Extragalactic sources towards the central region of the Galaxy
MMon. Not. R. Astron. Soc. , 1–24 (0000) Printed 14 November 2018 (MN L A TEX style file v2.2)
Extragalactic sources towards the central region of the Galaxy
Subhashis Roy (cid:63) A. Pramesh Rao & Ravi Subrahmanyan National Centre for Radio Astrophysics (TIFR),Pune University Campus, Post Bag No.3, Ganeshkhind, Pune 411 007, India. Australia Telescope National Facility, CSIRO, Locked bag 194, Narrabri, NSW 2390, Australia
ABSTRACT
We have observed a sample of 64 small diameter sources towards the central − ◦ < l < ◦ , − ◦ < b < ◦ of the Galaxy with the aim of studying the Faraday rotation measure nearthe Galactic Centre (GC) region. All the sources were observed at 6 and 3.6 cm wavelengthsusing the ATCA and the VLA. Fifty nine of these sources are inferred to be extragalactic. Theobservations presented here constitute the first systematic study of the radio polarisation prop-erties of the background sources towards this direction and increases the number of knownextragalactic radio sources in this part of the sky by almost an order of magnitude. Based onthe morphology, spectral indices and lack of polarised emission, we identify four Galactic HIIregions in the sample. Key words:
Galaxy: center – techniques: polarimetric – radio continuum: ISM – Galaxy: HIIregions
Since extragalactic sources are located outside the Galaxy, the ef-fect of ISM on the propagation properties of electromagnetic wavesfrom these objects can be modelled without distance ambiguitiesas in the cases of pulsars, and thereby allowing us to observethe integrated effect of the medium along large ( ∼
20 kpc) lineof sight distance. Unfortunately, only a few extragalactic sourceshave been identified within the central few degrees of the Galaxy( − ◦ < l < ◦ , − ◦ < b < ◦ ), which limits their usefulnessas probes to study the Galactic Centre (GC) ISM. High obscurationat optical wavelengths and the confusion due to the high concen-tration of stars at infrared wavelengths have prevented identifica-tion of extragalactic sources in this region. High angular resolutionstudies at centimetre wavelengths (e.g., Becker et al. (1994) at 5GHz and Zoonematkermani et al. (1990) at 1.4 GHz) have identi-fied compact radio sources, but in the presence of a large numberof Galactic sources near the Galactic Centre (GC), identifying theextragalactic sources is non-trivial, and only about half a dozen ex-tragalactic sources in this region have been identified (Bower et al.2001).To study the Faraday rotation measure (RM) near the centre ofthe Galaxy ( − ◦ < l < ◦ , − ◦ < b < ◦ ), we have selected asample of 64 small diameter ( < (cid:48)(cid:48) ) sources (see Sect. 1.1) in theregion, which we have studied with high angular resolution at 6 cm(C band) and 3.6 cm (X band) with the ATCA and the VLA. Allthe sources were studied for linear polarisation and the width of thefrequency channels were chosen to avoid bandwidth depolarisationup to a RM of 15,000 rad m − . Though the NVSS (Condon et al. (cid:63) E-mail: [email protected] >
350 rad m − ) its bandwidth of50 MHz would cause bandwidth depolarisation. Our observations,for the first time, provide reliable measurements of the polarisationproperties of the sources in the region. These observations havealmost an order of magnitude higher sensitivity (in Stokes I) andup to 3 times higher resolution as compared to the previous VLAGalactic plane survey (GPS), and this high sensitivity together withhigher resolution has helped to identify the Galactic sources in theinitial sample.In this paper, we provide information on the morphology, po-larisation fraction, spectral indices and rotation measure of thesesources, and in a companion paper (henceforth Paper II) draw in-ferences about the magnetic field in the GC region. We surveyed the literature and formed a sample of possible extra-galactic radio sources in the central − ◦ < l < ◦ , − ◦ < b < ◦ ofthe Galaxy. These sources were selected on the basis of their smallscale structure ( (cid:54) (cid:48)(cid:48) ) and non-thermal spectra ( α (cid:54) − .
4, S( ν ) ∝ ν α ). For the sources to have detectable linear polarisation andso be useful for the RM study, an estimate of the polarisation frac-tion of the sources are required. However, in the absence of anyreliable information on their polarisation fraction in the literature,we assumed the unresolved sources to be polarised at the mean po-larisation fraction of extragalactic small diameter sources of 2.5%(Saikia & Salter 1988). Sources with measured flux density greaterthan 10 mJy at 5 GHz were selected. The source catalogues usedfor this selection were VLA images of the GC region at 327 MHz(LaRosa et al. 2000), the VLA survey of the Galactic plane (GPS) c (cid:13) a r X i v : . [ a s t r o - ph ] D ec Subhashis Roy, A. Pramesh Rao & Ravi Subrahmanyan at 1.4 GHz (Zoonematkermani et al. 1990), (Helfand et al. 1992)and at 5 GHz (Becker et al. 1994). Sources observed by Lazio &Cordes (1998) and the 365 MHz Texas survey (Douglas et al. 1996)were also used for this purpose. In those cases where no flux den-sity estimates were available at 5 GHz, the flux densities at this fre-quency was estimated by extrapolating the 1.4 GHz flux densitiesusing spectral indices measured between 327 MHz and 1.4 GHz. Atotal of 64 sources were found that satisfied all of the above criteria.
Details of array configurations, frequencies used and thedate of radio observations are in Table 1. The ATCAobservations were made using a 6 km array configura-tion. Twelve sources, G357.435 − − − − − − − − − − − − − − − − π wrapin polarisation angles measured between two frequencies, 4more polarised sources from the pilot run G357.865 − − − uv -coverage and each source was observed ≈ −
312 and1748 −
253 were used to calibrate the antenna based amplitudesand phases (secondary calibrators), and their flux densities weremeasured based on the observation of the primary flux densitycalibrator PKS B1934 − (cid:54) φ )being given by φ =0.5 tan − ( U / Q ) (where, signs of Q and U areconsidered separately to unambiguously determine the value of φ ),we divided the Stokes U image by the Q image and measured thepolarisation angle and its error (AIPS task COMB). Finally, thepolarisation angle images at different frequency bands were fittedto the equation, φ = RM . λ + φ + n π (1) using the AIPS task RM. In this equation, n is an integer, λ is thewavelength, and φ denotes the intrinsic polarisation angle (i.e.,when the observing frequency tends to infinity). If the rms residualsexceed four times the expected rms noise, the fitted values wererejected.Since there were 16 frequency channels per 128 MHz band ofthe ATCA data, we tried to measure the RM from the ATCA ob-servations in two ways by using the AIPS task RM. (i) Since AIPStask RM cannot fit more than four frequency channels to measureRM, in order to maximise signal to noise ratio as well as to checkfor high RM in the data, we divided the central 12 frequency chan-nels of 4.8 and 5.9 GHz band into 3 equal parts. Polarisation angleswere measured from first and third part of each of these bands, andthese were used as input to the AIPS task RM. This allowed us tomeasure RM as high as 30,000 rad m − . (ii) If the RM measuredby the previous method is not very high (i.e., (cid:54) − , andwas the case for all except one source), data from each of the 4.8,5.3, 5.9 and 8.5 GHz band were averaged and polarisation anglemeasured from each of these bands. These polarisation angle im-ages and their error maps were used as the input to the AIPS taskRM. We used the VLA in its BnA configuration to observe therelatively weak sources in the sample. The default continuummode, which provides a single frequency channel of band-width 50 MHz in each IF band, was used. Observations werecentred at frequencies 4.63, 4.88, 8.33 and 8.68 GHz. 27 newsources, G353.410 − − − − − − − − − − − π wrap in polarisation angles measuredbetween two frequencies, 5 more sources from the ATCA pi-lot run, G358.002 − − − − c (cid:13)000
253 were used to calibrate the antenna based amplitudesand phases (secondary calibrators), and their flux densities weremeasured based on the observation of the primary flux densitycalibrator PKS B1934 − (cid:54) φ )being given by φ =0.5 tan − ( U / Q ) (where, signs of Q and U areconsidered separately to unambiguously determine the value of φ ),we divided the Stokes U image by the Q image and measured thepolarisation angle and its error (AIPS task COMB). Finally, thepolarisation angle images at different frequency bands were fittedto the equation, φ = RM . λ + φ + n π (1) using the AIPS task RM. In this equation, n is an integer, λ is thewavelength, and φ denotes the intrinsic polarisation angle (i.e.,when the observing frequency tends to infinity). If the rms residualsexceed four times the expected rms noise, the fitted values wererejected.Since there were 16 frequency channels per 128 MHz band ofthe ATCA data, we tried to measure the RM from the ATCA ob-servations in two ways by using the AIPS task RM. (i) Since AIPStask RM cannot fit more than four frequency channels to measureRM, in order to maximise signal to noise ratio as well as to checkfor high RM in the data, we divided the central 12 frequency chan-nels of 4.8 and 5.9 GHz band into 3 equal parts. Polarisation angleswere measured from first and third part of each of these bands, andthese were used as input to the AIPS task RM. This allowed us tomeasure RM as high as 30,000 rad m − . (ii) If the RM measuredby the previous method is not very high (i.e., (cid:54) − , andwas the case for all except one source), data from each of the 4.8,5.3, 5.9 and 8.5 GHz band were averaged and polarisation anglemeasured from each of these bands. These polarisation angle im-ages and their error maps were used as the input to the AIPS taskRM. We used the VLA in its BnA configuration to observe therelatively weak sources in the sample. The default continuummode, which provides a single frequency channel of band-width 50 MHz in each IF band, was used. Observations werecentred at frequencies 4.63, 4.88, 8.33 and 8.68 GHz. 27 newsources, G353.410 − − − − − − − − − − − π wrap in polarisation angles measuredbetween two frequencies, 5 more sources from the ATCA pi-lot run, G358.002 − − − − c (cid:13)000 , 1–24 xtragalactic sources towards the Galactic Centre Table 1.
