IR Spectral Energy Distribution Research Articles

JWST Reveals a Luminous Infrared Source at the Position of the Failed Supernova Candidate N6946-BH1

N6946-BH1 (BH1) is the first plausible candidate for a failed supernova (SN), a peculiar event in which a massive star disappears without the expected bright SN, accompanied by collapse into a black hole (BH). Following a luminous outburst in 2009, the source experienced a significant decline in optical brightness, while maintaining a persistent IR presence. While it was proposed to be a potential failed SN, such behavior has been observed in SN impostor events in nearby galaxies. Here, we present late-time observations of BH1, taken 14 yr after disappearance, using JWST’s NIRCam and MIRI instruments to probe a never before observed region of the object’s spectral energy distribution (SED). We show for the first time that all previous observations of BH1 (pre- and postdisappearance) are actually a blend of at least three sources. In the near-infrared, BH1 is notably fainter than the progenitor but retains similar brightness to its state in 2017. In the mid-infrared the flux appears to have brightened compared to the inferred fluxes from the best-fitting progenitor model. The total luminosity of the source is between 13% and 25% that of the progenitor. We also show that the IR SED appears consistent with polycyclic aromatic hydrocarbon features that arise when dust is illuminated by near-ultraviolet radiation. At present, the interpretation of BH1 remains uncertain. The observations match expectations for a stellar merger, but theoretical ambiguity in the failed SN hypothesis makes it hard to dismiss.

Detection of Extragalactic Anomalous Microwave Emission in NGC 2903 Using KVN Single-dish Observations

We present the results of the single-dish observations using the Korean VLBI Network to search for anomalous microwave emission (AME) in nearby galaxies. The targets were selected from ‘Mapping the dense molecular gas in the strongest star-forming galaxies' (MALATANG), a legacy survey project of the James Clerk Maxwell Telescope. The MALATANG galaxies are good representatives of local galaxies with enhanced nuclear activity associated with star formation and/or active galactic nuclei (AGNs), providing IR-bright galaxy samples; thus, they are good candidates for AME hosts. Combining with ancillary data, we investigated the radio–IR spectral energy distribution (SED), while searching for AME signals in five galaxies. The AME in NGC 2903 was well detected at a significant confidence level, whereas that in NGC 2146 and M82 was marginal. NGC 1068 and Arp 299 indicated no significant hints, and we provide upper limits for the AME. The best-fit SED exhibited local peaks of the AME components at higher frequencies and with stronger peak fluxes than those in previous studies. This suggested that AME originates from denser environments such as molecular clouds or photodissociation regions rather than warm neutral/ionized medium as commonly suggested by previous studies. Further, our AME-detected targets were observed to exhibit higher specific star formation rates than the other extragalactic AME hosts. Furthermore, AME favored starburst galaxies among our sample rather than AGN hosts. Consequently, this might imply that AGNs are excessively harsh environments for tiny dust to survive.

DiskMINT: A Tool to Estimate Disk Masses with CO Isotopologues

CO is one of the most abundant molecules in protoplanetary disks, and optically thin emission from its isotopologues has been detected in many of them. However, several past works have argued that reproducing the relatively low emission of CO isotopologues requires a very low disk mass or significant CO depletion. Here, we present a Python code, DiskMINT, which includes gas density and temperature structures that are both consistent with the thermal pressure gradient, isotope-selective chemistry, and conversion of CO into CO2 ice on grain surfaces. The code generates a self-consistent disk structure, where the gas disk distribution is obtained from a spectral energy distribution (SED)–derived dust disk structure with multiple grain sizes. We use DiskMINT to study the disk of RU Lup, a high-accreting star whose disk was previously inferred to have a gas mass of only ∼1.5 × 10−3 M ⊙ and gas-to-dust mass ratio of ∼4. Our best-fit model to the long-wavelength continuum emission can explain the total C18O luminosity as well as the C18O velocity and radial intensity profiles, and it obtains a gas mass of ∼1.2 × 10−2 M ⊙, an order of magnitude higher than previous results. A disk model with parametric Gaussian vertical distribution that better matches the IR SED can also explain the observables above with a similarly high gas mass ∼2.1 × 10−2 M ⊙. We confirm the conclusions of Ruaud et al. that optically thin C18O rotational lines provide reasonable estimates of the disk mass and can therefore be used as gas disk tracers.

