scholarly journals CO observations of major merger pairs at z =  0: molecular gas mass and star formation

2019 ◽  
Vol 627 ◽  
pp. A107 ◽  
Author(s):  
Ute Lisenfeld ◽  
Cong Kevin Xu ◽  
Yu Gao ◽  
Donovan L. Domingue ◽  
Chen Cao ◽  
...  
Keyword(s):  
Star Formation ◽  
High Mass ◽  
Molecular Gas ◽  
Mass Ratio ◽  
Star Forming ◽  
Dust Mass ◽  
Major Merger ◽  
Atomic Gas ◽  
Gas Ratio ◽  
Co Observations

We present CO observations of 78 spiral galaxies in local merger pairs. These galaxies represent a subsample of a Ks-band-selected sample consisting of 88 close major-merger pairs (HKPAIRs), 44 spiral–spiral (S+S) pairs, and 44 spiral–elliptical (S+E) pairs, with separation <20 h−1 kpc and mass ratio <2.5. For all objects, the star formation rate (SFR) and dust mass were derived from Herschel PACS and SPIRE data, and the atomic gas mass, MHI, from the Green Bank Telescope HI observations. The complete data set allows us to study the relation between gas (atomic and molecular) mass, dust mass, and SFR in merger galaxies. We derive the molecular gas fraction (MH2/M*), molecular-to-atomic gas mass ratio (MH2/MHI), gas-to-dust mass ratio and SFE (= SFR/MH2) and study their dependences on pair type (S+S compared to S+E), stellar mass, and the presence of morphological interaction signs. We find an overall moderate enhancement (∼2×) in both molecular gas fraction (MH2/M*) and molecular-to-atomic gas ratio (MH2/MHI) for star-forming galaxies in major-merger pairs compared to non-interacting comparison samples, whereas no enhancement was found for the SFE nor for the total gas mass fraction ((MHI + MH2)/M*). When divided into S+S and S+E, low mass and high mass, and with and without interaction signs, there is a small difference in SFE, a moderate difference in MH2/M*, and a strong difference in MH2/MHI between subsamples. For the molecular-to-atomic gas ratio MH2/MHI, the difference between S+S and S+E subsamples is 0.55 ± 0.18 dex and between pairs with and without interaction sign 0.65 ± 0.16 dex. Together, our results suggest that (1) star formation enhancement in close major-merger pairs occurs mainly in S+S pairs after the first close encounter (indicated by interaction signs) because the HI gas is compressed into star-forming molecular gas by the tidal torque; and (2) this effect is much weakened in the S+E pairs.

scholarly journals High Molecular-gas to Dust Mass Ratios Predicted in Most Quiescent Galaxies

2021 ◽  
Vol 922 (2) ◽  
pp. L30
Author(s):  
Katherine E. Whitaker ◽  
Desika Narayanan ◽  
Christina C. Williams ◽  
Qi Li ◽  
Justin S. Spilker ◽  
...  
Keyword(s):  
Star Formation ◽  
Molecular Gas ◽  
Formation Processes ◽  
Mass Ratio ◽  
Gas Reservoirs ◽  
Massive Galaxies ◽  
Star Forming ◽  
Hot Plasma ◽  
Dust Mass ◽  
High Metallicity

Abstract Observations of cold molecular gas reservoirs are critical for understanding the shutdown of star formation in massive galaxies. While dust continuum is an efficient and affordable tracer, this method relies upon the assumption of a “normal” molecular-gas to dust mass ratio, δ GDR, typically of order 100. Recent null detections of quiescent galaxies in deep dust continuum observations support a picture where the cold gas and dust have been rapidly depleted or expelled. In this work, we present another viable explanation: a significant fraction of galaxies with low star formation per unit stellar mass are predicted to have extreme δ GDR ratios. We show that simulated massive quiescent galaxies at 0 < z < 3 in the simba cosmological simulations have δ GDR values that extend >4 orders of magnitude. The dust in most simulated quiescent galaxies is destroyed significantly more rapidly than the molecular gas depletes, and cannot be replenished. The transition from star-forming to quiescent halts dust formation via star formation processes, with dust subsequently destroyed by supernova shocks and thermal sputtering of dust grains embedded in hot plasma. After this point, the dust growth rate in the models is not sufficient to overcome the loss of >3 orders of magnitude in dust mass to return to normal values of δ GDR despite having high metallicity. Our results indicate that it is not straight forward to use a single observational indicator to robustly preselect exotic versus normal ratios. These simulations make strong predictions that can be tested with millimeter facilities.

