scholarly journals Dense-gas tracers and carbon isotopes in five 2.5 < z < 4 lensed dusty star-forming galaxies from the SPT SMG sample

2018 ◽  
Vol 620 ◽  
pp. A115 ◽  
Author(s):  
M. Béthermin ◽  
T. R. Greve ◽  
C. De Breuck ◽  
J. D. Vieira ◽  
M. Aravena ◽  
...  
Keyword(s):  
Star Formation ◽  
Signal To Noise Ratio ◽  
High Redshift ◽  
Flux Ratio ◽  
Molecular Gas ◽  
Dense Gas ◽  
Gas Reservoirs ◽  
Star Forming ◽  
South Pole Telescope ◽  
Galaxy Sample

The origin of the high star formation rates (SFR) observed in high-redshift dusty star-forming galaxies is still unknown. Large fractions of dense molecular gas might provide part of the explanation, but there are few observational constraints on the amount of dense gas in high-redshift systems dominated by star formation. In this paper, we present the results of our Atacama large millimeter array (ALMA) program targeting dense-gas tracers (HCN(5-4), HCO+(5-4), and HNC(5-4)) in five strongly lensed galaxies from the South Pole Telescope (SPT) submillimeter galaxy sample. We detected two of these lines (S/N > 5) in SPT-125-47 at z = 2.51 and tentatively detected all three (S/N ∼ 3) in SPT0551-50 at z = 3.16. Since a significant fraction of our target lines is not detected, we developed a statistical method to derive unbiased mean properties of our sample taking into account both detections and non-detections. On average, the HCN(5-4) and HCO+(5-4) luminosities of our sources are a factor of ∼1.7 fainter than expected, based on the local L′HCN(5-4) − LIR relation, but this offset corresponds to only ∼2σ if we consider sample variance. We find that both the HCO+/HCN and HNC/HCN flux ratios are compatible with unity. The first ratio is expected for photo-dominated regions (PDRs) while the second is consistent with PDRs or X-ray dominated regions (XDRs) and/or mid-infrared (IR) pumping of HNC. Our sources are at the high end of the local relation between the star formation efficiency, determined using the LIR/[CI] and LIR/CO ratios, and the dense-gas fraction, estimated using the HCN/[CI] and HCN/CO ratios. Finally, in SPT0125-47, which has the highest signal-to-noise ratio, we found that the velocity profiles of the lines tracing dense (HCN, HCO+) and lower-density (CO, [CI]) molecular gas are similar. In addition to these lines, we obtained one robust and one tentative detection of 13CO(4-3) and found an average I 12CO(4-3)/I13CO(4-3) flux ratio of 26.1−3.5+4.5, indicating a young but not pristine interstellar medium. We argue that the combination of large and slightly enriched gas reservoirs and high dense-gas fractions could explain the prodigious star formation in these systems.

scholarly journals Planck’s Dusty GEMS

2021 ◽  
Vol 645 ◽  
pp. A45
Author(s):  
R. Cañameras ◽  
N. P. H. Nesvadba ◽  
R. Kneissl ◽  
S. König ◽  
C. Yang ◽  
...  
Keyword(s):  
Star Formation ◽  
High Redshift ◽  
Line Emission ◽  
Flux Ratio ◽  
Theoretical Models ◽  
High Density ◽  
Line Profiles ◽  
Dense Gas ◽  
Gas Reservoirs ◽  
Star Forming