Polar Dust Emission in Quasar IR SEDs and Its Correlation with Narrow-line Regions

Polar dust has been found to play an important role in the mid-infrared emission of nearby Seyfert nuclei. If and how often polar dust exists among the quasar population is unknown due to the lack of spatially resolved observations. In this Letter, we report correlations between the prominence of active galactic nucleus (AGN) forbidden line emission (commonly associated with the narrow-line region) and the dust mid-IR energy output among the archetypal Palomar-Green quasar sample and other bright type-1 AGNs drawn from the Sloan Digital Sky Survey, Spitzer, and Wide-field Infrared Survey Explorer (WISE) archives. The AGN mid-IR color differences traced by WISE W2 (∼4.6 μm)−W3 (∼12 μm) and W2 (∼4.6 μm)−W4 (∼22 μm), and near-IR to mid-IR spectral energy distributions (SEDs) constrained with the Two Micron All Sky Survey, WISE, and Spitzer data have clear trends with the relative strength of the forbidden line regions traced by the optical [O iii] and mid-IR [O iv] emission lines. These observations indicate that, where the lines are strong, a large fraction of the AGN emission at λ ≳ 5 μm comes from dust in the forbidden line regions. We find that the widely quoted universal AGN template is a result of averaging quasar SEDs with different levels of polar dust emission above the torus output and that the typical intrinsic IR SED of compact torus dust emission alone falls with increasing wavelength past 5 μm (in νF ν ). In addition, the association of polar dust with the forbidden lines suggests an alternative to the receding torus hypothesis for the decrease in infrared output with increasing AGN luminosity.

Diagnosing deceivingly cold dusty galaxies at 3.5 < z < 6: A substantial population of compact starbursts with high infrared optical depths

Using NOEMA and ALMA 3mm line scans, we measured spectroscopic redshifts of six new dusty galaxies at 3.5 < z < 4.2 by solidly detecting [CI](1-0) and CO transitions. The sample was selected from the COSMOS and GOODS-North super-deblended catalogs with far-infrared (FIR) photometric redshifts zphot > 6 based on template IR spectral energy distribution (SED) from known submillimeter galaxies at z = 4–6. Dust SED analyses explain the zphot overestimate from seemingly cold dust temperatures (Td) and steep Rayleigh-Jeans (RJ) slopes, providing additional examples of cold dusty galaxies impacted by the cosmic microwave background (CMB). We therefore studied the general properties of the enlarged sample of 10 “cold” dusty galaxies over 3.5 < z < 6. We conclude that these galaxies are deceivingly cold at the surface but are actually warm in their starbursting cores. Several lines of evidence support this scenario: (1) The high infrared surface density ΣIR and cold Td from optically thin models appear to violate the Stefan-Boltzmann law; (2) the gas masses derived from optically thin dust masses are inconsistent with estimates from dynamics and CI luminosities; (3) the implied high star formation efficiencies would conflict with cold Td; and (4) high FIR optical depth is implied even using the lower, optically thick dust masses. This work confirms the existence of a substantial population of deceivingly cold, compact dusty starburst galaxies at z ≳ 4, together with the severe impact of the CMB on their RJ observables, paving the way for the diagnostics of optically thick dust in the early Universe. Conventional gas mass estimates based on RJ dust continuum luminosities implicitly assume an optically thin case, which leads to overestimation of gas masses by a factor of 2–3 on average in compact dusty star-forming galaxies.

The star formation rates of QSOs

ABSTRACT We examine the far-infrared (FIR) properties of a sample of 5391 optically selected QSOs in the 0.5 < z < 2.65 redshift range down to log [νLν, 2500(erg s−1)] > 44.7, using SPIRE data from Herschel-ATLAS. We split the sample in a grid of 74 luminosity–redshift bins and compute the average optical–IR spectral energy distribution (SED) in each bin. By normalizing an intrinsic active galactic nucleus (AGN) template to the AGN optical power (at 5100 Å), we decompose the total IR emission (LIR; 8–1000 µm) into an AGN (LIR, AGN) and star-forming component (LIR, SF). We find that the AGN contribution to LIR increases as a function of AGN power, manifesting as a reduction of the ‘FIR bump’ in the average QSO SEDs. We note that LIR, SF does not correlate with AGN power; the mean star formation rates (SFRs) of AGN host galaxies are a function of redshift only and they range from ∼6 M⊙ yr−1 at z ∼ 0 to a plateau of ≲ 200 M⊙ yr−1 at z ∼ 2.6. Our results indicate that the accuracy of FIR emission as a proxy for SFR decreases with increasing AGN luminosity. We show that, at any given redshift, observed trends between IR luminosity (whether monochromatic or total) and AGN power (in the optical or X-rays) can be explained by a simple model which is the sum of two components: (i) the IR emission from star formation, uncorrelated with AGN power and (ii) the IR emission from AGN, directly proportional to AGN power in the optical or X-rays.

