scholarly journals Neutral carbon and highly excited CO in a massive star-forming main sequence galaxy at z = 2.2

2019 ◽  
Vol 628 ◽  
pp. A104 ◽  
Author(s):  
Drew Brisbin ◽  
Manuel Aravena ◽  
Emanuele Daddi ◽  
Helmut Dannerbauer ◽  
Roberto Decarli ◽  
...  
Keyword(s):  
Star Formation ◽  
Main Sequence ◽  
Far Infrared ◽  
Molecular Gas ◽  
Low Velocity ◽  
Star Forming ◽  
Luminous Infrared Galaxies ◽  
Submillimeter Galaxies ◽  
Co Emission ◽  
Gas Component

We used the Plateau De Bure Interferometer to observe multiple CO and neutral carbon transitions in a z = 2.2 main sequence disk galaxy, BX610. Our observation of CO(7-6), CO(4-3), and both far-infrared (FIR) [CI] lines complements previous observations of Hα and low-J CO, and reveals a galaxy that is vigorously forming stars with UV fields (Log(GG0−1) ≲ 3.25); although less vigorously than local ultra-luminous infrared galaxies or most starbursting submillimeter galaxies in the early universe. Our observations allow new independent estimates of the cold gas mass which indicate Mgas ∼ 2 × 1011 M⊙, and suggest a modestly larger αCO value of ∼8.2. The corresponding gas depletion timescale is ∼1.5 Gyr. In addition to gas of modest density (Log(n cm3) ≲ 3) heated by star formation, BX610 shows evidence for a significant second gas component responsible for the strong high-J CO emission. This second component might either be a high-density molecular gas component heated by star formation in a typical photodissociation region, or could be molecular gas excited by low-velocity C shocks. The CO(7-6)-to-FIR luminosity ratio we observe is significantly higher than typical star-forming galaxies and suggests that CO(7-6) is not a reliable star-formation tracer in this galaxy.

Tracing young SMBHs in the dusty distant universe – a Chandra view of DOGs

2020 ◽  
Vol 15 (S359) ◽  
pp. 17-21
Author(s):  
Karín Menéndez-Delmestre ◽  
Laurie Riguccini ◽  
Ezequiel Treister
Keyword(s):  
Star Formation ◽  
Main Sequence ◽  
Far Infrared ◽  
Host Galaxy ◽  
X Ray ◽  
Star Forming ◽  
Near Ir ◽  
X Ray Imaging ◽  
Combined Use ◽  
Dusty Galaxies

AbstractThe coexistence of star formation and AGN activity has geared much attention to dusty galaxies at high redshifts, in the interest of understanding the origin of the Magorrian relation observed locally, where the mass of the stellar bulk in a galaxy appears to be tied to the mass of the underlying supermassive black hole. We exploit the combined use of far-infrared (IR) Herschel data and deep Chandra ˜160 ksec depth X-ray imaging of the COSMOS field to probe for AGN signatures in a large sample of >100 Dust-Obscured Galaxies (DOGs). Only a handful (˜20%) present individual X-ray detections pointing to the presence of significant AGN activity, while X-ray stacking analysis on the X-ray undetected DOGs points to a mix between AGN activity and star formation. Together, they are typically found on the main sequence of star-forming galaxies or below it, suggesting that they are either still undergoing significant build up of the stellar bulk or have started quenching. We find only ˜30% (6) Compton-thick AGN candidates (NH > 1024 cm–2), which is the same frequency found within other soft- and hard-X-ray selected AGN populations. This suggests that the large column densities responsible for the obscuration in Compton-thick AGNs must be nuclear and have little to do with the dust obscuration of the host galaxy. We find that DOGs identified to have an AGN share similar near-IR and mid-to-far-IR colors, independently of whether they are individually detected or not in the X-ray. The main difference between the X-ray detected and the X-ray undetected populations appears to be in their redshift distributions, with the X-ray undetected ones being typically found at larger distances. This strongly underlines the critical need for multiwavelength studies in order to obtain a more complete census of the obscured AGN population out to higher redshifts. For more details, we refer the reader to Riguccini et al. (2019).

scholarly journals Molecular gas in the Herschel-selected strongly lensed submillimeter galaxies at z ~ 2–4 as probed by multi-J CO lines

2017 ◽  
Vol 608 ◽  
pp. A144 ◽  
Author(s):  
C. Yang ◽  
A. Omont ◽  
A. Beelen ◽  
Y. Gao ◽  
P. van der Werf ◽  
...  
Keyword(s):  
Star Formation ◽  
High Redshift ◽  
Line Emission ◽  
Far Infrared ◽  
Molecular Gas ◽  
Kinetic Temperature ◽  
Large Area ◽  
Line Energy ◽  
Submillimeter Galaxies ◽  
Dust Mass

