High-resolution Mid-infrared Imaging Research Articles

Supernova Ejecta with Crystalline Silicate Dust in the Supernova Remnant MSH 15–52

IRAS 15099-5856 in the young supernova remnant (SNR) MSH 15−52 is the first and only SNR-associated object with crystalline silicate dust detected so far, although its nature and the origin of the crystalline silicate are still unclear. In this paper, we present high-resolution mid-infrared (MIR) imaging observations of the bright central compact source IRS1 of IRAS 15099-5856 to study the spatial distributions of gas and dust and the analysis of its Spitzer MIR spectrum to explore the origin of IRS1. The MIR images obtained with the T-ReCS attached on the Gemini South telescope show a complicated, inhomogeneous morphology of IRS1 with bright clumps and diffuse emission in [Ne ii] 12.81 μm and Qa 18.30 μm, which confirms that IRS1 is an extended source externally heated by the nearby O star Muzzio 10, a candidate for the binary companion of the progenitor star. The Spitzer MIR spectrum reveals several ionic emission lines including a strong [Ne ii] 12.81 μm line, but no hydrogen line is detected. We model the spectrum using the photoionization code Cloudy with varying elemental composition. The elemental abundance of IRS1 derived from the model is close to that of supernova (SN) ejecta with depleted hydrogen and enhanced metals, particularly neon, argon, and iron. Our results imply that IRS1 originates from the SN ejecta and suggest the possibility of the formation of crystalline silicate in newly formed SN dust.

The Recent Mass Loss History of the Hypergiant RW Cep

In light of recent variability seen in RW Cep, we present an analysis of the spectral energy distribution of the star and unpublished, high spatial resolution mid-Infrared imaging. We derive a current mass-loss rate of ∼7 × 10−6 M ⊙ yr−1 for the star and clear evidence of a higher mass-loss rate phase ending no more than ∼100 yr ago.

Electrical detection of hyperbolic phonon-polaritons in heterostructures of graphene and boron nitride

Light properties in the mid-infrared can be controlled at a deep subwavelength scale using hyperbolic phonons-polaritons of hexagonal boron nitride. While propagating as waveguided modes hyperbolic phonons-polaritons can concentrate the electric field in a chosen nano-volume. Such a behavior is at the heart of many applications including subdiffraction imaging and sensing. Here we employ HPPs in heterostructures of hexagonal boron nitride and graphene as new nano-optoelectronic platform by uniting the benefits of efficient hot-carrier photoconversion in graphene and the hyperbolic nature of hexagonal boron nitride. We demonstrate electrical detection of hyperbolic phonons-polaritons by guiding them towards a graphene pn-junction. We shine a laser beam onto a gap in metal gates underneath the heterostructure, where the light is converted into hyperbolic phonons-polaritons. The hyperbolic phonons-polaritons then propagate as confined rays heating up the graphene leading to a strong photocurrent. This concept is exploited to boost the external responsivity of mid-infrared photodetectors, overcoming the limitation of graphene pn-junction detectors due to their small active area and weak absorption. Moreover this type of detector exhibits tunable frequency selectivity due to the hyperbolic phonons-polaritons, which combined with its high responsivity paves the way for efficient high-resolution mid-infrared imaging.

The Nuclear Infrared Emission of Low-Luminosity AGN

We have obtained high-resolution mid-infrared (MIR) imaging, nuclear spectral energy distributions (SEDs) and archival Spitzer spectra for 22 low-luminosity active galactic nuclei (LLAGN; Lbol < 5 × 1042 erg s−1). Infrared (IR) observations may advance our understanding of the accretion ows in LLAGN, the fate of the obscuring torus at low accretion rates, and, perhaps, the star formation histories of these objects. However, while comprehensively studied in higher-luminosity Seyferts and quasars, the nuclear IR properties of LLAGN have not yet been well-determined. In these proceedings we summarise the results for the LLAGN at the relatively high-luminosity, high-Eddington ratio end of the sample. Strong, compact nuclear sources are visible in the MIR images of these objects, with luminosities consistent with or slightly in execss of that predicted by the standard MIR/X-ray relation. Their broadband nuclear SEDs are diverse; some resemble typical Seyfert nuclei, while others possess less of a well-defined MIR "dust bump". Strong silicate emission is present in many of these objects. We speculate that this, together with high ratios of silicate strength to hydrogen column density, could suggest optically thin dust and low dust-to-gas ratios, in accordance with model predictions that LLAGN do not host a Seyfert-like obscuring torus.

