scholarly journals Observations of Dense Molecular Gas in a Quasar Host Galaxy at z = 6.42: Further Evidence for a Nonlinear Dense Gas-Star Formation Relation at Early Cosmic Times

2007 ◽  
Vol 671 (1) ◽  
pp. L13-L16 ◽  
Author(s):  
Dominik A. Riechers ◽  
Fabian Walter ◽  
Christopher L. Carilli ◽  
Frank Bertoldi
Keyword(s):  
Star Formation ◽  
Host Galaxy ◽  
Molecular Gas ◽  
Dense Gas

scholarly journals Major impact from a minor merger

2018 ◽  
Vol 615 ◽  
pp. A122 ◽  
Author(s):  
S. König ◽  
S. Aalto ◽  
S. Muller ◽  
J. S. Gallagher III ◽  
R. J. Beswick ◽  
...  
Keyword(s):  
Star Formation ◽  
Brightness Temperature ◽  
Central Region ◽  
Molecular Clouds ◽  
Molecular Gas ◽  
Transfer Model ◽  
Dense Gas ◽  
Giant Molecular Clouds ◽  
Minor Mergers ◽  
Co Emission

Context. Minor mergers are important processes contributing significantly to how galaxies evolve across the age of the Universe. Their impact on the growth of supermassive black holes and star formation is profound – about half of the star formation activity in the local Universe is the result of minor mergers. Aims. The detailed study of dense molecular gas in galaxies provides an important test of the validity of the relation between star formation rate and HCN luminosity on different galactic scales – from whole galaxies to giant molecular clouds in their molecular gas-rich centers. Methods. We use observations of HCN and HCO+ 1−0 with NOEMA and of CO3−2 with the SMA to study the properties of the dense molecular gas in the Medusa merger (NGC 4194) at 1′′ resolution. In particular, we compare the distribution of these dense gas tracers with CO2−1 high-resolution maps in the Medusa merger. To characterize gas properties, we calculate the brightness temperature ratios between the three tracers and use them in conjunction with a non-local thermodynamic equilibrium (non-LTE) radiative line transfer model. Results. The gas represented by HCN and HCO+ 1−0, and CO3−2 does not occupy the same structures as the less dense gas associated with the lower-J CO emission. Interestingly, the only emission from dense gas is detected in a 200 pc region within the “Eye of the Medusa”, an asymmetric 500 pc off-nuclear concentration of molecular gas. Surprisingly, no HCN or HCO+ is detected for the extended starburst of the Medusa merger. Additionally, there are only small amounts of HCN or HCO+ associated with the active galactic nucleus. The CO3−2/2−1 brightness temperature ratio inside “the Eye” is ~2.5 – the highest ratio found so far – implying optically thin CO emission. The CO2−1/HCN 1−0 (~9.8) and CO2−1/HCO+ 1−0 (~7.9) ratios show that the dense gas filling factor must be relatively high in the central region, consistent with the elevated CO3−1/2−1 ratio. Conclusions. The line ratios reveal an extreme, fragmented molecular cloud population inside the Eye with large bulk temperatures (T > 300 K) and high gas densities (n(H2) > 104 cm-3). This is very different from the cool, self-gravitating structures of giant molecular clouds normally found in the disks of galaxies. The Eye of the Medusa is found at an interface between a large-scale minor axis inflow and the central region of the Medusa. Hence, the extreme conditions inside the Eye may be the result of the radiative and mechanical feedback from a deeply embedded, young and massive super star cluster formed due to the gas pile-up at the intersection. Alternatively, shocks from the inflowing gas entering the central region of the Medusa may be strong enough to shock and fragment the gas. For both scenarios, however, it appears that the HCN and HCO+ dense gas tracers are not probing star formation, but instead a post-starburst and/or shocked ISM that is too hot and fragmented to form newstars. Thus, caution is advised in taking the detection of emission from dense gas tracers as evidence of ongoing or imminent star formation.

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 The interplay of dense gas and stars in M33

2009 ◽  
Vol 5 (H15) ◽  
pp. 415-415
Author(s):  
Carsten Kramer ◽  
Christof Buchbender ◽  
Guillermo Quintana-Lacaci ◽  
Jonathan Braine ◽  
Pierre Gratier ◽  
...  
Keyword(s):  
Star Formation ◽  
Ground State ◽  
Far Infrared ◽  
Major Axis ◽  
Radio Continuum ◽  
State Transitions ◽  
Molecular Gas ◽  
Dense Gas ◽  
Open Time

AbstractWe are studying the interplay of star formation and its ’fuel’, the molecular gas (diffuse and dense) at selected positions along the major axis of M33. We have observed the ground-state transitions of HCN, HCO+, and 13CO using the IRAM 30m telescope. These data will complement existing CO, HI, Spitzer, and radio continuum maps. Furthermore, these data will be complemented by far-infrared maps of [CII], H2O, [OI], [NII], and the dust continuum taken with Herschel in the open time key project HERM33ES.

scholarly journals ALMA view of RX J1131-1231: Sub-kpc CO (2-1) mapping of a molecular disk in a lensed star-forming quasar host galaxy