scholarly journals Tracing the total molecular gas in galaxies: [CII] and the CO-dark gas

2020 ◽  
Vol 643 ◽  
pp. A141 ◽  
Author(s):  
S. C. Madden ◽  
D. Cormier ◽  
S. Hony ◽  
V. Lebouteiller ◽  
N. Abel ◽  
...  
Keyword(s):  
Star Formation ◽  
Mass Fraction ◽  
Conversion Factor ◽  
Dwarf Galaxies ◽  
Dwarf Galaxy ◽  
Molecular Gas ◽  
Star Forming ◽  
Forming Efficiency ◽  
Low Metallicity ◽  
Co Observations

Context. Molecular gas is a necessary fuel for star formation. The CO (1−0) transition is often used to deduce the total molecular hydrogen but is challenging to detect in low-metallicity galaxies in spite of the star formation taking place. In contrast, the [C II]λ158 μm is relatively bright, highlighting a potentially important reservoir of H2 that is not traced by CO (1−0) but is residing in the C+-emitting regions. Aims. Here we aim to explore a method to quantify the total H2 mass (MH2) in galaxies and to decipher what parameters control the CO-dark reservoir. Methods. We present Cloudy grids of density, radiation field, and metallicity in terms of observed quantities, such as [O I], [C I], CO (1−0), [C II], LTIR, and the total MH2. We provide recipes based on these models to derive total MH2 mass estimates from observations. We apply the models to the Herschel Dwarf Galaxy Survey, extracting the total MH2 for each galaxy, and compare this to the H2 determined from the observed CO (1−0) line. This allows us to quantify the reservoir of H2 that is CO-dark and traced by the [C II]λ158 μm. Results. We demonstrate that while the H2 traced by CO (1−0) can be negligible, the [C II]λ158 μm can trace the total H2. We find 70 to 100% of the total H2 mass is not traced by CO (1−0) in the dwarf galaxies, but is well-traced by [C II]λ158 μm. The CO-dark gas mass fraction correlates with the observed L[C II]/LCO(1−0) ratio. A conversion factor for [C II]λ158 μm to total H2 and a new CO-to-total-MH2 conversion factor as a function of metallicity are presented. Conclusions. While low-metallicity galaxies may have a feeble molecular reservoir as surmised from CO observations, the presence of an important reservoir of molecular gas that is not detected by CO can exist. We suggest a general recipe to quantify the total mass of H2 in galaxies, taking into account the CO and [C II] observations. Accounting for this CO-dark H2 gas, we find that the star-forming dwarf galaxies now fall on the Schmidt–Kennicutt relation. Their star-forming efficiency is rather normal because the reservoir from which they form stars is now more massive when introducing the [C II] measures of the total H2 compared to the small amount of H2 in the CO-emitting region.

scholarly journals The ISM scaling relations in DustPedia late-type galaxies: A benchmark study for the Local Universe

2020 ◽  
Vol 633 ◽  
pp. A100 ◽  
Author(s):  
V. Casasola ◽  
S. Bianchi ◽  
P. De Vis ◽  
L. Magrini ◽  
E. Corbelli ◽  
...  
Keyword(s):  
Gas Phase ◽  
Stellar Mass ◽  
Scaling Relations ◽  
Molecular Gas ◽  
Mass Ratio ◽  
Late Type ◽  
Local Universe ◽  
Dust Mass ◽  
Atomic Gas ◽  
Galaxy Morphology

