The GLIMPSE (Galactic Legacy Mid-Plane Survey Extraordinaire) Point Source Catalog of 630 million mid-infrared sources toward the inner Galaxy, 10 , "l" 65 , 65 and "b" , 1, was used to determine the ...distribution of stars in Galactic longitude, l, latitude, b, and apparent magnitude, m. The counts versus longitude can be approximated by the modified Bessel function N = N sub(0)(l/l sub(0)) K sub(1)(l/l sub(0)), where l sub(0) is insensitive to limiting magnitude, band choice, and side of Galactic center: l sub(0) = 17-30 with a best-fit value in the 4.5 km band of l sub(0) = 24 c 4. Modeling the source distribution as an exponential disk yields a radial scale length of H sub(*) = 3.9 c 0.6 kpc. There is a pronounced north-south asymmetry in source counts for "l" 30, with 625% more stars in the north. For l = 10-30, there is a strong enhancement of stars of m = 11.5-13.5 mag. A linear bar passing through the Galactic center with half-length R sub(bar) = 4.4 c 0.5 kpc, tilted by h = 44 c 10 to the Sun-Galactic center line, provides the simplest interpretation of these data. We examine the possibility that enhanced source counts at l = 26-28, 31.5-34, and 306-309 are related to Galactic spiral structure. Total source counts are depressed in regions where the counts of red objects (m sub(K)-m sub(8.0) > 3) peak. In these areas, the counts are reduced by extinction due to molecular gas, high diffuse backgrounds associated with star formation, or both.
ABSTRACT
Using images from the
Spitzer
Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE), we have identified more than 300 extended 4.5 μm sources (Extended Green Objects (EGOs), for ...the common coding of the 4.5 band as green in three-color composite InfraRed Array Camera images). We present a catalog of these EGOs, including integrated flux density measurements at 3.6, 4.5, 5.8, 8.0, and 24 μm from GLIMPSE and the Multiband Imaging Photometer for
Spitzer
Galactic Plane Survey. The average angular separation between a source in our sample and the nearest
IRAS
point source is greater than 1′. The majority of EGOs are associated with infrared dark clouds (IRDCs), and where high-resolution 6.7 GHz CH
3
OH maser surveys overlap the GLIMPSE coverage, EGOs and 6.7 GHz CH
3
OH masers are strongly correlated. Extended 4.5 μm emission is thought to trace shocked molecular gas in protostellar outflows; the association of EGOs with IRDCs and 6.7 GHz CH
3
OH masers suggests that the extended 4.5 μm emission may pinpoint outflows specifically from massive protostars. The mid-IR colors of EGOs lie in regions of color–color space occupied by young protostars still embedded in infalling envelopes.
We determine and tabulate A sub( lambda )/A sub(K), the wavelength dependence of interstellar extinction, in the Galactic plane for 1.25 mu m less than or equal to lambda less than or equal to mu 8.0 ...mu m along two lines of sight: l = 42 degree and 284 degree . The first is a relatively quiescent and unremarkable region; the second contains the giant H II region RCW 49, as well as a "field" region unrelated to the cluster and nebulosity. Areas near these Galactic longitudes were imaged at J, H, and K bands by 2MASS and at 3-8 mu m by Spitzer for the GLIMPSE Legacy program. We measure the mean values of the color excess ratios (A sub( lambda ) - A sub(K))/(A sub(J) - A sub(K)) directly from the color distributions of observed stars. The extinction ratio between two of the filters, e.g., A sub(J)/A sub(K), is required to calculate A sub( lambda )/A sub(K) from those measured ratios. We use the apparent JHK magnitudes of giant stars along our two sight lines and fit the reddening as a function of magnitude (distance) to determine A sub(J)kpc super(-1), A sub(K)kpc super(-1), and A sub(J)/A sub(K). Our values of A sub( lambda )/A sub(K) show a flattening across the 3-8 mu m wavelength range, roughly consistent with the extinction measurements derived by Lutz and coworkers for the sight line toward the Galactic center.
The Bubbling Galactic Disk Churchwell, E; Povich, M. S; Allen, D ...