We present the IRAM-30 m observations of multiple-J CO (Jup mostly from 3 up to 8) and [C I](3P2 → 3P1) ([C I](2–1) hereafter) line emission in a sample of redshift ~2–4 submillimeter galaxies (SMGs). These SMGs are selected among the brightest-lensed galaxies discovered in the Herschel-Astrophysical Terahertz Large Area Survey (H-ATLAS). Forty-seven CO lines and 7 [C I](2–1) lines have been detected in 15 lensed SMGs. A non-negligible effect of differential lensing is found for the CO emission lines, which could have caused significant underestimations of the linewidths, and hence of the dynamical masses. The CO spectral line energy distributions (SLEDs), peaking around Jup ~ 5–7, are found to be similar to those of the local starburst-dominated ultra-luminous infrared galaxies and of the previously studied SMGs. After correcting for lensing amplification, we derived the global properties of the bulk of molecular gas in the SMGs using non-LTE radiative transfer modelling, such as the molecular gas density nH2 ~ 102.5–104.1 cm-3 and the kinetic temperature Tk  ~ 20–750 K. The gas thermal pressure Pth ranging from~105 K cm-3 to 106 K cm-3 is found to be correlated with star formation efficiency. Further decomposing the CO SLEDs into two excitation components, we find a low-excitation component with nH2 ~ 102.8–104.6 cm-3 and Tk  ~ 20–30 K, which is less correlated with star formation, and a high-excitation one (nH2 ~ 102.7–104.2 cm-3, Tk  ~ 60–400 K) which is tightly related to the on-going star-forming activity. Additionally, tight linear correlations between the far-infrared and CO line luminosities have been confirmed for the Jup ≥ 5 CO lines of these SMGs, implying that these CO lines are good tracers of star formation. The [C I](2–1) lines follow the tight linear correlation between the luminosities of the [C I](2–1) and the CO(1–0) line found in local starbursts, indicating that [C I] lines could serve as good total molecular gas mass tracers for high-redshift SMGs as well. The total mass of the molecular gas reservoir, (1–30) × 1010M⊙, derived based on the CO(3–2) fluxes and αCO(1–0) = 0.8 M⊙ ( K km s-1 pc2)-1, suggests a typical molecular gas depletion time tdep ~ 20–100 Myr and a gas to dust mass ratio δGDR ~ 30–100 with ~20%–60% uncertainty for the SMGs. The ratio between CO line luminosity and the dust mass L′CO/Mdust appears to be slowly increasing with redshift for high-redshift SMGs, which need to be further confirmed by a more complete SMG sample at various redshifts. Finally, through comparing the linewidth of CO and H2O lines, we find that they agree well in almost all our SMGs, confirming that the emitting regions of the CO and H2O lines are co-spatially located.

scholarly journals High-J CO Intensity Measurements for Galaxies Observed by the Herschel FTS

2015 ◽  
Vol 11 (S315) ◽  
pp. 26-29
Author(s):  
Julia Kamenetzky ◽  
Naseem Rangwala ◽  
Jason Glenn ◽  
Philip Maloney ◽  
Alex Conley
Keyword(s):  
Star Formation ◽  
Galaxy Evolution ◽  
Raw Material ◽  
Molecular Gas ◽  
Star Forming ◽  
Star Forming Regions ◽  
J 13 ◽  
Systematic Effects ◽  
Nearby Galaxies ◽  
Co Emission

AbstractMolecular gas is the raw material for star formation and is commonly traced by the carbon monoxide (CO) molecule. The atmosphere blocks all but the lowest-J transitions of CO for observatories on the ground, but the launch of the Herschel Space Observatory revealed the CO emission of nearby galaxies from J = 4−3 to J = 13−12. Herschel showed that mid- and high-J CO lines in nearby galaxies are emitted from warm gas, accounting for approximately 10% of the molecular mass, but the majority of the CO luminosity. The energy budget of this warm, highly-excited gas is a significant window into the feedback interactions among molecular gas, star formation, and galaxy evolution. Likely, mechanical heating is required to explain the excitation. Such gas has also been observed in star forming regions within our galaxy.We have examined all ~300 spectra of galaxies from the Herschel Fourier Transform Spectrometer and measured line fluxes or upper limits for the CO J = 4−3 to J = 13−12, [CI], and [NII] 205 micron lines in ~200 galaxies, taking systematic effects of the FTS into account. We will present our line fitting method, illustrate trends available so far in this large sample, and preview the full 2-component radiative transfer likelihood modeling of the CO emission using an illustrative sample of 20 galaxies, including comparisons to well-resolved galactic regions. This work is a comprehensive study of mid- and high-J CO emission among a variety of galaxy types, and can be used as a resource for future (sub)millimeter studies of galaxies with ground-based instruments.

