Galactic Legacy Infrared Mid-Plane Survey Extraordinaire Research Articles

Imaging of four Galactic supernova remnants in the mid-infrared, and their interaction with the interstellar medium

We provide mid-infrared (MIR) imaging, photometry and profiles for the Galactic supernova remnants (SNRs) G001.0-00.1, G355.9-02.5, G355.6-00.0, and W28 based upon data deriving for the Galactic Legacy Infrared Midplane Survey Extraordinaire (GLIMPSE). All of the sources show evidence for interaction with the interstellar medium (ISM), leading to curved frontal structures and apparent voids in the ISM. An analysis of the spectral energy distributions (SEDs) of Class I young stellar objects (YSOs) within the north-westerly interaction region of W28, and of the density of stars within the borders of the SNR, suggests that many of them may have been triggered by the SN event. 2-D radiative transfer modelling permits us to constrain the physical parameters of the sources. It is also noted that the location of Class I YSOs about the perimeter of G001.0-00.1, and close to frontal arcs associated with SNR G355.9-02.5, suggests that star formation may have been triggered by these SNRs as well. Finally, it is found that the MIR colours of the frontal structures appear consistent with shock excitation of the v = 0->0 transitions of H2, although it is conceivable that emission by polycyclic aromatic hydrocarbons (PAHs) may also play a role. Where the latter mechanism is relevant, then it is possible that emission derives from the shattering of larger grains in frontal regions, leading to increased volume densities of PAH carrying grains.

Unveiling the Unseen: The Mid-IR Galactic Disk

AbstractThe Spitzer mid-infrared (MIR) surveys, Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE) and MIPSGAL have revealed a new view of the disk of the Milky Way. Hallmarks of the Galactic disk at MIR wavelengths with spatial resolution <2″ are bubbles/HII regions, infrared dark clouds, young stellar objects (YSOs)/star formation regions, diffuse dust and extended polycyclic aromatic hydrocarbons (PAHs), and more than 100 million publically available archived stars with measured flux densities at 7 wavelengths and positions accurate to 0.1″. At mid-IR wavelengths, the cool components in the Galaxy are preferentially bright and highlight physical processes that are not obvious at other wavelength regimes.

THE FREQUENCY OF WARM DEBRIS DISKS AND TRANSITION DISKS IN A COMPLETE SAMPLE OF INTERMEDIATE-MASS GLIMPSE STARS: PLACING CONSTRAINTS ON DISK LIFETIMES

The incidence of dusty debris disks around low- and intermediate-mass stars has been investigated numerous times in order to understand the early stages of planet formation. Most notably, the Infrared Astronomical Satellite (IRAS) mission observed the entire sky at mid- and far-infrared (IR) wavelengths, identifying the first debris disk systems, but was unable to detect a statistically significant sample of warm debris disks due to its limited sensitivity at 12 μm. Using Tycho-2 Spectral Catalog stars previously shown to exhibit 8 μm mid-IR circumstellar excesses confirmed at 24 μm in the Spitzer Galactic Legacy Infrared MidPlane Survey Extraordinaire (GLIMPSE) survey, we investigate the frequency of mid-IR excesses among intermediate-mass (2-4 M ☉) stars in a complete volume-limited sample. Our study of 338 stars is four times larger than a complete sample of 12 μm sources from the IRAS Point Source Catalog. We find that 0.3% ± 0.3% of intermediate-mass stars exhibit a signature of a possible terrestrial-temperature debris disks at wavelengths of 8 μm and greater. We also find that 1.2% ± 0.6% of intermediate-mass stars exhibit evidence for circumstellar disks undergoing inner disk clearing, i.e., candidate transition disk systems. Using stellar lifetimes and the frequency of transition and primordial disks within a given spectral type, we find that pre-main-sequence disks around intermediate-mass stars dissipate in 5 ± 2 Myr, consistent with other studies.

Observations of 58 compact H ii regions at mid-infrared wavelengths

We present 3.6, 4.5, 5.8 and 8.0 μm photometry and mapping for 58 compact H II regions identified using the Spitzer Galactic Legacy Infrared Midplane Survey Extraordinaire (GLIMPSE). These are used to investigate trends in the colours, magnitudes and structures of the sources, together with spatial variations in flux ratio. It is concluded that most of the sources are remarkably similar, and have comparable variations in flux ratio as a function of position within the shells, together with very narrowly defined ranges of colour index. Systematic variations of surface brightnesses S with harmonic mean size Θ(HARM) also imply that S oc R -β , where β > 0.4; a result which may suggest that the widths of the emission zones are either more or less invariant, or increase with increasing source size. We note that the variation in longer wave flux ratios may imply the presence of polycyclic aromatic hydrocarbon (PAH) emission within large photodissociative regimes, evidence for which is also noted in colour imaging of the sources. The most intense 5.8 and 8 μm emission appears to be concentrated close to the interior ionization fronts, however, where fluorescent excitation of the PAH molecules and the number densities for the grain carriers are both likely to be at their greatest.