Astrophysical journal/The Astrophysical journal,
10/2006, Letnik:
649, Številka:
2
Journal Article
Recenzirano
Odprti dostop
A visual examination of the images from the Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE) has revealed 322 partial and closed rings that we propose represent partially or fully ...enclosed three-dimensional bubbles. We argue that the bubbles are primarily formed by hot young stars in massive star formation regions. We have found an average of about 1.5 bubbles per square degree. About 25% of the bubbles coincide with known radio H II regions, and about 13% enclose known star clusters. It appears that B4-B9 stars (too cool to produce detectable radio H II regions) probably produce about three-quarters of the bubbles in our sample, and the remainder are produced by young O-B3 stars that produce detectable radio H II regions. Some of the bubbles may be the outer edges of H II regions where PAH spectral features are excited and may not be dynamically formed by stellar winds. Only three of the bubbles are identified as known SNRs. No bubbles coincide with known planetary nebulae or W-R stars in the GLIMPSE survey area. The bubbles are small. The distribution of angular diameters peaks between 1' and 3' with over 98% having angular diameters less than 10' and 88% less than 4'. Almost 90% have shell thicknesses between 0.2 and 0.4 of their outer radii. Bubble shell thickness increases approximately linearly with shell radius. The eccentricities are rather large, peaking between 0.6 and 0.7; about 65% have eccentricities between 0.55 and 0.85.
The Spitzer Space Telescope Legacy Program SAGE-SMC allows global studies of resolved stellar populations in the SMC in a different environment than our Galaxy. Using the SAGE-SMC IRAC (3.6-8.0 mu m) ...and MIPS (24 and 70 mu m) catalogs and images combined with near-infrared (JHK sub(s)) and optical (UBVI) data, we identified a population of ~1000 intermediate- to high-mass young stellar objects (YSOs) in the SMC (three times more than previously known). Our method of identifying YSO candidates builds on the method developed for the Large Magellanic Cloud by Whitney et al. with improvements based on what we learned from our subsequent studies and techniques described in the literature. We perform (1) color-magnitude cuts based on five color-magnitude diagrams (CMDs), (2) visual inspection of multi-wavelength images, and (3) spectral energy distribution (SED) fitting with YSO models. For each YSO candidate, we use its photometry to calculate a measure of our confidence that the source is not a non-YSO contaminant, but rather a true YSO, based on the source's location in the color-magnitude space with respect to non-YSOs. We use this CMD score and the SED fitting results to define two classes of sources: high-reliability YSO candidates and possible YSO candidates. We found that, due to polycyclic aromatic hydrocarbon emission, about half of our sources have 3.6-4.5 and 4.5-5.8 colors not predicted by previous YSO models. The YSO candidates are spatially correlated with gas tracers.
One of the most significant challenges involved in efforts to understand the effects of repeated earthquake cycle activity is the computational costs of large‐scale viscoelastic earthquake cycle ...models. Computationally intensive viscoelastic codes must be evaluated at thousands of times and locations, and as a result, studies tend to adopt a few fixed rheological structures and model geometries and examine the predicted time‐dependent deformation over short (<10 years) time periods at a given depth after a large earthquake. Training a deep neural network to learn a computationally efficient representation of viscoelastic solutions, at any time, location, and for a large range of rheological structures, allows these calculations to be done quickly and reliably, with high spatial and temporal resolutions. We demonstrate that this machine learning approach accelerates viscoelastic calculations by more than 50,000%. This magnitude of acceleration will enable the modeling of geometrically complex faults over thousands of earthquake cycles across wider ranges of model parameters and at larger spatial and temporal scales than have been previously possible.