scholarly journals Weak CS emission in an extremely metal-poor galaxy DDO 70

2020 ◽  
Vol 496 (1) ◽  
pp. L38-L42
Author(s):  
Kaiyi Du ◽  
Yong Shi ◽  
Zhi-Yu Zhang ◽  
Junzhi Wang ◽  
Yu Gao
Keyword(s):  
Star Formation ◽  
Milky Way ◽  
Dwarf Galaxy ◽  
Signal To Noise Ratio ◽  
Formation Rate ◽  
Far Infrared ◽  
Molecular Gas ◽  
Solar Metallicity ◽  
Low Metallicity ◽  
Co Emission

ABSTRACT In most galaxies like the Milky Way, stars form in clouds of molecular gas. Unlike the CO emission that traces the bulk of molecular gas, the rotational transitions of HCN and CS molecules mainly probe the dense phase of molecular gas, which has a tight and almost linear relation with the far-infrared luminosity and star formation rate (SFR). However, it is unclear whether dense molecular gas exists at very low metallicity, and if exists, how it is related to star formation. In this work, we report ALMA observations of the CS J = 5 → 4 emission line of DDO 70, a nearby gas-rich dwarf galaxy with $\sim \!7{{\ \rm per\ cent}}$ solar metallicity. We did not detect CS emission from all regions with strong CO emission. After stacking all CS spectra from CO-bright clumps, we find no more than a marginal detection of CS J = 5 → 4 transition, at a signal-to-noise ratio of ∼3.3. This 3σ upper limit deviates from the $L^\prime _{\rm CS}$–LIR and $L^\prime _{\rm CS}$–SFR relationships found in local star-forming galaxies and dense clumps in the Milky Way, implying weaker CS emission at given infrared luminosity and SFR. We discuss the possible mechanisms that suppress CS emission at low metallicity.

scholarly journals The AGN contribution to the UV–FIR luminosities of interacting galaxies and its role in identifying the main sequence

2020 ◽  
Vol 499 (3) ◽  
pp. 4325-4369
Author(s):  
Andrés F Ramos Padilla ◽  
M L N Ashby ◽  
Howard A Smith ◽  
Juan R Martínez-Galarza ◽  
Aliza G Beverage ◽  
...  
Keyword(s):  
Star Formation ◽  
Main Sequence ◽  
Spectral Energy Distribution ◽  
Broad Band ◽  
Far Infrared ◽  
Stellar Mass ◽  
Spectral Energy ◽  
Star Forming ◽  
Nuclear Regions ◽  
The Impact

ABSTRACT Emission from active galactic nuclei (AGNs) is known to play an important role in the evolution of many galaxies including luminous and ultraluminous systems (U/LIRGs), as well as merging systems. However, the extent, duration, and exact effects of its influence are still imperfectly understood. To assess the impact of AGNs on interacting systems, we present a spectral energy distribution (SED) analysis of a sample of 189 nearby galaxies. We gather and systematically re-reduce archival broad-band imaging mosaics from the ultraviolet to the far-infrared using data from GALEX, SDSS, 2MASS, IRAS, WISE, Spitzer, and Herschel. We use spectroscopy from Spitzer/IRS to obtain fluxes from fine-structure lines that trace star formation and AGN activity. Utilizing the SED modelling and fitting tool cigale, we derive the physical conditions of the interstellar medium, both in star-forming regions and in nuclear regions dominated by the AGN in these galaxies. We investigate how the star formation rates (SFRs) and the fractional AGN contributions (fAGN) depend on stellar mass, galaxy type, and merger stage. We find that luminous galaxies more massive than about $10^{10} \,\rm {M}_{*}$ are likely to deviate significantly from the conventional galaxy main-sequence relation. Interestingly, infrared AGN luminosity and stellar mass in this set of objects are much tighter than SFR and stellar mass. We find that buried AGNs may occupy a locus between bright starbursts and pure AGNs in the fAGN–[Ne v]/[Ne ii] plane. We identify a modest correlation between fAGN and mergers in their later stages.