Journal of observationsEpoch Telescope Array Obs. Frequency No. ofconfig- time (GHz) sourcesuration (hours) observed06 Feb 2000 ATCA 6A 10 4.80 & 5.95 1230 Sept 2000 ATCA 6B 12 4.80 & 5.95 1202 Oct 2000 ATCA 6B 12 4.80 & 5.95 1206 Oct 2000 ATCA 6B 12 5.31 & 8.51 1408 Oct 2000 ATCA 6B 12 5.31 & 8.51 1311 Feb 2001 VLA BnA 06 4.63 & 4.88 2813 Feb 2001 VLA BnA 06 8.33 & 8.68 3212 Apr 2002 ATCA 6B 11 5.06 & 5.70 08
Based on the ATCA data, 24 sources were found to have at least onepolarised component. Images of these sources are shown in Fig. 3.The FWHM sizes of the beams in the ATCA images are ≈ (cid:48)(cid:48) × (cid:48)(cid:48) ,and the typical RMS noise is 0.23 mJy/beam in Stokes I and about0.15 mJy/beam in Stokes Q and U. These images show 7 of the 24sources to have a single unresolved component and the remainderare either partially resolved or have multiple components.Of the sources observed using the VLA, 21 have at least onepolarised component. Images of these sources along with 2 po-larised phase calibrators are shown in Fig. 4. The FWHM sizes ofthe beams in the VLA images are ∼ (cid:48)(cid:48) × . (cid:48)(cid:48) and the RMS noise istypically 75 µ Jy/beam. In these images, four sources appear as sin-gle unresolved components. Since 1741 −
312 and 1748 −
253 havebeen observed by both ATCA and the VLA, but 1741 −
312 has afaint emission around the compact source as seen in higher resolu-tion VLA maps, we have presented its properties in Stokes I fromthe VLA data.Stokes I images of the sources in the sample that were notdetected to have polarised emission are shown in Fig. 5 and Fig. 6respectively.The properties of the 24 polarised sources observed withATCA are presented in Table 2 and 21 sources observed with VLAare in Table 3. In these tables, the following conventions are used.Column 1: the source name using Galactic co-ordinates ( l ± b ).Column 2: the component designation; ‘N’ denotes Northern, ‘S’denotes Southern, ‘E’ denotes Eastern and ‘W’ denotes Western,‘C’ denotes central, ‘EX’ denotes highly extended and ‘R’ denotesring type. Columns 3 and 4: Right ascension (RA) and Declina-tion (DEC) of the radio intensity peaks of the components in J2000co-ordinates. Column 5: the deconvolved size of the componentswith their major and minor axes in arc-seconds and the positionangle (PA) in degrees (formatted as major axis × minor axis, PA).A few sources that are observed to have multiple resolved com-ponents in the 8.5 GHz images are, however, not well resolved inthe 4.8 GHz images. For these sources, we have measured the sizeparameters of the components from the 8.5 GHz images and weput a ‘*’ symbol beside these measured parameters. Columns 6and 7: the corresponding peak and total flux density of the com-ponents at 4.8 GHz in units of mJy beam − and mJy respectively.Column 8: total flux density of the component at 4.8 GHz as mea-sured by the VLA GPS survey. Column 9: percentage polarisationof the components. Column 10: spectral indices of the componentsmeasured between 8.5 and 4.8 GHz. A few of the sources are ex-tended over several synthesised beam-widths and for these sourceswe have convolved the 8.5 GHz images to the resolution at 4.8 GHzand then made spectral index images. The spectral indices of the in- dividual components are measured from these images, we put an ‘s’beside the spectral index for these extended sources. Columns 11and 12: spectral indices between 4.8 and 1.4 and between 1.4 and0.3 GHz respectively. Column 13: the source classification; ‘EG’denotes an extragalactic source (based on the morphology), and Gdenotes a Galactic source. Several sources show the morphologytypical of FR − I or FR − II sources and this is noted along with theextragalactic classification. Sources which appear unresolved (de-convolved source size << beam size) are denoted by U, slightlyresolved (deconvolved source size (cid:46) beam size) by SR, double byD and T denotes a triple source consisting of a pair of lobes anda core. C+E denotes a flat spectrum core with extended emissioneither in the form of a lobe or jet. If there are several objects in thefield which appear to be unrelated, we label the object as M.For computing spectral indices in Table 2 and 3, the 1.4 GHzflux densities of the sources have been taken from the VLA GPSand the NRAO VLA Sky Survey (NVSS) (Condon et al. 1998).If the measured flux density of a component in the GPS differsfrom that in the NVSS by more than 20%, we have put a ‘†’ markbeside the computed spectral indices (column 11). We have visu-ally examined the NVSS images of these sources and if we findthat the source is not in a confused region of the image we haveused the flux density from NVSS to compute the spectral index; insuch cases, we put ‘(N)’ beside the measured spectral index. Forthe source G359.871+0.171, the 1.4 GHz flux density has been as-sumed to be the same as that measured by Lazio et al. (1999) at1.5 GHz and we put ‘(L)’ beside its measured spectral index be-tween 4.8 and 1.4 GHz. For a few sources in the list, the 1.4 GHzflux density in unknown. In these cases, we put a ‘**’ in column11 and enter the spectral index between 4.8 and 0.3 GHz in column12 with ‘(0.3/4.8)’ written below. The P-band flux densities of thesources have been taken from the Texas survey at 365 MHz (Dou-glas et al. 1996). However, the Texas survey is known to have largeuncertainty in flux densities for sources near the Galactic plane andwhich is more near the complex GC region. Therefore, if any sourceis detected in the GC image at 330 MHz (LaRosa et al. 2000), wehave used their flux density to compute the spectral index (column12 in Table 2, 3 and column 11 in Table 4, 5) and put ‘GC’ in paren-thesis beside the spectral index measured. For 5 sources the fluxdensities at 330 MHz have been taken from Roy & Rao (2002), andwe put ‘(GM)’ beside the spectral index in column 12. We have alsotaken the flux densities of 3 sources at 330 MHz from S. Bhatnagar(private communication) and put ‘(GM1)’ in column 12. Many ofthe sources resolved at frequencies of 1.4 GHz and above appearunresolved in the low frequency Texas survey. For these sources,we only compare their integrated flux densities between 1.4 and0.3 GHz, and put ‘(i)’ beside the measured spectral index in col-umn 12.In Table 4 & 5 we present the properties of the sources whichare not detected in polarised emission. These tables are similar toTable 2 & 3, except that we have omitted the column representingpercentage polarisation (column 9 in Table 2 & 3). For the fourGalactic HII regions we have identified, we write ‘G − HII’ in col-umn 12 of this Table.The measured RM towards 44 sources (65 components) and2 secondary calibrators are given in Table 6, which is arranged asfollows:Column 1: the source name in Galactic co-ordinates (G l ± b). Col-umn 2 & 3: RA (J2000) and DEC (J2000) of the source compo-nents. The co-ordinates of these components are based on the peakin the polarised intensity (if the peak in the polarised intensity donot coincide with the peak in total intensity, the component position c (cid:13) , 1–24 Subhashis Roy, A. Pramesh Rao & Ravi Subrahmanyan will be slightly different than what is given in Table 2 & 3 basedon the peak in total intensity). Column 4 & 5: the measured RM(in rad m − ) and the error in these measurements at the positionof the peak in the polarised emission. Depolarisation fraction is de-fined as the ratio of the polarisation fraction of any component be-tween lower to that at higher frequency, and in column 6 we providethe depolarisation fraction (D) of the source components between4.8 and 8.5 GHz. Column 7: Percentage error in the depolarisationfraction ( ∆ (D) in %). Assuming that the emission mechanism issynchrotron, the orientation of the electric field in the radiation hasbeen used to infer the orientation of the magnetic field in the plasmaand we provide the direction of this magnetic field ( θ ) and the errorin this measurement ( ∆θ ) in columns 8 & 9 respectively. Column10: Reduced Chi-square ( χ ) of the fit of Equation 1 to the mea-sured polarisation angles. We show an example of bad fit ( χ =17)in Fig. 1, and one example of good fit ( χ =0.2) in Fig. 2. Column11: Measured polarisation angles at different frequencies. The ob-served frequencies (in MHz) and the measured polarisation angles(in degrees) are tabulated in pairs, and each frequency, polarisationangle pair are separated by commas.The source G359.2 − − ±
18 rad m − ). However, our samples areselected to measure the RM introduced by the GC region, but thissource only samples the local ISM, and its RM is not used in anyfurther analysis. The errors in the derived spectral indices depend on the accuraciesof the flux densities at different frequencies. One of the drawbacksof a Fourier synthesis array is that if a source is resolved on theshortest interferometer baseline, its flux density will most likelybe underestimated in the image. In the GC region, where the skydensity of sources is high and emission at various size scalesmay co-exist, confusion could be a significant source of errors inimaging and hence in flux density estimates. Because our radioobservations are performed at relatively high frequencies, thecontribution from extended Galactic synchrotron background isnegligible. Additionally, most of the sources in our sample havesmall angular sizes and, therefore, the problem of missing fluxdensity should be minimal. The ATCA and VLA observationswere both made using a single array at both the frequencies. Sinceproblem of any missing flux density increases with increase inobserving frequency, this might result in an underestimation of thesource spectral index. We have detected extended emission of upto ∼ (cid:48) scale in our 4.8 GHz images of G353.410 − − − − − − uv -range of the 8.5 GHz visibilities. A comparisonof the corresponding images with the original 4.8 GHz images(without the restriction in visibility coverage) shows that ex-cept for G353.410 − − − − − .0010 .0015 .0020 .0025 .0030 .0035 .0040 .0045406080100120140160180200 l P o l a r i s a ti on a ng l e ( (cid:176) ) .0010 .0015 .0020 .0025 .0030 .0035 .0040 .0045406080100120140160180200 l P o l a r i s a ti on a ng l e ( (cid:176) ) Figure 1.
An example of bad fit of Equation 1 to the measured po-larisation angles vs. square of wavelength plot (reduced χ =17). Thepolarisation angles are measured towards the source G358.002 − .0010 .0015 .0020 .0025 .0030 .0035 .0040 .0045−50050100150 l P o l a r i s a ti on a ng l e ( (cid:176) ) .0010 .0015 .0020 .0025 .0030 .0035 .0040 .0045−50050100150 l P o l a r i s a ti on a ng l e ( (cid:176) ) Figure 2.
An example of good fit of Equation 1 to the measured po-larisation angles vs. square of wavelength plot (reduced χ =0.2). Thepolarisation angles are measured towards the source G356.567+0.869.c (cid:13)000
An example of good fit of Equation 1 to the measured po-larisation angles vs. square of wavelength plot (reduced χ =0.2). Thepolarisation angles are measured towards the source G356.567+0.869.c (cid:13)000 , 1–24 xtragalactic sources towards the Galactic Centre indices between 8.5 and 4.8 GHz is less than 0.25. Among theabove 7 sources, 4 have been identified as HII regions. The spectralindices between 8.5 and 4.8 GHz of the 2 remaining extragalacticsources G356.905+0.082 and G358.149 − − ∼ Estimation of source spectral indices and the RM requires multi-frequency observations. Most of our multifrequency observationswere separated by a time period, which varies from a few days toan year or two. Any source variability in these timescale will af-fect the measured spectral indices and possibly the measured RM.However, we note that the variability of the extragalactic sourcesat frequencies higher than a few GHz is often intrinsic in nature(Wagner & Witzel 1995) and in some cases caused by interstel-lar scintillation (ISS) (Lovell et al. 2003). The typical variabil-ity timescale for intrinsic variability is from a few hours to years(Wagner & Witzel 1995), and from hours to months in the caseof ISS (Lovell et al. 2003). However, only the core dominated ob-jects with flat spectrum ( α > − .
5) can show significant variabil-ity in timescale of days or less (Wagner & Witzel 1995). Amongthe sources observed, only G356.905+0.082, G357.865 − − − − − − − − − − − − − − − − − − − χ =17, Table 6), and onepossible reason for this is source variability. Consequently, themeasured RM of G357.865 − − α . / . ). When the polarised emission from the source reaches the observer,rotation of the polarisation angle could occur (i) within the source,(ii) in the Inter Galactic Medium (IGM) or (iii) in the ISM of theGalaxy. Compared to the ISM of our Galaxy, the electron density ofthe IGM is very small, and consequently the Faraday rotation intro-duced by the IGM is negligible. However, if the synchrotron elec-trons are mixed with thermal electrons at the source, or, if there isan intervening galaxy, the ISM of which introduces RM, or if thereis cluster of galaxies along the line of sight, there can be Faradayrotation introduced outside our Galaxy. As discussed by Gardner& Whiteoak (1966); Kronberg et al. (1972); Vallee (1980), the po-larisation angle could deviate from the λ law due to the followingthree mechanisms.(i) If the synchrotron optical depth becomes significant at somefrequency, the polarisation direction makes a transition from par-allel to perpendicular to the projected magnetic field. (ii) If thereare multiple unresolved emission components with differing spec-tral indices and polarisation characteristics, it can cause complexwavelength dependent variations in polarisation angle. (iii) If thereare significant gradients in Faraday rotation across or through theemission region of the source, then also polarisation angle can havecomplex dependence on the observing wavelength. The polarisa-tion angles of the source G358.002 − λ law, and other than source variability (Sect. 3.2), itcould have been caused by one of the above processes.In the case of Faraday rotation outside the Galaxy, the Fara-day screen is likely to be located several orders of magnitude far-ther away than the GC ISM. As a result, emission from differentparts of the source is viewed within one synthesised beam, the lin-ear scale of which is much larger than what is sampled in our ISM.At such length scales ( ∼ c (cid:13) , 1–24 Subhashis Roy, A. Pramesh Rao & Ravi Subrahmanyan tervening Faraday screen is likely to be uncorrelated. As a result,there is differential Faraday rotation within the beam, which givesrise to source depolarisation. From the data, the RM towards thesource G358.917+0.072 is found to be the highest with a measuredvalue of 4768 rad m − , and it shows a high depolarisation fraction(0.3 between 4.8 and 8.5 GHz), which is likely to be caused bydifferential Faraday rotation (Kronberg et al. 1972).Following the arguments given above, if the reduced χ of thefit is greater that 4.6, the probability of occurrence of which is lessthan 1% (Bevington 1969) or any of the source component showsa depolarisation fraction of less than 0.6 (Table 6) between 4.8 and8.5 GHz, we suspect that there is significant RM introduced out-side the Galaxy and the RM towards those components have notbeen used any further in this or in deriving the properties of theFaraday screen in Paper II. We note that the intrinsic RM of mostof the extragalactic sources are quite small ∼
10 rad m − (Simard-Normandin & Kronberg 1980) and the RMs measured from oursample is quite high ( ∼ − ), and consequently the RMintroduced outside the Galaxy should have little effect on the RMsof most of the sources in our sample. c (cid:13)000
10 rad m − (Simard-Normandin & Kronberg 1980) and the RMs measured from oursample is quite high ( ∼ − ), and consequently the RMintroduced outside the Galaxy should have little effect on the RMsof most of the sources in our sample. c (cid:13)000 , 1–24 xtragalactic sources towards the Galactic Centre T a b l e : M ea s u r e dp a r a m e t e r s o f t h e po l a r i s e d s ou r ce s fr o m t h e A T C A d a t a S ou r ce C m p R AD E C S m a j × S m i n , P A S p S t S % α . / . α . / . α . / . N o t e s ( J )( J ) m J y m J y P o l n . . + . N . − . . × . , . . − . − . − . ( i ) E G – S R S . − . . × . , − . . + . E . − . . × . , . − . − . − . ( G M ) E G – T C . − . . × . , − . − . W . − . . × . , . − . − . ( i ) . + . E . − . . × . , . − . − . − . ( i ) E G – D W . − . . × . , − . − . . + . N . − . . × . , − . − . − . ( i ) E G – D S . − . . × . , − . − .