Aims. The purpose of this work is the characterization of the main scaling relations between all of the interstellar medium (ISM) components, namely dust, atomic, molecular, and total gas, and gas-phase metallicity, as well as other galaxy properties, such as stellar mass (Mstar) and galaxy morphology, for late-type galaxies in the Local Universe. Methods. This study was performed by extracting late-type galaxies from the entire DustPedia sample and by exploiting the large and homogeneous dataset available thanks to the DustPedia project. The sample consists of 436 galaxies with morphological stage spanning from T = 1−10, Mstar from 6 × 107 to 3 × 1011 M⊙, star formation rate from 6 × 10−4 to 60 M⊙ yr−1, and oxygen abundance from 12 + log(O/H) = 8−9.5. Molecular and atomic gas data were collected from the literature and properly homogenized. All the masses involved in our analysis refer to the values within the optical disks of galaxies. The scaling relations involving the molecular gas are studied by assuming both a constant and a metallicity-dependent CO-to-H2 conversion factor (XCO). The analysis was performed by means of the survival analysis technique, in order to properly take into account the presence of both detection and nondetection in the data. Results. We confirm that the dust mass correlates very well with the total gas mass, and find –for the first time– that the dust mass correlates better with the atomic gas mass than with the molecular one. We characterize important mass ratios such as the gas fraction, the molecular-to-atomic gas mass ratio, the dust-to-total gas mass ratio (DGR), and the dust-to-stellar mass ratio, and study how they relate to each other, to galaxy morphology, and to gas-phase metallicity. Only the assumption of a metallicity-dependent XCO reproduces the expected decrease of the DGR with increasing morphological stage and decreasing gas-phase metallicity, with a slope of about 1. The DGR, the gas-phase metallicity, and the dust-to-stellar mass ratio are, for our galaxy sample, directly linked to galaxy morphology. The molecular-to-atomic gas mass ratio and the DGR show a positive correlation for low molecular gas fractions, but for galaxies rich in molecular gas this trend breaks down. To our knowledge, this trend has never been found before, and provides new constraints for theoretical models of galaxy evolution and a reference for high-redshift studies. We discuss several scenarios related to this finding. Conclusions. The DustPedia database of late-type galaxies is an extraordinary tool for the study of the ISM scaling relations, thanks to its homogeneous collection of data for the different ISM components. The database is made publicly available to the whole community.

scholarly journals Rapid gas fueling in a barred potential by self-gravitational instability

1993 ◽  
Vol 153 ◽  
pp. 285-286
Author(s):  
Keiichi Wada ◽  
Asao Habe
Keyword(s):  
Galactic Center ◽  
Gravitational Instability ◽  
High Mass ◽  
Molecular Gas ◽  
Supply Rate ◽  
Triggering Mechanism ◽  
Star Forming ◽  
Star Forming Regions ◽  
Central Regions ◽  
Co Observations

Recent IRAS surveys have revealed that large infrared luminosities are originated from active star forming regions in galaxies (Soifer et al. 1986). Such starburst regions are frequently located in galactic central regions and CO observations indicate that these regions contain a large amount of molecular gas (e.g. Ishizuki et al. 1990). However, the triggering mechanism for starbursts and the mechanism of the high mass supply rate of gas into a galactic center are still unclear.

scholarly journals Molecular gas masses of gamma-ray burst host galaxies

2018 ◽  
Vol 617 ◽  
pp. A143 ◽  
Author(s):  
Michał J. Michałowski ◽  
A. Karska ◽  
J. R. Rizzo ◽  
M. Baes ◽  
A. J. Castro-Tirado ◽  
...  
Keyword(s):  
Star Formation ◽  
Gamma Ray ◽  
Statistical Significance ◽  
Molecular Gas ◽  
Host Galaxies ◽  
Star Forming ◽  
Kolmogorov Smirnov ◽  
Atomic Gas ◽  
Gas Accretion ◽  
Gas Properties

Context. Long gamma-ray bursts (GRBs) can potentially be used as a tool to study star formation and recent gas accretion onto galaxies. However, the information about gas properties of GRB hosts is scarce. In particular, very few carbon monoxide (CO) line detections of individual GRB hosts have been reported. It has also been suggested that GRB hosts have lower molecular gas masses than expected from their star formation rates (SFRs). Aims. The objectives of this paper are to analyse molecular gas properties of the first substantial sample of GRB hosts and test whether they are deficient in molecular gas. Methods. We obtained CO(2-1) observations of seven GRB hosts with the APEX and IRAM 30 m telescopes. We analysed these data together with all other hosts with previous CO observations. From these observations we calculated the molecular gas masses of these galaxies and compared them with the expected values based on their SFRs and metallicities. Reults. We obtained detections for 3 GRB hosts (980425, 080207, and 111005A) and upper limits for the remaining 4 (031203, 060505, 060814, and 100316D). In our entire sample of 12 CO-observed GRB hosts, 3 are clearly deficient in molecular gas, even taking into account their metallicity (980425, 060814, and 080517). Four others are close to the best-fit line for other star-forming galaxies on the SFR-MH2 plot (051022, 060505, 080207, and 100316D). One host is clearly molecule rich (111005A). Finally, the data for 4 GRB hosts are not deep enough to judge whether they are molecule deficient (000418, 030329, 031203, and 090423). The median value of the molecular gas depletion time, MH2/SFR, of GRB hosts is ∼0.3 dex below that of other star-forming galaxies, but this result has low statistical significance. A Kolmogorov–Smirnov test performed on MH2/SFR shows an only ∼2σ difference between GRB hosts and other galaxies. This difference can partly be explained by metallicity effects, since the significance decreases to ∼1σ for MH2/SFR versus metallicity. Conclusions. We found that any molecular gas deficiency of GRB hosts has low statistical significance and that it can be attributed to their lower metallicities; and thus the sample of GRB hosts has molecular properties that are consistent with those of other galaxies, and they can be treated as representative star-forming galaxies. However, the molecular gas deficiency can be strong for GRB hosts if they exhibit higher excitations and/or a lower CO-to-H2 conversion factor than we assume, which would lead to lower molecular gas masses than we derive. Given the concentration of atomic gas recently found close to GRB and supernova sites, indicating recent gas inflow, our results about the weak molecular deficiency imply that such an inflow does not enhance the SFRs significantly, or that atomic gas converts efficiently into the molecular phase, which fuels star formation. Only if the analysis of a larger GRB host sample reveals molecular deficiency (especially close to the GRB position) would this support the hypothesis of star formation that is directly fuelled by atomic gas.

