IR Luminosity Research Articles

The effect of active galactic nuclei on the cold interstellar medium in distant star-forming galaxies

In the framework of a systematic study with the ALMA interferometer of IR-selected main-sequence and starburst galaxies at z ∼ 1 − 1.7 at typical ∼1″ resolution, we report on the effects of mid-IR- and X-ray-detected active galactic nuclei (AGN) on the reservoirs and excitation of molecular gas in a sample of 55 objects. We find widespread detectable nuclear activity in ∼30% of the sample. The presence of dusty tori influences the IR spectral energy distribution of galaxies, as highlighted by the strong correlation among the AGN contribution to the total IR luminosity budget (fAGN = LIR, AGN/LIR), its hard X-ray emission, and the Rayleigh-Jeans to mid-IR (S1.2 mm/S24 μm) observed color, with evident consequences on the ensuing empirical star formation rate estimates. Nevertheless, we find only marginal effects of the presence and strength of AGN on the carbon monoxide CO (J = 2, 4, 5, 7) or neutral carbon ([C I](3P1 − 3P0), [C I](3P2 − 3P1)) line luminosities and on the derived molecular gas excitation as gauged by line ratios and the full spectral line energy distributions. The [C I] and CO emission up to J = 5, 7 thus primarily traces the properties of the host in typical IR luminous galaxies. However, our analysis highlights the existence of a large variety of line luminosities and ratios despite the homogeneous selection. In particular, we find a sparse group of AGN-dominated sources with the highest LIR, AGN/LIR, SFR ratios, ≳3, that are more luminous in CO (5−4) than what is predicted by the L′CO(5-4)−LIR, SFR relation, which might be the result of the nuclear activity. For the general population, our findings translate into AGN having minimal effects on quantities such as gas and dust fractions and star formation efficiencies. If anything, we find hints of a marginal tendency of AGN hosts to be compact at far-IR wavelengths and to display 1.8 times larger dust optical depths. In general, this is consistent with a marginal impact of the nuclear activity on the gas reservoirs and star formation in average star-forming AGN hosts with LIR > 5 × 1011 L⊙, typically underrepresented in surveys of quasars and submillimeter galaxies.

Calibration of mid- to far-infrared spectral lines in galaxies

Context. Mid- to far-infrared (IR) lines are suitable in the study of dust-obscured regions in galaxies because dust extinction strongly decreases with wavelength, and therefore IR spectroscopy allows us to explore the most hidden regions of galaxies, where heavily obscured star formation as well as accretion onto supermassive black holes at the nuclei of galaxies occur. This is mostly important for the so-called cosmic noon (i.e. at redshifts of 1 < z < 3), at which point most of the baryonic mass in galaxies has been assembled. Aims. Our goal is to provide reliable calibrations of the mid- to far-IR ionic fine-structure lines, the brightest H2 pure rotational lines, and the polycyclic aromatic hydrocarbon (PAH) features, which we used to analyse current and future observations in the mm-submm range from the ground, as well as mid-IR spectroscopy from the upcoming James Webb Space Telescope. Methods. We used three samples of galaxies observed in the local Universe: star-forming galaxies (SFGs, 196), active galactic nuclei (AGN; 90−150 for various observables), and low-metallicity dwarf galaxies (40). For each population, we derive different calibrations of the observed line luminosities versus the total IR luminosities. Results. Through the resulting calibrations, we derive spectroscopic measurements of the star formation rate (SFR) and of the black hole accretion rate (BHAR) in galaxies using mid- and far-IR fine-structure lines, H2 pure rotational lines and PAH features. In particular, we derive robust star formation tracers based on the following: the [CII]158 μm line; the sum of the two far-IR oxygen lines, the [OI]63 μm line, and the [OIII]88 μm line; a combination of the neon and sulfur mid-IR lines; the bright PAH features at 6.2 and 11.3 μm; as well as – for the first time – the H2 rotational lines at 9.7, 12.3, and 17 μm. We propose the [CII]158 μm line, the combination of the two neon lines ([NeII]12.8 μm and [NeIII]15.5 μm), and, for solar-like metallicity galaxies that may harbour an AGN, the PAH 11.3 μm feature as the best SFR tracers. On the other hand, a reliable measure of the BHAR can be obtained using the [OIV]25.9 μm and the [NeV]14.3 and 24.3 μm lines. For the most commonly observed fine-structure lines in the far-IR, we compare our calibration with the existing ALMA observations of high-redshift galaxies. We find an overall good agreement for the [CII]158 μm line for both AGN and SFGs, while the [OIII]88 μm line in high-z galaxies is in better agreement with the low-metallicity local galaxies (dwarf galaxy sample) than with the SFGs, suggesting that high-z galaxies might have strong radiation fields due to low metal abundances, as expected.

