MAGPIS: Publications

Giveon, U., Becker, R.H., and White, R.L., 2008, Astronomical Journal, 135, 1697

We present results from matching a Very Large Array Galactic plane catalog at 6 cm covering the first Galactic quadrant (350° <= l <= 42°, |b| <= 0.4°), the MSX6C Galactic plane catalog, and the Galactic Legacy Infrared Mid-Plane Survey Extraordinaire v1.0 (GLIMPSE I) catalog. The much higher angular resolution and better sensitivity provided by GLIMPSE should improve the identification of embedded Galactic star-forming regions, and enable the study of the relationships between the central stellar sources, the ionized gas, and the surrounding dust. The GLIMPSE catalog is so crowded compared to our 6 cm catalog that it actually leads to confusion in identifying chance alignments, but this is resolved when separating GLIMPSE into red (M_3.6µm - M_8µm > 2.5) and blue (M_3.6µm - M_8µm < 2.5) sub-catalogs. In spite of the improved properties of GLIMPSE, we find only 132 GLIMPSE-6cm high-reliability matches in the overlapping area of the two samples (10° <= l <= 42°, |b| <= 0.4°), of which 55 have a Midcourse Space Experiment (MSX) counterpart. Even though the matching results are less successful than expected, there are still some results of interest. First, we discover an obscuration effect around our candidates: the average local source density of blue sources, dominated by stars, is decreasing toward the radio positions; their average brightness increases, and their color reddens significantly, supporting the picture in which background sources disappear behind the opaque nebulae associated with the radio source. Second, the selected sources define near and mid-infrared color criteria, which are used to detect a total of 849 GLIMPSE sources in the entire GLIMPSE survey that have MSX matches and that show the same collective behavior. Only 15% of these sources are previously classified, mainly as H II regions, masers, young stellar objects, and molecular clouds.

This paper is available through the ADS.

Helfand, D.J., Gotthelf, E.V., Halpern, J.P., Camilo, F., Semler, D.R., Becker, R.H., and White, R.L. 2007, Astrophysical Journal, 665, 1297

We present a Chandra X-ray observation of G12.82-0.02, a shell-like radio supernova remnant coincident with the TeV gamma-ray source HESS J1813-178. We resolve the X-ray emission from the colocated Advanced Satellite for Cosmology and Astrophysics (ASCA) source into a point source surrounded by structured diffuse emission that fills the interior of the radio shell. The morphology of the diffuse emission strongly resembles that of a pulsar wind nebula. The spectrum of the compact source is well characterized by a power law with index ~1.3, typical of young and energetic rotation-powered pulsars. For a distance of 4.5 kpc, consistent with the X-ray absorption and an association with the nearby star formation region W33, the 2-10 keV X-ray luminosities of the putative pulsar and nebula are L_PSR=3.2x10³³ ergs s^-1 and L_PWN=1.410³⁴ ergs s^-1, respectively. Both the flux ratio of L_PWN/L_PSR=4.3 and the total luminosity of this system predict a pulsar spin-down power of E>10³⁷ ergs s^-1, placing it among the 10 most energetic young pulsars in the Galaxy. A deep search for radio pulsations using the Parkes telescope sets an upper limit of ~0.07 mJy at 1.4 GHz for periods >~50 ms. We discuss the energetics of this source and consider briefly the proximity of bright H II regions to this and several other High Energy Stereoscopic System (H.E.S.S.) sources, which may produce their TeV emission via inverse Compton scattering.

This paper is available through the ADS and through the astro-ph e-print archives.

Giveon, U., Richter, M.J., Becker, R.H., and White, R.L. 2007, Astronomical Journal, 133, 639

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 17.65µm, and 10 of them were also imaged at 24.5µm. 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.

This paper is available through the ADS.

Helfand, D.J., Becker, R.H., White, R.L., Fallon, A., and Tuttle, S. 2006, Astronomical Journal, 131, 2525