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 New emerging results on molecular gas, stars, and dust at z ~ 2, as revealed by low star formation rate and low stellar mass star-forming galaxies

2015 ◽  
Vol 11 (S319) ◽  
pp. 88-91
Author(s):  
Miroslava Dessauges-Zavadsky ◽  
Michel Zamojski ◽  
Daniel Schaerer ◽  
Françoise Combes ◽  
Eiichi Egami ◽  
...  
Keyword(s):  
Star Formation ◽  
High Redshift ◽  
Formation Rate ◽  
Molecular Gas ◽  
Mass Star ◽  
Single Star ◽  
Massive Galaxies ◽  
Star Forming ◽  
Formation Efficiency ◽  
Gas Ratio

AbstractRecent CO surveys of star-forming galaxies (SFGs) at z ~ 2 have revolutionized our picture of massive galaxies. It is time to expand these studies toward the more common z ~ 2 SFGs with SFR < 40 M⊙ yr−1 and M* < 2.5 × 1010 M⊙. We have derived molecular gas, stars, and dust in 8 such lensed SFGs. They extend the LIR–L'CO(1-0) distribution of massive z>1 SFGs and increase the spread of the SFG star formation efficiency (SFE). A single star formation relation is found when combining all existing CO-detected galaxies. Our low-M* SFGs also reveal a SFE decrease with M* as found locally. A rise of the molecular gas fraction (fgas) with redshift is observed up to z ~ 1.6, but it severely flattens toward higher redshifts. We provide the first insight into the fgas upturn at the low-M* end 109.4 < M*/M⊙ < 1010 reaching fgas ~ 0.7, it is followed by a fgas decrease toward higher M*. Finally, we find a non-universal dust-to-gas ratio among local and high-redshift SFGs and starbursts with near-solar metallicities.

scholarly journals Early- and late-stage mergers among main sequence and starburst galaxies at 0.2 ≤ z ≤ 2

2019 ◽  
Vol 485 (4) ◽  
pp. 5631-5651 ◽  
Author(s):  
A Cibinel ◽  
E Daddi ◽  
M T Sargent ◽  
E Le Floc’h ◽  
D Liu ◽  
...  
Keyword(s):  
Star Formation ◽  
Late Stage ◽  
Main Sequence ◽  
High Redshift ◽  
Formation Rate ◽  
Mass Ratio ◽  
Morphological Classification ◽  
Star Forming ◽  
Formation Mode ◽  
Major Merger

Abstract We investigate the fraction of close pairs and morphologically identified mergers on and above the star-forming main sequence (MS) at 0.2 ≤ z ≤2.0. The novelty of our work lies in the use of a non-parametric morphological classification performed on resolved stellar mass maps, reducing the contamination by non-interacting, high-redshift clumpy galaxies. We find that the merger fraction rapidly rises to ≥70 per cent above the MS, implying that – already at z ≳ 1 – starburst (SB) events (ΔMS ≥ 0.6) are almost always associated with a major merger (1:1 to 1:6 mass ratio). The majority of interacting galaxies in the SB region are morphologically disturbed, late-stage mergers. Pair fractions show little dependence on MS offset and pairs are more prevalent than late-stage mergers only in the lower half of the MS. In our sample, major mergers on the MS occur with a roughly equal frequency of ∼5–10 per cent at all masses ≳ 1010 M⊙. The MS major merger fraction roughly doubles between z = 0.2 and 2, with morphological mergers driving the overall increase at z ≳ 1. The differential redshift evolution of interacting pairs and morphologically classified mergers on the MS can be reconciled by evolving observability time-scales for both pairs and morphological disturbances. The observed variation of the late-stage merger fraction with ΔMS follows the perturbative 2-Star Formation Mode model, where any MS galaxy can experience a continuum of different star formation rate enhancements. This points to an SB–merger connection not only for extreme events, but also more moderate bursts which merely scatter galaxies upward within the MS, rather than fully elevating them above it.