scholarly journals Inefficient jet-induced star formation in Centaurus A

2017 ◽  
Vol 608 ◽  
pp. A98 ◽  
Author(s):  
Q. Salomé ◽  
P. Salomé ◽  
M.-A. Miville-Deschênes ◽  
F. Combes ◽  
S. Hamer
Keyword(s):  
Star Formation ◽  
Positive Feedback ◽  
Molecular Clouds ◽  
Milky Way ◽  
Data Cube ◽  
Molecular Gas ◽  
Star Forming ◽  
Star Forming Regions ◽  
Co Emission ◽  
Centaurus A

NGC 5128 (Centaurus A) is one of the best targets to study AGN feedback in the local Universe. At 13.5 kpc from the galaxy, optical filaments with recent star formation lie along the radio jet direction. This region is a testbed for positive feedback, here through jet-induced star formation. Atacama Pathfinder EXperiment (APEX) observations have revealed strong CO emission in star-forming regions and in regions with no detected tracers of star formation activity. In cases where star formation is observed, this activity appears to be inefficient compared to the Kennicutt-Schmidt relation. We used the Atacama Large Millimeter/submillimeter Array (ALMA) to map the 12CO(1–0) emission all along the filaments of NGC 5128 at a resolution of 1.3′′ ~ 23.8pc. We find that the CO emission is clumpy and is distributed in two main structures: (i) the Horseshoe complex, located outside the HI cloud, where gas is mostly excited by shocks and where no star formation is observed, and (ii) the Vertical filament, located at the edge of the HI shell, which is a region of moderate star formation. We identified 140 molecular clouds using a clustering method applied to the CO data cube. A statistical study reveals that these clouds have very similar physical properties, such as size, velocity dispersion, and mass, as in the inner Milky Way. However, the range of radius available with the present ALMA observations does not enable us to investigate whether or not the clouds follow the Larson relation. The large virial parameter αvir of the clouds suggests that gravity is not dominant and clouds are not gravitationally unstable. Finally, the total energy injection in the northern filaments of Centaurus A is of the same order as in the inner part of the Milky Way. The strong CO emission detected in the northern filaments is an indication that the energy injected by the jet acts positively in the formation of dense molecular gas. The relatively high virial parameter of the molecular clouds suggests that the injected kinetic energy is too strong for star formation to be efficient. This is particularly the case in the horseshoe complex, where the virial parameter is the largest and where strong CO is detected with no associated star formation. This is the first evidence of AGN positive feedback in the sense of forming molecular gas through shocks, associated with low star formation efficiency due to turbulence injection by the interaction with the radio jet.

scholarly journals CO Observations of Bright IRAS Galaxies

1987 ◽  
Vol 115 ◽  
pp. 653-653
Author(s):  
D. B. Sanders
Keyword(s):  
Star Formation ◽  
Molecular Clouds ◽  
Formation Rate ◽  
Far Infrared ◽  
Molecular Gas ◽  
Infrared Excess ◽  
Luminous Galaxies ◽  
Be Star ◽  
Co Emission ◽  
Co Observations

CO emission has been detected from 75 bright infrared galaxies with CZ = 2 000 – 16 000 km/s. These include the most distant and the most luminous galaxies (Arp 55, IR 1713+63) yet detected in CO. All of these galaxies are rich in molecular gas with Mtotal (H2) = 2 × 109 −6x1010 M⊙, and they have a strong far-infrared excess, with LFIR/LB = 2-40 and LFIR (40-400μ) = 1010 – 3 × 1012 L⊙. The primary luminosity source appears to be star formation in molecular clouds. A strong correlation is found between the FIR and 21-cm continuum flux, implying that the IMF is independent of the star formation rate. The ratio LFIR/M(H2) provides a measure of the current rate of star-formation, which is found to be a factor 3-20 larger in these galaxies than for the ensemble of molecular clouds in the Milky Way. VLA maps plus a few high resolution (14″-30″) CO (1-0) and CO (2-1) maps suggest that most of the luminosity comes from core regions 1-3 kpc in size. The abnormal concentration of molecular gas in these galactic cores is presumably the result of a collision or strong interaction with a nearby companion.

scholarly journals Radiative and mechanical feedback into the molecular gas in the Large Magellanic Cloud

2019 ◽  
Vol 628 ◽  
pp. A113 ◽  
Author(s):  
M.-Y. Lee ◽  
S. C. Madden ◽  
F. Le Petit ◽  
A. Gusdorf ◽  
P. Lesaffre ◽  
...  
Keyword(s):  
Far Infrared ◽  
Large Magellanic Cloud ◽  
Magellanic Cloud ◽  
Continuum Emission ◽  
Molecular Gas ◽  
Stellar Content ◽  
Low Velocity ◽  
Line Energy ◽  
Star Forming ◽  
30 Doradus