Searching Far and Long. I. Pilot ALMA 2 mm Follow-up of Bright Dusty Galaxies as a Redshift Filter

A complete census of dusty star-forming galaxies (DSFGs) at early epochs is necessary to constrain the obscured contribution to the cosmic star formation rate density (CSFRD); however, DSFGs beyond z ∼ 4 are both rare and hard to identify from photometric data alone due to degeneracies in submillimeter photometry with redshift. Here, we present a pilot study obtaining follow-up Atacama Large Millimeter Array (ALMA) 2 mm observations of a complete sample of 39 850 μm-bright dusty galaxies in the SSA22 field. Empirical modeling suggests 2 mm imaging of existing samples of DSFGs selected at 850 μm—1 mm can quickly and easily isolate the “needle in a haystack” DSFGs that sit at z > 4 or beyond. Combining archival submillimeter imaging with our measured ALMA 2 mm photometry (1σ ∼ 0.08 mJy beam−1 rms), we characterize the galaxies’ IR spectral energy distributions (SEDs) and use them to constrain redshifts. With available redshift constraints fit via the combination of six submillimeter bands, we identify 6/39 high-z candidates each with >50% likelihood to sit at z > 4, and find a positive correlation between redshift and 2 mm flux density. Specifically, our models suggest the addition of 2 mm to a moderately constrained IR SED will improve the accuracy of a millimeter-derived redshift from Δz/(1 + z) = 0.3 to Δz/(1 + z) = 0.2. Our IR SED characterizations provide evidence for relatively high-emissivity spectral indices (〈β〉 = 2.4 ± 0.3) in the sample. We measure that especially bright (S 850μ m > 5.55 mJy) DSFGs contribute ∼10% to the cosmic-averaged CSFRD from 2 < z < 5, confirming findings from previous work with similar samples.

Far-ultraviolet to FIR Spectral-energy Distribution Modeling of the Stellar Formation History of the M31 Bulge

Abstract M31 is being surveyed at far- and near-ultraviolet with the UVIT telescope on AstroSat. The central bulge of M31 was observed in the N279N (275–280 nm), N219M (200–240 nm), F172M (160–185 nm), F169M (145–175 nm), and F148W (120–180 nm) filters. These images are made publicly available here. The UVIT data are supplemented with Sloan Digital Sky Survey data in optical, Spitzer data in near-infrared and Herschel data in mid- and far-infrared. The resulting far-ultraviolet to IR spectral-energy distributions for the bulge and for 10 subregions, are modeled using combinations of simple stellar populations and with CIGALE models. We find a dominant old (10–12 Gyr) metal-rich ([Z/H] ∼ 0.3) population and a younger (600 Myr) solar abundance ([Z/H] ∼ 0) population throughout the bulge. For the innermost 120″ we find an additional very young (25 Myr) metal-poor ([Z/H] ∼ −0.7) population. The results are consistent with the most recent stellar population studies of the bulge, which find the two populations for the whole bulge and a third young population in the innermost bulge.

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 &gt; 5 × 1011 L⊙, typically underrepresented in surveys of quasars and submillimeter galaxies.

