scholarly journals Search and analysis of giant radio galaxies with associated nuclei (SAGAN)

2020 ◽  
Vol 643 ◽  
pp. A111
Author(s):  
P. Dabhade ◽  
F. Combes ◽  
P. Salomé ◽  
J. Bagchi ◽  
M. Mahato
Keyword(s):  
Star Formation ◽  
Galaxy Evolution ◽  
Large Fraction ◽  
Radio Galaxies ◽  
Gas Content ◽  
Molecular Gas ◽  
Disc Galaxy ◽  
Normal Galaxies ◽  
Upper Limits ◽  
Formation Efficiency

Radio galaxies with jets of relativistic particles are usually hosted by massive elliptical galaxies with active nuclei powered by accretion of interstellar matter onto a supermassive black hole. In some rare cases (< 5%), their jets drive the overall structure to sizes larger than 700 kpc, and they are called giant radio galaxies (GRGs). A very small fraction of the population of such radio galaxies contains molecular and atomic gas in the form of rings or discs that can fuel star formation. The origin of this gas is not well known; it has sometimes been associated with a minor merger with a gas-rich disc galaxy (e.g. Centaurus A) or cooling of material from a hot X-ray atmosphere (e.g. cooling flows). The giant radio jets might be the extreme evolution of these objects, and they can teach us about the radio galaxy evolution. We selected 12 targets from a catalogue of 820 GRGs that are likely to be in a gas-accretion and star formation phase. The targets were selected from the mid-infrared to contain heated dust. We report here the results of IRAM-30m observations, the molecular gas content, and the star formation efficiency, and we discuss the origin of the gas and disc morphology. Three out of our 12 targets are detected, and for the others, we report significant upper limits. We combine our three detections and upper limits with four additional detected GRGs from the literature to discuss the results. Most of the GRG targets belong to the main sequence, and a large fraction are in the passive domain. Their star formation efficiency is comparable to normal galaxies, except for two galaxies that are deficient in molecular gas with a short (∼200 Myr) depletion time, and a quiescent gas-rich giant spiral galaxy. In general, the depletion time is much longer than the lifetime of the giant radio jet.

scholarly journals Molecular Gas in Galaxies at all Redshifts

2010 ◽  
Vol 6 (S277) ◽  
pp. 47-54
Author(s):  
Françoise Combes
Keyword(s):  
Star Formation ◽  
Galaxy Evolution ◽  
Star Formation History ◽  
Gas Content ◽  
Continuum Emission ◽  
Massive Galaxies ◽  
Normal Galaxies ◽  
Galaxy Type ◽  
Formation History ◽  
Formation Efficiency

AbstractI review some recent results about the molecular content of galaxies, obtained essentially from the CO lines, but also dense tracers, or the dust continuum emission. New results have been obtained on molecular cloud physics, and their efficiency to form stars, shedding light on the Kennicutt-Schmidt law as a function of surface density and galaxy type. Large progress has been made on galaxy at moderate and high redshifts, allowing to interprete the star formation history and star formation efficiency as a function of gas content, or galaxy evolution. In massive galaxies, the gas fraction was higher in the past, and galaxy disks were more unstable and more turbulent. ALMA observations will allow the study of more normal galaxies at high z with higher spatial resolution and sensitivity.

scholarly journals Molecular gas in radio galaxies in dense megaparsec-scale environments at z = 0.4–2.6

2019 ◽  
Vol 623 ◽  
pp. A48 ◽  
Author(s):  
G. Castignani ◽  
F. Combes ◽  
P. Salomé ◽  
C. Benoist ◽  
M. Chiaberge ◽  
...  
Keyword(s):  
Star Formation ◽  
Radio Galaxies ◽  
Stellar Mass ◽  
Gas Content ◽  
Spectral Energy ◽  
Molecular Gas ◽  
Probability Method ◽  
Photometric Redshifts ◽  
Upper Limits ◽  
Co Emission

