecular clouds, and not only between atomic gas clouds, bring gas into the bridges. It is not currently known whether the galaxies and bridges are bound or whether they will continue to separate, releasing several 109 M⊙ of neutral gas into the intergalactic medium.

scholarly journals Stellar feedback from a massive Super Star Cluster in the Antennae merger

2015 ◽  
Vol 12 (S316) ◽  
pp. 190-195 ◽  
Author(s):  
Cinthya N. Herrera ◽  
Francois Boulanger
Keyword(s):  
Star Formation ◽  
Radiation Pressure ◽  
Angular Resolution ◽  
Massive Stars ◽  
Star Cluster ◽  
Molecular Gas ◽  
Structure And Dynamics ◽  
Stellar Feedback ◽  
Formation Efficiency ◽  
Co Gas

AbstractStellar feedback from massive stars can unbind and disperse large amount of molecular gas, affecting the star formation efficiency. Based on ALMA and VLT observations in the Antennae galaxies we study a massive (~ 107 M⊙) and young (~ 3 Myr) SSC, B1, associated with compact molecular and ionized emission, which suggests that it is embedded in its parent cloud. However, we found contradictories and puzzling results on the structure and dynamics of the matter around the cluster, indicating that SSC B1 is not embedded in its parent cloud after all. We propose that radiation pressure was highly enhanced at the early stages of the SSC formation, disrupting the parent cloud in < 3 Myr. We show evidences of outflowing gas from the parent cloud in the more extended CO gas. Higher angular resolution observations are needed to validate this interpretation and to understand the origin and fate of the component seen to be associated with SSC B1.

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