We present ALMA, NOEMA, and IRAM-30 m/EMIR observations of the high-density tracer molecules HCN, HCO+, and HNC in three of the brightest lensed dusty star-forming galaxies at z ≃ 3–3.5, part of the Planck’s Dusty Gravitationally Enhanced subMillimetre Sources (GEMS), with the aim of probing the gas reservoirs closely associated with their exceptional levels of star formation. We obtained robust detections of ten emission lines between Jup = 4 and 6, as well as several additional upper flux limits. In PLCK_G244.8+54.9, the brightest source at z = 3.0, the HNC(5–4) line emission at 0.1″ resolution, together with other spatially-integrated line profiles, suggests comparable distributions of dense and more diffuse gas reservoirs, at least over the most strongly magnified regions. This rules out any major effect from differential lensing. This line is blended with CN(4–3) and in this source, we measure a HNC(5–4)/CN(4–3) flux ratio of 1.76 ±0. 86. Dense-gas line profiles generally match those of mid-J CO lines, except in PLCK_G145.2+50.8, which also has dense-gas line fluxes that are relatively lower, perhaps due to fewer dense cores and more segregated dense and diffuse gas phases in this source. The HCO+/HCN ≳ 1 and HNC/HCN ∼ 1 line ratios in our sample are similar to those of nearby ultraluminous infrared galaxies (ULIRGs) and consistent with photon-dominated regions without any indication of important mechanical heating or active galactic nuclei feedback. We characterize the dense-gas excitation in PLCK_G244.8+54.9 using radiative transfer models assuming pure collisional excitation and find that mid-J HCN, HCO+, and HNC lines arise from a high-density phase with an H2 density of n  ∼  105–106 cm−3, although important degeneracies hinder a determination of the exact conditions. The three GEMS are consistent with extrapolations of dense-gas star-formation laws derived in the nearby Universe, adding further evidence that the extreme star-formation rates observed in the most active galaxies at z ∼ 3 are a consequence of their important dense-gas contents. The dense-gas-mass fractions traced by HCN/[CI] and HCO+/[CI] line ratios are elevated, but not exceptional as compared to other lensed dusty star-forming galaxies at z >  2, and they fall near the upper envelope of local ULIRGs. Despite the higher overall gas fractions and local gas-mass surface densities observed at high redshift, the dense-gas budget of rapidly star-forming galaxies seems to have evolved little between z ∼ 3 and z ∼ 0. Our results favor constant dense-gas depletion times in these populations, which is in agreement with theoretical models of star formation.

scholarly journals The lifecycle of molecular clouds in nearby star-forming disc galaxies

2019 ◽  
Vol 493 (2) ◽  
pp. 2872-2909 ◽  
Author(s):  
Mélanie Chevance ◽  
J M Diederik Kruijssen ◽  
Alexander P S Hygate ◽  
Andreas Schruba ◽  
Steven N Longmore ◽  
...  
Keyword(s):  
Star Formation ◽  
Flux Ratio ◽  
Molecular Gas ◽  
H Ii Regions ◽  
Dynamical Processes ◽  
Nearby Star ◽  
Star Forming ◽  
Spatially Resolved ◽  
Stellar Feedback ◽  
Disc Galaxies

ABSTRACT It remains a major challenge to derive a theory of cloud-scale ($\lesssim100$ pc) star formation and feedback, describing how galaxies convert gas into stars as a function of the galactic environment. Progress has been hampered by a lack of robust empirical constraints on the giant molecular cloud (GMC) lifecycle. We address this problem by systematically applying a new statistical method for measuring the evolutionary timeline of the GMC lifecycle, star formation, and feedback to a sample of nine nearby disc galaxies, observed as part of the PHANGS-ALMA survey. We measure the spatially resolved (∼100 pc) CO-to-H α flux ratio and find a universal de-correlation between molecular gas and young stars on GMC scales, allowing us to quantify the underlying evolutionary timeline. GMC lifetimes are short, typically $10\!-\!30\,{\rm Myr}$, and exhibit environmental variation, between and within galaxies. At kpc-scale molecular gas surface densities $\Sigma _{\rm H_2}\ge 8\,\rm {M_\odot}\,{{\rm pc}}^{-2}$, the GMC lifetime correlates with time-scales for galactic dynamical processes, whereas at $\Sigma _{\rm H_2}\le 8\,\rm {M_\odot}\,{{\rm pc}}^{-2}$ GMCs decouple from galactic dynamics and live for an internal dynamical time-scale. After a long inert phase without massive star formation traced by H α (75–90 per cent of the cloud lifetime), GMCs disperse within just $1\!-\!5\,{\rm Myr}$ once massive stars emerge. The dispersal is most likely due to early stellar feedback, causing GMCs to achieve integrated star formation efficiencies of 4–10 per cent. These results show that galactic star formation is governed by cloud-scale, environmentally dependent, dynamical processes driving rapid evolutionary cycling. GMCs and H ii regions are the fundamental units undergoing these lifecycles, with mean separations of $100\!-\!300\,{{\rm pc}}$ in star-forming discs. Future work should characterize the multiscale physics and mass flows driving these lifecycles.