We present the Multi-Array Galactic Plane Imaging Survey (MAGPIS), which maps portions of the first Galactic quadrant with an angular resolution, sensitivity and dynamic range that surpasses existing radio images of the Milky Way by more than an order of magnitude. The source detection threshold at 20 cm is in the range 1-2 mJy over the 85% of the survey region (5° < l < 32°, |b| < 0.8°) not covered by bright extended emission. We catalog over 3000 discrete sources (diameters mostly <30 arcsec) and present an atlas of ~400 diffuse emission regions. New and archival data at 90 cm for the whole survey area are also presented. Comparison of our catalogs and images with the MSX mid-infrared data allow us to provide preliminary discrimination between thermal and non-thermal sources. We identify forty-nine high-probability supernova remnant candidates, increasing by a factor of seven the number of known remnants with diameters smaller than 5 arcmin in the survey region; several are pulsar wind nebula candidates and/or very small diameter remnants (D<45 arcsec). We report the tentative identification of several hundred H II regions based on a comparison with the mid-IR data; they range in size from unresolved ultra-compact sources to large complexes of diffuse emission on scales of half a degree. In several of the latter regions, cospatial nonthermal emission illustrates the interplay between stellar death and birth. We comment briefly on plans for followup observations and our extension of the survey; when complemented by data from ongoing X-ray and mid-IR observations, we expect MAGPIS to provide the most complete census yet obtained of the birth and death of massive stars in the Milky Way.

This paper is available through the ADS, through the astro-ph e-print archives and on our web site.

Giveon, U., Becker, R.H., Helfand, D.J., and White, R.L. 2005, Astronomical Journal, 130, 156

We utilize a new VLA Galactic plane catalog at 1.4 GHz covering the first and second Galactic quadrants (340° < l < 120°, |b| < 0.8 deg with |b| < 1.8° for 350° < l < 40° and |b| < 2.5° for 100° < l < 105°) in conjunction with the MSX6C Galactic plane mid-infrared catalog to supplement and better understand our 5 GHz catalog (Giveon et al. 2005). A radio catalog of this region was first published by Zoonematkermani et al. (1990), but we have re-reduced the data with significantly improved calibration and mosaicing procedures, resulting in more than a tripling of the number of 1.4 GHz sources detected. Comparison of the new 1.4 GHz catalog and the MSX6C catalog resulted in a sample of 556 matches, out of which we estimate only 11 to be chance coincidences. Most of the matches show red MSX colors. The scale height of their Galactic latitude distribution is 24'-28' (FWHM) or ~60-70 pc (for a distance of 8.5 kpc), depending on longitude. The latitude distribution flattens out significantly above l~40° and the number of matches drops off sharply.

This paper is available through the ADS and through the astro-ph e-print archives.

White, R.L., Becker, R.H., and Helfand, D.J. 2005, Astronomical Journal, 130, 586

Archival data have been combined with recent observations of the Galactic Plane using the Very Large Array to create new catalogs of compact centimetric radio sources. The 20 cm source catalog covers a longitude range of -20° < l < 120°; the latitude coverage varies from ±0.8° to ±2.7°. The total survey area is ~331 sq deg; coverage is 90% complete at a flux density threshold of ~14 mJy, and over 5000 sources are recorded. The 6 cm catalog covers 43 sq deg in the region -10° < l < 42°, |b| < 0.4° to a 90% completeness threshold of 2.9 mJy; over 2700 sources are found. Both surveys have an angular resolution of ~6 arcsec. These catalogs provide a 30% (at 20 cm) to 50% (at 6 cm) increase in the number of high-reliability compact sources in the Galactic plane, as well as providing greatly improved astrometry, uniformity, and reliability; they should prove useful for comparison with new mid- and far-infrared surveys of the Milky Way.

This paper is available through the ADS and through the astro-ph e-print archives. Data from this paper are available on the MAGPIS catalogs page.

Giveon, U., Becker, R.H., Helfand, D.J., and White, R.L. 2005, Astronomical Journal, 129, 384

We use new VLA Galactic plane catalogs at 5 and 1.4 GHz covering the first Galactic quadrant (350°<l<42°, |b|<0.4°) in conjunction with the MSX6C Galactic plane catalog to construct a large sample of ultracompact H II regions. A radio catalog of this region was first published by Becker et al., but we have added new observations and rereduced the data with significantly improved calibration and mosaicking procedures, resulting in a tripling of the number of 5 GHz sources detected. Comparison of the new 5 GHz catalog and the MSX6C Galactic plane catalog resulted in a sample of 687 matches, out of which we estimate only 15 to be chance coincidences. Most of the matches show red Midcourse Space Experiment colors and a thermal radio spectrum. The scale height of their Galactic latitude distribution is very small (FWHM of 16' or ~40 pc). These properties suggest that the sample is dominated by young ultracompact H II regions, most of which are previously uncataloged.

This paper is available through the ADS and through the astro-ph e-print archives.