65 356 . − . E . − . . × . , − . − . − . ( i ) E G – D W . − . . × . , − . − . . − . C . − . . × . , − . − . − . E G – U . + . C . − . . × . , . − . − . − . ( G C ) E G – U . + . C . − . . × . , − . − . − . ( G C ) E G – U . − . C . − . . × . , . − . − . − . ( G C ) E G – S R . − . C . − . . × . , − . − . − . ( G C ) E G – U . + . E . − . . × . , − . − . − . ( G C ) E G – D W . − . . × . , − . − .
66 0 . + . E . − . . × . , − . − . E G – T C . − . . × . , − . − . ( G C ) W . − . . × . , − . − . . + . C . − . . × . , . . . E G – U . − . N . − . . × . , − . − . − . ( G C ) E G – D S . − . . × . , − . − . . + . N . − . . × . , − . − . − . ( G C ) E G – T C . − . . × . , . S . − . . × . , c (cid:13) , 1–24 Subhashis Roy, A. Pramesh Rao & Ravi Subrahmanyan S ou r ce C m p R AD E C S m a j × S m i n , P A S p S t S % α . / . α . / . α . / . N o t e s ( J )( J ) m J y m J y P o l . . − . E . − . . × . , − . − . − . ( i ) E G – D W . − . . × . , − . − . . + . C . − . . × . , . − . − . − . E G – U . + . S . − . . × . , − . − . − . ( i ) E G – D N . − . . − . S . − . . × . , − . − . − . ( i ) F R -II C . − . . × . , − . N . − . . × . , < - . − .
84 4 . − . E . − . . × . , − . − . − . ( i ) E G – D W . − . . × . , − . − . . − . C . − . . × . , ; − . − . − . E G – U . × . ,
84* 5 . + . E . − . . × . , ; − . − . − . ( i ) E G – T . × . , W . − . . × . , − . − . . − . S . − . . × . , − . − . − . E G – D N . − . − . . − . N . − . . × . , − . − . − . ( i ) E G – D S . − . . × . , − . − . N o t e : I n T a b l e , , a nd5o f t h i s p a p e r , t h e s y m bo l ss ho w nb e l o w i nd i ca t e t h e f o ll o w i ng ‘ * ’ – s i ze o f t h e ob j ec t e s ti m a t e d fr o m . GH z m a p s – S p ec t r a li nd e x e s ti m a t e dbyd i v i d i ng i m a g e s m a d ea t d i ff e r e n t fr e qu e n c i e s G – G a l ac ti c s ou r ce E G – E x t r a g a l ac ti c s ou r ce U – U n r e s o l v e d s ou r ce S R – S li gh tl y r e s o l v e d D – D oub l e s ou r ce T – T r i pp l e C + E – F l a t s p ec t r u m c o r e w it h e x t e nd e d e m i ss i on . M – M u lti p l e s ou r ce s i n t h e fi e l d †–1 . GH z G PSfl uxd e n s it yd i ff e r s fr o m NV SS by m o r e t h a n20 % ( N ) –1 . GH z fl uxd e n s it y t a k e n fr o m NV SS ( L ) – F l uxd e n s it y t a k e n fr o m L az i o e t a l . ( ) **–1 . GH z fl uxd e n s it yunkno w n c (cid:13)000
84* 5 . + . E . − . . × . , ; − . − . − . ( i ) E G – T . × . , W . − . . × . , − . − . . − . S . − . . × . , − . − . − . E G – D N . − . − . . − . N . − . . × . , − . − . − . ( i ) E G – D S . − . . × . , − . − . N o t e : I n T a b l e , , a nd5o f t h i s p a p e r , t h e s y m bo l ss ho w nb e l o w i nd i ca t e t h e f o ll o w i ng ‘ * ’ – s i ze o f t h e ob j ec t e s ti m a t e d fr o m . GH z m a p s – S p ec t r a li nd e x e s ti m a t e dbyd i v i d i ng i m a g e s m a d ea t d i ff e r e n t fr e qu e n c i e s G – G a l ac ti c s ou r ce E G – E x t r a g a l ac ti c s ou r ce U – U n r e s o l v e d s ou r ce S R – S li gh tl y r e s o l v e d D – D oub l e s ou r ce T – T r i pp l e C + E – F l a t s p ec t r u m c o r e w it h e x t e nd e d e m i ss i on . M – M u lti p l e s ou r ce s i n t h e fi e l d †–1 . GH z G PSfl uxd e n s it yd i ff e r s fr o m NV SS by m o r e t h a n20 % ( N ) –1 . GH z fl uxd e n s it y t a k e n fr o m NV SS ( L ) – F l uxd e n s it y t a k e n fr o m L az i o e t a l . ( ) **–1 . GH z fl uxd e n s it yunkno w n c (cid:13)000 , 1–24 xtragalactic sources towards the Galactic Centre S ou r ce C m p R AD E C S m a j × S m i n , P A S p S t S % α . / . α . / . α . / . N o t e s ( J )( J ) m J y m J y P o l . ( G C ) – P b a nd fl uxd e n s it y t a k e n fr o m ( L a R o s ae t a l . ) ( G M ) – P b a nd fl uxd e n s it y t a k e n fr o m R oy & R a o ( ) ( G M ) – P b a nd fl uxd e n s it y t a k e n fr o m S . B h a t n a g a r( p r i v a t ec o mm un i ca ti on ) ( i ) – S p ec t r a li nd e x e s ti m a t e d fr o m i n t e g r a t e d fl uxd e n s iti e s o f c o m pon e n t s T a b l e : M ea s u r e dp a r a m e t e r s o f t h e po l a r i s e d s ou r ce s fr o m V L A d a t a S ou r ce C m p R AD E C S m a j × S m i n , P A S p S t S % α . / . α . / . α . / . N o t e s ( J )( J ) m J y m J y P o l n . . − . C . − . . × . , . − . − . − . E G – U . + . E . − . . × . , . . − . − . − . ( i ) E G – D W . − . . × . , . . − . − . . − . N . − . . × . , . − . s − . ( N ) − . F R -II C . − . . × . , . . − . s S . − . . × . , − . s . + . C . − . . × . , − . − . ( G M )( i ) F R -I . − . C . − . . × . , . . . − . ( i ) C + E ( − ) . − . E . − . . × . , . − . s − . ( N ) − . F R -II C . − . . × . , . . . s W . − . . × . , − . s . + . N . − . . × . , . − . − . − . ( G C ) F R -II C . − . . × . , . . − . S . − . . × . , . . . − . − .
86 358 . − . E . − . . × . , . − . s − . ( i ) − . ( G C ) E G – D W . − . . × . , . . − . s . + . E . − . . × . , . . − . − . ( N ) − . ( G C ) F R -II W . − . . × . , . . − . . − . C . − . . × . , . . . − . ( G C )( i ) G ( M ou s e ) . + . E . − . . × . , . . −− . − . ( G C )( i ) F R -II C . − . . × . , . . . − . ( . / . ) W . − . . × . , . . . − . c (cid:13) , 1–24 Subhashis Roy, A. Pramesh Rao & Ravi Subrahmanyan S ou r ce C m p R AD E C S m a j × S m i n , P A S p S t S % α . / . α . / . α . / . N o t e s ( J )( J ) m J y m J y P o l . . − . E . − . . × . , . − . − . ( G C ) F R -II ? C . − . . × . , . . − . ( . / . ) W . − . . × . , . . − . . + . E . − . . × . , . . − . − . ( L ) − . ( G C ) F R -II C . − . . × . , . . − . − . ( L ) W . − . − . − . ( L ) . + . E . − . . × . , . . − . − . ( i ) − . ( G C ) E G – D W . − . . × . , . . − . . + . N . − . . × . , . . − . − . − . ( i ) F R -II S . − . . × . , . . − . − . . + . N . − . . × . , . . − . s − . ( i ) − . E G – D S . − . . × . , . . − . s . − . C . − . . × . , . . − . − . − . ( G M ) E G – S R . + . C . − . . × . , . − . − . . ( G M ) E G – U ( − ) . − . E . − . . × . , . . − . − . ( N )( i ) − . ( G M ) E G – D W . − . . , . , . . . . + . C . − . . × . , . . . ( G M ) E G – U ( . / . ) . + . C . − . . × . , . − . − . − . E G – S R . + . E . − . . × . , . − . s E G – T C . − . . × . , . . − . s − . ( N ) − . W . − . . × . , . − . s . + . N . − . . × . , . . − . − . − . ( i ) E G – D S . − . . × . , . . − . − . T a b l e : M ea s u r e dp a r a m e t e r s o f t h e unpo l a r i s e d s ou r ce s fr o m t h e A T C A d a t a S ou r ce C m p R AD E C S m a j × S m i n , P A S p S t S α . / . α . / . α . / . N o t e s ( J )( J ) . - . N . − . . × . , − . − . − . ( i ) E G – D c (cid:13)000
86 358 . − . E . − . . × . , . − . s − . ( i ) − . ( G C ) E G – D W . − . . × . , . . − . s . + . E . − . . × . , . . − . − . ( N ) − . ( G C ) F R -II W . − . . × . , . . − . . − . C . − . . × . , . . . − . ( G C )( i ) G ( M ou s e ) . + . E . − . . × . , . . −− . − . ( G C )( i ) F R -II C . − . . × . , . . . − . ( . / . ) W . − . . × . , . . . − . c (cid:13) , 1–24 Subhashis Roy, A. Pramesh Rao & Ravi Subrahmanyan S ou r ce C m p R AD E C S m a j × S m i n , P A S p S t S % α . / . α . / . α . / . N o t e s ( J )( J ) m J y m J y P o l . . − . E . − . . × . , . − . − . ( G C ) F R -II ? C . − . . × . , . . − . ( . / . ) W . − . . × . , . . − . . + . E . − . . × . , . . − . − . ( L ) − . ( G C ) F R -II C . − . . × . , . . − . − . ( L ) W . − . − . − . ( L ) . + . E . − . . × . , . . − . − . ( i ) − . ( G C ) E G – D W . − . . × . , . . − . . + . N . − . . × . , . . − . − . − . ( i ) F R -II S . − . . × . , . . − . − . . + . N . − . . × . , . . − . s − . ( i ) − . E G – D S . − . . × . , . . − . s . − . C . − . . × . , . . − . − . − . ( G M ) E G – S R . + . C . − . . × . , . − . − . . ( G M ) E G – U ( − ) . − . E . − . . × . , . . − . − . ( N )( i ) − . ( G M ) E G – D W . − . . , . , . . . . + . C . − . . × . , . . . ( G M ) E G – U ( . / . ) . + . C . − . . × . , . − . − . − . E G – S R . + . E . − . . × . , . − . s E G – T C . − . . × . , . . − . s − . ( N ) − . W . − . . × . , . − . s . + . N . − . . × . , . . − . − . − . ( i ) E G – D S . − . . × . , . . − . − . T a b l e : M ea s u r e dp a r a m e t e r s o f t h e unpo l a r i s e d s ou r ce s fr o m t h e A T C A d a t a S ou r ce C m p R AD E C S m a j × S m i n , P A S p S t S α . / . α . / . α . / . N o t e s ( J )( J ) . - . N . − . . × . , − . − . − . ( i ) E G – D c (cid:13)000 , 1–24 xtragalactic sources towards the Galactic Centre S ou r ce C m p R AD E C S m a j × S m i n , P A S p S t S α . / . α . / . α . / . N o t e s ( J )( J ) S . − . . × . , − . − . . - . C . − . . × . , − . − . ( G M ) E G – S R . + . C . − . . × . , − . − . ( G C ) E G – U . + . C . − . . × . , − . − . ( G C ) E G – U . + . C . − . . × . , − . − . − . ( G C ) E G – U . + . C . − . . × . , − . − . − . ( G C ) E G – U . + . C . − . . × . , − . − . − . ( G C ) E G – U . - . C . − . . × . , − . − . − . E G – U . - . C . − . . × . , − . − . − . E G – U . + . C . − . . × . , − . − . − . E G – U T a b l e : E s ti m a t e dp a r a m e t e r s o f t h e unpo l a r i s e d s ou r ce s fr o m t h e V L A d a t a S ou r ce C m p R AD E C S m a j × S m i n , P A S p S t S α . / . α . / . α . / . N o t e s ( J )( J ) . - . C . − . . × . , . . G – H II . + . E X . − . ∼ × , - − . . G – H II . - . E X . − . ∼ × , - − . . G – H II . + . C . − . . × . , − . − . − . E G – U . - . R . − . ∼ × , –12198 − . G – H II . + C . − . . × . , − . − . E G – M . + . C . − . . × . , − . − . − . E G – S R fl uxd e n s it yo f t h ec o m pon e n t n ea r t h e bo tt o m o f it s m a p ( F i g . ) fl uxd e n s it yo f t h ec o m pon e n t n ea r t h e t opo f it s m a p ( F i g . ) c (cid:13) , 1–24 Subhashis Roy, A. Pramesh Rao & Ravi Subrahmanyan
G354.740+0.138 IPOL 4800.000 MHZ Peak flux = 6.1946E-02 JY/BEAM Levs = 1.000E-03 * (-2, -1, 1, 2, 4, 6, 8, 10, 12,16, 20, 24, 32, 40, 48, 64, 80, 128) D E C L I NA T I O N ( J2000 ) RIGHT ASCENSION (J2000)17 31 57.6 57.4 57.2 57.0 56.8 56.6 56.4-33 18 253035404550 Pol line 1 arcsec = 1.2500E-03 JY/BEAM
G356.000+0.023 IPOL 4800.000 MHZ Peak flux = 3.5624E-02 JY/BEAM Levs = 1.000E-03 * (-2, -1, 1, 2, 4, 6, 8, 10, 12,16, 20, 24, 32, 40, 48, 64, 80, 128) D E C L I NA T I O N ( J2000 ) RIGHT ASCENSION (J2000)17 35 41.0 40.5 40.0 39.5 39.0-32 18 45505519 000510 Pol line 1 arcsec = 1.2500E-03 JY/BEAM
G356.161+1.635 IPOL 4800.000 MHZ Peak flux = 4.3791E-02 JY/BEAM Levs = 1.000E-03 * (-2, -1, 1, 2, 4, 6, 8, 10, 12,16, 20, 24, 32, 40, 48, 64, 80, 128) D E C L I NA T I O N ( J2000 ) RIGHT ASCENSION (J2000)17 29 44.5 44.0 43.5 43.0 42.5 42.0-31 17 505518 00051015 Pol line 1 arcsec = 1.2500E-03 JY/BEAM
G356.567+0.869 IPOL 4800.000 MHZ Peak flux = 2.0850E-02 JY/BEAM Levs = 1.000E-03 * (-2, -1, 1, 2, 4, 6, 8, 10, 12,16, 20, 24, 32, 40, 48, 64, 80, 128) D E C L I NA T I O N ( J2000 ) RIGHT ASCENSION (J2000)17 33 46.5 46.0 45.5 45.0 44.5-31 22 2530354045505523 0005 Pol line 1 arcsec = 1.2500E-03 JY/BEAM
G356.719--1.220 IPOL 4800 MHZPeak flux = 2.4151E-02 JY/BEAM Levs = 1.000E-03 * (-2, -1, 1, 2, 4, 6, 8, 10, 12,16, 20, 24, 32, 40, 48, 64, 80, 128) D E C L I NA T I O N ( J2000 ) RIGHT ASCENSION (J2000)17 42 28.4 28.2 28.0 27.8 27.6 27.4 27.2 27.0 26.8-32 22 000510152025 Pol line 1 arcsec = 1.2500E-03 JY/BEAM
G358.002--0.636 IPOL 4800.000 MHZ Peak contour flux = 2.7688E-01 JY/BEAM Levs = 1.000E-03 * (-2, -1, 1, 2, 4, 6, 8, 10, 12,16, 20, 24, 32, 40, 48, 64, 80, 128, 160, 192) D E C L I NA T I O N ( J2000 ) RIGHT ASCENSION (J2000)17 43 18.6 18.4 18.2 18.0 17.8 17.6 17.4 17.2 17.0-30 58 051015202530 Pol line 1 arcsec = 1.2500E-03 JY/BEAM
G358.917+0.072 IPOL 4800.000 MHZ Peak flux = 9.9553E-02 JY/BEAM Levs = 1.000E-03 * (-2, -1, 1, 2, 4, 6, 8, 10, 12,16, 20, 24, 32, 40, 48, 64, 80, 128) D E C L I NA T I O N ( J2000 ) RIGHT ASCENSION (J2000)17 42 44.6 44.4 44.2 44.0 43.8 43.6 43.4-29 49 0510152025 Pol line 1 arcsec = 1.2500E-03 JY/BEAM
G359.388+0.460 IPOL 4800.000 MHZ Peak contour flux = 3.8831E-02 JY/BEAM Levs = 1.000E-03 * (-2, -1, 1, 2, 4, 6, 8, 10, 12,16, 20, 24, 32, 40, 48, 64, 80, 128, 160, 192) D E C L I NA T I O N ( J2000 ) RIGHT ASCENSION (J2000)17 42 22.0 21.8 21.6 21.4 21.2 21.0 20.8-29 12 505513 00051015 Pol line 1 arcsec = 1.2500E-03 JY/BEAM
G359.844--1.843 IPOL 4800.000 MHZ Peak contour flux = 1.5443E-01 JY/BEAM Levs = 3.000E-03 * (-2, -1, 1, 2, 4, 6, 8, 10, 12,16, 20, 24, 32, 40, 48, 64, 80, 128, 160, 192) D E C L I NA T I O N ( J2000 ) RIGHT ASCENSION (J2000)17 52 31.6 31.4 31.2 31.0 30.8 30.6 30.4-30 00 5501 00051015 Pol line 1 arcsec = 1.2500E-03 JY/BEAM
Figure 3. ≈ (cid:48)(cid:48) × (cid:48)(cid:48) .c (cid:13)000
Figure 3. ≈ (cid:48)(cid:48) × (cid:48)(cid:48) .c (cid:13)000 , 1–24 xtragalactic sources towards the Galactic Centre G359.911--1.813 IPOL 4800.000 MHZ Peak contour flux = 1.3186E-01 JY/BEAM Levs = 3.000E-03 * (-2, -1, 1, 2, 4, 6, 8, 10, 12,16, 20, 24, 32, 40, 48, 64, 80, 128, 160, 192) D E C L I NA T I O N ( J2000 ) RIGHT ASCENSION (J2000)17 52 33.8 33.6 33.4 33.2 33.0 32.8 32.6 32.4-29 56 3540455055 Pol line 1 arcsec = 1.2500E-03 JY/BEAM
G359.993+1.591 IPOL 4800.000 MHZ Peak flux = 1.3038E-02 JY/BEAM Levs = 1.000E-03 * (-2, -1, 1, 2, 4, 6, 8, 10, 12,16, 20, 24, 32, 40, 48, 64, 80, 128) D E C L I NA T I O N ( J2000 ) RIGHT ASCENSION (J2000)17 39 27.4 27.2 27.0 26.8 26.6 26.4 26.2-28 06 0608101214161820222426 Pol line 1 arcsec = 1.2500E-03 JY/BEAM
G0.313+1.645 IPOL 4800.000 MHZ Peak flux = 1.7530E-02 JY/BEAM Levs = 1.000E-03 * (-2, -1, 1, 2, 4, 6, 8, 10, 12,16, 20, 24, 32, 40, 48, 64, 80, 128) D E C L I NA T I O N ( J2000 ) RIGHT ASCENSION (J2000)17 40 01.5 01.0 00.5 39 60.0-27 48 00051015202530 Pol line 1 arcsec = 1.2500E-03 JY/BEAM
G0.537+0.253 IPOL 4800.000 MHZPeak contour flux = 7.0774E-02 JY/BEAM Levs = 4.000E-03 * (-2, -1, 1, 2, 4, 6, 8, 10, 12,16, 20, 24, 32, 40, 48, 64, 80, 128, 160, 192) D E C L I NA T I O N ( J2000 ) RIGHT ASCENSION (J2000)17 45 53.2 53.0 52.8 52.6 52.4 52.2 52.0 51.8-28 20 152025303540 Pol line 1 arcsec = 1.2500E-03 JY/BEAM
G1.028--1.110 IPOL 4800.000 MHZ Peak contour flux = 4.0007E-02 JY/BEAM Levs = 1.000E-03 * (-2, -1, 1, 2, 4, 6, 8, 10, 12,16, 20, 24, 32, 40, 48, 64, 80, 128, 160, 192) D E C L I NA T I O N ( J2000 ) RIGHT ASCENSION (J2000)17 52 23.4 23.2 23.0 22.8 22.6 22.4 22.2 22.0-28 37 253035404550 Pol line 1 arcsec = 1.2500E-03 JY/BEAM
G1.035+1.559 IPOL 4800.000 MHZ Peak flux = 5.0230E-02 JY/BEAM Levs = 1.000E-03 * (-2, -1, 1, 2, 4, 6, 8, 10, 12,16, 20, 24, 32, 40, 48, 64, 80, 128, 160, 192) D E C L I NA T I O N ( J2000 ) RIGHT ASCENSION (J2000)17 42 06 05 04 03 02 01-27 13 003014 003015 0030 Pol line 1 arcsec = 1.2500E-03 JY/BEAM
G1.505--1.231 IPOL 4800.000 MHZPeak contour flux = 2.9948E-02 JY/BEAM Levs = 1.000E-03 * (-2, -1, 1, 2, 4, 6, 8, 10, 12,16, 20, 24, 32, 40, 48, 64, 80, 128, 160, 192) D E C L I NA T I O N ( J2000 ) RIGHT ASCENSION (J2000)17 54 00 53 59 58 57 56 55 54-28 15 304516 0015304517 001530 Pol line 1 arcsec = 1.2500E-03 JY/BEAM
G2.143+1.772 IPOL 4800.000 MHZ Peak flux = 4.5318E-02 JY/BEAM Levs = 1.000E-03 * (-2, -1, 1, 2, 4, 6, 8, 10, 12,16, 20, 24, 32, 40, 48, 64, 80, 128, 160, 192) D E C L I NA T I O N ( J2000 ) RIGHT ASCENSION (J2000)17 43 51.8 51.6 51.4 51.2 51.0 50.8 50.6-26 10 45505511 00051015 Pol line 1 arcsec = 1.2500E-03 JY/BEAM
G4.005+1.403 IPOL 4800.000 MHZ Peak flux = 5.1955E-02 JY/BEAM Levs = 1.000E-03 * (-2, -1, 1, 2, 4, 6, 8, 10, 12,16, 20, 24, 32, 40, 48, 64, 80, 128, 160, 192) D E C L I NA T I O N ( J2000 ) RIGHT ASCENSION (J2000)17 49 32.5 32.0 31.5 31.0-24 46 4045505547 000510 Pol line 1 arcsec = 1.2500E-03 JY/BEAM
Figure 3.