Key Points
With trained artificial neural networks, viscoelastic calculations can be accelerated by more than ~55,000%
Massive viscoelastic calculations, across large spatial and temporal scales and ranges of model parameters, may now take minutes to hours
These new representations of viscoelastic physics may lead to basic advances in the understanding of the underlying phenomenology
We report 269 mid-infrared bubbles within 10' of the Galactic center from visual inspection of the Spitzer GLIMPSE II Legacy Science program images. The surface density of bubbles is 65 deg(-2) or ...about 3 times that detected in longitudes l = 10'-65', because the inner 10' of longitude were more thoroughly searched for small bubbles. There is a gradient in the number of bubbles with longitude with an increase of about a factor of 2 from 2' to 10'; this is probably the result of several factors, including decreasing diffuse background brightness, confusion, and opacity with longitude. Bubble eccentricities are typically between 0.6 and 0.8, and > 50% show evidence for blowouts, which we suggest result from local density fluctuations of the ISM and/or anisotropic stellar winds and radiation fields. The fraction of bubbles identified with H II regions and clusters is only about half that found at l > 10'. This is largely a result of the much smaller angular diameter of bubbles cataloged in the inner Galaxy than in the outer Galaxy. At least 12% of the bubbles have morphologies suggestive of triggered star formation. Most of the bubbles that show evidence for triggered star formation in the inner Galaxy have not formed secondary bubbles; it is postulated that this may be because they are too young to have had time for this to occur.
We present a catalog of 1750 massive stars in the Large Magellanic Cloud (LMC), with accurate spectral types compiled from the literature, and a photometric catalog for a subset of 1268 of these ...stars, with the goal of exploring their infrared properties. The photometric catalog consists of stars with infrared counterparts in the Spitzer SAGE survey database, for which we present uniform photometry from 0.3 to 24 Delta *mm in the UBVIJHKs +IRAC+MIPS24 bands. The resulting infrared color-magnitude diagrams illustrate that the supergiant Be, red supergiant, and luminous blue variable (LBV) stars are among the brightest infrared point sources in the LMC, due to their intrinsic brightness, and at longer wavelengths, due to dust. We detect infrared excesses due to free-free emission among ~900 OB stars, which correlate with luminosity class. We confirm the presence of dust around 10 supergiant Be stars, finding the shape of their spectral energy distributions (SEDs) to be very similar, in contrast to the variety of SED shapes among the spectrally variable LBVs. The similar luminosities of Be supergiants (log L/L >= 4) and the rare, dusty progenitors of the new class of optical transients (e.g., SN 2008S and NGC 300 OT), plus the fact that dust is present in both types of objects, suggests a common origin for them. We find the infrared colors for Wolf-Rayet stars to be independent of spectral type and their SEDs to be flatter than what models predict. The results of this study provide the first comprehensive roadmap for interpreting luminous, massive, resolved stellar populations in nearby galaxies at infrared wavelengths.
A systematic and automated search of the extensive GLIMPSE mid-infrared survey data of the inner Galaxy was carried out to uncover new star clusters. This search has yielded 59 new clusters. Using ...our automated search algorithm, these clusters were identified as significant localized overdensities in the GLIMPSE point-source catalog (GLMC) and archive (GLMA). Subsequent visual inspection of the GLIMPSE image mosaics confirmed the existence of these clusters plus an additional 33 heavily embedded clusters missed by our detection algorithm, for a total of 92 newly discovered clusters. These previously uncataloged clusters range in type from heavily embedded to fully exposed clusters. More than half of the clusters have memberships exceeding 35 stars, and nearly all the clusters have diameters of 3' or less. The Galactic latitude distribution of the clusters reveals that the majority are concentrated toward the Galactic midplane. There is an asymmetry in the number of clusters located above and below the midplane, with more clusters detected below the midplane. We also observe an asymmetry in the number of clusters detected in the northern and southern halves of the Galaxy, with more than twice as many clusters detected in the south.
We present an analysis of wind-blown, parsec-sized, mid-infrared bubbles and associated star formation using the GLIMPSE IRAC, MIPSGAL MIPS, and MAGPIS VLA surveys. Three bubbles from the Churchwell ...et al. catalog were selected. The relative distribution of the ionized gas (based on 20 cm emission), PAH emission (based on 8 mum, 5.8 mum, and lack of 4.5 mum emission), and hot dust (24 mum emission) is compared. At the center of each bubble there is a region containing ionized gas and hot dust surrounded by PAHs. We identify the likely source(s) of the stellar wind and ionizing flux producing each bubble based on SED fitting to numerical hot stellar photosphere models. Candidate YSOs are also identified using SED fitting, including several sites of possible triggered star formation.
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