High Resolution Extinction Map Research Articles

Spatial Variations of Dust Opacity and Grain Growth in Dark Clouds: L1689, L1709, and L1712

The far-infrared (FIR) opacity of dust in dark clouds within the Ophiuchus molecular cloud is investigated through multiwavelength infrared observations from UKIDSS, Spitzer, and Herschel. Employing the infrared color excess technique with both near-infrared and mid-infrared photometric data, a high-resolution extinction map in the K band (A K ) is constructed for three dark clouds: L1689, L1709, and L1712. The derived extinction map has a resolution of 1′ and reaches a depth of A K ∼ 3 mag. The FIR optical depths τ 250 at a reference wavelength of 250 μm are obtained by fitting the Herschel PACS and SPIRE continuum data at 100, 160, 250, 350, and 500 μm using a modified blackbody model. The average dust opacity per unit gas mass at 250 μm, r κ 250, is determined through a pixel-by-pixel correlation of τ 250 with A K , yielding a value of approximately 0.09 cm2 g−1, which is about 2–3 times higher than the typical value in the diffuse interstellar medium. Additionally, an independent analysis across 16 subregions within the Ophiuchus cloud indicates spatial variations in dust opacity, with values ranging from 0.07 to 0.12 cm2 g−1. Although the observed trend of increasing dust opacity with higher extinction implies grain growth, our findings indicate that rapid grain growth has clearly not yet occurred in the dark clouds studied in this work.

High-resolution Extinction Map in the Direction of the Strongly Obscured Bulge Fossil Fragment Liller 1*

Abstract We used optical images acquired with the Wide Field Camera of the Advanced Camera for Surveys on board the Hubble Space Telescope and near-infrared data from Gemini Multi-conjugate Adaptive Optics System (GeMS)/Gemini South Adaptive Optics Imager (GSAOI) to construct a high-resolution extinction map in the direction of the bulge stellar system Liller 1. In spite of its appearance of a globular cluster, Liller 1 has been recently found to harbor two stellar populations with remarkably different ages, and it is the second complex stellar system with similar properties (after Terzan 5) discovered in the bulge, thus defining a new class of objects: the Bulge Fossil Fragments. Because of its location in the inner bulge of the Milky Way, very close to the Galactic plane, Liller 1 is strongly affected by large and variable extinction. The simultaneous study of both the optical and the near-infrared color–magnitude diagrams revealed that the extinction coefficient R V in the direction of Liller 1 has a much smaller value than commonly assumed for diffuse interstellar medium (R V = 2.5, instead of 3.1), in agreement with previous findings along different light paths to the Galactic bulge. The derived differential reddening map has a spatial resolution ranging from 1″ to 3″ over a field of view of about 90″ × 90″. We found that the absorption clouds show patchy substructures with extinction variations as large as δE(B − V) ∼ 0.9 mag.

High-resolution Extinction Map in the Direction of the Bulge Globular Cluster NGC 6440*

Abstract We used optical images acquired with the UVIS channel of the Wide Field Camera 3 on board the Hubble Space Telescope to construct the first high-resolution extinction map in the direction of NGC 6440, a globular cluster located in the bulge of our Galaxy. The map has a spatial resolution of 0.″5 over a rectangular region of about 160″ × 240″ around the cluster center, with the long side in the northwest/southeast direction. We found that the absorption clouds show patchy and filamentary substructures with extinction variations as large as δE(B − V) ∼0.5 mag. We also performed a first-order proper motion analysis to distinguish cluster members from field interlopers. After the field decontamination and the differential reddening correction, the cluster sequences in the color–magnitude diagram appear much better defined, providing the best optical color–magnitude diagram so far available for this cluster.

Structure and fragmentation of a high line-mass filament: Nessie

Context. An increasing number of hundred-parsec-scale, high line-mass filaments are being detected in the Galaxy. Their evolutionary path, including fragmentation towards star formation, is virtually unknown. Aims. We characterize the fragmentation within the hundred-parsec-scale, high line-mass Nessie filament, covering size-scales in the range ~0.1–100 pc. We also connect the small-scale fragments to the star-forming potential of the cloud. Methods. We combine near-infrared data from the VISTA Variables in the Via Lactea (VVV) survey with mid-infrared Spitzer/GLIMPSE data to derive a high-resolution dust extinction map for Nessie. We then apply a wavelet decomposition technique on the map to analyze the fragmentation characteristics of the cloud. The characteristics are then compared with predictions from gravitational fragmentation models. We compare the detected objects to those identified at a resolution approximately ten times lower from ATLASGAL 870 μm dust emission data. Results. We present a high-resolution extinction map of Nessie (2″ full-width-half-max, FWHM, corresponding to 0.03 pc). We estimate the mean line mass of Nessie to be ~627 M⊙ pc−1 and the distance to be ~3.5 kpc. We find that Nessie shows fragmentation at multiple size scales. The median nearest-neighbor separations of the fragments at all scales are within a factor of two of the Jeans’ length at that scale. However, the relationship between the mean densities of the fragments and their separations is significantly shallower than expected for Jeans’ fragmentation. The relationship is similar to the one predicted for a filament that exhibits a Larson-like scaling between size-scale and velocity dispersion; such a scaling may result from turbulent support. Based on the number of young stellar objects (YSOs) in the cloud, we estimate that the star formation rate (SFR) of Nessie is ~371 M⊙ Myr−1; similar values result if using the number of dense cores, or the amount of dense gas, as the proxy of star formation. The star formation efficiency is 0.017. These numbers indicate that by its star-forming content, Nessie is comparable to the Solar neighborhood giant molecular clouds like Orion A.