Constraining the Milky Way’s ultraviolet-to-infrared SED with Gaussian process regression

ABSTRACT Improving our knowledge of global Milky Way (MW) properties is critical for connecting the detailed measurements only possible from within our Galaxy to our understanding of the broader galaxy population. We here train Gaussian process regression (GPR) models on SDSS (Sloan Digital Sky Survey) galaxies to map from galaxy properties (stellar mass, apparent axial ratio, star formation rate, bulge-to-total ratio, disc scale length, and bar vote fraction) to ultraviolet (UV; GALEX FUV/NUV), optical (SDSS ugriz), and infrared (IR; 2MASS JHKs and WISE W1/W2/W3/W4) fluxes and uncertainties. With these models, we estimate the photometric properties of the MW, resulting in a full UV-to-IR spectral energy distribution (SED) as it would be measured externally, viewed face-on. We confirm that the MW lies in the green valley in optical diagnostic diagrams, but show for the first time that the MW is in the star-forming region in standard UV and IR diagnostics – characteristic of the population of red spiral galaxies. Although our GPR method predicts one band at a time, the resulting MW UV–IR SED is consistent with SEDs of local spirals with characteristics broadly similar to the MW, suggesting that these independent predictions can be combined reliably. Our UV–IR SED will be invaluable for reconstructing the MW’s star formation history using the same tools employed for external galaxies, allowing comparisons of results from in situ measurements to those from the methods used for extragalactic objects.

The infrared-radio correlation of star-forming galaxies is stronglyM⋆-dependent but nearly redshift-invariant sincez∼ 4

Over the past decade, several works have used the ratio between total (rest 8−1000μm) infrared and radio (rest 1.4 GHz) luminosity in star-forming galaxies (qIR), often referred to as the infrared-radio correlation (IRRC), to calibrate the radio emission as a star formation rate (SFR) indicator. Previous studies constrained the evolution ofqIRwith redshift, finding a mild but significant decline that is yet to be understood. Here, for the first time, we calibrateqIRas a function ofbothstellar mass (M⋆) and redshift, starting from anM⋆-selected sample of &gt; 400 000 star-forming galaxies in the COSMOS field, identified via (NUV − r)/(r − J) colours, at redshifts of 0.1 &lt; z &lt; 4.5. Within each (M⋆,z) bin, we stacked the deepest available infrared/sub-mm and radio images. We fit the stacked IR spectral energy distributions with typical star-forming galaxy and IR-AGN templates. We then carefully removed the radio AGN candidates via a recursive approach. We find that the IRRC evolves primarily withM⋆, with more massive galaxies displaying a systematically lowerqIR. A secondary, weaker dependence on redshift is also observed. The best-fit analytical expression is the following:qIR(M⋆, z) = (2.646 ± 0.024) × (1 + z)( − 0.023 ± 0.008)–(0.148 ± 0.013) × (log M⋆/M⊙ − 10). Adding the UV dust-uncorrected contribution to the IR as a proxy for the total SFR would further steepen theqIRdependence onM⋆. We interpret the apparent redshift decline reported in previous works as due to low-M⋆galaxies being progressively under-represented at high redshift, as a consequence of binning only in redshift and using either infrared or radio-detected samples. The lower IR/radio ratios seen in more massive galaxies are well described by their higher observed SFR surface densities. Our findings highlight the fact that using radio-synchrotron emission as a proxy for SFR requires novelM⋆-dependent recipes that will enable us to convert detections from future ultra-deep radio surveys into accurate SFR measurements down to low-M⋆galaxies with low SFR.

Measuring the total infrared light from galaxy clusters at z = 0.5–1.6: connecting stellar populations to dusty star formation

ABSTRACT Massive galaxy clusters undergo strong evolution from z ∼ 1.6 to z ∼ 0.5, with overdense environments at high-z characterized by abundant dust-obscured star formation and stellar mass growth which rapidly give way to widespread quenching. Data spanning the near- to far-infrared (IR) can directly trace this transformation; however, such studies have largely been limited to the massive galaxy end of cluster populations. In this work, we present ‘total light’ stacking techniques spanning $3.4\!-\!500\, \mu$m aimed at revealing the total cluster emission, including low-mass members and potential intracluster dust. We detail our procedures for WISE, Spitzer, and Herschel imaging, including corrections to recover the total stacked emission in the case of high fractions of detected galaxies. We apply our techniques to 232 well-studied log$\, M_{200}/\mathrm{M}_{\odot }\sim 13.8$ clusters in multiple redshift bins, recovering extended cluster emission at all wavelengths. We measure the averaged IR radial profiles and spectral energy distributions (SEDs), quantifying the total stellar and dust content. The near-IR profiles are well described by an NFW model with a high (c ∼ 7) concentration. Dust emission is similarly concentrated, albeit suppressed at $r\lesssim 0.3\,$Mpc. The measured SEDs lack warm dust, consistent with the colder SEDs of low-mass galaxies. We derive total stellar masses consistent with the theoretical Mhalo−M⋆ relation and specific star formation rates that evolve strongly with redshift, echoing that of log$\, M_{\star }/\mathrm{M}_{\odot }\gtrsim 10$ cluster galaxies. Separating out the massive population reveals the majority of cluster far-IR emission ($\sim 70\!-\!80{{\ \rm per\ cent}}$) is provided by the low-mass constituents, which differs from field galaxies. This effect may be a combination of mass-dependent quenching and excess dust in low-mass cluster galaxies.