THE NUCLEAR INFRARED EMISSION OF LOW-LUMINOSITY ACTIVE GALACTIC NUCLEI

We present high-resolution mid-infrared (MIR) imaging, nuclear spectral energy distributions (SEDs) and archival Spitzer spectra for 22 low-luminosity active galactic nuclei (LLAGN; Lbol \lesssim 10^42 erg/sec). Infrared (IR) observations may advance our understanding of the accretion flows in LLAGN, the fate of the obscuring torus at low accretion rates, and, perhaps, the star formation histories of these objects. However, while comprehensively studied in higher-luminosity Seyferts and quasars, the nuclear IR properties of LLAGN have not yet been well-determined. We separate the present LLAGN sample into three categories depending on their Eddington ratio and radio emission, finding different IR characteristics for each class. (I) At the low-luminosity, low-Eddington ratio (log Lbol/LEdd < -4.6) end of the sample, we identify "host-dominated" galaxies with strong polycyclic aromatic hydrocarbon bands that may indicate active (circum-)nuclear star formation. (II) Some very radio-loud objects are also present at these low Eddington ratios. The IR emission in these nuclei is dominated by synchrotron radiation, and some are likely to be unobscured type 2 AGN that genuinely lack a broad line region. (III) At higher Eddington ratios, strong, compact nuclear sources are visible in the MIR images. The nuclear SEDs of these galaxies are diverse; some resemble typical Seyfert nuclei, while others lack a well-defined MIR "dust bump". Strong silicate emission is present in many of these objects. We speculate that this, together with high ratios of silicate strength to hydrogen column density, could suggest optically thin dust and low dust-to-gas ratios, in accordance with model predictions that LLAGN do not host a Seyfert-like obscuring torus.

NO TRANSITION DISK? INFRARED EXCESS, PAH, H2, AND X-RAYS FROM THE WEAK-LINED T TAURI STAR DoAr 21

We present new high-resolution mid-infrared imaging, high-resolution optical spectroscopy, and Chandra grating X-ray spectroscopy of the weak-lined T Tauri star DoAr 21. DoAr 21 (age < 10^6 yr and mass ~ 2.2 M_sun) is a strong X-ray emitter, with conflicting evidence in the literature about its disk properties. It shows weak but broad H-alpha emission; polarimetric variability; PAH and H2 emission; and a strong, spatially-resolved 24-micron excess in archival Spitzer photometry. Gemini sub-arcsecond-resolution 9--18 micron images show that there is little or no excess mid-infrared emission within 100 AU of the star; the excess emission is extended over several arcseconds, is quite asymmetric, and is bright in the UV-excited 11.3 micron PAH emission feature. A new high-resolution X-ray grating spectrum from Chandra shows that the stellar X-ray emission is very hard and dominated by continuum emission; it is well-fit by a multi-temperature thermal model and shows no evidence of unusually high densities. We argue that the far-ultraviolet emission from the star's transition region is sufficient to excite the observed extended PAH and continuum emission, and that the H2 emission may be similarly extended and excited. This extended emission may be more akin to a small-scale photodissociation region than a protoplanetary disk, highlighting both the very young ages (< 10^6 yr) at which some stars are found without disks, and the extreme radiation environment around even late-type pre--main-sequence stars.

High-Resolution Mid-Infrared Imaging of Radio Ultracompact HiiRegions

We present data from mid-infrared Keck Telescope imaging of 18 radio-selected ultracompact H II region candidates at diffraction-limited resolution. The goal of these observations is to determine the sizes, luminosities, and morphologies of the mid-infrared-emitting dust surrounding the stellar sources. All 18 sources were imaged at 11.7 and 17.65 μm, and 10 of them were also imaged at 24.5 μm. All the sources were resolved. We have generated dust temperature and optical depth maps and combined them with radial velocity measurements and radio data (1.4 and 5 GHz) to constrain the properties of these star-forming regions. Half of our objects are excited by B-type stars, and all our objects have derived types that are later than an O6 star. We find a significant correlation between infrared and radio flux densities and a weaker one between infrared diameters and the central source ionizing photon rates. This latter correlation suggests that the more compact sources result from later spectral types rather than young age. Our new data may suggest a revision to the infrared color selection criteria of ultracompact H II regions at resolutions 1''. These 18 sources are part of a sample of 687 sources dominated by ultracompact H II regions selected by matching radio and infrared maps of the first Galactic quadrant by Giveon and coworkers. The new mid-infrared images constitute a significant improvement in resolving substructure at these wavelengths. If applied to all of this sample, our analysis will improve our understanding of embedded star formation in the Galaxy.