ALMA multiline survey of the ISM in two quasar host–companion galaxy pairs atz> 6

We present a multiline survey of the interstellar medium (ISM) in twoz > 6 quasar host galaxies, PJ231−20 (z = 6.59) and PJ308−21 (z = 6.23), and their two companion galaxies. Observations were carried out using the Atacama Large (sub-)Millimeter Array (ALMA). We targeted 11 transitions including atomic fine-structure lines (FSLs) and molecular lines: [NII]205 μm, [CI]369 μm, CO (Jup = 7, 10, 15, 16), H2O 312 − 221, 321 − 312, 303 − 212, and the OH163 μmdoublet. The underlying far-infrared (FIR) continuum samples the Rayleigh-Jeans tail of the respective dust emission. By combining this information with our earlier ALMA [CII]158 μmobservations, we explored the effects of star formation and black hole feedback on the ISM of the galaxies using the CLOUDY radiative transfer models. We estimated dust masses, spectral indexes, IR luminosities, and star-formation rates from the FIR continuum. The analysis of the FSLs indicates that the [CII]158 μmand [CI]369 μmemission arises predominantly from the neutral medium in photodissociation regions (PDRs). We find that line deficits agree with those of local luminous IR galaxies. The CO spectral line energy distributions (SLEDs) reveal significant high-JCO excitation in both quasar hosts. Our CO SLED modeling of the quasar PJ231−20 shows that PDRs dominate the molecular mass and CO luminosities forJup ≤ 7, while theJup ≥ 10 CO emission is likely driven by X-ray dissociation regions produced by the active galactic nucleus (AGN) at the very center of the quasar host. TheJup > 10 lines are undetected in the other galaxies in our study. The H2O 321 − 312line detection in the same quasar places this object on theLH2O − LTIRrelation found for low-zsources, thus suggesting that this water vapor transition is predominantly excited by IR pumping. Models of the H2O SLED and of the H2O-to-OH163 μmratio point to PDR contributions with high volume and column density (nH ∼ 0.8 × 105cm−3,NH = 1024cm−2) in an intense radiation field. Our analysis suggests a less highly excited medium in the companion galaxies. However, the current data do not allow us to definitively rule out an AGN in these sources, as suggested by previous studies of the same objects. This work demonstrates the power of multiline studies of FIR diagnostics in order to dissect the physical conditions in the first massive galaxies emerging from cosmic dawn.

Remarkably high mass and velocity dispersion of molecular gas associated with a regular, absorption-selected type I quasar

We present 3 mm observations of the quasar J0015+1842 at z = 2.63 with the NOrthern Extended Millimeter Array (NOEMA). Our data reveal molecular gas, traced with a Gaussian CO(3–2) line, with a remarkably high velocity dispersion (FWHM = 1010 ± 120 km s−1) that corresponds to a total molecular mass MH2 ≈ (3.4 − 17) × 1010 M⊙, depending on the adopted CO-to-H2 conversion factor αCO = (0.8 − 4.0) M⊙ (km s−1 pc2)−1. Assuming the 3 mm continuum emission is thermal, we derive a dust mass of about Mdust ∼ 5 × 108 M⊙. J0015+1842 is located in the molecular gas-rich region in the IR versus CO line luminosity diagram, in between the main locus of main-sequence and sub-millimetre galaxies and that of most other active galactic nuclei targeted so far for CO measurements. While the high velocity dispersion of the CO line suggests a merging system, J0015+1842 is observed to be a regular, only very moderately dust-reddened (AV ∼ 0.3 − 0.4) type I quasar from its UV-optical spectrum, from which we infer a mass of the super-massive black hole of about MBH ≈ 6 × 108 M⊙. We suggest that J0015+1842 is observed at a galaxy evolutionary stage where a massive merger has brought significant amounts of gas towards an actively accreting super-massive black hole (quasar). While the host still contains a large amount of dust and molecular gas with a high velocity dispersion, the quasar has already cleared the way towards the observer, likely through powerful outflows, as has recently been revealed by optical observations of the same object. High angular resolution observations of this and similar systems are expected to help us better determine the respective importance of evolution and orientation in the appearance of quasars and their host galaxies. These observations have the potential to investigate early feedback and star-formation processes in galaxies in their quasar phases.