Context. Low luminosity radio galaxies (LLRGs) typically reside in dense megaparsec-scale environments and are often associated with brightest cluster galaxies (BCGs). They are an excellent tool to study the evolution of molecular gas reservoirs in giant ellipticals, even close to the active galactic nucleus. Aims. We investigate the role of dense megaparsec-scale environment in processing molecular gas in LLRGs in the cores of galaxy (proto-)clusters. To this aim we selected within the COSMOS and DES surveys a sample of five LLRGs at z = 0.4−2.6 that show evidence of ongoing star formation on the basis of their far-infrared (FIR) emission. Methods. We assembled and modeled the FIR-to-UV spectral energy distributions (SEDs) of the five radio sources to characterize their host galaxies in terms of stellar mass and star formation rate. We observed the LLRGs with the IRAM-30 m telescope to search for CO emission. We then searched for dense megaparsec-scale overdensities associated with the LLRGs using photometric redshifts of galaxies and the Poisson Probability Method, which we have upgraded using an approach based on the wavelet-transform (wPPM), to ultimately characterize the overdensity in the projected space and estimate the radio galaxy miscentering. Color-color and color-magnitude plots were then derived for the fiducial cluster members, selected using photometric redshifts. Results. Our IRAM-30 m observations yielded upper limits to the CO emission of the LLRGs, at z = 0.39, 0.61, 0.91, 0.97, and 2.6. For the most distant radio source, COSMOS-FRI 70 at z = 2.6, a hint of CO(7→6) emission is found at 2.2σ. The upper limits found for the molecular gas content M(H2)/M⋆ <  0.11, 0.09, 1.8, 1.5, and 0.29, respectively, and depletion time τdep ≲ (0.2−7) Gyr of the five LLRGs are overall consistent with the corresponding values of main sequence field galaxies. Our SED modeling implies large stellar-mass estimates in the range log(M⋆/M⊙) = 10.9−11.5, typical for giant ellipticals. Both our wPPM analysis and the cross-matching of the LLRGs with existing cluster/group catalogs suggest that the megaparsec-scale overdensities around our LLRGs are rich (≲1014 M⊙) groups and show a complex morphology. The color-color and color-magnitude plots suggest that the LLRGs are consistent with being star forming and on the high-luminosity tail of the red sequence. The present study thus increases the still limited statistics of distant cluster core galaxies with CO observations. Conclusions. The radio galaxies of this work are excellent targets for ALMA as well as next-generation telescopes such as the James Webb Space Telescope.

scholarly journals High molecular gas content and star formation rates in local galaxies that host quasars, outflows, and jets

2020 ◽  
Vol 498 (2) ◽  
pp. 1560-1575 ◽  
Author(s):  
M E Jarvis ◽  
C M Harrison ◽  
V Mainieri ◽  
G Calistro Rivera ◽  
P Jethwa ◽  
...  
Keyword(s):  
Star Formation ◽  
Galaxy Evolution ◽  
Gas Content ◽  
Molecular Gas ◽  
Host Galaxies ◽  
Gas Reservoirs ◽  
Galaxy Population ◽  
Stellar Masses ◽  
Gas Fractions

ABSTRACT We use a sample of powerful $z\, \approx \, 0.1$ type 2 quasars (‘obscured’; log [LAGN/erg s$^{-1}]\, \gtrsim \, 45$), which host kpc-scale ionized outflows and jets, to identify possible signatures of AGN feedback on the total molecular gas reservoirs of their host galaxies. Specifically, we present Atacama Pathfinder EXperiment (APEX) observations of the CO(2–1) transition for nine sources and the CO(6–5) for a subset of three. We find that the majority of our sample reside in starburst galaxies (average specific star formation rates – sSFR – of 1.7 Gyr−1), with the seven CO-detected quasars also having large molecular gas reservoirs (average Mgas = 1.3 × 1010 M⊙), even though we had no pre-selection on the star formation or molecular gas properties. Despite the presence of quasars and outflows, we find that the molecular gas fractions (Mgas/M⋆ = 0.1–1.2) and depletion times (Mgas/SFR = 0.16–0.95 Gyr) are consistent with those expected for the overall galaxy population with matched stellar masses and sSFRs. Furthermore, for at least two of the three targets with the required measurements, the CO(6–5)/CO(2–1) emission-line ratios are consistent with star formation dominating the CO excitation over this range of transitions. The targets in our study represent a gas-rich phase of galaxy evolution with simultaneously high levels of star formation and nuclear activity; furthermore, the jets and outflows do not have an immediate appreciable impact on the global molecular gas reservoirs.

scholarly journals A molecular scan in the Hubble Deep Field North

2014 ◽  
Vol 10 (S309) ◽  
pp. 265-268
Author(s):  
Roberto Decarli ◽  
Fabian Walter ◽  
Chris Carilli ◽  
Dominik Riechers
Keyword(s):  
Galaxy Evolution ◽  
High Redshift ◽  
Broad Band ◽  
Gas Content ◽  
Continuum Emission ◽  
Molecular Gas ◽  
Normal Galaxies ◽  
Hubble Deep Field ◽  
The Universe ◽  
Selection Of

AbstractOur understanding of galaxy evolution has traditionally been driven by pre-selection of galaxies based on their broad-band continuum emission. This approach is potentially biased, in particular against gas-rich systems at high-redshift which may be dust-obscured. To overcome this limitation, we have recently concluded a blind CO survey at 3mm in a region of the Hubble Deep Field North using the IRAM Plateau de Bure Interferometer. Our study resulted in 1) the discovery of the redshift of the bright SMG HDF850.1 (z = 5.183); 2) the discovery of a bright line identified as CO(2-1) arising from a BzK galaxy at z = 1.785, and of other 6 CO lines associated with various galaxies in the field; 3) the detection of a few lines (presumably CO(3-2) at z ∼ 2) with no optical/NIR/MIR counterparts. These observational results allowed us to expand the parameter space of galaxy properties probed so far in high-z molecular gas studies. Most importantly, we could set first direct constraints on the cosmic evolution of the molecular gas content of the universe. The present study represents a first, fundamental step towards an unbiased census of molecular gas in ‘normal’ galaxies at high-z, a crucial goal of extragalactic astronomy in the ALMA era.

