Mid-infrared Extinction Law Research Articles

Probing the Distinct Extinction Law of the Pillars of Creation in M16 with JWST

Investigating the extinction law in regions of high dust extinction, such as the Pillars of Creation within the M16 region, is crucial for understanding the densest parts of the interstellar medium (ISM). In this study, we utilize observations from the Near-Infrared Camera and the Mid-Infrared Instrument onboard the James Webb Space Telescope (JWST) to analyze the color-excess ratios E(F090W − λ)/E(F090W − F200W) across a wavelength range of 0.9–7.7 μm. Our method involves performing linear regression on color–color diagrams to derive these ratios. The enhanced detection capabilities of JWST data allow us to probe the distinct extinction law to the densest regions in M16 corresponding to an extinction depth up to A V ∼ 60 mag. Remarkably, the resultant color-excess ratio curve exhibits a flatter profile than predicted by typical dust extinction models with R V = 5.5 for dense ISM environments. Moreover, we observe that the mid-infrared extinction law diverges from the near-infrared power law, showing a tendency for the slope to flatten as the wavelength increases. These findings have significant implications for our understanding of the dust properties in dense interstellar environments.

The Ultraviolet to Mid-infrared Extinction Law of the Taurus Molecular Cloud Based on the Gaia DR3, GALEX, APASS, Pan-STARRS1, 2MASS, and WISE Surveys

Interstellar-dust extinction law is essential for interpreting observations. In this work, we investigate the ultraviolet (UV)–mid-infrared (IR) extinction law of the Taurus molecular cloud and its possible variations. We select 504,988 dwarf stars (4200 K ≤ T eff ≤ 8000 K) and 4757 giant stars (4200 K ≤ T eff ≤ 5200 K) based on the stellar parameters of Gaia DR3 as tracers. We establish the T eff–intrinsic color relations and determine the intrinsic color indices and color excesses for different types of stars. In the determination of color excess ratios (CERs), we analyze and correct the curvature of CERs and derive the UV–mid-IR CERs of 16 bands. We consider different effective wavelengths for different types of stars when converting CERs to relative extinction and obtain the extinction law with a better wavelength resolution. In addition, we analyze the possible regional variation of extinction law and derive the average extinction law of R V = 3.13 ± 0.32 for the Taurus molecular cloud. Only 0.9% of subregions have deviations >3σ, indicating limited regional variation in the extinction law. We also discuss the effect of Gaia T eff overestimation on the determination of the Taurus extinction law and find that the effect is negligible.

The Optical to Mid-infrared Extinction Law Based on the APOGEE, Gaia DR2, Pan-STARRS1, SDSS, APASS, 2MASS, and WISE Surveys

Abstract A precise interstellar dust extinction law is critically important to interpret observations. There are two indicators of extinction: the color excess ratio (CER) and the relative extinction. Compared to the CER, the wavelength-dependent relative extinction is more challenging to be determined. In this work, we combine spectroscopic, astrometric, and photometric data to derive high-precision CERs and relative extinction from optical to mid-infrared (IR) bands. A group of 61,111 red clump (RC) stars are selected as tracers by stellar parameters from the Apache Point Observatory Galaxy Evolution Experiment survey. The multiband photometric data are collected from Gaia, APASS, Sloan Digital Sky Survey, Pan-STARRS1, Two Micron All Sky Survey, and Wide-field Infrared Survey Explorer surveys. For the first time, we calibrate the curvature of CERs in determining CERs E(λ − G RP)/E(G BP − G RP) from color excess–color excess diagrams. Through elaborate uncertainty analysis, we conclude that the precision of our CERs is significantly improved (σ < 0.015). With parallaxes from Gaia DR2, we calculate the relative extinction / for 5051 RC stars. By combining the CERs with the / , the optical–mid-IR extinction A λ / has been determined in a total of 21 bands. Given no bias toward any specific environment, our extinction law represents the average extinction law with the total-to-selective extinction ratio R V = 3.16 ± 0.15. Our observed extinction law supports an adjustment in parameters of the CCM R V = 3.1 curve, together with the near-IR (NIR) power-law index α = 2.07 ± 0.03. The relative extinction values of the Hubble Space Telescope (HST) and the James Webb Space Telescope (JWST) NIR bandpasses are predicted in 2.5% precision. As the observed reddening/extinction tracks are curved, the curvature correction needs to be considered when applying extinction correction.