The Evolution of the IR Luminosity Function and Dust-obscured Star Formation over the Past 13 Billion Years

Abstract We present the first results from the Mapping Obscuration to Reionization with ALMA (MORA) survey, the largest Atacama Large Millimeter/submillimeter Array (ALMA) blank-field contiguous survey to date (184 arcmin2) and the only at 2 mm to search for dusty star-forming galaxies (DSFGs). We use the 13 sources detected above 5σ to estimate the first ALMA galaxy number counts at this wavelength. These number counts are then combined with the state-of-the-art galaxy number counts at 1.2 and 3 mm and with a backward evolution model to place constraints on the evolution of the IR luminosity function and dust-obscured star formation in the past 13 billion years. Our results suggest a steep redshift evolution on the space density of DSFGs and confirm the flattening of the IR luminosity function at faint luminosities, with a slope of . We conclude that the dust-obscured component, which peaks at z ≈ 2–2.5, has dominated the cosmic history of star formation for the past ∼12 billion years, back to z ∼ 4. At z = 5, the dust-obscured star formation is estimated to be ∼35% of the total star formation rate density and decreases to 25%–20% at z = 6–7, implying a minor contribution of dust-enshrouded star formation in the first billion years of the universe. With the dust-obscured star formation history constrained up to the end of the epoch of reionization, our results provide a benchmark to test galaxy formation models, to study the galaxy mass assembly history, and to understand the dust and metal enrichment of the universe at early times.

Integral field spectroscopy of luminous infrared main-sequence galaxies at cosmic noon

ABSTRACT We present the results of an integral field spectroscopy survey of a sample of dusty (ultra) luminous infrared galaxies (U/LIRGs) at 2 < z < 2.5 using KMOS on the Very Large Telescope. The sample has been drawn from Herschel deep field surveys and benefits from ancillary multiwavelength data. Our goal is to investigate the physical characteristics, kinematics, and the drivers of star formation in the galaxies whose contribution dominates the peak of the cosmic star formation density. Two-thirds of the sample are main-sequence galaxies in contrast to the starburst nature of local U/LIRGs. Our kinematic study, unique in its focus on z ∼ 2 dusty star-forming galaxies, uses the H α emission line to find that ∼40 per cent appear to be isolated discs based on the ratio of rotational velocity to the velocity dispersion, suggesting steady-state mechanisms are sufficient to power the large star formation rates (SFRs). The ratio of obscured to unobscured star formation indicates the sample of galaxies experiences less dust obscuration compared to intermediate and local counterparts, while also hosting cooler dust than local U/LIRGs. In addition to H α we detect [N ii] 6583 Å in our targets and show the gas-phase metallicities do not exhibit the metal deficiency of local U/LIRGs. These results indicate that, despite their extreme IR luminosity, the underlying mechanisms driving the massive SFRs found at cosmic noon are due to scaled up disc galaxies as opposed to mergers.