Continuedc (cid:13) , 1–24 Subhashis Roy, A. Pramesh Rao & Ravi Subrahmanyan
G4.188--1.680 IPOL 4800.000 MHZ Peak flux = 2.9239E-02 JY/BEAM Levs = 1.000E-03 * (-2, -1, 1, 2, 4, 6, 8, 10, 12,16, 20, 24, 32, 40, 48, 64, 80, 128, 160, 192) D E C L I NA T I O N ( J2000 ) RIGHT ASCENSION (J2000)18 01 47.5 47.0 46.5 46.0 45.5 45.0 44.5 44.0-26 10 00153045 Pol line 1 arcsec = 1.2500E-03 JY/BEAM
G4.256--0.726 IPOL 4800.000 MHZ Peak flux = 1.3449E-02 JY/BEAM Levs = 1.000E-03 * (-2, -1, 1, 2, 4, 6, 8, 10, 12,16, 20, 24, 32, 40, 48, 64, 80, 128, 160, 192) D E C L I NA T I O N ( J2000 ) RIGHT ASCENSION (J2000)17 58 13.5 13.0 12.5 12.0 11.5-25 38 354045505539 00 Pol line 1 arcsec = 1.2500E-03 JY/BEAM
G5.260--0.754 IPOL 4800.000 MHZ Peak flux = 6.5684E-02 JY/BEAM Levs = 1.000E-03 * (-2, -1, 1, 2, 4, 6, 8, 10, 12,16, 20, 24, 32, 40, 48, 64, 80, 128, 160, 192) D E C L I NA T I O N ( J2000 ) RIGHT ASCENSION (J2000)18 00 32.2 32.0 31.8 31.6 31.4 31.2 31.0 30.8 30.6-24 47 101520253035 Pol line 1 arcsec = 1.2500E-03 JY/BEAM
G5.358+0.899 IPOL 4800.000 MHZ Peak flux = 3.1390E-02 JY/BEAM Levs = 1.000E-03 * (-2, -1, 1, 2, 4, 6, 8, 10, 12,16, 20, 24, 32, 40, 48, 64, 80, 128, 160, 192) D E C L I NA T I O N ( J2000 ) RIGHT ASCENSION (J2000)17 54 28.2 28.0 27.8 27.6 27.4 27.2 27.0 26.8-23 52 2530354045 Pol line 1 arcsec = 1.2500E-03 JY/BEAM
G5.511--1.515 IPOL 4800.000 MHZ Peak flux = 6.2588E-02 JY/BEAM Levs = 1.000E-03 * (-2, -1, 1, 2, 4, 6, 8, 10, 12,16, 20, 24, 32, 40, 48, 64, 80, 128, 160, 192) D E C L I NA T I O N ( J2000 ) RIGHT ASCENSION (J2000)18 03 60.0 59.8 59.6 59.4 59.2 59.0 58.8 58.6-24 56 2530354045505557 00 Pol line 1 arcsec = 1.2500E-03 JY/BEAM
G6.183--1.480 IPOL 4800.000 MHZ Peak flux = 1.9096E-02 JY/BEAM Levs = 1.000E-03 * (-2, -1, 1, 2, 4, 6, 8, 10, 12,16, 20, 24, 32, 40, 48, 64, 80, 128, 160, 192) D E C L I NA T I O N ( J2000 ) RIGHT ASCENSION (J2000)18 05 18.6 18.4 18.2 18.0 17.8 17.6 17.4-24 20 2025303540455055 Pol line 1 arcsec = 1.2500E-03 JY/BEAM
Figure 3.
Continued c (cid:13)000
Continued c (cid:13)000 , 1–24 xtragalactic sources towards the Galactic Centre G353.462--0.691 IPOL 4760.100 MHZ Peak flux = 9.8027E-02 JY/BEAM Levs = 3.000E-04 * (-2, -1, 1, 2, 4, 6, 8, 12, 16,20, 24, 32, 40, 48, 64, 96, 128, 160, 192, 224, 256,320) D E C L I NA T I O N ( J2000 ) RIGHT ASCENSION (J2000)17 31 55.7 55.6 55.5 55.4 55.3 55.2 55.1-34 49 555657585950 000102030405 Pol line 1 arcsec = 2.5000E-03 JY/BEAM
G354.815+0.775 IPOL 4760.100 MHZ Peak flux = 1.8204E-02 JY/BEAM Levs = 3.000E-04 * (-2, -1, 1, 2, 4, 6, 8, 12, 16,20, 24, 32, 40, 48, 64, 96, 128, 160, 192, 224, 256,320) D E C L I NA T I O N ( J2000 ) RIGHT ASCENSION (J2000)17 29 36.9 36.8 36.7 36.6 36.5 36.4 36.3 36.2 36.1 36.0-32 53 47484950515253545556 Pol line 1 arcsec = 2.5000E-03 JY/BEAM
G355.424--0.809 IPOL 4760.100 MHZ Peak flux = 1.0686E-02 JY/BEAM Levs = 3.000E-04 * (-2, -1, 1, 2, 4, 6, 8, 12, 16,20, 24, 32, 40, 48, 64, 96, 128, 160, 192, 224, 256,320) D E C L I NA T I O N ( J2000 ) RIGHT ASCENSION (J2000)17 37 32.8 32.6 32.4 32.2 32.0 31.8 31.6 31.4 31.2-33 14 354045505515 00051015 Pol line 1 arcsec = 2.5000E-03 JY/BEAM
G356.905+0.082 IPOL 4760.100 MHZ Peak flux = 4.1907E-02 JY/BEAM Levs = 3.000E-04 * (-2, -1, 1, 2, 4, 6, 8, 12, 16,20, 24, 32, 40, 48, 64, 96, 128, 160, 192, 224, 256,320) D E C L I NA T I O N ( J2000 ) RIGHT ASCENSION (J2000)17 37 45.0 44.5 44.0 43.5 43.0 42.5-31 30 505531 0005101520253035 Pol line 1 arcsec = 2.5000E-03 JY/BEAM
G358.149--1.675 IPOL 4760.100 MHZ Peak flux = 1.3556E-02 JY/BEAM Levs = 3.000E-04 * (-2, -1, 1, 2, 4, 6, 8, 12, 16,20, 24, 32, 40, 48, 64, 96, 128, 160, 192, 224, 256,320) D E C L I NA T I O N ( J2000 ) RIGHT ASCENSION (J2000)17 47 50 49 48 47 46 45-31 23 000510152025303540 Pol line 1 arcsec = 2.5000E-03 JY/BEAM
G358.156+0.028 IPOL 4760.100 MHZ Peak flux = 2.3702E-02 JY/BEAM Levs = 3.000E-04 * (-2, -1, 1, 2, 4, 6, 8, 12, 16,20, 24, 32, 40, 48, 64, 96, 128, 160, 192, 224, 256,320) D E C L I NA T I O N ( J2000 ) RIGHT ASCENSION (J2000)17 41 03.2 03.0 02.8 02.6 02.4-30 29 1820222426283032343638 Pol line 1 arcsec = 2.5000E-03 JY/BEAM
G358.930--1.197 IPOL 4760.100 MHZ Peak flux = 8.9001E-03 JY/BEAM Levs = 3.000E-04 * (-2, -1, 1, 2, 4, 6, 8, 12, 16,20, 24, 32, 40, 48, 64, 96, 128, 160, 192, 224, 256,320) D E C L I NA T I O N ( J2000 ) RIGHT ASCENSION (J2000)17 47 47.8 47.6 47.4 47.2 47.0 46.8 46.6 46.4 46.2-30 28 06081012141618202224 Pol line 1 arcsec = 2.5000E-03 JY/BEAM
G359.2-0.8 IPOL 4760.100 MHZ Peak flux = 1.6453E-02 JY/BEAM Levs = 3.000E-04 * (-2, -1, 1, 2, 4, 6, 8, 12, 16,20, 24, 32, 40, 48, 64, 96, 128, 160, 192, 224, 256,320) D E C L I NA T I O N ( J2000 ) RIGHT ASCENSION (J2000)17 47 16.0 15.5 15.0 14.5 14.0 13.5-29 57 4045505558 00051015 Pol line 1 arcsec = 2.5000E-03 JY/BEAM
G359.392+1.272 IPOL 4760.100 MHZ Peak flux = 6.9187E-03 JY/BEAM Levs = 3.000E-04 * (-2, -1, 1, 2, 4, 6, 8, 12, 16,20, 24, 32, 40, 48, 64, 96, 128, 160, 192, 224, 256,320) D E C L I NA T I O N ( J2000 ) RIGHT ASCENSION (J2000)17 39 13.6 13.4 13.2 13.0 12.8 12.6 12.4 12.2-28 46 505254565847 00020406 Pol line 1 arcsec = 2.5000E-03 JY/BEAM
Figure 4. µ Jy/beam and about 75 µ Jy/beam in Stokes Q and U. Typical beamsize of these images are ≈ (cid:48)(cid:48) × . (cid:48)(cid:48) .c (cid:13) , 1–24 Subhashis Roy, A. Pramesh Rao & Ravi Subrahmanyan
G359.604+0.306 IPOL 4760.100 MHZ Peak flux = 6.6578E-03 JY/BEAM Levs = 3.000E-04 * (-2, -1, 1, 2, 4, 6, 8, 12, 16,20, 24, 32, 40, 48, 64, 96, 128, 160, 192, 224, 256,320) D E C L I NA T I O N ( J2000 ) RIGHT ASCENSION (J2000)17 43 29.6 29.4 29.2 29.0 28.8 28.6 28.4 28.2-29 06 424446485052 Pol line 1 arcsec = 2.5000E-03 JY/BEAM
G359.710--0.904 IPOL 4760.100 MHZ Peak flux = 2.4146E-03 JY/BEAM Levs = 3.000E-04 * (-2, -1, 1, 2, 4, 6, 8, 12, 16,20, 24, 32, 40, 48, 64, 96, 128, 160, 192, 224, 256,320) D E C L I NA T I O N ( J2000 ) RIGHT ASCENSION (J2000)17 48 29.5 29.0 28.5 28.0 27.5-29 39 0406081012141618 Pol line 1 arcsec = 2.5000E-03 JY/BEAM
G359.871+0.179 IPOL 4760.100 MHZ Peak flux = 4.1368E-02 JY/BEAM Levs = 3.000E-04 * (-2, -1, 1, 2, 4, 6, 8, 12, 16,20, 24, 32, 40, 48, 64, 96, 128, 160, 192, 224, 256,320) D E C L I NA T I O N ( J2000 ) RIGHT ASCENSION (J2000)17 44 37.2 37.0 36.8 36.6 36.4 36.2-28 57 06081012141618 Pol line 1 arcsec = 2.5000E-03 JY/BEAM
G0.404+1.061 IPOL 4760.100 MHZ Peak flux = 1.3505E-02 JY/BEAM Levs = 3.000E-04 * (-2, -1, 1, 2, 4, 6, 8, 12, 16,20, 24, 32, 40, 48, 64, 96, 128, 160, 192, 224, 256,320) D E C L I NA T I O N ( J2000 ) RIGHT ASCENSION (J2000)17 42 28.5 28.4 28.3 28.2 28.1 28.0 27.9 27.8 27.7-28 02 0506070809101112131415 Pol line 1 arcsec = 2.5000E-03 JY/BEAM
G1.826+1.070 IPOL 4760.100 MHZ Peak flux = 9.8535E-03 JY/BEAM Levs = 3.000E-04 * (-2, -1, 1, 2, 4, 6, 8, 12, 16,20, 24, 32, 40, 48, 64, 96, 128, 160, 192, 224, 256,320) D E C L I NA T I O N ( J2000 ) RIGHT ASCENSION (J2000)17 45 47.8 47.6 47.4 47.2 47.0-26 49 0510152025 Pol line 1 arcsec = 2.5000E-03 JY/BEAM
G2.922+1.028 IPOL 4760.100 MHZ Peak flux = 2.1305E-02 JY/BEAM Levs = 3.000E-04 * (-2, -1, 1, 2, 4, 6, 8, 12, 16,20, 24, 32, 40, 48, 64, 96, 128, 160, 192, 224, 256,320) D E C L I NA T I O N ( J2000 ) RIGHT ASCENSION (J2000)17 48 29.5 29.4 29.3 29.2 29.1 29.0 28.9 28.8-25 54 1213141516171819202122 Pol line 1 arcsec = 2.5000E-03 JY/BEAM
G3.347--0.327 IPOL 4760.100 MHZ Peak flux = 4.8289E-03 JY/BEAM Levs = 3.000E-04 * (-2, -1, 1, 2, 4, 6, 8, 12, 16,20, 24, 32, 40, 48, 64, 96, 128, 160, 192, 224, 256,320) D E C L I NA T I O N ( J2000 ) RIGHT ASCENSION (J2000)17 54 38.6 38.5 38.4 38.3 38.2 38.1-26 13 474849505152535455 Pol line 1 arcsec = 2.5000E-03 JY/BEAM
G3.748--1.221 IPOL 4760.100 MHZ Peak flux = 1.1330E-02 JY/BEAM Levs = 3.000E-04 * (-2, -1, 1, 2, 4, 6, 8, 12, 16,20, 24, 32, 40, 48, 64, 96, 128, 160, 192, 224, 256,320) D E C L I NA T I O N ( J2000 ) RIGHT ASCENSION (J2000)17 58 59.8 59.6 59.4 59.2 59.0 58.8 58.6 58.4-26 19 555657585920 000102030405 Pol line 1 arcsec = 2.5000E-03 JY/BEAM
G3.928+0.253 IPOL 4760.100 MHZ Peak flux = 1.2020E-01 JY/BEAM Levs = 3.000E-04 * (-2, -1, 1, 2, 4, 6, 8, 12, 16,20, 24, 32, 40, 48, 64, 96, 128, 160, 192, 224, 256,320) D E C L I NA T I O N ( J2000 ) RIGHT ASCENSION (J2000)17 53 43.6 43.5 43.4 43.3 43.2 43.1-25 26 060708091011121314 Pol line 1 arcsec = 2.5000E-03 JY/BEAM
Figure 4.