scholarly journals A diversity of starburst-triggering mechanisms in interacting galaxies and their signatures in CO emission

2019 ◽  
Vol 625 ◽  
pp. A65 ◽  
Author(s):  
F. Renaud ◽  
F. Bournaud ◽  
O. Agertz ◽  
K. Kraljic ◽  
E. Schinnerer ◽  
...  
Keyword(s):  
Star Formation ◽  
Galaxy Evolution ◽  
High Redshift ◽  
Formation Rate ◽  
Temporal Variations ◽  
Interacting Galaxies ◽  
Dense Gas ◽  
Star Forming ◽  
Cloud Properties ◽  
Co Emission

The physical origin of enhanced star formation activity in interacting galaxies remains an open question. Knowing whether starbursts are triggered by an increase in the quantity of dense gas or an increase in the star formation efficiency therein would improve our understanding of galaxy evolution and make it possible to transfer the results obtained in the local Universe to high-redshift galaxies. In this paper, we analyze a parsec-resolution simulation of a model of interacting galaxies similar to the Antennae Galaxies. We find that the interplay of physical processes such as tides, shear, and turbulence shows complex and important variations in time and space, but that different combinations of these processes can produce similar signatures in observable quantities such as the depletion time and CO emission. Some clouds within the interacting galaxies exhibit an excess of dense gas (> 104 cm−3), while others only attain similarly high densities in the tail of their density distribution. The clouds with an excess of dense gas are found across all regions of the galaxies, but their number density varies between regions due to different cloud assembly mechanisms. This translates into variations in the scale dependence of quantities related to cloud properties and star formation. The super-linearity of the relationship between the star formation rate and gas density implies that the dense gas excess corresponds to a decrease in the depletion time, and thus leads to a deviation from the classical star formation regime that is visible up to galactic scales. We find that the αCO conversion factor between the CO luminosity and molecular gas mass exhibits stronger spatial than temporal variations in a system like the Antennae. Our results raise several caveats for the interpretation of observations of unresolved star-forming regions, but also predict that the diversity of environments for star formation will be better captured by the future generations of instruments.

scholarly journals GOODS-Herschel: Dust attenuation up to z∼4

2012 ◽  
Vol 8 (S292) ◽  
pp. 289-289 ◽  
Author(s):  
M. Pannella ◽  
D. Elbaz ◽  
E. Daddi
Keyword(s):  
Star Formation ◽  
High Redshift ◽  
Line Emission ◽  
Stellar Mass ◽  
Massive Galaxies ◽  
Star Forming ◽  
Main Driver ◽  
Galaxy Sample ◽  
Stellar Masses ◽  
Dust Attenuation

AbstractWe quantitatively explore in a unbiased way the evolution of dust attenuation up to z ≈ 4 as a function of galaxy properties. We have used one of the deepest datasets available at present, in the GOODS-N field, to select a star forming galaxy sample and robustly measure galaxy redshifts, star formation rates, stellar masses and UV restframe properties. Our main results can be summarized as follows: i) we confirm that galaxy stellar mass is a main driver of UV dust attenuation in star forming galaxies: more massive galaxies are more dust attenuated than less massive ones; ii) strikingly, we find that the correlation does not evolve with redshift: the amount of dust attenuation is the same at all cosmic epochs for a fixed stellar mass; iii) this finding explains why and how the SFR–AUV relation evolves with redshift: the same amount of star formation is less attenuated at higher redshift because it is hosted in less massive galaxies; iv) combining our finding with results from line emission surveys, we confirm that line reddening is larger than continuum reddening, at least up to z ≈ 1.5; v) given the redshift evolution of the mass-metallicity relation, we predict that star forming galaxies at a fixed metal content are more attenuated at high redshift. Finally, we explored the correlation between UV dust attenuation and the spectral slope: vi) the correlation is evolving with redshift with star forming galaxies at lower redshift having redder spectra than higher redshift ones for the same amount of dust attenuation.