Interstellar Weather Vanes: GLIMPSE Mid‐Infrared Stellar Wind Bow Shocks in M17 and RCW 49

We report the discovery of six infrared stellar wind bow shocks in the Galactic massive star formation regions M17 and RCW 49 from Spitzer GLIMPSE (Galactic Legacy Infrared Mid-Plane Survey Extraordinaire) images. The Infrared Array Camera (IRAC) on the Spitzer Space Telescope clearly resolves the arc-shaped emission produced by the bow shocks. We combine Two Micron All-Sky Survey (2MASS), Spitzer, MSX, and IRAS observations to obtain the spectral energy distributions (SEDs) of the bow shocks and their individual driving stars. We use the stellar SEDs to estimate the spectral types of the three newly identified O stars in RCW 49 and one previously undiscovered O star in M17. One of the bow shocks in RCW 49 reveals the presence of a large-scale flow of gas escaping the H II region at a few 102 km s−1. Radiation transfer modeling of the steep rise in the SED of this bow shock toward longer mid-infrared wavelengths indicates that the emission is coming principally from dust heated by the star driving the shock. The other five bow shocks occur where the stellar winds of O stars sweep up dust in the expanding H II regions.

A CATALOG OF EXTENDED GREEN OBJECTS IN THE GLIMPSE SURVEY: A NEW SAMPLE OF MASSIVE YOUNG STELLAR OBJECT OUTFLOW CANDIDATES

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 CH3OH maser surveys overlap the GLIMPSE coverage, EGOs and 6.7 GHz CH3OH 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 CH3OH 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.

INTRINSICALLY RED SOURCES OBSERVED BYSPITZERIN THE GALACTIC MIDPLANE

We present a highly reliable flux-limited census of 18,949 point sources in the Galactic midplane that have intrinsically red mid-infrared colors. These sources were selected from the Spitzer Space Telescope Galactic Legacy Infrared Midplane Survey Extraordinaire (GLIMPSE) I and II surveys of 274 deg2 of the Galactic midplane, and consist mostly of high- and intermediate-mass young stellar objects (YSOs) and asymptotic giant branch (AGB) stars. The selection criteria were carefully chosen to minimize the effects of position-dependent sensitivity, saturation, and confusion. The distribution of sources on the sky and their location in the Infrared Array Camera and the Multiband Image Photometer for Spitzer 24 μm color-magnitude and color-color space are presented. Using this large sample, we find that YSOs and AGB stars can be mostly separated by simple color-magnitude selection criteria into approximately 50%-70% of YSOs and 30%-50% of AGB stars. Planetary nebulae and background galaxies together represent at most 2%-3% of all the red sources. 1004 red sources in the GLIMPSE II region, mostly AGB stars with high mass-loss rates, show significant (≥0.3 mag) variability at 4.5 and/or 8.0 μm. With over 11,000 likely YSOs and over 7000 likely AGB stars, this is to date the largest uniform census of AGB stars and high- and intermediate-mass YSOs in the Milky Way Galaxy.

DISCOVERY OF HIGHLY OBSCURED GALAXIES IN THE ZONE OF AVOIDANCE

We report the discovery of 25 previously unknown galaxies in the zone of avoidance (ZoA). Our systematic search for extended extragalactic sources in the Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE) and MIPS Galactic Plane Survey (MIPSGAL) mid-infrared surveys of the Galactic plane has revealed two overdensities of these sources, located around l ~ 47° and 55° and |b| ≾ 1° in the Sagitta-Aquila region. These overdensities are consistent with the local large-scale structure found at similar Galactic longitude and extending from |b| ~ 4 to 40°. We show that the infrared spectral energy distribution of these sources is indeed consistent with those of normal galaxies. Photometric estimates of their redshift indicate that the majority of these galaxies are found in the redshift range z ≃ 0.01-0.05, with one source located at z ≃ 0.07. Comparison with known sources in the local universe reveals that these galaxies are located at similar overdensities in redshift space. These new galaxies are the first evidence of a bridge linking the large-scale structure between both sides of the Galactic plane at very low Galactic latitude and clearly demonstrate the feasibility of detecting galaxies in the ZoA using mid-to-far infrared surveys.

Planetary Nebulae Detected in theSpitzer Space TelescopeGLIMPSE Legacy Survey

We detected and imaged 30 planetary nebulae in the Sptizer Space Telescope Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE) survey. The distribution of warm dust is clearly shown in these images. From the derived fluxes at the 3.6, 4.5, 5.8, and 8.0 μm bands we are able to separate the photospheric, nebular, and dust emission components in the nebulae.