Detection of H2O and OH+ in z > 3 hot dust-obscured galaxies

Aims. In this paper we present the detection of H2O and OH+ emission in z > 3 hot dust-obscured galaxies (Hot DOGs). Methods. Using ALMA Band-6 observations of two Hot DOGs, we detected H2O(202 − 111) in W0149+2350, and H2O(312 − 303) and the multiplet OH+(11 − 01) in W0410−0913. These detections were serendipitous, falling within the side-bands of Band-6 observations aimed to study CO(9−8) in these Hot DOGs. Results. We find that both sources have luminous H2O emission with line luminosities of LH2O(202 − 111) > 2.2 × 108 L⊙ and LH2O(312 − 303) = 8.7 × 108 L⊙ for W0149+2350 and W0410−0913, respectively. The H2O line profiles are similar to those seen for the neighbouring CO(9–8) line, with line widths of full width at half maximum (FWHM) ∼800−1000 km s−1. However, the H2O emission seems to be more compact than the CO(9−8). OH+(11 − 01) is detected in emission for W0410−0913, with a FWHM = 1000 km s−1 and a line luminosity of LOH+(11 − 01) = 6.92 × 108 L⊙. The ratio of the observed H2O line luminosity over the IR luminosity, for both Hot DOGs, is consistent with previously observed star-forming galaxies and active galactic nuclei (AGN). The H2O/CO line ratio of both Hot DOGs and the OH+/H2O line ratio of W0410−0913 are comparable to those of luminous AGN found in the literature. Conclusions. The bright H2O(202 − 111), and H2O(312 − 303) emission lines are likely due to the combined high star formation levels and luminous AGN in these sources. The presence of OH+ in emission, and the agreement of the observed line ratios of the Hot DOGs with luminous AGN in the literature, would suggest that the AGN emission is dominating the radiative output of these galaxies. However, follow-up multi-transition observations are needed to better constrain the properties of these systems.

Turbulent Gas in Lensed Planck-selected Starbursts at z ∼ 1–3.5

Abstract Dusty star-forming galaxies at high redshift (1 < z < 3) represent the most intense star-forming regions in the universe. Key aspects to these processes are the gas heating and cooling mechanisms, and although it is well known that these galaxies are gas-rich, little is known about the gas excitation conditions. Only a few detailed radiative transfer studies have been carried out owing to a lack of multiple line detections per galaxy. Here we examine these processes in a sample of 24 strongly lensed star-forming galaxies identified by the Planck satellite (LPs) at z ∼ 1.1–3.5. We analyze 162 CO rotational transitions (ranging from J up = 1 to 12) and 37 atomic carbon fine-structure lines ([C i]) in order to characterize the physical conditions of the gas in the sample of LPs. We simultaneously fit the CO and [C i] lines and the dust continuum emission, using two different non-LTE, radiative transfer models. The first model represents a two-component gas density, while the second assumes a turbulence-driven lognormal gas density distribution. These LPs are among the most gas-rich, IR-luminous galaxies ever observed (μ L L IR ( 8 − 1000 μ m ) ∼ 10 13 − 14.6 L ⊙; 〈 μ L M ISM 〉 = (2.7 ± 1.2) × 1012 M ⊙, with μ L ∼ 10–30 the average lens magnification factor). Our results suggest that the turbulent interstellar medium present in the LPs can be well characterized by a high turbulent velocity dispersion ( 〈 ΔV turb 〉 ∼ 100 km s−1) and ratios of gas kinetic temperature to dust temperature 〈 T kin/T d 〉 ∼ 2.5, sustained on scales larger than a few kiloparsecs. We speculate that the average surface density of the molecular gas mass and IR luminosity, Σ M ISM ∼ 103–4 M ⊙ pc−2 and Σ L IR ∼ 1011–12 L ⊙ kpc−2, arise from both stellar mechanical feedback and a steady momentum injection from the accretion of intergalactic gas.

JWST/MIRI Simulated Imaging: Insights into Obscured Star Formation and AGNs for Distant Galaxies in Deep Surveys