Continued c (cid:13)000
Continued c (cid:13)000 , 1–24 xtragalactic sources towards the Galactic Centre G4.752+0.255 IPOL 4760.100 MHZ Peak flux = 2.6332E-02 JY/BEAM Levs = 3.000E-04 * (-2, -1, 1, 2, 4, 6, 8, 12, 16,20, 24, 32, 40, 48, 64, 96, 128, 160, 192, 224, 256,320) D E C L I NA T I O N ( J2000 ) RIGHT ASCENSION (J2000)17 55 33.7 33.6 33.5 33.4 33.3 33.2 33.1-24 43 26272829303132333435 Pol line 1 arcsec = 2.5000E-03 JY/BEAM
G5.791+0.794 IPOL 4760.100 MHZ Peak flux = 1.7783E-02 JY/BEAM Levs = 3.000E-04 * (-2, -1, 1, 2, 4, 6, 8, 12, 16,20, 24, 32, 40, 48, 64, 96, 128, 160, 192, 224, 256,320) D E C L I NA T I O N ( J2000 ) RIGHT ASCENSION (J2000)17 55 49.2 49.0 48.8 48.6 48.4 48.2 48.0-23 33 14161820222426 Pol line 1 arcsec = 2.5000E-03 JY/BEAM
G5.852+1.041 IPOL 4760.100 MHZ Peak flux = 9.1680E-03 JY/BEAM Levs = 3.000E-04 * (-2, -1, 1, 2, 4, 6, 8, 12, 16,20, 24, 32, 40, 48, 64, 96, 128, 160, 192, 224, 256,320) D E C L I NA T I O N ( J2000 ) RIGHT ASCENSION (J2000)17 55 01.3 01.201.101.000.900.800.700.600.500.4-23 22 303540455055 Pol line 1 arcsec = 2.5000E-03 JY/BEAM
G3.745+0.635 IPOL 4885.100 MHZ Peak contour flux = 4.4563E-01 JY/BEAM Levs = 3.000E-04 * (-2, -1, 1, 2, 4, 6, 8, 12, 16,20, 24, 32, 40, 48, 64, 96, 128, 160, 192, 224, 256,320) D E C L I NA T I O N ( J2000 ) RIGHT ASCENSION (J2000)17 51 51.7 51.6 51.5 51.4 51.3 51.2 51.1 51.0 50.9 50.8-25 23 5254565824 0002040608 Pol line 1 arcsec = 2.5000E-03 JY/BEAM
G357.864--0.996 IPOL 4760.100 MHZ Peak contour flux = 3.6981E-01 JY/BEAM Levs = 3.000E-04 * (-2, -1, 1, 2, 4, 6, 8, 12, 16,20, 24, 32, 40, 48, 64, 96, 128, 160, 192, 224, 256,320) D E C L I NA T I O N ( J2000 ) RIGHT ASCENSION (J2000)17 44 24.2 24.0 23.8 23.6 23.4 23.2 23.0 22.8 22.6-31 16 152025303540455055 Pol line 1 arcsec = 2.5000E-03 JY/BEAM
Figure 4.
Continuedc (cid:13) , 1–24 Subhashis Roy, A. Pramesh Rao & Ravi Subrahmanyan
BOTH: G354.719-1.117 IPOL 5952.000 MHZ Grey scale flux range= -2.24 76.34 MilliJY/BEAMCont peak flux = 7.6344E-02 JY/BEAM Levs = 1.000E-03 * (-2, -1, 1, 2, 4, 6, 8, 10, 12,16, 20, 24, 32, 40, 48, 64, 80, 128)0 20 40 60 D E C L I NA T I O N ( J2000 ) RIGHT ASCENSION (J2000)17 36 58.5 58.0 57.5 57.0-34 00 202530354045
BOTH: G357.435-0.519 IPOL 4800.000 MHZGrey scale flux range= -0.98 50.17 MilliJY/BEAMCont peak flux = 5.0169E-02 JY/BEAM Levs = 1.000E-03 * (-2, -1, 1, 2, 4, 6, 8, 10, 12,16, 20, 24, 28, 32, 40, 48, 64, 80, 96, 128)0 20 40 D E C L I NA T I O N ( J2000 ) RIGHT ASCENSION (J2000)17 41 27.5 27.0 26.5 26.0 25.5 25.0-31 23 0015304524 0015
BOTH: G358.591+0.046 IPOL 4800.000 MHZ Grey scale flux range= -4.46 27.72 MilliJY/BEAMCont peak flux = 2.7716E-02 JY/BEAM Levs = 1.000E-03 * (-2, -1, 1, 2, 4, 6, 8, 10, 12,16, 20, 24, 32, 40, 48, 64, 80, 128)0 10 20 D E C L I NA T I O N ( J2000 ) RIGHT ASCENSION (J2000)17 42 03.4 03.2 03.0 02.8 02.6 02.4 02.2 02.0-30 06 35404550
BOTH: G358.982+0.580 IPOL 4800.000 MHZGrey scale flux range= -0.93 43.20 MilliJY/BEAMCont peak flux = 4.3203E-02 JY/BEAM Levs = 1.000E-03 * (-2, -1, 1, 2, 4, 6, 8, 10, 12,16, 20, 24, 28, 32, 40, 48, 64, 80, 96, 128)0 10 20 30 40 D E C L I NA T I O N ( J2000 ) RIGHT ASCENSION (J2000)17 40 55.4 55.2 55.0 54.8 54.6 54.4 54.2 54.0 53.8 53.6-29 29 304530 0015
BOTH: G359.546+0.988 IPOL 4800.000 MHZ Grey scale flux range= -2.63 35.56 MilliJY/BEAMCont peak flux = 3.5557E-02 JY/BEAM Levs = 1.000E-03 * (-2, -1, 1, 2, 4, 6, 8, 10, 12,16, 20, 24, 32, 40, 48, 64, 80, 128)0 10 20 30 D E C L I NA T I O N ( J2000 ) RIGHT ASCENSION (J2000)17 40 42.4 42.2 42.0 41.8 41.6 41.4 41.2 41.0 40.8-28 48 000510152025
BOTH: G359.568+1.146 IPOL 4800.000 MHZGrey scale flux range= -1.2 112.3 MilliJY/BEAMCont peak flux = 1.1231E-01 JY/BEAM Levs = 1.000E-03 * (-2, -1, 1, 2, 4, 6, 8, 10, 12,16, 20, 24, 28, 32, 40, 48, 64, 80, 96, 128)0 50 100 D E C L I NA T I O N ( J2000 ) RIGHT ASCENSION (J2000)17 40 09.0 08.5 08.0 07.5 07.0-28 41 304542 001530
BOTH: G0.846+1.173 IPOL 4840.000 MHZ Grey scale flux range= -0.93 41.66 MilliJY/BEAMCont peak flux = 4.1658E-02 JY/BEAM Levs = 1.000E-03 * (-2, -1, 1, 2, 4, 6, 8, 10, 12,16, 20, 24, 32, 40, 48, 64, 80, 128, 160, 192)0 10 20 30 40 D E C L I NA T I O N ( J2000 ) RIGHT ASCENSION (J2000)17 43 11 10 09 08 07 06 05 04-27 35 4536 0015304537 001530
BOTH: G1.954--1.702 IPOL 4840.000 MHZ Grey scale flux range= -0.65 58.25 MilliJY/BEAMCont peak flux = 5.8255E-02 JY/BEAM Levs = 1.000E-03 * (-2, -1, 1, 2, 4, 6, 8, 10, 12,16, 20, 24, 32, 40, 48, 64, 80, 128, 160, 192)0 20 40 D E C L I NA T I O N ( J2000 ) RIGHT ASCENSION (J2000)17 56 50.5 50.0 49.5 49.0-28 07 2025303540455055
BOTH: G2.423--1.660 IPOL 4840.000 MHZ Grey scale flux range= -0.96 44.94 MilliJY/BEAMCont peak flux = 4.4937E-02 JY/BEAM Levs = 1.000E-03 * (-2, -1, 1, 2, 4, 6, 8, 10, 12,16, 20, 24, 32, 40, 48, 64, 80, 128, 160, 192)0 10 20 30 40 D E C L I NA T I O N ( J2000 ) RIGHT ASCENSION (J2000)17 57 44.5 44.0 43.5 43.0-27 41 45505542 00051015
BOTH: G4.898+1.292 IPOL 4840.000 MHZ Grey scale flux range= -0.73 50.35 MilliJY/BEAMCont peak flux = 5.0346E-02 JY/BEAM Levs = 1.000E-03 * (-2, -1, 1, 2, 4, 6, 8, 10, 12,16, 20, 24, 32, 40, 48, 64, 80, 128, 160, 192)0 20 40 D E C L I NA T I O N ( J2000 ) RIGHT ASCENSION (J2000)17 51 58.5 58.0 57.5 57.0 56.5 56.0-24 04 0005101520253035404550
Figure 5. ≈ (cid:48)(cid:48) × (cid:48)(cid:48) . c (cid:13)000
Figure 5. ≈ (cid:48)(cid:48) × (cid:48)(cid:48) . c (cid:13)000 , 1–24 xtragalactic sources towards the Galactic Centre BOTH: G353.410--0.360 IPOL 4760.100 MHZGrey scale flux range= -8.3 146.8 MilliJY/BEAMCont peak flux = 1.4680E-01 JY/BEAM Levs = 3.000E-03 * (-2, -1, 1, 2, 4, 6, 8, 12, 16,20, 24, 32, 40, 48, 64, 96, 128, 160, 192, 224, 256,320)0 50 100 D E C L I NA T I O N ( J2000 ) RIGHT ASCENSION (J2000)17 30 33 32 31 30 29 28 27 26 25-34 41 0015304542 0015
BOTH: G355.739+0.131 4760.100 MHZGrey scale flux range= -0.58 28.44 MilliJY/BEAMCont peak flux = 2.8437E-02 JY/BEAM Levs = 3.000E-04 * (-2, -1, 1, 2, 4, 6, 8, 12, 16,20, 24, 32, 40, 48, 64, 96, 128, 160, 192, 224, 256,320)0 10 20 D E C L I NA T I O N ( J2000 ) RIGHT ASCENSION (J2000)17 34 35.0 34.8 34.6 34.4 34.2 34.0 33.8 33.6 33.4 33.2-32 28 2025303540
BOTH: G358.643--0.034 IPOL 4760.100 MHZGrey scale flux range= -1.817 7.507 MilliJY/BEAMCont peak flux = 7.5069E-03 JY/BEAM Levs = 1.000E-03 * (-2, -1, 1, 2, 4, 6, 8, 12, 16,20, 24, 32, 40, 48, 64, 96, 128, 160, 192, 224, 256,320) 0 2 4 6 D E C L I NA T I O N ( J2000 ) RIGHT ASCENSION (J2000)17 42 30.5 30.0 29.5 29.0 28.5 28.0 27.5-30 06 0510152025303540455055
BOTH: G358.605+1.440 IPOL 4760.100 MHZGrey scale flux range= -0.51 37.90 MilliJY/BEAMCont peak flux = 3.7896E-02 JY/BEAM Levs = 3.000E-04 * (-2, -1, 1, 2, 4, 6, 8, 12, 16,20, 24, 32, 40, 48, 64, 96, 128, 160, 192, 224, 256,320)0 10 20 30 D E C L I NA T I O N ( J2000 ) RIGHT ASCENSION (J2000)17 36 39.2 39.1 39.0 38.9 38.8 38.7 38.6 38.5 38.4 38.3-29 21 2022242628303234
BOTH: G359.717--0.036 IPOL 4760.100 MHZGrey scale flux range= -2.54 11.60 MilliJY/BEAMCont peak flux = 1.1597E-02 JY/BEAM Levs = 1.000E-03 * (-2, -1, 1, 2, 4, 6, 8, 12, 16,20, 24, 32, 40, 48, 64, 96, 128, 160, 192, 224, 256,320) 0 5 10 D E C L I NA T I O N ( J2000 ) RIGHT ASCENSION (J2000)17 45 07.0 06.5 06.0 05.5 05.0 04.5 04.0-29 10 15304511 0015304512 00
BOTH: G4.005+0 IPOL 4760.100 MHZGrey scale flux range= -0.411 9.332 MilliJY/BEAMCont peak flux = 9.3323E-03 JY/BEAM Levs = 3.000E-04 * (-2, -1, 1, 2, 4, 6, 8, 12, 16,20, 24, 32, 40, 48, 64, 96, 128, 160, 192, 224, 256,320)0 2 4 6 8 D E C L I NA T I O N ( J2000 ) RIGHT ASCENSION (J2000)17 54 39.5 39.0 38.5 38.0 37.5 37.0 36.5 36.0 35.5 35.0-25 27 304528 0015
BOTH: G4.619+0.288 IPOL 4760.100 MHZGrey scale flux range= -0.43 22.09 MilliJY/BEAMCont peak flux = 2.2087E-02 JY/BEAM Levs = 3.000E-04 * (-2, -1, 1, 2, 4, 6, 8, 12, 16,20, 24, 32, 40, 48, 64, 96, 128, 160, 192, 224, 256,320)0 5 10 15 20 D E C L I NA T I O N ( J2000 ) RIGHT ASCENSION (J2000)17 55 08.4 08.3 08.2 08.1 08.0 07.9 07.8 07.7 07.6 07.5-24 49 1416182022242628