scholarly journals DYNAMO Survey: An Upclose View of Clumpy Galaxies

2014 ◽  
Vol 10 (S309) ◽  
pp. 129-132 ◽  
Author(s):  
David Fisher ◽  
Keyword(s):  
Star Formation ◽  
Velocity Dispersion ◽  
High Redshift ◽  
Molecular Gas ◽  
Gas Velocity ◽  
Star Forming ◽  
Turbulent Dynamo ◽  
Hα Emission ◽  
High Redshift Universe ◽  
Gas Fractions

AbstractWe highlight recent results on the DYNAMO survey of turbulent, clumpy disks galaxies found at z=0.1. Bright star forming DYNAMO galaxies are found to be very similar in properties to star forming galaxies in the high redshift Universe. Typical star formation rates of turbulent DYNAMO galaxies range 10-80 M⊙ yr−1. Roughly 2/3 of DYNAMO galaxies have Hα kinematics that are consistent with rotation. The typical gas velocity dispersion of DYNAMO galaxies is σHα ~ 20 - 60 km s−1. We show that, when convolved to the same resolution, maps of Hα emission in DYNAMO galaxies have essentially identical morphology as that of z ~ 1 - 3 galaxies. Finally, DYNAMO galaxies have high molecular gas fractions fmol ~ 20 - 35%. We note that DYNAMO galaxies are not dwarfs, typical masses are Mstar ~ 0.8 - 8 × 1010 M⊙. These data are all consistent with a scenario in which despite being at relatively low redshift the DYNAMO galaxies are forming stars similarly to that observed in the high-redshift Universe, that is to say star formation is occurring in very massive (Mclump ~ 109 M⊙), very large (rclump ~ 300 pc) clumps of gas.

scholarly journals SHARP – VI. Evidence for CO (1–0) molecular gas extended on kpc-scales in AGN star-forming galaxies at high redshift

2020 ◽  
Vol 495 (2) ◽  
pp. 2387-2407 ◽  
Author(s):  
C Spingola ◽  
J P McKean ◽  
S Vegetti ◽  
D Powell ◽  
M W Auger ◽  
...  
Keyword(s):  
Galaxy Formation ◽  
Surface Brightness ◽  
High Redshift ◽  
Host Galaxy ◽  
Molecular Gas ◽  
Host Galaxies ◽  
Gas Reservoirs ◽  
Star Forming ◽  
Radio Jets ◽  
First Time

ABSTRACT We present a study of the stellar host galaxy, CO (1–0) molecular gas distribution and AGN emission on 50–500 pc-scales of the gravitationally lensed dust-obscured AGN MG J0751+2716 and JVAS B1938+666 at redshifts 3.200 and 2.059, respectively. By correcting for the lensing distortion using a grid-based lens modelling technique, we spatially locate the different emitting regions in the source plane for the first time. Both AGN host galaxies have 300–500 pc-scale size and surface brightness consistent with a bulge/pseudo-bulge, and 2 kpc-scale AGN radio jets that are embedded in extended molecular gas reservoirs that are 5–20 kpc in size. The CO (1–0) velocity fields show structures possibly associated with discs (elongated velocity gradients) and interacting objects (off-axis velocity components). There is evidence for a decrement in the CO (1–0) surface brightness at the location of the host galaxy, which may indicate radiative feedback from the AGN, or offset star formation. We find CO–H2 conversion factors of around αCO = 1.5 ± 0.5 (K km s−1 pc2)−1, molecular gas masses of &gt;3 × 1010 M⊙, dynamical masses of ∼1011 M⊙, and gas fractions of around 60 per cent. The intrinsic CO line luminosities are comparable to those of unobscured AGN and dusty star-forming galaxies at similar redshifts, but the infrared luminosities are lower, suggesting that the targets are less efficient at forming stars. Therefore, they may belong to the AGN feedback phase predicted by galaxy formation models, because they are not efficiently forming stars considering their large amount of molecular gas.

scholarly journals The implications of the surprising existence of a large, massive CO disk in a distant protocluster

2017 ◽  
Vol 608 ◽  
pp. A48 ◽  
Author(s):  
H. Dannerbauer ◽  
M. D. Lehnert ◽  
B. Emonts ◽  
B. Ziegler ◽  
B. Altieri ◽  
...  
Keyword(s):  
Star Formation ◽  
High Redshift ◽  
Formation Rate ◽  
Optical Emission ◽  
Rotating Disk ◽  
Major Axis ◽  
Gas Content ◽  
Molecular Gas ◽  
Star Forming ◽  
Co Emission