Abstract The James Webb Space Telescope MIRI instrument will revolutionize extragalactic astronomy with unprecedented sensitivity and angular resolution in mid-IR. Here we assess the potential of MIRI photometry to constrain galaxy properties in the Cosmic Evolution Early Release Science (CEERS) survey. We derive estimated MIRI fluxes from the spectral energy distributions (SEDs) of real sources that fall in a planned MIRI pointing. We also obtain MIRI fluxes for hypothetical active galactic nucleus (AGN)–galaxy mixed models varying the AGN fractional contribution to the total IR luminosity (fracAGN). Based on these model fluxes, we simulate CEERS imaging (3.6 hr exposure) in six bands from F770W to F2100W using mirisim and reduce these data using jwst pipeline. We perform point-spread-function-matched photometry with tphot and fit the source SEDs with x-cigale, simultaneously modeling photometric redshift and other physical properties. Adding the MIRI data, the accuracy of both redshift and fracAGN is generally improved by factors of ≳2 for all sources at z ≲ 3. Notably, for pure-galaxy inputs (fracAGN = 0), the accuracy of fracAGN is improved by ∼100 times thanks to MIRI. The simulated CEERS MIRI data are slightly more sensitive to AGN detections than the deepest X-ray survey, based on the empirical L X–L 6 μm relation. Like X-ray observations, MIRI can also be used to constrain the AGN accretion power (accuracy ≈0.3 dex). Our work demonstrates that MIRI will be able to place strong constraints on the mid-IR luminosities from star formation and AGNs and thereby facilitate studies of the galaxy/AGN coevolution.

Extinction-free Census of AGNs in the AKARI/IRC North Ecliptic Pole Field from 23-band infrared photometry from Space Telescopes

ABSTRACT In order to understand the interaction between the central black hole and the whole galaxy or their co-evolution history along with cosmic time, a complete census of active galactic nucleus (AGN) is crucial. However, AGNs are often missed in optical, UV, and soft X-ray observations since they could be obscured by gas and dust. A mid-infrared (MIR) survey supported by multiwavelength data is one of the best ways to find obscured AGN activities because it suffers less from extinction. Previous large IR photometric surveys, e.g. Wide field Infrared Survey Explorer and Spitzer, have gaps between the MIR filters. Therefore, star-forming galaxy-AGN diagnostics in the MIR were limited. The AKARI satellite has a unique continuous nine-band filter coverage in the near to MIR wavelengths. In this work, we take advantage of the state-of-the-art spectral energy distribution modelling software, cigale, to find AGNs in MIR. We found 126 AGNs in the North Ecliptic Pole-Wide field with this method. We also investigate the energy released from the AGN as a fraction of the total IR luminosity of a galaxy. We found that the AGN contribution is larger at higher redshifts for a given IR luminosity. With the upcoming deep IR surveys, e.g. JWST, we expect to find more AGNs with our method.

Exploring galaxies-gravitational waves cross-correlations as an astrophysical probe

Gravitational waves astronomy has opened a new opportunity to study the Universe. Full exploitation of this window can especially be provided by combining data coming from gravitational waves experiments with luminous tracers of the Large Scale Structure, like galaxies. In this work we investigate the cross-correlation signal between gravitational waves resolved events, as detected by the Einstein Telescope, and actively star-forming galaxies. The galaxies distribution is computed through their UV and IR luminosity functions and the gravitational waves events, assumed to be of stellar origin, are self-consistently computed from the aforementioned galaxies distribution. We provide a state-of-the-art treatment both on the astrophysical side, {taking} into account the impact of the star formation and chemical evolution histories of galaxies, and in computing the cross-correlation signal, for which we include lensing and relativistic effects. {We find that the measured cross-correlation signal can be sufficiently strong to overcome the noise and provide a clear signal. As a possible application of this methodology, we consider a proof-of-concept case in which we aim at discriminating a metallicity dependence on the compact objects merger efficiency against a reference case with no metallicity dependence.} When considering galaxies with a Star Formation Rate ψ > 10 M⊙/yr, a Signal-to-Noise ratio around a value of 2–4 is gained after a decade of observation time, depending on the observed fraction of the sky. This formalism can be exploited as an astrophysical probe and could potentially allow to test and compare different astrophysical scenarios.