An Extremely Low Mid-infrared Extinction Law toward the Galactic Center and 4% Distance Precision to 55 Classical Cepheids

Abstract Distances and extinction values are usually degenerate. To refine the distance to the general Galactic Center region, a carefully determined extinction law (taking into account the prevailing systematic errors) is urgently needed. We collected data for 55 classical Cepheids projected toward the Galactic Center region to derive the near- to mid-infrared extinction law using three different approaches. The relative extinction values obtained are , , , and . We also calculated the corresponding systematic errors. Compared with previous work, we report an extremely low and steep mid-infrared extinction law. Using a seven-passband “optimal distance” method, we improve the mean distance precision to our sample of 55 Cepheids to 4%. Based on four confirmed Galactic Center Cepheids, a solar Galactocentric distance of R 0 = 8.10 ± 0.19 ± 0.22 kpc is determined, featuring an uncertainty that is close to the limiting distance accuracy (2.8%) for Galactic Center Cepheids.

The Optical–Mid-infrared Extinction Law of the l = 165° Sightline in the Galactic Plane: Diversity of the Extinction Law in the Diffuse Interstellar Medium

Abstract Understanding the effects of dust extinction is important to properly interpret observations. The optical total-to-selective extinction ratio, , is widely used to describe extinction variations in ultraviolet and optical bands. Since the extinction curve adequately represents the average extinction law of diffuse regions in the Milky Way, it is commonly used to correct observational measurements along sightlines toward diffuse regions in the interstellar medium. However, the value may vary even along different diffuse interstellar medium sightlines. In this paper, we investigate the optical–mid-infrared (mid-IR) extinction law toward a very diffuse region at in the Galactic plane, which was selected based on a CO emission map. Adopting red clump stars as extinction tracers, we determine the optical–mid-IR extinction law for our diffuse region in two APASS bands ( ), three XSTPS-GAC bands ( ), three 2MASS bands ( ), and two WISE bands ( ). Specifically, 18 red clump stars were selected from the APOGEE–RC catalog based on spectroscopic data in order to explore the diversity of the extinction law. We find that the optical extinction curves exhibit appreciable diversity. The corresponding ranges from 1.7 to 3.8, while the mean value of 2.8 is consistent with the widely adopted average value of 3.1 for Galactic diffuse clouds. There is no apparent correlation between value and color excess in the range of interest, from 0.2 to 0.6 mag, or with specific visual extinction per kiloparsec, .

Small Variation of the NIR and MIR Interstellar Extinction Laws

AbstractUsing the data from APOGEE, WISE, and GLIMPSE, we explored the variation of the near-infrared (NIR) and mid-infrared (MIR) interstellar extinction laws of the Milky Way. We derived the IR extinction laws towards a number of different sightlines, including 24 bins along Galactic latitude (b) and 592 plates observed by APOGEE. Our results indicate that E(J-H)/E(J-K) show only subtle variation along b, Galactic longitude (l), or the depth of E(J-K). This suggests that the NIR extinction law can be considered as universal. Similarly, E(K-W1, W2, W3, [3.6], [4.5], [5.8], [8.0])/E(J-K) also show only small variation along b, l, or the extinction depth. The MIR extinction curve is flat, indicating that the MIR extinction law is likely universal.

The mid-infrared extinction law in the darkest cores of the Pipe Nebula

Context. The properties of dust grains, in particular their size distribution, are expected to differ from the interstellar medium to the high-density regions within molecular clouds. Aims. We measure the mid-infrared extinction law produced by dense material in molecular cloud cores. Since the extinction at these wavelengths is caused by dust, the extinction law in cores should depart from that found in low-density environments if the dust grains have different properties. Methods. We use the unbiased LINES method to measure the slope of the reddening vectors in color-color diagrams. We derive the mid-infrared extinction law toward the dense cores B59 and FeSt 1-457 in the Pipe Nebula over a range of visual extinction between 10 and 50 magnitudes, using a combination of Spitzer/IRAC, and ESO NTT/VLT data. Results. The mid-infrared extinction law in both cores departs significantly from a power-law between 3.6 and 8 micron, suggesting that these cores contain dust with a considerable fraction of large dust grains. We find no evidence for a dependence of the extinction law with column density up to 50 magnitudes of visual extinction in these cores, and no evidence for a variation between our result and those for other clouds at lower column densities reported elsewhere in the literature. This suggests that either large grains are present even in low column density regions, or that the existing dust models need to be revised at mid-infrared wavelengths. We find a small but significant difference in the extinction law of the two cores, that we tentatively associate with the onset of star formation in B59.