scholarly journals Properties of the ISM in UV-luminous galaxies: clues from the low-redshift universe

2015 ◽  
Vol 11 (S315) ◽  
Author(s):  
Thiago S. Gonçalves
Keyword(s):  
Star Formation ◽  
Conversion Factor ◽  
High Redshift ◽  
Cosmic Time ◽  
Molecular Gas ◽  
Gas Reservoir ◽  
Local Universe ◽  
Star Forming ◽  
Luminous Galaxies ◽  
Co Observations

AbstractHow is gas converted into stars across cosmic time? Observations of star-forming galaxies at high redshift indicate that the conditions of the interstellar medium (ISM) were remarkably distinct from typical spirals in the local universe. Nevertheless, these observations are biased towards objects brighter than L*, due to the large luminosity distances involved. Here I present a survey targeting the molecular gas in galaxies at low redshift (z ~ 0.2) with ISM conditions remarkably similar to those observed at earlier epochs, including high star formation rates and lower metallicities. CO observations performed with CARMA indicate that these galaxies follow the same star-formation law as local spirals and other galaxies at the same redshift, albeit at much higher densities. We also present recent results from our ALMA program studying galaxies down to 12 + log(O/H) ~ 8, and discuss the implications of these data to our understanding of the molecular gas reservoir and the conversion factor between CO luminosity and gas mass in environments that are simultaneously low in metal content and extremely dense.

scholarly journals Evidence for supernova feedback sustaining gas turbulence in nearby star-forming galaxies

2020 ◽  
Vol 641 ◽  
pp. A70 ◽  
Author(s):  
Cecilia Bacchini ◽  
Filippo Fraternali ◽  
Giuliano Iorio ◽  
Gabriele Pezzulli ◽  
Antonino Marasco ◽  
...  
Keyword(s):  
Star Formation ◽  
Kinetic Energy ◽  
Surface Density ◽  
Neutral Medium ◽  
Molecular Gas ◽  
Driving Mechanism ◽  
Nearby Star ◽  
Star Forming ◽  
Radial Profiles ◽  
Atomic Gas

It is widely known that the gas in galaxy discs is highly turbulent, but there is much debate on which mechanism can energetically maintain this turbulence. Among the possible candidates, supernova (SN) explosions are likely the primary drivers but doubts remain on whether they can be sufficient in regions of moderate star formation activity, in particular in the outer parts of discs. Thus, a number of alternative mechanisms have been proposed. In this paper, we measure the SN efficiency η, namely the fraction of the total SN energy needed to sustain turbulence in galaxies, and verify that SNe can indeed be the sole driving mechanism. The key novelty of our approach is that we take into account the increased turbulence dissipation timescale associated with the flaring in outer regions of gaseous discs. We analyse the distribution and kinematics of HI and CO in ten nearby star-forming galaxies to obtain the radial profiles of the kinetic energy per unit area for both the atomic gas and the molecular gas. We use a theoretical model to reproduce the observed energy with the sum of turbulent energy from SNe, as inferred from the observed star formation rate (SFR) surface density, and the gas thermal energy. For the atomic gas, we explore two extreme cases in which the atomic gas is made either of cold neutral medium or warm neutral medium, and the more realistic scenario with a mixture of the two phases. We find that the observed kinetic energy is remarkably well reproduced by our model across the whole extent of the galactic discs, assuming η constant with the galactocentric radius. Taking into account the uncertainties on the SFR surface density and on the atomic gas phase, we obtain that the median SN efficiencies for our sample of galaxies are ⟨ηatom⟩ = 0.015−0.008+0.018 for the atomic gas and ⟨ηmol⟩ = 0.003−0.002+0.006 for the molecular gas. We conclude that SNe alone can sustain gas turbulence in nearby galaxies with only few percent of their energy and that there is essentially no need for any further source of energy.

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