Tracing circumnuclear dense gas in H2O maser galaxies

ABSTRACT A sample of 30 H$_{2}$O extra-galactic maser galaxies with their published HCN(J = 1 − 0) and HCO + (J = 1 − 0) observations has been compiled to investigate the dense gas correlation with H2O maser emission. Our sample number exceeds the size of the previous HCN samples studied so far by a factor of 3, and it is the first study on the possible relation with the dense gas tracer HCO + . We find a strong correlation between normalized H2O maser emission luminosity (LH2O/LCO) and normalized HCO + line luminosity (LHCO + /LCO). Moreover, a weak correlation has been found between LH2O/LCO and normalized HCN line luminosity (LHCN/LCO). The sample is also studied after excluding Luminous and ultraluminous infrared galaxy (U)LIRG sources, and the mentioned correlations are noticeably stronger. We show that ‘dense gas’ fractions as obtained from HCN and HCO + molecules tightly correlate with maser emission, especially for galaxies with normal IR luminosity (LIR < 1011 L⊙) and we show that HCO + is a better ‘dense gas’ tracer than HCN. Further systematic studies of these dense gas tracers with higher transition level lines are vital to probe megamaser physical conditions and to accurately determining how maser emission interrelates with the dense gas.

Far-infrared Photometric Redshifts: A New Approach to a Highly Uncertain Enterprise

Abstract This paper presents a new approach to deriving far-infrared (FIR) photometric redshifts for galaxies based on their reprocessed emission from dust at rest-frame FIR through millimeter wavelengths. FIR photometric redshifts (“FIR-z”) have been used over the past decade to derive redshift constraints for highly obscured galaxies that lack photometry at other wavelengths like the optical/near-IR. Most literature FIR-z fits are performed through minimization to a single galaxy’s FIR template spectral energy distribution (SED). The use of a single galaxy template, or modest set of templates, can lead to an artificially low uncertainty estimate on FIR-z's because real galaxies display a wide range in intrinsic dust SEDs. I use the observed distribution of galaxy SEDs (for well-constrained samples across ) to motivate a new FIR through millimeter photometric redshift technique called MMpz. The MMpz algorithm asserts that galaxies are most likely drawn from the empirically observed relationship between rest-frame peak wavelength, , and total IR luminosity, L ; the derived photometric redshift accounts for the measurement uncertainties and intrinsic variation in SEDs at the inferred L , as well as heating from the cosmic microwave background at . The MMpz algorithm has a precision of , similar to single-template fits, while providing a more accurate estimate of the FIR-z uncertainty with reduced chi-squared of order , compared to alternative FIR photometric redshift techniques (with ).

The Properties of the Interstellar Medium of Galaxies across Time as Traced by the Neutral Atomic Carbon [C i

Abstract We report Atacama Large Millimeter Array observations of the neutral atomic carbon transitions [C i] and multiple CO lines in a sample of ∼30 main-sequence galaxies at , including novel information on [C i] and CO for 7 of such normal objects. We complement our observations with a collection of >200 galaxies with coverage of similar transitions, spanning the z = 0–4 redshift interval and a variety of ambient conditions from local to high-redshift starbursts. We find systematic variations in the [C i]/IR and [C i]/high-J upper (J upper = 7) CO luminosity ratios among the various samples. We interpret these differences as increased dense molecular gas fractions and star formation efficiencies in the strongest high-redshift starbursts with respect to normal main-sequence galaxies. We further report constant / ratios across the galaxy populations and redshifts, suggesting that gas temperatures T exc traced by [C i] do not strongly vary. We find only a mild correlation with T dust and that, generally, T exc ≲ T dust. We fit the line ratios with classical photodissociation region models, retrieving consistently larger densities and intensities of the UV radiation fields in submillimeter galaxies than in main-sequence and local objects. However, these simple models fall short in representing the complexity of a multiphase interstellar medium and should be treated with caution. Finally, we compare our observations with the Santa Cruz semi-analytical model of galaxy evolution, recently extended to simulate submillimeter emission. While we confirm the success in reproducing the CO lines, we find systematically larger [C i] luminosities at fixed IR luminosity than predicted theoretically. This highlights the necessity of improving our understanding of the mechanisms regulating the [C i] emission on galactic scales. We release our data compilation to the community.