Embedded stellar populations towards young massive star formation regions – I. G305.2+0.2

We present deep, wide field J, H and Ks images taken with Infrared Imager and Spectrometer 2 (IRIS2) on the Anglo-Australian Telescope, towards the massive star formation region G305.2+0.2. Combined with 3.6, 4.5, 5.8 and 8.0 μm data from the Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE) survey on the Spitzer Space Telescope, we investigate the properties of the embedded stellar populations. After removing contamination from foreground stars, we separate the sources based on their infrared (IR) colour. Strong extended emission in the GLIMPSE images hampers investigation of the most embedded sources towards the known sites of massive star formation. However, we find a sizeable population of IR excess sources in the surrounding region free from these completeness effects. Investigation reveals the recent star formation activity in the region is more widespread than previously known. Stellar density plots show the embedded cluster in the region, G305.24+0.204, is offset from the dust emission. We discuss the effect of this cluster on the surrounding area and argue it may have played a role in triggering sites of star formation within the region. Finally, we investigate the distribution of IR excess sources towards the cluster, in particular their apparent lack towards the centre compared with its immediate environs.

The Bubbling Galactic Disk

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.

Infrared properties of ultracompact H II regions in the Galaxy and the LMC

AbstractWe report the preliminary results of the study on the infrared properties of ultracompact (UC) H II regions in our Galaxy and in the Large Magellanic Cloud (LMC) based on the GLIMPSE (the Galactic Legacy Infrared Mid-Plane Survey Extraordinaire) and SAGE (Surveying the Agents of a Galaxy's Evolution) data, respectively. We found that ~60% of the Galactic UC H II regions do not have IR counterparts. Large extinction and very strong stellar winds evacuating H II regions from dust may explain this result. The same effect is observed in the LMC. One of the goals of this research is to develop a means of identifying UC H IIs based on their mid-IR properties, e.g. positions on color-color and color-magnitude plots and/or shape of spectral energy distributions. GLIMPSE showed that bow shocks, protostellar jets/outflows, and bubbles are common phenomena in massive star formation regions (MSFRs).

Planetary nebulae in the GLIMPSE survey

We report the observations of planetary nebulae in the Spitzer Space Telescope Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE) survey. The distribution of warm dust is clearly shown in these images.

INFRARED SUPERNOVA REMNANTS IN THE SPITZER GLIMPSE FIELD

We have searched for infrared emission from supernova remnants (SNRs) included in the Spitzer Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE) field. At the positions of 100 known SNRs, we made 3.6, 4.5, 5.8, and 8.0 um band images covering the radio continuum emitting area of each remnant. In-depth examinations of four band images based on the radio continuum images of SNRs result in the identification of sixteen infrared SNRs in the GLIMPSE field. Eight SNRs show distinct infrared emission in nearly all the four bands, and the other eight SNRs are visible in more than one band. We present four band images for all identified SNRs, and RGB-color images for the first eight SNRs. These images are the first high resolution (<2") images with comparative resolution of the radio continuum for SNRs detected in the mid-infrared region. The images typically show filamentary emission along the radio enhanced SNR boundaries. Most SNRs are well identified in the 4.5 and 5.8 um bands. We give a brief description of the infrared features of the identified SNRs.

Massive star formation with Spitzer/GLIMPSE

The Spitzer Space Telescope is very efficient at moderate-depth infrared mapping. The Galactic Legacy Infrared Midplane Survey Extraordinaire (GLIMPSE) and other projects have now imaged most of the massive star formation regions in the inner Galaxy. In this case, quantity is quality–the large datasets allow statistical and global analysis of star forming regions that was previously difficult. Data such as the GLIMPSE survey is proving useful to study different evolutionary stages of massive star formation, from pre-protostellar clouds through feedback and triggered star formation. We discuss selected team results relevant to each of these stages: mapping infrared dark clouds and the mid-IR extinction law, studies using radiative transfer models of the entire protostellar population of star forming regions such as M16 and M17 (see also Whitney, this conference), feedback and star formation in the G305 and RCW79 giant HII regions, and GLIMPSE's comment on even older objects such as debris disks and PN. Continuing similar analysis will hopefully lead to better understanding of large-scale questions of Galactic star formation such as the total star formation rate and the relationships between star formation and Galactic structure.

