3. Additional data

3.1. Optical observations in HS 47.5/22

  The main source of optical information in HS 47.5/22 are the HQS plates. They were taken with the Calar Alto Schmidt telescope on Kodak IIIaJ plates covering the spectral range . Both the direct and spectral plate were scanned with a PDS (Hagen et al. 1995), and the scanned data were used in this work. During the HQS work, 27 optically selected quasars were found in the surveyed with ROSAT (filled circles in Fig. 1 (click here)), 3 of which were previously known.

The faintest sources visible on the objective prism plate have , while the depth of the direct plate is comparable with the blue plate of the POSS I. X-ray sources with no optical counterpart on the HQS direct plate were searched on the red POSS plate, and most of them were found.

3.2. Radio observations

 

3.2.1. Galactic hydrogen

As has been noted before, low resolution HI surveys gave an average value of for galactic hydrogen in HS 47.5/22. A new and better resolved map was obtained with the 100 m RT at Effelsberg (9' beam) to allow individual corrections. The observations were performed during two observing runs in 1989, resulting in a grid with separations and , slightly incomplete at the edges.

The measurements are contaminated by stray radiation arising from the sidelobes of the telescope, which can be removed through an all sky deconvolution provided the complete antenna pattern is known. Kalberla et al. (1980) use this method to correct their measurements with the 100 m RT. Lockman et al. (1986) take a different approach, they combine their spectra to synthetize the beam of the Stark Survey, which is practically uncontaminated (Stark et al. 1992). Any differences between the combined data and the corresponding Stark Survey spectra are attributed to stray radiation present in the former and are therefore subtracted.

Both approaches give a good accuracy but need large amounts of computer time and storage capacity. For the present work, the much easier though less accurate ( in ) time independent correction presented in Kalberla et al. (1980, their Sect. 4.2) is used. They found with several assumptions that the corrected main beam brightness temperature is

where is the observed profile area expressed in , and is the measured antenna temperature. The small size of HS 47.5/22 means that the distance to the Milky Way does not vary greatly so that it is possible to use one common correction factor. This factor is obtained by dividing values from the Stark Survey by the uncorrected 100 m RT values at the same positions, and averaging the results:

Figure 5 (click here) shows a contour plot of the corrected column density in HS 47.5/22. Empty grid positions have been filled with the weighted means of the neighbouring positions for the plot.

  
Figure 5: Contour plot of in HS 47.5/22. Contours are plotted in steps of , starting at (contour 1). Coordinates are B1950.0

Variations of a factor , already indicated in the low resolution surveys, could be confirmed on scales of less than 30'. Regions with high can be found near the eastern and along the southern borders of HS 47.5/22 and in the north western edge. The lowest value in the area between is less than . A high velocity cloud found by Hulsbosch & Wakker (1988) is present in our data as well. It is, however, not the reason for the variations in since the column density peaks of the cloud do not coincide with the overall maxima.

3.2.2. Radio continuum measurements

HS 47.5/22 was surveyed with the DRAO interferometer (Penticton/Canada) at 21cm and 74cm in March 1993. A full analysis of the DRAO observations is under way and will be published elsewhere.

In addition, HS 47.5/22 is located inside the area of several radio continuum surveys which became available during the project. Table 2 (click here) gives an overview of position accuracies and flux limits of these surveys. These catalogues are crosscorrelated with the X-ray source list. A source is considered identified if the X-ray and radio positions agree within the errors. Only a few X-ray sources match with objets from either catalogue; they are listed in Table 3 (click here). Two sources match with phase calibration sources in Patnaik et al. (1992); they are included in the table.

 

 

References flux limit pos.err.

87GB (6cm) (1)

GB 1.4 GHz (2) 100mJy

B3 408 MHz^a (3) 100mJy 15''/35''^b

Texas 365 MHz (4)

DRAO 21cm (5)

DRAO 74cm (5)

Table 2: Overview of Radio surveys covering the field

 

RXJ (1) (2) (3) (4) (5)

9 0943.5+4633 3'' D

27 0944.6+4638 19'' D

53 0945.6+4636 3'' 8'' 9'' 4'' 5'' D

64 0945.9+4619 12'' gal. cand.

180 0950.2+4553 28'' BLLaccand.^a

284 0953.6+4625 26'' 40'' 25'' D

317 0954.7+4608 43'' 37'' D

321 0954.8+4715 17'' 10'' D

347 0955.6+4721 22'' 19'' D

424 0957.7+4848 60'' 23'' D

425 0957.7+4745 21'' AGN^a

443 0958.3+4608 36'' AGN^a

446 0958.3+4725 4'' 9'' 18'' 5'' OK492^b

534 1000.9+4640 13'' 29'' AGN cand.

555 1001.5+4659 23'' AGN group^a

571 1003.1+4757 28'' unident. ^a: identified in this work. ^b: Peterson et al. (1978).

Table 3: This table contains the distances between X-ray sources and possible radio counterparts. The first column gives the X-ray sequence number (Table 5), the following ones contain the distances for the surveys (1) - (4) from Table 2 (click here) and (5) for Patnaik et al. (1992), and the last column gives the object type