SOFIA/HAWC+ View of an Extremely Luminous Infrared Galaxy: WISE 1013+6112

Abstract We present far-infrared (FIR) properties of an extremely luminous infrared galaxy (ELIRG) at z spec = 3.703, WISE J101326.25+611220.1 (WISE 1013+6112). This ELIRG is selected as an IR-bright dust-obscured galaxy based on the photometry from the Sloan Digital Sky Survey and the Wide-field Infrared Survey Explorer (WISE). In order to derive its accurate IR luminosity, we perform follow-up observations at 89 and 154 μm using the High-resolution Airborne Wideband Camera-plus (HAWC+) on board the 2.7 m Stratospheric Observatory For Infrared Astronomy (SOFIA) telescope. We conduct spectral energy distribution (SED) fitting with CIGALE using 15 photometric data (0.4–1300 μm). We successfully pin down FIR SED of WISE 1013+6112 and its IR luminosity is estimated to be L IR = (1.62 ± 0.08) × 1014 L ☉, making it one of the most luminous IR galaxies in the universe. We determine the dust temperature of WISE 1013+6112 is T dust = 89 ± 3 K, which is significantly higher than that of other populations such as submillimeter galaxies and FIR-selected galaxies at similar IR luminosities. The resultant dust mass is M dust = (2.2 ± 0.1) × 108 M ☉. This indicates that WISE 1013+6112 has a significant active galactic nucleus and star-forming activity behind a large amount of dust.

Enhancement of radiation characteristics and reduction of NOx emission in natural gas flame through silver-water nanofluid injection

The aim of the present work is to investigate the effect of low-flow-rate injection of silver-water nanofluid on the enhancement of thermal and radiative characteristics and reduction of NOx emission in natural gas flame. In our method, 0.009 Lit/min of 100-ppm silver-water nanofluid is directly injected into the natural gas flame at the equivalence ratio of 0.65. An SBG01 water cooled heat flux sensor is used to measure the total radiation of flame and IR photography method and luminosity measurement are used to determine the spectral emissivity of flame in infrared and visible wavelengths. Furthermore, a KIGAS 310 gas analyzer measures the concentrations of pollutant emissions. The results indicate that nanofluid injection enhances the IR radiation of natural gas flame and creates a high-value and uniform radiative heat flux distribution for flame. Solid nanoparticles, as foreign surfaces, enhance the nucleation rate and surface growth of soot particles, which are the best radiative species in flame. The other parameters which affect the flame radiation are increase in H2O concentration, as another radiative species, and increased number of tiny high temperature dark nanoparticles, as highly emissive bodies. Furthermore, although the nanofluid injection does not significantly change the concentration of carbonaceous pollutant emission, it decreases the NOx emission as much as 22.6%. The reduction of NOx emission is caused by decrease in the maximum flame temperature, due to absorption of heat by nanofluid droplets, and increase in the concentration of OH radicals, due to dissociation of H2O at the high temperatures of flame reaction zone.

Super Hot Cores in NGC 253: witnessing the formation and early evolution of super star clusters

ABSTRACT Using 0.2 arcsec (∼3 pc) ALMA images of vibrationally excited HC3N emission (HC3N*) we reveal the presence of eight unresolved Super Hot Cores (SHCs) in the inner 160 pc of NGC 253. Our LTE and non-LTE modelling of the HC3N* emission indicate that SHCs have dust temperatures of 200–375 K, relatively high H2 densities of (1−6) × 106 cm−3 and high IR luminosities of (0.1–1) × 108 L⊙. As expected from their short-lived phase (∼104 yr), all SHCs are associated with young super star clusters (SSCs). We use the ratio of luminosities from the SHCs (protostar phase) and from the free–free emission (ZAMS star phase), to establish the evolutionary stage of the SSCs. The youngest SSCs, with the larges ratios, have ages of a few 104 yr (proto-SSCs) and the more evolved SSCs are likely between 105 and 106 yr (ZAMS-SSCs). The different evolutionary stages of the SSCs are also supported by the radiative feedback from the UV radiation as traced by the HNCO/CS ratio, with this ratio being systematically higher in the young proto-SSCs than in the older ZAMS-SSCs. We also estimate the SFR and the SFE of the SSCs. The trend found in the estimated SFE ($\sim 40{{\ \rm per\ cent}}$ for proto-SSCs and $\gt 85{{\ \rm per\ cent}}$ for ZAMS-SSCs) and in the gas mass reservoir available for star formation, one order of magnitude higher for proto-SSCs, suggests that star formation is still going on in proto-SSCs. We also find that the most evolved SSCs are located, in projection, closer to the centre of the galaxy than the younger proto-SSCs, indicating an inside-out SSC formation scenario.