Discovery of a New Low-Latitude Milky Way Globular Cluster Using GLIMPSE

Spitzer Space Telescope imaging from the Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE) reveals a previously unidentified low-latitude rich star cluster near l = 313, b = -01. Near-infrared JHK' photometry from the Wyoming Infrared Observatory indicates an extinction of AV ≃ 15 ± 3 mag for cluster members. Analysis of 13CO features along the same sight line suggests a probable kinematic distance of 3.1–5.2 kpc. The new cluster has an angular diameter of ∼1–2 pc, a total magnitude corrected for extinction of m = 2.1, and a luminosity of MK ≃ -10.3 at 3.1 kpc. In contrast to young massive Galactic clusters with ages less than 100 Myr, the new cluster has no significant radio emission. Comparison with theoretical K-band luminosity functions indicates an age of at least several gigayears and a mass of at least 105 M⊙. Unlike known old open clusters, this new cluster lies in the inner Galaxy at RGC ≃ 6.1 kpc. We designate this object "GLIMPSE-C01" and present evidence that it is a Milky Way globular cluster passing through the Galactic disk. We also identify a region of star formation and fan-shaped outflows from young stellar objects in the same field as the cluster. The cluster's passage through the Galactic molecular layer may have triggered this star formation activity.

Discovery of a Distant Star Formation Region using GLIMPSE

Examination of early, in-orbit checkout (IOC) images of a portion of the Galactic plane obtained by the Infrared Array Camera (IRAC) aboard the Spitzer Space Telescope revealed the presence of an extended emission nebula with internal structure. The Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE) data show this nebula, located at l � 42 � and b � 0N5, contains bright point sources and two nonstellar regions. Ancillary data sets were used to help reveal the nature of this nebula and its exciting objects. In particular, 13 CO J ¼ 1 ! 0 line emission mapped by the Galactic Ring Survey (GRS) shows molecular gas associated with the infrared nebula. The 13 CO radial velocity yields a far-kinematic distance of 11.1 kpc to the nebula, since there is no evidence for H i self-absorption. At 11.1 kpc, the far-infrared luminosity of the nebula is 4:8;10 4 L� , and the mass of its molecular cloud is 1:1;10 4 M� . The spectral energy distribution rises steeply from 2.2 to 100 � m with an absorption feature at 10 � m, exhibiting the shape of a late Class 0 young stellar object (YSO). The radio continuum flux observed toward the nebula is consistent with the free-free emission from one or more massive YSOs (MYSOs) with spectral types in the range O9 to B0. This analysis demonstrates one technique the GLIMPSE team will use for revealing thousands of Galactic star formation regions.

RCW 49 at Mid‐Infrared Wavelengths: A GLIMPSE from the Spitzer Space Telescope

The luminous, massive star formation region RCW 49, located in the southern Galactic plane, was imaged with the Infrared Array Camera (IRAC) on the Spitzer Space Telescope as part of the Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE) program. The IRAC bands contain polycyclic aromatic hydro- carbon (PAH) features at 3.3, 6.2, 7.7, and 8.6 � m, as well as the Brline. These features are the major contributors to the diffuse emission from RCW 49 in the IRAC bands. The Spitzer IRAC images show that the dust in RCW 49 is distributed in a network of fine filaments, pillars, knots, sharply defined boundaries, bubbles, and bow shocks. The regions immediately surrounding the ionizing star cluster and W-R stars are evacuated of dust by stellar winds and radiation. The IRAC images of RCW 49 suggest that the dust in RCW 49 has been sculpted by the winds and radiation from the embedded luminous stars in the inner 5 0 (inner � 6 pc) of the nebula. At projected angular radii �> 5 0 from the central ionizing cluster, the azimuthally averaged infrared intensity falls off as � � � 3 . Both high-resolution radio and mid-IR images suggest that the nebula is density bounded along its western boundary. The filamentary structure of the dust in RCW 49 suggests that the nebula has a small dust filling factor and, as a consequence, the entire nebula may be slightly density bounded to H-ionizing photons. Subject headingg astrochemistry — dust, extinction — H ii regions — infrared: ISM — ISM: lines and bands

GLIMPSE. I. An SIRTF Legacy Project to Map the Inner Galaxy

ABSTRACTThe Galactic Legacy Infrared Mid‐Plane Survey Extraordinaire (GLIMPSE), a Space Infrared Telescope Facility (SIRTF) Legacy Science Program, will be a fully sampled, confusion‐limited infrared survey of 2/3 of the inner Galactic disk with a pixel resolution of ∼1.″2 using the Infrared Array Camera at 3.6, 4.5, 5.8, and 8.0 μm. The survey will cover Galactic latitudes |b|≤1° and longitudes |l| = 10°–65° (both sides of the Galactic center). The survey area contains the outer ends of the Galactic bar, the Galactic molecular ring, and the inner spiral arms. The GLIMPSE team will process these data to produce a point‐source catalog, a point‐source data archive, and a set of mosaicked images. We summarize our observing strategy, give details of our data products, and summarize some of the principal science questions that will be addressed using GLIMPSE data. Up‐to‐date documentation, survey progress, and information on complementary data sets are available on the GLIMPSE Web site.