HIGH-RESOLUTION REDDENING MAP IN THE DIRECTION OF THE STELLAR SYSTEM TERZAN 5

We have used optical images acquired with the Hubble Space Telescope to construct the first high-resolution extinction map in the direction of Terzan 5, a peculiar stellar system in the inner bulge of our Galaxy. The map has a spatial resolution of 8" X 8", over a total FoV of 200" X 200". The absorption clouds show a patchy structure on a typical scale of 20" and extinction variations as large as delta E(B-V) = 0.67 mag, especially in the direction of the center of the system. These correspond to an absolute color excess ranging from E(B-V)=2.15 mag, up to 2.82 mag. After the correction for differential reddening, two distinct red giant branches become clearly visible in the color magnitude diagram of Terzan 5 and they well correspond to the two sub-populations with different iron abundances recently discovered in this system.

The Dynamical State of the Starless Dense Core FeSt 1‐457: A Pulsating Globule?

High-resolution molecular line observations of CS (J = 2 → 1), HCO+ (J = 1 → 0), C18O (J = 1 → 0), C18O (J = 2 → 1), and N2H+ (J = 1 → 0) were obtained toward the starless globule FeSt 1-457 in order to investigate its kinematics and chemistry. The HCO+ and CS spectra show clear self-reversed and asymmetric profiles across the face of the globule. The sense of the observed asymmetry is indicative of the global presence of expansion motions in the outer layers of the globule. These motions appear to be subsonic and significantly below the escape velocity of the globule. Comparison of our observations with near-infrared extinction data indicate that the globule is gravitationally bound. Taken together, these considerations lead us to suggest that the observed expansion has its origin in an oscillatory motion of the outer layers of the globule, which itself is likely in a quasi-stable state near hydrostatic equilibrium. Analysis of the observed line widths of C18O and N2H+ (J = 1 → 0) confirm that thermal pressure is the dominant component of the cloud's internal support. A simple calculation suggests that the dominant mode of pulsation would be an l = 2 mode with a period of ~3 × 105 yr. Deformation of the globule due to the large amplitude l = 2 oscillation may be responsible for the double-peaked structure of the core detected in high-resolution extinction maps. Detailed comparison of the molecular-line observations and extinction data provides evidence for significant depletion of C18O and perhaps HCO+, while N2H+ (J = 1 → 0) may be undepleted to a cloud depth of ~40 mag of visual extinction.

2MASS wide field extinction maps

We present a 8 deg x 6 deg, high resolution extinction map of the Pipe nebula using 4.5 million stars from the Two Micron All Sky Survey (2MASS) point source catalog. The use of NICER, a robust and optimal technique to map the dust column density, allows us to detect a Av = 0.5 mag extinction at a 3-sigma level with a 1 arcmin resolution. We find for the Pipe nebula a normal reddening law, E(J-H) = (1.85 +/- 0.15) E(H-K). We measure the cloud distance using Hipparchos and Tycho parallaxes, and obtain ~130 pc. This, together with the total estimated mass, 10^4 Msun, makes the Pipe the closest massive cloud complex to Earth. We compare the NICER extinction map to the NANTEN 12CO observations and derive with unprecedented accuracy the relationship between the near-infrared extinction and the 12CO column density and hence (indirectly) the 12CO X-factor, that we estimate to be 2.91 10^20 cm^-2 K^-1 km^-1 s in the range Av <- [0.9, 5.4] mag. We identify ~1500 OH/IR stars located within the Galactic bulge in the direction of the Pipe field. This represents a significant increase of the known numbers of such stars in the Galaxy. Our analysis confirms the power and simplicity of the color excess technique to study molecular clouds. The comparison with the NANTEN 12CO data corroborates the insensitivity of CO observations to low column densities (up to approximately 2 mag in Av), and shows also an irreducible uncertainty in the dust-CO correlation of about 1 mag of visual extinction.

The visibility of the Galactic bulge in optical surveys. Application to the Gaia mission

The bulge is a region of the Galaxy which is of tremendous interest for understanding Galaxy formation. However, measuring photometry and kinematics in it raises several inherent issues, like high extinction in the visible and severe crowding. Here we attempt to estimate the problem of the visibility of the bulge at optical wavelengths, where large CCD mosaics allow to easily cover wide regions from the ground, and where future astrometric missions are planned. Assuming the Besancon Galaxy model and high resolution extinction maps, we estimate the stellar density as a function of longitude, latitude and apparent magnitude and we deduce the possibility of reaching and measuring bulge stars. The method is applied to three Gaia instruments, the BBP and MBP photometers, and the RVS spectrograph. We conclude that, while in the BBP most of the bulge will be accessible, in the MBP there will be a small but significant number of regions where bulge stars will be detected and accurately measured in crowded fields. Assuming that the RVS spectra may be extracted in moderately crowded fields, the bulge will be accessible in most regions apart from the strongly absorbed inner plane regions, because of high extinction, and in low extinction windows like the Baades's window where the crowding is too severe.