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 Molecular Gas in Hickson Compact Groups

1999 ◽  
Vol 186 ◽  
pp. 414-414
Author(s):  
S. Leon ◽  
F. Combes ◽  
T.K. Menon
Keyword(s):  
Star Formation ◽  
Compact Group ◽  
Gas Flow ◽  
Control Sample ◽  
Gas Content ◽  
Cloud Formation ◽  
Molecular Gas ◽  
Compact Groups ◽  
Hickson Compact Groups ◽  
Formation Efficiency

Compact groups are ideal sites to study the influence of strong dynamical evolution due to environment on molecular cloud formation and star formation efficiency. We have observed 70 galaxies belonging to 45 Hickson compact groups (HCGs) in the 12CO(1→0) and 12CO(2→1) lines, in order to determine their molecular content. We compare the gas content relative to blue and LFIR luminosities of galaxies in compact groups with respect to other samples in the literature, including various environments and morphological types. We find that there is some hint, of enhanced MH2/LB and Mdust/LB ratios in the galaxies from compact group with respect to our control sample, especially for the most compact groups, suggesting that tidal interactions can drive the gas component inwards, by removing its angular momentum, and concentrating it in the dense central regions, where it is easily detected. The threshold at 20–30 kpc in mean galaxy separation for the enhancement of H2 suggests that it must correspond to an acceleration of the merging process and a significant inward gas flow. The molecular gas content in compact group galaxies is similar to that in pairs and starburst samples. However, the total LFIR luminosity of HCGs is quite similar to that of the control sample, and therefore the star formation efficiency appears lower than in the control galaxies. However this assumes that the FIR spatial distributions are similar in both samples which is not the case at radio frequencies. Higher spatial resolution FIR data are needed to make a valid comparison. Given their short dynamical friction time-scale, it is possible that some of these systems are in the final stage before merging, leading to ultraluminous starburst phases. We also find for all galaxy samples that the H2 content (normalized to blue luminosity) is strongly correlated with LFIR, while the total gas content (H2+HI) is not.

scholarly journals Lensed quiescent galaxies at z ∼ 2: What quenched their star formation?

2019 ◽  
Vol 15 (S352) ◽  
pp. 281-281
Author(s):  
Allison Man
Keyword(s):  
Star Formation ◽  
Galaxy Evolution ◽  
Stellar Structure ◽  
Gas Content ◽  
Molecular Gas ◽  
Massive Galaxies ◽  
Quenching Mechanisms ◽  
Multiple Absorption ◽  
Pilot Sample ◽  
Outstanding Issue

AbstractA key outstanding issue in galaxy evolution studies is how galaxies quench their star formation. I will present new results from our VLT/X-Shooter, ALMA and VLA campaign of a pilot sample of lensed quiescent massive galaxies at z > 1.5. Lensing magnification enables us to spatially resolve the stellar structure and kinematics of these compact galaxies, that are otherwise barely resolvable even with HST. Our deep X-Shooter spectra provided multiple absorption lines enabling strong constraints on their stellar populations, namely their star formation rates, ages, dispersions, and in some cases metallicities. Our complementary ALMA+VLA programme probes their molecular gas content through CO emission. All these observations provide unparalleled constraints on their quenching mechanisms. Our results indicate that quiescent galaxies at z ∼ 2 (1) have short star formation timescales of a few hundred Myrs; (2) have a variety of stellar morphology from exponential disks to bulges; (3) are devoid of molecular gas; and (4) host low-luminosity active galactic nuclei which may be responsible for suppressing star formation. In addition to discussing the insights gained on quenching, I will highlight how these findings bring about new questions that can be addressed with future JWST and ALMA studies.

scholarly journals AGN feedback on the ISM of 3C 236

2012 ◽  
Vol 8 (S292) ◽  
pp. 374-374
Author(s):  
A. Labiano ◽  
S. García-Burillo ◽  
F. Combes ◽  
A. Usero ◽  
R. Soria-Ruiz ◽  
...  
Keyword(s):  
Radio Galaxies ◽  
Molecular Gas ◽  
Evolutionary Status ◽  
Radio Sources ◽  
Powerful Radio ◽  
Ionized Gas ◽  
Normal Galaxies ◽  
Spatially Resolved ◽  
Formation Efficiency ◽  
Co Emission