2018 ◽  
Vol 613 ◽  
pp. A34 ◽  
Author(s):  
D. Paraficz ◽  
M. Rybak ◽  
J. P. McKean ◽  
S. Vegetti ◽  
D. Sluse ◽  
...  
Keyword(s):  
Star Formation ◽  
Rotational Velocity ◽  
Spectral Energy Distribution ◽  
Optical Emission ◽  
Continuum Emission ◽  
Host Galaxy ◽  
Spectral Energy ◽  
Molecular Gas ◽  
Gas Velocity ◽  
Star Forming

We present ALMA 2-mm continuum and CO (2-1) spectral line imaging of the gravitationally lensed z = 0.654 star-forming/quasar composite RX J1131-1231 at 240–400 mas angular resolution. The continuum emission is found to be compact and coincident with the optical emission, whereas the molecular gas forms a complete Einstein ring, which shows strong differential magnification. The de-lensed source structure is determined on 400-parsec-scales resolution using a Bayesian pixelated visibility-fitting lens modelling technique. The reconstructed molecular gas velocity-field is consistent with a large rotating disk with a major-axis FWHM ~9.4 kpc at an inclination angle of i = 54° and with a maximum rotational velocity of 280 km s−1. From dynamical model fitting we find an enclosed mass within 5 kpc of M(r < 5 kpc) = (1.46 ± 0.31) × 1011 M⊙. The molecular gas distribution is highly structured, with clumps that are co-incident with higher gas velocity dispersion regions (40–50 km s−1) and with the intensity peaks in the optical emission, which are associated with sites of on-going turbulent star-formation. The peak in the CO (2-1) distribution is not co-incident with the AGN, where there is a paucity of molecular gas emission, possibly due to radiative feedback from the central engine. The intrinsic molecular gas luminosity is L′CO = 1.2 ± 0.3 × 1010 K km s−1 pc2 and the inferred gas mass is MH2 = 8.3 ± 3.0 × 1010 M⊙, which given the dynamical mass of the system is consistent with a CO–H2 conversion factor of α = 5.5 ± 2.0 M⊙ (K km s−1 pc2)−1. This suggests that the star-formation efficiency is dependent on the host galaxy morphology as opposed to the nature of the AGN. The far-infrared continuum spectral energy distribution shows evidence for heated dust, equivalent to an obscured star-formation rate of SFR = 69−25+41 × (7.3/μIR) M⊙ yr−1, which demonstrates the composite star-forming and AGN nature of this system.

scholarly journals Molecular gas in the central region of NGC 7213

2020 ◽  
Vol 641 ◽  
pp. A151
Author(s):  
F. Salvestrini ◽  
C. Gruppioni ◽  
F. Pozzi ◽  
C. Vignali ◽  
A. Giannetti ◽  
...  
Keyword(s):  
Star Formation ◽  
Emission Line ◽  
Large Scale ◽  
Host Galaxy ◽  
Molecular Gas ◽  
X Ray ◽  
Gas Kinematics ◽  
Star Formation Activity ◽  
Multi Wavelength

We present a multi-wavelength study (from X-ray to mm) of the nearby low-luminosity active galactic nucleus NGC 7213. We combine the information from the different bands to characterise the source in terms of contribution from the AGN and the host-galaxy interstellar medium. This approach allows us to provide a coherent picture of the role of the AGN and its impact, if any, on the star formation and molecular gas properties of the host galaxy. We focused our study on archival ALMA Cycle 1 observations, where the CO(2–1) emission line has been used as a tracer of the molecular gas. Using the 3DBAROLO code on ALMA data, we performed the modelling of the molecular gas kinematics traced by the CO(2–1) emission, finding a rotationally dominated pattern. The molecular gas mass of the host galaxy was estimated from the integrated CO(2–1) emission line obtained with APEX data, assuming an αCO conversion factor. Had we used the ALMA data, we would have underestimated the gas masses by a factor ∼3, given the filtering out of the large-scale emission in interferometric observations. We also performed a complete X-ray spectral analysis on archival observations, revealing a relatively faint and unobscured AGN. The AGN proved to be too faint to significantly affect the properties of the host galaxy, such as star formation activity and molecular gas kinematics and distribution.

scholarly journals Spatially resolved molecular gas properties of host galaxy of Type I superluminous supernova SN 2017egm

2020 ◽  
Vol 72 (4) ◽  
Author(s):  
Bunyo Hatsukade ◽  
Kana Morokuma-Matsui ◽  
Masao Hayashi ◽  
Nozomu Tominaga ◽  
Yoichi Tamura ◽  
...  
Keyword(s):  
Star Formation ◽  
Column Density ◽  
Formation Rate ◽  
Host Galaxy ◽  
Molecular Gas ◽  
Type I ◽  
Type Ii ◽  
Star Forming ◽  
Spatially Resolved ◽  
Normal Star

