Galaxy Zoo Talk

Gas or ...?

  • karthikeyan.d by karthikeyan.d

    Is that just (glowing) gas between the galaxies or tidal stream(s)?


  • Budgieye by Budgieye moderator

    It is a tidal stream of stars. Hydrogen gas only glows when it is hit by UV light, and then it fluoresces unusual colours.

    3.3 AGN-illuminated clouds, Voorwerpje


  • zoob1172 by zoob1172

    GZ1 catalog - NGC 7237 agn broadline elliptical ETG qso xray source "radio jet" 84 references

    info for 7237 =========

    1.3. 3C 442A

     3C 442A5 is associated with the interacting galaxy pair NGC 7236/7 at z = 0.027 (Greenstein 1962). Its 178 MHz luminosity of 2 × 1024 W Hz-1 sr-1 puts it below the FR I/FR II break. At the distance of 3C 442A, 1′′ is 0.54 kpc; the luminosity distance is 118 Mpc. In the radio (Birkinshaw et al. 1981; Comins & Owen 1991), 3C 442A shows a double-lobed structure with no sign of any jet, although a compact flat-spectrum radio core coincident with NGC 7237 suggests current AGN activity in that object. Comins & Owen argue that the compact features in and close to the lobes are unrelated to the source, which, if true, would make 3C 442A a member of the class of "fat doubles" or "relaxed doubles" (e.g., Laing 1993), a number of which are found in the 3CRR sample close to the FR I/FR II luminosity break. 3C 442A is remarkable for the detection by Comins & Owen of two filaments of steep-spectrum radio emission that cross the region containing the host galaxy, NGC 7237. Optically, this galaxy, an elliptical (assumed to be the host on the basis that it hosts a compact radio source) appears to be interacting with an S0 neighbor of similar luminosity to the northeast, NGC 7236. The two are separated by 35′′ (19 kpc) and are embedded in a common, distorted stellar envelope that also includes another, smaller elliptical 38′′ (21 kpc) to the southwest of NGC 7237, denoted NGC 7237C hereafter (Borne & Hoessel 1988). The measured radial velocities for NGC 7236 and NGC 7237 are very similar, suggesting an interaction close to the plane of the sky, which allowed Borne (1988) to make detailed models of the system. HST imaging (Martel et al. 1999) shows some weak evidence for dust emission in NGC 7237, but generally the inner parts of the system appear like an undisturbed elliptical, in contrast to 3C 285's host. NGC 7236/7 lies at the center of a group of galaxies (Comins & Owen 1991). In the X-ray, Hardcastle & Worrall (1999) used ROSAT data to show that the soft X-ray emission had relatively complex structure, with a small-scale extension around NGC 7237 as well as large-scale (3′, or 100 kpc) extension in a direction 

    perpendicular to the radio lobe axis.

    5 3C 442A is sometimes referred to as 3C 442 in the literature. Early maps of the field (e.g., Mackay 1969) showed the presence of two radio sources. One of these sources was extended and associated with the NGC 7236/7237 galaxy pair; the other, 28′ to the south-southeast, was compact, with a flux density around 1 Jy at 1.4 GHz, had a steep spectrum, and was not associated with any bright galaxy. Its 178 MHz flux density contributes to the measured 3CR flux (Véron 1977). The designation 3C 442A was given to the first source (apparently first used in print by Jenkins et al. 1977; subsequently adopted by Laing et al. 1983) to make it clear that the two were unrelated. The second source could have become known as 3C 442B, but is in fact generally referred to as 4C 13.83 or PKS 2212+131 and is coincident with an SDSS quasar with z = 1.90. Because of its distance from 3C 442A it is not detected in any of the X-ray data sets discussed in this paper.

    3.4.2. 3C 442A

     3C 442A shows striking X-ray structure related to the host interacting galaxy pair NGC 7236/7237 (Fig. 6). Both galaxies appear to have "tails" of extended, asymmetrical X-ray–emitting material, presumably radiating thermally (see below), with size scales around 40′′ (20 kpc). The tail of NGC 7237 lies in position angle ∼250° (north through east) and that of NGC 7236 in position angle ∼45°. The tail of NGC 7237 was seen with the ROSAT HRI by Hardcastle & Worrall (1999). As there is no evidence for corresponding emission in the optical image (Fig. 6), where the distorted isophotes of the two galaxies are on smaller scales (Borne & Hoessel 1988 ), the tails must be formed not by tidal processes but by some hydrodynamical process, such as ram pressure stripping (e.g., Acreman et al. 2003) or Bondi-Hoyle wake formation (Sakelliou 2000). The X-ray tails are in the direction expected from the compression of the outer optical isophotes, which suggests that NGC 7237 is currently moving toward the northeast and NGC 7236 toward the southwest (Borne & Hoessel 1988). Equally striking is the relationship between these tails and the filamentary structure in the radio, as seen in the right-hand panel of Figure 6. The brightest filament in the center of 3C 442A passes directly through the gap between the two tails (crossing the nucleus of NGC 7236), while the other bright filament in the system runs along the south boundary of the NGC 7237 tail. Given this, together with the qualitative similarity between the shape of the NGC 7237 tail (east-west at the west end, curving to northeast-southwest at the north end) and those of the two filaments, it seems almost certain that the filamentary structure arises from interaction between the radio plasma and the tails. We return to this point below (§ 4.5). 

    and more ...


  • Budgieye by Budgieye moderator in response to zoob1172's comment.

    Thank you for the detailed post. But the radio and X-ray light cannot be seen in the SDSS image. All we see is green, red and far red light, and so what we are seeing are stars.