Mid‐Infrared High Spatial Resolution Observations of NGC 1569: Detection of Embedded Embryos of Star Formation

We present high spatial resolution mid-infrared (MIR) imaging and spectroscopic observations of the dwarf galaxy NGC 1569 with COMICS on the Subaru telescope. The [S IV] 10.5 μm image clearly shows four pointlike sources and one extended source together with the diffuse emission. The brightest MIR source (MIR1) coincides with the intense H II region, which does not have a corresponding optical source and should thus be a source embedded in dust clouds. The infrared luminosity suggests that there are about 40 O7 stars associated with MIR1. The second brightest source located ~15 south of MIR1 (MIR2) is detected for the first time. This source is not seen in the radio continuum. These characteristics can be accounted for if ionizing regions in the source are compact and optically thick in the radio. The large infrared luminosity (~2 × 108 L☉) suggests that there are about 950 O7 stars in MIR2 and significant contributions from sources other than O-type stars, such as less massive stars and/or pre-main-sequence stars. If this interpretation is correct, MIR2 could be in a very early phase of massive star formation. The unidentified infrared (UIR) band at 11.2 μm is also detected in the spectrum of MIR2. The strength of the UIR band decreases with the [S IV] emission, suggesting that the UIR band weakens and the band carriers are destroyed in strong radiation fields. Super star cluster (SSC) A is also detected in the N-band images. The mid-infrared characteristics support the difference in the ages between two components of SSC A.

Nuclear embedded star clusters in NGC 7582

Abstract We report on the discovery of several compact regions of mid-infrared emission in the star-forming circumnuclear disc of the starburst/Seyfert 2 galaxy NGC 7582. The compact sources do not have counterparts in the optical and near-infrared, suggesting that they are deeply embedded in dust. We use the [Ne ii] 12.8-μm line emission to estimate the emission measure of the ionized gas, which in turn is used to assess the number of ionizing photons. Two of the brighter sources are found to have ionizing fluxes of ∼2.5 × 1052, whereas the fainter ones have ∼1 × 1052 photon s−1. Comparing with a 1-Myr-old starburst, we derive stellar masses in the range 3–5 × 105M⊙ and find that the number of O stars in each compact source is typically 0.6–1.6 × 103. We conclude that the compact mid-infrared sources are likely to be young, embedded star clusters, of which only a few are known so far. Our observation highlights the need for high-resolution mid-infrared imaging to discover and study embedded star clusters in the proximity of active galactic nuclei.

High Angular Resolution Mid-Infrared Imaging of Young Stars in Orion BN/KL

We present Keck Long Wavelength Spectrometer images of the Orion BN/KL star-forming region obtained in the first multiwavelength study to have 03-05 resolution from 4.7 to 22 μm. The young stellar objects designated infrared source n and radio source I are believed to dominate the BN/KL region. We have detected extended emission from a probable accretion disk around source n but infer a stellar luminosity on the order of only 2000 L☉. Although source I is believed to be more luminous, we do not detect an infrared counterpart even at the longest wavelengths. However, we resolve the close-by infrared source, IRc2, into an arc of knots ~103 AU long at all wavelengths. Although the physical relation of source I to IRc2 remains ambiguous, we suggest that these sources mark a high-density core (107-108 pc-3 over ~103 AU) within the larger BN/KL star-forming cluster. The high density may be a consequence of the core being young and heavily embedded. We suggest that the energetics of the BN/KL region may be dominated by this cluster core rather than one or two individual sources.

The stellar content of obscured Galactic giant H II regions

Current research using near-infrared techniques for investigating stellar populations in massive Galactic star clusters is reviewed. In particular, I discuss in some detail a survey of obscured Galactic Giant H ii (GH ii) regions and the associated stellar clusters embedded in them. The regions have been selected as the most luminous radio continuum sources. This selection criteria has the consequence that the observed clusters are among the youngest massive star clusters in the Galaxy. The emergent stellar populations are further studied through near-infrared spectroscopy of the brighter members, a number of which are young stellar objects with signatures of dense circumstellar material which might arise from in or out-flows, or in disks. New results from 8m class telescopes employing velocity resolved near-infrared spectroscopy and high angular resolution mid-infrared imaging hold great promise for future detailed investigations.