With an aim of probing the physical conditions and excitation mechanisms of warm molecular gas in individual star-forming regions, we performed Herschel SPIRE Fourier Transform Spectrometer (FTS) observations of 30 Doradus in the Large Magellanic Cloud. In our FTS observations, important far-infrared (FIR) cooling lines in the interstellar medium, including CO J = 4–3 to J = 13–12, [C I] 370 μm, and [N II] 205 μm, were clearly detected. In combination with ground-based CO J = 1–0 and J = 3–2 data, we then constructed CO spectral line energy distributions (SLEDs) on ~10 pc scales over a ~60 pc × 60 pc area and found that the shape of the observed CO SLEDs considerably changes across 30 Doradus. For example, the peak transition Jp varies from J = 6–5 to J = 10–9, while the slope characterized by the high-to-intermediate J ratio α ranges from ~0.4 to ~1.8. To examine the source(s) of these variations in CO transitions, we analyzed the CO observations, along with [C II] 158 μm, [C I] 370 μm, [O I] 145 μm, H2 0–0 S(3), and FIR luminosity data, using state-of-the-art models of photodissociation regions and shocks. Our detailed modeling showed that the observed CO emission likely originates from highly compressed (thermal pressure P∕kB ~ 107–109 K cm−3) clumps on ~0.7–2 pc scales, which could be produced by either ultraviolet (UV) photons (UV radiation field GUV ~ 103–105 Mathis fields) or low-velocity C-type shocks (pre-shock medium density npre ~ 104–106 cm−3 and shock velocity vs ~ 5–10 km s−1). Considering the stellar content in 30 Doradus, however, we tentatively excluded the stellar origin of CO excitation and concluded that low-velocity shocks driven by kiloparsec-scale processes (e.g., interaction between the Milky Way and the Magellanic Clouds) are likely the dominant source of heating for CO. The shocked CO-bright medium was then found to be warm (temperature T ~ 100–500 K) and surrounded by a UV-regulated low-pressure component (P∕kB ~ a few (104 –105) K cm−3) that is bright in [C II] 158 μm, [C I] 370 μm, [O I] 145 μm, and FIR dust continuum emission.

scholarly journals Starbursts in and out of the star-formation main sequence

2018 ◽  
Vol 616 ◽  
pp. A110 ◽  
Author(s):  
D. Elbaz ◽  
R. Leiton ◽  
N. Nagar ◽  
K. Okumura ◽  
M. Franco ◽  
...  
Keyword(s):  
Star Formation ◽  
Main Sequence ◽  
Near Infrared ◽  
Compact Star ◽  
Far Infrared ◽  
High Mass ◽  
Star Forming ◽  
Stellar Component ◽  
Public Data ◽  
Gas Fractions

Aims. We use high-resolution continuum images obtained with the Atacama Large Millimeter Array (ALMA) to probe the surface density of star formation in z ~ 2 galaxies and study the different physical properties between galaxies within and above the star-formation main sequence of galaxies. Methods. We use ALMA images at 870 μm with 0.2 arcsec resolution in order to resolve star formation in a sample of eight star-forming galaxies at z ~ 2 selected among the most massive Herschel galaxies in the GOODS-South field. This sample is supplemented with eleven galaxies from the public data of the 1.3 mm survey of the Hubble Ultra-Deep Field, HUDF. We derive dust and gas masses for the galaxies, compute their depletion times and gas fractions, and study the relative distributions of rest-frame ultraviolet (UV) and far-infrared (FIR) light. Results. ALMA reveals systematically dense concentrations of dusty star formation close to the center of the stellar component of the galaxies. We identify two different starburst regimes: (i) the classical population of starbursts located above the SFR-M⋆ main sequence, with enhanced gas fractions and short depletion times and (ii) a sub-population of galaxies located within the scatter of the main sequence that experience compact star formation with depletion timescales typical of starbursts of ~150 Myr. In both starburst populations, the FIR and UV are distributed in distinct regions and dust-corrected star formation rates (SFRs) estimated using UV-optical-near-infrared data alone underestimate the total SFR. Starbursts hidden in the main sequence show instead the lowest gas fractions of our sample and could represent the last stage of star formation prior to passivization. Being Herschel-selected, these main sequence galaxies are located in the high-mass end of the main sequence, hence we do not know whether these “starbursts hidden in the main sequence” also exist below 1011 M⊙. Active galactic nuclei (AGNs) are found to be ubiquitous in these compact starbursts, suggesting that the triggering mechanism also feeds the central black hole or that the active nucleus triggers star formation.

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.

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