Becker, R.H., White, R.L., Helfand, D.J., and Zoonematkermani, S. 1994, Astrophysical Journal Suppl, 91, 347

We have used the Very Large Array (VLA) to survey the inner Galaxy (|b| < 0.4°, l = 350-40°) at 5 GHz to a limiting sensitivity of between 2.5 and 10 mJy. The survey has resulted in a catalog of 1272 discrete sources (including 100 sources outside the formal survey area) of which we have tentatively identified approximately 450 as ultracompact H II regions and approximately 45 as planetary nebulae. Approximately 30% of the radio sources are detected in the Infrared Astronomy Satellite (IRAS) Point source Catalog. The results confirm a scale height of only 30 pc for ultracompact H II regions. We show that source lists generated from the IRAS Point Source Catalog alone suffer serious selection effects; the combination of the IRAS and radio surveys allows us to produce a much more complete census of the regions of massive star formation in our Galaxy.

This paper is available through the ADS.

Helfand, D.J., Zoonematkermani, S., Becker, R.H., and White, R.L., 1992, Astrophysical Journal Suppl, 80, 211

The results of the extension of the 20-cm Galactic-plane survey reported by Zoonematkermani to Galactic latitudes of ± 1.8° over the central region of the Milky Way are reported. A total of 1457 discrete radio sources down to flux densities of less than about 5 mJy, and 95 percent completion is achieved at 20 mJy. A detailed comparison of all radio sources from the survey in this longitude range with the IRAS Point Source Catalog provides classification for 13 percent of the objects, including 159 compact H II regions, and nearly 100 planetary nebulae, over 70 of which are identified. The identity of the remaining radio sources is discussed.

This paper is available through the ADS.

Becker, R.H., White, R.L., and Proctor, D.D. 1992, Astronomical Journal, 103, 544

A 140° strip along the Galactic plane with the VLA has been surveyed for OH masers. Fifty OH masers, including 14 new sources, were detected. The masers have a very narrow distribution in Galactic latitude and are probably Population I objects. A study of the IRAS counterparts to OH masers from this and other surveys reveals a strong correlation between the infrared colors of OH masers and Galactic latitude.

This paper is available through the ADS.

White, R.L., Becker, R.H., and Helfand, D.J. 1991, Astrophysical Journal 371, 148

The 20 cm Galactic plane survey (GPS) of Zoonematkermani et al. (1990) and the IRAS Point Source Catalog are compared using a new technique for distinguishing chance from true coincidences. The comparison shows that the GPS/IRAS sources are Galactic. Several classes of objects are identified. Most are shown to be ultracompact H II regions distributed with amazingly small scale height of 30 pc. It is shown that the IRAS-selected sample of UC H II regions of Wood and Churchwell (1989) is significantly contaminated by objects with a much thicker latitude distribution, which accounts for the larger scale height in that study. It is argued that only the combination of IR and radio observations can distinguish massive embedded O stars from the more numerous, lower mass embedded B stars. Practically all of the radio-selected PNs in the survey area have essentially identical IRAS colors, suggesting that they are in very similar evolutionary states.

This paper is available through the ADS.

Zoonematkermani, S., Helfand, D.J., Becker, R.H., White, R.L., and Perley, R. A. 1990, Astrophysical Journal Suppl, 74, 181

A survey of the Galactic plane in the longitude range l = -20 - 120 deg for Galactic latitudes 0.8° or less has been carried out at 1400 MHz using the VLA in the B configuration. A catalog of the 1992 discrete sources detected in this survey is presented here which is about 75 percent complete to a limiting peak flux density of 25 mJy for sources smaller than about 20 arcsec in diameter, although sources as faint as 8 mJy and as large as 90 arcsec are also included. The catalog includes for each entry a position accurate to less than about 3 arcsec, peak and integrated flux densities, source extent, and information on counterparts both from earlier radio surveys of the plane and from the IRAS point source caalog. An extensive analysis of the integrity and completeness of the survey is presented here; in separate publications, the source content of the survey as derived from statistical analyses of the spatial distribution of the sources and from radio, optical, and infrared followup observations, is discussed.

This paper is available through the ADS.

Becker, R.H., White, R.L., McLean, B. J., Helfand, D.J., and Zoonematkermani, S. 1990, Astrophysical Journal, 358, 485

A VLA survey of the Galactic plane at 20 cm in the longitude range 20 - 120° for Galactic latitudes |b| < 0.8° has resulted in a catalog of 1992 discrete radio sources. The survey has revealed a strong concentration of low-latitude objects within 50° of the Galactic center with a scale height of about 25 pc. This extreme Population I subset of the catalog is dominated by sources with diameters between 3 and 20 arcsec; most are associated with strong far-infrared sources and are likely to be compact and ultracompact H II regions. Other sources of particular interest and the properties of the various radio source populations represented in the survey are discussed.

This paper is available through the ADS.