BAT AGN Spectroscopic Survey. XI. The Covering Factor of Dust and Gas in Swift/BAT Active Galactic Nuclei

Abstract We quantify the luminosity contribution of active galactic nuclei (AGNs) to the 12 μm, mid-infrared (MIR; 5–38 μm), and total IR (5–1000 μm) emission in the local AGNs detected in the all-sky 70 month Swift/Burst Alert Telescope (BAT) ultrahard X-ray survey. We decompose the IR spectral energy distributions (SEDs) of 587 objects into the AGN and starburst components using templates for an AGN torus and a star-forming galaxy. This enables us to recover the emission from the AGN torus including the low-luminosity end, down to , which typically has significant host galaxy contamination. The sample demonstrates that the luminosity contribution of the AGN to the 12 μm, the MIR, and the total IR bands is an increasing function of the 14–150 keV luminosity. We also find that for the most extreme cases, the IR pure-AGN emission from the torus can extend up to 90 μm. The total IR AGN luminosity obtained through the IR SED decomposition enables us to estimate the fraction of the sky obscured by dust, i.e., the dust covering factor. We demonstrate that the median dust covering factor is always smaller than the median X-ray obscuration fraction above an AGN bolometric luminosity of . Considering that the X-ray obscuration fraction is equivalent to the covering factor coming from both the dust and gas, this indicates that an additional neutral gas component, along with the dusty torus, is responsible for the absorption of X-ray emission.

Polar Dust, Nuclear Obscuration, and IR SED Diversity in Type-1 AGNs*

Abstract Despite the hypothesized similar face-on viewing angles, the infrared emission of type-1 active galactic nuclei (AGNs) has diverse spectral energy distribution (SED) shapes that deviate substantially from the well-characterized quasar templates. Motivated by the commonly seen UV-optical obscuration and the discovery of parsec-scale mid-IR polar dust emission in some nearby AGNs, we develop semi-empirical SED libraries for reddened type-1 AGNs built on quasar intrinsic templates, assuming low-level extinction caused by an extended distribution of large dust grains. We demonstrate that this model can reproduce the nuclear UV to IR SED and the strong mid-IR polar dust emission of NGC 3783, the type-1 AGN with the most relevant and robust observational constraints. In addition, we compile 64 low-z Seyfert-1 nuclei with negligible mid-IR star formation contamination and satisfactorily fit the individual IR SEDs as well as the composite UV to mid-IR composite SEDs. Given the success of these fits, we characterize the possible infrared SED of AGN polar dust emission and utilize a simple but effective strategy to infer its prevalence among type-1 AGNs. The SEDs of high-z peculiar AGNs, including the extremely red quasars, mid-IR warm-excess AGNs, and hot dust-obscured galaxies, can be also reproduced by our model. These results indicate that the IR SEDs of most AGNs, regardless of redshift or luminosity, arise from similar circumnuclear torus properties but differ mainly due to the optical depths of extended obscuring dust components.

The [O iii] Profiles of Infrared-selected Active Galactic Nuclei: More Powerful Outflows in the Obscured Population

Abstract We explore the kinematics of ionized gas via the [O iii] λ5007 emission lines in active galactic nuclei (AGNs) selected on the basis of their mid-infrared (IR) emission, and split into obscured and unobscured populations based on their optical−IR colors. After correcting for differences in redshift distributions, we provide composite spectra of spectroscopically and photometrically defined obscured/Type 2 and unobscured/Type 1 AGNs from 3500 to 7000 Å. The IR-selected obscured sources contain a mixture of narrow-lined Type 2 AGNs and intermediate sources that have broad Hα emission and significantly narrower Hβ. Using both [O iii] luminosities and AGN luminosities derived from optical−IR spectral energy distribution fitting, we find evidence for enhanced large-scale obscuration in the obscured sources. In matched bins of luminosity we find that the obscured population typically has broader, more blueshifted [O iii] emission than in the unobscured sample, suggestive of more powerful AGN-driven outflows. This trend is not seen in spectroscopically classified samples, and is unlikely to be entirely explained by orientation effects. In addition, outflow velocities increase from small to moderate AGN E(B − V) values, before flattening out (as traced by FWHM) and even decreasing (as traced by blueshift). While difficult to fully interpret in a single physical model, due to both the averaging over populations and the spatially averaged spectra, these results agree with previous findings that simple geometric unification models are insufficient for the IR-selected AGN population, and may fit into an evolutionary model for obscured and unobscured AGNs.