Figure 6. µ Jy/beam, and beamsize of ≈ (cid:48)(cid:48) × . (cid:48)(cid:48) .c (cid:13) , 1–24 Subhashis Roy, A. Pramesh Rao & Ravi Subrahmanyan T a b l e : E s ti m a t e d R M t o w a r d s t h e b ac kg r ound s ou r ce s t o w a r d s t h e G C r e g i on S ou r ce N a m e R AD E CR M E rr o r D ∆ ( D ) θ ∆ θ χ M ea s u r e dpo l a r i s a ti on a ng l e s ( J )( J ) on ( % ) a t d i ff e r e n t fr e qu e n c i e s R M . - . . − . . . . − ± . , − ± . , ± . , ± . . + . . − . . . . ± . , − ± . , ± . , ± . . − . . . . − ± . , − ± . , ± . , ± . , ± . . + . . − . − . . . ± . , ± . , ± . , ± . . - . . − . . . . − ± . , − ± . , ± . , ± . . − . . . . − ± . , − ± . , ± . , ± . . + . . − . . . . ± . , ± . , ± . , ± . . − . . . . ± . , ± . , − ± . , − ± . . − . . . . ± . , ± . , − ± . , − ± . . + . . − . . . . ± . , − ± . , ± . , ± . . − . . . . ± . , − ± . , − ± . , − ± . . − . . . . ± . , − ± . , − ± . , − ± . . + . . − . . . . − ± . , ± . , ± . , − ± . . - . . − . − . . . − ± . , ± . , ± . , ± . . − . − . . . ± . , ± . , ± . , ± . . - . . − . . . . . . . ± . , − . ± . , . ± . , − . ± . ( - ) . - . . − . . . ± . , ± . , − ± . , − ± . , − ± . , ± . . - . . − . − . . . ± . , ± . , ± . , ± . . − . . . . ± . , ± . , − ± . , − ± . . − . . . . ± . , ± , ± . , − ± . . + . . − . . . . ± . , ± . , − ± . , − ± . . − . . . . ± . , ± . , − ± . , − ± . . + . . − . . . . − ± . , − ± . , − ± . , − ± . , − . ± . , − ± . . - . . − . − . . . − ± . , ± . , − ± . , − ± . . - . . − . − . . . − ± . , − ± . , − . ± . , − ± . ( M ou s e ) . + . . − . − . . . ± . , ± , ± . , . ± . , ± . , − . ± . c (cid:13)000
Figure 6. µ Jy/beam, and beamsize of ≈ (cid:48)(cid:48) × . (cid:48)(cid:48) .c (cid:13) , 1–24 Subhashis Roy, A. Pramesh Rao & Ravi Subrahmanyan T a b l e : E s ti m a t e d R M t o w a r d s t h e b ac kg r ound s ou r ce s t o w a r d s t h e G C r e g i on S ou r ce N a m e R AD E CR M E rr o r D ∆ ( D ) θ ∆ θ χ M ea s u r e dpo l a r i s a ti on a ng l e s ( J )( J ) on ( % ) a t d i ff e r e n t fr e qu e n c i e s R M . - . . − . . . . − ± . , − ± . , ± . , ± . . + . . − . . . . ± . , − ± . , ± . , ± . . − . . . . − ± . , − ± . , ± . , ± . , ± . . + . . − . − . . . ± . , ± . , ± . , ± . . - . . − . . . . − ± . , − ± . , ± . , ± . . − . . . . − ± . , − ± . , ± . , ± . . + . . − . . . . ± . , ± . , ± . , ± . . − . . . . ± . , ± . , − ± . , − ± . . − . . . . ± . , ± . , − ± . , − ± . . + . . − . . . . ± . , − ± . , ± . , ± . . − . . . . ± . , − ± . , − ± . , − ± . . − . . . . ± . , − ± . , − ± . , − ± . . + . . − . . . . − ± . , ± . , ± . , − ± . . - . . − . − . . . − ± . , ± . , ± . , ± . . − . − . . . ± . , ± . , ± . , ± . . - . . − . . . . . . . ± . , − . ± . , . ± . , − . ± . ( - ) . - . . − . . . ± . , ± . , − ± . , − ± . , − ± . , ± . . - . . − . − . . . ± . , ± . , ± . , ± . . − . . . . ± . , ± . , − ± . , − ± . . − . . . . ± . , ± , ± . , − ± . . + . . − . . . . ± . , ± . , − ± . , − ± . . − . . . . ± . , ± . , − ± . , − ± . . + . . − . . . . − ± . , − ± . , − ± . , − ± . , − . ± . , − ± . . - . . − . − . . . − ± . , ± . , − ± . , − ± . . - . . − . − . . . − ± . , − ± . , − . ± . , − ± . ( M ou s e ) . + . . − . − . . . ± . , ± , ± . , . ± . , ± . , − . ± . c (cid:13)000 , 1–24 xtragalactic sources towards the Galactic Centre S ou r ce N a m e R AD E CR M E rr o r D ∆ ( D ) θ ∆ θ χ M ea s u r e dpo l a r i s a ti on a ng l e s ( J )( J ) on ( % ) a t d i ff e r e n t fr e qu e n c i e s R M . + . . − . − . . . − ± . , − ± . , ± . , ± . . − . − . . . − ± . , − ± . , − ± . , − ± . . + . . − . − . . ± . , − ± . , − ± . , − ± . . - . . − . . ± . , − ± . , − ± . , ± . . − . . − ± . , ± . , ± . , − ± . . - . . − . − . . − ± . , ± . , − . ± . , − ± . . + . . − . . . . ± . , ± . , ± . , ± . . - . . − . . . ± . , ± . , ± . , ± . . + . . − . . . . ± . , − ± . , ± . , ± . . + . . − . − . . . ± . , ± . , ± . , ± . . + . . − . − . . . − ± . , − ± . , ± . , ± . . + . . − . − . . . ± . , − ± . , − ± . , − ± . , ± . , ± . . - . . − . − . . . − ± . , − ± . , − ± . , − ± . . − . . . . ± . , ± . , ± . , ± . . + . . − . − . . − . ± . , − . ± . , − . ± . , − . ± . . - . . − . . . . ± . , ± . , ± . , − ± . . − . . . . − ± . , ± . , ± . , ± . . + . . − . . . . . ± . , ± . , . ± . , . ± . . − . . . . − ± . , − ± . , ± . , ± . . + . . − . . . − ± . , − ± . , − ± . , − ± . . + . . − . . . . − ± . , − ± . , − ± . , ± . . − . . . . − ± . , − ± . , − ± . , − ± . . - . . − . − . . . ± . , ± . , ± . , ± . . + . . − . . . . . − . ± . , . ± . , . ± . , − . ± . ( - ) . - . . − . . . . − ± . , − ± . , − ± . , ± . . + . . − . . . . ± . , − ± . , − ± . , − ± . c (cid:13) , 1–24 Subhashis Roy, A. Pramesh Rao & Ravi Subrahmanyan S ou r ce N a m e R AD E CR M E rr o r D ∆ ( D ) θ ∆ θ χ M ea s u r e dpo l a r i s a ti on a ng l e s ( J )( J ) on ( % ) a t d i ff e r e n t fr e qu e n c i e s R M . + . . − . . . . ± . , ± . , ± . , ± . , ± . , ± . . - . . − . − . . . ± . , . ± . , − ± . , − ± . . - . . − . . . . − ± . , ± . , − ± . , ± . . + . . − . . . . ± . , ± . , ± . , ± . . − . . . . − ± . , − ± . , ± . , ± . . - . . − . . . . − ± . , ± . , ± . , − . ± . . + . . − . . . . − ± . , ± . , − ± . , − ± . . - . . − . . . . − ± . , − ± . , − ± . , − ± . . − . . . . − ± . , ± . , ± . , ± . . + . . − . . . . ± . , − ± . , ± . , − ± . . − . . . . − ± . , − ± . , − ± . , ± . . − . . . . ± . , ± . , ± . , ± . . + . . − . . . . − ± . , − ± . , ± . , ± . . − . . . . ± . , ± . , − ± . , − ± . . - . . − . − . . . ± . , − ± . , − ± . , − ± . , − ± . , − ± . c (cid:13)000
Figure 6. µ Jy/beam, and beamsize of ≈ (cid:48)(cid:48) × . (cid:48)(cid:48) .c (cid:13) , 1–24 Subhashis Roy, A. Pramesh Rao & Ravi Subrahmanyan T a b l e : E s ti m a t e d R M t o w a r d s t h e b ac kg r ound s ou r ce s t o w a r d s t h e G C r e g i on S ou r ce N a m e R AD E CR M E rr o r D ∆ ( D ) θ ∆ θ χ M ea s u r e dpo l a r i s a ti on a ng l e s ( J )( J ) on ( % ) a t d i ff e r e n t fr e qu e n c i e s R M . - . . − . . . . − ± . , − ± . , ± . , ± . . + . . − . . . . ± . , − ± . , ± . , ± . . − . . . . − ± . , − ± . , ± . , ± . , ± . . + . . − . − . . . ± . , ± . , ± . , ± . . - . . − . . . . − ± . , − ± . , ± . , ± . . − . . . . − ± . , − ± . , ± . , ± . . + . . − . . . . ± . , ± . , ± . , ± . . − . . . . ± . , ± . , − ± . , − ± . . − . . . . ± . , ± . , − ± . , − ± . . + . . − . . . . ± . , − ± . , ± . , ± . . − . . . . ± . , − ± . , − ± . , − ± . . − . . . . ± . , − ± . , − ± . , − ± . . + . . − . . . . − ± . , ± . , ± . , − ± . . - . . − . − . . . − ± . , ± . , ± . , ± . . − . − . . . ± . , ± . , ± . , ± . . - . . − . . . . . . . ± . , − . ± . , . ± . , − . ± . ( - ) . - . . − . . . ± . , ± . , − ± . , − ± . , − ± . , ± . . - . . − . − . . . ± . , ± . , ± . , ± . . − . . . . ± . , ± . , − ± . , − ± . . − . . . . ± . , ± , ± . , − ± . . + . . − . . . . ± . , ± . , − ± . , − ± . . − . . . . ± . , ± . , − ± . , − ± . . + . . − . . . . − ± . , − ± . , − ± . , − ± . , − . ± . , − ± . . - . . − . − . . . − ± . , ± . , − ± . , − ± . . - . . − . − . . . − ± . , − ± . , − . ± . , − ± . ( M ou s e ) . + . . − . − . . . ± . , ± , ± . , . ± . , ± . , − . ± . c (cid:13)000 , 1–24 xtragalactic sources towards the Galactic Centre S ou r ce N a m e R AD E CR M E rr o r D ∆ ( D ) θ ∆ θ χ M ea s u r e dpo l a r i s a ti on a ng l e s ( J )( J ) on ( % ) a t d i ff e r e n t fr e qu e n c i e s R M . + . . − . − . . . − ± . , − ± . , ± . , ± . . − . − . . . − ± . , − ± . , − ± . , − ± . . + . . − . − . . ± . , − ± . , − ± . , − ± . . - . . − . . ± . , − ± . , − ± . , ± . . − . . − ± . , ± . , ± . , − ± . . - . . − . − . . − ± . , ± . , − . ± . , − ± . . + . . − . . . . ± . , ± . , ± . , ± . . - . . − . . . ± . , ± . , ± . , ± . . + . . − . . . . ± . , − ± . , ± . , ± . . + . . − . − . . . ± . , ± . , ± . , ± . . + . . − . − . . . − ± . , − ± . , ± . , ± . . + . . − . − . . . ± . , − ± . , − ± . , − ± . , ± . , ± . . - . . − . − . . . − ± . , − ± . , − ± . , − ± . . − . . . . ± . , ± . , ± . , ± . . + . . − . − . . − . ± . , − . ± . , − . ± . , − . ± . . - . . − . . . . ± . , ± . , ± . , − ± . . − . . . . − ± . , ± . , ± . , ± . . + . . − . . . . . ± . , ± . , . ± . , . ± . . − . . . . − ± . , − ± . , ± . , ± . . + . . − . . . − ± . , − ± . , − ± . , − ± . . + . . − . . . . − ± . , − ± . , − ± . , ± . . − . . . . − ± . , − ± . , − ± . , − ± . . - . . − . − . . . ± . , ± . , ± . , ± . . + . . − . . . . . − . ± . , . ± . , . ± . , − . ± . ( - ) . - . . − . . . . − ± . , − ± . , − ± . , ± . . + . . − . . . . ± . , − ± . , − ± . , − ± . c (cid:13) , 1–24 Subhashis Roy, A. Pramesh Rao & Ravi Subrahmanyan S ou r ce N a m e R AD E CR M E rr o r D ∆ ( D ) θ ∆ θ χ M ea s u r e dpo l a r i s a ti on a ng l e s ( J )( J ) on ( % ) a t d i ff e r e n t fr e qu e n c i e s R M . + . . − . . . . ± . , ± . , ± . , ± . , ± . , ± . . - . . − . − . . . ± . , . ± . , − ± . , − ± . . - . . − . . . . − ± . , ± . , − ± . , ± . . + . . − . . . . ± . , ± . , ± . , ± . . − . . . . − ± . , − ± . , ± . , ± . . - . . − . . . . − ± . , ± . , ± . , − . ± . . + . . − . . . . − ± . , ± . , − ± . , − ± . . - . . − . . . . − ± . , − ± . , − ± . , − ± . . − . . . . − ± . , ± . , ± . , ± . . + . . − . . . . ± . , − ± . , ± . , − ± . . − . . . . − ± . , − ± . , − ± . , ± . . − . . . . ± . , ± . , ± . , ± . . + . . − . . . . − ± . , − ± . , ± . , ± . . − . . . . ± . , ± . , − ± . , − ± . . - . . − . − . . . ± . , − ± . , − ± . , − ± . , − ± . , − ± . c (cid:13)000 , 1–24 xtragalactic sources towards the Galactic Centre BOTH: G359.7-0 IPOL 8510.100 MHZ G359.7-0.ICL001.1Grey scale flux range= -1.121 3.463 MilliJY/BEAMCont peak flux = 3.4630E-03 JY/BEAM Levs = 5.000E-04 * (-2, -1, 1, 2, 4, 6, 8, 12, 16,20, 24, 32, 40, 48, 64, 96, 128, 160, 192, 224, 256,320)-1 0 1 2 3 D E C L I NA T I O N ( J2000 ) RIGHT ASCENSION (J2000)17 45 06.0 05.5 05.0 04.5 04.0 03.5-29 11 354045505512 00
Figure 7. − Extended unpolarised structures, typical of HII regions, areseen in the VLA images of the sources G353.410 − − − − − − Excluding the sources described above, the rest of the sources ob-served are either polarised or the deconvolved diameters implya brightness temperature greater than 10 K at 4.8 GHz. Exceptfor a few small diameter sources, all the other sources have steepspectral indices indicating the emission from these sources is non-thermal. The small diameter objects have flat spectra ( α (cid:62) − . K at 4.8 GHz should show self absorption (i.e., positivespectral index) at 0.3 GHz (otherwise, the required brightness tem-perature exceeds 10 K). Therefore, these objects with flat spectraat 0.3 GHz indicate that the emission from these small diametersources are also non-thermal. Among the non-thermal sources, theobject G359.2 − There are several types of Galactic sources that emit non-thermalemission.(i) Supernova Remnants (SNRs): These are the remnants of super-nova explosions. The electrons in these objects are accelerated tohigh energies near the expanding shock front. The SNRs are usuallyspherical in shape, and when projected on the sky appear like a ringfor the shell type SNRs, while they appear to be filled with emissionin the case of plerion-type SNRs. None of the non-thermal objectsin Tables 2, 3, 4 & 5 have such a morphology, indicating that thereis no resolved supernova remnant among these sources. However,if an SNR is young, its angular size will be small and will appearlike an unresolved source. Assuming an initial expansion velocityof 3000 km s − , an SNR at a distance of 10 kpc will expand to anangular size of 6 (cid:48)(cid:48) in about 100 years after the explosion. An ob-ject of angular size of 6 (cid:48)(cid:48) will be well resolved in our images andshould have a ring or filled centre morphology: the absence of theserule out any SNR older than 100 years in our sample. Since the ex-pected number of supernova explosions in our Galaxy is believedto be about 1 in 50 years, the probability of finding an SNR of ageless than 100 years in the central 12 ◦ × ◦ of the Galaxy is less than0.1, which suggests that there is no young SNR in our sample.(ii) Radio Pulsars: Pulsars typically have a very steep spec-trum, with spectral indices of − . − (cid:54) c (cid:13) , 1–24 Subhashis Roy, A. Pramesh Rao & Ravi Subrahmanyan by days to years and the measured spectral indices determined be-tween any two bands are quite close to the mean value (differencesare less than 0.6). Therefore, the flux densities of these sources havenot changed by more than a factor of two and this rules out the pos-sibility that there are transient sources in our catalogue.(iv) Galactic Microquasar: These are stellar-mass black holesin our Galaxy that mimic, on a smaller scale, many of the phenom-ena seen in quasars (see Mirabel & Rodríguez (1999), and the refer-ences therein). For a black hole accreting at the Eddington limit, thecharacteristic black body temperature at the last stable orbit in thesurrounding accretion disk is given by T ∼ × M − / (Rees1984). Therefore, compared to the AGNs, the emission from mi-croquasars are shifted towards higher frequencies and the micro-quasars are usually identified by their X-ray properties (Mirabel &Rodríguez 1999).Though many of the already known microquasars are highlyvariable, two of these sources, 1E1740.7 − −
258 (Martí et al. 2002), are per-sistent sources of both X-rays and relativistic jets. At radio wave-lengths, these two sources are morphologically similar to typical ra-dio galaxies, which have a central compact component and two ex-tended lobes. Therefore, based on morphology, microquasars can-not be separated from the distant radio galaxies. However, as men-tioned above, microquasars are believed to have X-ray counter-parts. We have searched the ROSAT PSPC all sky survey (Vogeset al. 1999) and a catalogue of soft X-ray sources ( | l | (cid:54) ◦ , | b | (cid:54) ◦ ) in the GC region (Sidoli et al. 2001). Twenty of our sourcesare also located within the boundary of the ASCA survey of the GCregion ( | l | (cid:54) ◦ , | b | (cid:54) ◦ ) (Sakano et al. 2002). However, noneof the radio sources in our sample were found to have any coun-terpart in these catalogues. Therefore, it is unlikely that any of thesources we have observed (Tables 2, 3, 4 & 5) is a microquasar. The expected number of extragalactic sources (N) in 1 square arcminute of the sky at 5 GHz and with a flux density limit of S mJy isN( > S)= 0 . × S − . (Ledden et al. 1980). Therefore, the ex-pected number of extragalactic sources seen through the central l × b = 12 ◦ × ◦ region of the Galaxy above a flux density limitof 20 mJy at 5 GHz is 168. However, as we selected sources withsteep spectral indices ( α < − . (cid:54) (cid:48)(cid:48) and excessiveconfusion prevails in the region, we could identify only 59 extra-galactic sources, which indicates that about two thirds of the extra-galactic sources in this region are yet to be identified. The medianangular size of these 59 sources is 7.6 (cid:48)(cid:48) , and the median flux densityat 1.4 GHz is 160 mJy. We have observed 64 sources towards the central − ◦ < l < ◦ , − ◦ < b < ◦ of the Galaxy using the 6 and 3.6 cm band of theATCA and the VLA. Based on our work described herein, 59 ofthese sources are classified to be extragalactic. This increases thenumber of known extragalactic radio sources towards this uniqueregion by almost an order of magnitude and provides the firstsystematic study of the polarisation properties of the backgroundsources in the region. We provide 4.8 GHz images of all the ob-served sources and measure the angular sizes and the spectral in-dices of these sources. Based on the morphology, spectral char- acteristics and polarisation properties, we identify 4 Galactic HIIregions in the sample. ACKNOWLEDGEMENTS
S.R. thanks D. J. Saikia for useful discussions. The Australia Tele-scope is funded by the Commonwealth of Australia for operationas a National Facility managed by CSIRO. The National Radio As-tronomy Observatory is a facility of the National Science Founda-tion operated under cooperative agreement by Associated Univer-sities, Inc.
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