MIT-GB catalog

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1986ApJS...61..105Lawrence+

5 GHz Radio Structure and Optical Identifications of sources from the MG survey II. Maps and Finding Charts

Lawrence C.R., Bennett C.L., Hewitt J.N., Langston G.I., Klotz S.E., Burke B.F.

Abstract

Nearly 1000 sources from the 5 GHz MIT-Green Bank (MG) survey have been observed with the VLA. We give ardio maps for 460 resolved sources, finding charts for 390 optical identification, and spectral indices between 1.4 and 5 GHz for 632 sources.

About 1000 sources, selected as described in IIa from a prelimenary version of the MIT-GB I catalog, have been observed with VLA. Of these, 632 appear in final MG source list (Bennett at al. 1986). Most of the remaining sources are either outside the MG dec. or Galactic latitude ranges or below the 5 sigma detection limit. About 20 sources observed at the VLA are within the MG sky area and above the 106 mJy completeness limit, even allowing for the large flux-density errors in the preliminary list, but do not appear in the MG catalog. These sources give an upper limit on the completeness of the MG survey of 97 %.

In previous paper (Lawrence et al., 1984, Ap.J., 278, L95, paper I) we classified the radio structures and summarized the optical identifications of 602 of these sources with |b| > 20^o. This subgroup has also been observed at 1.4 GHz with 305m Arecibo telescope. In this paper we describe of 949 sources, including maps of 460 extended sources, finding chats for 390 optical identifications, and 1.4 GHz flux densities for 632 sources.

Source selection

VLA observations were made in 1981 May, 1982 Feb., and 1982 Oct. Before each observing session, sources wer selected randomly by flux-density range from a preliminary MG source list. The flux density ranges were 100-500 mJy for 1981 May, 100-300 mJy for 1982 Feb., and 50-500 mJy for 1982 Oct. Many of the sourecs observed are also in the Texas 365 MHz preliminary +18^o strip (Douglas et al.1980) or the Arecibo 611 MHz survey (Durdin et al. 1975; Lawrence et al. 1983). After the random selection process, we augmented the observing list with about 70 Arecibo sources with alfa(611-4755) < +0.5, so that (with one exeption) every flat-spectrum Arecibo source for which a reliable position was determined in Lawrence et al. (1983) has been observed. A few Arecibo sources with steep spectra were included as well. The MG sources in the VLA sample, therefore, are statistically equivalent to a complete sample by flux-density range.

VLA observations were made at 4885 MHz in 1981 May (B-array, beam ~1.2"), 1982 Feb. (A-array beam ~0.4"), and 1982 Oct (B-array). Forty calibrators and 360 survey sources were observed in each 24 h. Either 3C286 and 3C48 was observed each day as a flux-density standard, and the flux-density system of Baars et al. (1977) was used.

1 Source name in IAU B1950.0 format. In the case of multiple components, the mean position was used unless one component was clear dominant or coincided with an optical identification. Sources followed by a filled circle (here M) appear in the final MG source list (MGI).
2-3 Positions (B1950.) of the main components of the sources, determined by a parabolic fit to the map values near local maxima.
4 Relative peak flux density of individual components in multicomponent sources. We give the peak flux density of each component as a fraction of the peak flux density in the map. The seperate intergated flux densities of multiple resolved components were not determined.
5 VLA configuration
6 S_vla/S_5 is the sum of the clean component flux densities; S5 is column (7). Values much different from unity indicate source variability, resolution, or perhaps lagre error in the VLA flux densities.
7 S_5, the 4.755 GHz flux density. Flux densities and error from Lawrence et al. (1983) were used if availble (indicated by a value for alfa_a in col.16). If not, and the source is in the MG list (marked by a filled circle (here M) in col.1, the MG flux density was used. Errors are then given by sigma = [18.4^2+(0.1S)^2]^(1/2) mJy. Flux densities for the remaining sources were taken from preliminary survey list, with errors of +-20%.
8 alfa(1414,4755), where S~nu^-alfa.
9 Spectral index error, in square brackets.
10 Structure classification. P - point; QP - quasi-point; Df - diffuse; CJ - core-jet; Cm - cometery; D - double; T - triple; M - miltiple; CD - core-double; and J - jet (see IVa).
11 Angular size. The maximum angular size of the source, measured between the 6% contour of resolved components (10% if the map had no 6% contour, and between peaks for unresolved components.
12 Optical classification. S - stellar object; G - galaxy; F - too faint to classify; E - epmty field.
13 Radio-optical position offset, in arcseconds. For multicomponent sources, the radio position used is either the one marked with an open circle (here ) in col.(3), or the mean position of the listed components. Exceptions are specified in col.(16). Optical positions have been corrected for systematic errors in the SAO catalog (see V).
14 Estimated magnitude (see Vb) of stellar objects or galaxies smaller than 12", from the POSS O print. For galaxies larger than 12", the maximum angular size is given in arc minutes (e.g. 4.3'. Plate limit objects are sometimes invisible on the prints; only the limiting magnitude for the plate on which the object was measured is given. Somewhat brighter objects will be missing on one print or the other if alfa_0 != 0.5. Errors are at least +- 0.5 mag for stellar objects, and are much larger for galaxies.
15 Same as col.12, but from the E print. For a few sources, r-band magnitudes have been measured, with errors of +-0.1 mag. These are identified in column (16).
16 Comments: (a) If the source appears in the Texas Preliminary +18^o strip (Douglas et al. 1980), the spectral index alfa(365,4755) and model structure are given in the form "alfa_t = spectral index[error] (structure size)," where the structure codes are P - point, D - double, and A - asymmetric double, and the size in arcseconds. (b) If the source appears in the Arecibo 611 MHz survey (Durdin et al. 1975), the spectral index alfa(611,4755) is given in form "alfa_a = spectral index[error]", (c) The fringe amplitude on the shortest spacings (see IVb) is given for some sources as "SS=approximate flux density." (d) The Hiwett-Barbidge (1980) QSO catalog and the Veron-Cetty and Veron (1983) radio catalog give redshifts for some of the sources. These are listed here for convenience if the referenced finding chart showed that the identification was correct, followed by (H) ar (V) to identify the catalog. Several incorrect identifications are noted. In another case, neither finding chart nor optical position has been published; the determined in the r photometry band (~6000-7000A; see Schneider, Gunn and Hoessel 1983), using the PFUEI CCD camera on the Palomar 200 inch (5m) telescope, are noted. Errors are +-0.1mag. (f) POSS objects that are near the radio position (and perhaps an accepted counterpart), but not accepted as identifications, are noted (see e.g., 0006+014). (g) Sources apperantly resolved at 1414 MHz, but not at 4755 MHz or 365 MHz, are noted (see VI). (h) "Large shift" means that the source is more than 3' (B-array) or 1' (A-array) from the center of the VLA field. The synthesized beam is radially smeared because of the finite bandwidth of the observations. Shifts of several minutes of arc may indicate a problem in the prelimenary survey source list (see IIa) (i) Other comments are self-explanatory.

Table 3. Summary of Observations
Line Source flg RA_1950   DEC_1950   I_rel VLA Svla S5/Jy a(1.4,5)   Struct   Optical ID
                                              /S_GB                 typ siz"  Off" mB   mR    Comments
----+----1----+----2----+----3----+----4----+----5----+----6----+----7----+----8----+----9----+----0----+----1----+----2----+----3--
02 0001+128M 00 01 07.06  +12 49 58.1  1.00 B 0.94 0.414 +0.83[0.11] D  9.2 E 0.0  0.0  0.0