The Spectral Energy Distribution of the Hyperluminous, Hot Dust-obscured Galaxy W2246–0526

Abstract Hot dust-obscured galaxies (Hot DOGs) are a luminous, dust-obscured population recently discovered in the WISE All-Sky survey. Multiwavelength follow-up observations suggest that they are mainly powered by accreting supermassive black holes (SMBHs), lying in dense environments, and being in the transition phase between extreme starburst and UV-bright quasars. Therefore, they are good candidates for studying the interplay between SMBHs, star formation, and environment. W2246−0526 (hereafter, W2246), a Hot DOG at z ∼ 4.6, has been taken as the most luminous galaxy known in the universe. Revealed by the multiwavelength images, the previous Herschel SPIRE photometry of W2246 is contaminated by a foreground galaxy (W2246f), resulting in an overestimation of its total IR luminosity by a factor of about two. We perform the rest-frame UV/optical-to-far-IR spectral energy distribution (SED) analysis with SED3FIT and re-estimate its physical properties. The derived stellar mass makes it among the most massive galaxies with spectroscopic redshift z &gt; 4.5. Its structure is extremely compact and requires an effective mechanism to puff-up. Most of (&gt;95%) its IR luminosity is from AGN torus emission, revealing the rapid growth of the central SMBH. We also predict that W2246 may have a significant molecular gas reservoir based on the dust mass estimation.

Dissecting the active galactic nucleus in Circinus – I. Peculiar mid-IR morphology explained by a dusty hollow cone

Recent high angular resolution observations resolved for the first time the mid-infrared (MIR) structure of nearby active galactic nuclei (AGN). Surprisingly, they revealed that a major fraction of their MIR emission comes from the polar regions. This is at odds with the expectation based on AGN unification, which postulates a dusty torus in the equatorial region. The nearby, archetypical AGN in the Circinus galaxy offers one of the best opportunities to study the MIR emission in greater detail. New, high quality MIR images obtained with the upgraded VISIR instrument at the Very Large Telescope show that the previously detected bar-like structure extends up to at least 40 pc on both sides of the nucleus along the edges of the ionization cone. Motivated by observations across a wide wavelength range and on different spatial scales, we propose a phenomenological dust emission model for the AGN in the Circinus galaxy consisting of a compact dusty disk and a large-scale dusty cone shell, illuminated by a tilted accretion disk with an anisotropic emission pattern. Undertaking detailed radiative transfer simulations, we demonstrate that such a model is able to explain the peculiar MIR morphology and account for the entire IR spectral energy distribution. Our results call for caution when attributing dust emission of unresolved sources entirely to the torus and warrant further investigation of the MIR emission in the polar regions of AGN.

Evolution of protoplanetary disks from their taxonomy in scattered light: Group I vs. Group II

High-resolution imaging reveals a large morphological variety of protoplanetary disks. To date, no constraints on their global evolution have been found from this census. An evolutionary classification of disks was proposed based on their IR spectral energy distribution, with the Group I sources showing a prominent cold component ascribed to an earlier stage of evolution than Group II. Disk evolution can be constrained from the comparison of disks with different properties. A first attempt of disk taxonomy is now possible thanks to the increasing number of high-resolution images of Herbig Ae/Be stars becoming available. Near-IR images of six Group II disks in scattered light were obtained with VLT/NACO in Polarimetric Differential Imaging, which is the most efficient technique to image the light scattered by the disk material close to the stars. We compare the stellar/disk properties of this sample with those of well-studied Group I sources available from the literature. Three Group II disks are detected. The brightness distribution in the disk of HD163296 indicates the presence of a persistent ring-like structure with a possible connection with the CO snowline. A rather compact (less than 100 AU) disk is detected around HD142666 and AK Sco. A taxonomic analysis of 17 Herbig Ae/Be sources reveals that the difference between Group I and Group II is due to the presence or absence of a large disk cavity (larger than 5 AU). There is no evidence supporting the evolution from Group I to Group II. Group II are not evolved version of the Group I. Within the Group II disks, very different geometries (both self-shadowed and compact) exist. HD163296 could be the primordial version of a typical Group I. Other Group II, like AK Sco and HD142666, could be smaller counterpart of Group I unable to open cavities as large as those of Group I.