The Mid-IR Extinction Law in the LMC

AbstractThe mid-infrared (MIR) extinction law in the Large Magellanic Cloud (LMC) at four IRAC bands is derived using the data of the Spitzer/SAGE Program. The derived mean extinctions are A[3.6]/AKs = 0.68±0.03, A[4.5]/AKs = 0.97±0.03, A[5.8]/AKs = 0.54±0.04, and A[8.0]/AKs = 0.58±0.07. The results show that: (1) The extinctions at [3.6], [5.8] and [8.0] of the LMC consist a flat curve, similar to that of the Milky Way (MW) predicted by the interstellar grain model at Rv = 5.5; (2) The extinction at [4.5] is clearly higher than the other three bands, which may be caused by the additional absorption of the 4.27μm CO2 ice and/or the 4.67μm CO ice in the LMC molecular clouds; (3) As far as individual sightlines are concerned, the MIR interstellar extinction law Aλ/AKs in the LMC varies with sightlines as the MW does.

DEEPJHKsANDSPITZERIMAGING OF FOUR ISOLATED MOLECULAR CLOUD CORES

We present observations in eight wavebands from 1.25-24 microns of four dense cores: L204C-2, L1152, L1155C-2, and L1228. Our goals are to study the YSO population of these cores and to measure the mid-infrared extinction law. With our combined near-infrared and Spitzer photometry, we classify each source in the cores as, among other things, background stars, galaxies, or embedded young stellar objects (YSOs). L1152 contains three YSOs and L1228 has seven, but neither L204C-2 nor L1155C-2 appear to contain any YSOs. We estimate an upper limit of 7x10^-5 to 5x10^-4 solar luminosities for any undiscovered YSOs in our cores. We also compute the line-of-sight extinction law towards each background star. These measurements are averaged spatially, to create chi-squared maps of the changes in the mid-infrared extinction law throughout our cores, and also in different ranges of extinction. From the chi-squared maps we identify two small regions in L1152 and L1228 where the outflows in those cores appear to be destroying the larger dust grains, thus altering the extinction law in those regions. On average, however, our extinction law is relatively flat from 3.6 to 24 microns for all ranges of extinction and in all four cores. From 3.6 to 8 microns this law is consistent with a dust model that includes larger dust grains than the diffuse interstellar medium, which suggests grain growth has occurred in our cores. At 24 microns, our extinction law is 2-4 times higher than predicted by dust models. However, it is similar to other empirical measurements.

THE MID-INFRARED EXTINCTION LAW IN THE OPHIUCHUS, PERSEUS, AND SERPENS MOLECULAR CLOUDS

We compute the mid-infrared extinction law from 3.6-24 microns in three molecular clouds: Ophiuchus, Perseus, and Serpens, by combining data from the Cores to Disks Spitzer Legacy Science program with deep JHKs imaging. Using a new technique, we are able to calculate the line-of-sight extinction law towards each background star in our fields. With these line-of-sight measurements, we create, for the first time, maps of the chi-squared deviation of the data from two extinction law models. Because our chi-squared maps have the same spatial resolution as our extinction maps, we can directly observe the changing extinction law as a function of the total column density. In the Spitzer IRAC bands, 3.6-8 microns, we see evidence for grain growth. Below $A_{K_s} = 0.5$, our extinction law is well-fit by the Weingartner & Draine (2001) $R_V = 3.1$ diffuse interstellar medium dust model. As the extinction increases, our law gradually flattens, and for $A_{K_s} >= 1$, the data are more consistent with the Weingartner & Draine $R_V = 5.5$ model that uses larger maximum dust grain sizes. At 24 microns, our extinction law is 2-4 times higher than the values predicted by theoretical dust models, but is more consistent with the observational results of Flaherty et al. (2007). Lastly, from our chi-squared maps we identify a region in Perseus where the IRAC extinction law is anomalously high considering its column density. A steeper near-infrared extinction law than the one we have assumed may partially explain the IRAC extinction law in this region.

3.2. ISO spectroscopy of the Galactic center and starburst nuclei

Since its launch in November 1995, the Infrared Space Observatory ISO has converted mid-infrared spectroscopy into a mature tool. Due to its proximity, brightness, and the wealth of complementary information, the center of our Galaxy remains a unique testbed for studies of galactic nuclei. A first analysis of the 2.4-45μm spectrum obtained with ISO-SWS (Fig. 1) has been presented by Lutz et al. (1996a). One of the surprises is a determination of the mid-infrared extinction law from comparison of the Galactic center hydrogen recombination line fluxes and case B expectations: The extinction law clearly lacks the deep minimum near 7μm expected for standard graphite/silicate mixes. External galaxies are less close to the ideal ‘screen’ case and cannot provide the detail of the GC recombination line spectrum needed to derive an extinction law. However, simple ratios of the strongest recombination lines are inconsistent with a classical extinction law and any dust configuration.