High resolution mid-infrared imaging of W3(OH)

We present results of our diffraction-limited mid-infrared imaging of the massive star-forming region W3(OH) with SpectroCam-10 on the 5-m Hale telescope at wavelengths of 8.8, 11.7, and 17.9 micron. The thermal emission from heated dust grains associated with the ultracompact HII region W3(OH) is resolved and has a spatial extent of ~2 arcsec in the N band. We did not detect the hot core source W3(H_2O) which implies the presence of at least 12 mag of extinction at 11.7 micron towards this source. These results together with other data were used to constrain the properties of W3(OH) and W3(H_2O) and their envelopes by modelling the thermal dust emission.

High Resolution Mid-Infrared Imaging of Ultraluminous Infrared Galaxies

Observations of ultraluminous infrared galaxies (ULIRGs) with an achieved resolution approaching the diffraction limit in the mid-infrared from 8 to 25 μm using the Keck Telescopes are reported. We find extremely compact structures, with spatial scales of less than 0.3 (diameter) in six of the seven ULIRGs observed. These compact sources emit between 30% and 100% of the mid-infrared energy from these galaxies. We have utilized the compact mid-infrared structures as a diagnostic of whether an AGN or a compact (100–300 pc) starburst is the primary power source in these ULIRGs. In Markarian 231, the upper limit on the diameter of the 12.5 μm source, 0.13, shows that the size of the infrared source must increase with increasing wavelength, consistent with AGN models. In IRAS 05189-2524 and IRAS 08572+3915 there is strong evidence that the source size increases with increasing wavelength. This suggests heating by a central source rather than an extended luminosity source, consistent with the optical classification as an AGN. The compact mid-infrared sources seen in the other galaxies cannot be used to distinguish the ultimate luminosity source. If these ULIRGs are powered by compact starbursts, the star formation rates seen in the central few hundred parsecs far exceed the global rates seen in nearby starburst galaxies, and approach the surface brightness of individual clusters in nearby starburst galaxies.

High-Resolution Mid-Infrared Imaging of the Nucleus of NGC 1068

We interpret the faint optical counterpart to the mid-infrared southern extension as being due to partial obscuration by the intervening disk of the host galaxy.

High-Resolution Mid-Infrared Imaging of Infrared-luminous Galaxies

view Abstract Citations (42) References (46) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS High-Resolution Mid-Infrared Imaging of Infrared-luminous Galaxies Miles, J. W. ; Houck, J. R. ; Hayward, T. L. ; Ashby, M. L. N. Abstract We present high-resolution mid-infrared (~10 micron) imaging of a flux-limited sample of galaxies with far-infrared luminosity L_FIR_ > 10^11^ L_sun_. This work was done to investigate whether the energy generation mechanism powering these infrared-luminous galaxies comes from massive bursts of star formation or from active galactic nuclei (AGNs). Our images trace the spatial extent of the warm (~>200 K) dust, which must lie close to the heating source. The majority of the sample galaxies are extended, which implies a starburst as the source of at least part of the energy. However, most of the galaxies also contain an unresolved nucleus, so the presence of an AGN cannot be ruled out. We argue that the observations are consistent with an evolutionary model in which the infrared-luminous galaxies are seen as dusty cocoons for the birth of quasars. Publication: The Astrophysical Journal Pub Date: July 1996 DOI: 10.1086/177412 Bibcode: 1996ApJ...465..191M Keywords: INFRARED: GENERAL; GALAXIES: STARBURST; GALAXIES: NUCLEI; GALAXIES: ACTIVE full text sources ADS | data products SIMBAD (15) NED (10)

High-resolution mid-infrared imaging and astrometry of the nucleus of the Seyfert galaxy NGC 1068

The Goddard Infrared Array Camera was used to obtain a high resolution image of the nucleus of NGC 1068 at 12.4 microns. In addition, the peak emission at 12.4 microns relative to the peak of the optical continuum was determined. The distribution of the 12.4 micron emission relates to both the forbidden O III 5007A 'ionization cone' and the optical continuum emission imaged by HST. This distribution is also found to have an alignment perpendicular to the plane of a putative molecular torus. It is suggested that the extended mid-infrared emission is thermal radiation from dust in circumnuclear clouds heated by the collimated optical/UV AGN source. A portion of the unresolved 12.4 micron emission possibly originates from the torus. The infrared emission peak is found to coincide with the apex of the ionization cone, which is presumed to be the location of the torus.