Abstract We present the results of CO(1–0) observations of the host galaxy of a Type I superluminous supernova (SLSN-I), SN 2017egm, one of the closest SLSNe-I at z = 0.03063, by using the Atacama Large Millimeter/submillimeter Array. The molecular gas mass of the host galaxy is Mgas = (4.8 ± 0.3) × 109 M⊙, placing it on the sequence of normal star-forming galaxies in an Mgas–star-formation rate (SFR) plane. The molecular hydrogen column density at the location of SN 2017egm is higher than that of the Type II SN PTF10bgl, which is also located in the same host galaxy, and those of other Type II and Ia SNe located in different galaxies, suggesting that SLSNe-I have a preference for a dense molecular gas environment. On the other hand, the column density at the location of SN 2017egm is comparable to those of Type Ibc SNe. The surface densities of molecular gas and the SFR at the location of SN 2017egm are consistent with those of spatially resolved local star-forming galaxies and follow the Schmidt–Kennicutt relation. These facts suggest that SLSNe-I can occur in environments with the same star-formation mechanism as in normal star-forming galaxies.

scholarly journals Large-scale Molecular Gas Distribution in the M17 Cloud Complex: Dense Gas Conditions of Massive Star Formation?

2020 ◽  
Vol 891 (1) ◽  
pp. 66 ◽  
Author(s):  
Quang Nguyen-Luong ◽  
Fumitaka Nakamura ◽  
Koji Sugitani ◽  
Tomomi Shimoikura ◽  
Kazuhito Dobashi ◽  
...  
Keyword(s):  
Star Formation ◽  
Large Scale ◽  
Massive Star ◽  
Molecular Gas ◽  
Dense Gas ◽  
Gas Distribution ◽  
Massive Star Formation ◽  
Cloud Complex

scholarly journals IMAGING THE MOLECULAR GAS IN Az= 3.9 QUASAR HOST GALAXY AT 0.″3 RESOLUTION: A CENTRAL, SUB-KILOPARSEC SCALE STAR FORMATION RESERVOIR IN APM 08279+5255

2008 ◽  
Vol 690 (1) ◽  
pp. 463-485 ◽  
Author(s):  
Dominik A. Riechers ◽  
Fabian Walter ◽  
Christopher L. Carilli ◽  
Geraint F. Lewis
Keyword(s):  
Star Formation ◽  
Host Galaxy ◽  
Molecular Gas

scholarly journals The WISSH quasars project

2020 ◽  
Vol 645 ◽  
pp. A33
Author(s):  
M. Bischetti ◽  
C. Feruglio ◽  
E. Piconcelli ◽  
F. Duras ◽  
M. Pérez-Torres ◽  
...  
Keyword(s):  
Black Hole ◽  
Star Formation ◽  
Detection Rate ◽  
Far Infrared ◽  
Final Host ◽  
Continuum Emission ◽  
Host Galaxy ◽  
Molecular Gas ◽  
Host Galaxies ◽  
Massive Black Hole

Context. Sources at the brightest end of the quasi-stellar object (QSO) luminosity function, during the peak epoch in the history of star formation and black hole accretion (z ∼ 2−4, often referred to as “Cosmic noon”) are privileged sites to study the cycle of feeding & feedback processes in massive galaxies. Aims. We aim to perform the first systematic study of cold gas properties in the most luminous QSOs, by characterising their host-galaxies and environment. These targets exhibit indeed widespread evidence of outflows at nuclear and galactic scales. Methods. We analyse ALMA, NOEMA and JVLA observations of the far-infrared continuum, CO and [CII] emission lines in eight QSOs (bolometric luminosity LBol ≳ 3 × 1047 erg s−1) from the WISE-SDSS selected hyper-luminous (WISSH) QSOs sample at z ∼ 2.4−4.7. Results. We report a 100% emission line detection rate and a 80% detection rate in continuum emission, and we find CO emission to be consistent with the steepest CO ladders observed so far. Sub-millimetre data reveal presence of (one or more) bright companion galaxies around ∼80% of WISSH QSOs, at projected distances of ∼6−130 kpc. We observe a variety of sizes for the molecular gas reservoirs (∼1.7−10 kpc), mostly associated with rotating disks with disturbed kinematics. WISSH QSOs typically show lower CO luminosity and higher star formation efficiency than infrared matched, z ∼ 0−3 main-sequence galaxies, implying that, given the observed SFR ∼170−1100 M⊙ yr−1, molecular gas is converted into stars in ≲50 Myr. Most targets show extreme dynamical to black-hole mass ratios Mdyn/MBH ∼ 3−10, two orders of magnitude smaller than local relations. The molecular gas fraction in the host-galaxies of WISSH is lower by a factor of ∼10−100 than in star forming galaxies with similar M*. Conclusions. Our analysis reveals that hyper-luminous QSOs at Cosmic noon undergo an intense growth phase of both the central super-massive black hole and of the host-galaxy. These systems pinpoint the high-density sites where giant galaxies assemble, where we show that mergers play a major role in the build-up of the final host-galaxy mass. We suggest that the observed low molecular gas fraction and short depletion timescale are due to AGN feedback, whose presence is indicated by fast AGN-driven ionised outflows in all our targets.

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.

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