A Controlled Study of Cold Dust Content in Galaxies from z = 0–2

Abstract At , the formation of new stars is dominated by dusty galaxies whose far-IR emission indicates they contain colder dust than local galaxies of a similar luminosity. We explore the reasons for the evolving IR emission of similar galaxies over cosmic time using (1) local galaxies from GOALS ( ), (2) galaxies at from 5MUSES ( ), and (3) IR luminous galaxies spanning from GOODS and Spitzer xFLS ( ). All samples have Spitzer mid-IR spectra, and Herschel and ground-based submillimeter imaging covering the full IR spectral energy distribution, allowing us to robustly measure , , and for every galaxy. Despite similar infrared luminosities, dusty star-forming galaxies (DSFG) have a factor of 5 higher dust masses and 5 K colder temperatures. The increase in dust mass is linked to an increase in the gas fractions with redshift, and we do not observe a similar increase in stellar mass or star formation efficiency. , a proxy for , is strongly correlated with independently of redshift. We measure merger classification and galaxy size for a subsample, and there is no obvious correlation between these parameters and or . In DSFG, the change in can fully account for the observed colder dust temperatures, suggesting that any change in the spatial extent of the interstellar medium is a second-order effect.

Predicting HCN, HCO+, multi-transition CO, and dust emission of star-forming galaxies

High-zstar-forming galaxies have significantly higher gas fractions and star-formation efficiencies per molecular gas mass than local star-forming galaxies. In this work, we take a closer look at the gas content or fraction and the associated star-formation rate in main sequence and starburst galaxies atz= 0 andz~ 1–2 by applying an analytical model of galactic clumpy gas disks to samples of local spiral galaxies, ULIRGs, submillimeter (smm), and high-zstar-forming galaxies. The model simultaneously calculates the total gas mass, Hi/H2mass, the gas velocity dispersion, IR luminosity, IR spectral energy distribution, CO spectral line energy distribution (SLED), HCN(1–0) and HCO+(1–0) emission of a galaxy given its size, integrated star formation rate, stellar mass radial profile, rotation curve, and ToomreQparameter. The model reproduces the observed CO luminosities and SLEDs of all sample galaxies within the model uncertainties (~0.3 dex). Whereas the CO emission is robust against the variation of model parameters, the HCN and HCO+emissions are sensitive to the chemistry of the interstellar medium. The CO and HCN mass-to-light conversion factors, including CO-dark H2, are given and compared to the values found in the literature. All model conversion factors have uncertainties of a factor of two. Both the HCN and HCO+emissions trace the dense molecular gas to a factor of approximately two for the local spiral galaxies, ULIRGs and smm-galaxies. Approximately 80% of the molecular line emission of compact starburst galaxies originates in non-self-gravitating gas clouds. The effect of HCN infrared pumping is small but measurable (10–20%). The gas velocity dispersion varies significantly with the ToomreQparameter. TheQ= 1.5 model yields high-velocity dispersions (vdisp≫ 10 km s-1) consistent with available observations of high-zstar-forming galaxies and ULIRGs. However, we note that these high-velocity dispersions are not mandatory for starburst galaxies. The integrated Kennicutt-Schmidt law has a slope of approximately 1 for the local spirals, ULIRGs, and smm-galaxies, whereas the slope is 1.7 for high-zstar-forming galaxies. The model shows Kennicutt-Schmidt laws with respect to the molecular gas surface density with slopes of approximately 1.5 for local spiral galaxies, high-zstar-forming galaxies. The relation steepens for compact starburst galaxies. The model star-formation rate per unit area is, as observed, proportional to the molecular gas surface density divided by the dynamical timescale. Our relatively simple analytic model together with the recipes for the molecular line emission appears to capture the essential physics of galactic clumpy gas disks.