AbstractWe have carried out 1mm/3mm continuum and 12CO(2−1) line high resolution observations to identify the footprints of AGN feedback on 3C 236. The CO emission comes from a spatially resolved disk characterized by a regular rotating pattern. Within the limits imposed by the sensitivity and velocity coverage of our data, we do not detect any outflow signatures in the cold molecular gas. Re-inspection of optical and IR spectra, shows the presence of a previously unknown ionized gas outflow. The star-formation efficiency in 3C 236, is consistent with the value measured in normal galaxies, which follow the canonical Kennicutt-Schmidt law. This result, confirmed to hold in other young radio sources examined in this work, is in stark contrast with the factor of 10–50 lower SFE that has been claimed to characterize evolved powerful radio galaxies. The recent reactivation of the AGN in 3C 236 is a likely explanation for the early evolutionary status of its molecular disk.

scholarly journals H2 content of galaxies inside and around intermediate redshift clusters

2019 ◽  
Vol 15 (S359) ◽  
pp. 158-162
Author(s):  
Damien Spérone-Longin
Keyword(s):  
Star Formation ◽  
Large Fraction ◽  
Formation Rate ◽  
Gas Content ◽  
Cluster Center ◽  
Molecular Gas ◽  
Ample Evidence ◽  
Cluster Galaxies ◽  
Star Forming ◽  
Medium Mass

AbstractDense environments have an impact on the star formation rate of galaxies. As stars form from molecular gas, looking at the cold molecular gas content of a galaxy gives useful insights on its efficiency in forming stars. However, most galaxies observed in CO (a proxy for the cold molecular gas content) at intermediate redshifts, are field galaxies. Only a handful of studies focused on cluster galaxies. I present new results on the environment of one medium mass cluster from the EDisCS survey at z ˜ 0.5. 27 star-forming galaxies were selected to evenly sample the range of densities encountered inside and around the cluster. We cover a region extending as far as 8 virial radii from the cluster center. Indeed there is ample evidence that star formation quenching starts already beyond 3 cluster virial radii. I discuss our CO(3-2) ALMA observations, which unveil a large fraction of galaxies with low gas-to-stellar mass ratios.

scholarly journals The ALPINE-ALMA [C II] survey

2020 ◽  
Vol 643 ◽  
pp. A5 ◽  
Author(s):  
M. Dessauges-Zavadsky ◽  
M. Ginolfi ◽  
F. Pozzi ◽  
M. Béthermin ◽  
O. Le Fèvre ◽  
...  
Keyword(s):  
Star Formation ◽  
Rest Frame ◽  
Formation Rate ◽  
Cosmic Time ◽  
Mean Value ◽  
Gas Content ◽  
Molecular Gas ◽  
Massive Galaxies ◽  
Star Forming ◽  
Normal Galaxies

The molecular gas content of normal galaxies at z >  4 is poorly constrained because the commonly used molecular gas tracers become hard to detect at these high redshifts. We use the [C II] 158 μm luminosity, which was recently proposed as a molecular gas tracer, to estimate the molecular gas content in a large sample of main sequence star-forming galaxies at z = 4.4 − 5.9, with a median stellar mass of 109.7 M⊙, drawn from the ALMA Large Program to INvestigate [C II] at Early times survey. The agreement between the molecular gas masses derived from [C II] luminosities, dynamical masses, and rest-frame 850 μm luminosities extrapolated from the rest-frame 158 μm continuum supports [C II] as a reliable tracer of molecular gas in our sample. We find a continuous decline of the molecular gas depletion timescale from z = 0 to z = 5.9, which reaches a mean value of (4.6 ± 0.8) × 108 yr at z ∼ 5.5, only a factor of between two and three shorter than in present-day galaxies. This suggests a mild enhancement of the star formation efficiency toward high redshifts. Our estimates also show that the previously reported rise in the molecular gas fraction flattens off above z ∼ 3.7 to achieve a mean value of 63%±3% over z = 4.4 − 5.9. This redshift evolution of the gas fraction is in line with that of the specific star formation rate. We use multi-epoch abundance-matching to follow the gas fraction evolution across cosmic time of progenitors of z = 0 Milky Way-like galaxies in ∼1013 M⊙ halos and of more massive z = 0 galaxies in ∼1014 M⊙ halos. Interestingly, the former progenitors show a monotonic increase of the gas fraction with redshift, while the latter show a steep rise from z = 0 to z ∼ 2 followed by a constant gas fraction from z ∼ 2 to z = 5.9. We discuss three possible effects, namely outflows, a pause in gas supply, and over-efficient star formation, which may jointly contribute to the gas fraction plateau of the latter massive galaxies.

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