Tips learned from panchromatic modeling of AGNs

AbstractI will review the tips learned from panchromatic modeling of active galactic nuclei (AGNs), based on our recent work to study the relationship between AGN and star formation (SF). Several AGN SED models are compared, and a significant AGN contribution is found in the IR luminosities and corresponding star formation rates (SFRs). I will review the AGN-SF relation and how different parameters and sample selections affect the observed correlation. I will then report on the constant ratio discovered between the SFR and the black hole mass accretion rate (BHAR), and their implications on the gas supply and galaxy formation history of these systems. Caveats and important questions to answer are summarized at the end.

The OTELO survey

Aims. We take advantage of the capabilities of the OSIRIS Tunable Emission Line Object (OTELO) survey to select and study the AGN population in the field. In particular, we aim to perform an analysis of the properties of these objects, including their demography, morphology, and IR luminosity. Focusing on the population of Hα emitters at z ∼ 0.4, we also aim to study the environments of AGN and non-AGN galaxies at that redshift. methods. We make use of the multiwavelength catalogue of objects in the field compiled by the OTELO survey, unique in terms of minimum flux and equivalent width. We also take advantage of the pseudo-spectra built for each source, which allow the identification of emission lines and the discrimination of different types of objects. Results. We obtained a sample of 72 AGNs in the field of OTELO, selected with four different methods in the optical, X-rays, and mid-infrared bands. We find that using X-rays is the most efficient way to select AGNs. An analysis was performed on the AGN population of OTELO in order to characterise its members. At z ∼ 0.4, we find that up to 26% of our Hα emitters are AGNs. At that redshift, AGNs are found in identical environments to non-AGNs, although they represent the most clustered group when compared to passive and star-forming galaxies. The majority of our AGNs at any redshift were classified as late-type galaxies, including a 16% proportion of irregulars. Another 16% of AGNs show signs of interactions or mergers. Regarding the infrared luminosity, we are able to recover all the luminous infrared galaxies (LIRGs) in the field of OTELO up to z ∼ 1.6. We find that the proportion of LIRGs and ultra-luminous infraed galaxies (ULIRGs) is higher among the AGN population, and that ULIRGs show a higher fraction of AGNs than LIRGs.

Clustering of extremely red objects in the AKARI NEP-deep field

Abstract We study the clustering property of extremely red objects (EROs) using Canada–France–Hawaii Telescope (CFHT) surveys with 0.55 deg2 in the AKARI north ecliptic pole (NEP) deep field. EROs are selected by the color criterion of r′ − Ks > 3.66, which is equivalent to (R − Ks)Vega > 5. We conducted the clustering analysis for two magnitude-limited cases, Ks < 20.3 (N = 363) and Ks < 20.9 (N = 727), using two-point angular correlation represented by a single power-law function. By fixing a power-law (with 0.8), the correlation lengths of EROs with Ks < 20.3 and Ks < 20.9 are 9.10 ± 1.86 and 7.81 ± 1.21 h−1 Mpc, respectively. We find that bias factors of EROs with Ks < 20.3 and Ks < 20.9 are 3.19 ± 0.59 and 2.83 ± 0.40, respectively, revealing that EROs reside in dark matter halos heavier than $\sim 10^{13}\, M_{\odot }$. To investigate possible descendants of EROs with Ks < 20.9, we calculate how the bias for dark matter halos that host EROs evolves by accounting for mass growth of halos along the redshift. We find that halos hosting EROs evolve into halos hosting local massive galaxies with 2–$7\, L^{*}$. It suggests that passive EROs with Ks < 20.9 are likely to be progenitors of massive galaxies in the present universe. The comparison between passive EROs (pEROs) and star-forming EROs (sEROs) classified by near-infrared colors shows that pEROs seem to be connected with more massive local galaxies. By fitting spectral energy distributions (SEDs), we estimate active galactic nucleus (AGN) contribution for 68 sEROs which are selected in mid-IR bands. AGN contributions to the IR luminosity are less than $10\%$ except for six sEROs. At least in the IR-selected sEROs, the contribution of AGN seems to be not significant.