It is not yet known if the properties of molecular gas in distant protocluster galaxies are significantly affected by their environment as galaxies are in local clusters. Through a deep, 64 h of effective on-source integration with the Australian Telescope Compact Array (ATCA), we discovered a massive, Mmol = 2.0 ± 0.2× 1011 M⊙, extended, ~40 kpc, CO(1–0)-emitting disk in the protocluster surrounding the radio galaxy, MRC 1138−262. The galaxy, at zCO = 2.1478, is a clumpy, massive disk galaxy, M∗ ~ 5 × 1011 M⊙, which lies 250 kpc in projection from MRC 1138−262 and is a known Hα emitter, named HAE229. This source has a molecular gas fraction of ~30%. The CO emission has a kinematic gradient along its major axis, centered on the highest surface brightness rest-frame optical emission, consistent with HAE229 being a rotating disk. Surprisingly, a significant fraction of the CO emission lies outside of the UV/optical emission. In spite of this, HAE229 follows the same relation between star-formation rate and molecular gas mass as normal field galaxies. HAE229 is the first CO(1–0) detection of an ordinary, star-forming galaxy in a protocluster. We compare a sample of cluster members at z > 0.4 thatare detected in low-order CO transitions, with a similar sample of sources drawn from the field. We confirm findings that the CO-luminosity and full-width at half maximum are correlated in starbursts and show that this relation is valid for normal high-z galaxies as well as for those in overdensities. We do not find a clear dichotomy in the integrated Schmidt-Kennicutt relation for protocluster and field galaxies. Our results suggest that environment does not have an impact on the “star-formation efficiency” or the molecular gas content of high-redshift galaxies. Not finding any environmental dependence in these characteristics, especially for such an extended CO disk, suggests that environmentally-specific processes such as ram pressure stripping do not operate efficiently in (proto)clusters.

scholarly journals An ALMA/NOEMA survey of the molecular gas properties of high-redshift star-forming galaxies

2020 ◽  
Author(s):  
Jack E Birkin ◽  
Axel Weiss ◽  
J L Wardlow ◽  
Ian Smail ◽  
A M Swinbank ◽  
...  
Keyword(s):  
High Redshift ◽  
Strong Support ◽  
Molecular Gas ◽  
Early Type ◽  
Coma Cluster ◽  
Gas Reservoirs ◽  
Line Energy ◽  
Star Forming ◽  
Flux Limit ◽  
Baryonic Mass

Abstract We have used ALMA and NOEMA to study the molecular gas reservoirs in 61 ALMA-identified submillimetre galaxies (SMGs) in the COSMOS, UDS and ECDFS fields. We detect 12CO (Jup = 2–5) emission lines in 50 sources, and [C i](3P1 − 3P0) emission in eight, at z = 1.2–4.8 and with a median redshift of 2.9 ± 0.2. By supplementing our data with literature sources we construct a statistical CO spectral line energy distribution and find that the 12CO line luminosities in SMGs peak at Jup ∼ 6, consistent with similar studies. We also test the correlations of the CO, [C i] and dust as tracers of the gas mass, finding the three to correlate well, although the CO and dust mass as estimated from the 3-mm continuum are preferable. We estimate that SMGs lie mostly on or just above the star-forming main sequence, with a median gas depletion timescale, tdep = Mgas/SFR, of 210 ± 40 Myr for our sample. Additionally, tdep declines with redshift across z ∼ 1–5, while the molecular gas fraction, μgas = Mgas/M*, increases across the same redshift range. Finally, we demonstrate that the distribution of total baryonic mass and dynamical line width, Mbaryon–σ, for our SMGs is consistent with that followed by early-type galaxies in the Coma cluster, providing strong support to the suggestion that SMGs are progenitors of massive local spheroidal galaxies. On the basis of this we suggest that the SMG populations above and below an 870-μm flux limit of S870 ∼ 5 mJy may correspond to the division between slow- and fast-rotators seen in local early-type galaxies.

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 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.

Sign in / Sign up

Export Citation Format

Share Document